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The Reactivity of an Iron( II )/Iron( III ) System with Polyamine Ligands in Ethanol: An Electrochemical Study
Author(s) -
UgaldeSaldivar Víctor M.,
SosaTorres Martha E.,
González Ignacio
Publication year - 2003
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200390130
Subject(s) - chemistry , ligand (biochemistry) , reactivity (psychology) , disproportionation , imine , double bond , medicinal chemistry , redox , photochemistry , stereochemistry , inorganic chemistry , polymer chemistry , organic chemistry , receptor , alternative medicine , pathology , catalysis , medicine , biochemistry
Abstract The pentadentate ligand picdien [L A ; 1,9‐bis(2′‐pyridyl)‐2,5,8‐triazanonane)] and [Fe(DMSO) 6 ](NO 3 ) 3 produce the hexacoordinate coordination compound [FeL′ B ] 2+ after reaction in ethanol. This compound shows a change in the oxidation state of Fe III to Fe II as well as an increase in the denticity of the starting ligand L A . The new ligand L′ B {1,9‐bis(2′‐pyridyl)‐5‐[(ethoxy‐2′‐pyridyl)methyl]‐2,5,8‐triazanon‐1‐ene} has an imine carbon−nitrogen double bond. This study provides evidence for the nature of the intermediate species during the formation of [FeL′ B ](BPh 4 ) 2 . A systematic study was performed based on the evolution of the voltammograms observed after the addition of ligand (L A , L B ) or base (LiOEt) to Fe III , Fe II solutions or stoichiometric metal‐ligand mixtures (L B is L′ B without the imine group). The stability of FeL A 3+ and FeL A 2+ species in acidic media and under nitrogen atmosphere was confirmed. The reactivity of FeL B 3+ and FeL A 3+ systems was found to be very similar, and the reduction products were found to be Fe II species with simultaneous ligand oxidation, which, in both cases, produces an imine double bond, giving rise to an intramolecular redox reaction. The following disproportionation equation describes the general form of this process: 2 FeL 3+ ⇄ FeL 2+ + FeL′ 2+ + 2 H + . The oxidation was verified by the double bond formation in L A and L B giving rise to L′ A and L′ B as can be seen in the general equation: R 1 −CH 2 −NH−R 2 ⇄ R 1 −CH=N−R 2 + 2 H + + 2e − . The disproportionation reaction for FeL A 3+ and FeL B 3+ species depends on the acidity level of the media: this reaction cannot be verified in acidic media, while neutral and slightly basic media favour formation of the Fe II species with L′ A and L′ B . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)