Mechanistic study of catalytic copper-diaminocarbene (NHC) systems through computational ab initio, as well as experimental chemical studies

The goal of this project is to fully characterize the mechanism of the (NHC)-Cu(I) catalyzed hydrosilylation reaction of carbonyls by experimental methods, kinetic studies and DFT calculations. We first developed two synthetic pathways to unprecedented (NHC)Cu(I) bifluoride complexes and tested there catalytic activity in several known Cu(I) catalyzed reaction, demonstrating high catalytic activities. During these trials, we established the first Cu-catalyzed diastereoselective allylation of (R)-N-tert-butanesulfinyl aldimines, which enables efficient, simple and general synthesis of enantiomerically enriched homoallylic amines at room temperatures in high yields. The self-activating mechanism of these (NHC) copper(I) (bi)fluoro pre-catalysts was elucidated by a combined theoretical and experimental NMR study, showing bifluoride copper(I) complexes to be auto-activating catalysts. The plausibility of the catalytic cycle is then investigated by a theoretical DFT study, on small model systems. Computations show both steps of the catalytic cycle to involve a 4 center metathesis transition state. Finally, we present a detailed computational study of this reaction on realistic model systems. This study is supported by kinetic investigations, using in situ FTIR measurements. The calculations validate the previously proposed reaction mechanism and explain the high activity of (OR1)xR2(3-x)Si-H type of silanes. Experimental evidence in favor of the monomeric (NHC)-Cu-H form of the catalyst is also given. Combining experimental and theoretical results furthermore highlights a Lewis base activation of the hydrosilane, leading to a modified suggestion for the mechanistic scheme of the catalytic cycle.