Imine hydrosilylation using an iron complex catalyst: A computational study

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 (HSiMe 3 ) 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)SiMe 3 , 1 ) is formed from the reaction of pre‐catalyst, CpFe(CO) 2 Me, and hydrosilane through CO migratory insertion into the FeMe 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 HSiMe 3 follows a σ‐bond metathesis pathway. The calculations also showed that, in the catalytic cycle, the imine coordinates to 1 to form an FeCN three‐membered ring intermediate accompanied by silyl group migration. This intermediate then reacts with HSiMe 3 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 HSiMe 3 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.