Synthesis and Characterization of Iridium(I) and Iridium(III) Complexes Containing Dialkylbiphenylphosphines

The synthesis and characterization of iridium complexes containing the PCy2biPh ligand (PCy2biPh = 2-(dicyclohexylphosphino)­biphenyl), is described. Chloride abstraction from (COD)­Ir­(PCy2biPh)­Cl with Na­(BArF)4 affords [(COD)­Ir­(PCy2biPh)]­[B­(ArF)4] (1, ArF = 3,5-bis­(trifluoromethyl)­phenyl). Heating 1 in benzene results in dehydrogenation of one of the cyclohexyl groups on the phosphine ligand with COD serving as the hydrogen acceptor, leading to the new complex 2, with benzene coordinated in an η6 fashion to the metal center. Complex 1 reacts with H2 to produce the Ir­(III) dihydride complex [(PCy2biPh)­IrH2]­[B­(ArF)4] (3). Initial studies of transfer dehydrogenation and attempts at benzene hydrogenation using 1 and 3 are described.