Mechanistic Investigations of the Ruthenium-Catalyzed Synthesis of Acrylate Salt from Ethylene and CO<sub>2</sub>
Kohei Takahashi, Yo Hirataka, Tatsuyoshi Ito, Nobuharu Iwasawa
Abstract
Here we describe detailed mechanistic analyses of the ruthenium-catalyzed synthesis of acrylate salt from ethylene and CO2. All of the primary steps of the catalytic cycle, that is (i) oxidative cyclization of ethylene and CO2 to give ruthenalactones, (ii) thermal β-H elimination of ruthenalactones to hydrido acrylato complexes, and (iii) base-mediated generation of ethylene-coordinated, zerovalent ruthenium complexes from hydrido acrylato complexes, are found to proceed more rapidly on the more electron rich complexes. These results suggest that the last two processes proceed through the cationic ruthenium complexes generated by dissociation of carboxylate anions. As another possible pathway for the catalytic acrylate synthesis, base-promoted cleavage of a ruthenalactone to an ethylene-coordinated, zerovalent ruthenium complex is also studied, and the reaction is found to proceed smoothly, where the rate of the reaction is dependent on the basicity of the base. In contrast to the stoichiometric reactivities, electron-deficient ruthenium complexes exhibited higher activity in the catalytic acrylate synthesis.