Synthesis and reactivity of half-sandwich (η5-C5Me5)Ir(iii) complexes of a cyclometallated aryl phosphine ligand

Abstract

Reaction of the Ir(III) dimer [(η⁵-C₅Me₅)IrCl₂]₂ with PMeXyl₂ (Xyl = 2,6-C₆H₃Me₂), in the presence of the poorly coordinating base 2,2,6,6-tetramethyl piperidine, gives a chloride complex 1-Cl, resulting from hydrogen chloride elimination involving one of the phosphine benzylic hydrogen atoms and concomitant cyclometallation. Related compounds containing other halide or pseudohalide ligands, 1-Br, 1-Cl, 1-SCN, can be made, the latter featuring S-coordination of the ambidentate thiocyanate to the soft Ir(III) Lewis acid centre, as suggested by IR data and demonstrated by X-ray crystallography. Hydride 2-H, and alkyl derivatives 3 (Me) and 4 (CH₂SiMe₃) can also be prepared from 1-Cl and appropriate hydride and alkylating reagents. An interesting H/D exchange chemistry that occurs in the presence of CD₃OD has been disclosed for 1-Cl, 1-Br and 2-H. For the halide derivatives, deuterium incorporation takes place into the methylene and methyl sites of their cyclometallated ligand, whereas for 2-H only the hydride and methylene (Ir–CH₂) protons participate in the exchange, which is strikingly accelerated by catalytic amounts of acids.