Mechanistic insight into Ni-mediated decarbonylation of unstrained ketones: the origin of decarbonylation catalytic activity

Abstract

Mechanistic details of the decarbonylation of unstrained ketones by (IMes^Me)Ni and (IMes^Me)NiCO complexes with a N-heterocyclic carbene ligand (IMes^Me) have been explored by density functional theory calculations. The calculated mechanism sheds light on the origin of realization for the decarbonylation catalytic cycle. (IMes^Me)Ni mediates the first decarbonylation cycle and generates a biaryl product and (IMes^Me)NiCO, which is inactive for the substrate 4-methyl-4′-trifluoromethyl benzophenone 1. However, (IMes^Me)NiCO can mediate the decarbonylation of 3-quinolinyl ketone 2 and realize the catalytic cycle. The decarbonylation step is the rate-determining step controlling whether the transformation can be mediated catalytically. The stabilization energy E⁽²⁾ of BD_{C(O)–C(methyl phenyl)} → LV_Ni for the decarbonylation transition state plays a dominant role in the catalytic cycle. In addition, an electron-withdrawing group on the arene can stabilize the orbital energies facilitating the initial C–C(O) oxidative addition step. A moderate linear correlation is observed between the oxidative addition barriers and the charges transferred from (IMes^Me)Ni to the benzoyl moiety.