Synthesis, Structure and Proton-Coupled Electron Transfer of (mu)-Oxo-(mu)-chloro and (mu)-Oxo-(mu)-alkoxo Dimeric Molybdenum (III) Ethylenediamine Complexes

An oxo- and chloro-bridged dinuclear molybdenum(III) ethylenediamine complex, [Mo2((mu)-O)((mu)-Cl)(en)4]^3+, was synthesized by the reaction of [MoCl3(thf)3] with ethylenediamine in DMF. (mu)-Oxo-(mu)-alkoxo-bridged dimolybdenum(III) ethylenediamine complexes [Mo2((mu)-O)((mu)-OMe)(en)4]^3+, [Mo2((mu)-O)((mu)-OEt)(en)4]^3+, and [Mo2((mu)-O)((mu)-OPr)(en)4]^3+ were obtained by reactions of the mononuclear complex with ethylenediamine in methanol, ethanol, and propanol, respectively, where each solution contained LiBr. Bridged dimeric structures of these complexes were determined by X-ray crystallography. In an acidic aqueous solution, these oxobridged complexes underwent protonation on the bridging oxygen atoms and changes to the corresponding hydroxo-bridged complexes. Cyclic voltammetric measurements (pH 1.0-10.0) of complexes [Mo2((mu)-O)((mu)-Cl)(en)4]^3+, [Mo2((mu)-O)((mu)-OMe)(en)4]^3+, and [Mo2((mu)-O)((mu)-OEt)(en)4]^3+ clearly showed that, accompanied by the oxidation of the complex, the coordinated amine is deprotonated, and the complex becomes a corresponding amido-coordinated complex.