Diiron oxadithiolate type models for the active site of iron-only hydrogenases and biomimetic hydrogen evolution catalyzed by Fe 2(μ-SCH2OCH2S-μ)(CO)6

Article abstract of DOI:10.1021/om0507373

The biomimetic chemistry of single and double oxadithiolatodiiron- containing model compounds for the active site of Fe-only hydrogenases (FeHases) has been systematically studied. The simplest such model, Fe ₂(μ-SCH₂OCH₂S

Full text of DOI:10.1021/om0507373

6126
Organometallics 2005, 24, 6126-6135
Diiron Oxadithiolate Type Models for the Active Site of
Iron-Only Hydrogenases and Biomimetic Hydrogen
Evolution Catalyzed by Fe2(µ-SCH2OCH2S-µ)(CO)6
Li-Cheng Song,* Zhi-Yong Yang, Hong-Zhu Bian, Yang Liu, Hu-Ting Wang,
Xu-Feng Liu, and Qing-Mei Hu
State Key Laboratory of Elemento-Organic Chemistry, Department of Chemistry,
Nankai University, Tianjin 300071, People’s Republic of China
Received August 26, 2005
The biomimetic chemistry of single and double oxadithiolatodiiron-containing model
compounds for the active site of Fe-only hydrogenases (FeHases) has been systematically
studied. The simplest such model, Fe2(µ-SCH2OCH2S-µ)(CO)6 (1), was prepared by reaction
of (µ-S2)Fe2(CO)6 with 2 equiv of Et3BHLi followed by direct treatment with excess (ClCH2)2O
or by successive treatment with 2 equiv of CF3CO2H and excess (ClCH2)2O in the presence
of Et3N. Further reaction of 1 with 1 equiv of Me3NO in MeCN at room temperature followed
by treatment of the intermediate Fe2(µ-SCH2OCH2S-µ)(CO)5L (L ) MeCN or Me3N) with 1
equiv of Et4NCN, PPh3, or Cp(CO)2FeSPh gave the single models Fe2(µ-SCH2OCH2S-µ)-
(CO)5La (2, La ) (CN)(Et4N); 3, PPh3; 4, Cp(CO)2FeSPh) in 62-93% yields, whereas the in
situ treatment of the intermediate Fe2(µ-SCH2OCH2S-µ)(CO)5L with 0.5 equiv of 1,4-
(CN)2C6H4, (η5-Ph2PC5H4)2Fe (dppf), or (η5-Ph2PC5H4)2Ru (dppr) afforded the double models
[Fe2(µ-SCH2OCH2S-µ)(CO)5]2Lb (5, Lb ) 1,4-(CN)2C6H4; 6, dppf; 7, dppr) in 57-90% yields.
However, in contrast to 5-7, the double models [Fe2(µ-SCH2OCH2S-µ)(CO)n]2Lc (8, n ) 5, Lc
) (Ph2PCH2CH2OCH2)2; 9, n ) 4, Lc ) [(Ph2PCH2)2NCH2]2) could be prepared by direct
reaction of 1 in toluene at reflux with 0.5 equiv of diphosphine (Ph2PCH2CH2OCH2)2 and
tetraphosphine [(Ph2PCH2)2NCH2]2 in 86% and 56% yields, respectively. 1-9 were character-
ized by elemental analysis and spectroscopy, and particularly for 1, 2, and 4-9 by X-ray
diffraction analysis. The structural features of some model compounds are compared with
those of the active site of FeHases. While the cyclic voltammetric behavior of 1 and 5 was
studied, 1 was found to be a catalyst for proton reduction of acetic acid to give hydrogen
under the corresponding electrochemical conditions. An EECC mechanism for such electro-
catalytic H2 production is preliminarily suggested.
Introduction
site of FeHases, so-called H-cluster,10 consists of a
butterfly Fe2S2 subcluster that bears three unusual
ligands, CO, CN-, and Cys-S-Fe4S4, and a less defined
three-light-atom linker possibly composed of carbon as
in a 1,3-propanedithiolate bridge or any combination of
C, N, and O atoms5,11 bridged between two S atoms of
the butterfly Fe2S2 subsite (Figure 1).
The structural studies concerning the active site of
FeHases have greatly promoted the designed synthesis
of model compounds for the active site that can perform
the catalytic function similar to those in the natural
systems.1,2 To date, numerous models for the active
diiron subsite have been synthesized, such as diiron
propanedithiolate (PDT) derivatives,12-15 diiron aza-
Hydrogenases are highly efficient enzymes that cata-
lyze both the reduction of protons and the oxidation of
hydrogen in a variety of microorganisms.1 Among such
enzymes the Fe-only hydrogenases (FeHases) have
recently received considerable attention because of their
unusual structures and particularly their unique func-
tion for production of hydrogen, an alternative “clean”
energy source.2 The X-ray crystallographic3-6 and IR
spectroscopic7-9 studies have revealed that the active
* To whom correspondence should be addressed. Fax: 0086-22-
23504853. E-mail: lcsong@nankai.edu.cn.
(1) (a) Adams, M. W. W.; Stiefel, E. I. Science 1998, 282, 1842. (b)
Cammack, R. Nature 1999, 397, 214.
(2) (a) Darensbourg, M. Y.; Lyon, E. J.; Zhao, X.; Georgakaki, I. P.
PNAS 2003, 100, 3683. (b) Evans, D. J.; Pickett, C. J. Chem. Soc. Rev.
2003, 32, 268. (c) Alper, J. Science 2003, 299, 1686.
(3) Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C.
Science 1998, 282, 1853.
(4) Nicolet, Y.; Piras, C.; Legrand, P.; Hatchikian, E. C.; Fontecilla-
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(5) Nicolet, Y.; De Lacey, A. L.; Verne`de, X.; Fernandez, V. M.;
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Darensbourg, M. Y. J. Am. Chem. Soc. 2001, 123, 9710.
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10.1021/om0507373 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 11/01/2005

Diiron Oxadithiolate Type Models
Organometallics, Vol. 24, No. 25, 2005 6127
Figure 1. Composite structure for the active site based
on the crystal structures of FeHases (X ) CH2, NH, or O).
dithiolate (ADT) derivatives,16-18 and the very recently
reported diiron PDT derivatives with a cubic Fe4S4
cluster.19 In a recent communication we preliminarily
reported several diiron oxadithiolate (ODT) type model
compounds.20 Now, in this paper we will describe the
detailed synthesis and structural characterization re-
garding those briefly reported compounds and some
others that are new, containing either a single or a
double diiron oxadithiolate moiety. In addition,we will
also report the electrochemical properties associated
with two representative compounds and the biomimetic
hydrogen evolution catalyzed by the parent compound
of these described ODT type models.
Figure 2. ORTEP view of 1 with 30% probability level
ellipsoids.
Scheme 1
Results and Discussion
Synthesis and Characterization of Model Com-
pounds Containing a Single Diiron Oxadithiolate
Moiety. The parent compound of this series is Fe2(µ-
SCH2OCH2S-µ)(CO)6 (1), which was prepared by reac-
tion of (µ-S2)Fe2(CO)6 with 2 equiv of LiBEt3H in THF
at -78 °C, followed by treatment of the intermediate
(µ-LiS)2Fe2(CO)621a with excess bis(chloromethyl) ether.
This compound could also be prepared by treatment of
the intermediate (µ-LiS)2Fe2(CO)6 with ca. 2 equiv of
CF3CO2H and subsequent treatment of the intermediate
Table 1. Selected Bond Lengths (Å) and Angles
(deg) for 1, 2, and 4
1
Fe(1)-S(1)
Fe(1)-S(2)
S(1)-C(4)
S(2)-C(5)
2.2526(10) 1Fe(1)-Fe(1A)
2.2526(11) Fe(1A)-S(2)
2.5113(13)
2.2526(11)
1.385(5)
1.828(4)
1.836(4)
C(5)-O(4)
C(4)-O(4)
1.413(5)
21b
(µ-HS)2Fe2(CO)6 with excess (ClCH2)2O in the pres-
S(1)-Fe(1)-S(2)
84.97(4)
C(4)-S(1)-Fe(1) 110.14(11)
C(5)-O(4)-C(4) 135.0(3)
ence of Et3N (Scheme 1). In fact, 1 had been prepared
before our synthesis by another method and character-
ized by spectroscopy.17 Our solid IR spectrum of 1
S(1)-Fe(1)-Fe(1A) 56.12(2)
C(4)-S(1)-Fe(1A)
Fe(1)-S(1)-Fe(1A) 67.76(4)
110.14(11) O(4)-C(4)-S(1) 115.7(3)
O(4)-C(5)-S(2) 115.6(3)
showed four strong bands in the range 2077-1989 cm-1
,
2
and the reported solution IR spectrum17 displayed five
strong bands in the region 2079-1987 cm-1, all assign-
able to its terminal carbonyls. Both the above-mentioned
IR spectra, except some minor differences such as in
band number, are very similar to the solution IR
spectrum of its PDT analogue Fe2(µ-SCH2CH2CH2S-µ)-
(CO)6, which showed three strong bands from 2072
to 1993 cm-1 for its terminal carbonyl ligands.22 To
confirm the structure of 1 and to get its detailed
structural information, we carried out the X-ray crystal-
Fe(1)-S(1)
Fe(1)-S(2)
S(1)-C(8)
Fe(2)-S(1)
2.2640(16) Fe(2)-S(2)
2.2699(18) C(7)-O(7)
2.2386(17)
1.415(7)
2.5121(13)
1.149(6)
1.840(6)
Fe(1)-Fe(2)
2.2461(17) N(1)-C(6)
S(1)-Fe(2)-Fe(1) 56.49(4)
S(2)-Fe(2)-S(1) 85.49(7)
Fe(2)-S(1)-Fe(1) 67.70(5)
N(1)-C(6)-Fe(2) 176.5(5)
S(2)-Fe(2)-Fe(1) 56.73(5)
C(8)-O(7)-C(7)
112.6(5)
S(1)-Fe(1)-S(2)
84.35(6)
S(2)-Fe(1)-Fe(2) 55.55(4)
4
Fe(2)-S(2)
Fe(2)-S(1)
S(2)-C(8)
Fe(1)-S(1)
2.2556(14) Fe(2)-Fe(3)
2.2998(17) Fe(3)-S(3)
2.5026(14)
2.2687(15)
1.404(5)
1.809(5)
C(8)-O(8)
(14) (c) Lyon, E. J.; Georgakaki, I. P.; Reibenspies, J. H.; Darens-
bourg, M. Y. J. Am. Chem. Soc. 2001, 123, 3268.
(15) Razavet, M.; Davies, S. C.; Hughes, D. L.; Barclay, J. E.; Evans,
D. J.; Fairhurst, S. A.; Liu, X.; Pickett, C. J. Dalton Trans. 2003, 586.
(16) Lawrence, J. D.; Li, H.; Rauchfuss, T. B.; Be´nard, M.; Rohmer,
M.-M. Angew. Chem., Int. Ed. 2001, 40, 1768.
2.3016(14) Fe(3)-S(2)
2.2670(15)
S(1)-Fe(2)-S(2)
103.03(4)
Fe(3)-S(3)-Fe(2) 66.72(5)
S(2)-Fe(2)-S(3) 84.67(6)
S(3)-Fe(2)-Fe(3) 56.38(4)
S(3)-Fe(3)-Fe(2) 56.90(4)
S(2)-Fe(2)-Fe(3) 56.62(3)
S(1)-Fe(2)-Fe(3) 145.02(4)
S(2)-Fe(3)-S(3)
84.71(6)
(17) Li, H.; Rauchfuss, T. B. J. Am. Chem. Soc. 2002, 124, 726.
(18) Ott, S.; Kritikos, M.; Åkermark, B.; Sun, L. Angew. Chem., Int.
Ed. 2003, 42, 3285.
lographic study of 1. Figure 2 shows its ORTEP draw-
ing, while Table 1 lists the selected bond lengths and
angles. As shown in Figure 2, complex 1 is indeed
composed of an oxadithiolate ligand bridged between
two iron atoms each with three terminal CO ligands.
The coordination geometry of the iron atoms in 1,
similar to its PDT analogue Fe2(µ-SCH2CH2CH2S-µ)-
(19) Tard, C.; Liu, X.; Ibrahim, S. K.; Bruschi, M.; De Gioia, L.;
Davies, S. C.; Yang, X.; Wang, L.-S.; Sawers, G.; Pickett, C. J. Nature
2005, 433, 610.
(20) Song, L.-C.; Yang, Z.-Y.; Bian, H.-Z.; Hu, Q.-M. Organometallics
2004, 23, 3082.
(21) (a) Seyferth, D.; Henderson, R. S.; Song, L.-C. Organometallics
1982, 1, 125. (b) Seyferth, D.; Henderson, R. S.; Song, L.-C. J.
Organomet. Chem. 1980, 192, C1.

6128 Organometallics, Vol. 24, No. 25, 2005
Song et al.
Scheme 2
Figure 3. ORTEP view of 2 with 30% probability level
ellipsoids.
(CO)6,22 is roughly square pyramidal with each iron
atom being displaced by about 0.38 Å from the pyrami-
dal base toward the apical direction. The Fe-Fe bond
length in 1 is equal to 2.5113(13) Å, ca. 0.1 Å shorter
than those reported for the oxidized state diiron subsite
in the enzyme structures (2.62 and 2.60 Å)3,4 and only
0.04 Å shorter than that in the reduced state diiron
subsite of the enzyme structure (2.55 Å).5 In addition,
as can be seen in Figure 2, the bridgehead oxygen atom
is disordered (50%), which agrees very well with the
solution 1H NMR spectrum of 1 showing only one singlet
at 4.21 ppm.
Interestingly, it was found that the ODT-type model
compounds with a single diiron oxadithiolate moiety can
be prepared from parent compound 1 in good to excellent
yields. For instance, when 1 was reacted with 1 equiv
of decarbonylation agent Me3NO‚2H2O in MeCN at
room temperature followed by treatment of the inter-
mediate Fe2(µ-SCH2OCH2S-µ)(CO)5L (L ) MeCN or
Me3N)13 with 1 equiv of Et4NCN, PPh3, or Cp(CO)2-
FeSPh, the corresponding single ODT type model com-
pounds [Fe2(µ-SCH2OCH2S-µ)(CO)5(CN)](Et4N) (2), Fe2(µ-
SCH2OCH2S-µ)(CO)5(PPh3) (3), and [Fe2(µ-SCH2OCH2S-
µ)(CO)5][Cp(CO)2FeSPh] (4) were produced in 62%, 93%,
and 72% yields, respectively (Scheme 2).
Compounds 2-4 have been characterized by elemen-
tal analysis, IR and 1H NMR spectroscopy. The IR
spectra of 2-4 showed several absorption bands in the
range 2041-1907 cm-1 for their terminal carbonyls,
which lie at much lower frequency relative to those
(2077-1989 cm-1) of parent compound 1. This is obvi-
ously due to the increased strength of back-bonding
between iron atoms and the attached carbonyls by CO
substitution with the stronger electron-donating ligands
CN-, PPh3, and Cp(CO)2FeSPh. The 1H NMR spectrum
of 2 displayed a singlet at 4.09 ppm assigned to two
magnetically identical protons in its methylene groups,
whereas 3 and 4 exhibited two broad singlets at 4.2-
3.3 ppm attributed to two magnetically different protons
in their methylene groups.
Figure 4. ORTEP view of 4 with 30% probability level
ellipsoids.
Figure 3 shows that 2 is the (Et4N)+ salt of complex
anion [Fe2(µ-SCH2OCH2S-µ)(CO)5(CN)]-, in which the
CN- ligand occupies an equatorial coordination site of
one Fe atom. This is in accordance with its position in
the H-cluster of FeHases.3-6 The fact that the distances
between Fe(2) and its attached CO-carbon atoms are
shorter than those around Fe(1) proves the increased
strength of back-bonding between Fe(2) and C(4)O(4)
or C(5)O(5) caused by coordination of the strong σ-donor
ligand CN-. In addition, the bridgehead oxygen atom
in 2, in contrast to that in parent complex 1, is fixed
completely opposite the Fe atom attached to the CN-
ligand, which could be attributed to the strong electro-
static repulsion between the negatively charged CN-
ligand and the electronegative O atom.
Figure 4 indicates that complex 4 contains a metallo-
thioether ligand Cp(CO)2FeSPh, which is coordinated
via its S atom to one of the Fe atoms of the butterfly
Fe2S2 cluster. Interestingly, this simple metallo-thio-
ether seems to be a good ligand for mimicking to a
certain degree the real, complicated metallo-thioether
ligand Cys-S-Fe4S4,3-6 since they are both coordinated
to one of the Fe atoms of the butterfly Fe2S2 cluster
through the S atom in their Fe-thioether structural
units. While the metal-metal bond Fe(2)-Fe(3) is
2.5026(14) Å, the nonbonded metal-metal Fe(1)‚‚‚Fe-
(2) distance is 3.866 Å. The bond lengths Fe(1)-S(1)
(2.3016(14) Å) and Fe(2)-S(1) (2.2998(17) Å) are virtu-
ally the same, whereas the Fe-S bond lengths (2.2556-
(14)-2.2821(14) Å) in its butterfly cluster core are quite
different. As can be seen intuitively in Figure 4, the
bridgehead O atom points opposite the axially substi-
tuted metallo-thioether ligand, which is possibly in order
to avoid the strong steric repulsion between the bulky
ligand Cp(CO)2FeSPh and the bridgehead O atom when
it points to the bulky ligand.
The molecular structures of 2 and 4 were unambigu-
ously confirmed by crystal X-ray diffraction analysis.
While ORTEP views of 2 and 4 are presented in Figures
3 and 4, their selected bond lengths and angles are given
in Table 1.
(22) Lyon, E. J.; Georgakaki, I. P.; Reibenspies, J. H.; Darensbourg,
M. Y. Angew. Chem., Int. Ed. 1999, 38, 3178.

Diiron Oxadithiolate Type Models
Organometallics, Vol. 24, No. 25, 2005 6129
Scheme 3
Unfortunately, the molecular structure of 3 has not
been characterized so far by X-ray diffraction, due to
lack of X-ray quality single crystals. However, it is
believed that the PPh3 ligand in 3 is most likely
substituted axially at one of its two Fe atoms. This is
because such an axially substituted pattern has been
found in similar substituted complexes, such as the
mono-PPh3-substituted derivative (µ-cyclo-C6H11S)(µ-n-
C5H11S)Fe2(CO)5(PPh3)23 and the bis-PPh3-substituted
complex (µ-i-C3H7S)(µ-PhCH2S)Fe2(CO)4(PPh3)2.24
Synthesis and Characterization of Model Com-
pounds Containing a Double-Diiron Oxadithiolate
Moiety. Similar to the double-cubane MoFe3S4 model
for the Mo/Fe cofactor of nitrogenases that has two
active sites,25 we further prepared a series of model
compounds containing two diiron oxadithiolate active
sites by reaction of parent compound 1 with 1 equiv of
Me3NO‚2H2O in MeCN at room temperature followed
by treatment of the intemediate Fe2(µ-SCH2OCH2S-µ)-
(CO)5L (L ) MeCN or Me3N)13 with 0.5 equiv of 1,4-
diisocyanobenzene, 1,1′-bis(diphenylphosphino)ferrocene
(dppf), or 1,1′-bis(diphenylphosphino)ruthenocene (dppr),
affording the corresponding double ODT type model
compounds [Fe2(µ-SCH2OCH2S-µ)(CO)5]2[1,4-(CN)2C6H4]
(5), [Fe2(µ-SCH2OCH2S-µ)(CO)5]2[(η5-Ph2PC5H4)2Fe] (6),
and [Fe2(µ-SCH2OCH2S-µ)(CO)5]2[(η5-Ph2PC5H4)2Ru] (7)
in 57%, 90%, and 84% yields, respectively (Scheme 3).
However, when 1 was directly reacted with 0.5 equiv of
diphosphine ligand (Ph2PCH2CH2OCH2)2 or tetraphos-
phine ligand [(Ph2PCH2)2NCH2]2 in toluene at reflux,
the corresponding double ODT type model compounds
[Fe2(µ-SCH2OCH2S-µ)(CO)5]2(Ph2PCH2CH2OCH2)2 (8)
and [Fe2(µ-SCH2OCH2S-µ)(CO)4]2[(Ph2PCH2)2NCH2]2 (9)
were obtained in 86% and 56% yields, respectively
(Scheme 3).
Compounds 5-9 have been fully characterized by
elemental analysis, spectroscopy, and X-ray diffraction
techniques. For example, the IR spectra of 5-9 dis-
played three absorption bands in the range 2047-1900
cm-1 for their terminal carbonyls. These bands are
located at much lower frequency relative to those of
parent compound 1 on the basis of the same reason for
1
2-4. In addition, the H NMR spectra of 5-9 showed
the corresponding proton signals for their respective
organic groups, whereas the 31P NMR spectra of 6-9
exhibited one singlet at ca. 50 ppm for their identical P
atoms in each of their bridging ligands.
The molecular structures of 5-9 have been unequivo-
cally confirmed by X-ray diffraction methods. While
ORTEP views of 5-9 are shown in Figures 5-9, selected
bond lengths and angles are listed in Table 2.
It can be seen in Figure 5 that model compound 5
indeed consists of two diiron oxadithiolate moieties,
(23) Song, L.-C.; Hu, Q.-M.; Wang, J.-T.; Lin, X.-Y.; Zheng, Q.-T.;
Zhang, S.-D.; Shen, F.-L.; Wu, S. Acta Chim. Sin. 1986, 44, 558.
(24) Song, L.-C.; Hu, Q.-M.; Wang, R.-J.; Wang, H.-G. Acta Chim.
Sin. 1988, 46, 984.
(25) Kovacs, J. A.; Bashkin, J. K.; Holm, R. H. J. Am. Chem. Soc.
1985, 107, 1784.
Figure 5. ORTEP view of 5 with 30% probability level
ellipsoids.

6130 Organometallics, Vol. 24, No. 25, 2005
Song et al.
Table 2. Selected Bond Lengths (Å) and Angles
(deg) for 5-9
5
Fe(1)-Fe(2)
Fe(1)-S(1)
Fe(2)-S(1)
2.4938(11) Fe(1)-S(2)
2.2453(13) Fe(2)-C(1)
2.2551(12) Fe(2)-S(2)
2.2366(12)
1.777(4)
2.2490(12)
S(1)-Fe(1)-Fe(2) 56.54(3)
S(2)-Fe(1)-S(1) 84.90(4)
S(2)-Fe(1)-Fe(2) 56.46(4)
Fe(1)-S(1)-Fe(2) 67.30(4)
C(7)-O(6)-C(6)
112.9(3)
S(1)-Fe(2)-Fe(1) 56.16(4)
6
Fe(1)-S(1)
Fe(1)-S(2)
Fe(2)-S(1)
2.2612(19) Fe(2)-S(2)
2.2571(19)
1.830(6)
1.405(7)
Figure 6. ORTEP view of 6 with 30% probability level
ellipsoids.
2.279(2)
2.268(2)
S(1)-C(6)
O(6)-C(7)
S(1)-Fe(1)-S(2)
83.97(7)
S(1)-Fe(1)-Fe(2) 55.96(6)
S(2)-Fe(1)-Fe(2) 55.50(5)
S(1)-Fe(2)-Fe(1) 55.72(5)
Fe(2)-S(2)-Fe(1) 68.20(6)
C(8)-P(1)-Fe(1)
117.9(2)
7
Fe(2)-Fe(1)
Fe(1)-S(1)
Fe(2)-S(1)
2.5383(11) Fe(1)-S(2)
2.2543(15) Fe(2)-S(2)
2.2559(16) P(1)-C(8)
2.2716(15)
2.2689(17)
1.808(4)
P(1)-Fe(1)-S(1)
S(1)-Fe(1)-S(2)
106.19(5)
84.00(5)
S(2)-Fe(1)-Fe(2) 55.96(4)
S(1)-Fe(2)-S(2) 84.02(5)
S(1)-Fe(2)-Fe(1) 55.72(4)
S(1)-Fe(1)-Fe(2) 55.78(4)
8
Fe(2)-Fe(1)
Fe(1)-P(1)
Fe(1)-S(1)
2.512(2)
2.242(3)
2.256(3)
Fe(2)-S(1)
S(1)-C(11)
O(11)-C(12)
2.252(3)
1.824(9)
1.393(11)
Figure 7. ORTEP view of 7 with 30% probability level
ellipsoids.
P(1)-Fe(1)-S(1)
109.18(10) S(2)-Fe(1)-S(1)
84.14(10)
S(2)-Fe(1)-Fe(2) 55.80(7)
S(1)-Fe(2)-Fe(1) 56.22(7)
P(1)-Fe(1)-Fe(2) 151.94(8)
S(1)-Fe(1)-Fe(2) 56.05(7)
9
Fe(1)-P(1)
Fe(1)-S(2)
Fe(2)-S(1)
2.2107(19) O(5)-C(6)
2.2673(18) N(1)-C(31)
1.398(8)
1.448(9)
2.5363(14)
2.266(2)
Fe(1)-Fe(2)
P(1)-Fe(1)-P(2)
P(1)-Fe(1)-S(2)
92.89(7)
93.82(7)
Fe(1)-S(1)-Fe(2) 68.13(5)
C(31)-P(1)-Fe(1) 113.1(2)
P(1)-Fe(1)-Fe(2) 111.63(6)
C(6)-O(5)-C(5)
113.1(5)
the two isocyano groups is 1.840 (3) Å, which lies in the
range 1.759-1.875 Å found for other isonitrile com-
plexes.26
Figure 8. ORTEP view of 8 with 30% probability level
ellipsoids.
The double ODT type model compounds 6 and 7, as
shown in Figures 6 and 7, contain an organometallic
diphosphine dppf or dppr ligand, which is axially
coordinated to two iron atoms of the two diiron oxa-
dithiolate structural units through two P atoms of the
diphosphine ligand. Both structures are centrosymmet-
ric. However, while in 6 the two bridgehead O atoms
point in the direction of diphosphine dppf, the two O
atoms in 7 are directed opposite diphosphine dppr. The
bond lengths of Fe(1)-Fe(2) in 6 (2.5430(16) Å) and in
7 (2.5383(11) Å) are very close to those in the oxidized
form (2.62 and 2.60 Å)3,4 and the reduced form (2.55 Å)5
of the enzymes.
Similar to 6 and 7, the double ODT type model 8, as
shown in Figure 8, includes an ether chain-bridged
diphosphine ligand (Ph2PCH2CH2OCH2)2, which is axi-
ally bonded to two iron atoms of the two ODT moieties.
It is particularly interesting that model compound 9
(Figure 9) contains a tetraphosphine ligand [(Ph2PCH2)2-
NCH2]2, which is chelated to two iron atoms of each
ODT moiety through an equatorial P-Fe bond and an
Figure 9. ORTEP view of 9 with 30% probability level
ellipsoids.
which are joined together through an equatorially
substituted 1,4-diisocyanobenzene ligand. This molecule
is centrosymmetric. Both bridgedhead O atoms of the
oxadithiolates point opposite the diisocyano ligand. This
is probably due to the greater electrostatic repulsion
between the electronegative diisocyano ligand (a stron-
ger σ-donor than CO) and the electronegative O atoms
when they point in the direction of the diisocyano ligand.
The distance between Fe(1) or Fe(1A) and C atoms of
(26) (a) Lawrence, J. D.; Rauchfuss, T. B.; Wilson, S. R. Inorg. Chem.
2002, 41, 6193. (b) Lai, C.-H.; Lee, W.-Z.; Miller, M. L.; Reibenspies,
J. H.; Darensbourg, D. J.; Darensbourg, M. Y. J. Am. Chem. Soc. 1998,
120, 10103. (c) Nehring, J. L.; Heinekey, D. M. Inorg. Chem. 2003, 42,
4288.

Diiron Oxadithiolate Type Models
Organometallics, Vol. 24, No. 25, 2005 6131
Figure 11. Cyclic voltammogram of 5 (1 mM) in 0.1 M
Figure 10. Cyclic voltammogram of 1 (1 mM) in 0.1 M
n-Bu4NPF6/MeCN at a scan rate of 100 mV‚s-1
.
n-Bu4NPF6/MeCN at a scan rate of 100 mV‚s-1
.
axial P-Fe bond, respectively. In addition, this molecule
is centrosymmetric and the two bridgehead O atoms are
directed toward the tetraphosphine ligand.
-0.61 and + 0.23 V. These two oxidation peaks are
probably due to some unknown species generated from
decomposition of 1 during the course of cyclic voltam-
metric determination. In fact, such cyclic voltammetric
behavior is similar to those exhibited by its PDT- and
ADT-bridged analogues.27-31
Finally, it is worth pointing out that the bond lengths
of Fe(1)-Fe(2) in 8 (2.512(2) Å) and 9 (2.5363(14) Å)
are very close to those in 6 and 7, as well as in the
oxidized form and the reduced form of the enzymes
(2.62, 2.60, and 2.55 Å, respectively).3-5 In addition, the
strong σ-donor nature of diphosphine and particularly
tetraphosphine in 8 and 9 would make their Fe-Fe
bonds more electron-rich and thus might facilitate
protonation of the diiron subsite, the important step
for the possible electrocatalytic proton reduction to
dihydrogen.27-31
Electrochemistry of Model Compounds 1 and 5.
Although the electrochemical properties of the PDT
type27-29 and ADT type30,31 model compounds were
previously reported, no such properties have been
reported in the literature so far concerning the ODT
type model compounds.
Now, we report the electrochemical properties of 1 and
5 as representatives of the single and double ODT type
model compounds. The cyclic voltammograms of 1 and
5 are shown in Figures 10 and 11, respectively. Inter-
estingly, as shown in Figure 10, the single model 1
displays three electrochemical events, which include one
irreversible oxidation at +0.81 V, one quasi-reversible
reduction at -1.59 V, and one irreversible reduction at
- 2.10 V, respectively. The bulk electrolysis of 1 (0.022
mM) at - 1.80 V in MeCN demonstrated that the two
reduction events are one-electron processes, which can
be assigned to the FeIFeI + e- f Fe0FeI and Fe0FeI +
e- f Fe0Fe0 couples. However, the oxidation process
occurring at +0.81 V is a two-electron process, at-
tributed to the FeIFeI f FeIIFeII + 2 e- couple, since its
peak current is about twice as much as that of each of
the one-electron reduction processes mentioned above.
In addition, it is worth pointing out that in Figure 10
there are still two small irreversible oxidation peaks at
As can be seen in Figure 11, the double model 5 shows
two quasi-reversible reductions at -1.65 and -1.82 V,
as well as two irreversible oxidations at +0.50 and
+0.85 V, respectively. The potential difference between
the two reductions of 5 is 0.17 V, which is much smaller
than that (0.51 V) between the two reductions of 1.
Therefore, the two reductions of 5 should be assigned
to the two sequential one-electron reduction events of
the two iron atoms in the two diiron subsites. In
addition, the two iron atoms in the two diiron subsites
should be distant from the diisonitrile ligand since 1,4-
diisocyanobenzene is a stronger electron-donating ligand
than CO, namely, FeIFeI(CNC6H4) + e- f Fe0FeI-
(CNC6H4) and (C6H4NC)FeIFeI + e- f (C6H4NC)FeIFe0.
This is consistent with the first reduction peak of 5
being negatively shifted by -0.06 V and the second
reduction peak negatively shifted by -0.23 V relative
to the first reduction peak of 1, respectively. Similarly,
since the values of their two oxidation peak currents
are close to those of their two reduction peak currents,
the two irreversible oxidation processes of 5 can be
attributed to the two sequential one-electron oxidation
processes of the two iron atoms attached to the diisoni-
trile ligand: FeIFeI(CNC6H4) f FeIFeII(CNC6H4) + e-
and (C6H4NC)FeIFeI f (C6H4NC)FeIIFeI + e-. Namely,
the iron atom that is in the first diiron subsite and
attached to the diisonitrile ligand is first oxidized and
then the iron atom in the next diiron subsite and
attached to the diisonitrile ligand is oxidized.
More interestingly, we further found that 1 has the
catalytic ability to reduce the protons of acetic acid, a
weak acid, to give hydrogen under electrochemical
conditions. This catalytic behavior was studied by cyclic
voltammetry in the presence of HOAc (0-10 mM) in
MeCN (Figure 12). When the first 2 mM of acetic acid
was added, the current intensity of the initial first
reduction peak at -1.59 V was slightly increased but
did not continue to grow with sequential increments of
the acid. However, in contrast to this, when the first 2
mM of the acid was added, the initial second reduction
at -2.10 V shifted slightly negatively and the current
(27) Gloaguen, F.; Lawrence, J. D.; Rauchfuss, T. B. J. Am. Chem.
Soc. 2001, 123, 9476.
(28) Mejia-Rodriguez, R.; Chong, D.; Reibenspies, J. H.; Soriaga, M.
P.; Darensbourg, M. Y. J. Am. Chem. Soc. 2004, 126, 12004.
(29) Borg, S. J.; Behrsing, T.; Best, S. P.; Razavet, M.; Liu, X.;
Pickett, C. J. J. Am. Chem. Soc. 2004, 126, 16988.
(30) Ott, S.; Kritikos, M.; Åkermark, B.; Sun, L.; Lomoth, R. Angew.
Chem., Int. Ed. 2004, 43, 1006.
(31) Liu, T.; Wang, M.; Shi, Z.; Cui, H.; Dong, W.; Chen, J.;
Åkermark, B.; Sun, L. Chem. Eur. J. 2004, 10, 4474.

6132 Organometallics, Vol. 24, No. 25, 2005
Song et al.
Scheme 4a
a All the carbonyls attached to Fe atoms are omitted for
clarity.
Figure 12. Cyclic voltammgrams of 1 (1 mM) with HOAc
(0, 2, 4, 6, 8, 10 mM) in 0.1 M n-Bu4NPF6/MeCN at a scan
reduction at -1.59 V to give intermediate 1-. Further
reduction of 1- at -2.10 V produces intermediate 12-
rate of 100 mV‚s-1
.
,
which is then protonated on its electron-rich Fe core by
acetic acid to generate intermediate 1H-. Finally,
further protonation of 1H- yields hydrogen. It is worth
pointing out that in the absence of 1 the proton
reduction of acetic acid occurred at -2.3 V; thus the
electrocatalyst 1 lowers the reduction electropotential
of acetic acid up to -0.20 V.
While this mechanism is similar to that proposed for
the carbon chain-bridged all-carbonyl diiron com-
plexes,32 it is different from the CCEE mechanism
proposed for the H2 production from HOTs catalyzed by
the PDT type model [Fe2(µ-SCH2CH2CH2S-µ)(CO)4(CN)-
(Me3P)]-, in which the electron density at the Fe-Fe
bond is remarkably increased by substitution of the
strong electron-donating Me3P and CN- ligands.27 It is
also different from the CECE mechanism for H2 produc-
tion from HOAc catalyzed by the ADT type model Fe2-
(µ-SCH2)2N(4-NO2C6H4)(CO)6, since in this model the
bridged central N atom is first protonated before reduc-
tion. In our case, the bridged central oxygen atom in 1
is a weaker Lewis base than the corresponding nitrogen
atom in the ADT type model compound,31 and thus it
cannot be protonated before reduction by the weak acid
HOAc.
Figure 13. Dependence of current heights of the electro-
catalytic peaks of 1 (1 mM) on concentration of HOAc.
intensity of the second reduction continuously increased
linearly with increasing concentration of the acid (Fig-
ure 13). Such observations are typical of an electrocata-
lytic proton reduction process. Further evidence for the
electrocatalytic activity of 1 was obtained by bulk
electrolysis of a MeCN solution of 1 (0.33 mM) with
acetic acid (6.6 mM) at -2.16 V, a potential slightly
beyond the second reduction peak. The initial rate of
the electrolysis is ca. 5 times higher than that in the
absence of the catalyst. The rate of electrolysis slowed
as the proton concentration decreased, and over the
course of 1 h, the total charge passed through the cell
approached its maximum, namely 11 F per mol of 1.
This corresponds to 5.5 turnovers. In such a preparative
scale experiment, bubbles of H2 were clearly seen. Gas
chromatographic analysis indicated that the hydrogen
yield was 100 ((10)%.
Experimental Section
General Comments. All manipulations were performed
using standard Schlenk and vacuum-line techniques under N2
atmosphere. Dichloromethane was distilled over P2O5 under
N2. Acetonitrile was distilled once from P2O5 and then freshly
distilled from CaH2 under N2 before use. Toluene, THF, and
hexane were purified by distillation under N2 from sodium/
benzophenone ketyl. LiBEt3H (1 M in THF), Et4NCN, Me3-
NO‚2H2O, and Ph3P were available commercially and used as
received. (µ-S2)Fe2(CO)6,21a (ClCH2O)2O,33 Cp(CO)2FeSPh,34 1,4-
diisocyanobenzene,35 1,1′-bis(diphenylphosphino)ferrocene,36
1,1′-bis(diphenylphosphio)ruthenocene,37 [Ph2PCH2CH2OCH2]2,38
and [(Ph2PCH2)2NCH2]239 were prepared according to literature
procedures. Preparative TLC was carried out on glass plates
Scheme 4 shows the suggested EECC (electrochemi-
cal-electrochemical-chemical-chemical) mechanism for
this electrocatalytic H2 production based on similar
reported cases27,31,32 and the electrochemical observa-
tions described above. That is, in the presence of acetic
acid model compound 1 will first undergo one-electron
(33) Buc, S. R. Org. Synth. 1956, 36, 1.
(34) Ahamad, M.; Bruce, R.; Knox, G. R. J. Organomet. Chem. 1966,
6, 1.
(35) Efraty, A.; Feinstein, I.; Wackerle, L.; Goldman, A. J. Org.
Chem. 1980, 45, 4059.
(32) Chong, D.; Georgakaki, I. P.; Mejia-Rodriguez, R.; Sanabria-
Chinchilla, J.; Soriaga, M. P.; Darensbourg, M. Y. Dalton Trans. 2003,
4158.
(36) Bishop, J. J.; Davison, A.; Katcher, M. L.; Lichtenberg, D. W.;
Merril, R. E.; Smart, J. C. J. Organomet. Chem. 1971, 27, 241.

Diiron Oxadithiolate Type Models
Organometallics, Vol. 24, No. 25, 2005 6133
(26 × 20 × 0.25 cm) coated with silica gel H (10-40 µm). IR
spectra were recorded on a Bruker Vector 22 infrared spec-
trophotometer. 1H (31P) NMR were recorded on a Bruker AC-P
200 NMR spectrometer. Elemental analyses were performed
on an Elementar Vario EL analyzer. Melting points were
determined on a Yanaco MP-500 apparatus and were uncor-
rected.
MeCN (15 mL) was treated with a solution of Me3NO‚2H2O
(0.056 g, 0.50 mmol) in MeCN (10 mL) at room temperature
for 10-15 min. To this mixture was added a solution of Cp-
(CO)2FeSPh (0.143 g, 0.50 mmol) in MeCN (10 mL), and then
the mixture was stirred for 1 h. After removal of solvent, the
residue was subjected to TLC by using Et2O/petroleum ether
(1:1 v/v) as eluent to give 4 as a brown-red solid (0.233 g, 72%),
mp 114-116 °C. Anal. Calcd for C20H14Fe3O8S3: C, 37.18; H,
2.18. Found: C, 37.23; H, 2.23. IR (KBr disk): νCtO 2034 (vs),
1992 (vs), 1974 (vs), 1964 (s), 1914 (s) cm-1. 1H NMR (200 MHz,
CDCl3): δ 7.19-7.68 (m, 5H, C6H5), 4.99 (s, 5H, C5H5), 4.14
(br s, 2H, 2CHHOCHH), 3.90 (br s, 2H, 2CHHOCHH) ppm.
Preparation of Fe2(µ-SCH2OCH2S-µ)(CO)6 (1). Method
i: A solution of (µ-S2)Fe2(CO)6 (0.172 g, 0.50 mmol) in THF
(20 mL) was cooled to -78 °C by a dry ice/acetone bath. To
this solution was added Et3BHLi (1.0 mL, 1.0 mmol) by
syringe. At the midpoint of the addition the reaction solution
turned from red to a dark emerald green; for the rest of the
addition it remained green. To this green solution was added
(at -78 °C) bischloromethyl ether (0.173 g, 1.50 mmol), and
the color changed back to red. The dry ice/acetone bath was
removed, and the red mixture was stirred for 3 h at room
temperature. Solvent was removed in vacuo, and the residue
was subjected to TLC using CH2Cl2/petroleum ether (1:4 v/v)
as eluent. From the main orange-red band, 1 (0.117 g, 60%)
was obtained as a red solid, mp 110-112 °C. Anal. Calcd for
C8H4Fe2O7S2: C, 24.77; H, 1.04. Found: C, 24.32; H, 1.51. IR
Preparation
of
[Fe2(µ-SCH2OCH2S-µ)(CO)5]2[1,4-
(CN)2C6H4] (5). To the red solution of 1 (0.194 g, 0.50 mmol)
in CH2Cl2/MeCN (15 mL) (1:2 v/v) were successively added a
solution of Me3NO‚2H2O (0.056 g, 0.50 mmol) in MeCN (15
mL) and a solution of 1,4-diisocyanobenzene (0.032 g, 0.25
mmol) in CH2Cl2 (10 mL). The mixture was stirred at room
temperaure for 1 h. The same workup as for 3 afforded 5 (0.120
g, 57%) as a red solid, mp 176 °C (dec). Anal. Calcd for C22H12-
Fe4N2O12S4: C, 31.16; H, 1.43; N, 3.30. Found: C, 31.23; H,
1.47; N, 3.20. IR (KBr disk): νNdC 2121 (vs); νCtO 2040 (s), 2010
(vs), 1971 (vs) cm-1. 1H NMR (200 MHz, CDCl3): 7.28 (s, 4H,
C6H4), 4.19 (s, 8H, 4SCH2) ppm.
(KBr disk): νCtO 2077 (s), 2035 (vs), 2002 (vs), 1989 (vs) cm-1
.
1H NMR (200 MHz, CDCl3): 4.21 (s, 4H, 2CH2) ppm. Method
ii: A solution of (µ-S2)Fe2(CO)6 (0.688 g, 2.0 mmol) in THF (30
mL) was cooled to -78 °C, and then Et3BHLi (4.0 mL, 4.0
mmol) was added. After the mixture was stirred at this
temperature for 15 min, trifluoroacetic acid (0.32 mL, 4.3
mmol) was added, and this mixture was stirred for an
additional 10 min. Then bischloromethyl ether (0.450 g, 3.0
mmol) and triethylamine (1.12 mL, 8.0 mmol) were added and
stirred for 30 min at -78 °C and for 4 h at room temperature.
The same workup as for method i afforded 1 (0.200 g, 26%).
Preparation
of
[Fe2(µ-SCH2OCH2S-µ)(CO)5]2[(η5-
Ph2PC5H4)2Fe] (6). A solution of 1 (0.194 g, 0.50 mmol) in
MeCN (15 mL) was treated with a solution of Me3NO‚2H2O
(0.056 g, 0.50 mmol) in MeCN (10 mL) at room temperature.
The mixture was stirred for 20 min, and then to this mixture
was added (η5-Ph2PC5H4)2Fe (dppf) (0.139 g, 0.25 mmol). The
new mixture was stirred at room temperature for 4 h. After
solvent removal, the residue was subjected to TLC using
petroleum ether/acetone (4:1 v/v) as eluent to give 6 as a red
solid (0.288 g, 90%), mp 171 °C (dec). Anal. Calcd for C48H36-
Fe5O12P2S4: C, 45.25; H, 2.85. Found: C, 45.45; H, 3.01. IR
(KBr disk): νCtO 2047 (vs), 1983 (vs), 1933 (s) cm-1. 1H NMR
(200 MHz, CDCl3): δ 7.38-7.60 (m, 20H, 4C6H5), 4.25 (d, 8H,
2C5H4), 3.50, 3.65 (2d, 8H, 4SCH2) ppm. 31P NMR (81.0 MHz,
CDCl3, H3PO4): 54.16 (s) ppm.
Preparation of [Fe2(µ-SCH2OCH2S-µ)(CN)(CO)5](Et4N)
(2). To the red solution of 1 (0.194 g, 0.50 mmol) in MeCN (15
mL) was added a solution of Me3NO‚2H2O (0.056 g, 0.50 mmol)
in MeCN (10 mL) at room temperature. The mixture was
stirred at this temperature for 10-15 min and then cooled to
ca. -40 °C. To this cooled mixture was added a solution of
Et4NCN (0.078 g, 0.50 mmol) in MeCN (10 mL). After 0.5 h,
the mixture was allowed to warm to room temperature and
stirred for an additional 1 h. After removal of solvent, the
residue was throughly washed with CH2Cl2/Et2O (1:5 v/v) and
hexane, respectively. 2 (0.160 g, 62%) was obtained as a red
solid, mp 106 °C (dec). Anal. Calcd for C16H24Fe2N2O6S2: C,
37.22; H, 4.69. N, 5.42. Found: C, 37.10; H, 4.62; N, 5.49. IR
(KBr disk): νCtN 2088 (s); νCtO 2030 (vs), 1987 (vs), 1968 (vs),
1945 (s), 1907 (vs) cm-1. 1H NMR (200 MHz, CDCl3): 4.09 (s,
4H, 2SCH2), 3.31 (q, J ) 6.2 Hz, 8H, 4CH2CH3), 1.34 (br s,
12H, 4CH2CH3) ppm.
Preparation
of
[Fe2(µ-SCH2OCH2S-µ)(CO)5]2[(η5-
Ph2PC5H4)2Ru] (7). The same procedure was followed as for
6, but (η5-Ph2PC5H4)2Ru (dppr) (0.150 g, 0.25 mmol) was used.
7 (0.278 g, 84%) was obtained as a red solid, mp 192 °C (dec).
Anal. Calcd for C48H36Fe4O12P2RuS4: C, 43.67; H, 2.73.
Found: C, 43.63; H, 2.75. IR (KBr disk): νCtO 2047 (vs), 1984
(vs), 1935 (s) cm-1. 1H NMR (200 MHz, CDCl3): 7.36-7.62 (m,
20H, 4C6H5), 4.56 (d, 8H, 2C5H4), 3.54, 3.68 (2d, 8H, 4SCH2)
ppm. 31P NMR (81.0 MHz, CDCl3, H3PO4): 53.63 (s) ppm.
Preparation
of
[Fe2(µ-SCH2OCH2S-µ)(CO)5]2-
(Ph2PCH2CH2OCH2)2 (8). To a solution of 1 (0.194 g, 0.50
mmol) in toluene (20 mL) was added (Ph2PCH2CH2OCH2)2
(0.123 g, 0.25 mmol). The mixture was stirred at reflux for 2
h. After removal of solvent at reduced pressure, the residue
was subjected to TLC using petroleum ether/Et2O (5:2 v/v) as
eluent to give 8 as a red solid (0.260 g, 86%), mp 146 °C (dec).
Anal. Calcd for C44H40Fe4O14P2S4: C, 43.78; H, 3.32. Found:
C, 43.61; H, 3.29. IR (KBr disk): νCtO 2047 (vs), 1981 (vs),
1933 (s) cm-1. 1H NMR (200 MHz, CDCl3): 7.39-7.72 (m, 20H,
4C6H5), 3.63-3.75 (m, 12H, 4SCH2, 2PCH2CH2O), 3.40 (s, 4H,
OCH2CH2O), 2.75-2.90(m, 4H, 2PCH2) ppm. 31P NMR (81.0
MHz, CDCl3, H3PO4): 48.09 (s) ppm.
Preparation of Fe2(µ-SCH2OCH2S-µ)(CO)5(PPh3) (3). A
solution of Me3NO‚2H2O (0.056 g, 0.50 mmol) in MeCN (10
mL) at room temperature was added to a solution of 1 (0.194
g, 0.50 mmol) and PPh3 (0.131 g, 0.50 mmol) in MeCN (15 mL).
The mixture was stirred at this temperature for 1 h. Solvent
was removed, and the residue was subjected to TLC using CH2-
Cl2/petroleum ether (1:3 v/v) as eluent. From the main red
band, 3 (0.290 g, 93%) was obtained as a red solid, mp 204-
205 °C. Anal. Calcd for C25H19Fe2O6PS2: C, 48.26; H, 3.08.
Found: C, 47.98; H, 3.07. IR (KBr disk): νCtO 2041 (vs), 1978
(vs), 1957 (vs), 1935 (s) cm-1. 1H NMR (200 MHz, CDCl3): 7.71,
7.42 (2 br s, 15H, 3C6H5), 3.74 (br s, 2H, 2CHHOCHH), 3.38
(br s, 2H, 2CHHOCHH). 31P NMR (81.0 MHz, CDCl3, H3PO4):
63.93 (s) ppm.
Preparation
of
[Fe2(µ-SCH2OCH2S-µ)(CO)4]2-
[(Ph2PCH2)2NCH2]2 (9). The same procedure was followed
as for 8, but [(Ph2PCH2)2NCH2]2 (0.223 g 0.25 mmol) and the
eluent of petroleum ether/CH2Cl2 (5:3 v/v) were employed. 9
(0.213 g, 56%) was obtained as a red solid, mp 183 °C (dec).
Anal. Calcd for C66H60Fe4N2O10P4S4: C, 52.27; H, 3.99; N, 1.85.
Found: C, 51.99; H, 3.91, N, 2.03. IR (KBr disk): νCtO 2023
Preparation
of
[Fe2(µ-SCH2OCH2S-µ)(CO)5][Cp-
(CO)2FeSPh] (4). A solution of 1 (0.194 g, 0.50 mmol) in
(37) Li, S.; Wei, B.; Low, P. M. N.; Lee, H. K.; Andy Hor, T. S.; Xue,
F.; Mak, T. C. W. J. Chem. Soc., Dalton Trans. 1997, 1289.
(38) Heuer, B.; Pope, S. J. A.; Reid, G. Polyhedron 2000, 19, 743.
(39) Grim, S. O.; Matienzo, L. J. Tetrahedron Lett. 1973, 2951.
1
(vs), 1949 (vs), 1900 (s) cm-1. H NMR (200 MHz, CDCl3): δ
7.10-7.68 (m, 40H, 8C6H5), 3.88-3.24 (m, 16H, 4SCH2, 4

6134 Organometallics, Vol. 24, No. 25, 2005
Table 3. Crystal Data and Structural Refinement Details for 1, 2, 4, and 5
Song et al.
1
2
4
5
mol formula
mol wt
cryst syst
space group
a/Å
C8H4Fe2O7S2
387.93
C
16H24Fe2N2O6S2
C
20H14Fe3O8S3
C22H12Fe4N2O12S4
516.19
646.04
847.98
monoclinic
P2(1)/m
6.833 (3)
13.633(6)
7.711(3)
90
monoclinic
C2/c
32.554(12)
11.294(4)
13.655(5)
90
orthorhombic
P2(1)2(1)2(1)
11.021(7)
13.173(8)
16.851(10)
90
monoclinic
C2/c
29.406(13)
7.598(3)
15.657(7)
90
b/Å
c/Å
R/deg
â/deg
109.421(6)
90
114.653(11)
90
90
90
113.949(7)
90
γ/deg
V/Å3
677.4(5)
2
4563(3)
8
2446(2)
4
3088(2)
4
Z
Dc/g‚cm-3
abs coeff/mm-1
F(000)
1.902
1.503
1.754
1.824
2.470
1.486
2.055
2.173
384
2128
1296
1688
2θmax/deg
no. of reflns
no. of indep reflns
index ranges
52.70
50.10
52.88
54.82
3205
11 336
14 551
8628
1442
3992
5025
3171
-3 e h e 8
-16 e k e 11
-9 e l e 8
1.012
-38 e h e 37
-13 e k e 11
-15 e l e 16
1.009
-13 e h e 13
-16 e k e 8
-20 e l e 20
0.974
-25 e h e 35
-8 e k e 9
-18 e l e 19
1.029
goodness of fit
R
0.0324
0.0605
0.405/-0.299
0.0552
0.1071
0.821/-0.335
0.0362
0.0599
0.346/-0.358
0.0354
0.0794
0.7006/-0.292
Rw
largest diff peak
and hole/e Å-3
Table 4. Crystal Data and Structural Refinement Details for 6-9
6
7
8
9
mol formula
C
48H36Fe5O12P2S4‚3CH2Cl2
C
48H36Fe4O12P2RuS4‚2PhCl
C44H40Fe24O14P2S4
C66H60Fe4N2O10P4S4‚
2PhCl‚2CH2Cl2
1911.64
triclinic
P1h
mol wt
1528.98
triclinic
P1h
1544.52
monoclinic
C2/c
33.484(12)
9.174(3)
21.475(8)
90
1206.34
monoclinic
P2(1)/n
15.931(9)
18.653(11)
17.065(10)
90
cryst syst
space group
a/Å
10.422(6)
13.454(6)
14.360(8)
117.430(12)
106.307(10)
94.840(10)
1660.4(14)
1
11.244(6)
13.596(7)
15.158(7)
76.821(9)
72.850(9)
81.230(8)
2146.9(19)
2
b/Å
c/Å
R/deg
â/deg
109.0645
90
101.361(10)
90
γ/deg
V/Å3
6235(4)
4
4972(5)
4
Z
Dc/g‚cm-3
abs coeff/mm-1
F(000)
1.529
1.645
1.612
1.479
1.534
1.476
1.440
1.077
770
3112
2456
978
2θmax/deg
no. of reflns
no. of indep reflns
index ranges
53.08
52.80
50.00
53.28
9482
17 329
25 217
12 458
6645
6373
8746
8812
-12 e h e 13
-16 e k e 8
-14 e l e 17
1.015
-41 e h e 41
-11 e k e 10
-26 e l e 23
1.172
-16 e h e 18
-22 e k e 12
-20 e l e 20
1.040
-14 e h e 12
-17 e k e 17
-19 e l e 8
1.034
goodness of fit
R
0.0576
0.1432
0.738/-0.624
0.0496
0.1063
0.860/-0.551
0.0649
0.1449
0.744/-0.530
0.0675
0.1500
0.937/-0.688
Rw
largest diff peak
and hole/e Å-3
PCH2), 2.24 (s, 4H, 2NCH2) ppm. 31P NMR (81.0 MHz, CDCl3,
H3PO4): δ 54.32 (s) ppm.
by using the geometric method. Details of crystal data, data
collections, and structure refinements are summarized in
Tables 3 and 4, respectively.
X-ray Structure Determination of 1, 2, and 4-9. Single
crystals of 1, 2, and 4-9 suitable for X-ray diffraction analyses
were grown by slow evaperation of their haxane solution at
about 4 °C. Each single crystal was mounted on a Bruker
SMART 1000 automated diffractometer, respectively. Data
were collected at room temperature, using graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å) in the ω-2θ scanning
mode. Absorption corrections were performed using SADABS.
The structures were solved by direct methods using the
SHELXS-97 program40 and refined by full-matrix least-squares
techniques (SHELXL-97)41 on F2. Hydrogen atoms were located
Electrochemistry. Acetonitrile (Fisher Chemicals, HPLC
grade) for electrochemistry assays was used directly without
further purification. A solution of 0.1 M n-Bu4NPF6 in CH3-
CN was used as electrolyte in all cyclic voltammetric experi-
ments. The electrolyte solution was degassed by bubbling with
dry N2 for 10 min before measurement. Electrochemical
measurements were made using a BAS Epsilon potentiostat.
All voltammograms were obtained in a three-electrode cell
with a 3 mm diameter glassy carbon working, platinum
counter, and Ag/Ag+ (0.01 M AgNO3/0.1 M n-Bu4NPF6 in CH3-
(40) Sheldrick, G. M. SHELXS97, A Program for Crystal Structure
Solution; University of Go¨ttingen: Germany, 1997.
(41) Sheldrick, G. M. SHELXL97, A Program for Crystal Structure
Refinement; University of Go¨ttingen: Germany, 1997.

Diiron Oxadithiolate Type Models
Organometallics, Vol. 24, No. 25, 2005 6135
CN) reference electrode under N2 atmosphere. The working
electrode was polished with 1 µm diamond paste and sonicated
in water for 10 min prior to use. All potentials are quoted
against the ferrocene/ferrocenium (Fc/Fc+) potential. Bulk
electrolyses for electrocatalytic reactions were carried out
under N2 atmosphere using a BAS Epsilon potentiostat.
Electrocatalytic experiments were run on a glassy carbon rod
(A ) 2.9 cm2) in a two-compartment, gastight, H-type elec-
trolysis cell containing ca. 25 mL of CH3CN. The electrolyses
of solutions were carried out under hydrodynamic conditions,
vigorously stirring the solutions, to mitigate mass transport
complications. Gas chromatography was performed with a
Shimadzu gas chromatograph GC-9A under isothermal condi-
tions with nitrogen as a carrier gas and a thermal conductivity
detector.
Acknowledgment. We are grateful to the National
Natural Science Foundation of China, the State Key
Laboratory of Organometallic Chemistry, and the Spe-
cialized Research Fund for the Doctoral Program of
Higher Education of China for financial support of this
work.
Supporting Information Available: Full tables of crystal
data, atomic coordinates and thermal parameters, and bond
lengths and angles for 1, 2, and 4-9 as CIF files. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM0507373