Preparation and reactivity of iridium(III) hydride complexes with pyrazole and imidazole ligands

Pyrazole IrHCl2(HRpz)P2 [P = PPh3, PiPr3; R = H, 3-Me], bis(pyrazole) [IrHCl(HRpz)2(PPh3)2]BPh4 and imidazole IrHCl2(HIm)(PPh3)2 derivatives were prepared by allowing the IrHCl2(PPh3)3 complex to react with the appropriate azole in refluxing 1,2-dichloroethane. Nitrile IrHCl2(CH3CN)(PPh3)2 and 2,2′-bipyridine (bpy) [IrHCl(bpy)(PPh3)2]BPh4 derivatives were also prepared using IrHCl2(PPh3)3 as a precursor. The complexes were characterised spectroscopically (IR and NMR) and a geometry in solution was also established. Protonation with Brønsted acid of pyrazole IrHCl2(Hpz)(PPh3)2 and imidazole IrHCl2(HIm)(PPh3)2 complexes proceeded with the loss of the azole ligands and the formation of the unstable IrHCl2(PPh3)2 derivative. Vinyl IrCl2{CHdouble bond; length as m-dashC(H)R1}(HRpz)P2 and IrCl2{CHdouble bond; length as m-dashC(H)R1}(HIm)P2 (R1 = Ph, p-tolyl, COOCH3; P = PPh3, PiPr3) complexes were prepared by allowing hydride-pyrazole IrHCl2(HRpz)P2 and hydride-imidazole IrHCl2(HIm)P2 to react with an excess of terminal alkyne in 1,2-dichloroethane. The complexes were characterised spectroscopically and by the X-ray crystal structure determination of the IrCl2{CHdouble bond; length as m-dashC(H)Ph}(Hpz)(PPh3)2 derivative.