Controlled oxidation of organic sulfides to sulfoxides under ambient conditions by a series of titanium isopropoxide complexes using environmentally benign H2O2 as an oxidant?

Dalton Transactions Pub Date: 2010-01-28 DOI: 10.1039/B921720G

Abstract

Controlled oxidation of organic sulfides to sulfoxides under ambient conditions has been achieved by a series of titanium isopropoxide complexes that use environmentally benign H2O2 as a primary oxidant. Specifically, the [N,N′-bis(2-oxo-3-R1-5-R2-phenylmethyl)-N,N′-bis(methylene-R3)-ethylenediamine]Ti(OiPr)2 [R1 = t-Bu, R2 = Me, R3 = C7H5O2 (1b); R1 = R2 = t-Bu, R3 = C7H5O2 (2b); R1 = R2 = Cl, R3 = C7H5O2 (3b) and R1 = R2 = Cl, R3 = C6H5 (4b)] complexes efficiently catalyzed the sulfoxidation reactions of organic sulfides to sulfoxides at room temperature within 30 min of the reaction time using aqueous H2O2 as an oxidant. A mechanistic pathway, modeled using density functional theory for a representative thioanisole substrate catalyzed by 4b, suggested that the reaction proceeds via a titanium peroxo intermediate 4c′, which displays an activation barrier of 22.5 kcal mol?1 (ΔG?) for the overall catalytic cycle in undergoing an attack by the S atom of the thioanisole substrate at its σ*-orbital of the peroxo moiety. The formation of the titanium peroxo intermediate was experimentally corroborated by a mild ionization atmospheric pressure chemical ionization (APCI) mass spectrometric technique.

Graphical abstract: Controlled oxidation of organic sulfides to sulfoxides under ambient conditions by a series of titanium isopropoxide complexes using environmentally benign H2O2 as an oxidant
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