Mixed-ligand complexes of paddlewheel dinuclear molybdenum as hydrodehalogenation catalysts for polyhaloalkanes

We developed a hydrodehalogenation reaction of polyhaloalkanes catalyzed by paddlewheel dimolybdenum complexes in combination with 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (MBTCD) as a non-toxic H-atom source as well as a salt-free reductant. A mixed-ligated dimolybdenum complex Mo(2)(OAc)(2)[CH(NAr)(2)](2) (3a, Ar = 4-MeOC(6)H(4)) having two acetates and two amidinates exhibited high catalytic activity in the presence of (n)Bu(4)NCl, in which [(n)Bu(4)N](2)[Mo(2){CH(NAr)(2)}(2)Cl(4)] (9a), derived by treating 3a with ClSiMe(3) and (n)Bu(4)NCl, was generated as a catalytically-active species in the hydrodehalogenation. All reaction processes, oxidation and reduction of the dimolybdenum complex, were clarified by control experiments, and the oxidized product, [(n)Bu(4)N][Mo(2){CH(NAr)(2)}(2)Cl(4)] (10a), was characterized by EPR and X-ray diffraction studies. Kinetic analysis of the hydrodehalogenation reaction as well as a deuterium-labelling experiment using MBTCD-d(8) suggested that the H-abstraction was the rate-determining step for the catalytic reaction.