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 [MoCp(μ-κ:κ,η-PCH)(CO)(η-HMes*)(PMe)] () toward different diazoalkanes and organic azides was investigated. The pyramidal phosphinidene ligand in displayed a strong nucleophilicity, enabling these reactions to proceed rapidly even below room temperature. Thus, reacted rapidly at 253 K with different diazoalkanes NCRR' (R,R' = H,H, Ph,Ph, H,COEt) to give the corresponding P:P-bridged phosphadiazadiene derivatives as major products which, however, could not be isolated.

Chemistry of CS- and SCNPh-adducts of the pyramidal phosphinidene-bridged complex [MoCp(μ-κ:κ,η-PCH)(CO)(η-HMes*)(PMe)].

The title complex reacted readily with CS and SCNPh to give the phosphinidene-cumulene adducts [MoCp{μ-κ:κ,η-P(CS)CH}(CO)(η-HMes*)(PMe)] and [MoCp{μ-κ:κ,η-P(C(NPh)S)CH}(CO)(η-HMes*)(PMe)] respectively (Mes* = 2,4,6-CHBu), as a result of the formal insertion of the C[double bond, length as m-dash]S bond of the heterocumulene into the metallocene Mo-P bond of the phosphinidene complex. The newly formed species bear a pyramidal P atom with a lone electron pair involved in fast inversion, and displayed strong nucleophilicity which enabled easy addition at the P site of carbon-based electrophiles and chalcogen atoms, while the uncoordinated S and N atoms were also competitive nucleophilic sites in these complexes. These air-sensitive materials readily added an O molecule in the solid state, to give the corresponding derivatives [MoCp{μ-κ:κ,η-OP(O)(C(X)S)CH}(CO)(η-HMes*)(PMe)] (X = S, NPh), and the CS adduct reacted selectively with S in solution to give the sulfide derivative [MoCp{μ-κ:κ,η-P(S)(CS)CH}(CO)(η-HMes*)(PMe)], which was stabilized through methylation, thus yielding the cationic complex [MoCp{μ-κ:κ,η-P(S)(C(SMe)S)CH}(CO)(η-HMes*)(PMe)].

Cycloaddition Reactions of the Phosphinidene-Bridged Complex [MoCp(μ-κ:κ,η-PCH)(CO)(η-HMes*)] with Diazoalkanes and Other Heterocumulenes.

The title phosphinidene complex reacted at room temperature with CS and SCNPh to give the phosphanyl derivatives [MoCp{μ-κ:κ,η-P(CS)CH}(CO)(η-HMes*)] and [MoCp{μ-κ:κ,η-P(C(NPh)S)CH}(CO)(η-HMes*)], respectively (Mes* = 2,4,6-CHBu), which result from a [2 + 2] cycloaddition of a C═S bond in the organic reagent to the Mo═P bond of the phosphinidene complex, with further insertion of S into the remaining Mo-P bond, in the CS reaction. The title complex also reacted with diazoalkanes NCRR' at room temperature to give the corresponding phosphaalkene derivatives [MoCp{μ-η:κ,η-P(CRR')CH}(CO)(η-HMes*)] (CRR' = CH, CPh, CH(SiMe)). These products follow from a formal [2 + 1] cycloaddition of the carbene CRR' fragment to the Mo═P bond of the parent compound but were shown to proceed through a [3 + 2] cycloaddition of the diazoalkane molecule, followed by N elimination.

Electronic Structure and Multisite Basicity of the Pyramidal Phosphinidene-Bridged Dimolybdenum Complex [Mo2(η(5)-C5H5)(μ-κ(1):κ(1),η(5)-PC5H4)(η(6)-C6H3(t)Bu3)(CO)2(PMe3)].

The title phosphinidene complex could be sequentially protonated with HBF4·OEt2 or [H(OEt2)2](BAr'4) to give the phosphido-bridged derivatives [Mo2Cp(μ-κ(1):κ(1),η(5)-HPC5H4)(η(6)-HMes*)(CO)2(PMe3)]X and then the hydrides [Mo2Cp(H)(μ-κ(1):κ(1),η(5)-HPC5H4)(η(6)-HMes*)(CO)2(PMe3)]X2 (X = BF4, BAr'4; Ar' = 3,5-C6H3(CF3)2; Mes* = 2,4,6-C6H2(t)Bu3). Density functional theory (DFT) calculations revealed that the most favored site for initial electrophilic attack is the metallocene Mo atom, but attachment of the electrophile to the phosphinidene P atom gives more stable products. This was in agreement with all other reactions investigated, which invariably involved the attachment of the added electrophile at the P site.