One-Electron Oxidation Chemistry and Subsequent Reactivity of Diiron Imido Complexes

Abstract

The chemical oxidation and subsequent group transfer activity of the unusual diiron imido complexes Fe­(^<i>i</i>PrNP­Ph₂)₃FeNR (R = <i>tert</i>-butyl (^<i>t</i>Bu), <b>1</b>; adamantyl, <b>2</b>) was examined. Bulk chemical oxidation of <b>1</b> and <b>2</b> with Fc­[PF₆] (Fc = ferrocene) is accompanied by fluoride ion abstraction from PF₆^– by the iron center <i>trans</i> to the FeNR functionality, forming F–Fe­(^<i>i</i>PrNP­Ph₂)₃FeNR (^<i>i</i>Pr = isopropyl) (R = ^<i>t</i>Bu, <b>3</b>; adamantyl, <b>4</b>). Axial halide ligation in <b>3</b> and <b>4</b> significantly disrupts the Fe–Fe interaction in these complexes, as is evident by the >0.3 Å increase in the intermetallic distance in <b>3</b> and <b>4</b> compared to <b>1</b> and <b>2</b>. Mössbauer spectroscopy suggests that each of the two pseudotetrahedral iron centers in <b>3</b> and <b>4</b> is best described as Fe^III and that one-electron oxidation has occurred at the tris­(amido)-ligated iron center. The absence of electron delocalization across the Fe–FeNR chain in <b>3</b> and <b>4</b> allows these complexes to readily react with CO and ^<i>t</i>BuNC to generate the Fe^IIIFe^I complexes F–Fe­(^<i>i</i>PrNP­Ph₂)₃Fe­(CO)₂ (<b>5</b>) and F–Fe­(^<i>i</i>PrNPPh₂)₃­Fe­(^<i>t</i>BuNC)₂ (<b>6</b>), respectively. Computational methods are utilized to better understand the electronic structure and reactivity of oxidized complexes <b>3</b> and <b>4</b>