Sulfoxidation with hydrogen peroxide catalyzed by [SeO(4){WO(O(2))(2)}(2)](2-)

Area of Science:

• Inorganic Chemistry
• Catalysis
• Oxidation Reactions

Background:

• Selective oxidation of sulfur-containing compounds is crucial in organic synthesis and materials science.
• Peroxotungstates are known catalysts for oxidation, but their efficiency and selectivity can vary.
• Understanding the mechanism of electrophilic oxidation is key to designing effective catalysts.

Purpose of the Study:

• To synthesize and characterize a novel selenium-containing dinuclear peroxotungstate catalyst.
• To investigate the catalytic activity and selectivity of this catalyst for the oxidation of cyclic sulfides.
• To elucidate the reaction mechanism and the role of electrophilicity in the oxidation process.

Main Methods:

• Synthesis of the dinuclear peroxotungstate [(n-C(4)H(9))(4)N](2)[SeO(4){WO(O(2))(2)}(2)] (I).
• Catalytic oxidation reactions using 30% aqueous H(2)O(2) with various cyclic mono- and disulfides.
• Kinetic studies, Hammett analysis, and computational investigations to determine reaction mechanisms and electrophilicity.

Main Results:

• Catalyst I selectively oxidized cyclic disulfides to monosulfoxides using one equivalent of H(2)O(2).
• Dibenzothiophene was oxidized to the corresponding sulfone in 98% yield with two equivalents of H(2)O(2) under mild conditions.
• Negative Hammett rho value and low X(SO) value confirmed catalyst I as a strong electrophilic oxidant.
• Reactivity of peroxotungstates correlated with heteroatom type and electrophilicity; stronger electrophilicity led to higher activity.
• Kinetic and computational studies indicated electrophilic attack of peroxo oxygen on sulfur as the key step.

Conclusions:

• The selenium-containing dinuclear peroxotungstate is a highly active and selective catalyst for sulfide oxidation.
• The catalyst functions as a strong electrophilic oxidant, with the reaction mechanism involving nucleophilic attack at the sulfur atom.
• Catalyst design based on heteroatom and electrophilicity is crucial for optimizing peroxotungstate-catalyzed sulfoxidation.