Song et al.
Scheme 1
However, we recently found a method by which A can be
conveniently prepared with a moderate yield. That is, the
treatment of (µ-LiS)2Fe2(CO)6 (prepared from (µ-S2)Fe2(CO)6
and Et3BHLi)30 with 1,3-dibromo-2-propanol resulted in the
formation of A in 42% yield (Scheme 2). The structure of
A obtained by this method has been fully characterized by
elemental analysis, spectroscopy, and X-ray crystallography.
For example, the IR spectrum of A showed five absorption
bands in the range 2078-1973 cm-1 for its terminal
carbonyls and one broad band at 3302 cm-1 for its hydroxy
group. The 1H NMR spectrum displayed a multiplet around
3.10 ppm for the hydrogen atom attached to its bridgehead
C atom, and it displayed a triplet at 1.50 ppm and a doublet/
doublet at 2.79 ppm for the axial and the equatorial
hydrogens in its two CH2S groups, respectively. The crystal
structure of A determined by X-ray diffraction analysis
contains 0.5 CHCl3 molecules per molecule of A.31 While
Figure 1 shows its ORTEP plot, Table 1 lists its selected
bond lengths and angles. As can be seen in Figure 1, complex
A contains a hydroxylpropanedithiolate ligand, which is
bridged between two Fe atoms of the diiron subsite to form
two fused six-membered rings Fe1S1C7C8C9S2 and
Fe2S1C7C8C9S2. The hydroxyl group and the hydrogen
atom attached to the bridgehead C8 atom reside in the
common equatorial and axial positions of the above-
mentioned chair and boat-shaped six-membered rings, re-
spectively. In addition, the Fe-Fe bond length of our A
(2.5164 Å) is actually the same as that reported (2.524 Å)31
and is very close to those reported for similar diiron carbonyl
complexes.23,28,32
the two iron atoms of the [2Fe2S] cluster are connected to
CO and CN- ligands and are bridged by a dithiolate
SCH2XCH2S cofactor (Scheme 1). This structural informa-
tion has encouraged chemists to synthesize a wide variety
of H-cluster models.15–28 Among these models, the C-
functionalized propanedithiolate (PDT) and the N-function-
alized azadithiolate (ADT) models are of particular interest,
since they could be easily modified by functional transforma-
tion reactions to get a variety of biomimetic analogues with
novel structure and improved catalytic properties.18,19,26 In
this paper, we report the synthesis, structural characterization,
and properties of a new series of C-functionalized PDT
models obtained by functional transformation reactions of
the known complex [(µ-SCH2)2CH(OH)]Fe2(CO)6 (A).29 In
addition, a new synthetic method for complex A and the
biomimetic H2 evolution catalyzed by one of the new models
are also described.
Results and Discussion
Synthesis and Characterization of Starting Complex
[(µ-SCH2)2CH(OH)]Fe2(CO)6 (A). Since 1982, when Hutt-
ner first prepared complex A by oxidative addition method
of Fe3(CO)12 with dithiol HSCH2CH(OH)CH2SH,29 no other
synthetic method for this complex has been reported.
Synthesis and Characterization of Model Complexes
[(µ-SCH2)2CHO2CPh]Fe2(CO)6
(1),
[(µ-SCH2)2-
CHO2CC5H4N-4]Fe2(CO)6 (2), [(µ-SCH2)2CHO2CC4H3O-
2]Fe2(CO)6 (3), and [(µ-SCH2)2CHO2CC4H3S-2]Fe2(CO)6
(4). The C-functionalized PDT-type models 1-4 were
prepared via functional transformation reactions of the
C-hydroxyl group of complex A. Thus, acylation of A with
benzoyl chloride or 4-pyridinecarboxylic acid chloride in
CH2Cl2 in the presence of Et3N gave the expected C-benzoate
and C-pyridinecarboxylate complexes 1 and 2 in 63% and
61% yields, respectively, whereas A reacted with 2-furan-
carbonyl chloride or 2-thiophenecarbonyl chloride under
similar conditions to afford the corresponding C-furancar-
boxylate and C-thiophenecarboxylate complexes 3 and 4 in
70% and 58% yields, respectively (Scheme 3).
Complexes 1-4 are air-stable red solids, which have been
characterized by elemental analysis and spectroscopy. The
IR spectra of 1-4 displayed five to six absorption bands in
the region 2076-1937 cm-1 for their terminal carbonyls and
one absorption band in the range 1735-1718 cm-1 for their
ester carbonyls. The 1H NMR spectra of 1-4 showed a broad
(15) Gloaguen, F.; Lawrence, J. D.; Schmidt, M.; Wilson, S. R.; Rauchfuss,
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J. Am. Chem. Soc. 2001, 123, 3268.
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Darensbourg, M. Y. Organometallics 2007, 26, 3976.
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2001, 123, 9476.
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4546 Inorganic Chemistry, Vol. 47, No. 11, 2008