Highly reactive catalysts for aerobic thioether oxidation: The Fe-substituted polyoxometalate/hydrogen dinitrate system

A new type of polyoxometalate (POM), one with a hydrogen dinitrate group associated with a d-electron-substituted polyoxometalate, FeIII[H(ONO2)2]PW11O395− (1), has been developed that catalyzes highly effective aerobic sulfoxidation (RR′S + 0.5 O2 → RR′SO) under ambient conditions (1 atm of air at room temperature). Comparison of the rates for aerobic sulfoxidation of the mustard simulant 2-chloroethyl ethyl sulfide (CEES) catalyzed by 1 and several other species reported to be catalysts for this class of reactions, including NO+, NO2, (NH4)2CeIV(NO3)6 and AuIIICl2NO3(CH3CN) indicate that 1 is clearly the most effective catalyst. Conversions and selectivities for the desired sulfoxide decontamination product (CEESO in these studies) are both effectively quantitative. The low or nonexistent catalytic activity of FeII(NO)PW11O396−, Fe(NO3)3 and HNO3 argues strongly that nitrosyl and nitrate derivatives of the Fe polyoxometalate and nitric acid are not species important in catalytic turnover. The techniques of single crystal X-ray diffraction, solution NMR, FTIR, TGA, DSC, cyclic voltammetry, elemental and wet chemical analyses were applied to the characterization of 1 and these are collectively consistent with the α-Keggin structure with a strongly associated hydrogen dinitrate group and a more weakly associated nitrate of crystallization.

Figure optionsDownload as PowerPoint slide