Highly active and selective Zn(II)-NN′O Schiff base catalysts for the cycloaddition of CO2 to epoxides

• Zn(II) complexes with tridentate NN′O-donor ligands were prepared.
• They are active combined with a co-catalyst for the reaction of CO2 and epoxides.
• Cyclic carbonates were selectively obtained even with the more hindered substrates.
• The best activity was obtained in expanded neat substrate in CO2 as reaction media.
• The initial TOF for the cycloaddition of CO2 to styrene oxide was 3733 h−1.

Mononuclear Zn(II) complexes with tridentate NN′O-donor base Schiff ligand N-(2-pyridyl)methyl-2-hydroxy-3,5-di-tert-butylbenzaldimine (1H) combined with a co-catalyst are active for the cycloaddition of CO2 and epoxides. They provide cyclic carbonates selectively even with the more hindered substrates such as cyclohexene oxide and methyl epoxyoleate. The best conditions were achieved running the reaction in expanded neat substrate in CO2 as reaction media. The activity obtained for the cycloaddition of CO2 to styrene oxide reached an initial TOF of 3733 h−1. The solid state structures of [Zn(1)2] and [Zn(1)(OAc)2]n were determined by X-ray diffraction methods. Relative stability of the species in solution was analysed by DFT calculations.

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