Reactivity of (Pyridine-Diimine)Fe Alkyl Complexes with Carbon Dioxide

The reaction of CO2 with (PDI)­FeMe (1), (PDI)­Fe­(Me)­PMe3 (1-PMe3) and [(PDI)­FeMe]­[BPh4] (2, PDI = 2,6-(2,6-iPr2–C6H3–NCMe)2–C5H3N) generates (PDI)­Fe­OAc (3), (PDI)­Fe­(OAc)­PMe3 (3-PMe3), and [(PDI)­FeOAc]­[BPh4] (4), respectively. Kinetic data and solvent effects provide evidence that these reactions occur by precoordination of CO2 to the Fe center regardless of the charge state and thus favor an insertion mechanism for carboxylation. Carboxylation of 1-PMe3 requires initial dissociation of PMe3 to generate 1, which reacts with CO2; 1-PMe3 itself does not react directly with CO2. CO2 reacts 5 times faster with neutral 1 than with cationic 2 (at 0 °C), which is ascribed to the higher nucleophilicity of the Fe–Me group in 1.