165881-83-4Relevant academic research and scientific papers
Reduction of CO2 Directed toward Carbon-Carbon Bond Formation
Tanaka, Koji
, p. 17 - 29 (1998)
This paper describes electrochemical reduction of CO2 directed toward carbon-carbon bond formation via metal-CO2 adducts. An electrophilic attack of CO2 to penta-coordinated low valent polypyridyl Ru complexes affords a Ru-η1-CO2 adduct, which is easily converted to Ru-CO species either by an acid-base equilibrium in protic media and oxide transfer to CO2 under aprotic conditions. Two-electron reduction of resultant Ru-CO in protic solutions competitively causes a cleavage of the Ru-CO bond (CO evolution) and formation of a thermally labile Ru-CHO bond. Besides further reduction of the latter to Ru-CH2OH as precursors to CH3OH and HOOCCH2OH, Ru-CHO reacts with CO2 to afford HCOOH with regenerating Ru-CO as the precursor to CO. Thus, the difficulty of multi-electron reduction of CO2 in protic solutions is ascribed to the thermal lability and strong hydride donor character of Ru-CHO. On the other hand, two-electron reduction of Ru-CO in the presence of (CH3)4N+ or CH3I under aprotic conditions produces thermally stable R-C(O)CH3, which works as a precursor to CH3C(O)CH3. Two-electron reduction of M3(μ3-S)2 clusters (M = Co, Rh, Ir) causes an M-M bond cleavage and the nucleophilicity of the μ3-S ligand is also enhanced. As a result, two CO2 molecules reductively activated probably on μ3-S and metal sites undergo the coupling reaction to give oxalate selectively.
