Synthesis of BINAM-Based Chiral Di-1,2,3-triazolylidene Complexes and Application of the Di-NHC RhI Catalyst in Enantioselective Hydrosilylation

Despite the prolific use of (di-)NHC complexes in homogeneous catalysis, there are relatively few reports on their successful application in asymmetric transformations. In this work the atropisomeric binaphthyl backbone was combined with readily obtainable 1,2,3-triazolylidenes to develop a strongly electron-donating C-2-symmetric ligand. The ligand was efficiently synthesized in a three-step procedure in an overall yield of 91% starting from commercially available materials. Strategies for the synthesis of the corresponding di-NHC silver(I), palladium(II), rhodium(I), and iridium(I) complexes have been developed. The rhodium(I) complex was employed in the catalytic asymmetric hydrosilylation of ketones, providing good conversions at catalyst loadings as low as 0.2 mol-% and giving chiral inductions of up to 51% ee.