LATE-TRANSITION-METAL MU-OXO AND MU-IMIDO COMPLEXES .8. RHODIUM IMIDO AMIDO COUPLING REACTIONS WITH CARBON-MONOXIDE

Treating tautomeric mixtures of Rh2(mu-NR)(CO)2(mu-dppm)2 and Rh2(mu-NHR)(CO)2(mu-dppm-H)(mu-dppm) (dppm = bis(diphenylphosphino)methane, dppm-H = bis(diphenylphosphino)methanide) (1/2) or Rh2(mu-NHMe)(CO)2(mu-dppm-H)(mu-dppm) (2; R = Me) in CH2Cl2 or benzene with 1 equiv of CO gives Rh2(mu-eta(1):eta(1)-RNCO)(CO)2(mu-dppm)2 (3; R = Me, Ph, p-MePh, p-FPh, p-BrPh). Excess CO gives Rh2(mu-CO)(CO)2(mu-dppm)2, RNCO, and (RNH)2CO (R = Ph, p-MePh, p-MeOPh, p-BrPh, p-FPh, o-MePh) or Rh2[mu-eta(1):eta(1)-C(O)N(Me)C(O)](mu-CO)(CO)2(mu-dppm)2 (4) and Rh2(mu-CO)(CO)2(mu-dppm)2 (R = Me). An X-ray crystal structure determination of 4 shows a "cradle" geometry with bridging cis phosphines and a dimetallacycloimide structure formed by insertion of CO into both Rh-N bonds. Crystals from CH2Cl2 are triclinic (P1BAR) with a = 12.117 (3) angstrom, b = 20.344 (4) angstrom, c = 11.160 (3) angstrom, alpha = 98.53 (2)-degrees, beta = 102.21 (2)-degrees, gamma = 91.21 (2)-degrees, V = 2655.1 (2) angstrom 3, and Z = 2. Spectroscopic data indicate the formation of small amounts of the analogues of 4 (R = Ph, p-MePh, p-MeOPh, p-BrPh, p-FPh) at 2 atm of CO pressure and larger amounts at 35 atm. Treating Rh2(mu-eta(1):eta(1)-RNCO)(CO)2(mu-dppm)2 (3; R = p-FPh) with p-MePhNCO under a CO atmosphere gives a mixture of ureas, [(p-MePh)NH]2CO, (p-MePh)NHCOHN(p-FPh), and [(p-FPh)NH]2CO.