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