Ketone synthesized cobaloxime/organocobaloxime catalysts for cyclic carbonate synthesis from CO 2 and epoxides: Characterization and electrochemistry Ahmet Kilic a, * , Mehmet Veysi Kilic a , Mahmut Ulusoy a , Mustafa Durgun a , Emine Aytar a , Metin Dagdevren b , Ismail Yilmaz b a Harran University, Chemistry Department, Osmanbey Campus, 63190 Sanliurfa, Turkey b Istanbul Technical University, Chemistry Department, 34469 Istanbul, Maslak, Turkey article info Article history: Received 25 March 2014 Received in revised form 20 May 2014 Accepted 21 May 2014 Available online 11 June 2014 Keywords: Cobaloxime Electrochemistry Spectroscopy Carbon dioxide Cyclic carbonate abstract 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 CO 2 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 (NEt 3 ) or triphenyl phosphine (PPh 3 ). 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, CO 2 pressure and reaction time, were investigated. A dioxime ligand (LH 2 )(1) was obtained in two steps from 4-methylpropiophenone as ketone. Reaction of CoCl 2 .6H 2 O with the dioxime ligand (LH 2 )(1) and 4-tertbutyl pyridine afforded six-coordinate mono- nuclear cobaloxime or organocobaloxime (2e3) complexes. The mononuclear cobaloxime or organo- cobaloxime (2e3) complexes were used as precursors for building trinuclear cobaloximes or organocobaloxime (4e11) complexes. All compounds were fully characterized by 1 H and 13 C NMR spectra, FT-IR spectra, UVeVis spectra, molar conductivity measurements, melting point measurements, magnetic susceptibility measurements, and LC-MS spectroscopic studies as well as by cyclic voltammetry. © 2014 Elsevier B.V. All rights reserved. Introduction In recent years, the synthesis of cyclic carbonate from CO 2 and epoxides has received much attention because CO 2 is the most inexpensive and renewable carbon resource from the viewpoint of green chemistry and atom economy [1e4]. On the other hand, CO 2 is considered the major greenhouse gas contributing to global warming. Since the beginning of the industrial revolution in about 1850, the average atmospheric concentration of CO 2 has increased from 280 ppm to 370 ppm and as a result, the average global temperature has increased between 0.6  C and 1  C in the same period [5,6]. The uncontrolled CO 2 gas emission increase may contribute to sea level increases and many other problems occur- ring worldwide. In this context, the efficient transformation of CO 2 under mild conditions into useful chemical compounds is very attractive from both an industrial and an academic viewpoint [7]. One way for efficient transformation of CO 2 , is cycloaddition of CO 2 to epoxides to produce five-membered cyclic carbonates under appropriate conditions (Scheme 1). Synthesized cyclic carbonates such as ethylene carbonate, and propylene carbonate have been widely used for various purposes, for instance, as valuable organic synthetic intermediates, electro- lytic elements of lithium secondary batteries, polar aprotic solvents, monomers for synthesizing polycarbonates and chemical in- gredients for preparing medicines or agricultural chemicals, phar- maceutical or fine chemical intermediates, and are applied broadly in both industrial and academic areas [1,8e12]. For cyclic carbonate synthesis from CO 2 and epoxides, various catalytic systems have been developed including homogeneous [13e16] and heterogeneous catalysis [17e21]. In this paper, our aim is to draw attention to cyclic carbonate synthesis from CO 2 and epoxides through assistance from homogeneous catalysts. Thus, we * Corresponding author. Tel.: þ90 414 318 3587; fax: þ90 414 318 3541. E-mail address: kilica63@harran.edu.tr (A. Kilic). Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem http://dx.doi.org/10.1016/j.jorganchem.2014.05.023 0022-328X/© 2014 Elsevier B.V. All rights reserved. Journal of Organometallic Chemistry 767 (2014) 150e159