Efficient pathway for CO2 transformation to cyclic carbonates by heterogeneous Cu and Zn salen complexes

A series of silica supported Salen type Zn(II) and Cu(II) complexes were prepared and characterized. The obtained materials were characterized by X-ray diffraction (XRD), sorption measurement (BET), Fourier transform infrared spectroscopy (FT-IR), atomic absorption spectroscopy (AAS), atomic force microscopy (AFM), scanning electron micrograph (SEM), thermal and elemental analysis. The chemical fixation of CO2 to form cyclic carbonates in the presence of a Lewis base was efficiently performed by this heterogeneous catalyst system. Very high yield and conversions were obtained at 1.0 MPa CO2 atmosphere without an addition of any solvent. The active heterogeneous Cu-DTBSA was efficiently transformed CO2 into cyclic carbonates while the reusability of the Cu-DTBSA is eight times with minimal decrease in yield.

Graphical abstractVery high yield of cyclic carbonate (TON = 28,665; TOF: 9555) was obtained while using the catalyst Cu-DTBSA complex that has 3,5-ditert-butyl salicylaldimine substituent. The catalyst (Cu-DTBSA) can be reused up to eight times with only a slight decrease in catalytic activity if epichlorohydrin is used as a substrate.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Immobilized Cu and Zn schiff base complexes used as catalyst precursors. ► Catalysts for cycloaddition of CO2 to epoxides. ► Selectively very high yield (TON=28,665) was obtained by immobilized Cu-DTBSA complex. ► Cu-DTBSA can be reused up to eight times with only a slight decrease in catalytic activity.