Experimental and computational studies of two new mono- and dinuclear iridium complexes containing a Buchwald biphenyl phosphine ligand

The reaction of [(eta(4)-1,5-C8H12)(2)Ir-2(mu-Cl)(2)] with 2-di-t-butylphosphino-2'-methylbiphenyl (t-Bu(2)Pbiph(Me)) in the presence of AgBF4 afforded the dichlorido-bridged Ir-Ag complex [(eta(4)-1,5-C8H12)Ir(mu-Cl)(2)Ag(t-Bu(2)Pbiph(Me))] (1) which was fully characterized by a single crystal X-ray diffraction study. Sequential treatment of the diiridium precursor first with the silver salt and then with the phosphine yielded cyclometalated [(eta(4)-1,5-C8H12)Ir(t-Bu(2)Pbiph(Me)-H+)] (2). Detailed DFT calculations gave evidence that the phosphine ligand of 2 forms a strained four-membered iridaheterocycle through orthometalation rather than a sterically congested six-membered chelate structure through C-H activation on the remote phenyl ring. The phosphonium salt [t-Bu2P(H)biph(Me)]BF4 was isolated as a by-product of the preparations of 1 and 2; its crystal structure was determined. (C) 2007 Elsevier B.V. All rights reserved.