title: Controlling the Reactivity of Bifunctional Ligands: Carboxylate-Bridged Nonheme Diiron(II) Complexes Bearing Free Thiol Groups.
abstract: Carboxylate-bridged nonheme diiron(II) complexes, bearing free functional groups in general, and free thiol groups in particular, were sought. While the addition of sodium γ-hydroxybutyrate into a mixture of Fe(BF4)2·6H2O, HN-Et-HPTB, and Et3N afforded the complex [Fe2(N-Et-HPTB)(μ-O2C-(CH2)3-OH)](BF4)2 (2) (where N-Et-HPTB is the anion of N,N,N',N'-tetrakis(2-(1-ethylbenzimidazolyl))-2-hydroxy-1,3-diaminopropane), a similar, straightforward process could not be used for the synthesis of diiron(II) complexes with free thiol groups. In order to circumvent this problem, a new class of thiolate bridged diiron(II) complexes, [Fe2(N-Et-HPTB)(μ-SR(1))](BF4)2 (R(1) = Me (1a), Et (1b), (t)Bu (1c), Ph (1d)) was synthesized. Selective proton exchange reactions of one representative compound, 1b, with reagents of the type HS-R(2)-COOH yielded the target compounds, [Fe2(N-Et-HPTB)(μ-O2C-R(2)-SH)](BF4)2 (R(2) = C6H4 (3a), CH2CH2 (3b), CH2(CH2)5CH2 (3c)). Redox properties of the complexes 3a-3c were studied in comparison with the complex, [Fe2(N-Et-HPTB)(μ-O2CMe)](BF4)2 (5). Reaction of (Cp2Fe)(BF4) with 1b yielded [Fe(II)2(N-Et-HPTB)(DMF)3](BF4)3·DMF (4) (when crystallized from DMF/diethyl ether), which might indicate the formation of a transient ethanethiolate bridged {Fe(II)Fe(III)} species, followed by a rapid internal redox reaction to generate diethyldisulfide and the solvent coordinated diiron(II) complex, 4. This possibility was supported by a comparative cyclic voltammetric study of 1a-1c and 4. Prospects of the complexes of the type 3a-3c as potential building blocks for the synthesis of nonheme diiron(II) complexes covalently attached with other redox active metals has been substantiated by the synthesis of the complexes, [Fe2(N-EtHPTB)(μ-O2C-R(2)-S)Cu(Me3TACN)](BF4)2 (R = p-C6H4 (7a), CH2CH2 (7b)). All the compounds were characterized by a combination of single-crystal X-ray structure determinations and/or elemental analysis.
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science , 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata-700032, India.
authors.forename: Nabhendu
authors.initials: N
authors.lastname: Pal
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science , 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata-700032, India.
authors.forename: Amit
authors.initials: A
authors.lastname: Majumdar