$CO_2$ conversion on a single metal center

Abstract

Conversion of carbon dioxide has been one of the major research topic in recent years not only to contribute to find the solution for the global climate change and but also to recycle $CO_2$ as a cheap and abundant C1 source to produce useful chemicals and renewable energy fuels. The major challenge for the conversion of $CO_2$ into energy-bearing products is to find the suitable catalysts. Even with remarkable advances in the $CO_2$ reduction chemistry using transition metal complexes, their efficiencies and selectivity are not good enough to be utilized in chemical industry. One of the most researched fields is a coupling reaction of $CO_2$ with epoxide generating industrially important chemicals: polycarbonate and cyclic carbonate. Researches that have been done on selectivity issue were controls on concentrations or types of co-catalyst and pressure of $CO_2$ and etc. Thus, to synthesize more selective catalysts for coupling of $CO_2$ with epoxide, carbonate moieties have importance on both generating polycarbonate and cyclic carbonate because the carbonate moieties are diverged to whether polycarbonate or cyclic carbonate. In chapter 1, possible intermediate-like species, Al-oxide and Al-carbonate, are synthesized and characterized with various spectroscopies including X-ray crystallography. For synthesizing more selective catalysts, further studies are prerequisite. Although thorough and continuous researches on $CO_2$ reduction and conversion have been done for decades, catalysts for conversion of $CO_2$ are still remained in big challenges. In nature, among several CO dehydrogenases (CODH), a Ni-Fe complex in the C cluster converts $CO_2$ to CO. On this system, the nickel center is the key of the conversion, and thus understanding the nickel-$CO_2$ bindings of the system is important. In chapter 2, several nickel monocarbonyl complexes with different oxidation states are synthesized to show reactivity with $CO_2$ . The complexes are supported by a redox-noninocent PPP ligand $(PPP^- = ^-P[2–PiPr_2–C_6H_4]_2)$, to mimic the active nickel site on CODH. One of them shows clean conversion of $CO_2$ having P-$CO_2$ – moiety on central P of the PPP ligand. To investigate unique nickel-$CO_2$ adducts, further researches to tune nucleophilicity of the central phosphide are in progress.