Synthesis of Fe and Cu metal complexes derived from ‘SNS’ Pincer type ligands and their efficient catalyst precursors for the chemical fixation of $$\hbox {CO}_{2}$$ CO 2

Abstract

Two novel tridentate SNS pincer type ligands, 2,6-bis[[(2 $$^\prime $$ -methoxyphenyl)thio]methyl]pyridine (L1) and 2,6-bis[[(2 $$^\prime $$ -chlorophenyl)thio]methyl]pyridine (L2), each possessing two sulfur and one nitrogen donor functionalities (SNS), based on 2,6-bis(thioether)pyridine ligands were prepared and metallised with $$\hbox {CuCl}_{2}\cdot 2\hbox {H}_{2}\hbox {O}$$ and $$\hbox {FeCl}_{2}\cdot 4\hbox {H}_{2}\hbox {O}$$ metal salts. Two new unanticipated complexes were obtained from the L2 ligand, the dimeric bidentate Cu(I) complex $$[\mathbf{Cu}_{\mathbf{2}}({\varvec{\upkappa }}^{\mathbf{2}}\mathbf{-L2})_{\mathbf{2}}{} \mathbf{Cl}_{\mathbf{2}}]$$ and tridentate Fe(II) complex $$[\mathbf{Fe}({\varvec{\upkappa }}^{\mathbf{3}}{} \mathbf{-L2})\mathbf{Cl}_{\mathbf{2}}]$$ while two new tridentate pincer-type complexes M( $$\upkappa ^{3}$$ -L1) $$\hbox {Cl}_{2}$$ ] ( $$\hbox {M} = \hbox {Cu},\hbox { Fe}$$ ) were formed from the L1 ligand. It was observed that the structure of this Cu(I) complex has a tetrahedral geometry using single crystal X-ray diffraction analysis. In addition, catalytic properties of metal complexes towards the formation of cyclic carbonates from $$\hbox {CO}_{2}$$ and epoxides were investigated. The less sterically hindered Fe(II) complex with the L1 ligand $$[\mathbf{Fe}({\varvec{\upkappa }}^{\mathbf{3}}\mathbf{-L1})\mathbf{Cl}_{\mathbf{2}}]$$ (2) showed the best catalytic activity. Several parameters including temperature, time, epoxide identity and $$\hbox {CO}_{2}$$ pressure were investigated to find the optimum catalytic reaction conditions. Moreover, DFT studies of these compounds are presented in the study. Two novel tridentate SNS pincer type ligands and their metal complexes were synthesized and characterized. In addition, the catalytic properties of the metal complexes towards the formation of cyclic carbonates from $$\hbox {CO}_{2}$$ and epoxides were investigated. The less sterically hindered [Fe( $$\upkappa ^{3}$$ -L1) $$\hbox {Cl}_{2}$$ ] (2) showed the best catalytic activity. Several parameters including temperature, time, epoxide identity and $$\hbox {CO}_{2}$$ pressure were investigated to find the optimum catalytic reaction conditions. Moreover, DFT studies of these compounds are presented in the study.