Substituent effect and ligand exchange control the reactivity in ruthenium(II)-catalyzed hydroacylation of isoprenes and aldehydes ‖ A DFT study

Abstract

Density functional theory (DFT) was used to investigate the reaction mechanisms of ruthenium(II)-catalyzed hydroacylation of isoprene with benzaldehyde, and o-methoxyl, m-methoxyl and p-methoxyl benzaldehyde. All intermediates and transition states were entirely optimized at the B3LYP/6-31G(d,p) level (LANL2DZ(f) for Ru). The results demonstrated that the hydroacylation had two different catalytic cycles (path I and II), path II was more favorable than path I. Ru(II)-catalyzed hydroacylation began from the first catalytic cycle, and the nucleophilic reaction was the rate-determining step. The activation barriers of hydrogen migration were the highest in two catalytic cycles, so the hydrogen migration was the rate-determining step. The activation barrier of hydrogen migration could be broken down to two parts: the free energy of exchange ([Formula: see text]) and the relative free energy of transition state ([Formula: see text]). The ligand exchange energy ([Formula: see text]) had more contribution to the activation barrier than the relative free energy of transition state ([Formula: see text]), so the ligand exchange would control these hydroacylation. Furthermore, our calculations also described the substituent effect, and the results indicated that four aldehydes showed different chemical reactivity, and benzaldehyde and m-methoxyl benzaldehyde were predicted to have the best reactivity in ruthenium hydride-catalyzed hydroacylation.