P,N-type phosphaalkene-based Ir(i) complexes: synthesis, coordination chemistry, and catalytic applications

Abstract

Phosphaalkenes are an emerging class of ligands with unique electronic properties that can be regarded as tuneable variants of the ubiquitous CO ligand. Our group has recently reported the synthesis of the P,N-type phosphaalkene ligand quin-CHPMes* (1, quin = 2-quinolinyl) and its coordination chemistry with Rh(I) was investigated. In this study, we present the synthesis and characterisation of iridium(I) complex [(quin-CHPMes*)₂IrCl] (5), which showed a versatile reactivity upon chloride abstraction with AgOTf in different coordinating solvents affording pyridine-coordinated cationic Ir(I) complex [(quin-CHPMes*)₂Ir(py)][OTf] (6) and C–H bond activated cyclometallated Ir(III)-hydrido complex 8. Treatment of complex 5 with CO, (CH₃)₂Mg or NaN₃, respectively, produced three types of five-coordinate Ir(I) complexes 9, 10 and 11 in excellent yields. Complex 6 was found to be less active as a catalyst in the N-alkylation of aniline with benzyl alcohol than complex 5, likely due to the instability of Ir complex 6 in the presence of base at higher temperatures. Complex 5 has also been tested as a catalyst in the Guerbet-type coupling of methanol and ethanol to iso-butanol, which is a promising biofuel candidate, and showed good conversion and selectivity towards the desired iso-butanol.