Synthesis, structure, and photoinduced catalysis of [FeFe]-hydrogenase active site models covalently linked to a porphyrin or metalloporphyrin moiety

Article abstract of DOI:10.1021/om900141x

A series of novel light-driven-type models, which contain a single diiron- ADT(azadithiolate) unit or two and four diiron-ADT units covalently bonded to a photosensitizer porphyrin or metalloporphyrin, have been synthesized and structurally characterized.

Full text of DOI:10.1021/om900141x

3834 Organometallics 2009, 28, 3834–3841
DOI: 10.1021/om900141x
Synthesis, Structure, and Photoinduced Catalysis of [FeFe]-Hydrogenase
Active Site Models Covalently Linked to a Porphyrin or
Metalloporphyrin Moiety†
Li-Cheng Song,* Liang-Xing Wang, Ming-Yi Tang, Chang-Gong Li, Hai-Bin Song, and
Qing-Mei Hu
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University,
Tianjin 300071, People’s Republic of China
Received February 22, 2009
A series of novel light-driven-type models, which contain a single diiron- ADT(azadithiolate)
unit or two and four diiron-ADT units covalently bonded to a photosensitizer porphyrin
or metalloporphyrin, have been synthesized and structurally characterized. Reaction of complex
[( μ-SCH2)2NC6H4CHO]Fe2(CO)6 (A) with PhCHO, pyrrole, and CF3CO2H in CH2Cl2 followed by
treatment with p-chloranil gave light-driven models 5-[( μ-SCH2)2NFe2(CO)6phenyl]-10,15,20-tri-
phenylporphyrin (1), 5,15-[( μ-SCH2)2NFe2(CO)6phenyl]2-10,20-diphenylporphyrin (2), and 5,
10-[( μ-SCH2)2NFe2(CO)6phenyl]2-15,20-diphenylporphyrin (3). While light-driven model 5,10,15,
20-[( μ-SCH2)2NFe2(CO)6phenyl]4porphyrin (4) could be similarly prepared by reaction of complex
A with pyrrole and CF3CO2H followed by treatment with p-chloranil, model 1 could also be prepared
by another new method involving a final cyclization step of ( μ-HOCH2S)2Fe2(CO)6 with
(p-aminophenyl)triphenylporphyrin. In addition, the PPh3-substituted model 5-[( μ-SCH2)2NFe2-
(CO)5(PPh3)phenyl]-10,15,20-triphenylporphyrin (5) was prepared by reaction of 1 with PPh3 in the
presence of Me3NO, whereas treatment of 1 with Zn(OAc)2 afforded the metalloporphyrin-contain-
ing model 5-[( μ-SCH2)2NFe2(CO)6phenyl]-10,15,20-triphenylporphyrinozinc (6). X-ray crystallo-
graphic studies confirmed that (i) model 3 consists of two diiron-ADT units, which are connected to
the two ortho-benzene rings of the porphyrin macrocycle, and (ii) model 6 contains one molecule of
MeOH, which is axially coordinated to the Zn atom of the metalloporphyrin macrocycle. Particularly
noteworthy is that model 1 was found to be a photoactive catalyst for photoinduced H2 production,
and a possible pathway for such H2 production is suggested.
Introduction
ported,1 a great variety of structural and functional model
compounds for the active site of [FeFe]Hases, so-called H-
clusters, have appeared in the literature.2-5 Among these
model compounds, the light-driven-type models (which con-
Since the high-quality crystal structures of [FeFe]-hydro-
genases (hereafter referred to as [FeFe]Hases) were re-
tain a photosensitive cationic complex [Ru(terpyridyl)2]2+ 4c
,
porphyrin macrocycle,4e or metalloporphyrin macrocycle4f
attached to the catalytic diiron subsite) are of particular
interest. This is because such models can allow chemists to
explore if the photoexcited electron could be transferred
intramolecularly from its photosensitive moiety to a diiron
subsite and then could reduce a proton to give hydrogen, a
† Dedicated to Professor Dietmar Seyferth on the occasion of his 80th
birthday and in recognition of his outstanding contributions to organometallic
chemistry.
*To whom correspondence should be addressed. Fax: 0086-22-
23504853. E-mail: lcsong@nankai.edu.cn.
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2009 American Chemical Society
pubs.acs.org/Organometallics
Published on Web 06/11/2009

Article
Organometallics, Vol. 28, No. 13, 2009 3835
highly efficient, “clean”, and renewable fuel.6,7 It follows
that such a study is not only closely related to production
of hydrogen fuel but also closely related to solar energy
utilization.8,9
and the porphyrin-functionalized model compounds 1-3 is
believed to involve cocyclization of complex A with PhCHO
and pyrrole in the presence of catalyst CF3CO2H followed by
oxidation of the resulting porphyrinogens with p-chloranil.
In principle, this synthetic method due to inclusion of the two
different aldehydes of A and PhCHO should produce not
only H2TPP and compounds 1-3 with a single diiron-ADT
unit and two diiron-ADT units but also another two com-
pounds with three and four diiron-ADT units. However, in
this case although H2TPP and 1-3 were obtained, the latter
two compounds were not able to be isolated due to their too
small amounts. Fortunately, one of the latter two, namely,
compound 4, with four diiron-ADT units, was successfully
prepared by using the Lindsey method involving only one
kind of aldehyde. Thus, treatment of A with pyrrole and
CF3CO2H in CH2Cl2 at room temperature followed by
oxidation of the intermediate porphyrinogen at reflux with
p-chloranil in a molar ratio of A:pyrrole:CF3CO2H:p-chlor-
anil = 1:1:1:0.75 resulted in formation of model 4 in 14%
yield (Scheme 2).
In view of the structural characterization of 1 being
described in our communication,4e we now report the struc-
tural characterizations of new compounds 2-4. Compounds
2-4 are air-stable solids. For example, the IR spectra of 2-4
displayed three absorption bands in the range 2075-1992
cm-1 for their terminal carbonyls15 and one absorption band
in the region 3314-3365 cm-1 for N-H vibrations of their
pyrrole rings.16 The 1H NMR spectra of 2-4 each exhibited
one singlet in the region 4.43-4.63 ppm for CH2 groups in
their diiron-ADT units and another singlet in the upfield
range from -2.71 to -2.81 ppm for NH groups in their
pyrrole rings due to strong shielding effects of the porphyrin
macrocycle.17 The mass spectrum of 4 showed a molecular
ion M++H peak at m/z 2154.4961. All observed peaks are
isotopically resolved and in good agreement with their
corresponding theoretical distributions (see Supporting In-
formation). Actually, compound 3 is the isomer of 2, whose
structure was confirmed by X-ray diffraction analysis. While
the molecular structure of 3 is shown in Figure 1, Table 1 lists
its selected bond lengths and angles. As can be seen in
Figure 1, compound 3 contains two diiron-ADT units, which
are covalently connected through the bridgehead N1 and N2
atoms to C15 and C56 of the two ortho-benzene rings. In
addition, the two diiron-ADT units each have a chair and a
boat six-membered ring, whose common N1 and N2 atoms
are bound to C15 or C56 by an axial type of bond. The bond
On the basis of our previous studies on light-driven-type
models,4e,4f we continued to investigate their synthesis,
structure, and properties. Now, we have synthesized a series
of new light-driven models, which contain a photosensitive
porphyrin or metalloporphyrin moiety covalently bonded to
a single diiron-ADT(azadithiolate) unit or two and four
diiron-ADT units. Why we chose porphyrin and metallo-
porphyrin as photosensitizers to construct such models
is because they can absorb as much as ca. 45% of the energy
of sunlight, and the lifetime of their excited triplet states is
much longer than those of common RuII-based photosensi-
tizers.10,11 In addition, we chose diiron-ADT unit to con-
struct this type of models because the ADT bridge was
recently suggested to play a key role in H2 production
catalyzed by natural enzymes.12,13 In this paper we report
the synthetic and structural studies regarding such new light-
driven models. In addition, the photoinduced H2 production
catalyzed by one of such models is also described.
Results and Discussion
Synthesis of Porphyrin-Functionalized Light-Driven Mod-
els 1-4 by the Lindsey Method and Their Structural Char-
acterizations. When p-benzaldehyde-substituted diiron-
ADT complex A reacted with benzaldehyde, pyrrole, and
CF3CO2H in CH2Cl2 at room temperature followed by
treatment of the resulting mixture with p-chloranil at reflux
in a molar ratio of 1:1:2:2:1.5 between the five starting
materials, we isolated four products of tetraphenylporphyrin
(H2TPP) and the porphyrin-functionalized light-driven
model compounds 1-3 in 14%, 18%, 8%, and 17% yields,
respectively (Scheme 1). However, in contrast to this, as
described in our communication,4e with treatment of com-
plex A with benzaldehyde, pyrrole, and CF3CO2H in CH2Cl2
at room temperature followed by treatment with p-chloranil
at reflux in a molar ratio of 1:3:4:4:3 between the five starting
materials, only two compounds, namely, H2TPP and 1,
could be obtained, in 19% and 23% yields, without obtain-
ing any appreciable amounts of 2 and 3. Such observations
imply that both types and yields of the porphyrin-containing
model compounds produced from the Lindsey method14 are
substantially influenced by the utilized molar ratio of the five
starting materials.
˚
˚
lengths of Fe1-Fe2 (2.5013 A) and Fe3-Fe4 (2.5049 A)
˚
According to the reported mechanistic study of the Lind-
sey method,14 the above-mentioned formation of H2TPP
in 3 are almost the same as that of Fe1-Fe2 (2.5000 A) in 1
and very close to those found in similar diiron carbonyl
complexes.18 The C-N bond lengths (1.356-1.377 A) in the
˚
porphyrin macrocycle of 3 are nearly the same as the
˚
(6) Lubitz, W.; Tumas, W. Chem. Rev. 2007, 107, 3900.
(7) Alper, J. Science 2003, 299, 1686.
corresponding ones (1.364-1.378 A) of 1, lying between
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1981, 14, 376. (b) Bard, A. J.; Fox, M. A. Acc. Chem. Res. 1995, 28, 141.
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Principles and Applications of Organotransition Metal Chemistry, 2nd
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Darensbourg, M. Y. Angew. Chem., Int. Ed. 1999, 38, 3178. (c) Song,
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Marguerettaz, A. M. J. Org. Chem. 1987, 52, 827.

3836 Organometallics, Vol. 28, No. 13, 2009
Song et al.
Scheme 1
Scheme 2
the normal single and double C-N bond lengths.19 The four
benzene rings are twisted with respect to the planar porphyr-
in macrocycle in order to minimize the steric repulsions
between the two ortho-hydrogen atoms in each of the four
phenyl groups with the two proximal pyrrole rings. The
dihedral angles between the porphyrin plane and the benzene
rings involving C18 and C53 are 71.9° and 87.7°, respec-
tively. It follows that the spectroscopic data of 2-4 and the
crystallographic data of 3 are very similar to the correspond-
ing data of 14e and coincide very well with their structures
shown in Schemes 1 and 2.
Synthesis of Light-Driven Model 1 by a New Method and Its
Reactions with PPh3 and Zn(OAc)2 to Give Porphyrin- and
Metalloporphyrin-Functionalized Light-Driven Models 5 and
6. Model 1 couldbeprepared by another synthetic method in a
much higher yield (43%). This method involves a “one-pot”
reaction of the bridging thiol complex ( μ-HS)2Fe2(CO)6 (pre-
pared by reaction of ( μ-S2)Fe2(CO)6 with Et3BHLi followed
by treatment of ( μ-LiS)2Fe2(CO)6 with CF3CO2H)20 with
(19) (a) Silvers, S. J.; Tulinsky, A. J. Am. Chem. Soc. 1967, 89, 3331.
(b) Sessler, J. L.; Johnson, M. R.; Creager, S. E.; Fettinger, J. C.; Ibers, J.
A. J. Am. Chem. Soc. 1990, 112, 9310.
(20) Seyferth, D.; Henderson, R. S.; Song, L.-C. J. Organomet. Chem.
1980, 192, C1.

Article
Organometallics, Vol. 28, No. 13, 2009 3837
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for 3
Fe(1)-S(1)
Fe(1)-S(2)
Fe(2)-S(2)
Fe(2)-S(1)
2.266(2)
2.269(2)
2.259(2)
2.279(3)
N(1)-C(15)
Fe(1)-Fe(2)
Fe(3)-Fe(4)
N(3)-C(22)
1.413(7)
2.5013(17)
2.5049(7)
1.367(7)
S(1)-Fe(1)-S(2)
S(1)-Fe(1)-Fe(2)
S(2)-Fe(1)-Fe(2)
S(2)-Fe(2)-S(1)
84.72(7)
56.85(7)
56.27(5)
84.67(8)
S(2)-Fe(2)-Fe(1)
N(3)-C(22)-C(21)
C(13)-N(1)-C(14)
C(22)-N(3)-C(25)
56.67(6)
126.4(5)
114.1(5)
111.1(4)
˚
to the corresponding one (2.55 A) in the reduced form of the
natural enzymes.12 In addition, as can be seen in Figure 3,
there is one molecule of MeOH axially coordinated to the
˚
Zn1 atom with a Zn1-O8 bond length of 2.179 A. The
coordinated MeOH apparently originated from the mixed
solvent CHCl3/MeOH used in the single-crystal growing
process. The sum of bond angles around N5 is 356.7°, a
value very close to 360°, implying that the p-orbital of the N5
atom is well conjugated with the π-system of the disubsti-
tuted benzene ring. In addition, the four benzene rings
around the metalloporphyrin moiety are twisted relative to
the porphyrin plane with a dihedral angle from 61.2° to 68.1°
in order to reduce the steric repulsions between the proximal
hydrogen atoms of the benzene and pyrrole rings in the
metalloporphyrin macrocycle.
Figure 1. Molecular structure of 3 with 30% probability level
ellipsoids.
Photoinduced Hydrogen Evolution Catalyzed by Light-
Driven Model 1. The photoinduced catalytic systems for H2
production usually consist of four separate components: an
electron donor, a photosensitizer, a catalyst, and a proton
source.22-26 However, recently a three-component system
was used for study of the photoinduced H2 production.27
This system is composed of an electron donor, a proton
source, and a light-driven model that contains a photosensi-
tizer ZnTPP coordinatively bonded to a simple H-cluster
model. It is worth pointing out that this coordinatively
assembled model (in fact, it was not isolated and fully
characterized; for the isolated and fully characterized one,
see ref 4f) is different from our covalently assembled light-
driven models 1-6. In order to examine if such covalently
assembled models could act as photoactive catalysts to
achieve the expected H2 production, we chose model 1 to
constitute a three-component system with electron donor
and proton source, which was utilized to carry out the
expected H2 production experiments.
Interestingly, it was found that H2 indeed was produced
when a 500 W Hg lamp with a UV cutoff filter (λ >400 nm)
irradiated a CH2Cl2 solution consisting of model 1, electron
donor EtSH, and proton source CF3CO2H (TFA) (entry 1,
Table 3). However, when the same experiment was carried
out in the absence of EtSH or TFA, only a trace amount of
H2 could be detected (entries 2/3, Table 3). Furthermore,
no H2 was delected when the experiment was run without
light irradiation or in the absence of model 1, or in the
case in which model 1 was replaced by an equimolar
mixture of photosensitizer H2TPP and simple model
37% aqueous formaldehyde in THF from -78 °C to room
temperature and subsequent treatment of the resulting com-
plex ( μ-HOCH2S)2Fe2(CO)6 with (p-aminophenyl)triphe-
nylporphyrin (Scheme 3).
21
On the basis of the improved synthesis of model 1, we
further studied its chemical reactivities, leading to the pre-
paration of its PPh3 and porphyrinozinc derivatives. Thus,
treatment of 1 with 1 equiv of decarbonylating agent Me3NO
in mixed solvent CH2Cl2/MeCN at room temperature fol-
lowed by treatment with 1 equiv of PPh3 resulted in forma-
tion of the PPh3-monosubstituted derivative 5 in 46% yield,
whereas 1 was treated with excess Zn(OAc)2 in MeOH at
room temperature to afford the photosensitizer ZnTPP-
containing model compound 6 in 91% yield (Scheme 4).
Compounds 5 and 6 are air-stable solids, which were
1
characterized by elemental analysis and IR and H NMR
spectroscopy, as well as for 6 by X-ray crystallography. The
IR spectra of 5 and 6 showed three absorption bands in the
region 2043-1933 or 2073-1998 cm-1 for their terminal
carbonyls, respectively. The former three bands for 5 are
considerably red-shifted relative to those corresponding to
1-4 and 6, obviously due to one of their carbonyls being
replaced by the stronger electron donor PPh3.15 The 1H
NMR spectrum of 5 displayed one singlet at -2.76 ppm
for the two protons attached to N atoms in its pyrrole rings,17
but in that of 6 this type of singlet disappeared, consistent
with the two protons of 1 being replaced by metal cation
Zn2+. The 31P NMR spectrum of 5 exhibited one singlet at
65.66 ppm for the P atom in its PPh3 ligand. The molecular
structure of 6 was unambiguously confirmed by X-ray
crystallography. Figure 2 shows its ORTEP plot, whereas
Table 2 lists its selected bond lengths and angles. As shown in
Figure 2, compound 6 comprises one diiron-ADT unit and
one metalloporphyrin moiety, which are covalently bonded
together through N5 and C42 atoms by an axial type of
(22) Ozawa; Haga, M.; Sakai, K. J. Am. Chem. Soc. 2006, 128, 4926.
(23) Rau, S.; Walther, D.; Vos, J. G. Dalton Trans. 2007, 915.
(24) Fihri, A.; Artero, V.; Razavet, M.; Baffert, C.; Leibl, W.;
Fontecave, M. Angew. Chem., Int. Ed. 2008, 47, 564.
(25) Rosenthal, J.; Bachman, J.; Dempsey, J. L.; Esswein, A. J.; Gray,
T. G.; Hodgkiss, J. M.; Manke, D. R.; Luckett, T. D.; Pistorio, B. J.;
Veige, A. S.; Nocera, D. G. Coord. Chem. Rev. 2005, 249, 1316.
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gen Energy 2002, 27, 621.
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bond. The Fe1-Fe2 bond length of 6 (2.500 A) is very close
˚
(21) Stanley, J. L.; Rauchfuss, T. B.; Wilson, S. R. Organometallics
2007, 26, 1907.
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B.; Sun, L. J. Phys. Chem. B 2008, 112, 8198.

3838 Organometallics, Vol. 28, No. 13, 2009
Song et al.
Scheme 3
Scheme 4
(0.31) found by using the covalently assembled complex 1 is
considerably low relative to those obtained by using the
other types of covalently assembled photocatalysts,22,24 it is
the first example to realize such H2 prodution by using the
covalently assembled H-cluster model as a photoactive
catalyst.
According to our above-mentioned observations and
some reported mechanisms for similar cases,11,28 we suggest
a pathway to accout for the photoinduced H2 production
catalyzed by light-driven model 1 (Figure 4). That is, when
model 1 is irradiated, the electron of the porphyrin moiety of
1 can be excited to give 1*. Then, the photoexcited electron
can be transferred intramolecularly to the diiron-ADT unit
to give the charge-separated species 1(. After 1( reduces a
proton to give H2, it becomes 1+ with a positive charge on
the porphyrin moiety of 1. Furthermore, when 1+ gets one
electron from the sacrificial electron donor D, the photo-
catalyst 1 is regenerated and the catalytic cycle is completed.
Finally, it should be noted that this proposed pathway is
mainly speculative and some of its suggested intermediates
still need to be further identified.
[( μ-SCH2)2NH]Fe2(CO)6 (HADT) (entries 4-6, Table 3). It
follows that electron donor EtSH, proton source TFA, light-
driven model 1, and the light irradiation are essential for such
photoinduced H2 production. In addition, the experiments
(entries 1/5, Table 3) proved that the separated photosensi-
tive and catalytic moieties cannot replace the corresponding
light-driven model 1 to achieve such photoinduced H2 pro-
duction. In fact, this is consistent with our previous com-
parative study4e on the fluorescence emission spectrum of
model 1 with those of H2TPP and an equimolar mixture of
H2TPP and HADT, which revealed that an efficient intra-
molecular electron transfer occurs from the photoexcited
porphyrin moiety to the covalently linked diiron-ADT unit,
but not the intermolecular electron transfer between the two
separate components H2TPP and HADT. Figure 3 shows the
time dependence of photoinduced H2 production by using
EtSH and p-HSC6H4CO2H as electron donors. As can be
seen in Figure 3, during 1 h irradiation the turnover number
(TON, calculated based on the catalytic diiron subsite) in the
EtSH case reaches 0.31, whereas that in the p-HSC6H4CO2H
case is equal to 0.14. This means that EtSH is a better
electron donor than p-HSC6H4CO2H. Although the TON
Concluding Remarks
We have synthesized six novel light-driven models, 1-6,
by the Lindsey method with some modifications, as well as
by Me3NO-assisted CO substitution of 1 with PPh3 and by
porphyrin N coordination of 1 with metal cation Zn2+. In
addition, we have also prepared model 1 in a much higher
yield by another method involving a final cyclization step
between (μ-HOCH2S)2Fe2(CO)6 and (p-aminophenyl)tri-
phenylporphyrin. The structural characterization of 1-6
revealed that (i) model 1 contains a photosensitive tetraphe-
nylporphyrin moiety covalently bonded to the N atom of a
single diiron-ADT unit, (ii) models 2-4 consist of a tetra-
phenylporphyrin moiety covalently bonded to each N atom
of the two and four diiron-ADT units, and (iii) models 5 and
6 contain a porphyrin moiety or a metalloporphyrin moiety,
which is covalently bonded to the N atom of either the all-CO
diiron-ADT unit or the PPh3-substituted diiron-ADT unit.
(28) (a) Okura, I.; Kinumi, Y. Bull. Chem. Soc. Jpn. 1990, 63, 2922.
(b) Miller, D.; McLendon, G. Inorg. Chem. 1981, 20, 950. (c) Amao, Y.;
Tomonou, Y.; Okura, I. Sol. Energy Mater. Sol. Cells 2003, 79, 103.

Article
Organometallics, Vol. 28, No. 13, 2009 3839
Figure 2. Molecular structure of 6 MeOH with 30% probability level ellipsoids.
3
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for 6
Fe(1)-S(1)
Fe(1)-S(2)
Fe(2)-S(2)
Fe(2)-S(1)
2.283(3)
2.275(3)
2.268(3)
2.285(3)
N(5)-C(42)
Fe(1)-Fe(2)
N(1)-C(1)
N(1)-Zn(1)
1.419(9)
2.500(2)
1.375(8)
2.069(6)
S(1)-Fe(1)-S(2)
S(1)-Fe(1)-Fe(2)
S(2)-Fe(1)-Fe(2)
S(2)-Fe(2)-S(1)
85.08(9)
56.86(6)
56.48(8)
85.18(8)
Fe(1)-S(1)-Fe(2)
C(46)-N(5)-C(45)
C(1)-N(1)-Zn(1)
N(1)-Zn(1)-N(3)
66.37(8)
113.6(6)
126.0(4)
166.8(2)
Interestingly, the covalently assembled light-driven model 1
was found to be a catalyst for H2 production in the presence
of a suitable electron donor and the proton source TFA
under light irradiation. A possible pathway for such photo-
induced H2 production is suggested, which involves an
intramolecular electron transfer process from the photosen-
sitive porphyrin moiety to the catalytic diiron-ADT unit.
Further studies are in progress to see if the more diiron-
ADT-units-containing models 2-4 and the metalloporphyr-
in-containing model 6 could have higher photocatalytic
activity than model 1. In addition, further structural mo-
difications of models 1-4 to improve their photocatalytic
capability will also be carried out by means of the facile
substitution of their Fe-attached terminal carbonyls with
other ligands2c and the potential coordination capability of
their porphyrin macrocycles with other metal cations.10,11
Figure 3. Time dependence of photoinduced H2 production from
CH2Cl2 solutions (10 mL) consisting of EtSH (9, 10 mM) or
p-HSC6H4CO2H (4, 10 mM) and TFA (10 mM) catalyzed by
model 1 (0.1 mM).
CH2O, pyrrole, benzaldehyde, CF3CO2H, tetrachlorobenzo-
quinone (p-chloranil), Me3NO 2H2O, PPh3, EtSH, and
3
p-HSC6H4CO2H were available commercially and used as
received. Preparative TLC was carried out on glass plates
(25 Â 15 Â 0.25) coated with silica gel G (10-40 μm). IR spectra
were recorded on a Bio-Rad FTS 135 infrared spectrophoto-
meter. 1H and 31P NMR spectra were taken on a Bruker
Avance 300 and a Varian Mercury Plus 400 NMR spectrometer,
respectively. Elemental analyses were performed with an Ele-
mentar Vario EL analyzer, while ESI-MS data were obtained on
a Bruker APEX IV FT-MS instrument operated in ESI positive
mode. Melting points were determined on a Yanaco MP-500
apparatus and were uncorrected.
Experimental Section
General Comments. All reactions were carried out under an
atmosphere of highly purified nitrogen by using standard
Schlenk and vacuum-line techniques. Dichloromethane was
distilled from CaH2 under N2, methanol from Mg powders,
and tetrahydrofuran from Na/benzophenone ketyl. Acetonitrile
was distilled once from P2O5 and then from CaH2 under N2.
( μ-S)2Fe2(CO)6,29 [( μ-SCH2)2NC6H4CHO]Fe2(CO)6 (A),4e
and (p-aminophenyl)triphenylporphyrin17a were prepared ac-
cording to literature procedures. Et3BHLi, Zn(OAc)2, aqueous
Preparation of 5-[( μ-SCH2)2NFe2(CO)6phenyl]-10,15,20-tri-
phenylporphyrin (1), 5,15-[( μ-SCH2)2NFe2(CO)6phenyl]2-10,20-
diphenylporphyrin (2), and 5,10-[( μ-SCH2)2NFe2(CO)6phenyl]2-
15,20-diphenylporphyrin (3) by the Lindsey Method Involving
PhCHO and Substituted Benzaldehyde A. The mixture of sub-
stituted benzaldehyde A (0.295 g, 0.60 mmol), PhCHO (0.06
mL, 0.60 mmol), pyrrole (0.08 mL, 1.2 mmol), and CF3CO2H
(0.09 mL, 1.2 mmol) in CH2Cl2 (240 mL) was stirred at room
(29) Seyferth, D.; Henderson, R. S.; Song, L.-C. Organometallics
1982, 1, 125.

3840 Organometallics, Vol. 28, No. 13, 2009
Song et al.
Table 3. Photocatalytic H2 Production Experiments in CH2Cl2
Solutions by Using EtSH as the Sacrificial Electron Donora
electron
donor
proton
source
irradiation
time
entry
photocatalyst
TON
1
2
3
4
5
6
model 1
model 1
model 1
model 1
H2TPP/HADT
EtSH
TFA
TFA
1 h
1 h
1 h
0.31
<0.01
<0.01
0
0
0
EtSH
EtSH
EtSH
EtSH
TFA
TFA
TFA
1 h
1 h
a TONs are calculated based on model 1.
temperature in the dark for 15 h to give a purple-red solution. To
this solution was added p-chloranil (0.221 g, 0.90 mmol), and the
new mixture was refluxed for 1 h to give a brown-green solution.
Solvent was removed at reduced pressure, and the residue was
subjected to flash column chromatography (Al2O3, CH2Cl2).
The eluate was evaporated at reduced pressure to a volume
suitable for TLC separation using CH2Cl2/petroleum ether
(v/v = 1:1) as eluent. From the first band, H2TPP (0.013 g,
14%) was obtained as a purple solid, which was identified by
Figure 4. Proposed photocatalytic pathway for H2 production
catalyzed by model 1.
solution. Solvent was removed at reduced pressure, and the
residue was subjected to flash column chromatography (Al2O3,
CH2Cl2). The eluate was evaporated in vacuo to a suitable
volume for TLC separation using CH2Cl2/acetone (v/v=1:1)
as eluent. From the first band, 4 (0.092 g, 57%) was obtained as a
purple solid, mp 156 °C (dec). Anal. Calcd for C76H42Fe8-
N8O24S8: C, 42.37; H, 1.96; N, 5.20. Found: C, 42.11; H, 1.95;
N, 5.29. IR (KBr disk): νNH 3365 (m); νCtO 2075 (vs), 2033 (vs),
1
comparison of its IR and H NMR spectra with those of the
authentic sample.17,18
From the second band, model compound 1 (0.036 g, 18%)
was obtained as a purple-red solid, which was also identified by
comparison of its IR and 1H NMR spectra with those previously
reported.14 From the third band, compound 2 (0.032 g, 8%) was
obtained as a purple-red solid, mp 220 °C (dec). Anal. Calcd for
C60H36Fe4N6O12S4: C, 52.05; H, 2.62; N, 6.07. Found: C, 52.24;
H, 2.69; N, 5.87. IR (KBr disk): νNH 3325 (m); νCtO 2075 (s),
2034 (vs), 1992 (vs) cm-1. 1H NMR (300 MHz, CDCl3): -2.81
(s, 2H, 2NH), 4.43 (s, 8H, 4CH2), 6.92, 6.94 (2s, 4H, 4 m-H of
C6H4), 7.66, 7.68 (2s, 6H, 4 m-H of C6H5, 2 p-H of C6H5), 8.00,
8.03 (2s, 4H, 4 o-H of C6H4), 8.13, 8.15 (2s, 4H, 4 o-H of C6H5),
8.77 (s, 8H, pyrrole rings) ppm. From the fourth band, 3 (0.070
g, 17%) was obtained as a purple-red solid, mp 214 °C (dec).
Anal. Calcd for C60H36Fe4N6O12S4: C, 52.05; H, 2.62; N, 6.07.
Found: C, 51.97; H, 2.87; N, 5.93. IR (KBr disk): νNH 3314 (m);
1
1998 (vs) cm-1. H NMR (300 MHz, CDCl3): -2.71 (s, 2H,
2NH), 4.63 (s, 16H, 8CH2), 7.13, 7.16 (2s, 8H, 8 m-H of C6H4),
8.17, 8.19 (2s, 8H, 8 o-H of C6H4), 8.88 (s, 8H, pyrrole rings)
ppm. ESI-MS: m/z 2154.4961 [M++H].
Preparation of 5-[( μ-SCH2)2NFe2(CO)5(PPh3)phenyl]-10,15,20-
triphenylporphyrin (5) by CO Substitution of 1 with PPh3. A
solution of Me3NO 2H2O (0.004 g, 0.034 mmol) in MeCN
3
(5 mL) was added gradually to a stirred solution of model
1 (0.034 g, 0.034 mmol) in CH2Cl2 (10 mL) at room temperature.
After the mixture was stirred at this temperature for 20 min,
PPh3 (0.010 g, 0.034 mmol) was added and the new mixture
was stirred at room temperature for 1 h. Volatiles were removed
under vacuum, and the residue was subjected to TLC using
CH2Cl2/petroleum ether (v/v = 1:1) as eluent. From the main
band, compound 5 (0.018 g, 46%) was obtained as a purple-red
solid, mp 195 °C (dec). Anal. Calcd for C69H48Fe2N5O5PS2:
C, 67.16; H, 3.92; N, 5.68. Found: C, 67.13; H, 3.91; N, 5.75. IR
ν
CtO 2073 (vs), 2034 (vs), 1997 (vs) cm-1. 1H NMR (300 MHz,
CDCl3): -2.74 (s, 2H, 2NH), 4.57 (s, 8H, 4CH2), 7.06, 7.09 (2s,
4H, 4 m-H of C6H4), 7.75, 7.77 (2s, 6H, 4 m-H of C6H5, 2 p-H of
C6H5), 8.12, 8.15 (2s, 4H, 4 o-H of C6H4), 8.21, 8.24 (2s, 4H, 4
o-H of C6H5), 8.86 (s, 8H, pyrrole rings) ppm.
Preparation of 5-[( μ-SCH2)2NFe2(CO)6phenyl]-10,15,20-tri-
phenylporphyrin (1) by a New Method. A red solution of
( μ-S)2Fe2(CO)6 (0.172 g, 0.50 mmol) in THF (10 mL) was cooled
to -78 °C and then treated dropwise with Et3BHLi (1.0 mL,
1.0 mmol) to give a green solution containing ( μ-LiS)2Fe2(CO)6.
After stirring for 15 min, CF3CO2H (0.16 mL, 2.0 mmol) was
added to cause an immediate color change from green to red,
indicating the complete conversion of ( μ-LiS)2Fe2(CO)6 to
( μ-HS)2Fe2(CO)6. After the mixture was stirred for an addi-
tional 10 min at -78 °C, 37% aqueous formaldehyde (0.085 mL,
1.0 mmol) was added. The new mixture was allowed to warm to
room temperature and stirred at this temperature for 1 h to give
( μ-HOCH2S)2Fe2(CO)6. After ( p-aminophenyl)triphenylpor-
phyrin (0.30 g, 0.50 mmol) was added, the new mixture was
stirred at room temperature for 1.5 h. Solvent was removed in
vacuo, and the residue was subjected to TLC using CH2Cl2/
petroleum ether (v/v=2:1) as eluent. From the purple band,
1 (0.215 g, 43%) was obtained as a purple-red solid.
Preparation of 5,10,15,20-[( μ-SCH2)2NFe2(CO)6phenyl]4por-
phyrin (4) by the Lindsey Method Involving Only the Substituted
Benzaldehyde A without PhCHO. A solution of A (0.147 g, 0.30
mmol), pyrrole (0.021 mL, 0.30 mmol), and CF3CO2H (0.023
mL, 0.30 mmol) in CH2Cl2 (30 mL) was stirred at room
temperature in the dark for 24 h to give a purple-red solution.
To this solution was added p-chloranil (0.055 g, 0.225 mmol),
and the new mixture was refluxed for 1 h to give a brown-green
(KBr disk): νNH 3317 (m); νCtO 2043 (vs), 1985 (vs), 1933 (s) cm-1
.
1H NMR (300 MHz, CDCl3): -2.76 (s, 2H, 2NH), 3.21, 4.41,
4.44 (3s, 4H, 2CH2), 6.97, 6.99 (2s, 2H, 2 m-H of C6H4), 7.51 (s, 9H,
3 p-H and 6 m-H of P(C6H5)3), 7.75 (s, 9H, 3 p-H and 6 m-H
of C6H5), 7.85 (s, 6H, 6 o-H of P(C6H5)3), 8.05, 8.07 (2s, 2H,
2 o-H of C6H4), 8.21, 8.23 (2s, 6H, 6 o-H of C6H5), 8.84 (s, 8H,
pyrrole rings) ppm. 31P NMR (121 MHz, CDCl3, 85% H3PO4):
65.66 (s) ppm.
Preparation of 5-[( μ-SCH2)2NFe2(CO)6phenyl]-10,15,20-tri-
phenylporphyrinozinc (6) by Coordination Reaction of 1 with Zn-
(OAc)2. To a saturated MeOH solution (2 mL) of Zn(OAc)2 was
added model 1 (0.100 g, 0.100 mmol), and then the mixture was
stirred at room temperature for 10 h. The resulting mixture was
filtered, and the filtrate was sequentially washed using an
aqueous solution saturated with NaHCO3 or NaCl. The sepa-
rated organic layer was dried with anhydrous MgSO4. After
removal of MgSO4, volatiles were evaporated under vacuum
and the residue was subjected to TLC using CH2Cl2/petroleum
ether (v/v = 2:1) as eluent. From the main band, compound 6
(0.097 g, 91%) was obtained as a purple-red solid, mp 220 °C
(dec). Anal. Calcd for C52H31Fe2N5O6S2Zn: C, 58.75; H, 2.94;
N, 6.59. Found: C, 58.51; H, 3.10; N, 6.47. IR (KBr disk): νCtO
2073 (s), 2034 (vs), 1998 (vs) cm-1. 1H NMR (400 MHz, CDCl3):
4.38 (s, 4H, 2CH2), 6.99, 7.01 (2s, 2H, 2 m-H of C6H4), 7.75-
7.77 (m, 9H, 3 p-H and 6 m-H of C6H5), 8.14, 8.16 (2s, 2H, 2 o-H

Article
Organometallics, Vol. 28, No. 13, 2009 3841
Table 4. Crystal Data and Structure Refinement Details for 3 and 6
lysis, the evolved H2 was withdrawn periodically using a gastight
syringe, which was analyzed by gas chromatography on a
Shimadazu GC-2014 instrument with a thermal conductivity
detector and a carbon molecular sieve column (3 mmÂ2.0 m)
and N2 as the carrier gas. The total amount of H2 produced
during 1 h irradiation is 0.31Â10-3 mmol when using EtSH,
whereas the corresponding amount of H2 is 0.14Â10-3 mmol
when EtSH was replaced by p-HSC6H4CO2H.
3
6
mol formula
C
60H36Fe4N6O12 C52H31Fe2N5O6
S4 C6H4Cl2 S2Zn 2MeOH
3
3
mol wt
cryst syst
space group
1531.58
triclinic
P1
1127.09
triclinic
P1
˚
a/A
12.306(8)
16.377(10)
18.815(11)
106.470(5)
100.242(9)
105.804(9)
3363(4)
2
17.693(15)
17.919(15)
19.180(17)
109.077(8)
110.158(13)
102.100(2)
5026(7)
4
X-ray Structure Determination of 3 and 6. Single crystals of 3
suitable for X-ray diffraction analysis were grown by slow
evaporation of its o-Cl2C6H4/hexane solution at room tempera-
ture, whereas those of 6 were obtained by slow diffusion of
MeOH into its CHCl3 solution at room temperature. A single
crystal of 3 or 6 was mounted on a Rigaku MM-007 (rotating
anode) diffractometer equipped with a Saturn 70CCD. Data
were collected at room temperature, using a confocal mono-
˚
b/A
˚
c/A
R/deg
β/deg
γ/deg
3
˚
V/A
Z
Dc/g cm-3
abs coeff/mm-1
F(000)
1.513
1.114
1552
1.489
1.186
2304
˚
chromator with Mo KR radiation (λ = 0.71070 A) in the ω-φ
scanning mode. Data collection, reduction, and absorption
correction were performed by the CRYSTALCLEAR pro-
gram.31 The structures were solved by direct methods using
the SHELXS-97 program32 and refined by full-matrix least-
squares techniques (SHELXL-97)33 on F2. Hydrogen atoms
were located by using the geometric method. Details of crystal
data, data collections, and structure refinements are summar-
ized in Table 4.
index ranges
-14 e h e 14
-19 e k e 19
-22 e l e 22
50
30 324
11 775
1.093
0.0753
0.1872
-20 e h e 21
-21 e k e 21
-21 e l e 22
50.02
37 545
17 379
1.112
0.0865
0.1826
2θmax/deg
no. of rflns
no. of indep rflns
goodness of fit
R
Rw
largest diff peak and hole/e A
-3
˚
0.577 and -0.625 0.746 and -0.681
Acknowledgment. We are grateful to the National
Natural Science Foundation of China and the Research
Fund for the Doctoral Program of Higher Education of
China for financial support.
of C6H4), 8.22, 8.24 (2s, 6H, 6 o-H of C6H5), 8.96, 8.98 (2s, 8H,
pyrrole rings) ppm.
Photoinduced H2 Evolution Catalyzed by Light-Driven Model
1. A 30 mL Schlenk flask equipped with a N2 inlet tube, a serum
cap, a magnetic stir-bar, and a water-cooling jacket was charged
with model 1 (1 mg, 0.001 mmol), EtSH (7 μL, 0.1 mmol) or
p-HSC6H4CO2H (15 mg, 0.1 mmol), CF3CO2H (7 μL, 0.1
mmol), and CH2Cl2 (10 mL). While stirring, the resulting
solution was thoroughly deoxygenated by bubbling with nitro-
gen and then was irradiated through a Pyrex-glass filter (λ>400
nm) using a 500 W Hg lamp at about 25 °C (controlled by the
cooling jacket) for 1 h. The purpose of using such a UV cutoff
filter is to obtain visible light and to avoid decomposition of
EtSH and p-HSC6H4CO2H.30 During the photoinduced cata-
Supporting Information Available: Full tables of crystal data,
atomic coordinates, and thermal parameters and bond lengths
and angles for 3 and 6 as CIF files. The ESI-MS spectrum of 4.
These materials are available free of charge via the Internet at
http://pubs.acs.org.
(31) Sheldrick, G. M. SADABS, A Program for Empirical Absorption
€
Correction of Area Detector Data; University of Gottingen: Germany,
1996.
(32) Sheldrick, G. M. SHELXS97, A Program for Crystal Structure
€
Solution; University of Gottingen: Germany, 1997.
(33) Sheldrick, G. M. SHELXL97, A Program for Crystal Structure
(30) Weiss, J.; Fishgold, H. Nature 1936, 137, 71.
€
Refinement; University of Gottingen: Germany, 1997.