Please join Yale Chemistry for a Silliman seminar in inorganic chemistry with Prof. Richard Schrock, Frederick G. Keyes Professor of Chemistry Emeritus at MIT and Distinguished Professor and George K. Helmkamp Founder’s Chair of Chemistry at the University of California, Riverside.
Abstract: Although the olefin metathesis reaction was discovered over 60 years ago, only in the last few years has it been shown how Mo and W alkylidene complexes are formed from olefins. Alkylidenes can be formed photochemically from metallacyclopentane complexes (made through addition of an olefins to a d2 olefin complex), either through a ring-contraction to yield a metallacyclobutane or through abstraction of an a hydrogen atom. A common intermediate is proposed to arise through photolytic cleavage of a M-Ca bond. A second method of forming an alkylidene consists of adding a proton to an olefin to give an alkyl complex and removal of an a proton from the alkyl so formed (the “Hcat” mechanism). The proton can be provided by an external acid or a bound proton source such as a primary amine. Internal alkylidenes are energetically favored over terminal alkylidenes and are formed preferentially if both terminal and internal alkyls are accessible. Recently it has been found that olefins themselves, if they contain an allylic CH, can provide the proton required for an Hcat reaction at room temperature.
Richard R. Schrock received his PhD in inorganic chemistry from Harvard University in 1971. After one year as an NSF postdoctoral fellow at Cambridge University and three years at the Central Research and Development Department of E. I. duPont de Nemours and Company in Wilmington Delaware, he moved to MIT in 1975. He became full professor in 1980 and the Frederick G. Keyes Professor of Chemistry in 1989. Since 2018 he has been the F. G. Keyes Professor Emeritus at MIT and the Distinguished Professor and George K. Helmkamp Founder’s Chair of Chemistry at the University of California, Riverside. His past research interests have included included the organometallic chemistry of the early transition metals, the metathesis of olefins and acetylenes, polymers made through olefin metathesis methods, and the catalytic reduction of dinitrogen to ammonia. His current research interests are restricted to alkylidene complexes and olefin metathesis reactions. He has received numerous awards and medals, the most prominent of which is the Nobel Prize in Chemistry in 2005, which he shared with R. H. Grubbs and Y. Chauvin. He has supervised over 200 PhD students and postdocs and published over 630 scientific papers.
Schrock is perhaps best known as the discoverer of alpha hydrogen abstraction reactions in high oxidation state metal alkyl complexes that yield high oxidation state “carbene” (alkylidene) and “carbyne” (alkylidyne) complexes. High oxidation state alkylidene complexes (“Schrock carbenes”) are the active catalysts for the olefin metathesis reactions, and much effort has been expended in learning how to design, synthesize, and control the activity of olefin metathesis catalysts. Schrock also showed that alkylidyne complexes (again high oxidation state) were the active species in the acetylene metathesis reaction, and that alkylidynes could be prepared in a reaction between metal-metal triple bonds and acetylenes. His interests include kinetic and mechanistic studies of high oxidation state early transition metal organometallic species, as well as the development of molybdenum and tungsten catalysts for metathesis reactions of relevance to organic synthesis. He also is active in studies concerned with the ring-opening-metathesis polymerization (ROMP) of cyclic olefins. Finally, he was the first to show that molecular nitrogen could be reduced catalytically to ammonia under mild conditions by a molybdenum catalyst in the presence of protons and electrons. For more information on Prof. Schrock’s research: Schrock Publications
