Transition Metal Catalyzed Eco-friendly Reaction Development Using Sustainable C1 Source

Abstract

This study presents an investigation of transition metal mediated catalysis utilizing abundant C1 carbon sources such as carbon dioxide and methanol, with the corresponding state-of-the-art reactions explained in Chapter 1. The employed carbon capture and utilization (CCU) strategy (Chapter 2) involves the direct capture of carbon dioxide from exhaust gas and its subsequent use in organic transformations, achieving efficiencies similar to those observed for hyper-pure CO2 from a commercial source, even for highly air- and moisture-sensitive reactions. The CO2-capturing aqueous ethanolamine solution can be continuously recycled without decreasing the reaction efficiency. Transfer hydrogenation of organic formates and cyclic carbonates was achieved for the first time using a readily available ruthenium catalyst (Chapter 3). Nontoxic and low-cost 2-propanol was employed both as a solvent and hydrogen source, circumventing the use of flammable H2 gas under high pressure. This method provides an indirect way of producing methanol from carbon dioxide under mild conditions, also presenting an operationally simple and environmentally benign reduction of formates and carbonates. An unprecedented urea synthesis was accomplished directly from methanol and amines (Chapter 4), being highly atom economical and producing hydrogen as the sole byproduct. Commercially available ruthenium pincer complexes were used as catalysts. In addition, no additives such as bases, oxidants, or hydrogen acceptors were required. Furthermore, unsymmetrical urea derivatives were successfully obtained via a one-pot two-step reaction. Two abnormal N-heterocyclic carbene (aNHC) gold(I)complexes, [(aNHC)AuCl], were prepared from C2-protected imidazolium salts (Chapter 5). These air-stable compounds were synthesized by transmetalation, using (Me2S)AuCl and the corresponding silver salt, and were fully characterized by NMR, mass spectrometry, and X-ray crystallography. The catalytic activities of these NHC-based Au complexes were also compared in the hydration of alkynes, with traditional NHC-based Au complexes exhibiting higher efficiency.