The reaction mechanisms of boron amidinate and small molecules: a density function theory study

摘要

Density functional theory calculations have been carried out to explore the reaction mechanisms for the reactions of “frustrated Lewis pairs” (FLPs) with small molecules. Four reactions were studied in the present investigation. A new N-heterocyclic carbene borane, boron amidinate compound HC(iPrN)₂B(C₆F₅)₂ (1), classified as FLPs, was chosen as the common reactant of these reactions. It was used to react with CO₂, CO, and two terminal alkynes, methylacetylene and phenylacetylene. The reactions of 1 with CO₂ and CO can both be regarded as the concerted addition mechanisms. In these reactions, the formations of the C2–N2 and B–O1 bonds take place simultaneously. For the reactions of 1 and methylacetylene or phenylacetylene, our calculations indicated that a deprotonation pathway and the connection between B atoms and terminal alkyne C atoms occur by a concerted manner simultaneously, together with the connection between N2 and hydrogen atoms. We also investigated the reaction mechanisms according to the frontier molecular orbital (FMO) theory and carried out electric charge analyses, finding that the two results were consistent with each other perfectly. Electric charges transfer from HOMO of 1_OPEN to LUMO of CO₂ or CO. In contrast, electric charges transfer from HOMO of methylacetylene or phenylacetylene to LUMO of 1_OPEN.