Low-Temperature N-O Bond Cleavage in Nitrosyl Ligands Induced by the Unsaturated Dimolybdenum Anion [Mo2(η5-C5H5)2(μ-PPh2)(μ-CO)2]-

The unsaturated anion [Mo2Cp2(μ-PPh2)(μ-CO)2]- (1) (Na þ salt) reacts with the nitrosyl complexes [MCp0(CO)2(NO)]BF4 (M = Mn, Re; Cp0 = η5-C5H4Me) rapidly at about 193 K. Upon warming of the resulting mixtures up to 243 K orange solutions are obtained, shown to contain the corresponding oxo- and nitride-bridged tetracarbonyl complexes [Mo2MCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)4] as the major product, which could be isolated only for M = Re. Above 253 K, however, these compounds experience spontaneous decarbonylation to yield the unsaturated tricarbonyl derivatives [Mo2MCp2Cp0(μ-N)(μ-O)(μ-PPh2)(CO)3] (Mo-Mo = 2.840 A ° for the Mn compound, according to density functional theory (DFT) calculations). These complexes in turn react rapidly with air to give the corresponding dioxodicarbonyl derivatives [Mo2MCp2Cp0(μ-N)(μ-O)(μ-PPh2)(O)(CO)2] almost quantitatively. The structure of the latter product (M = Re) was determined by X-ray diffraction methods (Mo-Mo = 2.763(1) A° ). In contrast with the N-O bond cleavage easily taking place in the above reactions, the direct nitrosylation of 1 with N-methyl-N-nitroso-p-toluenesulfonamide induces no bond cleavage process in the nitrosyl ligand, but just gives the electron-precise tricarbonyl derivative [Mo2Cp2(μ-PPh2)(CO)3(NO)] or, in the presence of CNtBu, a mixture of the new isocyanide complexes [Mo2Cp2(μ-PPh2)(CNtBu)(CO)2(NO)] and [Mo2Cp2(μ-PPh2)- (μ-η1:η2-CNtBu)(CO)(NO)]. Separate experiments indicated that these isocyanide complexes cannot be converted one into each other, nor can they be obtained through thermal substitution reactions on the above tricarbonyl product.