Low-temperature N-O bond cleavage in nitrosyl ligands induced by the unsaturated dimolybdenum anion [Mo2(eta(5)-C5H5)2(mu-PPh2)(mu-CO)2]-.

The unsaturated anion [Mo(2)Cp(2)(mu-PPh(2))(mu-CO)(2)](-) (1) (Na(+) salt) reacts with the nitrosyl complexes [MCp'(CO)(2)(NO)]BF(4) (M = Mn, Re; Cp' = eta(5)-C(5)H(4)Me) 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 [Mo(2)MCp(2)Cp'(mu-N)(mu-O)(mu-PPh(2))(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 [Mo(2)MCp(2)Cp'(mu-N)(mu-O)(mu-PPh(2))(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 [Mo(2)MCp(2)Cp'(mu-N)(mu-O)(mu-PPh(2))(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 [Mo(2)Cp(2)(mu-PPh(2))(CO)(3)(NO)] or, in the presence of CN(t)Bu, a mixture of the new isocyanide complexes [Mo(2)Cp(2)(mu-PPh(2))(CN(t)Bu)(CO)(2)(NO)] and [Mo(2)Cp(2)(mu-PPh(2))(mu-eta(1):eta(2)-CN(t)Bu)(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.