Oxidative desulfurization removes sulfides from petroleum to reduce sulfur emission from fossil fuel combustion. An important part of this process is sulfide oxidation that can be done catalytically with metal complexes upon H2O2 activation. To this end, the impact of the catalyst ligand size on sulfide oxidation was explored by analyzing two tetradentate Salen-like group 6 complexes. Both novel catalysts contained a molybdenum (VI) dioxo moiety with either an overhanging methyl or t-butyl ligation. The title reaction was the oxidation of thioanisole to the sulfoxide and sulfone. Kinetics runs (1H NMR) yielded well behaved Arrhenius plots for both the methyl and t-butyl MoO2 catalysts (5% loading) upon equimolar H2O2 addition with Ea of 51±3 kJ/mol and 61±3 kJ/mol, respectively. This indicates the steric effect for sulfide à sulfoxide oxidation by these octahedral, tetradentate Mo(VI) dioxo complexes. However, the larger t-butyl ligation was more effective it taking the sulfoxide to the sulfone in the double oxidation. Similar results were also found for the tungsten analog that will also be presented along with electronic effects for this sulfide oxidation by this new class of group 6 complexes.

Sulfide oxidation by group 6 tetradentate complexes: Towards a mechanistic understanding

ACS Spring 2022

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