Imine hydrosilylation using an iron complex catalyst: A computational study

Abstract

The reaction mechanism for imine hydrosilylation in the presence of an iron methyl complex and hydrosilane was studied using density functional theory at the M06/6‐311G(d,p) level of theory. Benzylidenemethylamine (PhCH = NMe) and trimethylhydrosilane (HSiMe3) were employed as the model imine and hydrosilane, respectively. Hydrosilylation has been experimentally proposed to occur in two stages. In the first stage, the active catalyst (CpFe(CO)SiMe3, 1) is formed from the reaction of pre‐catalyst, CpFe(CO)2Me, and hydrosilane through CO migratory insertion into the FeMe bond and the reaction of the resulting acetyl complex intermediate with hydrosilane. In the second stage, 1 catalyzes the reaction of imine with hydrosilane. Calculations for the first stage showed that the most favorable pathway for CO insertion involved a spin state change, that is, two‐state reactivity mechanism through a triplet state intermediate, and the acetyl complex reaction with HSiMe3 follows a σ‐bond metathesis pathway. The calculations also showed that, in the catalytic cycle, the imine coordinates to 1 to form an FeCN three‐membered ring intermediate accompanied by silyl group migration. This intermediate then reacts with HSiMe3 to yield the hydrosilylated product through a σ‐bond metathesis and regenerate 1. The rate‐determining step in the catalytic cycle was the coordination of HSiMe3 to the three‐membered ring intermediate, with an activation energy of 23.1 kcal/mol. Imine hydrosilylation in the absence of an iron complex through a [2 + 2] cycloaddition mechanism requires much higher activation energies. © 2018 Wiley Periodicals, Inc.