New Early Transition Metal Metallocene Chemistry

University Of Chicago, Chicago IL

Investigators

Abstract

This award by the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Richard F. Jordan of the University of Chicago to develop efficient methods for the stereoselective synthesis of chiral ansa-metallocenes and to expand the fundamental understanding of the properties of d0 metal olefin complexes that are models for transient intermediates in olefin polymerization reactions. Metallocene complexes of early transition metals, such as Ti, Zr and Hf, are important in organic synthesis and closely related cationic complexes are the active species in olefin polymerizations. Chiral ansa-metallocenes, in which the two cyclopentadienyl rings are linked, are important stereoselective olefin polymerization catalysts and have been employed as enantioselective catalysts or reagents for other olefin reactions. Metallocene compounds with ligands that can control the face-selectivity of cyclopentadienyl ligands will be prepared involving 6-membered chelate rings in bis-amide complexes that adopt twist conformations, which complement 2-fold symmetric rac-metallocenes and strongly disfavor meso-metallocene structures. This first part of this research will: 1) develop streamlined ansa-metallocene syntheses based on chelate-controlled salt-elimination and amine-elimination reactions, 2) establish the generality of this approach for group 4 and group 3/lanthanide ansa-metallocenes with diverse structures, 3) understand the stereocontrol mechanisms in chelate-controlled ansa-metallocenes with synthesis through studies of the conformational and dynamic properties of group 4 metal bis-amide complexes, and 4) design chiral group-4 metal bis-amide precursors for the enantioselective synthesis of ansa-metallocenes. The second part of this research is to use alkoxy metallocene olefin complexes as models for the similar alkyl metallocene olefin cation complexes that are involved in olefin polymerization. The alkoxide model systems exhibit enhanced thermal stability and do not undergo olefin insertion, which enables studies of the metal-olefin bonding. Models are designed to provide a detailed picture of how d0 metal species bind and activate olefins. This project will provide rigorous and broad training for graduate students and postdoctoral fellows in challenging organometallic synthesis, modern spectroscopic methods and mechanistic studies, and facilitate the application of the targeted compounds in economically important catalytic syntheses. Synthetic routes to enantioselective catalytic reagents will be devised and models of complexes that catalyze the polymerization of olefins will be used to gain insight as to how these catalysts operate.