My research involves the mechanisms of organometallic reactions and developing an understanding of homogeneous catalysis.
Reductions Catalyzed by Metal Complexes with Both Hydridic and Acidic Hydrogens
For many years, we have sought to find reagents capable of simultaneously delivering a hydridic hydrogen and a protic hydrogen to polar molecules. Our initial efforts involved hertobimetallic hydrides. More recently, we initiated studies of the diruthenium hydrogenation catalysts discovered by Youval Shvo. The proposed key intermediate (C5Ph4OH)Ru(CO)2H has an electronically coupled acidic OH unit and a hydridic RuH unit. We have found that aldehydes are reduced by simultaneous transfer of H+ from OH and H- from RuH, this occurs outside the coordination sphere of the metal. We have developed improved iron hydrogenation catalysts and are now attempting to make enantioselective variants of the iron catalysts.
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 like BISBI with wide natural bite angles gave a much higher % n-aldehyde than diphosphines with narrow bite angles.