Mechanism of Aldehyde-Selective Wacker-Type Oxidation of Unbiased Alkenes with a Nitrite Co-Catalyst

Abstract

Traditional Wacker-type oxidations of unbiased alkenes produce ketones as major products. Recently, Grubbs’ group reported a Wacker-type oxidation system in which aldehydes (rather than ketones) have been generated predominantly in the presence of a nitrite co-catalyst. To elucidate the mechanistic origin of the aldehyde selectivity, density functional theory (DFT) studies have been conducted in this study. Two oxymetalation pathways, i.e., syn addition and anti addition pathways, were considered for various possible active species including monomeric Pd, bimetallic Pd–Pd, heterobimetallic Pd–Cu, and heterobimetallic Pd–Ag complexes. It is found that syn addition is kinetically more favored than anti addition in general. Meanwhile, the most feasible oxymetalation processes occur on the heterobimetallic Pd–Cu complexes. Investigations on the subsequent aldehyde formation process show that 1,2-H shift mechanism on tBuOH-ligated Pd–Cu complexes is superior to the betaH-elimination mechanism. Besides, the 1,2...