Titanium(IV) Alkoxide‐Carbamate Complexes: Synthesis and Catalytic Potential in H2O2‐Oxidation of Organic Sulfides

Abstract

AbstractNovel titanium alkoxide‐carbamate complexes, i. e. [Ti(OiPr)2(O2CNR2)2]m (R=Et, 1; R=iPr, 2; R=Bn=CH2Ph, 3), were synthesized in 87–94 % yields by using two distinct synthetic approaches, i. e. the reaction of [Ti(OiPr)4] with [Ti(O2CNR)4] (1 : 1 molar ratio) in dichloromethane solution, and the addition of [Ti(OiPr)4] to amine/CO2 mixture in toluene (amine/Ti ratio=2). The liquid products 1–3 were characterized by elemental analysis, IR and NMR spectroscopy, and the structure of 1 was optimized by DFT calculations. Combined, experimental and theoretical outcomes suggest a trinuclear structure for 1–3, with the carbamates acting as bridging bidentate ligands. Compound 2 revealed the most effective of the series in promoting the oxidation of a series of organic sulfides into the corresponding sulfones, working generally better than 1 and 3 and the homoleptic counterparts [Ti(OiPr)4] or [Ti(O2CNEt2)4]. However, [Ti(OiPr)4] exhibited the best performance in the conversion of tetrahydrothiophene to tetrahydrothiophene 1,1‐dioxide, instead [Ti(O2CNEt2)4] was the most suitable catalyst for the mono‐oxygenation of dibenzylsulfide. NMR and DFT studies indicate that mononuclear bis‐methanol adducts, bearing the solvent molecules trans‐located with respect to the isopropoxides, are plausible active species in the catalytic cycle.