Implications of CO₂ Activation by Frustrated Lewis Pairs in the Catalytic Hydroboration of CO₂: A View Using N/Si⁺ Frustrated Lewis Pairs

A series of base-stabilized silylium species were synthesized and their reactivity toward CO₂ explored, yielding the characterization of a novel N/Si⁺ FLP-CO₂ adduct. These silicon species are active catalysts in the hydroboration of CO₂ to the methoxide level with 9-BBN, catecholborane (catBH), and pinacolborane (pinBH). Both experiments and DFT calculations highlight the role of the FLP-CO₂ adduct in the catalysis. Depending on the nature of the hydroborane reductant, two distinct mechanisms have been unveiled. While 9-BBN and catBH are able to reduce an intermediate FLP-CO₂ adduct, the hydroboration of CO₂ with pinBH follows a different and novel path where the B–H bond is activated by the silicon-based Lewis acid catalyst. In these mechanisms, the formation of a highly stabilized FLP-CO₂ adduct is found detrimental to the kinetics of the reaction.