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Download fileControlling the Reactivity of Bifunctional Ligands: Carboxylate-Bridged Nonheme Diiron(II) Complexes Bearing Free Thiol Groups
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posted on 2016-03-09, 15:59 authored by Nabhendu Pal, Amit MajumdarCarboxylate-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.