Reactive intermediates in catalytic alkenylation; pathways for Mizoroki–Heck, oxidative Heck and Fujiwara–Moritani reactions

Abstract

Several closely related palladium-catalysed reactions involve the addition of Pd–C across an alkene, and subsequent β-elimination of Pd–H to give a more substituted alkene. The Pd–C precursor, normally possessing an sp² carbon bound to palladium, can be formed in several different ways, leading to sub-classes of reaction based on a common principle and convergent outcomes. The reaction pathway can vary from simple to highly subtle depending on the nature of the reactants and the ligation of the catalyst. Mechanistic analysis provides results that elucidate the pathway and link the different reaction types. The identification of reactive intermediates by NMR, ES-MS and other spectroscopic techniques, or by less direct methods, is an integral part of the process. This Feature Article covers ligand-free palladium catalysis, including the contributions of the authors, and separates catalysis where ligands are involved into cationic and neutral pathways.