Dendrimeric organotelluride catalysts for the activation of hydrogen peroxide. Improved catalytic activity through statistical and stereoelectronic effects

摘要

Dendrimeric polyorganotellurides are prepared in high yield using propyloxy spacers to connect the organotelluride groups to the core molecules. The polyorganotellurides catalyze the oxidation of thiophenol with hydrogen peroxide to give diphenyl disulfide in homogeneous solutions (5% CH2Cl2/MeOH or 46% CH2Cl2/MeOH). The polyorganotellurides with two, three, four, and six catalytic groups show roughly statistical increases for the number of catalytic groups relative to the corresponding monotellurides. Catalysts containing [4-(dimethylamino)-phenyl]telluro groups and n-hexyltelluro groups are oxidized more rapidly by hydrogen peroxide and also show greater catalytic activity than the corresponding catalysts containing phenyltelluro groups. A combination of statistical effects and stereoelectronic effects give a 26-fold increase in catalytic activity from 1-phenoxy-3-(phenyltelluro)propane (23a; nu(0) = 12 muM min(-1)) to dendrimer 22c with six n-hexyltelluro groups (nu(0) = 312 muM min(-1)) for the oxidation of 1.0 x 10(-3) M PhSH with 3.75 x 10(-3) M H2O2 in the presence of 1.0 x 10(-5) M catalyst. The rate of appearance of PhSSPh, with a molar extinction coefficient, epsilon, of 1.24 x 10(-3) L mol(-1) cm(-1) at 305 nm, was monitored at 305 nm. [References: 35]