1-Butyl-3-methyl-imidazolium Acetate as a Highly Active and Selective Organocatalyst for CO2 Hydrosilylation: Insights into the Reaction Mechanism

Valorization of CO2 as a C1 synthon for synthesizing value-added chemicals and polymers reduces the emissions of this greenhouse gas in the atmosphere and paves the way to new synthetic routes in sustainable chemistry. In this contribution, the commercially available ionic liquid 1-butyl-3-methyl imidazolium acetate [BMIm][Ac] has been successfully tested as an organocatalyst in CO2 hydrosilylation to produce formoxysilane in moderate to good yields under a very low catalyst loading (0.1 mol %). The H-1, C-13, and Si-29 NMR spectroscopy monitoring of CO2 reduction in the presence of a stoichiometric amount of dimethylphenylsilane (Me2PhSiH) allowed identifying the anionic pentacoordinate organosilicon species [Me2PhSi(OCHO)(Ac)](-) resulting from the nucleophilic attack of the acetate anion to the silane, determining the activation of the hydride transfer from the silicon atom to CO2; this species was characterized by Si-29 NMR spectroscopy and identified in the negative electrospray ionization mass spectrometry (ESI-MS) spectrum of the reaction mixture. The kinetic investigation of the reaction pathway, combined with density functional theory (DFT) modeling, corroborated this mechanistic hypothesis and contributed to shed light on the reaction mechanism.