P-N And N-Mo Bond Formation Processes In The Reactions Of A Pyramidal Phosphinidene-Bridged Dimolybdenum Complex With Diazoalkanes And Organic Azides

The reactivity of the complex [Mo2Cp(mu-kappa(1) :kappa(1) ,eta(5)-PC5H4)-(CO)(2)(eta(6)-HMes*)(PMe3)] (1) toward different diazoalkanes and organic azides was investigated. The pyramidal phosphinidene ligand in 1 displayed a strong nucleophilicity, enabling these reactions to proceed rapidly even below room temperature. Thus, 1 reacted rapidly at 253 K with different diazoalkanes N2CRR' (R,R' = H,H, Ph,Ph, H,CO2Et) to give the corresponding P:P-bridged phosphadiazadiene derivatives as major products which, however, could not be isolated. Reaction of the latter with [H(OEt2)(2)](BAr'(4)) yielded the corresponding cationic derivatives [Mo2Cp {mu-kappa(1) p:kappa(1) p,eta(5)-P (NMeNCHCO2Et)C5H4} (eta(6)-HMes*) (CO)(2), (PMe3)] - (BAr4'), which were isolated in ca. 70% yield. The related species [Mo2Cp (mu-kappa(1) p:kappa(1 )p,eta(5)-P(NMeNCHCO2Et)C5H4 (eta(6)-H Mes*)- (CO)(2) (PMe3)](BAr4') was isolated upon reaction of the ethyl diazoacetate derivative with Mel and subsequent anion exchange with Na(BAr4'). Reaction of 1 with aryl azides (4-C6H4Me)N-3 and (4-C6H4F)N-3 proceeded rapidly at low temperature to give possibly the corresponding P:P-bridged phosphaimine derivatives as major products, which could be neither isolated. Protonation of these products with [H(OEt2)(2)](BAr4') gave the corresponding aminophosphanyl complexes [Mo2Cp (mu-kappa(1) p:kappa(1 )p,eta(5)-P(NHR)C5H4} (eta(6)-HMes*)(CO)(2)(PMe3)](BAr4'), isolated in ca. 75% yield. In contrast, the result of reactions of 1 with benzyl azide was strongly dependent on temperature, including the temperature in the subsequent methylation step that gave isolable cationic derivatives. By a careful choice of experimental conditions, different complexes having methylated phosphatriazadiene ligands were isolated, such as [Mo2Cp (mu-kappa(1) p:kappa(1 )p,eta(5)-P(NNNMeCH2Ph)C5H4}(eta(6)-HMes*)(CO)(2) (PMe3)](BAr'(4)) and the metallacyclic derivatives syn- and anti-[Mo2Cp (mu-kappa(1) p:kappa(1 )p,eta(5)-P(NMeNNCH2Ph)C5H4}(eta(6)-HMes*)(CO)(PMe3)](BAr4'). Density functional theory calculations, along with NMR monitoring experiments, revealed that the formation of the latter products stemmed from different and kinetically favored phosphatriazadiene intermediates, thermodynamically disfavored with respect to the denitrogenation process, otherwise yielding phosphaimine derivatives.