Synthesis, structure and properties of the face-sharing bioctahedral Mo2X6(PMe2Ph)3 (X = Br, I) compounds
Résumé
The title compounds were obtained by reacting the corresponding MoX3(THF)3 complexes with PMe2Ph in a 2 : 3 ratio in refluxing toluene. The compounds assume a face-sharing, bioctahedral structure with three bridging halide ligands, the coordination geometries being completed by one terminal halide and two phosphines for one metal centre, and by two terminal halides and one phosphine for the other one. A comparison with the known chloride analogue shows that the metal-metal separation increases in the order Cl < Br < I and, correspondingly, the paramagnetism of the molecule also increases as shown by solid-state magnetic susceptibility measurements and by the paramagnetic shifts in the solution 1H NMR spectrum. The NMR spectrum indicates an equilibrium in solution between anti and gauche isomers. NMR monitoring of the reaction between Mo2Br6(PMe2Ph)3 and PMe2Ph shows evidence for the formation of the edge-sharing bioctahedral Mo2Br6(PMe2Ph)4 as a short-lived intermediate, the mononuclear MoBr3(PMe2Ph)3 being the final product.
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