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Novel constrained Schiff-base ligands (inden) were developed based on the well-known salen ligands. Chromium complexes supported by the constrained inden ligands were successfully synthesized and used as catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO 2 ). The catalyst having tert-butyl ( t Bu) groups as substituents in combination with tetrabutylammonium bromide (TBAB) as a cocatalyst exhibited very high catalytic activity with a turnover frequency of up to 14800 h −1 for the conversion of CO 2 and propylene oxide into propylene carbonate exclusively at 100 °C and 300 psi of CO 2 under solvent-free conditions. The catalyst was found to be highly active for various epoxide substrates to produce terminal cyclic carbonates in 100% selectivity.

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Figure 4. Photographic images of paper-based sensors derived from 1 and 2 after a) treatment with anion solutions. b) treatment with CN À at various concentrations under fluorescent black light radiation.ChemistrySelect Communications