文摘
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-SR1)](BF4)2 (R1 = Me (1a), Et (1b), tBu (1c), Ph (1d)) was synthesized. Selective proton exchange reactions of one representative compound, 1b, with reagents of the type HS–R2–COOH yielded the target compounds, [Fe2(N-Et-HPTB)(μ-O2C–R2–SH)](BF4)2 (R2 = 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 [FeII2(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 {FeIIFeIII} 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–R2–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.
