Analysis of Autoinduction, Inhibition, and Autoinhibition in a Rh-Catalyzed C–C Cleavage: Mechanism of Decyanative Aryl Silylation

The mechanism the Chatani–Tobisu rhodium-catalyzed decyanative silylation of aryl nitriles by hexamethyldisilane (Me3Si-SiMe3) has been investigated by in situ NMR spectroscopy. The production of Ar-SiMe3 evolves in three distinct phases: slow catalyst induction is followed by a period of rapidly accelerating turnover and then, after approximately three catalyst turnovers, the onset of progressive inhibition. The processes giving rise to these phenomena have been elucidated by isotopic labeling (13C/15N) and kinetic analysis, and it is shown that, in addition to facilitating catalyst turnover to generate Ar-SiMe3, the reactants serve other roles. Me3Si-SiMe3 functions as a slow exogenous precatalyst activator and as a moderately powerful catalyst inhibitor. In contrast, ArCN acts as a precatalyst inhibitor. Moreover, the coproduct from the reaction (trimethylsilyl cyanide, Me3SiCN) acts as a powerful endogenous precatalyst activator and catalyst inhibitor, together giving rise to sigmoidal temporal concen...