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

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-CH=PMes* (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-CH=PMes*)(2)IrCl] (5), which showed a versatile reactivity upon chloride abstraction with AgOTf in different coordinating solvents affording pyridine-coordinated cationic Ir(I) complex [(quinCH=PMes*)(2)Ir(py)][OTf] (6) and C-H bond activated cyclometallated Ir(III)-hydrido complex 8. Treatment of complex 5 with CO, (CH3)(2)Mg 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.

Automated summary

Phosphaalkenes are a new class of ligands similar to CO with unique electronic properties. We synthesized and characterized an iridium(I) complex with a phosphaalkene ligand, which showed versatile reactivity with different solvents or reagents. This complex exhibited good catalytic activity in the conversion of methanol and ethanol to iso-butanol, a promising biofuel candidate.