Synthesis, structure and properties of the face-sharing bioctahedral Mo 2X 6(PMe 2Ph) 3 (X = Br, I) compounds

Abstract

The title compounds were obtained by reacting the corresponding MoX 3(THF) 3 complexes with PMe 2Ph 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 Mo 2Br 6(PMe 2Ph) 3 and PMe 2Ph shows evidence for the formation of the edge-sharing bioctahedral Mo 2Br 6(PMe 2Ph) 4 as a short-lived intermediate, the mononuclear MoBr 3(PMe 2Ph) 3 being the final product.