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

The reaction of [(η4-1,5-C8H12)2Ir2(μ-Cl)2] with 2-di-t-butylphosphino-2′-methylbiphenyl (t-Bu2PbiphMe) in the presence of AgBF4 afforded the dichlorido-bridged Ir–Ag complex [(η4-1,5-C8H12)Ir(μ-Cl)2Ag(t-Bu2PbiphMe)] (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 [(η4-1,5-C8H12)Ir(t-Bu2PbiphMe–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)biphMe]BF4 was isolated as a by-product of the preparations of 1 and 2; its crystal structure was determined.

Graphical abstractReaction of the Buchwald phosphine t-Bu2PbiphMe with [(η4-1,5-C8H12)2Ir2(μ-Cl)2] in the presence of Ag+ ions produced [(η4-1,5-C8H12)Ir(μ-Cl)2Ag(t-Bu2PbiphMe)]. Precipitation of the bridging chlorides prior to the addition of the phosphine afforded the four-membered metalaheterocycle [(η4-1,5-C8H12)Ir(2-t-Bu2PC6H3C6H4Me-2′-κC6,κP)].Figure optionsDownload full-size imageDownload as PowerPoint slide