Research Interests

My research lies at the interface between organometallic chemistry and homogeneous catalysis. We study the mechanisms of homogeneously catalyzed reactions. We also make model compounds related to key intermediates in catalysis and study the mechanisms of their reactions to get a better understanding of individual steps in homogeneously catalyzed reactions. In addition, we develop new organometallic reagents for organic synthesis and are designing new heterobimetallic catalysts. Several Current projects are outlined below. d0 Transition Metal-Alkyl-Alkene Complexes: Models for a Key Intermediate in Metallocene Catalyzed Alkene Polymerization. The generally accepted mechanism for Ziegler-Natta alkene polymerization involves coordination of an alkene to a transition metal alkyl complex followed by addition of the alkyl group to a coordinated alkene. Recently, we synthesized the first directly observed d0- metal-alkyl-alkene complex. Studies of these complexes give insight into the high reactivity of the catalysts and helps to explain the stereochemistry of polymerizations. Hydroformylation with Chelating Diphosphines with Wide Natural Bite Angles Near 120 degrees. Chelating diphosphines with large P-M-P bite angles near 120 degrees are interesting in the development of catalysts with controlled local geometry. In rhodium catalyzed hydroformylation, the key HRh(CO)2L2 catalysts are known to be mixtures of diequatorial diphosphine and equatorial-apical diphosphine complexes. We set out to test the hypothesis that very different regioselectivities of aldehyde formation might be obtained from diequatorial diphosphine rhodium complexes and from equatorial-apical diphosphine rhodium complexes. We found a strong correlation between regioselectivity for n-aldehyde formation and natural bite angle. Chelates with wide natural bite angles gave much higher percentage n-aldehyde than diphosphines with narrow bite angles. We are now doing experiments to probe the role of steric and electronic effects in controlling this regioselectivity. Pi-Propargyl Complexes. p-Propargyl complexes are the triple bond analog of p-allyl metal complexes which have proven so useful in organic synthesis. We recently synthesized some of the first complexes of this type and found that nucleophiles selectively attack the central carbon of the propargyl unit. We are designing catalytic reactions that utilize this fundamental chemistry.

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Section 14: Chemistry