Multiple, Disparate Redox Pathways Exhibited by a Tris(pyrrolido)ethane Iron Complex

摘要

Iron(III) complexes of the tris(pyrrolide)- ethane trianion have been synthesized by reaction of oneand two-electron oxidants with [(tpe)Fe(THF)][Li(THF)_4] (tpe = tris(5-mesitylpyrrolyl)ethane). X-ray crystallography, ~(57)Fe Mo?ssbauer, ~1H NMR and EPR spectroscopy, SQUID magnetometry, and density functional theory calculations were employed to rigorously establish the iron 3+ oxidation state. All oxidants employed are proposed to operate via an innersphere electron transfer mechanism. Dialkyl peroxides and dibenzyldisulfide served to oxidize iron by one electron, and group transfer of an aryl nitrene unit to the Fe~(2+) starting material resulted in formation of Fe~(3+) amido species following H-atom abstraction by a presumed nitrenoid intermediate. Single electron transfer to and from diphenyldiazoalkane was also observed to yield a diphenyldiazomethanyl radical anion antiferromagnetically coupled to the S = 5/2 Fe~(3+). Isolation of Fe~(3+) complexes of tpe, in comparison with previous results wherein the tpe ligand was the redox active moiety, presents an unusual juxtaposition of two noncommunicating redox reservoirs, each accessible via different reaction pathways (namely, inner- and outer-sphere electron transfer).