Formation of C−X Bonds Through Stable Low-Electron Count Cationic Pt(IV) Alkyl Complexes Stabilized by N-Heterocyclic Carbenes.

ABSTRACT: Cationic five coordinate Pt(IV) alkyl complexes stabilized by bulky N-heterocyclic carbenes have been isolated and fully characterized. Related species have been postulated as key intermediates in carbon-heteroatom coupling reactions, and most particularly in Shilov-type chemistry. The alkyl groups exhibit a pronounced electrophilic character and can undergo nucleophilic addition of pyridine, bromide or iodide to form new carbon-heteroatom bonds. Nevertheless, direct reductive coupling to form C–X bonds can be operative in the absence of an external nucleophile source. Coordinatively unsaturated platinum complexes in +2 or +4 oxidation states have been invoked as key intermediates in several stoichiometric and catalytic processes.1 The first example of a crystallographically characterized low electron count PtII complex was reported more than two decades ago,2 and in recent years th