Mechanisms of Transition Metal Catalyzed Reactions in Hydrocarbons

California Institute Of Technology, Pasadena CA

Investigators

Abstract

With this award, the Chemical Catalysis Program of the Division of Chemistry is funding Professor Robert H. Grubbs of the California Institute of Technology to carry out fundamental studies on olefin metathesis catalysts based on the element, ruthenium. Olefins (organic compounds containing carbon-carbon double bonds) are a key linkage in many important organic compounds that are used for pharmaceuticals, commodity chemicals and polymeric materials. Olefin metathesis is a reaction that consists of breaking and rearranging carbon-carbon double bonds in organic molecules. The olefin metathesis reaction has revolutionized the synthesis of organic molecules relevant to natural and unnatural products for treatment of diseases such as hepatitis C and AIDS, as well as the synthesis of specialty materials. Professor Grubbs is studying ways to make the catalysts more reactive and selective than any previous catalysts. The broader impacts of the research could be wide ranging in terms of furthering the role of olefin metathesis in chemical science, advancing commercial uses of olefin metathesis, and training and educating students. The Grubbs research group is performing synthetic, mechanistic, structural, and reactivity studies of newly designed catalysts for the olefin metathesis reaction. The present generation of catalysts is highly active but tends to give a mix of different isomers. Over the past several years, considerable progress has been made in developing catalysts for the synthesis of Z-isomers of olefins in high yield and stereoselectivity, but to make a catalyst that selectively makes the E-isomer has proven to be more difficult. The strategies used to develop Z-selective catalysts are being modified, with guidance from theoretical modeling, to design new complexes with the goal of reaching an E-selective system. The geometry of the substituents on the metallacycle controls the geometry of the double bond produced in the reaction. In the Z-selective catalyst, chelated ligand systems force the metallacycle and the N-heterocyclic carbene ligand together so that all the subsitutents on the intermediate metallacycle are forced to one side of the metallacycle. In the present work, Professor Grubss is using the same design strategies to form ligand arrays that force the substituents trans to each other in the metallacycle so that the resulting olefin will be trans (E). In addition to the applications of the E-selective catalysts, the pathway to them will test and broaden the mechanistic model for the factors that control catalyst selectivity and activity.