{"id":342,"date":"2024-07-25T14:07:35","date_gmt":"2024-07-25T21:07:35","guid":{"rendered":"https:\/\/dornsife.usc.edu\/williams-group\/?page_id=342"},"modified":"2026-04-19T20:32:03","modified_gmt":"2026-04-20T03:32:03","slug":"publications","status":"publish","type":"page","link":"https:\/\/dornsife.usc.edu\/williams-group\/publications\/","title":{"rendered":"Publications"},"content":{"rendered":"\n\n\n \n \n\n\n\n\n\n\n\n
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\n Publications\n <\/h2>\n\n\n<\/div>\n \n \n <\/div>\n\n\n <\/div><\/div>\n\n\n\n\n \n \n\n\n\n\n\n\n\n
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Recent Advancements in Chemical Valorization of Legacy and Emerging Fiber-Reinforced Polymer Composites<\/b><\/span>
\nMadison Fette, Ding-Yuan Lim, Zehan Yu, Steven R. Nutt, Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

Fiber-reinforced polymer (FRP) composites are increasingly crucial in the global effort to shift toward sustainable energy sources and more fuel-efficient transportation technologies. These materials are excellent in service; however, poor end-of-life (EoL) recycling options compromise the sustainability of FRPs. Current methods, including pyrolysis and mechanical recycling, are inadequate at preserving value from the fibers or polymers. By contrast, chemical recycling methods demonstrate promise to recover high-value fibers and chemicals from composite materials. Novel, chemically engineered resin systems further enable fiber\/matrix separation to facilitate the recycling process. Particularly within the past 5 years, there has been a growing interest in targeting monomer recovery from composite matrices. This review provides a comprehensive overview of recent developments in selective depolymerization of current (legacy) composite materials and strategies for facile polymer disconnection in novel resin systems. Advantages and limitations across recycling strategies for both legacy and novel composites underscore key remaining challenges in composite sustainability.<\/p>\n

ChemSusChem<\/em>, 2026<\/strong>, 19<\/em>, e70637<\/p>\n

DOI: 10.1002\/cssc.70637<\/a><\/p>\n

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Monomer and fiber recovery from prepreg via chemical solvolysis<\/b><\/span>
\nZehan Yu, Andrew R. Rander, E. Aaron Martinez, Ding-Yuan Lim, Travis J. Williams, and Steven R. Nutt<\/p>\n

Chemical recycling offers a valorization pathway for expired prepregs with the potential to recover both monomers and well-preserved fiber fabrics, yet this approach has been largely overlooked. Here, we present the first chemical recycling protocol capable of realizing this potential, recovering both fine chemical monomers and intact, re-manufacturable fiber fabrics from expired amine\/epoxy prepregs. From bisphenol A diglycidyl ether (DGEBA)\/3,3\u2032-diaminodiphenyl sulfone (3,3\u2032-DDS) prepregs, an organic solvent wash in ethyl acetate at 75 \u00b0C and ambient pressure enabled isolation of 3,3\u2032-DDS in high yield (up to 90 %) and high purity through liquid\u2013liquid extraction and recrystallization. DGEBA-derived species were also isolated and subsequently converted to bisphenol A (BPA) with high purity and yield (up to 72 %) under hydrothermal conditions developed in this work. Carbon fiber (CF) fabrics were further cleaned under depolymerization conditions, retaining >92 % tensile strength and >98 % modulus, while preserving fabric architecture. The recovered CF fabrics were remanufactured into prepregs to produce second-generation composites that were well consolidated and exhibited short beam shear (SBS) strength comparable to virgin composites. Diamine hardener, 3,3\u2032-DDS, was derivatized under the depolymerization conditions and then restored to the parent diamine through hydrogenolysis. Collectively, this work establishes the first closed-loop chemical recycling pathway that valorizes resin, hardener, and fiber fabric from expired prepreg.<\/p>\n

Composites Part B: Engineering<\/em>, 2026<\/strong><\/p>\n

DOI: 10.1016\/j.compositesb.2025.113345 <\/a><\/p>\n

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C-N Bond Formation Through Hydrogen Borrowing<\/b><\/span>
\nAnju Nalikezhathu, Alexander Maertens, Carlos Navarro, Adriane Tam, Van Do, Long Zhang, Travis J. Williams<\/p>\n

Hydrogen-borrowing amination is a metal- or enzyme-catalyzed N-alkylation process that uses alcohols as alkyl transfer agents. In this reaction, alcohol dehydrogenation affords a carbonyl compound, which then undergoes condensation with an amine nucleophile. The imine or iminium salt product is subsequently reduced by a metal hydride generated during the preceding dehydrogenation step. This methodology is a green alternative to classical C\uf8ffN bond-forming reactions such as nucleophilic substitution and reductive amination. Hydrogen-borrowing N-alkylation is an atom economical, cost-efficient, and environmentally benign method, making it an attractive approach for the preparation of amines and nitrogen-containing groups. Continued development of these reactions has enabled the preparation of challenging substrates, and facilitated tandem and multistep reaction sequences, mainly promoted by ruthenium- and iridium-based catalytic systems. This chapter describes the history, mechanism, stereochemistry, scope and limitations, and synthetic applications of hydrogen-borrowing amination reactions. The tabular survey includes extensive coverage of coupling reactions that use a variety of nitrogen nucleophiles (i.e., ammonia, higher amines, heterocycles, acyl hydrazides, amides, iminophosphoranes, nitriles) and alcohol electrophiles.<\/p>\n

Organic Reactions<\/em>, 2026<\/strong><\/p>\n

DOI: 10.1002\/0471264180.or118.02<\/a><\/p>\n

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N-Alkylation by Hydrogen Borrowing: Pharmaceutical Applications and Comparison with Other Methods<\/b><\/span>
\nAnju Nalikezhathu and Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

Formation of C\u2013N bonds is a quintessential transformation in organic synthesis. Among the various methods to access them, hydrogen borrowing catalysis offers a green, atom-economical, and cost-effective approach, with water being the sole by-product. In this reaction, amines are alkylated using alcohol coupling partners in the presence of a transition metal catalyst. Several catalytic systems have been developed and utilized in the synthesis of pharmaceutical intermediates and complex natural products, thereby replacing conventional amination reactions with hydrogen borrowing reactions that deliver improved selectivity and yield. In this short review, we compare hydrogen borrowing N-alkylation with other classical and modern C\u2013N bond forming reactions and discuss applications in pharmaceutical synthesis.<\/p>\n

Synthesis<\/em>, 2025<\/strong><\/p>\n

DOI: 10.1055\/a-2646-8383<\/a><\/p>\n

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Ethanol as a hydrogen carrier with a value-added co-product<\/b><\/span>
\nAndrew R. Rander, Shayna R. Kohl, Valeriy Cherepakhin, Long Zhang, Van K. Do, Hanna Breunig, and Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

Traditional liquid organic hydrogen carriers (LOHCs) rely on return\/re-charge of the carrier and financial subsidy. We show here that ethanol, available at scale from fermentation, can be a revenue-positive hydrogen carrier, owing to the value of its potassium acetate co-product, itself an emerging fertilizer.<\/p>\n

Sustainable Energy Fuels<\/em>, 2025<\/strong>, 9<\/em>, 942-946<\/p>\n

DOI: 10.1039\/d4se01524j<\/a><\/p>\n

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Fiber and monomer recovery from an amine-cured epoxy composite using molten NaOH\u2013KOH<\/b><\/span>
\nY. Justin Lim, Zehan Yu, Valeriy Cherepakhin, Travis J. Williams, and Steven R. Nutt<\/p>\n

\"Abstract<\/p>\n

We report a rapid route to reclaim carbon fiber (CF) fabric and monomeric chemicals from amine-epoxy CF-reinforced polymer (CFRP) composites. We use a reaction that occurs in molten NaOH-KOH eutectic to selectively cleave aryl ether and amine linkages, which involves two temperature-dependant mechanisms. Bisphenol-A is isolated in up to quantitative yields, and recovered CF fabric is remanufactured into 2nd-generation CFRPs.<\/p>\n

Green Chem.<\/em>, 2025<\/strong>, 27<\/em>, 2184-2188<\/p>\n

DOI: 10.1039\/d4gc05299d<\/a><\/p>\n

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Recycling organoiridium waste to [(1,5-cyclooctadiene)IrCl]2<\/b><\/span>
\nValeriy Cherepakhin, and Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

We report the first process for iridium element recovery from organoiridium waste that is quantitative, pyrolysis-free, and generates no iridium metal. The key step is oxidative degradation of the waste by bleach to crude iridium(IV) hydroxide. Its treatment with hydrazine and then hydrogen peroxide gives synthetically important hexachloroiridic acid, which is converted to [(1,5-cyclooctadiene)IrCl]2 in 87% yield.<\/p>\n

Green Chem.<\/em>, 2024<\/strong>, 26<\/em>, 3146-3148<\/p>\n

DOI: 10.1039\/d4gc00151f<\/a><\/p>\n

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Composite Recycling with Biocatalytic Thermoset Reforming<\/b><\/span>
\nClarissa Olivar, Zehan Yu, Ben Miller, Maria Tangalos, Cory B. Jenkinson, Steven R. Nutt, Berl R. Oakley, Clay C. C. Wang, and Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

Carbon fiber reinforced polymers (CFRPs, or composites) are increasingly replacing traditional manufacturing materials used in the automobile, aerospace, and energy sectors. With this shift, it is vital to develop end-of-life processes for CFRPs that retain the value of both the carbon fibers and the polymer matrix. Here we demonstrate a strategy to upcycle pre- and postconsumer polystyrene-containing CFRPs, cross-linked with unsaturated polyesters or vinyl esters, to benzoic acid. The thermoset matrix is upgraded via biocatalysis utilizing an engineered strain of the filamentous fungus Aspergillus nidulans, which gives access to valuable secondary metabolites in high yields, exemplified here by (2Z,4Z,6E)-octa-2,4,6-trienoic acid. Reactions are engineered to preserve the carbon fibers with much of their sizing so that the isolated carbon fiber plies are manufactured into new composite coupons that exhibit mechanical properties comparable to those of virgin manufacturing substrates. In sum, this represents the first system to reclaim a high value from both the fiber fabric and polymer matrix of a CFRP.<\/p>\n

J. Am. Chem. Soc.<\/em>, 2024<\/strong>, 146<\/em>, 30004-30008<\/p>\n

DOI: 10.1021\/jacs.4c10838<\/a><\/p>\n

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A Polymer Degradation and Remanufacturing Experiment in the High School Classroom<\/b><\/span>
\nY. Justin Lim, Brandon Wong, Katie Macfee, Alexa Cueva, E. Aaron Martinez, Cameron Paxton, Robin Barnes, Eric Kleinsasser and Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

Most students enter college without any exposure to polymer science, which leads to the poor understanding and slow implementation of plastic recycling programs in the United States. To address the knowledge gap in chemical recycling, we introduce a 2-part laboratory experiment that was conducted in multiple high schools and public outreach events to demonstrate the depolymerization of PET via aminolysis and the remanufacturing of cleaved PET fragments into a new aramid polymer. Student experiences were evaluated with two postlab assignments.<\/p>\n

J. Chem. Educ.<\/em>, 2024<\/strong>, 101<\/em>, 131-135<\/p>\n

DOI: 10.1021\/acs.jchemed.3c00692<\/a><\/p>\n

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A rapid electrochemical method to recycle carbon fiber composites using methyl radicals<\/b><\/span>
\nZehan Yu, Y. Justin Lim, Travis Williams, and Steven Nutt<\/p>\n

\"Abstract<\/p>\n

We introduce an electrochemical approach to recycle carbon fiber (CF) fabrics from amine-epoxy carbon fiber-reinforced polymers (CFRPs). Our novel method utilizes a Kolbe-like mechanism to generate methyl radicals from CH3COOH to cleave C\u2013N bonds within epoxy matrices via hydrogen atom abstraction. Recovered CFs are then remanufactured into CFRPs without resizing.<\/p>\n

Chem. Commun.<\/em>, 2023<\/strong>, 59<\/em>, 8107-8110<\/p>\n

DOI: 10.1039\/D3GC01765F<\/a><\/p>\n

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AEROBIC DEPOLYMERIZATION OF AMINE\u2013EPOXY THERMOSET COMPOSITES<\/b><\/span>
\nCarlos A. Navarro, Yijia Ma, Katelyn Michael, Hanna Brenuig, Steven R. Nutt, Travis J. Williams<\/p>\n

Recent supply chain shortages, particularly virgin carbon fiber shortfalls, have advanced technological solutions to recover and reuse carbon fibers from waste composites. We present catalytic, aerobic conditions for depolymerizing amine-linked epoxy thermoset matrix polymers commonly used in high-performance carbon fiber-reinforced polymer (CFRP) materials. Unlike other recycling methods, this process preserves the fibers aligned and woven in the same pattern as the parent material and returns valuable materials from the thermoset matrix. Preliminary life-cycle analyses of this process relative to existing technologies reveal an opportunity to reduce energy investment in virgin carbon fiber manufacturing by 54% if executed at scale.<\/p>\n

SAMPE 2023<\/em>, Seattle, WA, 9<\/p>\n

DOI: 10.33599\/nasampe\/s.23.0185<\/a><\/p>\n

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An ambient pressure, direct hydrogenation of ketones<\/b><\/span>
\nLong Zhang, Zhiyao Lu, Andrew R. Rander and Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

We report two bifunctional (pyridyl)carbene-iridium(I) complexes that catalyze ketone and aldehyde hydrogenation at ambient pressure. Aryl, heteroaryl, and alkyl groups are demonstrated, and mechanistic studies reveal an unusual polarization effect in which the rate is dependant of proton, rather than hydride, transfer. This method introduces a convenient, waste-free alternative to traditional borohydride and aluminum hydride reagents.<\/p>\n

Chem. Commun.<\/em>, 2023<\/strong>, 59<\/em>, 8107-8110<\/p>\n

DOI: 10.1039\/d3cc01014g<\/a><\/p>\n

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SSELECTIVE CLEAVAGE OF AMINE-LINKED EPOXY COMPOSITE MATRICES BY OXYGEN<\/b><\/span>
\nY. Justin Lim, Carlos A. Navarro, Steven R. Nutt, Travis J. Williams<\/p>\n

This presentation will describe conditions for the use of oxygen as a reagent for the selective cleavage of thermoset composites. Carbon fiber-reinforced polymer (CFRP) composites have a prominent role in aviation, sporting goods, marine, and other manufacturing sectors and are accumulating en masse as waste, both at end-of-life and as manufacturing defects. We have recently introduced a method to use oxygen itself along with an appropriate catalyst selectively to disassemble such fully-cured composite wastes to recover both ordered carbon fiber sheets and organic materials suitable for re-manufacturing of second-life resin systems.<\/p>\n

SAMPE 2023<\/em>, Seattle, WA, 12<\/p>\n

DOI: 10.33599\/nasampe\/s.23.0206<\/a><\/p>\n

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Synthesis of 1,4-Diazacycles by Hydrogen Borrowing<\/b><\/span>
\nAnju Nalikezhathu, Adriane Tam, Valeriy Cherepakhin, Van K. Do and Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

We report the syntheses of 1,4-diazacycles by diol\u2013diamine coupling, uniquely made possible with a (pyridyl)phosphine-ligated ruthenium(II) catalyst (1). The reactions can exploit either two sequential N-alkylations or an intermediate tautomerization pathway to yield piperazines and diazepanes; diazepanes are generally inaccessible by catalytic routes. Our conditions tolerate different amines and alcohols that are relevant to key medicinal platforms. We show the syntheses of the drugs cyclizine and homochlorcyclizine in 91% and 67% yields, respectively.<\/p>\n

Org. Lett.<\/em>, 2023<\/strong>, 25<\/em> (10), 1754\u20131759<\/p>\n

DOI: 10.1021\/acs.orglett.3c00468<\/a><\/p>\n

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Polystyrene Upcycling into Fungal Natural Products and a Biocontrol Agent<\/b><\/span>
\nChris Rabot, Yuhao Chen, Shu-Yi Lin, Ben Miller, Yi-Ming Chiang, C. Elizabeth Oakley, Berl R. Oakley, Clay C. C. Wang and Travis J. Williams<\/p>\n

\"Abstract<\/p>\n

Polystyrene (PS) is one of the most used yet infrequently recycled plastics. Although manufactured on the scale of 300 million tons per year globally, current approaches toward PS degradation are energy- and carbon-inefficient, slow, and\/or limited in the value that they reclaim. We recently reported a scalable process to degrade post-consumer polyethylene-containing waste streams into carboxylic diacids. Engineered fungal strains then upgrade these diacids biosynthetically to synthesize pharmacologically active secondary metabolites. Herein, we apply a similar reaction to rapidly convert PS to benzoic acid in high yield. Engineered strains of the filamentous fungus Aspergillus nidulans then biosynthetically upgrade PS-derived crude benzoic acid to the structurally diverse secondary metabolites ergothioneine, pleuromutilin, and mutilin. Further, we expand the catalog of plastic-derived products to include spores of the industrially relevant biocontrol agent Aspergillus flavus Af36 from crude PS-derived benzoic acid.<\/p>\n

J. Am. Chem. Soc.,<\/em> 2023<\/strong>, 145<\/em> (9), 5222\u20135230<\/p>\n

DOI: 10.1021\/jacs.2c12285<\/a><\/p>\n

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Conversion of Polyethylenes into Fungal Secondary Metabolites<\/b><\/span>
\nChris Rabot, Yuhao Chen, Swati Bijlani, Yi-Ming Chiang, C. Elizabeth Oakley, Berl R. Oakley, Travis J. Williams, Clay C. C. Wang<\/p>\n

\"Abstract<\/p>\n

Waste plastics represent major environmental and economic burdens due to their ubiquity, slow breakdown rates, and inadequacy of current recycling routes. Polyethylenes are particularly problematic, because they lack robust recycling approaches despite being the most abundant plastics in use today. We report a novel chemical and biological approach for the rapid conversion of polyethylenes into structurally complex and pharmacologically active compounds. We present conditions for aerobic, catalytic digestion of polyethylenes collected from post-consumer and oceanic waste streams, creating carboxylic diacids that can then be used as a carbon source by the fungus Aspergillus nidulans. As a proof of principle, we have engineered strains of A. nidulans to synthesize the fungal secondary metabolites asperbenzaldehyde, citreoviridin, and mutilin when grown on these digestion products. This hybrid approach considerably expands the range of products to which polyethylenes can be upcycled.<\/p>\n

Angew. Chem. Int. Ed.<\/em>, 2023<\/strong>, 62<\/em>, e202217970.<\/p>\n

DOI: 10.1002\/anie.202214609<\/a><\/p>\n

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Kinetics and mechanistic details of bulk ZnO dissolution using a thiol-imidazole system<\/b><\/span>
\nKristopher M. Koskela, Stephen J. Quiton, Shaama Mallikarjun Sharada, Travis J. Williams and Richard L. Brutchey<\/p>\n

\"Graphical<\/p>\n

Oxide dissolution is important for metal extraction from ores and has become an attractive route for the preparation of inks for thin film solution deposition; however, oxide dissolution is often kinetically challenging. While binary \u201calkahest\u201d systems comprised of thiols and N-donor species, such as amines, are known to dissolve a wide range of oxides, the mechanism of dissolution and identity of the resulting solute(s) remain unstudied. Here, we demonstrate facile dissolution of both bulk synthetic and natural mineral ZnO samples using an \u201calkahest\u201d that operates via reaction with thiophenol and 1-methylimidazole (MeIm) to give a single, pseudotetrahedral Zn(SPh)2(MeIm)2 molecular solute identified by X-ray crystallography. The kinetics of ZnO dissolution were measured using solution 1H NMR, and the reaction was found to be zero-order in the presence of excess ligands, with more electron withdrawing para-substituted thiophenols resulting in faster dissolution. A negative entropy of activation was measured by Eyring analysis, indicating associative ligand binding in, or prior to, the rate determining step. Combined experimental and computational surface binding studies on ZnO reveal stronger, irreversible thiophenol binding compared to MeIm, leading to a proposed dissolution mechanism initiated by thiol binding to the ZnO surface with the liberation of water, followed by alternating MeIm and thiolate ligand additions, and ultimately cleavage of the ligated zinc complex from the ZnO surface. Design rules garnered from the mechanistic insight provided by this study should inform the dissolution of other bulk oxides into inks for solution processed thin films.<\/p>\n

Catal. Sci.<\/em>, 2022<\/strong>, 13<\/em>, 3208-3215<\/p>\n

DOI: 10.1039\/D1SC06667F<\/a><\/p>\n

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Pressurized formic acid dehydrogenation: an entropic spring replaces hydrogen compression cost<\/b><\/span>
\nVan K. Do, Nicolas Alfonso Vargas, Anthony J. Chavez, Long Zhang, Valeriy Cherepakhin, Zhiyao Lu,a Robert P. Currier, Pavel A. Dub, John C. Gordon and Travis J. Williams<\/p>\n

\"Graphical<\/p>\n

Formic acid is unique among liquid organic hydrogen carriers (LOHCs), because its dehydrogenation is highly entropically driven. This enables the evolution of high-pressure hydrogen at mild temperatures that is difficult to achieve with other LOHCs, conceptually by releasing the \u201cspring\u201d of energy stored entropically in the liquid carrier. Applications calling for hydrogen-on-demand, such as vehicle filling, require pressurized H2. Hydrogen compression dominates the cost for such applications, yet there are very few reports of selective, catalytic dehydrogenation of formic acid at elevated pressure. Herein, we show that homogenous catalysts with various ligand frameworks, including Noyori-type tridentate (PNP, SNS, SNP, SNPO), bidentate chelates (pyridyl)NHC, (pyridyl)phosphine, (pyridyl)sulfonamide, and their metallic precursors, are suitable catalysts for the dehydrogenation of neat formic acid under self-pressurizing conditions. Quite surprisingly, we discovered that their structural differences can be related to performance differences in their respective structural families, with some tolerant or intolerant of pressure and others that are significantly advantaged by pressurized conditions. We further find important roles for H2 and CO in catalyst activation and speciation. In fact, for certain systems, CO behaves as a healing reagent when trapped in a pressurizing reactor system, enabling extended life from systems that would be otherwise deactivated.<\/p>\n

Catal. Sci. Technol.<\/em>, 2022<\/strong>, 12<\/em>, 7182-7189<\/p>\n

DOI: 10.1039\/D2CY00676F<\/a><\/p>\n

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Out of Thin Air? Catalytic Oxidation of Trace Aqueous Aldehydes with Ambient Dissolved Oxygen<\/b><\/span>
\nEuna Kim, Georgia B. Cardosa, Katarina E. Stanley, Travis J. Williams, and Daniel L. McCurry<\/i><\/p>\n

\"Abstract<\/p>\n

Water reuse is expanding due to increased water scarcity. Water reuse facilities treat wastewater effluent to a very high purity level, typically resulting in a product water that is essentially deionized water, often containing less than 100 \u03bcg\/L organic carbon. However, recent research has found that low-molecular-weight aldehydes, which are toxic electrophiles, comprise a significant fraction of the final organic carbon pool in recycled wastewater in certain treatment configurations. In this manuscript, we demonstrate oxidation of trace aqueous aldehydes to their corresponding acids using a heterogeneous catalyst (5% Pt on C), with ambient dissolved oxygen serving as the terminal electron acceptor. Mass balances are essentially quantitative across a range of aldehydes, and pseudo-first-order reaction kinetics are observed in batch reactors, with kobs varying from 0.6 h\u20131 for acetaldehyde to 4.6 h\u20131 for hexanal, while they are low for unsaturated aldehydes. Through kinetic and isotopic labeling experiments, we demonstrate that while oxygen is essential for the reaction to proceed, it is not involved in the rate-limiting step, and the reaction appears to proceed primarily through a base-promoted \u03b2-hydride elimination mechanism from the hydrated gem-diol form of the corresponding aldehyde. This is the first report we are aware of that demonstrates useful abiotic oxidation of a trace organic contaminant using dissolved oxygen.<\/p>\n

Environ. Sci. Technol.<\/em> 2022<\/strong>, 56<\/em>, (12), 8756\u20138764<\/p>\n

DOI: 10.1021\/acs.est.2c00192<\/a><\/p>\n

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Catalyst carbonylation: a hidden, but essential, step in reaction initiation<\/b><\/span>
\nNicolas Alfonso, Van K. Do, Anthony J. Chavez, Yuhao Chen and Travis J. Williams<\/i><\/p>\n

\"Graphical<\/p>\n

The proliferation of increasingly useful reactions for hydrogen transfer in organic synthesis has included the introduction of many new homogeneous catalysts into the organic synthesis lexicon. Unlike the proliferation of palladium-based cross-coupling reactions in which the mechanism is generally conserved, we are learning that these emerging hydrogen transfer catalysts have a rich diversity of mechanisms for catalyst activation, speciation, C\u2013H bond cleavage and formation, and ultimately deactivation. We find that an underappreciated commonality in the catalytic activation for some of these systems is the generation of a (carbonyl)metal group, which dominates the downstream speciation of the catalyst system. In this mini-review we highlight a few well-documented cases of this phenomenon as food for thought for those who are designing new catalytic systems to introduce into this dynamic and impactful area.<\/p>\n

Catal. Sci. Technol<\/em>.<\/i>, 2021<\/strong>,11<\/em>, 2361-2368<\/p>\n

DOI: 10.1039\/D1CY00322D<\/a><\/p>\n

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Catalytic, aerobic depolymerization of epoxy thermoset composites\u00a0<\/b><\/span>
\nCarlos A. Navarro, Yijia Ma, Katelyn H. Michael, Hanna M. Breunig, Steven R. Nutt and Travis J. Williams\u00a0<\/i><\/p>\n

\"Graphical<\/p>\n

We present catalytic, aerobic conditions for depolymerizing amine-linked epoxy thermoset matrix polymers commonly used in high-performance carbon fiber-reinforced polymer (CFRP) materials. Unlike other recycling methods, this process preserves the fibers aligned and woven in the same pattern as the parent material and returns valuable materials from the thermoset matrix.<\/p>\n

Green Chem.<\/em>, 2021<\/strong>, 23<\/em>, 6356-6360<\/p>\n

DOI: 10.1039\/D1GC01970H<\/a><\/p>\n

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A Structural Chemistry Look At Composites Recycling<\/b><\/span>
\nCarlos A. Navarro, Cassondra R. Griffin, Boyang Zhang, Zehan Yu, Steven R. Nutt, and Travis J. Williams<\/i><\/p>\n

\"Chemistry-high-ress\"<\/p>\n

Composite materials, especially carbon fiber-reinforced polymers (CFRPs), are high-performance class of structural materials now commonly used in aircraft, marine, and other applications, with emerging large-scale use in the automotive and civil engineering applications. The difficulty of recycling these materials is a key obstacle preventing their further application in larger markets. For decades, the engineering community has pursued physical methods to recover value from end-of-life composite waste. This work has generated scalable methods to recover modest value from CFRP waste, but because of their low value recovery, these are applied to a small fraction of CFRP waste. By contrast, relatively few methods to recycle CFRPs have been based on strategic approaches systematically to deconstruct the thermoset polymers that hold them together. In this Focus Article, we will show the emergence of these structure-focused approaches to CFRP recycling and illustrate the path of this research toward the ultimate realization of methods to recover both the reinforcing fibers and the thermoset materials that comprise modern CFRPs.<\/p>\n

Navarro, C. A.,; Giffin, C. R.; Zhang, B.,; Yu, Z.,; Nutt, S. R.; Williams, T. J.;Mater. Horiz.<\/i> 2021<\/b>,7<\/i>,2479
\nDOI:10.1039\/DoMH01085E<\/a><\/p>\n

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Direct Oxidation of Primary Alcohols to Carboxylic Acids<\/b><\/span>
\nValeriy Cherepakhin and Travis J. Williams<\/i><\/p>\n

\"Direct<\/a><\/p>\n

Three complexes based on an Ir\u2013M (M = FeII, CoII, and NiII) heterobimetallic core and 2-(diphenylphosphino)pyridine (Ph2PPy) ligand were synthesized via the reaction of trans-[IrCl(CO)(Ph2PPy)2] and the corresponding metal chloride. Their structures were established by single-crystal X-ray diffraction as [Ir(CO)(\u03bc-Cl)(\u03bc-Ph2PPy)2FeCl2]\u00b72CH2Cl2 (2), [IrCl(CO)(\u03bc-Ph2PPy)2CoCl2]\u00b72CH2Cl2 (3), and [Ir(CO)(\u03bc-Cl)(\u03bc-Ph2PPy)2NiCl2]\u00b72CH2Cl2 (4). Time-dependent DFT computations suggest a donor\u2013acceptor interaction between a filled 5dz2 orbital on iridium and an empty orbital on the first-row metal atom, which is supported by UV-vis studies. Magnetic moment measurements show that the first-row metals are in their high-spin electronic configurations. Cyclic voltammetry data show that all the complexes undergo irreversible decomposition upon either reduction or oxidation. Reduction of 4 proceeds through an ECE mechanism. While these complexes are not stable to electrocatalysis conditions, the data presented here refine our understanding of the bonding synergies of the first-row and third-row metals.<\/p>\n

Cherepakhin, V.; Williams, T. J.;Synthesis<\/i> 2021<\/b>, DOI:10.1055\/s-0040-1706102<\/a><\/p>\n

 <\/p>\n

\n

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Ruthenium Catalyzed Tandem Pictet-Spengler Reaction<\/b><\/span>
\nAnju Nalikezhathu, Valeriy Cherepakhin and Travis J. Williams<\/i><\/p>\n

\"Ruthenium<\/a><\/p>\n

We report a pyridyl-phosphine ruthenium(II) catalyzed tandem alcohol amination\/Pictet\u2013Spengler reaction sequence to synthesize tetrahydro-\u03b2-carbolines from an alcohol and tryptamine. Our conditions use a Lewis acid cocatalyst, In(OTf)3, that is compatible with typically base catalyzed amination and an acid catalyzed Pictet\u2013Spengler cyclization. This method proceeds well with benzylic alcohols, heterocyclic carbinols, and aliphatic alcohols. We also show how combining this reaction with a subsequent cycloamination enables a direct synthesis of tetracyclic alkaloids like harmicine.<\/p>\n

Nalikezhathu, A.; Cherepakhin, V.; Williams, T. J.; Org. Lett.<\/i> 2020<\/b>, 22<\/i>, 4979-4984
\nDOI:10.1021\/acsorglett.oco1485 <\/a><\/p>\n

 <\/p>\n

\n

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Recovery and Reuse of Acid-Digested Amine\/Epoxy-Based Composite Matrices<\/b><\/span>
\nYija Ma, Carlos A. Navarro, Travis J. Williams, and Steven R. Nutt<\/i><\/p>\n

\"Recovery<\/a><\/p>\n

Chemical recycling of thermoset composites has been focused largely on recovering high-value carbon fibers with property retention, while recovery and reuse of decomposed polymer matrix residues is generally overlooked, despite the fact that matrix recycling constitutes an essential component of a sustainable approach to the overall problem. Our previous study demonstrated that oxidative acid digestion can be deployed effectively to recover near-virgin quality carbon fibers from amine-cured epoxy composites. In the present study, we investigate the viability of recovery and reuse of the decomposed amine\/epoxy residue after acid digestion of the matrix, effectively closing the recycling loop. We find that polymer matrix residues recovered from acid digestion solutions via neutralization and precipitation contain molecular components of the epoxies in which aromatic regions are preserved. The recovered matrix residues are blended into virgin resin formulations and two approaches are evaluate for potential reuse. Approach I utilizes the matrix residue as an accelerator for a virgin anhydride\/epoxy formulation that contains no accelerator and thus cannot be self-catalyzed. We discover that adding matrix residue produces catalytic effects on the curing reaction. In general, anhydride\/epoxy samples blended and cured with recovered matrix residues are homogenous and exhibit thermal and mechanical properties comparable to specimens cured with a commercial accelerator. Approach II deployed the matrix residue as a filler for virgin anhydride-based epoxies with a commercial accelerator to produce blended formulations. In such cases, blended formulations yielded acceptable retention of thermal and mechanical properties, provided the fraction of matrix residue added did not exceed 10 wt%.<\/p>\n

Ma, Y.; Navarro, C. A.; Williams, T. J.; Nutt, S. R.; Poly. Degrad. Stab.<\/i> 2020<\/b>, 175<\/i>,108125
\nDOI:10.1016\/j.polymddegradstab.2020.109125 <\/a><\/p>\n

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\n

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A New Mechanism of Metal-Ligand Cooperative Catalysis in Transfer Hydrogenation of Ketones<\/b><\/span>
\nIvan Demianets, Valeriy Cherepakhin, Alexander Maertens, Paul J. Lauridsen, Shaama Mallikarjun Sharada, and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

We report iridium catalysts IrCl(\u03b75-Cp\u204e)(\u03ba2-(2-pyridyl)CH2NSO2C6H4X) (1-Me, X = CH3 and 1-F, X = F) for transfer hydrogenation of ketones with 2-propanol that operate by a previously unseen metal-ligand cooperative mechanism. Under the reaction conditions, complexes 1 (1-Me and 1-F) derivatize to a series of catalytic intermediates: Ir(\u03b75-Cp\u204e)(\u03ba2-(C5H4N)CHNSO2Ar) (2), IrH(\u03b75-Cp\u204e)(\u03ba2-(2-pyridyl)CH2NSO2Ar) (3), and Ir(\u03b75-Cp\u204e)(\u03ba3-(2-pyridyl)CH2NSO2Ar) (4). The structures of 1-Me and 4-Me were established by single-crystal X-ray diffraction. A rate-determining, concerted hydrogen transfer step (2 + R2CHOH \u21c4 3 + R2CO) is suggested by kinetic isotope effects, Eyring parameters (\u0394H\u2260 = 29.1(8) kcal mol\u22121 and \u0394S\u2260 = \u221217(19) eu), proton-hydride fidelity, and DFT calculations. According to DFT, a nine-membered cyclic transition state is stabilized by an alcohol molecule that serves as a proton shuttle.<\/p>\n

Demiantes, I.; Cherepakhin, V.; Maertens, A.; Lauridsen, P. J.; Mallikarjun Sharada, S; Williams, T. J.; Polyhedron<\/i> 2020<\/b>, 182<\/i>, 114508
\nDOI:10.1016\/j.poly.2020.114508 <\/a><\/p>\n

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\n

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A Walk in Nature. Sesquiterpene Lactones as Multi-Target Agents Involved in Inflammatory Pathways<\/b><\/span>
\nAdriana Coricello, James D. Adams, Eric J. Lein, Christopher Nguyen, Filomena Perri, Travis J. Williams, and Francesca Aiello<\/i><\/p>\n

Inflammatory states are among the most common and most treated medical conditions. Inflammation comes along with swelling, pain and uneasiness in using the affected area. Inflammation is not always a simple symptom; more often is part of a defensive response of the body to an external threat or is a sign that the damaged tissue has not healed yet and needs to rest. The management of the pain associated with an inflammatory state could be a tricky task. In fact, most remedies simply quench the pain, leaving the inflammatory state unaltered. This review focuses on sesquiterpene lactones, a class of natural compounds, that represents a future promise in the treatment of inflammation. Sesquiterpene lactones are efficient inhibitors of multiple targets of the inflammatory process. Their natural sources are often ancient remedies with relevant traditional uses in folk medicines. This work also aims to elucidate how these compounds may represent the starting material for the development of new anti-inflammatory drugs.<\/p>\n

Coricello, A.; Adams, J. D.; Lein, E.; Nguyen, C.; Perri, F.; Williams, T. J.; Aiello, F.;
\nCura. Med. Chem.<\/i> 2020<\/b>, 27<\/i>, 1501-1514
\nDOI:10.2174\/0929867325666180719111123 <\/a><\/p>\n

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\n

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Catalyst Evolution In Ruthenium-Catalyzed Coupling of Amines and Alcohols<\/b><\/span>
\nValeriy Cherepakhin, and Travis J. Williams<\/i><\/p>\n

\"Catalyst<\/a><\/p>\n

We describe the mechanism, scope, and catalyst evolution for our ruthenium-based coupling of amines and alcohols, which proceeds from a [(\u03b76-cymene)RuCl(PyCH2PtBu2)]OTf (1) precatalyst. The method selectively produces secondary amines through a hydrogen borrowing mechanism and is successfully applied to several heterocyclic carbinol substrates. Under the reaction conditions, precatalyst 1 evolves through a series of catalytic intermediates: [(\u03b76-cymene)RuH(PyCH2PtBu2)]OTf (3), [Ru3H2Cl2(CO)(PyCH2PtBu2)2{\u03bc-(C5H3N)CH2PtBu2}]OTf (4), and a diastereomeric pair of [Ru2HCl(CO)2(PyCH2PtBu2)2(\u03bc-O2CnPr)]X (trans-5, X = Cl; cis-6, X = OTf). The structures of 4 and 6 were established by single-crystal X-ray diffraction. A study of catalytic activity shows that 4 is a dormant (but alive) form of the catalyst, whereas 5 and 6 are the ultimate dead forms. Electrochemical studies show that 4 is redox active and undergoes electrochemically reversible one-electron oxidation at E1\/2 = 0.442 V (vs Fc+\/Fc) in CH2Cl2 solution. We discuss the factors that govern the formation of 3\u20136 and the role of selective ruthenium carbonylation, which is essential for enabling generation of the active catalyst. We also connect these discoveries to the identification of conditions for amination of aliphatic alcohols, which eluded us until we understood the catalyst\u2019s complex speciation behavior.<\/p>\n

Cherepakhin, V.; Williams, T. J.; ACS Catal.<\/i> 2020<\/b>, 10<\/i>, 56-65
\nDOI:10.1021\/acscatal.9b03679 <\/a><\/p>\n

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Surface Coordination Chemistry of Germanium Nanocrystals Synthesized by Microwave-Assisted Reduction<\/b><\/span>
\nSarah R. Smock, Katayoon Tabatabaei, Travis J. Williams, Susan M. Kauzlarich and Richard L. Brutchey<\/i><\/p>\n

\"Surface<\/a><\/p>\n

As surface ligands play a critical role in the colloidal stability and optoelectronic properties of semiconductor nanocrystals, we used solution NMR experiments to investigate the surface coordination chemistry of Ge nanocrystals synthesized by a microwave-assisted reduction of GeI2 in oleylamine. The as-synthesized Ge nanocrystals are coordinated to a fraction of strongly bound oleylamide ligands (with covalent X-type Ge\u2013NHR bonds) and a fraction of more weakly bound (or physisorbed) oleylamine, which readily exchanges with free oleylamine in solution. The fraction of strongly bound oleylamide ligands increases with increasing synthesis temperature, which also correlates with better colloidal stability. Thiol and carboxylic acid ligands bind to the Ge nanocrystal surface only upon heating, suggesting a high kinetic barrier to surface binding. These incoming ligands do not displace native oleylamide ligands but instead appear to coordinate to open surface sites, confirming that the as-prepared nanocrystals are not fully passivated. These findings will allow for a better understanding of the surface chemistry of main group nanocrystals and the conditions necessary for ligand exchange to ultimately maximize their functionality.<\/p>\n

Smock, S. R.; Tabatabaei, K.; Williams, T. J.; Kauzlarich, S. M.; Brutchey, R. L.; Nanoscale<\/i>
\n2020<\/b>, 12<\/i>, 2764-2772
\nDOI:10.1039\/C9NRo9233A<\/a><\/p>\n

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\n

Optical pKa Control in a Bifunctional Iridium Complex<\/b><\/span>
\nIvan Demianets, Johnathan R. Hunt, Jahan M. Dawlaty, and Travis J. Williams<\/i><\/p>\n

\"Optical<\/a><\/p>\n

There are few ways to switch a catalyst\u2019s reactivity on or off, or change its selectivity, with external radiation; many of these involve photochemical activation of a catalyst. In the case of homogeneous late-transition-metal catalysts, the metal complex itself is frequently the chromophore involved in such reactivity switching. We show here a base-pendant ligand\u2013metal bifunctional scaffold wherein a photobase, a compound that becomes more basic in the excited state (pKa < pKa*), is used to switch the proton acceptor ability on an active site of the complex. The system differs from those with metal-centered chromophores, because the photobase operates independently of the metal. While excellent progress has been made in photoacid chemistry, neither a photoacid nor a photobase has been designed into the structure of a transition-metal catalyst where the metal is not part of the chromophore. We find that quinoline is an efficient photobase that preserves its unique properties in the close proximity of an iridium center: the efficacy of the photobase (9.3 < pKa* < 12.4) in the iridium complex is unhindered relative to the free quinoline. We apply this notion to successful photodriven deprotonation of an aliphatic alcohol, thus showing the first case of metal-orthogonal optical pKa control in a transition-metal complex.<\/p>\n

Demianets, I.; Hunt, J. R.; Dawlaty, J. M.; Williams, T. J.; Organometallics.<\/i> 2020<\/b>, 38<\/i>, 200-204
\nDOI:10.1020\/organomet.8boo778 <\/a><\/p>\n

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Conformational Twisting of a Formate-Bridged Diiridium Complex Enables Catalytic Formic. Acid Dehydrogenation<\/b><\/span>
\nPaul J. Lauridsen, Zhiyao Lu, Jeff J. A. Celaje, Elyse A. Kedzie, and Travis J. Williams<\/i><\/p>\n

\"Conformational<\/a><\/p>\n

We previously reported that iridium complex 1a enables the first homogeneous catalytic dehydrogenation of neat formic acid and enjoys unusual stability through millions of turnovers. Binuclear iridium hydride species 5a, which features a provocative C2-symmetric geometry, was isolated from the reaction as a catalyst resting state. By synthesizing and carefully examining the catalytic initiation of a series of analogues to 1a, we establish here a strong correlation between the formation of C2-twisted iridium dimers analogous to 5a and the reactivity of formic acid dehydrogenation: an efficient C2 twist appears unique to 1a and essential to catalytic reactivity.<\/p>\n

Lauridsen, P. J.; Lu, Z.; Celaje, J. J.; Kedzie, E. A.; Williams, T. J.; Dalton Trans<\/i> 2018<\/b>, 47<\/i>, 13559-13564
\nDOI:10.1039\/C8DT03268H<\/a><\/p>\n

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\n

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Quantifying the Thermodynamics of Ligand Binding to CsPbBr3 Quantam Dots<\/b><\/span>
\nSara R. Smock, Travis J. Williams, and Richard L. Brutchey<\/i><\/p>\n

\"Quantifying<\/a><\/p>\n

Cesium lead halide perovskites are an emerging class of quantum dots (QDs) that have shown promise in a variety of applications; however, their properties are highly dependent on their surface chemistry. To this point, the thermodynamics of ligand binding remain unstudied. Herein, 1H\u2005NMR methods were used to quantify the thermodynamics of ligand exchange on CsPbBr3 QDs. Both oleic acid and oleylamine native ligands dynamically interact with the CsPbBr3 QD surface, having individual surface densities of 1.2\u20131.7\u2005nm\u22122. 10\u2010Undecenoic acid undergoes an exergonic exchange equilibrium with bound oleate (Keq=1.97) at 25\u2009\u00b0C while 10\u2010undecenylphosphonic acid undergoes irreversible ligand exchange. Undec\u201010\u2010en\u20101\u2010amine exergonically exchanges with oleylamine (Keq=2.52) at 25\u2009\u00b0C. Exchange occurs with carboxylic acids, phosphonic acids, and amines on CsPbBr3 QDs without etching of the nanocrystal surface; increases in the steady\u2010state PL intensities correlate with more strongly bound conjugate base ligands.<\/p>\n

Smock, S. R.; Williams, T. J.; Brutchey, R. L.; Agnew. Chem. Int. Ed.<\/i> 2018<\/b>, 57<\/i>, 11711-11715
\nDOI:10.1002\/anie.201806<\/a><\/p>\n

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Iridium-Based Hydride Transfer Catalysts: from Hydrogen Storage to Fine Chemicals<\/b><\/span>
\nZhiyao Lu, Valeriy Cherepakhin, Ivan Demianets, Paul J. Lauridsen, and Travis J. Williams<\/i><\/p>\n

\"Iridium-Based<\/a><\/p>\n

Selective hydrogen transfer remains a central research focus in catalysis: hydrogenation and dehydrogenation have central roles, both historical and contemporary, in all aspects of fuel, agricultural, pharmaceutical, and fine chemical synthesis. Our lab has been involved in this area by designing homogeneous catalysts for dehydrogenation and hydrogen transfer that fill needs ranging from on-demand hydrogen storage to fine chemical synthesis. A keen eye toward mechanism has enabled us to develop systems with excellent selectivity and longevity and demonstrate these in a diversity of high-value applications. Here we describe recent work from our lab in these areas that are linked by a central mechanistic trichotomy of catalyst initiation pathways that lead highly analogous precursors to a diversity of useful applications.<\/p>\n

Lu, Z.; Cherepakhin, V.; Demianets, I.; Lauridsen, P. J.; Williams, T. J.; Chem. Commun.<\/i> 2018<\/b>, 54<\/i>, 7711-7724
\nDOI:10.1039\/C8CCo3412E <\/a><\/p>\n

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Recycling Benzoxazine-Epoxy Composites via Catalytic Oxidation<\/b><\/span>
\nJonathan N. Lo, Steven R. Nutt, and Travis J. Williams<\/i><\/p>\n

\"Recycling<\/a><\/p>\n

Carbon fiber-reinforced polymers (CFRPs) are structural composites used in the aerospace and sporting goods industries. Their chief appeal lies in their high specific properties, which generally outperform metallic counterparts. There is a contemporary need for viable methods for recycling CRFPs at the end of their lifecycles and for utilizing the considerable production waste (ca. 30%) of CFRP part manufacturing. The cost associated with these waste streams is a principal economic driver inhibiting the penetration of CRFPs into larger-scale manufacturing, particularly in the automotive industry. Reported techniques for CRFP degradation involve pyrolysis or mechanical grinding of the CFRP, processes which are outlawed in some jurisdictions and can reduce the thermomechanical properties of the recycled products. In this study, we report a conceptually different approach to degrading a commercial blended benzoxazine\/epoxy resin under mild, oxidative conditions. The thermosetting resin is polymerized, characterized, and then catalytically depolymerized via hydride abstraction with a ruthenium catalyst. These results demonstrate a concept for sustainable recycling of CFRP composites.<\/p>\n

Lo, J.; Nutt, S. R.; Williams T. J.; ACS Sustain. Chem. Eng.<\/i> 2018<\/b>, 6<\/i>, 7227-7231
\nDOI:10.1021\/acssuschemeng.8b01790 <\/a><\/p>\n

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Eliminating Porosity in an RTM Benzoxoazin Resin<\/b><\/span>
\nJonathan Lo, Xingyue Zhang, Travis J. Williams, and Steven R. Nutt<\/i><\/p>\n

Use of benzoxazine resins in composites is limited by volatile-induced porosity, which degrades the thermomechanical properties of the product. In the present study, we demonstrate how to eliminate cure-induced volatilization and volatile-induced defects in benzoxazine composite laminates, using a chemistry-based approach. Like most resins formulated for high-temperature service, benzoxazine and benzoxazine\u2013epoxy blends generally include solvent additives. Consequently, composite parts produced with such resins exhibit higher levels of cure-induced volatile release, often leading to porosity in the final manufactured part. Here, we develop a method to eliminate porosity by analyzing volatile release and the effects of residual solvent in a pre-commercial benzoxazine\u2013epoxy system designed for liquid molding by resin transfer molding. Utilizing thermogravimetric analysis, nuclear magnetic resonance spectroscopy, and dynamic mechanical analysis, we correlate the concentration of residual solvent remaining within the final manufactured part with the Tg, degradation temperature, and dynamic modulus. Lastly, a resin synthesis method is demonstrated that eliminates residual solvent in order to produce composite parts with optimal surface finish and thermomechanical properties. The report outlines a methodology for optimizing blended resin chemistry for production of high-quality composite parts.<\/p>\n

Lo, J.; Zhang, X.; Williams T. J.; Nutt, S. R.; J. Composite Materials.<\/i> 2018<\/b>, 1481-1493
\nDOI:10.1177\/0021998317727048 <\/a><\/p>\n

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Upgrading Biodiesel from Vegetable Oils By Hydrogen Transfer to its Fatty Esters<\/b><\/span>
\nZhiyao Lu, Valeriy Cherepakhin, Talya Kapenstein, and Travis J. Williams<\/i><\/p>\n

\"Upgrading<\/a><\/p>\n

Conversion of vegetable-derived triglycerides to fatty acid methyl esters (FAMEs) is a popular approach to the generation of biodiesel fuels and the basis of a growing industry. Drawbacks of the strategy are that (a) the glycerol backbone of the triglyceride is discarded as waste, and (2) most available natural triglycerides in the U.S. are multiunsaturated or fully saturated, giving inferior fuel performance and causing engine problems. Here we show that catalysis by iridium complex 1 can address both of these problems through selective reduction of triglycerides high in polyunsaturation. This is realized using hydrogen from methanol or those imbedded in the triglyceride backbone, concurrently generating lactate as a value-added C3 product. Additional methanol or glycerol as a hydrogen source enables reduction of corn and soybean oils to >80% oleate. The cost of the iridium catalyst is mitigated by its recovery through aqueous extraction. The process can be further driven with a supporting iron-based catalyst for the complete saturation of all olefins. Preparative procedures are established for synthesis and separation of methyl esters of the hydrogenated fatty acids, enabling instant access to upgraded biofuels.<\/p>\n

Lu, Z.; Cherepakhin, V.; Kapenstein, T.; Williams, T. J.; ACS Sustain. Chem. Eng.<\/i> 2018<\/b>, 6<\/i>, 5749-5753
\nDOI:10.1021\/assuschemeng.8boo653 <\/a><\/p>\n

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An Iridium Catalyst for Acceptorless Dehydrogenation of Alcohols to Carboxylic Acids<\/b><\/span>
\nValeriy Cherepakhin and Travis J. Williams<\/i><\/p>\n

\"An<\/a><\/p>\n

We introduce iridium-based conditions for the conversion of primary alcohols to potassium carboxylates (or carboxylic acids) in the presence of potassium hydroxide and either [Ir(2-PyCH2(C4H5N2))(COD)]OTf (1) or [Ir(2-PyCH2PBu2t)(COD)]OTf (2). The method provides both aliphatic and benzylic carboxylates in high yield and with outstanding functional group tolerance. We illustrate the application of this method to a diverse variety of primary alcohols, including those involving heterocycles and even free amines. Complex 2 reacts with alcohols to form the crystallographically characterized catalytic intermediates [IrH(\u03b71,\u03b73-C8H12)(2-PyCH2PtBu2)] (2a) and [Ir2H3(CO)(2-PyCH2PtBu2){\u03bc-(C5H3N)CH2PtBu2}] (2c). The unexpected similarities in reactivities of 1 and 2 in this reaction, along with synthetic studies on several of our iridium intermediates, enable us to form a general proposal of the mechanisms of catalyst activation that govern the disparate reactivities of 1 and 2, respectively, in glycerol and formic acid dehydrogenation. Moreover, careful analysis of the organic intermediates in the oxidation sequence enable new insights into the role of Tishchenko and Cannizzaro reactions in the overall oxidation.<\/p>\n

Cherepakhin, V.; Williams, T. J.; ACS Catal.<\/i> 2018<\/b>, 8<\/i>, 3754-3763
\nDOI:10.1021\/acscatal.8boo105 <\/a><\/p>\n

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Mechanism and Catalysis of Oxidative Degredation of Fiber-Reinforced Epoxy Composites<\/b><\/span>
\nCarlos A. Navarro, Elyse A. Kedzie, Yija Ma, Katelyn H. Micheal, Steven R. Nutt, and Travis J. Williams<\/i><\/p>\n

\"Mechanism<\/a><\/p>\n

Carbon fiber-reinforced polymer (CFRP) materials are widely used in aerospace and recreational equipment, but there is no efficient procedure for their end-of-life recycling. Ongoing work in the chemistry and engineering communities emphasizes recovering carbon fibers from such waste streams by dissolving or destroying the polymer binding. By contrast, our goal is to depolymerize amine-cured epoxy CFRP composites catalytically, thus enabling not only isolation of high-value carbon fibers, but simultaneously opening an approach to recovery of small molecule monomers that can be used to regenerate precursors to new composite resin. To do so will require understanding of the molecular mechanism(s) of such degradation sequences. Prior work has shown the utility of hydrogen peroxide as a reagent to affect epoxy matrix decomposition. Herein we describe the chemical transformations involved in that sequence: the reaction proceeds by oxygen atom transfer to the polymer\u2019s linking aniline group, forming an N-oxide intermediate. The polymer is then cleaved by an elimination and hydrolysis sequence. We find that elimination is the slower step. Scandium trichloride is an efficient catalyst for this step, reducing reaction time in homogeneous model systems and neat cured matrix blocks. The conditions can be applied to composed composite materials, from which pristine carbon fibers can be recovered.<\/p>\n

Navarro, C. A.; Kedzie, E. A.; Ma, Y.; Micheal K. H.; Nutt, S. R.; Williams, T. J.; Top. Catal.<\/i> 2018<\/b>, 61<\/i>, 704-709
\nDOI:10.1007\/s1124-018-0917-2<\/a><\/p>\n

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The Treatment of Pain with Topical Sesquiterpenes. Frontiers in Natural Product Chemistry<\/b><\/span>
\nJames D. Adams, Ian S. Haworth, Adrianna Coricello, Filomena Perri, Christopher Nguyen, Francesca Aiello, Travis J. Williams and Eric J. Lein <\/i><\/p>\n

The best and safest treatment for pain is with topical treatments on the skin. This is most evident with acupuncture that occurs in the skin, is safe and effective. Even broken bones, post-operative pain, replaced hips, replaced knees, cancer pain and other severe pain can be treated effectively and safely with topical medicines. A liniment is available that has been used in many acute and chronic pain patients with success as will be discussed. Cyclooxygenase-2 is found in the skin and is induced in chronic pain conditions. Oral medications do not reach high enough concentrations in the skin to inhibit the enzyme. Instead, oral nonsteroidal anti-inflammatory medications poison the body and are toxic to the stomach and kidneys. These oral medications cause at least 10,000 ulcer deaths yearly in the USA. They also cause clotting problems that lead to heart attacks and strokes. Pain is sensed in the skin at sensory afferent neurons. The activities of pain sensing transient receptor potential cation channels in these neurons are increased by prostaglandins made by cyclooxygenase-2. Pain is best treated with topical preparations that penetrate the skin in small amounts, inhibit cyclooxygenase-2 and are not poisonous to the body. Sesquiterpenes are 15 carbon compounds found in plants and can penetrate the skin. These compounds down regulate the transcription of cyclooxygenase-2 through an NF-kB mediated mechanism and may also inhibit cyclooxygenase-2 and other targets directly. This review is a discussion of the medicinal chemistry and pharmacology of sesquiterpenes that permits these molecules to relieve severe and chronic pain.<\/p>\n

Adams, J. D.; Haworth, I.; Coricello, A.; Perri, F.; Nguyen, C.; Aiello, F.; Williams T. J.; Lein, E. J.; Bentham Science.<\/i> 2017<\/b>, 3<\/i>, 176-195
\nDOI:10.2174\/97816810853401170301 <\/a><\/p>\n

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Comparison of Three Methods for the Methylation of Aliphatic and Aromatic Compounds<\/b><\/span>
\nHyejung Lee, Sarah J. Feakins, Zhiyao Lu, Arndt Schimmelmann, Alex L. Sessions, Jessica E. Tierney, and Travis J. Williams<\/i><\/p>\n

Methylation protocols commonly call for acidic, hot conditions that are known to promote organic 1H\/2H exchange in aromatic and aliphatic C\u2013H bonds. Here we tested two such commonly used methods and compared a third that avoids these acidic conditions, to quantify isotope effects with each method and to directly determine acidic\u2010exchange rates relevant to experimental conditions.We compared acidic and non\u2010acidic methylation approaches catalyzed by hydrochloric acid, acetyl chloride and EDCI (1\u2010ethyl\u20103\u2010(3\u2010dimethylaminopropyl)carbodiimide)\/DMAP (4\u2010dimethylaminopyridine), respectively. These were applied to two analytes: phthalic acid (an aromatic) and octacosanoic acid (an aliphatic). We analyzed yield by gas chromatography\/flame ionization (GC\/FID) and hydrogen and carbon isotopic compositions by isotope ratio mass spectrometry (GC\/IRMS). We quantified the 1H\/2H exchange rate on dimethyl phthalate under acidic conditions with proton nuclear magnetic resonance (1H\u2010NMR) measurements. The \u03b42H and \u03b413C values and yield were equivalent among the three methods for methyl octacosanoate. The two acidic methods resulted in comparable yield and isotopic composition of dimethyl phthalate; however, the non\u2010acidic method resulted in lower \u03b42H and \u03b413C values perhaps due to low yields. Concerns over acid\u2010catalyzed 1H\/2H exchange are unwarranted as the effect was trivial over a 12\u2010h reaction time. We find product isolation yield and evaporation to be the main concerns in the accurate determination of isotopic composition. 1H\/2H exchange reactions are too slow to cause measurable isotope fractionation over the typical duration and reaction conditions used in methylation. Thus, we are able to recommend continued use of acidic catalysts in such methylation reactions for both aliphatic and aromatic compounds.<\/p>\n

Lee, H.; Feakins, S. J.; Lu, Z.; Schimmelmann, A.; Sessions, A. L.; Tierney, J. E.; Williams T. J.;
\nRapid Commun. Mass Spec.<\/i> 2017<\/b>, 31<\/i>, 1633-1640
\nDOI:10.1002\/rcm.7947 <\/a><\/p>\n

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Ruthenium-Catalyzed Ammonia Borane Dehydrogenation: Mechanism and Utility <\/b><\/span>
\nXingyue Zhang, Lisa Kam, Ryan Trerise, and Travis J. Williams<\/i><\/p>\n

\"Ruthenium-Catalyzed\"<\/a><\/p>\n

One of the greatest challenges in using H2 as a fuel source is finding a safe, efficient, and inexpensive method for its storage. Ammonia borane (AB) is a solid hydrogen storage material that has garnered attention for its high hydrogen weight density (19.6 wt %) and ease of handling and transport. Hydrogen release from ammonia borane is mediated by either hydrolysis, thus giving borate products that are difficult to rereduce, or direct dehydrogenation. Catalytic AB dehydrogenation has thus been a popular topic in recent years, motivated both by applications in hydrogen storage and main group synthetic chemistry. This Account is a complete description of work from our laboratory in ruthenium-catalyzed ammonia borane dehydrogenation over the last 6 years, beginning with the Shvo catalyst and resulting ultimately in the development of optimized, leading catalysts for efficient hydrogen release. We have studied AB dehydrogenation with Shvo\u2019s catalyst extensively and generated a detailed understanding of the role that borazine, a dehydrogenation product, plays in the reaction: it is a poison for both Shvo\u2019s catalyst and PEM fuel cells. Through independent syntheses of Shvo derivatives, we found a protective mechanism wherein catalyst deactivation by borazine is prevented by coordination of a ligand that might otherwise be a catalytic poison. These studies showed how a bidentate N\u2013N ligand can transform the Shvo into a more reactive species for AB dehydrogenation that minimizes accumulation of borazine. Simultaneously, we designed novel ruthenium catalysts that contain a Lewis acidic boron to replace the Shvo -OH proton, thus offering more flexibility to optimize hydrogen release and take on more general problems in hydride abstraction. Our scorpionate-ligated ruthenium species (12) is a best-of-class catalyst for homogeneous dehydrogenation of ammonia borane in terms of its extent of hydrogen release (4.6 wt %), air tolerance, and reusability. Moreover, a synthetically simplified ruthenium complex supported by the inexpensive bis(pyrazolyl)borate ligand is a comparably good catalyst for AB dehydrogenation, among other reactions. In this Account, we present a detailed, concise description of how our work with the Shvo system progressed to the development of our very reactive and flexible dual-site boron-ruthenium catalysts.<\/p>\n

Zhang, X.; Kam, L.; Trerise, R.; Williams, T. J.; A.. Chem. Res.<\/i> 2017<\/b>, 86-95
\nDOI:10.1021\/acs.accounts.6boo482 <\/a><\/p>\n

 <\/p>\n

\n

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A Base and Solvent-Free Ruthenium-Catalyzed Alkylation of Amines<\/b><\/span>
\nJeff Joseph. A. Celaje, Xingyue Zhang, Forrest Zhang, Lisa Kam, Jessica R. Herron, and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

A (pyridyl)phosphine-ligated ruthenium(II) catalyst is reported for the chemoselective benzylic N-alkylation of amines, via a hydrogen-borrowing mechanism. The catalyst operates under mild conditions, neat, and without a base or other additive. These conditions offer remarkable functional group compatibility for applications in organic synthesis, including reactions involving phenols and anilines, which are very difficult to achieve. Mechanistic studies suggest that, unlike other catalysts for this reaction, the redox steps are fast and reversible while imine formation is slow. We perceive that this is the origin of the selectivity realized with these reaction conditions.<\/p>\n

Celaje, J. J.; Zhang, X.; Zhang, F.; Kam, L.; Herron, J. R.; Williams, T. J.; ACS Catal.<\/i>
\n2017<\/b>, 7<\/i>, 1136-1142
\nDOI:10.1021\/acscatal.6bo30888 <\/a><\/p>\n

 <\/p>\n

\n

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Di(carbene)-Supported Nickel Systems for CO2 Reduction Under Ambient Conditions <\/b><\/span>
\nZhiyao Lu and Travis J. Williams<\/i><\/p>\n

\"Dicarbone\"<\/a><\/p>\n

Di(carbene)-supported nickel species 1 and 2 are efficient catalysts for the room-temperature reduction of CO2 to methanol in the presence of sodium borohydride. The catalysts feature unusual stability, particularly for a base metal catalyst, enabling >1.1 million turnovers of CO2. Moreover, while other systems involve more expensive reducing reagents, sodium borohydride is inexpensive and easily handled. Furthermore, effecting reduction in the presence of water enables direct access to methanol. Preliminary mechanistic data collected are most consistent with a mononuclear nickel active species that mediates rate-determining reduction of a boron formate.<\/p>\n

Lu, Z.; Williams, T. J.; ACS Catal.<\/i> 2016<\/b>, 6<\/i>, 6670-6673
\nDOI:10.1021\/acscatal.6bo2101 <\/a><\/p>\n

 <\/p>\n

\n

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A Prolific Catalyst for Dehydrogenation of Neat Formic Acid<\/b><\/span>
\nJeff Joseph A. Celaje, Zhiyao Lu, Elyse A. Kedzie, Nicholas J. Terrile, Jonathan N. Lo, and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

Formic acid is a promising energy carrier for on-demand hydrogen generation. Because the reverse reaction is also feasible, formic acid is a form of stored hydrogen. Here we present a robust, reusable iridium catalyst that enables hydrogen gas release from neat formic acid. This catalysis works under mild conditions in the presence of air, is highly selective and affords millions of turnovers. While many catalysts exist for both formic acid dehydrogenation and carbon dioxide reduction, solutions to date on hydrogen gas release rely on volatile components that reduce the weight content of stored hydrogen and\/or introduce fuel cell poisons. These are avoided here. The catalyst utilizes an interesting chemical mechanism, which is described on the basis of kinetic and synthetic experiments.<\/p>\n

Celaje, J. A.; Lu, Z.; Kedzie, E. A.; Terrile, N. J.; Lo, J. N.; Williams, T. J. Nat. Commun.<\/i> 2016<\/b>, 7<\/i>, 11308
\nDOI: 10.1038\/ncomms11308 <\/a><\/p>\n

 <\/p>\n

\n

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Dehydrogenation of Ammonia Borane through the Third Equivalent of Hydrogen<\/b><\/span>
\nXingyue Zhang, Lisa Kam, and Travis J. Williams<\/i><\/p>\n

\"Dehydrogenation<\/a><\/p>\n

Ammonia borane (AB) has high hydrogen density (19.6 wt%), and can, in principle, release up to 3 equivalents of H2<\/sub> under mild catalytic conditions. A limited number of catalysts are capable of non-hydrolytic dehydrogenation of AB beyond 2 equivalents of H2<\/sub> under mild conditions, but none of these is shown directly to derivatise borazine, the product formed after 2 equivalents of H2<\/sub> are released. We present here a high productivity ruthenium-based catalyst for non-hydrolytic AB dehydrogenation that is capable of borazine dehydrogenation, and thus exhibits among the highest H2<\/sub> productivity reported to date for anhydrous AB dehydrogenation. At 1 mol% loading, (phen)Ru(OAc)2<\/sub>(CO)2<\/sub> (1) effects AB dehydrogenation through 2.7 equivalents of H2<\/sub> at 70 \u00b0C, is robust through multiple charges of AB, and is water and air stable. We further demonstrate that catalyst 1 has the ability both to dehydrogenate borazine in isolation and dehydrogenate AB itself. This is important, both because borazine derivatisation is productivity-limiting in AB dehydrogenation and because borazine is a fuel cell poison that is commonly released in H2<\/sub> production from this medium.<\/p>\n

Zhang, X.; Kam, L.; Williams, T. J. Dalton Trans.<\/i> 2016<\/b>, 45<\/i>, 7672-7677
\nDOI: 10.1039\/c6dt00604c <\/a><\/p>\n

 <\/p>\n

\n

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A Prolific Catalyst for Selective Conversion of Neat Glycerol to Lactic Acid<\/b><\/span>
\nZhiyao Lu, Ivan Demianets, Rasha Hamze, Nicholas J. Terrile, and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

We report the synthesis and reactivity of a very robust iridium catalyst for glycerol to lactate conversion. The high reactivity and selectivity of this catalyst enable a sequence for the conversion of biodiesel waste stream to lactide monomers for the preparation of poly(lactic acid). Furthermore, experimental data collected with this system provide a general understanding of its reactive mechanism.<\/p>\n

Lu, Z.; Demianets, I.; Hamze, R.; Terrile, N. J.; Williams, T. J. ACS Catal.<\/i> 2016<\/b>, 6<\/i>, 2014-2017
\nDOI: 10.1021\/acscatal.5b02732 <\/a><\/p>\n

 <\/p>\n

\n

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Nitrogen-Based Ligands Accelerate Ammonia Borane Dehydrogenation with the Shvo Catalyst<\/b><\/span>
\nXingyue Zhang, Zhiyao Lu, Lena K. Foellmer, and Travis J. Williams<\/i><\/p>\n

\"Nitrogen-Based<\/a><\/p>\n

We previously reported that quantitative poisoning, a test for homogeneous catalysis, behaves oddly in the dehydrogenation of ammonia borane (AB) by Shvo\u2019s catalyst, whereas the \u201cpoison\u201d 1,10-phenanthroline (phen) accelerates catalysis and apparently prevents catalyst deactivation. Thus, we proposed a protective role for phen in the catalysis. Herein we account for the mechanistic origin of this accelerated AB dehydrogenation in the presence of phen and define the relevance boundaries of our prior proposal. In so doing, we present syntheses for novel amine- and pyridine-ligated homologues of the Shvo catalyst and show their catalytic efficacy in AB dehydrogenation. These catalysts are synthetically easy to access, air stable, and rapidly release over 2 equiv of H2<\/sub>. The mechanisms of these reactions are also discussed.<\/p>\n

Zhang, X.; Lu, Z.; Lena, K. F.; Williams, T. J. Organometallics<\/i> 2015<\/b>, 34<\/i>,
\n3732-3738
\nDOI: 10.1021\/acs.organomet.5b00409 <\/a><\/p>\n

 <\/p>\n

\n

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A (Fluoroalkyl)Guanidine Modulates the Relaxivity of a Phosphonate-Containing T1<\/sub>-Shortening Contrast Agent<\/b><\/span>
\nXinping Wu, Anna C. Dawsey, Buddhima N. Siriwardena-Mahanama, Matthew J. Allen, and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

Responsive magnetic resonance imaging (MRI) contrast agents, those that change their relaxivity according to environmental stimuli, have promise as next generation imaging probes in medicine. While several of these are known based on covalent modification of the contrast agents, fewer are known based on controlling non-covalent interactions. We demonstrate here accentuated relaxivity of a T1<\/sub>-shortening contrast agent, Gd-DOTP5-<\/sup> based on non-covalent, hydrogen bonding of Gd-DOTP5-<\/sup> with a novel fluorous amphiphile. By contrast to the phosphonate-containing Gd-DOTP5-<\/sup> system, the relaxivity of the analogous clinically approved contrast agent, Gd-DOTA–<\/sup> is unaffected by the same fluorous amphiphile under similar conditions.<\/p>\n

Mechanistic studies show that placing the fluorous amphiphile in proximity of the gadolinium center in Gd-DOTP5-<\/sup> caused an increase in \u03c4m<\/sub> (bound-water residence lifetime or the inverse of water exchange rate, \u03c4m<\/sub> = 1\/kex<\/sub>) and an increase in \u03c4R<\/sub> (rotational correlation time), with \u03c4R<\/sub> being the factor driving enhanced relaxivity. Further, these effects were not observed when Gd-DOTA–<\/sup> was treated with the same fluorous amphiphile. Thus, Gd-DOTP5-<\/sup> and Gd-DOTA–<\/sup> respond to the fluorous amphiphile differently, presumably because the former binds to the amphiphile with higher affinity. (DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraphosphonic acid; DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid).<\/p>\n

Wu, X.; Dawsey, A. C.; Siriwardena-Mahanama, B. N.; Allen, M. J.; Williams, T. J. J. Fluor. Chem.<\/i> 2014<\/b>, 168<\/i>, 177-183
\nDOI: 10.1016\/j.jfluchem.2014.09.018 <\/a><\/p>\n

 <\/p>\n

\n

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Control of Emission Colour with N-heterocyclic Carbene (NHC) Ligands in Phosphorescent Threecoordinate copper(I) Complexes<\/b><\/span>
\nValentina A. Krylova, Peter I. Djurovich, Brian L. Conley, Ralf Haiges, Matthew T. Whited, Travis J. Williams and Mark E. Thompson<\/i><\/p>\n

\"Control<\/a><\/p>\n

A series of three phosphorescent mononuclear (NHC)\u2013copper(I) complexes were prepared and characterized. Photophysical properties were found to be largely controlled by the NHC ligand chromophore. Variation of the NHC ligand leads to emission colour tuning over 200 nm range from blue to red, and emission efficiencies of 0.16\u20130.80 in the solid state.<\/p>\n

Krylova, V. A.; Djurovich, P. I.; Conley, B. L.; Haiges, R.; Whited, M. T.; Williams, T. J.; Thompson, M. E. Chem. Commun.<\/i> 2014<\/b>, 50<\/i>, 7176-7179
\nDOI: 10.1039\/C4CC02037E <\/a><\/p>\n

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\n

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Synthesis, Structure, and Conformational Dynamics of Rhodium and Iridium Complexes of Dimethylbis(2-pyridyl)borate<\/b><\/span>
\nMegan K. Pennington-Boggio, Brian L. Conley, Michael G. Richmond, and Travis J. Williams<\/i><\/p>\n

\"Synthesis,<\/a><\/p>\n

Rhodium(I) and Iridium(I) borate complexes of the structure [Me2<\/sub>B(2-py)2<\/sub>]ML2<\/sub> (L2<\/sub> = (tBuNC)2<\/sub>, (CO)2<\/sub>, (C2<\/sub>H4<\/sub>)2<\/sub>, cod, dppe) were prepared
\nand structurally characterized (cod = 1,5-cyclooctadiene; dppe = 1,2-diphenylphosphinoethane). Each contains a boat-configured chelate ring that participates in a boat-to-boat ring flip. Computational evidence shows that the ring flip proceeds through a transition state
\nthat is near planarity about the chelate ring.<\/p>\n

We observe an empirical, quantitative correlation between the barrier of this ring flip and the \u03c0 acceptor ability of the ancillary ligand groups on the metal. The ring flip barrier correlates weakly to the Tolman and Lever ligand parameterization schemes, apparently because these combine both \u03c3 and \u03c0 effects while we propose that the ring flip barrier is dominated by \u03c0 bonding. This observation is consistent with metal-ligand \u03c0 interactions becoming temporarily available only in the near-planar transition state of the chelate ring flip and not the boat-configured ground state. Thus, this is a first-of-class observation of metal-ligand \u03c0 bonding governing conformational dynamics.<\/p>\n

Pennington-Boggio, M. K.; Conley, B. L.; Richmond, M. G.; Williams, T. J. Polyhedron<\/i> 2014<\/b>, 84<\/i> 24-31
\nDOI: 10.1016\/j.poly.2014.05.042 <\/a><\/p>\n

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Adenostoma Dasciculatum, California Chamise, Chemistry and Use in Skin Conditions<\/b><\/span>
\nAlexis Bouttemy, Osvaldo Ruiter Faria Filho, James David Adams, and Travis Williams<\/i><\/p>\n

Adenostoma fasciculatum is used traditionally to treat skin conditions such as eczema. The plant was found to contain monoterpenoids, including hydroquinone and geranial. Other terpenoids were found, including the triterpenoids 7\u03b1-hydroxybaruol and glutinol, the diterpenoids thalianol and thaliandiol as well as the steroids suberosol and campesterol. The new compound, 7\u03b1-hydroxybaruol, was further analyzed by two-dimensional nuclear magnetic resonance (NMR) imaging, 13C NMR and high-resolution high-performance liquid chromatography combined with mass spectrometry. A balm was made from the plant with olive oil and bees wax. Several patients tried the balm and reported improvements in Adams disease, eczema symptoms and seborrhea within 1 week.<\/p>\n

Boutemy, A.; Filho, O. R.; Adams, J. D.; Williams T.J.; Inter. Med. Int.<\/i> 2014<\/b>, 1<\/i>, 25-31
\nDOI:10.1159\/000362630<\/a><\/p>\n

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\n

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Synthesis and Characterization of Dimethyldi(2-pyridyl)borate Nickel(II) Complexes: A Unimolecular Square Planar to Square Planar Rotation Around Nickel(II)<\/b><\/span>
\nJeff A. Celaje, Megan K. Pennington-Boggio, Robinson W. Flaig, Michael G. Richmond, and Travis J. Williams<\/i><\/p>\n

\"Synthesis<\/a><\/p>\n

The syntheses of novel dimethylbis(2-pyridyl)borate nickel(II) complexes 4 and 6 are reported. These complexes were unambiguously characterized by X-ray analysis. In dichloromethane solvent, complex 4 undergoes a unique square-planar to square-planar rotation around the nickel(II) center, for which activation parameters of \u0394H = 12.2(1) kcal mol-1<\/sup> and \u0394S = 0.8(5) eu were measured via NMR inversion recovery experiments. Complex 4 was also observed to isomerize via a relatively slow ring flip: \u0394H = 15.0(2) kcal mol-1<\/sup>; and \u0394S = \u22124.2(7) eu. DFT studies support the experimentally measured rotation activation energy (cf. calculated \u0394H = 11.1 kcal mol-1<\/sup>) as well as the presence of a high-energy triplet intermediate (\u0394H = 8.8 kcal mol-1<\/sup>).<\/p>\n

Celaje, J. A.; Pennington-Boggio, M. K.; Flaig, R. W.; Richmond, M. G.; Williams, T. J. Organometallics<\/i> 2014<\/b>, 33<\/i>, 2019-2026
\nDOI: 10.1021\/om500173j <\/a><\/p>\n

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\n

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Non-Covalent Self Assembly Controls the Relaxivity of Bound Gd Complexes<\/b><\/span>
\nVincent Li, Yoo-Jin Ghang, Richard J. Hooley, and Travis J. Williams<\/i><\/p>\n

\"Non-Covalent<\/a><\/p>\n

The relaxivity of a magnetically responsive Gd complex can be controlled by non-covalent molecular recognition with a water-soluble deep cavitand. Lowered relaxivity is conferred by a self-assembled micellar \u201coff state\u201d, and the contrast can be regenerated by addition of a superior guest.<\/p>\n

Li, V.; Ghang, Y-J.; Hooley, R. J.; Williams, T. J. Chem. Commun.<\/i> 2014<\/b>, 50<\/i>, 1375-1377
\nDOI: 10.1039\/C3CC48389D <\/a><\/p>\n

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\n

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A Dual Site Catalyst for Mild, Selective Nitrile Reduction<\/b><\/span>
\nZhiyao Lu and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

We report a novel ruthenium bis(pyrazolyl)borate scaffold that enables cooperative reduction reactivity in which boron and ruthenium centers work in concert to effect selective nitrile reduction. The pre-catalyst compound [\u03ba3<\/sup>-(1-pz)2<\/sub>HB(N = CHCH3<\/sub>)] Ru(cymene)+<\/sup> TfO–<\/sup> (pz = pyrazolyl) was synthesized using readily-available materials through a straightforward route, thus making it an appealing catalyst for a number of reactions.<\/p>\n

Lu, Z.; Williams, T. J. Chem. Commun.<\/i> 2014<\/b>, 50<\/i>, 5391-5393
\nDOI:10.1039\/C3CC47384H <\/a><\/p>\n

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A noncovalent, fluoroalkyl coating monomer for phosphonate-covered nanoparticles<\/b><\/span>
\nVincent Li, Andy Y. Chang, and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

Gadolinium-containing phosphonate-coated gold nanoparticles were prepared and then non-covalently coated with an amphiphilic fluorous monomer. The monomer spontaneously self-assembles into a non-covalent monolayer shell around the particle. The binding of the shell utilizes a guanidinium\u2013phosphonate interaction analogous to the one exploited by the Wender molecular transporter system. Particle\u2013shell binding was characterized by a 27% decrease in 19<\/sup>F T1<\/sub> of the fluorous shell upon exposure to the paramagnetic gadolinium in the particle and a corresponding increase in hydrodynamic diameter from 3 nm to 4 nm. Interestingly, a much smaller modulation of 19<\/sup>F T1<\/sub> is observed when the shell monomer is treated with a phosphonate-free particle. By contrast, the phosphonate-free particle is a much more relaxive 1<\/sup>H T1<\/sub> agent for water. Together, these observations show that the fluoroalkylguanidinium shell binds selectively to the phosphonate-covered particle. The system’s relaxivity and selectivity give it potential for use in 19F based nanotheranostic agents.<\/p>\n

Li, V.; Chang, A. Y.; Williams, T. J. Tetrahedron<\/i> 2013<\/b>, 69<\/i>, 7741-7745
\nDOI:10.1016\/j.tet.2013.05.092<\/a><\/p>\n

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Introductory Chemistry: A Molar Relaxivity Experiment in the High School Classroom<\/b><\/span>
\nAnna C. Dawsey, Kathryn L. Hathaway, Susie Kim and Travis J. Williams<\/i><\/p>\n

\"Introductory<\/a><\/p>\n

Dotarem and Magnevist, two clinically available magnetic resonance imaging (MRI) contrast agents, were assessed in a high school science classroom with respect to which is the better contrast agent. Magnevist, the more efficacious contrast agent, has negative side effects because its gadolinium center can escape from its ligand. However, Dotarem, though a less efficacious contrast agent, is a safer drug choice. After the experiment, students are confronted
\nwith the FDA warning on Magnevist, which enabled a discussion of drug efficacy versus safety. We describe a laboratory experiment in which NMR spin lattice relaxation rate measurements are used to quantify the relaxivities of the active ingredients of Dotarem and Magnevist. The spin lattice relaxation rate gives the average amount of time it takes the excited nucleus to relax back to the original state. Students learn by constructing molar relaxivity curves based on inversion recovery data sets that Magnevist is more relaxive than Dotarem. This experiment is suitable for any analytical chemistry laboratory with access to NMR.<\/p>\n

Dawsey, A. C.; Hathaway, K. L.; Kim, S.; Williams, T. J. J. Chem. Educ.<\/i> 2012<\/b>, 90<\/i>, 922-925
\nDOI:10.1021\/ed3006902<\/a><\/p>\n

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Chemical Composition and Antinociceptive Activity of California Sagebrush Reaction<\/b><\/span>
\nPauline Fontaine, Vincent Wong, Travis J. Williams, Cecilia Garcia, and James D. Adams<\/i><\/p>\n

Artemisia californica, California sagebrush, has been reported to have pain relieving activity and is a traditional medicine of the Chumash Indians of California. Pain relieving activity of a traditional sagebrush preparation was examined in patients suffering from arthritis and other pain. The preparation was examined by gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography-mass spectrometry (HPLC-MS) to identify the compounds present. A traditional tincture of sagebrush was produced and used on 42 patients with moderate to severe pain. All patients reported pain relief within 10 to 20 min. Sagebrush was examined by GC-MS and HPLC-MS and was found to contain monoterpenoids, lipids, flavonoids and sesquiterpenes. The major monoterpenoid found is eucalyptol. Of the monoterpenoids, camphor and eucalyptol have reported pain relieving activity. They interact with transient receptor potential cation channel vanilloid 3 (TRPV3), transient receptor potential ankyrin-repeat 1 (TRPA1) and transient receptor potential melastatin 8 (TRPM8) receptors to produce pain relief that lasts for several hours.<\/p>\n

Fontaine P.; Wong, V.; Williams, T. J., Garcia C.; Adams J. D.; Journal of Pharmacognosy and Phytotherapy<\/i> 2013<\/b>, 5<\/i>, 1-11
\nDOI:10.5897\/JPP11.053<\/a><\/p>\n

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Alcohol Dehydrogenation with a Dual Site Ruthenium, Boron Catalyst Occurs at Ruthenium<\/b><\/span><\/p>\n

Zhiyao Lu, Brock Malinoski, Ana Victoria Flores, Denver Guess, Brian L. Conley, and Travis J. Williams<\/i><\/p>\n

The complex [(\u03ba3<\/sup>-(N,N,O-py2<\/sub>B(Me)OH)Ru(NCMe)3<\/sub>]+<\/sup> TfO–<\/sup> (1) is a catalyst for transfer dehydrogenation of alcohols, which was designed to function through a cooperative transition state in which reactivity was split between boron and ruthenium. We show here both stoichiometric and catalytic evidence to support that in the case of alcohol oxidation, the mechanism most likely involves reactivity only at the ruthenium center.<\/p>\n

Lu, Z.; Malinoski, B.; Flores, A. V.; Guess, D.; Conley, B. L.; Williams, T. J. Catalysts<\/i>
\n2012<\/b>, 2<\/i>, 412-421
\nDOI:10.3390\/catal2040412<\/a><\/p>\n

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A Three-Stage Mechanistic Model for Ammonia\u2013Borane Dehydrogenation by Shvo\u2019s Catalyst<\/b><\/span>
\nZhiyao Lu, Brian L. Conley, Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

We propose a mechanistic model for three-stage dehydrogenation of ammonia\u2013borane (AB) catalyzed by Shvo\u2019s cyclopentadienone-ligated ruthenium complex. We provide evidence for a plausible mechanism for catalyst deactivation and the transition from fast catalysis to slow catalysis and relate those findings to the invention of a second-generation catalyst that does not suffer from the same deactivation chemistry. The primary mechanism of catalyst deactivation
\nis borazine-mediated hydroboration of the ruthenium species that is the active oxidant in the fast catalysis case. This transition is characterized by a change in the rate law for the reaction and changes in the apparent resting state of the catalyst. Also, in this slow catalysis situation, we see an additional intermediate in the sequence of boron, nitrogen species, aminodiborane. This occurs with concurrent generation of NH3, which itself does not strongly affect
\nthe rate of AB dehydrogenation.<\/p>\n

Lu, Z.; Conley, B. L.; Williams, T. J. Organometallics<\/i> 2012<\/b>, 31<\/i>, 6705-6714
\nDOI:10.1021\/om300562d<\/a><\/p>\n

\n

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A Ruthenium-Catalyzed Coupling of Alkynes with 1,3-Diketone<\/b><\/span>
\nMegan K. Pennington-Boggio, Brian L. Conley, and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

Ruthenium(III) chloride hydrate is a convenient catalyst for the addition of active methylene compounds to aryl alkynes. These reactions are rapid, operationally simple, and high yielding in cases. Most significantly, no precautions are required to exclude air or water from the
\nreactions. All reagents are commercially available at reasonable prices, and the reactions can be conducted in disposable glassware with minimal solvent.<\/p>\n

Pennington-Boggio, M. K.; Conley, B. L.; Williams, T. J. J. Organometallic Chem.<\/i> 2012<\/b>, 716<\/i>, 6-10
\nDOI: 10.1016\/j.jorganchem.2012.05.017<\/a><\/p>\n

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\n

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Dual Site Catalysts for Hydride Manipulation<\/b><\/span>
\nBrian L. Conley and Travis J. Williams<\/i><\/p>\n

This comment describes our efforts to develop dual site catalysts for hydride manipulation. We began by analyzing the mechanism of alcohol oxidation with the ruthenium-based Shvo catalyst, which utilizes a proton transfer to template a hydride transfer from carbon
\nto ruthenium in a single transition state. In our project we are working to extend this concept of reactivity from the use of proton transfer as a templating interaction for hydride transfer to the use of a Lewis acid to coordinate and direct a substrate to a metal. Along these lines, we have found that ammonia borane, a popular and high-weight-content hydrogen storage material, has been one of our best model substrates with which to study hydride transfer mechanisms. Our ongoing studies have thus far given new insight into the reactivity of the Shvo system, particularly regarding dehydrogenation of ammonia borane, and have enabled us to design a new, prolific,
\nair- and water-tolerant, and reusable catalyst for ammonia borane dehydrogenation.<\/p>\n

Conley, B. L.; Williams, T. J. Comments Inorg. Chem.<\/i> 2012<\/b>, 32<\/i>, 195-218
\nDOI: 10.1080\/02603594.2011.642087<\/a><\/p>\n

\n

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Copper-Catalyzed Oxidation of Azolines to Azoles<\/b><\/span>
\nAnna C. Dawsey, Vincent Li, Kimberly C. Hamilton, Jianmei Wang and Travis J. Williams<\/i><\/p>\n

\"Copper-Catalyzed<\/a><\/p>\n

We report herein convenient, aerobic conditions for the oxidation of thiazolines to thiazoles and data regarding the oxidation mechanism. These reactions feature operationally simple and environmentally benign conditions and proceed in good yield to afford the corresponding azoles,
\nthus enabling the inexpensive preparation of valuable molecular building blocks. Incorporation of a novel diimine-ligated copper catalyst, [(Mes<\/sup>DABMe<\/sup>)CuII<\/sup>(OH2<\/sub>)3<\/sub>]2+<\/sup> [\u2212OTf]2<\/sub>, provides increased reaction efficiency in many cases. In other cases copper-free conditions involving a stoichiometric quantity of base affords superior results.<\/p>\n

Dawsey, A. C.; Li, V.; Hamilton, K. C.; Wang, J.; Williams, T. J. Dalton Trans.<\/i> 2012<\/b>,
\n41<\/i>, 7994-8002
\nDOI: 10.1039\/C2DT00025C<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

Synthesis and Phosphonate Binding of Guanidine-Functionalized Fluorinated Amphiphiles<\/b><\/span>
\nXinping Wu, Emine Boz, Amy M. Sirkis, Andy Y. Chang, Travis J. Williams<\/i><\/p>\n

\"Synthesis<\/a><\/p>\n

We report herein convenient procedures for the use of highly fluorinated \u03b1,\u03c9-diols (e.g. 1) as building blocks for the rapid assembly of amphiphilic materials containing a fluorous phase region. We describe expedient conversion of the parent diols to both symmetrically and asymmetrically substituted amphiphiles via the installation of an intermediate trifluoromethanesulfonyl ester. These sulfonate esters are versatile and easily manipulated intermediates, which can be readily converted to a variety of nitrogen, halogen, and carbon groups. Moreover, we show that for guanidine-terminated fluorous amphiphiles, these molecules can bind phosphonic acid groups in aqueous media. Thus, these materials offer a new strategy for decorating phosphorylated biomolecules with fluorine-rich coatings.<\/p>\n

Wu, X.; Boz, E.; Sirkis, A. M.; Chang, A. Y.; Williams, T. J. J. Fluor. Chem.<\/i> 2012<\/b>,
\n135<\/i>, 292-302
\nDOI: 10.1016\/j.jfluchem.2011.12.011<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

A Robust, Air-Stable, Reusable Ruthenium Catalyst for Dehydrogenation of Ammonia Borane<\/b><\/span>
\nBrian L. Conley, Denver Guess and Travis J. Williams<\/i><\/p>\n

\"A<\/a><\/p>\n

We describe an efficient homogeneous ruthenium catalyst for the dehydrogenation of ammonia borane (AB). This catalyst liberates more than 2 equiv of H2 and up to 4.6 system wt % H2 from concentrated AB suspensions under air. Importantly, this catalyst is robust, delivering
\nseveral cycles of dehydrogenation at high [AB] without loss of catalytic activity, even with exposure to air and water.<\/p>\n

Conley, B. L.; Williams, T. J. J. Am. Chem. Soc.<\/i> 2011<\/b>, 133<\/i>, 14212-14215
\nDOI: 10.1021\/ja2058154<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

An Inversion Recovery NMR Kinetics Experiment<\/b><\/span>
\nTravis J. Williams, Allan D. Kershaw, Vincent Li and Xinping Wu<\/i><\/p>\n

\"An<\/a><\/p>\n

A convenient laboratory experiment is described in which NMR magnetization transfer by inversion recovery is used to measure the kinetics and thermochemistry of amide bond rotation. The experiment utilizes Varian spectrometers with the VNMRJ 2.3 software, but can be easily adapted to any NMR platform. The procedures and sample data sets in this article will enable instructors to use inversion recovery as a laboratory activity in applied NMR classes and provide research students with a convenient template with which to acquire inversion recovery data on research samples.<\/p>\n

Williams, T. J.; Kershaw, A. D.; Li, V.; Wu, X. J. Chem. Ed.<\/i> 2011<\/b>, 88<\/i>,
\n665-669
\nDOI: 10.102\/ed1006822<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

Dehydrogenation of Ammonia-borane by Shvo’s Catalyst<\/b><\/span>
\nBrian L. Conley and Travis J. Williams<\/i><\/p>\n

\"Dehydrogenation<\/a><\/p>\n

Shvo’s cyclopentadienone-ligated ruthenium complex is an efficient catalyst for the liberation of exactly two molar equivalents of hydrogen from ammonia-borane, a prospective hydrogen storage medium. The mechanism for the dehydrogenation features a ruthenium hydride resting state from which dihydrogen loss is the rate-determining step.<\/p>\n

Conley, B. L.; Williams, T. J. Chem. Commun.<\/i> 2010<\/b>, 46<\/i>, 4815-4817
\nDOI:10.1039\/C003157G<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

Thermochemistry and Molecular Structure of a Remarkable Agostic Interaction in a Heterobifunctional Ruthenium\u2212Boron Complex<\/b><\/span>
\nBrian L. Conley and Travis J. Williams<\/i><\/p>\n

\"Thermochemistry<\/a><\/p>\n

A boron-pendant ruthenium species forms a unique agostic methyl bridge between the boron and ruthenium atoms in the presence of a ligating solvent, acetonitrile. NMR inversion\u2212recovery experiments enabled the activation and equilibrium thermochemistry for formation of the agostic bridge to be measured. The mechanism for bridge formation involves displacement of an acetonitrile ligand; thus, this is a rare example of a case where an agostic C\u2212H ligand
\ncompetitively displaces another tightly binding ligand from a coordinatively saturated complex. Characterization of this complex gives unique insights into the development of C\u2212H activation catalysis based on this ligand\u2212metal bifunctional motif.<\/p>\n

Conley, B. L.; Williams, T. J. J. Am. Chem. Soc.<\/i> 2010<\/b>, 132<\/i>, 1764-1765
\nDOI: 10.1021\/ja909858a<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

Discovery, Applications, and Catalytic Mechanisms of Shvo\u2019s Catalyst<\/b><\/span>
\nBrian L. Conley, Megan K. Pennington-Boggio, Emine Boz and Travis J. Williams<\/i><\/p>\n

\"Discovery,<\/a><\/p>\n

Chem. Rev.<\/i> 2010<\/b>, 110 (4)<\/i>, 2294-2312
\nDOI:10.1021\/cr9003133<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

Mechanism of Hydride Abstraction by Cyclopentadienone-Ligated Carbonylmetal Complexes (M = Ru, Fe)<\/b><\/span>
\nMegan K. Thorson, Kortney L. Klinkel, Jianmei Wang, Travis J. Williams<\/i><\/p>\n

\"Mechanism<\/a><\/p>\n

Cyclopentadienone-ligated ruthenium complexes, such as Shvo’s catalyst, are known to oxidize reversibly alcohols to the corresponding carbonyl compounds. The mechanism of this reaction has been the subject of some controversy, but it is generally believed to proceed through
\nconcerted transfer of proton and hydride, respectively, to the cyclopentadienone ligand and the ruthenium center. In this paper we further study the hydride transfer process as an example of a coordinatively directed hydride abstraction by adding quantitative understanding to some features of this mechanism that are not well understood. We find that an oxidant as weak as acetone can be used to re-oxidize the intermediate ruthenium hydride without catalyst re-oxidation becoming rate-limiting. Furthermore, C\u2013H cleavage is a significantly electrophilic event, as demonstrated by a Hammett reaction parameter of \u03c1 = \u20130.89. We then describe how the application of our mechanistic insights obtained from the study have enabled us to extend the ligand-directed hydride abstraction strategy to include a rare example of an iron(0) oxidation catalyst.<\/p>\n

European Journal of Inorganic Chemistry<\/i> 2009<\/b>, (2)<\/i>, 295-302
\nDOI:10.1002\/ejic.200800975<\/a><\/p>\n

\n

 <\/p>\n

C-H Bond Activation Mediated by Air-Stable [(diimineMII(OH)]22+ Dimers (M = Pd, Pt)<\/b><\/span>
\nTravis J. Williams, Andrew J. M. Caffyn, Nilay Hazari, Paul F. Oblad, Jay A. Labinger, John E. Bercaw<\/i><\/p>\n

\"C-H<\/a><\/p>\n

Air- and water-tolerant C\u2212H activation is observed in reactions of [(diimine)Pt(\u03bc2-OH)]22+ dimers with allylic and benzylic C\u2212H groups. The reactions proceed in good yields under mild conditions. Mechanistic studies indicate that the active species is the monomeric [(diimine)Pt(OH2)]2+ dication. The related palladium species, [(diimine)Pd(\u03bc2-OH)]22+, exhibit similar stoichiometric activations and also effect catalytic oxidation of cyclohexene to benzene with molecular oxygen as the terminal oxidant.<\/p>\n

Williams, T. J., Caffyn, A. J.; Hazari, N.; Oblad, P. F.; Labinger, J. A.; Bercaw, J. E.; J. Am. Chem. Soc.<\/i> 2008<\/b>, 130<\/i>, 2418-2419
\nDOI:10.1021\/ja076740q<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

Cyclopentadienone Synthesis by Rhodium(I)-Catalyzed [3+2] Cycloaddition Reactions of Cyclopropenones and Alkynes<\/b><\/span>
\nPaul A. Wender, Thomas J. Paxton, Travis J. Williams<\/i><\/p>\n

\"Cyclopentadienone<\/a><\/p>\n

The Rh(I)-catalyzed [3 + 2] cycloaddition of cyclopropenones and alkynes is found to provide a highly efficient and regiocontrolled route to cyclopentadienones (CPDs), building blocks of widespread use in the synthesis of natural and non-natural products, therapeutic leads, polymers, dendrimers, devices, and antigen presenting scaffolds. The versatility of the method is explored with 23 examples representing a wide range of alkyne variations (arylalkyl-, dialkyl-, heteroarylalkyl-) and diaryl- as well as arylalkylcyclopropenones. The reactions often proceed in high yield using minimal catalyst loadings and in all cases examined proceed with high or complete regioselectivity. The reaction is readily scalable to produce gram quantities of cycloadduct and provides a unique and versatile route to CPDs that would be otherwise difficult to obtain.<\/p>\n

Wender, P. A.; Paxton, T. J.; Williams, T. J.; J. Am. Chem. Soc.<\/i> 2006<\/b>, 128<\/i>,
\n14814-148159
\nDOI:10.1021\/ja065868p<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

The Intermolecular Dienyl Pauson-Khand Reaction <\/b><\/span>
\nPaul A. Wender, Nicole M. Deschamps, Travis J. Williams<\/i><\/p>\n

\"The<\/p>\n

Drei\u2010Komponenten\u2010[2+2+1]\u2010Cycloadditionen gelingen mit Dienen statt Alkenen in einer intermolekularen, RhI\u2010katalysierten Variante der Pauson\u2010Khand\u2010Reaktion (siehe Schema). Die h\u00f6here Reaktivit\u00e4t der Diene erm\u00f6glicht einen effizienten Zugang zu Alkenylcyclopentenonen ausgehend von leicht erh\u00e4ltlichen Ausgangsstoffen. R1, R2=Alkyl, Silyl, Carbonyl; R3=Me, Bn.<\/p>\n

Wender, P. A.; Deschamps, N. M.; Williams, T. J.; Agnew. Chem. Int. Ed.<\/i> 2004<\/b>, 43<\/i>, 3076-3079
\nDOI:10.1002\/ange200454117<\/a><\/p>\n

 <\/p>\n

\n

 <\/p>\n

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