Electrocatalytic Reduction of CO2 to Methanol by Iron Tetradentate Phosphine Complex Through Amidation Strategy.

The iron complex of tetradentate tris[2-(diphenylphosphino) ethyl]phosphine (PP3 ), [Fe(PP3 )(MeCN)2 ](BF4 )2 , was able to electrocatalytically reduce CO2 to formate with a Faradaic efficiency (FE) of approximately 97.3 % in acetonitrile. Upon addition of diethylamine as a cocatalyst, electrocatalytic reduction to methanol was achieved with an FE of 68.5 %, and other products were formamide and formate. A mechanistic study suggested that the [FeH(PP3 )](BF4 ) hydride complex was the active species in the electrocatalysis. Added amine as cocatalyst could react with CO2 to form carbamate, which could then be reduced to formamide and further to methanol. By contrast, free CO2 could only be reduced to formate as the end-product.

Cobalt Complex with Redox-Active Imino Bipyridyl Ligand for Electrocatalytic Reduction of Carbon Dioxide to Formate.

An imino bipyridine cobalt(II) complex was developed for the electrocatalytic reduction of CO2 to formate in acetonitrile with a faradaic efficiency of approximately 80 %. For comparison, a symmetric bis-imino pyridine complex showed lower catalytic activity because of less conjugation in the system. Cyclic voltammetry, electron paramagnetic resonance and IR spectroscopy studies provided mechanistic details and the structures of the key intermediates. DFT calculations confirmed the role of large π-conjugated groups for stabilizing key intermediates through electronic conjugation.