Cooperative Bond Activation Reactions with Nickel and Palladium Carbene Complexes with a PCcarbeneS Pincer Ligand

A new PCcarbeneS ligand has been designed to stabilize late transition metal carbene complexes with Schrock-type reactivity for bond activations via metal–ligand cooperation. This ligand combines previous approaches to such complexes by stabilizing the carbene moiety through either charge delocalization into adjacent aryl groups or the use of an anion-stabilizing substituent. Nickel and palladium complexes of the PCcarbeneS pincer ligand could be prepared by dehydrohalogenation of the precursors (PCsp3S)­NiCl and (PCsp3S)­PdCl and were characterized in solution and solid state. X-ray diffraction (XRD) analyses as well as density functional theory (DFT) studies demonstrate that the electronic structure of these complexes can be described by a carbene as well as a zwitterionic complex with a M–C single bond. Due to the strong nucleophilic character at the carbon atom, both complexes are highly reactive and undergo sulfur transfer to form thioketone complexes. The nickel carbene complex is capable of cooperative O–H and N–H bond activations including ammonia activation across the NiC bond.