DIRHODIUM(II) RAKIS[N,N-DIMETHYL-2-PYRROLIDONE-5(S)-CARBOXAMIDE] - STRUCTURAL EFFECTS ON ENANTIOSELECTION IN METAL CARBENE TRANSFORMATIONS

The preparation and structural characterization of dirhodium(II) akis[ N,N-dimethyl-2-pyrrolidone-5(S)-carboxamide], Rh2(5S-DMAP)4, a new ste rically-demanding catalyst for enantioselective metal carbene transfor mations, is described. The pyrrolidone ligands are arrayed around the dirhodium(II) core with two oxygen and two nitrogen donor atoms, each oriented cis, bound to each octahedral rhodium. The crystal structure of this compound has been determined to be that of Rh2(5S-DMAP)4(CH3CN )2.CH3CN.6H2O: space group P2(1)2(1)2, with cell constants a = 12.685( 4), b = 15.050(3), c = 24.035(4) angstrom; v = 4588.5(1.9) angstrom3, Z = 4, R = 0.0316, Rh-Rh distance = 2.4538(5) angstrom. Decreased acti vity for diazodecomposition catalyzed by Rh2(5S-DMAP)4 is observed, an d enantiocontrol for cyclopropanation and carbon-hydrogen insertion is lower than expected by analogy to the corresponding dirhodium(II) tet rakis[methyl 2-pyrrolidone-5(S)-carboxylate], Rh2(5S-MEPY)4. Electroni c stabilization of the intermediate metal carbene is absent in reactio ns catalyzed by Rh2(5S-DMAP)4.