Reactivity of a Fe(III)-Bound Methoxide Supported with a Tris(thiolato)phosphine Ligand: Activation of C–Cl Bond in CH2Cl2 by Nucleophilic Attack of a Fe(III)–OCH3 Moiety
† Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan
∥ Department of Chemistry, National Taiwan Normal University, Taipei 116, Taiwan
Inorg. Chem., 2016, 55 (2), pp 566–572
DOI: 10.1021/acs.inorgchem.5b02135
Publication Date (Web): December 23, 2015
Copyright © 2015 American Chemical Society
Synopsis
A five-coordinate iron(III) methoxide complex supported by a tris(thiolato)phosphine ligand is obtained. The iron(III) center adopts a trigonal-bipyramidal geometry with the electronic structure of an intermediate-spin state (S = 2/3). The redox chemistry to access an iron(II) complex and an iron(IV) complex is also established. The iron(III)-bound methoxide demonstrates a strong nucleophilic reactivity to activate the C−Cl bond in CH2Cl2, leading to the formation of an iron(III) chloride complex that is isolated and characterized.
Abstract
Two mononuclear nonheme FeIII complexes, [PPh4][FeIII(PS3″)(OCH3)] (1) and [PPh4][FeIII(PS3″)(Cl)] (2), supported by a tris(benzenethiolato)phosphine derivative PS3″ (PS3″ = P(C6H3-3-Me3Si-2-S)33–) have been synthesized and characterized. The structures resolved from X-ray crystallography show that FeIII centers in both complexes adopt distorted trigonal-bipyramidal geometry with a methoxide or a chloride binding in the axial position. The magnetic data for both are consistent with intermediate-spin FeIII centers with a C3 symmetry (S = 3/2 ground state). The bound methoxide in 1 is labile and can be replaced by a CH3CN molecule. The forming FeIII–CH3CN species can be further reduced by cobaltcene quantitatively to a stable FeII–CH3CN complex, [Fe(PS3″)(CH3CN)]−. One-electron oxidation of 2 by ferrocenium gave a FeIVanalogue, [FeIV(PS3″)(Cl)]. Importantly, the FeIII–OCH3 moiety in complex 1 acts as a strong nucleophile that activates the C–Cl bond in CH2Cl2, leading to the formation of complex 2quantitatively. Complex 1 also reacts with other electrophiles, benzyl chloride and benzyl bromide, to generate FeIII–X species (X = Cl or Br). The reactions were investigated and monitored by UV–vis–NIR, NMR, and ESI-MS spectroscopies.
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