A theoretical study on the mechanism of methylation of N-methylaniline with CO₂ and sily hydrides

The mechanism of methylation of N-methylaniline with CO₂ and the phenylsilane (PhSiH₃) was studied using density functional theory (DFT) at the M05-2X(THF, SMD)/6-311++G**//M05-2X/6-31G* level. The calculations show that the three-component reaction takes place from the reduction of CO₂ with PhSiH₃, forming the formoxysilane (FOS) species. This hydrosilylation step requires the highest activation free energy barrier (41.6 kcal/mol), and thus can be regarded as the rate-determining step (RDS) for the entire reaction. Once the FOS species is formed, its subsequent formylation with the amine to formamide (FA) species and the two successive reductions of the FA species to the desired methylamine (MA) product are easy to proceed. Furthermore, our calculations show that 1,3-diphenyldisiloxan-1-ol (PhSiH₂OSiHOHPh) is together formed with the product MA. The Si–H bond activity in PhSiH₂OSiHOHPh is higher than that in reactant PhSiH₃ and intermediate phenylsilanol (PhSiH₂OH). Thus, there exists a product catalysis as the activation free energy barrier for the FOS species formation is lowered to 36.9 kcal/mol when this species is used as a reducing agent