Selective carbonylation of benzene to benzaldehyde using a phosphorus–nitrogen PN3P–rhodium(i) complex

Abstract

A PN³P pincer ligand (1) bearing dicyclopentylphosphine substituents reacts with [Rh(COD)Cl]₂ (COD = 1,5-cyclooctadiene) to produce the complex (PN³P)RhCl (2). Treatment of a benzene solution of 2 with KN(SiMe₃)₂ stimulates a dearomatization process, and C–H activation of benzene is achieved through the rearomatization of the central pyridine ring. This deprotonation/reprotonation of the NH arm of 2 gives the phenyl complex (PN³P)Rh(C₆H₅) (3). The subsequent introduction of CO gas into 3 yields the benzoyl complex (PN³P)RhCO (C₆H₅) (4), which can release benzaldehyde upon treatment with diluted HCl solution and regenerates 2.