Reduction of CO2 to CO using low-coordinate iron:: Formation of a four-coordinate iron dicarbonyl complex and a bridging carbonate complex

A reduced diiron(I) complex reacts with CO2 to give two iron-containing products. One product has a carbonate bridge, which isomerizes rapidly at -70 degrees C and may be derived from an oxodiiron intermediate. The formation of this product releases free CO, which leads to a four-coordinate iron dicarbonyl complex. This product is the first crystallographically characterized example of a four-coordinate iron dicarbonyl species, a moiety that may be present in the active site of Hmd (iron-sulfur cluster free) hydrogenase.