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(PBu2tPh)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 pπ orbitals and metal dπ 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(PBu2tPh) and IrH(CO)(PBu2tPh)2 have been characterized by multinuclear NMR and IR spectroscopy. The reaction of Ir(H)2(F)(PBu2tPh)2 with CO in a glass vessel yields crystalline [Ir(H)2(CO)2(PBu2tPh)2][SiF5] and [Ir(CO)2(PBu2tPh)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(PBu2tPh)2][SiF5], a=8.293(2), b=12.462(5), c=16.333(7) A, β=98.21(2)° with Z=2. Crystallographic data (P21/n at -172 °C) for [Ir(CO)2(PBu2tPh)2][SiF5]·C6D6, a=13.041(7), b=12.998(5), c=22.553(13) A, β=97.50(2)° with Z=4.