Reactions of Anilines and Benzamides with a Fourteen-Electron Iridium(I) Bis(Phosphinite) Complex: N-H Oxidative Addition versus Lewis Base Coordination.
Anilines react with (POCOP)Ir(C(6)H(5))(H), 12, (POCOP = 2,6-(OPtBu(2))(2)C(6)H(3)) to yield equilibrium mixtures of 12, the Ir(I) sigma-complexes (POCOP)Ir(NH(2)Ar), 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) sigma-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(C(2)H(4)). Kinetic analysis of these reactions for 14e,f,g bearing electron-withdrawing aryl groups (Ar- = p-CF(3)C(6)H(4)-, C(6)F(5)-, 3,5-bis(CF(3))C(6)H(3)-) shows the rate is independent of ethylene concentration. The DeltaG(double dagger) values for these reductive eliminations fall in the range of 21-22 kcal/mol. X-Ray analysis establishes 14f (Ar- = C(6)F(5)-) 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- = C(6)F(5)-) 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.
Sykes
Alison Cartwright
AC
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3290.
White
Peter
P
Brookhart
Maurice
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