Cross-Dehydrogenative Coupling of Secondary Amines with Silanes Catalyzed by Agostic Iridium-NSi Species

Abstract

An active catalytic system for the cross-dehydrogenative coupling (CDC) of a wide range of secondary amines with silanes is reported. The iridium(III) derivatives [Ir(H)(X)(κ²-NSi^DMQ)(L)] (NSi^DMQ = {4,8-dimethylquinoline-2-yloxy}dimethylsilyl; L = coe, X = Cl, 2; L = coe, X = OTf, 3; L = PCy₃, X = Cl, 4; L = PCy_3, X = OTf, 5), which are stabilized by a weak yet noticeable Ir···H–C agostic interaction between the iridium and one of the C–H bonds of the 8-Me substituent of the NSi^DMQ ligand, have been prepared and fully characterized. These species have proven to be effective catalysts for the CDC of secondary amines with hydrosilanes. The best catalytic performance (TOF_1/2 = 79,300 h^–1) was obtained using 5 (0.25 mol %), N-methylaniline, and HSiMe₂Ph. The catalytic activity of the species [Ir(H)(OTf)(κ²-NSi^Q)(PCy₃)] (10, NSi^Q = {quinoline-2-yloxy}dimethylsilyl) and [Ir(H)(OTf)(κ²-NSi^MQ)(PCy₃)] (11, NSi^MQ = {4-methylquinoline-2-yloxy}dimethylsilyl), related to 5 but lacking the 8-Me substituent, is markedly lower than that found for 5. This fact highlights the crucial role of the 8-Me substituent of the NSi^DMQ ligand in enhancing the catalytic performance of these iridium complexes.