Silicon containing new salicylaldimine Pd(II) and Co(II) metal complexes as efficient catalysts in transformation of carbon dioxide (CO2) to cyclic carbonates

A new series of metal complexes of salicyladimine ligands with Pd(II) and Co(II) have been prepared and characterized by different techniques (elemental analysis, UV–vis, FT-IR, 1H NMR spectra, magnetic susceptibility measurements). Electronic spectra and magnetic susceptibility measurements reveal square planar geometry for Pd(II) metal complex and tetrahedral geometry for Co(II) metal complex. The synthesized Pd(II) and Co(II) complexes were also tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and liquid epoxides which served as both reactant and solvent. The results showed that the [M(L3)2] (M = Pd or Co) complexes bearing 5-methyl substituent on the aryl ring are more efficient than the other Pd(II) and Co(II) metal complexes for the formation of cyclic organic carbonates from carbon dioxide. These catalysts, [Pd(L3)2] and [Co(L3)2] complexes and location (p-position of phenoxy) of electron donating methyl substituent in particular, effectively promote the of carbon dioxide activation with liquid epoxides under solvent-free homogeneous conditions. Furthermore, [Pd(L3)2] can be reused more than eight times with a minimal loss of its original catalytic activities.

Graphical abstractThe synthesized Pd(II) and Co(II) complexes were tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and epoxides effectively. [M(L3)2] complexes bearing 5-methyl substituent (more electron donating) on the aryl ring are more efficient than the other Pd(II) and Co(II) metal complexes. The first active report of a Pd(II) metal complex that can be reused more than eight times with a minimal loss of its original catalytic activities.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We have described synthesis, spectroscopic and catalytic properties in chemical fixation of CO2 using new series metal complexes. ► The synthesized metal complexes also tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and epoxides effectively. ► Schiff base containing Pd(II) as the metal centre have not been used as catalysts for chemical fixation of carbon dioxide.