title: Reinvestigation of the formation of a mononuclear Fe(III) hydroperoxido complex using high pressure kinetics.
abstract: Previous stopped flow kinetic experiments suggested an interchange associative mechanism for the ligand substitution reaction, [Fe(bztpen)(OMe)](2+) + H(2)O(2)--> {[Fe(bztpen)(OMe)(HOOH)](2+)}(++)--> [Fe(bztpen)(OOH)](2+) + MeOH (bztpen = N-benzyl-N, N',N'tris(2-methylpyridyl)-ethylenediamine). Thus a seven-coordinate transition state containing both the leaving methoxide and the incoming hydrogen peroxide ligands was proposed. On the basis of high pressure kinetic data we can now conclude that this is not the case since the rate of the reaction is independent of pressure for the formation of the purple low spin transient hydroperoxido complex, [Fe(bztpen)(OOH)](2+). [Fe(bztpen)(OOH)](2+) has so far proved to be too short-lived for solid state isolation. As part of our ongoing pursuit of this elusive species we have structurally characterised the nitrosyl and acetate iron(II) complexes, [Fe(bztpen)(NO)](OTf)(2) and [Fe(bztpen)(OAc)](BPh(4)), as well as the air stable Co(II) complexes [Co(bztpen)Cl)]BF(4), [Co(metpen)Cl]SbF(6) and [Co(bztpen)(OAc)]BPh(4). We did not realise our aim of accessing stable Co(III) hydroperoxido or peroxido complexes by reaction of the cobalt complexes with H(2)O(2).
authors.affiliation: Institute for Inorganic and Analytical Chemistry, University of Giessen, Heinrich-Buff-Ring 58, 35392, Giessen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Nebe
authors.forename: Alexander
authors.initials: A
authors.lastname: Beitat
authors.forename: Christian
authors.initials: C
authors.lastname: Würtele
authors.forename: Carlos
authors.initials: C
authors.lastname: Dücker-Benfer
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik
authors.forename: Christine J
authors.initials: CJ
authors.lastname: McKenzie
authors.forename: Siegfried
authors.initials: S
authors.lastname: Schindler
mesh_terms: D003035:Cobalt; D018360:Crystallography, X-Ray; D005290:Ferric Compounds; D005296:Ferrous Compounds; D006861:Hydrogen Peroxide; D007501:Iron; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009569:Nitric Oxide; D010100:Oxygen; D011312:Pressure
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D008024:Ligands; D009569:Nitric Oxide; D003035:Cobalt; D006861:Hydrogen Peroxide; D007501:Iron; D010100:Oxygen