Reactions of Phosphine Ligands with Iridium Complexes Leading to C(sp3)−H Bond Activation

Abstract

Treatment of [Ir 2 (μ-Cl) 2 (coe) 4 ] (coe = cyclooctene) with the short-bite bifunctional N,P-donor ligand 1-benzyl-2-imidazolyldiphenylphosphine (Ph 2 PBnIm) resulted in the oxidative addition of the C(sp 3 )-H bond from thebenzyl group to the metal to give [IrHCl-{Ph 2 P(CHPh)Im}(Ph 2 PBnIm)] (1), fully characterized by an X-ray study. The related ligand 2-pyridyldiphenylphosphine (Ph 2 PPy) reacted with [Ir 2 (μ-Cl) 2 (coe) 4 ] to give the mononuclear iridium(I) complex [IrCl(Ph 2 PPy) 2 ] (2), which showed P,N-chelating and P-coordinated ligands. Addition of Ph 2 PBnIm to 2 produced the replacement of the P-coordinated Ph 2 PPy ligand along with the benzyl C-H bond addition to iridium to give [IrHCl{Ph 2 P(CHPh)Im}-(Ph 2 PPy)]. This result indicates that mononuclear complexes of the type [IrCl(Ph 2 PBnIm)-(L)] (L = P,N-chelating ligand) are the active species undergoing the C-H bond activation reaction. A related C-H bond activation process of the methylene group of dppm occurs in the reaction of [Ir 2 (μ-Cl) 2 (coe) 4 ] with dppm in toluene to give the hydrido complex with one deprotonated dppm ligand [IrHCl(Ph 2 PCHPPh 2 )(dppm)] (4). On the other hand, the hydride migrates to the methanide carbon in 4 on dissolving the complex in CD 2 Cl 2 to establish an equilibrium with [IrCl(dppm) 2 ] without H/D exchange. Protonating agents such as HBF 4 .Et 2 O and water reacted with complex 4 easily to give [IrHCl(dppm) 2 ]X (X = BF 4 , OH). The mononuclear complex 2 was found to be highly reactive. Reactions of 2 with O 2 , H 2 , and dichloromethane gave the complexes [IrCl(O 2 )(Ph 2 PPy) 2 ], [IrCl(H) 2 (Ph 2 PPy) 2 ], and [IrCl 2 (CH 2 Cl)-(Ph 2 PPy) 2 ], respectively.