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.