Reactions of Anilines and Benzamides with a Fourteen-Electron Iridium(I) Bis(Phosphinite) Complex: N-H Oxidative Addition versus Lewis Base Coordination

摘要

Anilines react with (POCOP)Ir(C6H5)(H), >12, (POCOP = 2,6-(OPtBu2)2C6H3) to yield equilibrium mixtures of >12, the Ir(I) σ-complexes (POCOP)Ir(NH2Ar), >13, and the Ir(III) oxidative addition adducts (POCOP)Ir(H)(NHAr), >14. Quantitative studies of these equilibria for a series of anilines were carried out. Anilines possessing electron-withdrawing groups favor the Ir(III) oxidative addition adduct over the Ir(I) sigma complex. Low temperature studies using p-chloroaniline show that the Ir(I) σ-complex is the kinetic product of reaction and is likely the precursor to the Ir(III) oxidative addition adduct. Reductive elimination of complexes >14 in the presence of ethylene led to the corresponding anilines and the ethylene complex (POCOP)Ir(C2H4). Kinetic analysis of these reactions for >14e,f,g bearing electron-withdrawing aryl groups (Ar- = p-CF3C6H4-, C6F5-, 3,5-bis(CF3)C6H₃-) shows the rate is independent of ethylene concentration. The ΔG^‡ values for these reductive eliminations fall in the range of 21–22 kcal/mol. X-Ray analysis establishes >14f (Ar- = C₆F₅-) as a square pyramidal complex with the hydride occupying the apical site. Reaction of >12 with benzamides >21a,b yields quantitatively the Ir(III) oxidative addition adducts, (POCOP)Ir(H)(NHC(O)Ar), >22. X-Ray analysis of >22b (Ar- = C₆F₅-) shows significant interaction of the carbonyl oxygen with Ir in the site trans to hydride. The barrier to reductive elimination of >22a, 29 kcal/mol, is substantially higher than for complexes >14e,f,g.