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(iPrNPPh2)3Fe NR (R = tert-butyl (tBu), 1; adamantyl, 2) was examined. Bulk chemical oxidation of 1 and 2 with Fc[PF6] (Fc = ferrocene) is accompanied by fluoride ion abstraction from PF6- by the iron center trans to the Fe NR functionality, forming F-Fe( iPrNPPh2)3Fe NR (iPr = isopropyl) (R = tBu, 3; adamantyl, 4). Axial halide ligation in 3 and 4 significantly disrupts the Fe-Fe interaction in these complexes, as is evident by the >0.3 Å increase in the intermetallic distance in 3 and 4 compared to 1 and 2. Mössbauer spectroscopy suggests that each of the two pseudotetrahedral iron centers in 3 and 4 is best described as FeIII 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 3 and 4 allows these complexes to readily react with CO and tBuNC to generate the FeIIIFeI complexes F-Fe( iPrNPPh2)3Fe(CO)2 (5) and F-Fe( iPrNPPh2)3Fe(tBuNC)2 (6), respectively. Computational methods are utilized to better understand the electronic structure and reactivity of oxidized complexes 3 and 4. © 2014 American Chemical Society.