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(OAc)[CH(NAr)] (, Ar = 4-MeOCH) having two acetates and two amidinates exhibited high catalytic activity in the presence of BuNCl, in which [ BuN][Mo{CH(NAr)}Cl] (), derived by treating with ClSiMe and BuNCl, 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, [ BuN][Mo{CH(NAr)}Cl] (), was characterized by EPR and X-ray diffraction studies. Kinetic analysis of the hydrodehalogenation reaction as well as a deuterium-labelling experiment using MBTCD- suggested that the H-abstraction was the rate-determining step for the catalytic reaction.