'Pincer' Pyridine-Dicarbene-Iridium Complexes: Facile C—H Activation and Unexpected η~2-Imidazol-2-ylidene Coordination

摘要

Anionic 2,6-diphosphinomethylphenyl (P-C-P), 2,6-diphos-phinitophenyl (PO-C-OP), and neutral 2,6-diphosphinome-thylpyridine (P-N-P) "pincer" complexes of iridium have been studied as catalysts in important organometallic transformations, including alkane dehydrogenation (in the presence or absence of an H2 acceptor), dehydrogenation of primary amines to nitriles, and dehydrogenation of borane-amine complexes. Furthermore, interesting stoichiometric, intermolecular C-H activations of substituted aromatic compounds (anisole, acetophenone, and halobenzenes) have been realized. This remarkable reactivity is, in part, due to the thermal stability and rigidity that the "pincer" imparts on the Ir center, although reports of ligand "non-innocence" have appeared. Intramolecular metalations of ligand OH bonds are known in [Ir(P-C-P)] complexes. Owing to the relevance of these catalytic transformations to the atom- and energy-efficient use of organic molecules, the further development of new Ir "pincer" complexes with improved activity and selectivity is a goal of much current research.