SusChEM: Extending organochromium chemistry - stable alkyl hydrides and high-valent alkylidenes

University Of Delaware, Newark DE

Investigators

Abstract

The Chemical Catalysis Program of the Chemistry Division supports the project by Professor Klaus Theopold. Professor Theopold is a faculty member in the Department of Chemistry and Biochemistry at the University of Delaware. He is extending the organometallic chemistry of chromium in previously unexplored directions. One part of this project aims to explore the activation of carbon-hydrogen bonds of simple hydrocarbons. The activation and functionalization of carbon (C)-hydrogen (H) bonds is a significant challenge and offers opportunities for the synthesis of useful organic molecules. The other part of this project explores the reactivity of chromium alkylidenes in the highest possible oxidation state (VI) of that metal. Such molecules are rare and their potential for catalytic transformation were unknown prior to this work. Accordingly, the research project is uncovering new catalytic reaction pathways that aid modern synthetic organic chemistry. The work lies at the interface of inorganic and organic chemistry. Its broad reach is designed to train synthetic chemists at all levels. Professor Theopold's outreach activities include service as judge for a high school science fair, volunteer work for the Franklin Institute, a science museum in Philadelphia, PA, and the publication of a textbook for General Chemistry courses for Science, Technology, Engineering and Mathematics majors. Previous work in the Theopold laboratory has led to the discovery of several unusually stable dinuclear chromium alkyl hydrides of the type LCr(mu-R)(mu-H)CrL, which may be seen as products of the C-H activation of hydrocarbons, and which in turn engage in C-H activation reactions of simple hydrocarbons. One part of the project is to identify synthetic routes for the preparation and structural characterization of a wider range of such compounds. This study facilitates an examination of their relative stability and reactivity. The program also includes investigations of the mechanism of their reaction with hydrocarbons, leading to alkyl group exchange. In another extension of chromium chemistry, a rare chromium alkylidene has been prepared and its structure determined. This project involves the synthesis of alkylidenes of the type (ArN)2Cr(VI)=CHR. The reactivity of these unusually high-valent compounds has not previously been explored in any detail. Potential catalytic applications involve olefin metathesis and polymerization. The synthetic work is augmented by relevant DFT calculations. Prof. Theopold's research group is diverse and offers educational opportunities to students underrepresented in science fields and students with disabilities.