Presidential Green Chemistry Challenge: 2007 Academic Award

Professor Michael J. Krische of the University of Texas at Austin

Hydrogen-Mediated Carbon–Carbon Bond Formation

Innovation and Benefits: A fundamental aspect of chemistry involves creating chemical bonds between carbon atoms. Chemical processes commonly used to make such bonds usually also generate significant amounts of waste. Professor Krische developed a broad new class of chemical reactions that make bonds between carbon atoms using hydrogen and metal catalysts. This new class of reactions can be used to convert simple chemicals into complex substances, such as pharmaceuticals, pesticides, and other important chemicals, with minimal waste.

Summary of Technology: Reductions mediated by hydrogen, termed "hydrogenations", rank among the most widely used catalytic methods employed industrially. They are generally used to form carbon-hydrogen (C–H) bonds. Professor Michael J. Krische and his coworkers at the University of Texas at Austin have developed a new class of hydrogenation reactions that form carbon-carbon (C–C) bonds. In these metal-catalyzed reactions, two or more organic molecules combine with hydrogen gas to create a single, more complex product. Because all atoms present in the starting building-block molecules appear in the final product, Professor Krische's reactions do not generate any byproducts or wastes. Hence, Professor Krische's C–C bond-forming hydrogenations eliminate pollution at its source.

Prior to Professor Krische's work, hydrogen-mediated C–C bond formations were limited almost exclusively to the use of carbon monoxide in reactions such as alkene hydroformylation (1938) and the Fischer-Tropsch reaction (1923). These prototypical hydrogen-mediated C–C bond formations are practiced industrially on an enormous scale. Yet, despite the importance of these reactions, no one had engaged in systematic research to develop related C–C bond-forming hydrogenations. Only a small fraction of hydrogenation's potential as a method of C–C coupling had been realized, and the field lay fallow for nearly 70 years.

Professor Krische's hydrogen-mediated couplings circumvent the use of preformed organometallic reagents, such as Grignard and Gilman reagents, in carbonyl and imine addition reactions. Such organometallic reagents are highly reactive, typically moisture-sensitive, and sometimes pyrophoric, meaning that they combust when exposed to air. Professor Krische's coupling reactions take advantage of catalysts that avoid the hazards of traditional organometallic reagents. Further, using chiral hydrogenation catalysts, Professor Krische's couplings generate C–C bonds in a highly enantioselective fashion.

Catalytic hydrogenation has been known for over a century and has stood the test of time due its efficiency, atom economy, and cost-effectiveness. By exploiting hydrogenation as a method of C–C bond formation, Professor Krische has added a broad, new dimension to one of chemistry's most fundamental catalytic processes. The C–C bond-forming hydrogenations developed by Professor Krische allow chemists to create complex organic molecules in a highly selective fashion, eliminating both hazardous starting materials and hazardous waste. Commercial application of this technology may eliminate vast quantities of hazardous chemicals. The resulting increases in plant and worker safety may enable industry to perform chemical transformations that were too dangerous using traditional reagents.

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