The coordination chemistry of the diphosphine− ketone ligand 2,2′-bis(diphenylphosphino)benzophenone ( Ph dpbp) with nickel is reported. The ketone moiety does not bind to Ni(II) in the complex ( Ph dpbp)NiCl 2 , whereas reduction to Ni(I) or Ni(0) induces η 2 (C,O) coordination of the ketone to form the pseudotetrahedral complexes ( Ph dpbp)NiCl and ( Ph dpbp)Ni(PPh 3 ). DFT calculations indicate that the metal− ketone bond is dominated by π back-donation; hence, Ph dpbp functions as a hemilabile acceptor ligand in this series of complexes.

Metal-ligand cooperativity in homogeneous catalysis is emerging as a powerful tool for the design of efficient transition-metal catalysts. This perspective highlights recent advances in the use of neutral π-coordinating ligands, tethered to a transition-metal center by other donor ligands, as cooperative reaction centers. The state-of-the-art organometallic complexes, including π-coordinating ligands originating from C[double bond, length as m-dash]C, C[double bond, length as m-dash]E (E = O, N) and boron containing moieties, are described here, with special attention on their specific reactivity. Geometric and electronic aspects of ligand design and their influence on the coordination mode and reactivity of the π-system are discussed.

π-Coordinating ligands are commonly found in intermediate structures in homogeneous catalysis, and are gaining interest as supporting ligands for the development of cooperative catalysts. Herein, we systematically investigate the binding of the ketone group, a strongly accepting π ligand, to mid-to-late metals of the first transition series. To this end, the coordination of 2,2'-bis(diphenylphosphino)benzophenone ( dpbp), which features a ketone moiety flanked by two strongly binding P-donor groups, to Fe, Co, Ni, and Cu was explored. The ketone moiety does not bind to the metal in M complexes, whereas M complexes (Fe, Co, Ni) adopt an η (C,O) coordination. A structural and computational investigation of periodic trends in this series was performed. These data suggest that the coordination of the ketone to M can mostly be described by the resonance extremes of the Dewar-Chatt-Duncanson model, that is, the π complex and the metallaoxacycle extreme, with a possible minor contribution from a ketyl radical resonance structure in the case of the iron complex.