Sulfide and Sulfoxide Oxidations by Mono- and Diperoxo Complexes of Molybdenum. A Density Functional Study

The molecular mechanism for the oxidation of sulfides to sulfoxides and subsequent oxidation to
sulfones by diperoxo, MoO(O2)2(OPH3) (I), and monoperoxo, MoO2(O2)(OPH3) (II), complexes of
molybdenum was studied using density functional calculations at the b3lyp level and the transition
state theory. Complexes I and II were both found to be active species. Sulfide oxidation by I or II
shows similar activation free energy values of 18.5 and 20.9 kcal/mol, respectively, whereas
sulfoxides are oxidized by I (ΔG⧧ = 20.6 kcal/mol) rather than by II (ΔG⧧ = 30.3 kcal/mol). Calculated
kinetic and thermodynamic parameters account for the spontaneous overoxidation of sulfides to
sulfones as has been experimentally observed. The charge decomposition analysis (CDA) of the
calculated transition structures of sulfide and sulfoxide oxidations revealed that I and II are stronger
electrophilic oxidants toward sulfides than they are toward sulfoxides.

本研究通过密度泛函计算在b3lyp水平上，结合过渡态理论，探讨了二过氧钼复合物MoO(O2)2(OPH3)（I）和单过氧钼复合物MoO2(O2)(OPH3)（II）将硫化物氧化为亚砜，进而进一步氧化为砜的分子机制。研究发现，复合物I和II均具有活性。使用I或II进行硫化物氧化时，其活化自由能值分别为18.5和20.9 kcal/mol，表现出相似性；而亚砜的氧化则主要由I（ΔG⧧ = 20.6 kcal/mol）而非II（ΔG⧧ = 30.3 kcal/mol）催化。计算得到的动力学和热力学参数能够解释硫化物自发过度氧化为砜的现象，与实验观察结果相符。对硫化物和亚砜氧化过程中计算得到的过渡态结构进行电荷分解分析（CDA）显示，I和II对硫化物的亲电氧化能力相较于对亚砜更强。