Cyclohexane-Based Phosphinite Iridium Pincer Complexes: Synthesis, Characterization, Carbene Formation, and Catalytic Activity in Dehydrogenation Reactions

Abstract

Metalation of two cyclohexane-based phosphinite pincer ligands, cis-POCyPO (4) and trans-POCyPO (5) (POCyPO = {1,3-bis-[(di-tert-butylphosphinito]cyclohexane}−), is reported. In line with previously published results (Dalton Trans. 2009, 8626, DOI: 10.1039/B910798C), ligand 4 undergoes aromatization to give benzene-based complex (POCOP)IrHCl (3) at high temperatures in the presence of [Ir(COD)Cl]2. However, here we present the isolation of carbene complex (POCyOP)═IrCl (6) which is an intermediate in the aromatization process; upon reaction with H2, 6 can be readily transformed to the corresponding hydrido-chloride 8. Metalation of trans-POCyOP ligand 5 gives hydrido-chloride 13 which only upon further heating can be converted to the corresponding carbene 14. A mechanistic study of hydrogenation of carbene 6 is reported, as well as interesting ambient temperature CO-induced C–H activation in β-position of 6, a process that under other circumstances takes place around 200 °C. The cis complex (POCyOP)IrHCl ...