HX elimination from Ir(H)2X(PBu2tPh)2 promoted by CO coordination: assessment of X ligand influence

Abstract

The coordinatively unsaturated complexes Ir(H)₂X(PBu₂^tPh)₂ [X=Cl, Br, I, N₃, NCNSiMe₃, NHC(O)CH₃, OC(O)CF₃, OSO₂CF₃, OC(O)CH₃, SPh, OPh, F] all react within the mixing time in arene solvents to bind carbon monoxide. Subsequent reactivity of these CO adducts reductively to eliminate HX is dependent on the magnitude of the inherent destabilization caused by filled-filled repulsions between the ligand p_π orbitals and metal d_π orbitals. This destabilization is not sufficient to promote the loss of HX when X=Cl, Br, I, N₃, NCNSiMe₃, NHC(O)CH₃ or OC(O)CF₃. When X=OC(O)CH₃ or SPh, metastable CO adducts are formed that ultimately lose HX. The complexes containing OPh or F quickly lose HX upon reaction with CO. The unusual iridium(I) complexes IrH(CO)₂(PBu₂^tPh) and IrH(CO)(PBu₂^tPh)₂ have been characterized by multinuclear NMR and IR spectroscopy. The reaction of Ir(H)₂(F)(PBu₂^tPh)₂ with CO in a glass vessel yields crystalline [Ir(H)₂(CO)₂(PBu₂^tPh)₂][SiF₅] and [Ir(CO)₂(PBu₂^tPh)₂][SiF₅]·C₆D₆, both characterized by X-ray diffraction. The latter, although approximately square planar, has a C–Ir–C angle of only 162.7°. Crystallographic data (Pc at -165 °C) for [Ir(H)₂(CO)₂(PBu₂^tPh)₂][SiF₅], a=8.293(2), b=12.462(5), c=16.333(7) Å, β=98.21(2)° with Z=2. Crystallographic data (P2₁/n at -172 °C) for [Ir(CO)₂(PBu₂^tPh)₂][SiF₅]·C₆D₆, a=13.041(7), b=12.998(5), c=22.553(13) Å, β=97.50(2)° with Z=4.