Titanium Alkoxide Complexes as Catalysts for the Synthesis of Cyclic Carbonates from Carbon Dioxide and Epoxides

Abstract

Titanium alkoxides can catalyze efficient and selective synthesis of cyclic carbonates through CO2 insertion into epoxides when tetrabutylammonium bromide or iodide is used as a cocatalyst. Of the series of synthesized titanium alkoxides, the most active catalyst was one bearing an aliphatic bidentate alkoxide ligand, and it produced propylene carbonate under benign conditions (100 °C, 15 bar CO2, 3 h) with turnover frequencies of up to 116 h–1. The effect of reaction parameters such as pressure, temperature, and catalyst/cocatalyst molar ratio were also studied in order to optimize the catalytic system.

Sterically (un)encumbered mer-tridentate N-heterocyclic carbene complexes of titanium(iv) for the copolymerization of cyclohexene oxide with CO2

“…The NHC-Ti catalytic systems show very limited activity in the coupling of PO (TOF = 7-15 h −1 ) or SO (TOF = 2-7 h −1 ) with CO 2 in comparison to other titanium complexes: titanocene, 50,51 Cp(tetrazole) TiCl 2 , 52 (tetrazole)TiCl 3 (THF), (tetrazole) 2 TiCl 2 , 52 (bis-salphen) (TiCl 2 ) 2 31 and Ti-alkoxides. 53 In the previous study on CO 2 /CHO copolymerization catalyzed by monomeric NHC-Ti(IV) complexes, 29 it was shown that bulky ionic cocatalysts such as [PPN]Cl salts were important for the selective formation of PCHC. A similar trend was observed here and all complexes exclusively promote formation of completely alternated PCHC (≥99%) (runs 1-2 and 3-5, Table 1), supporting our assertion that a nucleophilic anion with bulky countercation is required for the NHC-Ti systems.…”

Heterodinuclear titanium/zinc catalysis: synthesis, characterization and activity for CO2/epoxide copolymerization and cyclic ester polymerization

“…[71][72][73][74][75][76][77][78] Whilst a range of catalysts are known, those based on zinc showed particular promise and there is also recent precedent for titanium complexes showing activity. 79 Therefore, it was of interest to investigate heterodinuclear titanium-zinc catalysts for the alternating copolymerization.…”

Two POM-based compounds containing Zn-capped Keggin anions as decent heterogeneous catalysts for sulfur oxidation and CO2 cycloaddition reactions

“…It is noteworthy that compound 2 exhibits outstanding catalytic activity for sulfur oxidation with 99% conversion for dibenzothiophene (DBT) into dibenzothiophene sulfone (DBTO 2 ) at 55 °C. Moreover, catalyst 2 also showed appealing catalytic activity in the CO 2 cycloaddition reaction, [34][35][36][37] with carbon dioxide as the reaction material transforming into cyclic carbonate, which may not only provide an economical and green reaction path to use in environmental protection, but also confirm that 2 can be used as a bifunctional material with great promise.…”