Theoretical Insights on the Interaction of N-Heterocyclic Carbenes with Tetravalent Silicon Reagents

Lewis acid–base type interaction between N-heterocyclic carbene (NHC) and tetravalent silicon reagent (SiR) has been investigated computationally. This NHC–Si interaction is of fundamental importance to the understanding of variety of NHC catalyzed organic transformations involving silicon compounds such as cyanosilylation, trifluoromethylsilylation, etc. Geometries of 24 NHCs, 10 silicon reagents, and their 61 Lewis acid–base complexes have been optimized using the B3LYP/6-31+G(d,p) and M05-2X/6-31+G(d,p) level of theory. The strength of NHC–Si interaction has been assessed in terms of binding energy of the complexes, charge transfer (CT) and the length of Si–CNHC bond. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis at M052X/6-31+G(d,p) level of theory has been carried out to get a deeper understanding of the nature of bonding and charge delocalization. Proton affinity of the NHCs and fluoride affinity of the SiRs have been calculated and correlated with the binding energy of the resulting complexes.