Ketone synthesized cobaloxime/organocobaloxime catalysts for cyclic carbonate synthesis from CO₂ and epoxides: Characterization and electrochemistry

Herein we report the synthesis and characterization of a new series of synthesized mono- and trinuclear cobaloxime/organocobaloximes from ketone that act as catalysts for cyclic carbonate synthesis from CO₂ and epoxides under appropriate conditions (2 h, 100 °C and 1.6 MPa pressure). These reactions were carried out with and without co-catalyst, namely, 4-dimethylaminopyridine (DMAP), pyridine (py), triethyl amine (NEt₃) or triphenyl phosphine (PPh₃). In the catalytic experiments, the 4-dimethylaminopyridine (DMAP) was used as co-catalyst, since the DMAP was a more active base with higher yield compared to other Lewis bases. In addition, various factors influencing the cycloaddition reaction, such as co-catalyst, temperature, CO₂ pressure and reaction time, were investigated. A dioxime ligand (LH₂) (1) was obtained in two steps from 4-methylpropiophenone as ketone. Reaction of CoCl₂.6H₂O with the dioxime ligand (LH₂) (1) and 4-tertbutyl pyridine afforded six-coordinate mononuclear cobaloxime or organocobaloxime (2-3) complexes. The mononuclear cobaloxime or organocobaloxime (2-3) complexes were used as precursors for building trinuclear cobaloximes or organocobaloxime (4-11) complexes. All compounds were fully characterized by ¹H and ¹³C NMR spectra, FT-IR spectra, UV-Vis spectra, molar conductivity measurements, melting point measurements, magnetic susceptibility measurements, and LC-MS spectroscopic studies as well as by cyclic voltammetry.