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

Novel 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 add...

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Bibliographic Details
Published in:European journal of inorganic chemistry 2022-10, Vol.2022 (30), p.n/a
Main Authors: Bresciani, Giulio, Bortoluzzi, Marco, Marchetti, Fabio, Pampaloni, Guido
Format: Article
Language:English
Subjects:
Adducts
Alkoxide ligands
Carbamates (tradename)
Chemical analysis
Chemical synthesis
Density functional calculations
Dichloromethane
Hydrogen peroxide
Infrared spectroscopy
Inorganic chemistry
Metal carbamates
NMR spectroscopy
Oxidation
Oxygenation
Sulfide oxidation
Sulfides
Sulfones
Titanium
Toluene
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Summary:Novel 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. The first examples of mixed alkoxide‐carbamate complexes are reported based on titanium. The catalytic behavior in oxidation reactions of the new compounds has been explored and is compared to that of related homoleptic complexes.
ISSN:1434-1948
1099-0682
DOI:10.1002/ejic.202200402