A Well-Defined Isocyano Analogue of HCo(CO)4. 1: Synthesis, Decomposition, and Catalytic 1,1-Hydrogenation of Isocyanides

Reported here is the synthesis and characterization of the tetrakis(m-terphenyl isocyanide)cobalt hydride HCo(CNArMes2)4 (1; ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3). Monohydride 1 serves as a well-defined isocyano analogue of the tetracarbonyl hydride HCo(CO)4. While tetrakis-phosphine analogues of HCo(CO)4 have been reported previously, these compounds have failed to exhibit a reactivity profile that can be compared and contrasted with HCo(CO)4 in a systematic fashion. Herein, HCo(CNArMes2)4 (1) is shown to be a readily accessed and reactive complex that allows for this comparison. For example, HCo(CNArMes2)4 (1) is found to decompose smoothly to the κ1-C-iminoformyl complex Co(η6-(Mes)-κ1C-C(H)NArMes2)(CNArMes2) (2). Kinetic analysis of this decomposition and that of the d1-isotopomer DCo(CNArMes2)4 (1-d1) revealed a unimolecular process characterized by a large primary kH/kD isotope effect (3.2(6)) and no dependence on the presence of free CNArMes2. These data point to rate-limiting hydride α-migration and ...