Structure and dynamics of heterometallic clusters derived from addition of metal carbonyl fragments to the unsaturated hydride [W2Cp2(μ-H)(μ-PPh2)(NO)2]

Abstract

The title complex reacted with [Fe₂(CO)₉] to give the trinuclear derivative [FeW₂Cp₂(μ-H)(μ-PPh₂)(CO)₄(NO)₂] (W–W = 3.044(1) Å) as a result of full insertion of the 16-electron Fe(CO)₄ fragment into the tricentric W–H–W bond of the parent substrate. In contrast, the reactions with the THF adducts [M(CO)₅(THF)] (M = W, Mo) and [MnCp′(CO)₂(THF)] (Cp′ = C₅H₄Me) yielded the μ₃-hydride derivatives [MW₂Cp₂(μ₃-H)(μ-PPh₂)(CO)₅(NO)₂] (W–W = 3.006(1) to 3.164(1) Å for the W₃ compound) and [MnW₂Cp₂Cp′(μ₃-H)(μ-PPh₂)(CO)₂(NO)₂] respectively, all of them resulting from addition (rather than insertion) of the corresponding 16-electron fragment to the W₂H moiety of the parent compound. Density Functional Theory calculations revealed that edge- and face-bridged hydride clusters were of similar energy in the W₂Fe system, while the face-bridged structure was significantly more stable (by more than ca. 40 kJ mol⁻¹) for the W₃ system. Both clusters displayed fast rearrangement in solution involving a flapping movement of the puckered PW₂M core of these molecules. This was combined, in the W₂Fe cluster, with fast exchange between the almost isoenergetic edge- and face-bridged hydride isomers. The reactions of the title compound with several carbonyl dimers were also examined as an additional synthetic approach to the rational synthesis of heterometallic clusters, but were unsuccessful except in the case of [Co₂(CO)₈], which reacted at 253 K in the dark to give a mixture of the binuclear complex [CoWCp(μ-PPh₂)(CO)₄(NO)] (Co–W = 2.8623(6) Å) and the trinuclear cluster [CoW₂Cp₂(μ-PPh₂)(CO)₄(NO)₂] (W–W = 3.1654(4) Å; W–Co = 2.638(1), 2.829(1) Å), the latter resulting from formal replacement of the hydride ligand with the 17-electron fragment Co(CO)₄, which displayed an asymmetric binding to the W₂ centre.