Oxido-molybdenum complexes obtained by Cl/O interchange between MoCl5 and carboxylic acids: a crystallographic, spectroscopic and computational study.

The direct interaction of MoCl5 with a series of carboxylic acids has been elucidated for the first time. The reactions proceed with release of hydrogen chloride and Cl/O interchange between the metal centre and one equivalent of organic substrate: this feature is unique in the context of the chemistry generally shown by transition metal halides with carboxylic acids. The dinuclear complexes [MoOCl2(κ(1)-CX3CO2H)(μ-Cl)]2 (X = H, 1a; X = Cl, 1b) and Mo2O2Cl6(μ-CH3CO2H), 2a, were isolated as the prevalent metal products of the 1:2 molar reactions of MoCl5 with CH3COOH and CCl3COOH. Evidence for the formation of Mo2O2Cl6(μ-CCl3CO2H), 2b, was achieved by allowing MoCl5 to react with CCl3COOH in 2:3 ratio. Instead the reactions of MoCl5 with a three-fold molar excess of RCOOH afforded the mononuclear complexes MoOCl3(κ(1)-RCO2H)2 (R = CH3, 3a; CCl3, 3b; CHCl2, 3c; CMe3, 3d) in 50–60% yields. The new compounds were characterized by analytical and spectroscopic techniques, moreover the X-ray molecular structures were ascertained for 1a, 1b and 2a; 1a and 1b display single Mo–Mo bond. DFT calculations were carried out in order to shed light into structural aspects.