Thermally Stable Diazoalkane Derivatives of the Unsaturated Ditungsten Hydride [W₂Cp₂(H)(μ-PCy₂)(CO)₂]

The title compound reacted rapidly with N2CH­(SiMe3) at room temperature to give the electron-precise hydride [W2Cp2(H)­(μ-PCy2)­(CO)2­{N-N2CH­(SiMe3)}] (W–W = 2.9907(5) Å), in which the diazoalkane molecule is N-bound strongly to one of the metal centers, formally acting as an imido-like four-electron donor. Reaction with N2CPh2 led instead to a mixture of two products, the analogous diphenyldiazomethane complex [W2Cp2(H)­(μ-PCy2)­(CO)2­(N-N2CPh2)] and the bis­(diazoalkane) derivative [W2Cp2(H)­(μ-PCy2)­(CO)2­(N-N2CPh2)2], the latter having no metal–metal bond and bearing two inequivalent diazoalkane ligands bound to the same metal center (W–N = 1.78(1), 1.82(1) Å), whereas its dicarbonyl metal fragment displays a transoid geometry in the crystal, but a cisoid one in solution. These two compounds follow from competitive reaction pathways, since independent experiments revealed that the above mono­(diazoalkane) complexes did not add a second diazoalkane molecule even under thermal activation. In contrast, the title compound reacted with excess N2CH2 to yield two new methyl derivatives requiring the participation of two molecules of reagent, the diazomethane complex [W2Cp2(CH3)­(μ-PCy2)­(CO)2(N-N2CH2)] and the 30-electron phosphinomethyl-bridged complex [W2Cp2(CH3)­(μ-C:P-CH2PCy2)­(μ-CO)­(CO)], along with small amounts of the known methyl-bridged complex [W2Cp2(μ-CH3)­(μ-PCy2)­(CO)2]. The two new complexes follow from denitrogenation of one diazomethane molecule followed by insertion of methylene into the W–H bond to yield a methyl ligand, while the second diazomethane molecule either remains bound through its nitrogen atom or undergoes denitrogenation followed by insertion of methylene into a W–P bond, to yield a phosphinomethyl ligand. Once more, no denitrogenation of the coordinated diazomethane ligand in the first complex was observed even under thermal or photochemical activation.