Heterobinuclear alkyl complexes of rhodium and iridium. Migratory insertion or Ir-to-Rh migration of a methyl group in reactions with small molecules

The reaction of [RhIr(CO)(3)(dppm)(2)] (dppm = Ph(2)PCH(2)PPh(2)) with methyl triflate yields [RhIr(CH3)(Co)(3)(dppm)(2)][CF3SO3] (2), having the methyl group and two terminal carbonyls on Ir and one carbonyl on Rh. An Ir --> Rh dative bond is proposed, giving Rh+ a 16e square-planar configuration. Reaction of 2 with hydrogen at ambient temperature yields [RhIrH-(CO)(2)(mu-H)(2)(dppm)(2)](+) and methane. At 0 degrees C the intermediate [RhIrH(CH3)(CO)(2)(mu-H)(dppm)(2)][CF3SO3] is observed which under H-2 yields the trihydride species and CH4 upon warming. Protonation of 2 with HCl and CF3SO3H yields [RhIr(CH3)(CO)(2)(mu-H)(mu-Cl)-(dppm)(2)](+) and [RhIr(CH3)(CO)(2)(mu-H)(mu-CO)(dppm)(2)](+2), respectively. The reaction of 2 with CO resulted in decomposition to several unidentified products. Reaction of 2 with CN(t)Bu yields the iminoacyl product [RhIr(CO)(2)(mu-(t)BuN=CMe)(dppm)(2)](+) via migratory insertion. Two intermediates in the formation of the iminoacyl species were identified at low temperature yielding some information about the subsequent migratory insertion. Although the reaction of 2 with SO2 does not yield the SO2-insertion product, it does yield [RhIr(C(O)-CH3)(CO)(2)(mu-SO2)(dppm)(2)](+), the product of methyl migration to Rh and migratory insertion of the methyl to a carbonyl group. A mechanism is proposed on the basis of the characterization of low-temperature intermediates. With ethylene, the substitution of one carbonyl in 2 and migration of the methyl group to Rh occurs. The structures of [RhIr(CH3)(CO)(3)(dppm)(2)][CF3SO3]. CH2Cl2 (2) and [RhIr(CO)(2)(mu-(t)BuN=CMe)(dppm)(2)][CF3SO3] (8) have been determined by X-ray crystallography. Compound 2 has a trigonal bipyramidal ligand arrangement at Ir with the methyl group opposite Rh. In addition the 18e Ir forms a dative bond to Rh giving the latter a square planar geometry. Compound 8 has an ''A-frame'' geometry in which the bridging iminoacyl group binds to Rh via nitrogen and to Ir via carbon.