LAUSR

Abstract Oxidation is fundamental for many chemical processes and the search for chemoselective oxidants is relevant because most substrates have different functional groups. For unsaturated organo-heteroatom (E) substrates R 1 E(CH 2 ) n CH CR 2 H, the olefin and/or the heteroatom can be oxidized. It is known that molybdenum oxodiperoxo [MoO(O 2 ) 2 L] complexes can selectively oxidize sulfide groups in the presence of alkenes. Thus, the effects of the substituents (R 1 and R 2 ) and of the separation n between the functional groups on the chemoselectivity were investigated by methods based on the density functional theory (DFT) for sulfides (E = S). The chemoselectivity was quantified by the difference between the Gibbs energy of activation at the double bond (TS@C C) and at the heteroatom (TS@E) oxidation pathways, ΔΔ ‡ G  = Δ ‡ G (TS@C C) − Δ ‡ G (TS@E). Consistent with experimental observations, this oxidation is chemoselective towards the heteroatom (E = S, Se, and PCH 3 ) for any unsaturated substrate or ancillary ligand L in the complex. For unsaturated organosulfur compounds, it is shown that an increase in the electronegativity of R 1 leads to a decrease of the chemoselectivity, which can be correlated with the atomic charge at the sulfur center. The separation n affects the chemoselectivity similarly to the electronegativity of R 1 , namely, differences between sp 2 and sp 3 carbon centers. The ancillary ligand L = OPH 3 , pyrazole, pyridine N -oxide, and Si(OH) 4 , affects the reactivity of the complex and its chemoselectivity, where L = Si(OH) 4 shows the highest reactivity and the least selectivity; however, ΔΔ ‡ G is still large enough (4.3 kcal/mol) to provide high chemoselectivity. This agrees with the experimental observations related to the oxidations by [MoO(O 2 ) 2 L] complexes supported on silica. These quantitative results and the qualitative trends and correlations can be helpful in the design of more efficient and greener Mo-based oxidants.