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

Abstract

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(κ¹-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(κ¹-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.