Boosting N-Heterocyclic Carbene Radical Organocatalysis with Nickel Chemistry: A Rational Mechanistic Study-based Approach.

A cooperative NHC/nickel catalytic methodology has been developed for the synthesis of ketones employing aromatic aldehydes and tertiary alkyl iodides. All key steps of the postulated catalytic cycle were validated with comprehensive stoichiometric and electrochemical studies, including reduction of NiII by the deprotonated Breslow intermediate, Ni0 promoted halogen-atom abstraction to generate transient tertiary alkyl radicals and coupling between the latter with the persistent acyl thiazolium radical intermediate. Such broadly proposed and accepted, yet elusive, acyl thiazolium radical intermediate has been isolated and stud-ied by a single-crystal X-ray diffraction study.