The use of a cis-dioxomolybdenum(VI) dinuclear complex with quadradentate 1,4-benzenediylbis(benzyldithiocarbamate)(2-) as model compound for the active site of oxo transfer molybdoenzymes: reactivity, kinetics, and catalysis.

Dinuclear cis-dioxomolybdenum(VI) complex [{MoO(2)(Bz(2)Benzenediyldtc)}(2)] coordinated by a quadradentate dithiocarbamate (Bz(2)Benzenediyldtc(2-)=1,4-benzenediylbis(benzyldithiocarbamate)(2-)) has been prepared and characterized by elemental analysis, (13)C NMR, IR and UV-vis spectroscopy. The kinetics of the oxygen atom transfer between [{MoO(2)(Bz(2)Benzenediyldtc)}(2)] and PPh(3) was studied spectrophotometrically in CH(2)Cl(2) medium at 520 nm and four different temperatures, 288, 293, 298 and 303 K, respectively. The reaction follows second order kinetics with the rate constant k=0.163(2)M(-1)S(-1) and its increasingly strong absorption at 520 nm clearly indicate the formation of a μ-oxo molybdenum(V) species as a product. Despite the steric restrictions imposed by the ligand structure to prevent the formation of Mo(V) species, experimental evidence confirms its interference during the process. The product can then be formulated as [MoO(2)(Bz(2)Benzenediyldtc)(2)Mo(2)O(3)(Bz(2)Benzenediyldtc)(2)MoO(2)] which has one μ-oxomolybdenum(V) moiety. An Eyring plot allows the activation parameters ΔH(‡)=64.2(1) kJ mol(-1) and ΔS(‡)=-45.1(6) J K(-1) mol(-1) to be determined from the temperature dependence of the rate constant, suggesting an associative transition state for the oxo transfer reaction. Catalytic oxygen atom transfer reaction from DMSO to PPh(3) was also followed by monitoring the chemical shift changes in (31)P NMR spectroscopy. The substrate oxidation process follows a well-defined catalytic cycle capable of 100% conversion for the reaction of PPh(3) and DMSO without intervention of Mo(V) formation during about 36 h.