The C 3 vanadium(V) amine triphenolate complex 1f has been characterized as a structural and functional model of vanadium haloperoxidases. The complex catalyzes efficiently sulfoxidations at room temperature using hydrogen peroxide as the terminal oxidant, yielding the corresponding sulfoxides in quantitative yields and high selectivities (catalyst loading down to 0.01%, TONs up to 9900, and TOFs up to 8000 h (-1)) as well as bromination of 1,3,5-trimethoxybenzene (catalyst loading down to 0.05%, TONs up to 1260, and TOFs up to 220 h (-1)).
The polyhedral oligomeric silsesquioxane trisilanolate vanadium(V) complex 1 efficiently catalyzes oxidations at room temperature using cumyl hydroperoxide as the terminal oxidant. Sulfoxidations and N-oxidations have been carried out yielding the corresponding products in good yields. The addition of a Lewis base as a coligand can markedly affect reactivity, stability, and chemo- and stereo-selectivity. A proposal for the intermolecular activation, using Gutmann analysis supported by MP2/TZVP calculations, is presented.
Interest in the catalytic
activation of peroxides, together with
the requirement of stereoselectivity for the production of enantiopure
sulfoxides, has made sulfoxidation the ideal playground for theoretical
and experimental physical organic chemists investigating oxidation
reactivity. Efforts have been dedicated for elucidating the catalytic
pathway regarding these species and for dissecting out the dominant
factors influencing the yield and stereochemistry. In this article,
Ti(IV) and Hf(IV) aminotriphenolate complexes have been prepared and
investigated as catalysts in the presence of peroxides in sulfide
oxidation. Experimental results have been combined with theoretical
calculations obtaining detailed mechanistic information on oxygen
transfer processes. The study revealed that steric issues are mainly
responsible for the formation of intermediates in the oxidation pathway.
In particular, we could highlight the occurrence of a blended situation
where the steric effects of sulfides, ligands, and oxidants influence
the formation of different intermediates and reaction pathways.
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