Synthesis and characterization of single, double, and triple butterfly [2Fe2E] (E = Se, S) cluster complexes related to the active site of [FeFe]-hydrogenases

Article abstract of DOI:10.1021/om200395g

As the active site mimics of [FeFe]-hydrogenases, 14 new butterfly [2Fe2E] (E = Se, S) cluster complexes have been prepared by various synthetic routes. The N-substituted single-butterfly [2Fe2Se] complexes [(μ-SeCH ₂)₂NC(O)R]Fe₂(CO)₆ (1, R = Me; 2, R = Ph; 3, R = PhCH₂O) were prepared by reactions of the in situ formed (μ-LiSe)₂Fe₂(CO)₆ with RC(O)N(CH ₂Cl)₂, whereas the corresponding [2Fe2S] complexes [(μ-SCH₂)₂NC₆H₄R-p]Fe ₂(CO)₆ (4, R = CO₂Et; 5, R = CH₂OH) were produced by reaction of the in situ generated (μ-HS)₂Fe ₂(CO)₆ with aqueous CH₂O followed by treatment with p-RC₆H₄NH₂. The parent single-butterfly [2Fe2Se] complex [(μ-SeCH₂)₂NH]Fe₂(CO) ₆ (6) could be prepared by reaction of the N-substituted complex 3 with deprotecting reagent BBr₃, BF₃·OEt ₂/EtSH, or BF₃·OEt₂/Me₂S, whereas the N-substituted single-butterfly [2Fe2Se] complexes [(μ-SeCH ₂)₂NC(O)R]Fe₂(CO)₆ (7, R = Et; 8, R = PhCH₂) were produced by reactions of 6 with acylating agents RC(O)Cl in the presence of Et₃N. While the known parent single-butterfly [2Fe2S] complex [(μ-SCH₂)₂NH]Fe ₂(CO)₆ reacted with 2,6-[ClC(O)]₂C ₅H₃N to afford double-butterfly [2Fe2S] complex [Fe ₂(CO)₆(μ-SCH₂)₂NC(O)] ₂(2,6-C₅H₃N) (9), the new N-hydroxyethyl- substituted single-butterfly [2Fe2Se] complex [(μ-SeCH₂) ₂N(CH₂)₂OH]Fe₂(CO)₆ (10) could be obtained by the in situ reaction of (μ-HSe)₂Fe ₂(CO)₆ with (HOCH₂)₂N(CH ₂)₂OH. Interestingly, complex 10 could react with [ClC(O)]₂CH₂ or 1,3,5-[ClC(O)]₃C ₆H₃ in the presence of Et₃N to give the corresponding double-butterfly [2Fe2Se] complex [Fe₂(CO) ₆(μ-SeCH₂)₂N(CH₂) ₂O₂C]₂CH₂ (11) and triple-butterfly complex [Fe₂(CO)₆(μ-SeCH₂) ₂N(CH₂)₂O₂C]₃(1,3,5- C₆H₃) (12), whereas the known single-butterfly [2Fe2S] complex [(μ-SCH₂)₂N(CH₂)₂OH] Fe₂(CO)₆ could react with 2,6-[ClC(O)]₂C ₅H₃N and 1,3,5-[ClC(O)]₃C₆H ₃ in the presence of Et₃N to afford the corresponding double-butterfly [2Fe2S] complex [Fe₂(CO)₆(μ-SCH ₂)₂N(CH₂)₂O₂C] ₂(2,6-C₅H₃N) (13) and triple-butterfly complex [Fe₂(CO)₆(μ-SCH₂)₂N(CH ₂)₂O₂C]₃(1,3,5-C₆H ₃) (14), respectively. All the new complexes 1-14 have been characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for 1-4, 7-9, and 14. In addition, the electrochemical study indicated that complexes 1 and 2 can catalyze the proton reduction of HOAc to give hydrogen.

Full text of DOI:10.1021/om200395g

ARTICLE
pubs.acs.org/Organometallics
Synthesis and Characterization of Single, Double, and Triple Butterfly
[2Fe2E] (E = Se, S) Cluster Complexes Related to the Active Site of
[FeFe]-Hydrogenases
Wei Gao, Li-Cheng Song,* Bang-Shao Yin, Hui-Ning Zan, De-Fu Wang, and Hai-Bin Song
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
S Supporting Information
b
ABSTRACT: As the active site mimics of [FeFe]-hydrogenases,
14 new butterfly [2Fe2E] (E = Se, S) cluster complexes have
been prepared by various synthetic routes. The N-substituted
single-butterfly [2Fe2Se] complexes [(μ-SeCH2)2NC(O)R]Fe2-
(CO)6 (1, R = Me; 2, R = Ph; 3, R = PhCH2O) were prepared
by reactions of the in situ formed (μ-LiSe)2Fe2(CO)6 with
RC(O)N(CH2Cl)2, whereas the corresponding [2Fe2S] com-
plexes [(μ-SCH2)2NC6H4R-p]Fe2(CO)6 (4, R = CO2Et; 5, R =
CH2OH) were produced by reaction of the in situ generated
(μ-HS)2Fe2(CO)6 with aqueous CH2O followed by treatment
with p-RC6H4NH2. The parent single-butterfly [2Fe2Se] com-
plex [(μ-SeCH2)2NH]Fe2(CO)6 (6) could be prepared by
reaction of the N-substituted complex 3 with deprotecting reagent BBr3, BF3 OEt2/EtSH, or BF3 OEt2/Me2S, whereas the
3
3
N-substituted single-butterfly [2Fe2Se] complexes [(μ-SeCH2)2NC(O)R]Fe2(CO)6 (7, R = Et; 8, R = PhCH2) were produced by
reactions of 6 with acylating agents RC(O)Cl in the presence of Et3N. While the known parent single-butterfly [2Fe2S] complex
[(μ-SCH2)2NH]Fe2(CO)6 reacted with 2,6-[ClC(O)]2C5H3N to afford double-butterfly [2Fe2S] complex [Fe2(CO)6(μ-
SCH2)2NC(O)]2(2,6-C5H3N) (9), the new N-hydroxyethyl-substituted single-butterfly [2Fe2Se] complex [(μ-SeCH2)2N-
(CH2)2OH]Fe2(CO)6 (10) could be obtained by the in situ reaction of (μ-HSe)2Fe2(CO)6 with (HOCH2)2N(CH2)2OH.
Interestingly, complex 10 could react with [ClC(O)]2CH2 or 1,3,5-[ClC(O)]3C6H3 in the presence of Et3N to give the
corresponding double-butterfly [2Fe2Se] complex [Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]2CH2 (11) and triple-butterfly complex
[Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (12), whereas the known single-butterfly [2Fe2S] complex [(μ-SCH2)2N-
(CH2)2OH]Fe2(CO)6 could react with 2,6-[ClC(O)]2C5H3N and 1,3,5-[ClC(O)]3C6H3 in the presence of Et3N to afford the
corresponding double-butterfly [2Fe2S] complex [Fe2(CO)6(μ-SCH2)2N(CH2)2O2C]2(2,6-C5H3N) (13) and triple-butterfly
complex [Fe2(CO)6(μ-SCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (14), respectively. All the new complexes 1À14 have been
characterized by elemental analysis and spectroscopy, as well as by X-ray crystallography for 1À4, 7À9, and 14. In addition, the
electrochemical study indicated that complexes 1 and 2 can catalyze the proton reduction of HOAc to give hydrogen.
’ INTRODUCTION
iron atoms of the [2Fe2S] cluster are bridged by a dithiolate
ligand, as well as being connected with CO and CNÀ ligands.
Recently, the bridging dithiolate was suggested as an azadithio-
late SCH2NHCH2S or its N-substituted species.15À17 On the
basis of structural studies regarding the active site of [FeFe]-
hydrogenases, a great variety of butterfly [2Fe2E] (E = Se, S)
cluster complexes as biomimetic models for the active site of
[FeFe]-hydrogenases have been synthesized.18À21 Herein, as
part of our project concerning the butterfly Fe/E (E = Se, S)
cluster chemistry and the [FeFe]-hydrogenase biomimetic chem-
istry, we report the synthesis, structure, and some properties of a
new series of Fe/E (E = Se, S) cluster complexes containing one,
The butterfly [2Fe2E] (E = Se, S) cluster complexes have
received ever more attention in recent years, largely due to their
unique structure and novel properties,1À9 and particularly the
biologically close relevance to [FeFe]-hydrogenases.10 [FeFe]-
hydrogenases are a class of natural enzymes that can catalyze
reversible proton reduction to give molecular H2 in a variety of
microorganisms.11,12 During 1998 and 1999, the successful
determination of the high-quality crystal structures of the [FeFe]-
hydrogenases CpI and DdH established13,14 that they both
contain a structurally uncommon active site, which consists of
a butterfly [2Fe2S] cluster with one of its iron atoms connected
to a cubane-like [4Fe4S] cluster via the sulfur atom of a cysteinyl
ligand. The [4Fe4S] cluster is actually responsible for the
electron transfer, whereas the [2Fe2S] cluster is responsible for
the formation and activation of hydrogen. In addition, the two
Received: May 18, 2011
Published: July 06, 2011
r
2011 American Chemical Society
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Scheme 1
Scheme 2
Figure 2. Molecular structure of 2 with 30% probability level ellipsoids.
Selected bond lengths (Å) and angles (deg): Fe(1)ÀFe(2) =
2.5401(10), Fe(1)ÀSe(1) = 2.3842(9), Fe(1)ÀSe(2) = 2.3814(9),
Fe(2)ÀSe(1) = 2.3909(9), Fe(2)ÀSe(2) = 2.3739(9), Se(1)ÀC(7) =
1.998(5), N(1)ÀC(9) = 1.378(6), N(1)ÀC(7) = 1.430(6); Fe(1)ÀSe-
(1)ÀFe(2) = 64.27(3), Fe(1)ÀSe(2)ÀFe(2) = 64.57(3), Se(1)ÀFe-
(1)ÀSe(2) = 86.20(3), Se(1)ÀFe(1)ÀFe(2) =57.99(3), Se(2)ÀFe(1)À
Fe(2) = 57.57(3).
Figure 1. Molecular structure of 1 with 30% probability level ellip-
soids. Selected bond lengths (Å) and angles (deg): Fe(1)ÀFe(2) =
2.5523(17), Fe(1)ÀSe(1) = 2.3753(14), Fe(1)ÀSe(2) = 2.3659(16),
Fe(2)ÀSe(1) = 2.3825(16), Fe(2)ÀSe(2) = 2.3743(16), Se(1)ÀC(7) =
1.974(10), N(1)ÀC(9) = 1.380(10), N(1)ÀC(7) = 1.432(9); Fe(1)À
Se(1)ÀFe(2) = 64.88(5), Fe(1)ÀSe(2)ÀFe(2) = 65.15(5), Se(1)À
Fe(1)ÀSe(2) = 87.03(5), Se(1)ÀFe(1)ÀFe(2) = 57.70(5), Se(2)À
Fe(1)ÀFe(2) = 57.58(4).
Figure 3. Molecular structure of 3 with 30% probability level ellipsoids.
Selected bond lengths (Å) and angles (deg): Fe(1)ÀFe(2) =
2.5417(11), Fe(1)ÀSe(1) = 2.3750(10), Fe(1)ÀSe(2) = 2.3850(12),
Fe(2)ÀSe(1) = 2.3872(9), Fe(2)ÀSe(2) = 2.3787(8), Se(2)ÀC(8) =
1.987(4), N(1)ÀC(9) = 1.374(5), N(1)ÀC(8) = 1.425(5); Fe(1)ÀSe-
(1)ÀFe(2) = 64.51(3), Fe(1)ÀSe(2)ÀFe(2) = 64.49(4), Se(1)ÀFe-
(1)ÀSe(2) = 87.03(4), Se(1)ÀFe(1)ÀFe(2) =57.98(3), Se(2)ÀFe(1)À
Fe(2) = 57.63(3).
two, or three butterfly [2Fe2E] cluster cores, which are closely
related to the active site of [FeFe]-hydrogenases.
complexes 1À3 could be prepared by treatment of (μ-LiSe)2Fe2-
(CO)6 (generated in situ from (μ-Se2)Fe2(CO)6 and Et3BHLi)3
with the corresponding N,N-bis(chloromethyl)amide in THF
from À78 °C to room temperature in 22À36% yields (Scheme 1).
In addition, the N-substituted single-butterfly [2Fe2S] com-
plexes 4 and 5 were found to be prepared by reaction of
(μ-HS)2Fe2(CO)6 (formed in situ from (μ-LiS)2Fe2(CO)6
’ RESULTS AND DISCUSSION
Synthesis and Characterization of [(μ-SeCH2)2NC(O)R]Fe2
(CO)6 (1, R = Me; 2, R = Ph; 3, R = PhCH2O) and [(μ-
SCH2)2NC6H4R-p]Fe2(CO)6 (4, R = CO2Et; 5, R = CH2OH). We
found that the N-substituted single-butterfly [2Fe2Se] cluster
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Figure 4. Molecular structure of 4 with 30% probability level ellipsoids. Selected bond lengths (Å) and angles (deg): Fe(1)ÀFe(2) = 2.5103(10),
Fe(1)ÀS(1) = 2.2706(8), Fe(1)ÀS(2) = 2.2574(9), Fe(2)ÀS(1) = 2.2619(9), Fe(2)ÀS(2) = 2.2608(9), N(1)ÀC(9) = 1.402(3), O(7)ÀC(15) =
1.209(3), N(1)ÀC(8) = 1.422(3); Fe(1)ÀS(1)ÀFe(2) = 67.26(4), Fe(1)ÀS(2)ÀFe(2) = 67.50(3), S(1)ÀFe(1)ÀS(2) = 85.37(3), S(1)ÀFe-
(1)ÀFe(2) = 56.20(3), S(2)ÀFe(1)ÀFe(2) = 56.31(3), S(1)ÀFe(2)ÀS(2) = 85.49(4).
Scheme 3
Scheme 4
and CF3CO2H)22 with 37% aqueous formaldehyde in THF from
À78 °C to room temperature and subsequent treatment of the
complex 4 includes an N-p-ethoxycarbonylbenzene-substituted
azadithiolate (ADT) ligand bridged between its two Fe(CO)3
units to form the boat six-membered ring Fe1S1C8N1C7S2 and
chair six-membered ring Fe2S1C8N1C7S2, respectively. In
addition, as can be seen intuitively, the N-substituted ADS and
ADT ligands in 1À4 are all attached to the common N1 atoms of
the two fused six-membered rings with an axial type of bond
N1ÀC9. The Fe1ÀFe2 bond lengths of 1 (2.5523 Å), 2 (2.5401 Å),
3 (2.5417 Å), and 4 (2.5103 Å) are very close to those of the other
diiron ADT- and ADS-type model complexes.24
Synthesis and Characterization of [(μ-SeCH2)2NH]Fe2(CO)6
(6), [(μ-SeCH2)2NC(O)R]Fe2(CO)6 (7, R = Et; 8, R = PhCH2), and
[Fe2(CO)6(μ-SCH2)2NC(O)]2(2,6-C5H3N) (9). We initially tried
to prepare the parent single-butterfly [2Fe2Se] complex 6 by
using a synthetic method similar to that for preparation of its
sulfur analogue [(μ-SCH2)2NH]Fe2(CO)6,25 namely, the meth-
od using the “click” reaction of the three components: parafor-
maldehyde, (NH4)2CO3, and (μ-HSe)2Fe2(CO)6. However,
unfortunately, this “click” reaction failed to give parent complex
6. Latter, we imagined that the N-substituted complex 3 might be
regarded as a derivative of parent complex 6 with the N-carbo-
benzoxy protecting group. So, we decided to use the N-depro-
tecting method to prepare parent complex 6. As a result, complex
23
resulting intermediate (μ-HOCH2S)2Fe2(CO)6 with substi-
tuted aniline p-RC6H4NH2 in 64% and 69% yields, respectively
(Scheme 2).
Complexes 1À5 are air-stable red solids, which were char-
acterized by elemental analysis and spectroscopy, and for 1À4 by
X-ray crystallography. For example, the IR spectra of 1À5 showed
several absorption bands in the range 2072À1977 cmÀ1 for their
terminal carbonyls, whereas 1À4 exhibited one additional band
in the range 1716À1650 cmÀ1 for their organic carbonyls and 5
displayed one broad band at 3451 cmÀ1 for its hydroxy group. In
addition, the 1H NMR spectra of 1À3 showed one multiplet at
4.0À4.8 ppm for their two SeCH2 groups, whereas 4 and 5
exhibited one singlet at 4.36 and 4.31 ppm for their two SCH2
groups, respectively.
The molecular structures of 1À4 were unequivocally con-
firmed by X-ray diffraction analysis. Their ORTEP plots with
selected bond lengths and angles are presented in Figures 1À4.
As shown in Figures 1À3, complexes 1À3 each contain an
N-acylated azadiselenolate (ADS) ligand bridged between their
two Fe(CO)3 units to form the two fused six-membered rings
Fe1Se1C7N1C8Se2 and Fe2Se1C7N1C8Se2 with a chair con-
formation and a boat conformation, respectively. Similar to 1À3,
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Scheme 5
Figure 5. Molecular structure of 7 with 30% probability level ellipsoids.
Selected bond lengths (Å) and angles (deg): Fe(1)ÀFe(2) = 2.5342(7),
Fe(1)ÀSe(1) = 2.3807(6), Fe(1)ÀSe(2) = 2.3780(6), Fe(2)ÀSe(1) =
2.3786(9), Fe(2)ÀSe(2) = 2.3862(7), Se(2)ÀC(8) = 2.000(3), N(1)À
C(9) = 1.386(4), N(1)ÀC(7) = 1.427(4); Fe(1)ÀSe(1)ÀFe(2) =
64.35(3), Fe(1)ÀSe(2)ÀFe(2) = 64.27(2), Se(1)ÀFe(1)ÀSe(2) =
86.87(3), Se(1)ÀFe(1)ÀFe(2) = 57.79(3), Se(2)ÀFe(1)ÀFe(2) =
58.02(2), Se(1)ÀFe(2)ÀSe(2) = 86.729(18).
Figure 6. Molecular structure of 8 with 30% probability level ellipsoids.
Selected bond lengths (Å) and angles (deg): Fe(1)ÀFe(2) =
2.5500(13), Fe(1)ÀSe(1) = 2.3698(12), Fe(1)ÀSe(2) = 2.3782(12),
Fe(2)ÀSe(1) = 2.3758(12), Fe(2)ÀSe(2) = 2.3646(12), Se(1)ÀC(7) =
1.978(6), N(1)ÀC(9) = 1.375(8), N(1)ÀC(7) = 1.424(8); Fe(1)ÀSe-
(1)ÀFe(2) = 65.01(4), Fe(1)ÀSe(2)ÀFe(2) = 65.05(4), Se(1)ÀFe-
(1)ÀSe(2) = 86.92(4), Se(1)ÀFe(1)ÀFe(2) =57.61(4), Se(2)ÀFe(1)À
Fe(2) = 57.22(4).
6 was successfully prepared when the three boron-based depro-
tecting reagents BF3 OEt2/Me2S,26 BBr3,27 and BF3 OEt2/
(μ-LiSe)2Fe2(CO)6 with N,N-bis(chloromethyl)acetamide as
described above. Similar to parent complex 6, the known S
analogue, namely, parent complex [(μ-SCH2)2NH]Fe2(CO)6,25
could react with 2,6-pyridinedicarboxylic acid dichloride and
Et3N in CH2Cl2 to afford the double-butterfly [2Fe2S] cluster
complex 9 in 57% yield (Scheme 5).
3
3
EtSH28 were used (Scheme 3). All the deprotecting reactions
of 3 with the three boron-based reagents were carried out in
CH2Cl2 under mild conditions and in moderate yields (31À57%).
However, the best one uses the BF3 OEt2/Me2S reagent, since
3
the reaction time is shorter (4 h) and the yield is higher (57%).28
Furthermore, we found that parent complex 6 could be used as
a starting material to prepare a variety of N-substituted deriva-
tives. Actually, one of our purposes is to find a synthetic method
to prepare complex 6. Thus, treatment of a CH2Cl2 solution of 6
with monoacylating agent EtC(O)Cl or PhCH2C(O)Cl in the
presence of Et3N resulted in formation of the corresponding
N-substituted complexes 7 and 8 in 89% and 73% yields,
respectively (Scheme 4). Interestingly, this method for prepara-
tion of such N-substituted cluster complexes is both conve-
nient and produces high yields. For example, complex 1 could
be prepared by this method in 85% yield, but it was pre-
pared only in 22% yield by the method involving reaction of
While complexes 6À8 are air-sensitive red solids, complex 9 is
an air-stable red solid. They were all characterized by elemental
analysis and spectroscopy, as well as for 7À9 by X-ray diffraction
analysis. Similar to 1À5, the IR spectra of 6À9 also showed
several absorption bands in the range 2080À1984 cmÀ1 for their
terminal carbonyls, whereas 6 displayed another band at
3379 cmÀ1 for its NH group, and 7À9 exhibited another band
in the region 1683À1654 cmÀ1 for their amide carbonyls. While
1
the H NMR spectrum of parent complex 6 displayed two
singlets at 3.74 and 3.93 ppm for its two SeCH2 groups,
derivatives 7 and 8 exhibited one multiplet at 3.9À4.5 ppm for
their two SeCH2 groups, and double-butterfly [2Fe2S] complex
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ARTICLE
9 displayed two singlets at 4.31 and 4.50 ppm for its four SCH2
groups.
complex, although its phenylene-diacyl analogue [Fe2(CO)6(μ-
SCH2)2NC(O)]2(1,4-C6H4) was previously prepared.24a
Synthesis and Characterization of [(μ-SeCH2)2N(CH2)2OH]
Fe2(CO)6 (10), [Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]2CH2 (11), Fe2-
(CO)6(μ-SeCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (12), [Fe2(CO)6(μ-
SCH2)2N(CH2)2O2C]2(2,6-C5H3N) (13),and[Fe2(CO)6(μ-SCH2)2N-
(CH2)2O2C]3(1,3,5-C6H3) (14). It was found that the N-substi-
tuted single-butterfly [2Fe2Se] cluster complex 10 could be
prepared by treatment of (μ-HSe)2Fe2(CO)6 (generated in situ
from (μ-LiSe)2Fe2(CO)6 and CF3CO2H) with N,N-bis(hydroxy-
methyl)ethanolamine (generated in situ from ethanolamine and
paraformaldehyde) in THF from À78 °C to room temperature in
39% yield (Scheme 6).
It was further found that the single-butterfly [2Fe2Se]
complex 10 and the known sulfur analogue [(μ-SCH2)2N-
(CH2)2OH]Fe2(CO)629 could be easily converted to the corre-
sponding double- and triple-butterfly [2Fe2E] (E = Se, S) cluster
complexes under the action of di- and triacylating reagents. For
example, treatment of 10 with propanedioyl dichloride or 1,3,5-
benzenetricarbonyl trichloride in CH2Cl2 in the presence of
Et3N afforded the corresponding bridged double-butterfly
[2Fe2Se] complex 11 and triple-butterfly complex 12 in 56%
and 16% yields, respectively (Scheme 7). Furthermore, the
corresponding double-butterfly [2Fe2S] complex 13 and
triple-butterfly complex 14 could be produced in 61% and 53%
yields by reaction of the sulfur analogue [(μ-SCH2)2N-
(CH2)2OH]Fe2(CO)6 with 2,6-pyridinedicarboxylic acid dich-
loride or 1,3,5-benzenetricarbonyl trichloride under similar con-
ditions (Scheme 8).
In order to confirm the structures of complexes 7À9, X-ray
crystal diffraction analyses of 7À9 were undertaken. Their
ORTEP drawings with selected bond lengths and angles are
depicted in Figures 5À7. As shown in Figures 5 and 6, the
molecular structures of 7 and 8 are very similar to those of 1À3.
For example, they all have an N-substituted ADS ligand bridged
between their two Fe(CO)3 groups. Their N-substituents are all
connected to the bridgehead N1 atom by the N1ÀC9 axial bond
of the corresponding two fused six-membered rings. The
Fe1ÀFe2 bond lengths of 7 (2.5342 Å) and 8 (2.5500 Å) are
very close to those of 1À4 and the other diiron ADT- and ADS-
type model complexes.24
Interstingly, in contrast to the ADS ligand-containing single-
butterfly complexes 7 and 8, complex 9, as shown in Figure 7,
contains two diiron ADT moieties, which are combined together
by the 2,6-dicarbonylpyridine unit to form a double-butterfly
[2Fe2S] cluster complex. The 2,6-dicarbonylpyridine group is
linked to the two diiron ADT moieties through axial-type bonds
C15ÀN1 and C21ÀN3. In addition, the dihedral angle between
the two triangles N1C13C14 and O13C15C16, or N3C22C23
and O14C20C21, is only about 3.5°, which implies that the π
system of its amide carbonyls is well conjugated with the p obital
of its bridgehead N1 atoms. In fact, this is the first crystal-
lographycally characterized N-diacyl-bridged ADT-type model
Complexes 10À12 are air-sensitive red solids, whereas com-
plexes 13 and 14 are air-stable red solids. All the elemental
analysis, IR, and 1H NMR spectroscopic data are consistent with
their structures shown in Schemes 7 and 8. For example, the IR
spectra of 10À14 displayed several absorption bands in the range
2075À1983 cmÀ1 for their terminal carbonyls, whereas 10
exhibited one additional band at 3455 cmÀ1 for its hydroxyl
group, and 11À14 showed one additional band in the region
1753À1727 cmÀ1 for their ester carbonyls. The 1H NMR
spectrum of 10 exhibited three singlets at 1.43, 2.95, and 3.52
ppm for its HOCH2CH2N group and two multiplets at 3.9À4.1
1
ppm for its two SeCH2 groups. The H NMR spectrum of 11
showed two multiplets at 3.8À4.3 ppm for its four SeCH2
groups, whereas 12 displayed one multiplet at 3.9À4.3 ppm for
its six SeCH2 groups. In addition, 13 and 14 each showed one
singlet at 3.72 and 3.66 ppm for their four and six SCH2 groups,
respectively.
Fortunately, the molecular structure of triple-butterfly com-
plex 14 has been unambiguously confirmed by X-ray crystal-
lographic study. The ORTEP view for this complex with selected
bond lengths and angles is presented in Figure 8. As can be
seen in Figure 8, complex 14 indeed consists of three ADT-
bridged butterfly [2Fe2S] cluster cores, which are combined
together by a 1,3,5-trisubstituted benzene moiety to give a
Figure 7. Molecular structure of 9 with 30% probability level ellipsoids.
Selected bond lengths (Å) and angles (deg): Fe(1)ÀFe(2) =
2.5144(10), Fe(3)ÀFe(4) = 2.5126(12), Fe(1)ÀS(1) = 2.2559(13),
Fe(1)ÀS(2) = 2.2489(14), Fe(2)ÀS(1) = 2.2496(15), Fe(2)ÀS(2) =
2.2480(14), O(13)ÀC(15) = 1.225(5), N(1)ÀC(15) = 1.379(5);
Fe(1)ÀS(1)ÀFe(2) = 67.85(4), Fe(1)ÀS(2)ÀFe(2) = 67.99(5), S(1)À
Fe(1)ÀS(2) = 85.13(5), S(1)ÀFe(1)ÀFe(2) = 55.96(4), S(2)ÀFe(1)À
Fe(2) = 55.99(4).
Scheme 6
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Scheme 7
Scheme 8
star-like compound. In addition, it is worth pointing out that (i)
the three ADT-bridged butterfly cluster cores are all connected
to the central benzene ring moiety via the axial bonds N1ÀC9,
N2ÀC20, and N3ÀC31, (ii) each of the six iron atoms is attached
to three terminal carbonyls and adopts a square-pyramidal
geometry, (iii) the bond lengths of Fe1ÀFe2 (2.5006 Å),
Fe3ÀFe4 (2.5068 Å), and Fe5ÀFe6 (2.5097 Å) are slightly
shorter than those of the oxidized form (2.62 or 2.60 Å)13,14 and
reduced form (2.55 Å)16 of [FeFe]-hydrogenases. To the best of
our knowledge, it is the first crystallographically characterized
ADT type of [FeFe]-hydrogenase model complex with three
butterfly [2Fe2S] cluster cores.
Similarly, the oxidation peaks of 1 (+0.72 V) and 2 (+0.73 V)
could be attributed to the two-electron oxidation processes
from FeIFeI to FeIIFeII. It follows that the cyclic voltammetric
behavior of 1 and 2 is very similar to that of the propanedi-
selenolate-bridged diiron complex [μ-Se(CH2)3Se-μ]Fe2-
(CO)6 (its three corresponding peaks at À1.61, À2.15, and
+0.73 V).24c However, it is worth noting that the first reduc-
tion peaks of 1 and 2 are positively shifted by 110 and 130 mV
relative to that of [μ-Se(CH2)3Se-μ]Fe2(CO)6, respectively.
This is obviously due to 1 or 2 having a stronger electron-
withdrawing group MeC(O)N or PhC(O)N in their disele-
nolate ligands.
Electrochemistry of 1 and 2. The electrochemical behavior
of the representative complexes 1 and 2 was studied in MeCN
under CO by cyclic voltammetric techniques.30 Table 1 lists
their electrochemical data, and Figures 9 and 10 display their
cyclic voltammograms, respectively. It is shown that both 1
and 2 exhibit one quasi-reversible reduction, one irreversible
reduction, and one irreversible oxidation. The first and second
reduction peaks of 1 (À1.50 and À1.97 V) and 2 (À1.48 and
À1.95 V) could be assigned to the one-electron reduction
processes from FeIFeI to FeIFe0 and FeIFe0 to Fe0Fe0, which
were supported by the calculated values of 1.05 and 0.95
Faraday/equiv obtained by the bulk electrolysis of a MeCN
solution of 1 at À1.70 V and 2 at À1.68 V, respectively.
The cyclic voltammograms of 1 and 2 in the presence of acetic
acid HOAc (pKa = 22.3 in MeCN) are presented in Figures 11 and
12, respectively. For comparison, the cyclic voltammograms of 1
and 2 without HOAc are also included. As shown in Figures 11 and
12, when the first 2 mM HOAc was added, the first reduction peak
of 1 at À1.51 V or 2 at À1.49 V slightly increased, but it did not
grow with sequential addition of the acid. However, upon
addition of 2À10 mM HOAc, the second reduction peak of 1
at À1.98 V or 2 at À1.97 V considerably increased and continued to
grow with sequential addition of the acid. The rapid increments in
current height of the reduction peak show an electrocatalytic
process.24c,31À34
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Figure 9. Cyclic voltammogram of 1 (1 mM) in 0.1 M n-Bu4NPF6/
MeCN under CO at a scan rate of 100 mV sÀ1
.
Figure 8. Molecular structure of 14 with 30% probability level ellip-
soids. Selected bond lengths (Å) and angles (deg): Fe(1)ÀFe(2) =
2.5006(10), Fe(3)ÀFe(4) = 2.5068(10), Fe(5)ÀFe(6) = 2.5097(11),
Fe(1)ÀS(1) = 2.2702(13), Fe(1)ÀS(2) = 2.2649(15), Fe(2)ÀS(1) =
2.2597(13), O(8)ÀC(11) = 1.207(5), N(1)ÀC(9) = 1.456(5); Fe-
(1)ÀS(1)ÀFe(2) = 67.01(4), Fe(1)ÀS(2)ÀFe(2) = 66.67(4), S-
(1)ÀFe(1)ÀS(2)
=
84.79(5), S(1)ÀFe(1)ÀFe(2)
= 56.29(4),
S(2)ÀFe(1)ÀFe(2) = 57.05(4).
Table 1. Electrochemical Data of 1 and 2a
Epc(V) FeIFeI/
Epc(V) FeIFe0/
Epa(V) FeIFeI/
compound
FeIFe0
Fe0Fe0
FeIIFeII
1
2
À1.50
À1.48
À1.97
À1.95
+0.72
+0.73
Figure 10. Cyclic voltammogram of 2 (1 mM) in 0.1 M n-Bu4NPF6/
MeCN under CO at a scan rate of 100 mV sÀ1
a All potentials are versus Fc/Fc+ in 0.1 M n-Bu4NPF6/MeCN.
.
characterized by elemental analysis and spectroscopy, as well as
for 1 and 2 by cyclic voltammetry and for 1À4, 7À9, and 14 by
X-ray crystallography.
’ CONCLUSIONS
We have successfully prepared a series of new butterfly
[2Fe2E] (E = Se, S) cluster complexes (1À14) by different
synthetic methods. While the N-substituted single-butterfly
complexes 1À5 and 10 were prepared by the tandem reactions
starting from (μ-E2)Fe2(CO)6, the double- and triple-butterfly
complexes 11À14 could be prepared by functional transforma-
tion reactions of the N-hydroxyethyl group of new complex 10
and its S analogue [(μ-SCH2)2N(CH2)2OH]Fe2(CO)6. Parti-
cularly noteworthy is that butterfly complex 6 could not be
prepared by the known method for preparation of its analogue
[(μ-SCH2)2NH]Fe2(CO)6, but it could be prepared by a new
method involving removal of the N-substituent of complex 3 by
using one of the three boron-based deprotecting reagents. In
addition, the N-substituted single-butterfly [2Fe2Se] complexes
7 and 8 could be obtained by monoacylation reactions of
complex 6, whereas double-butterfly [2Fe2S] complex 9 was
prepared by diacylation reaction of [(μ-SCH2)2NH]Fe2(CO)6
in high yield. It should be noted that all the new complexes 1À14
contain at least one azadithiolate- or azadiselenolate-bridged
butterfly [2Fe2E] cluster moiety. So, these complexes are
structurally very similar to the diiron catalytic center in the active
site of [FeFe]-hydrogenases. Complexes 1À14 have been fully
’ EXPERIMENTAL SECTION
General Comments. All reactions were performed using standard
Schlenk and vacuum-line techniques under N2. All manipulations
involving selenium compounds should be carried out in a well-ventilated
hood since the Se-containing compounds are usually highly toxic. THF
was distilled from sodium/benzophenone ketyl under N2, whereas
dichloromethane was distilled from CaH2. While (μ-S2)Fe2(CO)6,1
(μ-Se2)Fe2(CO)6,3 RC(O)N(CH2Cl)2 (R = Me, Ph, PhCH2O),35 [(μ-
SCH2)2NH]Fe2(CO)6,25 propanedioyl dichloride,36 and 1,3-pyridine-
dicarbonyl dichloride37 were prepared according to published methods,
other chemicals were purchased from commercial suppliers and used as
received. Preparative TLC was carried out on glass plates (25 Â 15 Â
0.25 cm) coated with silica gel G (10À40 μm), whereas column
chromatography was performed packed with ZCX-II silica gel
(200À300 mesh). IR spectra were recorded on a Bio-Rad FTS 135 or
1
a Bio-Rad FTS 60000 infrared spectrophotometer. H NMR spectra
were taken on a Bruker Avance 300 NMR or a Varian Mercury Plus 400
NMR spectrometer, respectively. Elemental analyses were performed
with an Elementar Vario EL analyzer. Melting points were determined
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(vs); νCdO 1650 (m) cmÀ1
.
1H NMR (300 MHz, CDCl3, TMS):
4.25À4.72 (m, 4H, 2SeCH2), 7.40À7.54 (m, 5H, C6H5) ppm. 3 was
prepared using the same procedure as that for 1, except that
PhCH2O2CN(CH2Cl)2 (0.248 g, 1.00 mmol) was employed. From
the main red band, 3 was obtained as a red solid (0.211 g, 34%), mp
141 °C (dec). Anal. Calcd for C16H11Fe2NO8Se2: C, 31.25; H, 1.80; N,
2.28. Found: C, 31.28; H, 1.95; N, 2.27. IR (KBr disk): νCꢀO 2069 (s),
1
2028 (vs), 1990 (vs); νCdO 1716 (m) cmÀ1. H NMR (400 MHz,
CDCl3, TMS): 4.02À4.50 (m, 4H, 2SeCH2), 5.18 (s, 2H, OCH2), 7.37
(s, 5H, C6H5) ppm.
Preparation of [(μ-SCH2)2NC6H4R-p]Fe2(CO)6 (4, R = CH2OH;
5, R = CO2Et). A red solution of (μ-S2)Fe2(CO)6 (0.344 g, 1.00 mmol)
in THF (20 mL) was cooled to À78 °C, and then Et3BHLi (2.0 mL, 2.00
mmol) was added. The mixture was stirred at À78 °C for 15 min, and
then CF3CO2H (0.20 mL, 2.00 mmol) was added to give a brown-red
solution containing (μ-HS)2Fe2(CO)6. After aqueous CH2O (0.16 mL,
2.00 mmol) was added, the mixture was warmed to room temperature
and stirred at this temperature for 1 h, and then p-H2NC6H4CO2Et
(0.165 g, 1.00 mmol) was added. The new mixture was stirred for 5 h.
Volatiles were removed in vacuo, and the residue was subjected to TLC
separation using CH2Cl2/petroleum ether (1:2 v/v) as eluent. From the
main red band, 4 was obtained as a red solid (0.341 g, 64%), mp
118À119 °C. Anal. Calcd for C17H13Fe2NO8S2: C, 38.16; H, 2.45; N,
2.62. Found: C, 38.27; H, 2.49; N, 2.79. IR (KBr disk): νCꢀO 2072 (s),
Figure 11. Cyclic voltammogram of 1 (1 mM) with HOAc
(0À10 mM) in 0.1 M n-Bu4NPF6/MeCN under CO at a scan rate of
100 mV sÀ1
.
1
2033 (vs), 2001 (vs), 1994 (s); νCdO 1699 (s) cmÀ1. H NMR (400
MHz, CDCl3, TMS): 1.40 (t, 3H, J = 7.0 Hz, CH3), 4.36 (s, 6H, OCH2,
2SCH2), 6.74, 6.77, 8.00, 8.02 (AB q, 4H, C6H4) ppm. 5 was prepared by
the same procedure as that for 4, but p-H2NC6H4CH2OH (0.123 g, 1.00
mmol) was used instead of p-H2NC6H4CO2Et . From the main red
band, 5 was obtained as a red solid (0.340 g, 69%), mp 133À134 °C.
Anal. Calcd for C15H11Fe2NO7S2: C, 36.54; H, 2.25; N, 2.84. Found: C,
36.75; H, 2.25; N, 3.00. IR (KBr disk): νCꢀO 2071 (s), 2034 (vs), 2010
(vs), 1991 (vs), 1977 (vs); νOH 3451 (br s) cmÀ1. 1H NMR (300 MHz,
CDCl3, TMS): 1.56 (br s, 1H, OH), 2.28 (s, 2H, OCH2), 4.31 (s, 4H,
2SCH2), 6.65, 6.69, 7.11, 7.12 (AB q, 4H, C6H4) ppm.
Preparation of [(μ-SeCH2)2NH]Fe2(CO)6 (6). Method (i): To a
stirred solution of 3 (0.307 g, 0.50 mmol) in CH2Cl2 (15 mL) were
Figure 12. Cyclic voltammogram of 2 (1 mM) with HOAc
(0À10 mM) in 0.1 M n-Bu4NPF6/MeCN under CO at a scan rate of
added BF3 OEt2 (0.61 mL, 4.85 mmol) and Me2S (0.99 mL, 13.55
3
100 mV sÀ1
.
mmol). After the mixture was stirred at room temperature for 1.5 h,
additional Me2S (0.81 mL, 11.10 mmol) was added. The new mixture
was stirred for another 2.5 h and then washed with water (5 mL Â 2).
The organic layer was separated and then evaporated to dryness at
reduced pressure. The residue was subjected to column chromatography
under anaerobic conditions using 1:2 v/v CH2Cl2/petroleum ether
as eluent. From the main red band, 6 was obtained as a dark red solid
(0.138 g, 57%), mp 68 °C (dec). Anal. Calcd for C8H5Fe2NO6Se2: C,
19.99; H, 1.05; N, 2.91. Found: C, 20.07; H, 1.24; N, 2.69. IR (KBr disk):
νCꢀO 2060 (s), 2021 (vs), 1984 (vs); νNH 3379 (w) cmÀ1. 1H NMR
(400 MHz, CDCl3, TMS): 1.82 (s, 1H, NH), 3.74, 3.93 (2s, 4H,
2SeCH2) ppm.
on an X-4 apparatus from Beijing Tech Instrument Co. Ltd. and were
uncorrected.
Preparation of [(μ-SeCH2)2NC(O)R]Fe2(CO)6 (1, R = Me; 2,
R = Ph; 3, R = PhCH2O). A purple-red solution of (μ-Se)2Fe2(CO)6
(0.438 g, 1.00 mmol) in THF (25 mL) was cooled to À78 °C, and then
Et3BHLi (2.0 mL, 2.00 mmol) was added. The mixture was stirred
at À78 °C for 20 min to give a brown-red solution containing
(μ-LiSe)2Fe2(CO)6. After MeC(O)N(CH2Cl)2 (0.156 g, 1.00 mmol)
was added, the new mixture was warmed to room temperature and
stirred at this temperature for 12 h. Volatiles were removed in vacuo, and
the residue was subjected to TLC separation using CH2Cl2/petroleum
ether (3:1 v/v) as eluent. From the main red band, 1 was obtained as a
red solid (0.114 g, 22%), mp 121 °C (dec). Anal. Calcd for C10H7Fe2-
NO7Se2: C, 22.97; H, 1.35; N, 2.68. Found: C, 23.14; H, 1.44; N, 2.65.
IR (KBr disk): νCꢀO 2070 (s), 2028 (vs), 1989 (vs); νCdO 1667
Method (ii): While stirring, a solution of 3 (0.307 g, 0.50 mmol) in
CH2Cl2 (15 mL) was cooled to about À10 °C, and then BBr3 (0.63 mL,
2.50 mmol) was added. After the mixture was stirred at this temperature
for 1 h, it was warmed to room temperature and stirred at this tempera-
ture for 2 h. The same workup as that used in method (i) afforded
0.105 g (44%) of 6.
1
(m) cmÀ1. H NMR (300 MHz, CDCl3, TMS): 2.12 (s, 3H, CH3),
Method (iii): To a stirred solution of 3 (0.307 g, 0.50 mmol) in
4.07À4.43 (m, 4H, 2SeCH2) ppm. 2 was prepared using the same
procedure as that for 1, except that PhC(O)N(CH2Cl)2 (0.218 g, 1.00
mmol) was utilized in place of MeC(O)N(CH2Cl)2. From the main red
band, 2 was obtained as a red solid (0.212 g, 36%), mp 135 °C (dec).
Anal. Calcd for C15H9Fe2NO7Se2: C, 30.80; H, 1.55; N, 2.39. Found: C,
30.73; H, 1.75; N, 2.49. IR (KBr disk): νCꢀO 2068 (s), 2026 (vs), 1988
CH2Cl2 (15 mL) was sequentially added BF3 OEt2 (0.63 mL, 5.00
3
mmol) and EtSH (1.10 mL, 14.50 mmol). After the mixture was stirred
at room temperature for 11 h, volatiles were removed at reduced
pressure. The residue was subjected to column chromatography under
anaerobic conditions to develop a major red band, from which 0.073 g
(31%) of 6 was obtained.
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Preparation of [(μ-SeCH2)2NC(O)R]Fe2(CO)6 (1, R = Me; 7,
R = Et; 8, R = PhCH2). A stirred solution of 6 (0.240 g, 0.50 mmol) in
CH2Cl2 (15 mL) was cooled to 0 °C, and then Et3N (0.07 mL, 0.50
mmol) and MeC(O)Cl (0.04 mL, 0.50 mmol) were added. After the
mixture was stirred at 0 °C for 0.5 h, it was allowed to warm to room
temperature and then stirred at this temperature for 5 h. Solvent was
removed in vacuo, and the residue was subjected to TLC separation
using CH2Cl2/petroleum ether (2.5:1 v/v) as eluent. From the main red
band, 1 was obtained as a red solid (0.221 g, 85%), which was identified
TLC separation using CH2Cl2/petroleum ether (2:1 v/v) as eluent.
From the main red band, 11 was obtained as a red solid (0.157 g, 56%),
mp 36À38 °C. Anal. Calcd for C23H18Fe4N2O16Se4: C, 24.72; H, 1.62;
N, 2.51. Found: C, 24.81; H, 1.52; N, 2.33. IR (KBr disk): νCꢀO 2064
(s), 2020 (vs), 1983 (vs); νCdO 1736 (m) cmÀ1. 1H NMR (400 MHz,
CDCl3, TMS): 3.03 (s, 4H, 2NCH2CH2O), 3.30 (s, 2H, O2CCH2CO2),
4.01 (s, 4H, 2NCH2CH2O), 3.86À3.96, 4.17À4.24 (2 m, 8H, 4SeCH2)
ppm. 12 was prepared by the same procedure as that for 11, but
1,3,5-[ClC(O)]3C6H3 (0.044 g, 0.17 mmol) was used instead of
[ClC(O)]2CH2. From the main red band, 12 was obtained as a red
solid (0.047 g, 16%), mp 136 °C (dec). Anal. Calcd for C39H27Fe6-
N3O24Se6: C, 27.07; H, 1.57; N, 2.43. Found: C, 27.28; H, 1.78; N,
2.41. IR (KBr disk): νCꢀO 2064 (s), 2020 (vs), 1983 (vs); νCdO
1
by comparison of its IR and H NMR spectra to those of the sample
prepared by the method involving reaction of (μ-LiSe)2Fe2(CO)6 with
N,N-bis(chloromethyl)acetamide described above. Similarly, 7 and 8
were prepared by this acylation method, except that MeC(O)Cl used for
preparing 1 was replaced by EtC(O)Cl (0.04 mL, 0.50 mmol) and
PhCH2C(O)Cl (0.07 mL, 0.50 mmol), respectively. From the main red
band, 7 was obtained as a red solid (0.240 g, 89%), mp 110 °C (dec).
Anal. Calcd for C11H9Fe2NO7Se2: C, 24.61; H, 1.69; N, 2.61. Found: C,
24.68; H, 1.79; N, 2.42. IR (KBr disk): νCꢀO 2066 (s), 2035 (vs), 2026
(vs), 2001 (vs), 1985 (vs); νCdO 1683 (s) cmÀ1. 1H NMR (400 MHz,
CDCl3, TMS): 1.16 (t, 3H, J = 6.0 Hz, CH2CH3), 2.29 (q, 2H, J = 6.1
Hz, CH2CH3), 3.95À4.45 (m, 4H, 2SeCH2) ppm. 8 was obtained as a
red solid (0.219 g, 73%), mp 119 °C (dec). Anal. Calcd for C16H11Fe2-
NO7Se2: C, 32.09; H, 1.85; N, 2.34. Found: C, 32.19; H, 1.95; N, 2.39.
IR (KBr disk): νCꢀO 2068 (s), 2026 (vs), 1988 (vs); νCdO 1666
(m) cmÀ1. 1H NMR (400 MHz, CDCl3, TMS): 3.73 (s, 2H, PhCH2),
3.92À4.45 (m, 4H, 2SeCH2), 7.16À7.30 (m, 5H, C6H5) ppm.
1
1730 (m) cmÀ1. H NMR (400 MHz, CDCl3, TMS): 3.19 (s, 6H,
3NCH2CH2O), 3.99À4.27 (m, 18H, 3NCH2CH2O, 6SeCH2), 8.70 (s,
3H, C6H3) ppm.
Preparation of [Fe2(CO)6(μ-SCH2)2N(CH2)2O2C]2(2,6-C5H3N)
(13) and [Fe2(CO)6(μ-SCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (14).
To a red solution of [(μ-SCH2)2N(CH2)2OH]Fe2(CO)6 (0.217 g,
0.50 mmol) in CH2Cl2 (15 mL) were added Et3N (0.33 mL, 2.32 mmol)
and 2,6-[ClC(O)]2C5H3N (0.065 g, 0.32 mmol). The mixture was
stirred at room temperature for 14 h. Solvent was removed in vacuo, and
the residue was subjected to TLC separation using CH2Cl2/petroleum
ether (2:1 v/v) as eluent. From the main red band, 13 was obtained as a
red solid (0.152 g, 61%), mp 66À88 °C. Anal. Calcd for C27H19Fe4-
N3O16S4: C, 32.66; H, 1.93; N, 4.23. Found: C, 32.83; H, 2.18; N, 4.18.
IR (KBr disk): νCꢀO 2075 (s), 2031 (vs), 1995 (vs); νCdO 1727
Preparation of [Fe2(CO)6(μ-SCH2)2NC(O)]2(2,6-C5H3N) (9).
To a stirred solution of [(μ-SCH2)2NH]Fe2(CO)6 (0.192 g, 0.50
mmol) in CH2Cl2 (15 mL) were added Et3N (0.09 mL, 0.68 mmol)
and 2,6-[ClC(O)]2C5H3N (0.051 g, 0.25 mmol). The mixture was
stirred at room temperature for 12 h. Solvent was removed in vacuo, and
the residue was subjected to TLC separation using CH2Cl2/petroleum
ether (2:1 v/v) as eluent. From the main red band, 9 was obtained as
a red solid (0.129 g, 57%), mp 132À133 °C. Anal. Calcd for C23H11Fe4-
N3O14S4: C, 30.52; H, 1.23; N, 4.64. Found: C, 30.76; H, 1.45; N,
4.60. IR (KBr disk): νCꢀO 2080 (s), 2037 (vs), 1999 (vs); νCdO 1654
(m) cmÀ1 1H NMR (400 MHz, CDCl3, TMS): 3.19 (s, 4H,
.
2NCH2CH2O), 3.72 (s, 8H, 4SCH2), 4.30 (s, 4H, 2NCH2CH2O),
8.02, 8.25 (2s, 3H, C5H3N) ppm. 14 was prepared by the same
procedure as that for 13, but 1,3,5-[ClC(O)]3C6H3 (0.044 g, 0.17
mmol) was used instead of 2,6-[ClC(O)]2C5H3N. From the main red
band, 14 was obtained as a red solid (0.129 g, 53%), mp 122À124 °C.
Anal. Calcd for C39H27Fe6N3O24S6: C, 32.32; H, 1.88; N, 2.90. Found:
C, 32.14; H, 2.10; N, 3.17. IR (KBr disk): νCꢀO 2074 (vs), 2031 (vs),
1995 (vs); νCdO 1728 (s) cmÀ1. 1H NMR (400 MHz, CDCl3, TMS):
3.15 (s, 6H, 3NCH2CH2O), 3.66 (s, 12H, 6SCH2), 4.27 (s, 6H,
3NCH2CH2O), 8.73 (s, 3H, C6H3) ppm.
1
(m) cmÀ1. H NMR (400 MHz, CDCl3, TMS): 4.31, 4.50 (2s, 8H,
4SCH2), 8.04 (s, 3H, C5H3N) ppm.
X-ray Structure Determinations of 1À4, 7À9, and 14. Single
crystals of 1À4, 7À9, and 14 suitable for X-ray diffraction analysis were
grown by slow evaporation of the CHCl3/petroleum ether solutions at
about À4 °C. Each crystal was mounted on a Rigaku MM-007 (rotating
anode) diffractometer equipped with Saturn 70CCD. Data were collected at
room temperature, using a confocal monochromator with Mo KR radiation
(λ = 0.71073 Å) in the ωÀϕ scanning mode. Data collection, reduction,
and absorption correction were performed by the CRYSTALCLEAR
program.38 The structures were solved by direct methods using the
SHELXS-97 program39 and refined by full-matrix least-squares techniques
(SHELXL-97)40 on F2. Hydrogen atoms were located by using the
geometric method. Details of crystal data, data collections, and structure
refinements are summarized in Tables 2 and 3, respectively (see Supporting
Information).
Electrochemistry. Acetonitrile (Fisher Chemicals, HPLC grade)
was used for performance of electrochemistry. A solution of 0.1 M
n-Bu4NPF6 in MeCN was used as electrolyte in all cyclic voltammetric
experiments. The electrolyte solution was degassed by bubbling with
CO for about 10 min before measurement. Electrochemical measure-
ments were made using a BAS Epsilon potentiostat. All voltammograms
were obtained in a three-electrode cell with a 3 mm diameter glassy
carbon working electrode, a platinum counter electrode, and an Ag/Ag+
(0.01 M AgNO3/0.1 M n-Bu4NPF6 in MeCN) reference electrode
under CO. The working electrode was polished with 0.05 μm alumina
paste and sonicated in water for about 10 min. Bulk electrolysis was run
on a vitreous carbon rod (A = 2.9 cm2) in a two-compartment, gastight,
Preparation of [(μ-SeCH2)2N(CH2)2OH]Fe2(CO)6 (10). A solu-
tion of (μ-Se2)Fe2(CO)6 (0.438 g, 1.00 mmol) in THF (20 mL) was
cooled to À78 °C, and then Et3BHLi (2.00 mL, 2.00 mmol) was added.
After the mixture was stirred at this temperature for 20 min, trifluoroacetic
acid (0.17 mL, 2.20 mmol) was added, and then the new mixture was stirred
for an additional 20 min. To the resultant mixture, containing (μ-HSe)2Fe2-
(CO)6, was added a THF solution of HO(CH2)2N(CH2OH)2 (prepared
by stirring a mixture of 2-aminoethanol (0.06 mL, 1.00 mmol) and
paraformaldehyde (0.120 g, 4.00 mmol) in THF (14 mL) at room
temperature for 10 h). After the mixture was warmed to room temperature
and stirred for 8 h, solvent was removed in vacuo. The residue was subjected
to column chromatography using CH2Cl2/petroleum ether/MeOH
(5:1:0.17 v/v/v) as eluent under anaerobic conditions. From the main
band, 10 was obtained as a dark red solid (0.202 g, 39%), mp 79À81 °C.
Anal. Calcd for C10H9Fe2NO7Se2: C, 22.89; H, 1.73; N, 2.67. Found: C,
23.16; H, 1.74; N, 2.74. IR (KBr disk): νCꢀO 2064 (s), 2021 (vs), 1983
(vs); νOH 3455 (m) cmÀ1. 1H NMR (300 MHz, CDCl3, TMS): 1.43 (br s,
1H, OH), 2.95 (s, 2H, NCH2CH2OH), 3.52 (s, 2H, NCH2CH2OH),
3.94À3.97, 4.29À4.31 (2 m, 4H, 2SeCH2) ppm.
Preparation of [Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]2CH2 (11)
and [Fe2(CO)6(μ-SeCH2)2N(CH2)2O2C]3(1,3,5-C6H3) (12). To a
red solution of 10 (0.262 g, 0.50 mmol) in CH2Cl2 (15 mL) cooled to
0 °C were added Et3N (0.07 mL, 0.50 mmol) and [ClC(O)]2CH2
(0.024 mL, 0.25 mmol). After the mixture was stirred at 0 °C for 0.5 h, it
was warmed to room temperature and stirred at this temperature for 12
h. Solvent was removed in vacuo, and then the residue was subjected to
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Organometallics
ARTICLE
H-type electrolysis cell containing ca. 25 mL of MeCN. Gas chroma-
tography was performed with a Shimadzu gas chromatograph GC-2014
under isothermal conditions with nitrogen as a carrier gas and a thermal
conductivity detector.
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S
Supporting Information. Full tables of crystal data, atomic
b
coordinates, thermal parameters, and bond lengths and angles for
1À4, 7À9, and 14 as CIF files, as well as Tables 2 and 3. This
material is available free of charge via the Internet at http://pubs.
acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: 0086-22-23504853. E-mail: lcsong@nankai.edu.cn.
’ ACKNOWLEDGMENT
We are grateful to the National Natural Science Foundation
of China (20972073), the Tianjin Natural Science Foundation
(09JCZDJC27900), and 973 (2011CB935902) for financial
support.
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