Reactivity of (Pyridine-Diimine)Fe Alkyl Complexes
with Carbon Dioxide
- Publication date
- Publisher
Abstract
The reaction of CO<sub>2</sub> with (PDI)FeMe (<b>1</b>), (PDI)Fe(Me)PMe<sub>3</sub> (<b>1-PMe</b><sub><b>3</b></sub>) and [(PDI)FeMe][BPh<sub>4</sub>] (<b>2</b>, PDI = 2,6-(2,6-<sup><i>i</i></sup>Pr<sub>2</sub>–C<sub>6</sub>H<sub>3</sub>–NCMe)<sub>2</sub>–C<sub>5</sub>H<sub>3</sub>N) generates (PDI)FeOAc
(<b>3</b>), (PDI)Fe(OAc)PMe<sub>3</sub> (<b>3-PMe</b><sub><b>3</b></sub>), and [(PDI)FeOAc][BPh<sub>4</sub>] (<b>4</b>), respectively. Kinetic data and solvent
effects provide evidence that these reactions occur by precoordination
of CO<sub>2</sub> to the Fe center regardless of the charge state
and thus favor an insertion mechanism for carboxylation. Carboxylation
of <b>1-PMe</b><sub><b>3</b></sub> requires initial dissociation
of PMe<sub>3</sub> to generate <b>1</b>, which reacts with CO<sub>2</sub>; <b>1-PMe</b><sub><b>3</b></sub> itself does
not react directly with CO<sub>2</sub>. CO<sub>2</sub> reacts 5 times
faster with neutral <b>1</b> than with cationic <b>2</b> (at 0 °C), which is ascribed to the higher nucleophilicity
of the Fe–Me group in <b>1</b>
