LATE-TRANSITION-METAL MU-OXO AND MU-IMIDO COMPLEXES .4. PREPARATION AND CHARACTERIZATION OF RHODIUM MU-IMIDO AMIDO A-FRAME COMPLEXES

Treating Rh2(CO)2Cl2(μ-dxpm)2 (dxpm = bis(diphenylphosphino)methane (dppm) or bis(dimethylphosphino)methane (dmpm)) with 2 equiv of LiNHR (R = Me, Ph, p-MeOPh, p-MePh, o-MePh, o,o'-Me2Ph, p-FPh, p-BrPh, p-NO2Ph) gives Rh2(μ-NR)(CO)2(μ-dxpm)2 (1), its tautomer Rh2(μ-NHR)(CO)2(μ-dxpm)(μ-dxpm-H) (2), or equilibrium mixtures of 1 and 2(1/2) (dxpm-H = bis(diphenylphosphino)methanide or bis(dimethylphosphino)methanide). The position of the tautomeric equilibrium is determined by the electron-donating properties of R, steric effects, and the solvent. Both tautomers have been characterized by X-ray crystal structure determinations. Crystals of tautomer 1 (dppm, R = p-NO2Ph) from CH2C12/Et2O are monoclinic (C2/c) with a = 11.337 (4) Å, b = 36.451 (8) Å, c = 12.821 (3) Å, β = 90.59 (3)°, V= 5297.7 Å3, and Z = 4. The structure is typical of A-frame complexes and contains a planar imido nitrogen at the apex. The structure of 2 (dppm, R = Me) clearly shows the presence of the dppm-H and the NHMe ligands. Crystals from toluene are triclinic (PI) with a = 10.459 (12) Å, b = 14.348 (3) Å, c = 20.867 (6) Å, α = 104.96 (2)°, β= 101.12 (4)°, γ = 93.47 (6)°, V= 2948.3 Å3, and Z = 2. The solid-state structure consists of one independent A-frame molecule with a bridging NHMe group and two independent, disordered, toluene molecules of crystallization. Protonation of 1, 2, or 1/2 gives [Rh2(μ-NHR)(CO)2(μ-dxpm)2]+ (3), which can be recycled back to the starting complex(es) with LiNHR. Hydrolysis of solutions of 1/2 (dppm, R = Ph) gives Rh2(μ-O)(CO)2(dppm)2 (4) as found by an X-ray crystal structure determination. Crystals from toluene/ether are orthorhombic (Pccn) with a = 13.598 (6) Å, b = 17.642 (8) Å, c = 19.283 (7) Å, V = 4626.0 Å3, and Z = 4. © 1993, IEEE. All rights reserved. © 1990, American Chemical Society. All rights reserved.