The electron-withdrawing effect of ligands showed an inverse relation with temperature dependency in the solvent-free catalysis of the selective transformation of CO₂ to cyclic carbonate by electronically varied Zn-complexes.

Abstract

A series of mononuclear bis-ligated Zn(II) octahedral complexes [Zn(L^Mes)₂] (Zn^Mes ), [Zn(L^OMe)₂] (Zn^OMe ), [Zn(L^CF3)₂] (Zn^CF3 ), and [Zn(L^Cl)₂] (Zn^Cl ) have been synthesized using tridentate N/N/N donors, maleonitrile tethered, half-reduced Schiff base ligands, ((2-(benzylamino)-3-((E)-(pyridin-2-ylmethylene)amino)maleonitrile) derivatives, HL^Mes , HL^OMe, HL^CF3 and HL^Cl ). All the compounds were well characterized by spectroscopy and structurally. The noncovalent interactions present in the lattice of Zn-complexes were studied in detail to explain the origin of molecular architecture using Hirshfeld surface (HS) analysis. The catalytic activity for the coupling of CO₂ with epoxides under mild and solvent free condition was demonstrated. The variable electronic effect of ligands due to different substitution at the ligand's backbone was correlated with the variation in catalytic yield. The reverse electronic effect of the ligand due to the rise of temperature in the yield of catalysis was mechanistically explained in terms of the way to the formation of the active catalyst.