Synthesis, structures, and properties of diiron azadithiolate complexes containing a subphthalocyanine moiety as biomimetic models for [FeFe]-hydrogenases

Article abstract of DOI:10.1002/ejic.201300038

The first two model compounds for [FeFe]-hydrogenases that contain a subphthalocyanine (SubPc) macrocycle, namely, [{(μ-SCH₂) ₂N(CH₂)₂CO₂-3-C₆H ₄S₂C₆H₄-3′-O(SubPc)}Fe ₂(CO)₆] (5) and [{(μ-SCH₂) ₂NC₆H₄-4-O(SubPc)}Fe₂(CO) ₆] (8), have been synthesized and structurally characterized. The treatment of chlorosubphthalocyanine (SubPc-Cl, 1) with (3-HOC₆H ₄S)₂ in toluene gave the corresponding phenoxy-substituted SubPc derivative 3-HOC₆H₄S₂C₆H ₄-3′-O(SubPc) (2) in 78 % yield, whereas the reaction of in-situ-generated [(μ-HOCH₂S)₂Fe₂(CO) ₆] (3) with β-alanine afforded diiron complex [{(μ-CH ₂S)₂N(CH₂)₂CO₂H}Fe ₂(CO)₆] (4) in 53 % yield. Further treatment of 2 with 4 in the presence of N,N′-dicyclocarbodiimide (DCC) and N,N-dimethyl-4- aminopyridine (DMAP) in CH₂Cl₂ resulted in the formation of model compound 5 in 86 % yield. Model compound 8 could be prepared by two methods. One method involves the reaction of in-situ-generated 3 with 4-aminophenol in tetrahydrofuran (THF) to give diiron complex [{(μ-CH ₂S)₂NC₆H₄OH-4}Fe₂(CO) ₆] (6) in 61 % yield and further treatment of SubPc-Cl (1) with 6 in toluene to give 8 in 13 % yield. The other method involves the reaction of SubPc-Cl (1) with silver triflate (AgOTf) followed by treatment of the resulting intermediate SubPc-OTf (7) with 6 in the presence of Et₃N to produce 8 in a much higher yield (59 %). All the new precursors (2, 4, and 6) and the model compounds 5 and 8 have been fully characterized by elemental analysis and various spectroscopy techniques, as well by X-ray crystallography for 2, 4, 6, and 8. In addition, the photoinduced H₂ production catalyzed by model 8 was preliminarily investigated. Copyright

Full text of DOI:10.1002/ejic.201300038

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DOI:10.1002/ejic.201300038
Synthesis, Structures, and Properties of Diiron
Azadithiolate Complexes Containing a Subphthalocyanine
Moiety as Biomimetic Models for [FeFe]-Hydrogenases
Li-Cheng Song,*[a] Fei-Xian Luo,[a] Hao Tan,[a] Xiao-Jing Sun,[a]
Zhao-Jun Xie,[a] and Hai-Bin Song[a]
Keywords: Enzyme models / Metalloenzymes / Hydrogenases / Iron / Sulfur / Subphthalocyanine
The first two model compounds for [FeFe]-hydrogenases that
contain a subphthalocyanine (SubPc) macrocycle, namely,
[{(μ-SCH2)2N(CH2)2CO2-3-C6H4S2C6H4-3Ј-O(SubPc)}Fe2-
(CO)6] (5) and [{(μ-SCH2)2NC6H4-4-O(SubPc)}Fe2(CO)6] (8),
have been synthesized and structurally characterized. The
treatment of chlorosubphthalocyanine (SubPc-Cl, 1) with (3-
HOC6H4S)2 in toluene gave the corresponding phenoxy-sub-
stituted SubPc derivative 3-HOC6H4S2C6H4-3Ј-O(SubPc) (2)
in 78% yield, whereas the reaction of in-situ-generated [(μ-
HOCH2S)2Fe2(CO)6] (3) with β-alanine afforded diiron com-
plex [{(μ-CH2S)2N(CH2)2CO2H}Fe2(CO)6] (4) in 53% yield.
Further treatment of 2 with 4 in the presence of N,NЈ-dicy-
clocarbodiimide (DCC) and N,N-dimethyl-4-aminopyridine
(DMAP) in CH2Cl2 resulted in the formation of model com-
pound 5 in 86% yield. Model compound 8 could be prepared
by two methods. One method involves the reaction of in-situ-
generated 3 with 4-aminophenol in tetrahydrofuran (THF) to
give diiron complex [{(μ-CH2S)2NC6H4OH-4}Fe2(CO)6] (6) in
61% yield and further treatment of SubPc-Cl (1) with 6 in
toluene to give 8 in 13% yield. The other method involves
the reaction of SubPc-Cl (1) with silver triflate (AgOTf) fol-
lowed by treatment of the resulting intermediate SubPc-OTf
(7) with 6 in the presence of Et3N to produce 8 in a much
higher yield (59%). All the new precursors (2, 4, and 6) and
the model compounds 5 and 8 have been fully characterized
by elemental analysis and various spectroscopy techniques,
as well by X-ray crystallography for 2, 4, 6, and 8. In addition,
the photoinduced H2 production catalyzed by model 8 was
preliminarily investigated.
the biomimetic chemistry of [FeFe]-hydrogenases, we de-
cided to design and synthesize two such light-driven models
(namely, complexes 5 and 8, see below) in which the photo-
sensitizer SubPc is attached through an organic chain to the
central N atom of an azadithiolate (ADT) ligand in a sim-
ple ADT-type model. Subphthalocyanines are regarded as
the lower homologues of phthalocyanines. The basic skel-
eton of these 14 π electron aromatic macrocycles contains
three diiminoisoindoline units N-fused around a boron cen-
ter and they have a C3-symmetrical cone-shaped struc-
ture.[17] We utilized SubPc as the photosensitizer for the
construction of light-driven models mainly because (i)
SubPcs are excellent chromophores with tunable properties
for photoinduced electron and/or energy transfer,[18,19]
which is closely related to one of the key steps required for
hydrogen production catalyzed by natural enzymes, and (ii)
SubPcs exhibit strong electronic absorption, high fluores-
cence quantum yields, small Stokes shifts, and very low re-
organization energies,[20,21] which are all fundamental requi-
sites for efficient electron and/or energy transfer and, thus,
for efficient photoinduced H2 production. A simple ADT-
type model was employed as a catalytic site to construct
this type of light-driven model because the dithiolate ligand
in the H cluster was recently suggested to be an azadithiol-
ate, in which the central N atom plays an important role
Introduction
[FeFe]-Hydrogenases are natural metalloenzymes in
many microbes and can catalyze the reversible reduction of
protons to hydrogen with rapid rates.[1] X-ray crystallo-
graphic[2] and IR spectroscopic[3] studies revealed that the
active site of [FeFe]-hydrogenases, the so-called H cluster,[4]
consists of a dithiolate-bridged butterfly [Fe2S2] cluster
linked to a cubane-like [Fe4S4] cluster through a single cys-
teinyl S atom (Figure 1). Structural studies of the active site
of [FeFe]-hydrogenases prompted synthetic chemists to pre-
pare a variety of model compounds.[5–10] In recent years, we
and others have reported a special type of model compound
(so-called light-driven models), in which a photosensitizer
(such as a porphyrin, metalloporphyrin, or pyridine-based
ruthenium or rhenium complex) is bound to a simple H-
cluster model in an attempt to achieve photoinduced H2
production.[9,11–16] However, no light-driven model in which
a subphthalocyanine (SubPc) photosensitizer is attached to
a simple H cluster has been reported. Therefore, to develop
[a] Department of Chemistry, State Key Laboratory of Elemento-
Organic Chemistry,
Tianjin 300071, China
E-mail: lcsong@nankai.edu.cn
Homepage: http://www.nankai.edu.cn
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for the heterocyclic cleavage or formation of H2 in the enzy-
matic catalytic process.[22,23] Now, we report the synthesis,
structural characterization, and properties of the first two
such light-driven model compounds, one with a flexible
chain and the other with a rigid chain between the SubPc
photosensitizer and the diiron–ADT catalytic site.
Figure 1. Basic structure of the H cluster determined by protein X-
ray crystallography (X = C, N, or O).
Results and Discussion
Synthesis and Characterization of the SubPc-Containing
ADT-Type Model Compound with a Flexible Organic
Chain
To synthesize the SubPc-containing model compound
[{(μ-SCH2)2N(CH2)2CO2-3-C6H4S2C6H4-3Ј-O(SubPc)}Fe2-
(CO)6] (5), we first prepared its two precursors, namely the
phenoxy-substituted SubPc derivative 3-HOC6H4S2C6H4-
3Ј-O(SubPc) (2) and the carboxyethyl-substituted diiron
complex [{μ-(SCH2)2N(CH2)2CO2H}Fe2(CO)6] (4). As
shown in Scheme 1, the SubPc derivative 2 can be prepared
in 78% yield by a condensation reaction of SubPc-Cl
(1)[24] with 3,3-disulfanediyldiphenol in toluene at reflux,
and diiron complex 4 is prepared by a ring-closure reaction
Scheme 1. Synthetic route to model 5 via 2 and 4.
of [(μ-HOCH2S)2Fe2(CO)6] (3, prepared in situ by the se- ganic and terminal carbonyl groups, respectively. The 11B
quential reaction of [(μ-S2)Fe2(CO)6] with Et3BHLi, NMR spectra of 2 and 5 displayed singlets at δ = –14.83
CF3CO2H, and aqueous CH2O)[25] with β-alanine in tetra- and –14.82 ppm for their respective B atoms.[20] The IR
hydrofuran (THF) from –78 °C to room temperature in spectra of 2 and 5 exhibited strong absorption bands at ca.
53% yield. Finally, the expected SubPc-containing ADT 1048 cm–1, which are attributed to the B–O stretching vi-
model complex 5, which has a flexible OC6H4S2C6H4- brations.[18] In addition, precursor 4 and model compound
O2C(CH2)2 bridge between its B and N atoms, is obtained 5 displayed several absorption bands in the range 2072–
in 86% yield by an esterification reaction between the phen- 1975 cm–1 for their terminal carbonyl groups.[27]
ol-containing SubPc 2 and the carboxy-containing diiron
complex 4 in the presence of N,NЈ-dicyclocarbodiimide mined by X-ray diffraction owing to the lack of suitable
(DCC) and N,N-dimethyl-4-aminopyridine (DMAP). single crystals, the single-crystal molecular structures of its
Although the crystal structure of model 5 was not deter-
Compounds 2, 4, and 5 are air-stable solids and have precursors 2 and 4 were successfully determined. The OR-
been fully characterized by various spectroscopic methods TEP views of 2 and 4 are shown in Figures 2 and 3, and
1
and elemental analysis. For example, the H NMR spec- their selected bond lengths and angles are given in Table 1.
trum of 2 displays two typical AAЈBBЈ multiplets at δ = The structure of 2 is shown in Figure 2 and is very similar
7.92–7.94 and 8.87–8.89 ppm for the Hβ and Hα protons in to those of previously reported SubPc derivatives.[26,28–32]
the SubPc ring,[18,20] whereas 5 exhibited two broad singlets The SubPc macrocycle of 2 has a cone-shaped conforma-
at δ = 7.85 and 8.81 ppm for its Hβ and Hα protons. The tion with the tetrahedral boron atom pointing away from
phenoxy groups attached to the B atoms in 2 and 5 dis- the macrocyclic base and the phenoxy group axially bonded
played the corresponding signals at δ = 5.43–6.96 or 5.25– to the boron atom. The B–O bond length (1.446 Å), the
6.85 ppm, respectively. These signals are considerably up- average B–N bond length (1.489 Å), and the B–O–C bond
field-shifted owing to shielding by the subphthalocyanine angle (115.1°) of 2 are comparable with those found in
ring current.[26] The 13C NMR spectra of 4 and 5 showed other SubPc derivatives.[33–35] In the structure of 2, there
signals at δ = 178.2/207.7 and 168.7/206.6 ppm for their or- is an intramolecular hydrogen bond between its phenolic
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hydroxy group O(2)H(2) and the macrocycle N(3) atom [the Table 1. Selected bond lengths [Å] and angles [°] for 2 and 4.
bond length and angle of the hydrogen bond O(2)–H(2)···
N(3) are 1.964 Å and 178.15°, respectively]. The axial phen-
2
S(2)–C(31)
S(2)–S(1)
S(1)–C(29)
1.797(3)
2.0255(11)
1.787(3)
1.385(3)
N(4)–B(1)
N(5)–B(1)
N(2)–B(1)
O(1)–B(1)
1.493(4)
1.486(4)
1.490(4)
1.446(4)
oxy group is more tilted toward the macrocycle because of
this hydrogen bond and has a B–O–C bond angle of 115.1°
and a C(29)–S(1)–S(2)–C(31) torsion angle of 80.72°. The O(1)–C(25)
C(9)–N(4)–B(1) 123.1(2)
C(25)–O(1)–B(1) 115.1(2)
C(17)–N(5)–B(1) 123.2(3)
C(1)–N(2)–B(1) 122.2(3)
C(8)–N(2)–B(1) 123.2(3)
O(1)–B(1)–N(2) 115.3(2)
N(5)–B(1)–N(2) 104.9(2)
N(2)–B(1)–N(4) 103.6(2)
C(29)–S(1)–S(2) 104.22(10)
C(31)–S(2)–S(1) 106.91(11)
S–S bond length of 2 (2.0261 Å) is actually the same as that
of 1,2-bis(3-nitrophenyl) disulfane (2.026 Å)[36] and is very
close to that for 1,2-bisphenyl disulfane (2.029 Å).[37]
4
Fe(1)–C(1)
Fe(1)–S(1)
Fe(1)–S(2)
Fe(1)–Fe(2)
S(2)–Fe(1)–Fe(2) 56.69(4)
S(1)–Fe(2)–S(2) 84.62(5)
S(1)–Fe(2)–Fe(1) 56.46(4)
S(2)–Fe(2)–Fe(1) 56.33(4)
1.802(5)
Fe(2)–C(6)
Fe(2)–S(1)
Fe(2)–S(2)
N(1)–C(7)
S(1)–Fe(1)–S(2) 84.73(6)
S(1)–Fe(1)–Fe(2) 56.28(4)
Fe(2)–S(1)–Fe(1) 67.25(5)
C(8)–N(1)–C(9) 120.3(5)
1.809(6)
2.2598(16)
2.2607(14)
2.5002(10)
2.2551(15)
2.2702(15)
1.421(7)
The Fe1–Fe2 bond length (2.5002 Å) and the sum of the
C–N–C bond angles around the N1 atom (253.1°) are very
close to those of the other diiron ADT-type model com-
plexes.[38–40]
Figure 2. ORTEP view of 2 with 30% probability level ellipsoids.
Synthesis and Characterization of the SubPc-Containing
ADT-Type Model Compound with a Rigid Organic Chain
To examine the influence of the organic bridge between
the B atom of the macrocycle and the N atom of the diiron–
ADT subsite, we prepared another SubPc-containing light-
driven model compound with a rigid OC6H4 organic chain,
namely, model compound [{(μ-SCH2)2N-4-C6H4O-
SubPc}Fe2(CO)6] (8). As shown in Scheme 2, model com-
pound 8 can be prepared by two methods. The first method
afforded 8 in low yield (13%) and involves a direct conden-
sation reaction between SubPc-Cl (1) and the phenol-con-
taining diiron complex [{(μ-SCH2)2NC6H4OH-4}Fe2(CO)6]
Figure 3. ORTEP view of 4 with 30% probability level ellipsoids.
As can be seen in Figure 3, compound 4 consists of a
carboxyethyl-substituted azadithiolate ligand that bridges
two Fe(CO)3 units to form two fused six-membered rings.
The Fe1S1C8N1C7S2 six-membered ring adopts a chair
conformation, whereas the Fe2S2C7N1C8S1 six-membered
ring adopts a boat conformation. This complex exists as
only one isomer, in which the carboxyethyl functionality is
connected to the bridgehead N1 atom by an axial bond. Scheme 2. Synthetic route to model 8 via 6 and 7.
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(6). Similarly to 4, complex 6 was prepared in 61% yield by the B–O bond length (1.423 Å), the average B–N bond
ring-closure reaction of the in-situ-prepared [(μ- length (1.499 Å), and the B–O–C bond angle (119.64°) of 8
a
HOCH2S)2Fe2(CO)6] (3) with 4-aminophenol in THF from
–78 °C to room temperature. The second method has two
steps. The first step involves the anion-exchange reaction
between SubPc-Cl (1) and silver triflate (AgOTf) to give the
expected OTf-substituted SubPc derivative 7.[20] The second
step involves the in situ reaction of 7 with diiron complex
6 in the presence of Et3N to afford 8 in a much higher yield
(59%). Notably, the OTf-substituted SubPc derivative 7 was
previously reported to be a very reactive intermediate and
1
was characterized in situ by H/11B NMR spectroscopy.[20]
Compounds 6 and 8 are also air-stable solids and have
been characterized by elemental analysis and various spec-
1
troscopic techniques. For example, the H NMR spectrum
of 6 showed two broad singlets at δ = 4.25 and 4.58 ppm
for its (CH2S)2N and OH groups, respectively, and that of
8 displayed two broad singlets at δ = 7.92 and 8.86 ppm for
the Hβ and Hα protons of its SubPc ring.[18,20] The phenoxy
group attached to the B atom in 8 showed two doublets at
δ = 5.39 and 6.14 ppm, which are significantly upfield-
shifted for the same reason as those for 2 and 5 indicated
above.[26] The 13C NMR spectra of 6 and 8 exhibited signals
at δ ≈ 207.0 ppm for their terminal carbonyl groups, and
the 11B NMR spectrum of 8 displayed signals at δ =
–14.81 ppm for its B atom.[20] The IR spectrum of 6 showed
a broad band at 3690 cm–1 for its OH group and three
bands in the range 2074–1964 cm–1 for its terminal carbonyl
groups, and that of 8 displayed a strong band at 1055 cm–1
for its B–O stretching vibration[18] and three bands in the
Figure 4. ORTEP view of 6 with 30% probability level ellipsoids.
region 2073–1994 cm–1 for its terminal carbonyl groups.[27]
.
The molecular structures of 6 and 8 were unequivocally
established by X-ray diffraction analysis. The ORTEP views
are depicted in Figures 4 and 5, and Table 2 lists selected
bond lengths and angles. As can be seen in Figures 4 and
5, both 6 and 8 contain a diiron–ADT moiety in which the
six-membered ring Fe1S2C8N1C7S1 for
Fe2S2C8N7C7S1 for 8 adopts a boat conformation and the
six-membered ring Fe2S2C8N1C7S1 for and
6
or
Figure 5. ORTEP view of 8 with 30% probability level ellipsoids.
6
Fe1S1C7N7C8S2 for 8 are in a chair conformation. The
substituted benzene rings are all attached to bridgehead N1
and N7 atoms of 6 and 8 by axial bonds. The Fe1–Fe2 bond
lengths of 2.5061 Å for 6 and 2.5047 Å for 8 are very close
to those of complex 4 and the other ADT-type model com-
plexes previously reported,[38–40] but they are somewhat
shorter than those in the natural enzymes (2.55–
2.60 Å).[2a–2c] The sum of the C–N–C bond angles around
the bridgehead N1 and N7 atoms increases from 350.7° for
6 to 356.6° for 8; this is apparently caused by the increased
steric repulsion between their SubPc macrocycles and the
cis-oriented terminal carbonyl groups. The structure of the
SubPc macrocycle in 8 is very similar to those of 2 and the
previously reported SubPc derivatives.[26,28–32] For example,
(i) the SubPc macrocycle has a cone-shaped conformation
and the tetrahedral boron atom points away from the
macrocyclic base, (ii) the phenoxy substituent is axially
bonded to the boron atom, which is coordinated with three
nitrogen atoms in a trigonal-pyramidal geometry, and (iii)
Table 2. Selected bond lengths [Å] and angles [°] for 6 and 8.
6
Fe(1)–S(1)
Fe(1)–S(2)
Fe(1)–Fe(2)
N(1)–C(8)
2.2484(9)
2.2774(9)
2.5061(11)
1.441(3)
Fe(2)–S(1)
Fe(2)–S(2)
S(1)–C(7)
S(2)–C(8)
2.2607(9)
2.2638(9)
1.843(2)
1.855(2)
S(1)–Fe(1)–S(2)
84.72(4)
C(8)–S(2)–Fe(1) 113.67(8)
Fe(2)–S(2)–Fe(1) 66.99(3)
C(8)–N(1)–C(7) 113.0(2)
C(9)–N(1)–C(7) 120.0(2)
S(1)–Fe(2)–Fe(1) 56.00(3)
S(2)–Fe(2)–Fe(1) 56.77(2)
Fe(1)–S(1)–Fe(2) 67.53(3)
8
Fe(1)–S(1)
Fe(1)–Fe(2)
Fe(2)–S(2)
Fe(2)–S(1)
C(7)–N(7)–C(8)
S(1)–Fe(1)–S(2)
S(2)–Fe(2)–Fe(1) 56.53(2)
S(1)–Fe(2)–Fe(1) 56.22(2)
S(1)–Fe(1)–Fe(2) 56.65(2)
2.2596(8)
2.5047(6)
2.2571(7)
2.2709(8)
114.3(2)
84.98(3)
N(1)–B(1)
N(3)–B(1)
O(7)–B(1)
N(1)–C(15)
Fe(1)–S(1)–Fe(2) 67.12(2)
O(7)–B(1)–N(3) 116.98(19)
C(15)–N(1)–B(1) 122.8(2)
N(3)–B(1)–N(1) 102.5(2)
C(12)–O(7)–B(1) 119.64(19)
1.503(3)
1.494(3)
1.423(3)
1.363(3)
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are close to those of 2 and some other previously reported sities of the fluorescence emission bands of 5 and 8 relative
SubPc derivatives.[26,28–32] Notably, 8 is the first light-driven to that of 1 could be attributed to strong intramolecular
model with a SubPc macrocycle covalently linked to a di- electron transfer (ET) from the photoexcited state of the
iron–ADT moiety to be prepared and crystallographically SubPc macrocycle to the covalently bonded diiron sub-
characterized.
site.[9,13,43–45] In addition, the much higher quenching effi-
ciency of model 8 relative to that of 5 demonstrates that the
rigid short chain of 8 is much more favorable for intramo-
lecular ET from the SubPc macrocycle to the diiron subsite.
Notably, such an intramolecular ET is one of the important
steps required for reduction of protons to hydrogen cata-
lyzed by natural enzymes.
Study on UV/Vis Absorption Spectra and Fluorescence
Emission Spectra of 1, 5, and 8
The UV/Vis absorption spectra and fluorescence emis-
sion spectra of some SubPc compounds have been investi-
gated.[30,41–44] To understand the photochemical behavior of
our model compounds, we determined the UV/Vis absorp-
tion spectra and fluorescence emission spectra of 5 and 8
along with those of 1 under the same conditions for com-
parison. As shown in Figure 6, the UV/Vis spectra of these
three compounds all display one Soret band in the range
304–306 nm and two Q bands in the regions 505–507 and
561–563 nm. The Soret and Q bands of 5 and 8 are slightly
blueshifted by a maximum of 2 nm relative to the corre-
sponding bands of 1 [For the UV/Vis data of 5 and 8, see
Exp. Sect.; the UV/Vis data of 1 are λmax (logε) = 563
(4.91), 507 (4.35), 306 (4.67) nm]. This implies that axial
substitution of the chlorine atom by the phenoxy-attached
diiron subunits in 5 and 8 has a negligible influence on their
UV/Vis spectra, which are dominated by the very strong π–
π* transitions associated with the 14 π electron systems of
the SubPc units.[28d,32,43]
Figure 7. Fluorescence emission spectra (λex = 530 nm) of 1, 5, and
8 in THF (5ϫ10–6 m).
Study on Photoinduced H2 Evolution Under the Action of a
Three-Component System Containing Model 8
Catalytic systems for photoinduced H2 evolution usually
consist of four separate components: an electron donor, a
photosensitizer, a catalyst, and a proton source.[46–50] How-
ever, we have recently reported photoinduced H2 evolution
by a three-component system. This system comprises an
electron donor, a proton source, and a light-driven model
that contains a photosensitizer tetraphenylporphyrin moi-
ety attached to a simple ADT-type model for the active site
of [FeFe]-hydrogenase.[13,51] To check if our photosensitizer
SubPc-containing light-driven models could be act as pho-
toactive catalysts to realize the expected H2 evolution, we
chose 8 (as it has a much higher quenching efficiency than
5) to constitute a three-component system with an electron
donor and a proton source for the H2 evolution experi-
Figure 6. UV/Vis spectra of 1, 5, and 8 in THF (5ϫ10–6 m).
Axially substituted SubPc derivatives are known to be ments. It was found that (i) when a 500 W Hg lamp with a
fluorescent emitters with electron- and/or energy-donating UV cutoff filter (λ Ͼ 400 nm) irradiated a THF solution of
or accepting capabilities.[42–44] As shown in Figure 7, the the three-component system consisting of model 8, electron
fluorescence emission spectra of reference compound 1 and donor EtSH, and proton source HOAc, H2 was indeed pro-
model compounds 5 and 8 exhibit fluorescence emission duced. (ii) As shown in Figure 8, during the first 30 min
bands at 576, 576, and 575 nm, respectively. Although the of irradiation, the H2 evolution increased rapidly, and then
three emission bands are almost located at the same posi- became very slow. The reason for fast reduction of the H2
tion, the band intensities of 5 and 8 are strongly quenched evolution speed could be attributed to decomposition of
relative to that of 1; the quenching efficiencies are 68% and model 8 under the light irradiation, as the red color of
94%, respectively. The remarkable decrease in the inten- model 8 nearly disappeared after the first 30 min of irradia-
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tion.
A
total of 90 min irradiation produced catalytic function under light irradiation. Further studies in
0.11ϫ10–3 mmol of H2, which corresponds to a turn over this direction will be performed in the near future in this
number (TON) of 0.11. (iii) When the same experiment was laboratory.
performed in the absence of any the three components, no
H2 evolution was observed. It follows that the presence of
Experimental Section
electron donor EtSH, proton source HOAc, light-driven
model 8, and light irradiation are essential for such photo-
induced H2 evolution.
General Comments: All reactions were performed by using standard
Schlenk and vacuum-line techniques under highly prepurified N2.
Solvents were distilled under nitrogen by using standard pro-
cedures. Chlorosubphthalocyanine (1, SubPc-Cl)[52] and [(μ-S2)-
Fe2(CO)6][53] were prepared according to the published methods.
Other chemicals such as silver trifluoromethanesulfonate (AgOTf),
4-(dimethylamino)pyridine (DMAP), and N,NЈ-dicyclocarbodi-
imide (DCC) were purchased from commercial suppliers and used
without further purification. Preparative TLC was performed on
glass plates (26ϫ20ϫ0.25 cm) coated with silica gel H (10–40 μm).
IR spectra were recorded with a Bruker Tensor 27 infrared spectro-
1
photometer. H, 13C, and 11B NMR spectra were recorded with a
Bruker Avance 400 NMR spectrometer. Elemental analyses were
performed with an Elementar Vario EL analyzer. UV/Vis spectra
and fluorescence emission spectra were recorded with a Hitachi U-
3900 spectrophotometer and a Hitachi F-4600 spectrophotometer,
respectively. Melting points were determined with an X-4 micro-
scopic melting point apparatus.
3-HOC6H4S2C6H4-3Ј-O(SubPc) (2):
A 50 mL Schlenk flask
equipped with a magnetic stir-bar, a septum cap, and a reflux con-
denser topped with a nitrogen inlet tube was charged with
SubPc-Cl (0.860 g, 2.00 mmol), 3,3Ј-disulfanediyldiphenol (1.500 g,
6.00 mmol), and toluene (30 mL). The reaction mixture was heated
to reflux for 16 h and then cooled down to room temperature. After
removal of the solvent at reduced pressure, the residue was washed
with methanol/water (v/v = 4:1) and then subjected to silica gel
column chromatography with toluene/THF (v/v = 5:1) as eluent.
From the major pink band, 2 was obtained as a pink solid (1.00 g,
Figure 8. Time dependence of photoinduced H2 evolution from
THF solutions (10 mL) consisting of EtSH (10 mm) and HOAc
(10 mm) in the presence of model 8 (0.1 mm).
Summary
1
78%); m.p. Ͼ 250 °C. H NMR (400 MHz, CDCl3): δ = 5.43 (dd,
We have synthesized and structurally characterized two
SubPc-containing light-driven model compounds: one (5)
with a flexible chain and the other (8) with a rigid chain,
each bridged between the SubPc B atom and the diiron sub-
unit N atom. In addition, to synthesize 5 and 8, one SubPc
derivative 2 and two diiron complexes 4 and 6 were also
prepared and structurally characterized. X-ray crystallo-
graphic studies revealed that model 8 consists of a SubPc
macrocycle and a diiron–ADT subunit that are axially
bonded by a rigid chain to their SubPc B atom and diiron
subunit N atom. A comparative study of the fluorescence
emission spectra of model compounds 5 and 8 with the ref-
erence compound 1 shows that the fluorescence emission
bands of 5 and 8 at 576 and 575 nm are strongly quenched
relative to that of 1; the quenching efficiencies are 68 and
94%, respectively. This could be attributed to strong intra-
molecular ET from the photoinduced SubPc macrocycle to
the covalently bonded diiron subunit. In addition, the much
higher quenching efficiency of model 8 relative to 5 demon-
strates that the rigid short chain in 8 is much more favorable
than the flexible long chain in 5 for intramolecular electron
transfer. Finally, it should be noted that the catalytic effi-
ciency of model 8 for the photoinduced H2 evolution is very
low owing to its severe decomposition. Therefore, the pho-
J = 2.0, 8.0 Hz, 1 H, 23-H), 5.57 (t, J = 2.0 Hz, 1 H, 27-H), 6.73
(t, J = 8.0 Hz, 1 H, 25-H), 6.96 (d, J = 8.4 Hz, 1 H, 26-H), 7.07
(d, J = 7.2 Hz, 1 H, 29-H), 7.11 (dd, J = 2.0, 8.0 Hz, 1 H, 33-H),
7.32 (t, J = 8.0 Hz, 1 H, 31-H), 7.48 (t, J = 2.0 Hz, 1 H, 32-H),
7.92–7.94, (AAЈBBЈ system, 6 H, 2-H, 3-H, 9-H, 10-H, 16-H, 17-
H), 8.87–8.89 (AAЈBBЈ system, 6 H, 1-H, 4-H, 8-H, 11-H, 15-H,
18-H) ppm. 13C NMR (100 MHz, CDCl3): δ = 112.8, 114.6, 116.4,
116.9 (4 C, C-23, C-27, C-29, C-33), 117.9, 119.6 (2 C, C-25, C-
31), 122.0 (6 C, C-1, C-4, C-8, C-11, C-15, C-18), 129.7, 130.0 (2
C, C-26, C-32), 130.1 (6 C, C-2, C-3, C-9, C-10, C-16, C-17), 130.3
(6 C, C-4a, C-7a, C-11a, C-14a, C-18a, C-21a), 136.4, 136.5 (2 C,
C-24, C-30), 151.1 (6 C, C-5, C-7, C-12, C-14, C-19, C-21), 153.2,
158.0 (2 C, C-22, C-28) ppm. 11B NMR (128.3 MHz, CDCl3,
BF ·Et O): δ = –14.83 (s) ppm. IR (KBr disk): ν = 3218 (w, O–H),
˜
3
2
1584 (s), 1459 (vs), 1435 (s), 1288 (s), 1134 (vs), 1050 (vs, B–O),
764 (s), 741 (vs) cm–1. C36H21BN6O2S2 (644.5): calcd. C 67.09, H
3.28, N 13.04; found C 67.07, H 3.35, N 12.95.
[{μ-(SCH2)2N(CH2)2CO2H}Fe2(CO)6] (4):
A red solution of
[(μ-S2)Fe2(CO)6] (0.860 g, 2.50 mmol) in THF (30 mL) was cooled
to –78 °C and then Et3BHLi (5.00 mL, 5.00 mmol) was added
dropwise to give a green solution containing [(μ-LiS)2Fe2(CO)6]. To
this solution was added CF3CO2H (0.50 mL, 5.00 mmol) and the
solution changed immediately from green to red, which indicated
the complete conversion of [(μ-LiS)2Fe2(CO)6] to [(μ-HS)2Fe2-
(CO)6]. The mixture was stirred for another 10 min, and 37% aque-
ous CH2O (0.50 mL, 5.00 mmol) was added. The new mixture was
tostability of model 8 should be enhanced to improve its warmed to room temperature and stirred at this temperature for
Eur. J. Inorg. Chem. 2013, 2549–2557
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FULL PAPER
1 h to give [(μ-HOCH2S)2Fe2(CO)6]. β-Alanine (0.223 g,
2.50 mmol) was added, and the mixture was stirred at room tem-
perature for 3 h. The solvent was removed under reduced pressure,
and the residue was subjected to TLC separation with CH2Cl2/
was stirred in toluene (30 mL) at room temperature for 2 h. Diiron
complex 6 (0.764 g, 1.60 mmol) and triethylamine (0.140 mL,
1.00 mmol) were added, and the mixture was stirred for 2 h. The
solvent was then removed under reduced pressure to give a sticky
petroleum ether (v/v = 1:1) as eluent. From the major red band, 4 residue. The residue was subjected to TLC separation with CHCl3/
was obtained as a red solid (0.603 g, 53%); m.p. 125–126 °C. 1H
ethyl acetate (v/v = 30:1) as eluent. From the major pink band, 8
NMR (300 MHz, CDCl3): δ = 2.37 (br. s, 2 H, NCH2CH2CO2H), (0.412 g, 59%) was obtained as a pink solid; m.p. Ͼ 250 °C. 1H
3.01 (br. s, 2 H, NCH2CH2CO2H), 3.56 [br. s, 4 H, (CH2S)2N] ppm. NMR (400 MHz, CDCl3): δ = 4.07 [s, 4 H, (SCH2)2N], 5.39 (d, J
13C NMR (100 MHz, CDCl3): δ = 32.8 (NCH2CH2CO2), 52.0
= 7.2 Hz, 2 H, 23-H, 27-H), 6.14 (d, J = 7.2 Hz, 2 H, 24-H, 26-H),
(NCH2CH2CO2), 52.7 (SCH2N), 178.2 (C=O), 207.7 (CϵO) ppm. 7.92 (br. s, 6 H, 2-H, 3-H, 9-H, 10-H, 16-H, 17-H), 8.86 (br. s, 6
IR (KBr disk): ν = 2069 (s), 2032 (vs), 2002 (vs), 1991 (vs), 1975
H, 1-H, 4-H, 8-H, 11-H, 15-H, 18-H) ppm. 13C NMR (100 MHz,
(s, CϵO), 1702 (vs, C=O) cm–1. C11H9Fe2NO8S2 (459.0): calcd. C CDCl3): δ = 50.1 (SCH2N), 116.8 (2 C, C-23, C-27), 120.5 (2 C, C-
˜
28.78, H 1.98, N 3.05; found C 28.64, H 2.00, N 3.02.
24, C-26), 122.2 (6 C, C-1, C-4, C-8, C-11, C-15, C-18), 129.9 (6
C, C-2, C-3, C-9, C-10, C-16, C-17), 131.0 (6 C, C-4a, C-7a, C-
11a, C-14a, C-18a, C-21a), 139.4, 146.4 (2 C, C-22, C-25), 151.3 (6
C, C-5, C-7, C-12, C-14, C-19, C-21), 206.9 (CϵO) ppm. 11B NMR
(128.3 MHz, CDCl3, BF3·Et2O): δ = –14.81 (s) ppm. IR (KBr disk):
[{(μ-SCH2)2N(CH2)2CO2-3-C6H4S2C6H4-3Ј-O(SubPc)}Fe2(CO)6]
(5): A mixture of the simple ADT-type model [{(μ-SCH2)2N-
(CH2)2CO2H}Fe2(CO)6] (4, 0.184 g, 0.40 mmol), SubPc derivative
2 (0.130 g, 0.20 mmol), and DMAP (0.024 g, 0.02 mmol) in CH2Cl2
(30 mL) was stirred at 0 °C for 30 min and then DCC (0.248 g,
1.20 mmol) was added. The mixture was stirred at room tempera-
ture for 12 h. The solvent was removed under reduced pressure,
and the residue was subjected to TLC separation with CHCl3/ethyl
acetate (v/v = 40:1) as eluent. From the major pink band, 5 was
ν = 2073 (s), 2033 (vs), 1994 (vs, CϵO), 1614 (w), 1459 (s), 1433
˜
(m), 1288 (m), 1253 (s), 1055 (s, B–O), 763 (m), 742 (s) cm–1. UV/
Vis (THF): λmax (logε) = 561 (5.05), 505 (4.51), 304 (4.83) nm.
C38H20BFe2N7O7S2 (873.25): calcd. C 52.27, H 2.32, N 11.23;
found C 52.33, H 2.27, N 11.12.
1
obtained as a pink solid (0.186 g, 86%); m.p. Ͼ 250 °C. H NMR
Photoinduced H2 Evolution Catalyzed by Model 8: A 30 mL Schlenk
flask fitted with a N2 inlet tube, a septum cap, a magnetic stir bar,
and a water-cooling jacket was charged with model 8 (0.87 mg,
0.001 mmol), EtSH (7.4 μL, 0.1 mmol), HOAc (5.7 μL, 0.1 mmol),
and THF (10 mL). The resulting solution was stirred and thor-
oughly deoxygenated by bubbling nitrogen through it. The solution
was then irradiated at about 25 °C (controlled by the cooling
(400 MHz, CDCl3): δ = 2.50 (br. s, 2 H, NCH2CH2CO2), 3.09 (br.
s, 2 H, NCH2CH2CO2), 3.60 [br. s, 4 H, (CH2S)2N], 5.25 (br. s, 1
H, 23-H), 5.61 (br. s, 1 H, 27-H), 6.70 (br. s, 2 H, 25-H, 26-H),
6.85 (br. s, 1 H, 29-H), 6.98 (br. s, 1 H, 33-H), 7.10 (br. s, 1 H, 31-
H), 7.20 (br. s, 1 H, 32-H), 7.85 (br. s, 6 H, 2-H, 3-H, 9-H, 10-H,
16-H, 17-H), 8.81 (br. s, 6 H, 1-H, 4-H, 8-H, 11-H, 15-H, 18-H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 32.4 (NCH2CH2CO2), jacket) through a Pyrex filter (λ Ͼ 400 nm) by using a 500 W Hg
50.9 (NCH2CH2CO2), 51.8 (SCH2N), 116.7, 116.8, 118.7, 118.9 (4
C, C-23, C-27, C-29, C-33), 119.3, 123.5 (2 C, C-25, C-31), 121.2
lamp. The UV cutoff filter was used to obtain visible light and to
avoid decomposition of EtSH.[35] During the photoinduced cataly-
(6 C, C-1, C-4, C-8, C-11, C-15, C-18), 128.3, 128.7 (2 C, C-26, C- sis, the evolved H2 was withdrawn periodically by using a gas-tight
32), 128.8 (6 C, C-2, C-3, C-9, C-10, C-16, C-17), 129.9 (6 C, C- syringe. The H2 was analyzed by gas chromatography with a Shim-
4a, C-7a, C-11a, C-14a, C-18a, C-21a), 136.0, 137.9 (2 C, C-24, C- adazu GC-2014 instrument equipped with a thermal conductivity
30), 149.6, 152.3 (2 C, C-22, C-28), 150.3 (6 C, C-5, C-7, C-12, C-
14, C-19, C-21), 168.7 (C=O), 206.6 (CϵO) ppm. 11B NMR
(128.3 MHz, CDCl3, BF3·Et2O): δ = –14.82 (s) ppm. IR (KBr disk):
detector and a carbon molecular sieves column (3 mmϫ2.0 m) and
with N2 as the carrier gas. The total amount of H2 produced during
90 min of irradiation was 0.11ϫ10–3 mmol.
ν = 2072 (s), 2030 (vs), 1993 (vs, CϵO), 1759 (m, C=O), 1584 (m),
˜
X-ray Structure Determinations of 2, 4, 6, and 8: Single crystals of
2, 4, 6, and 8 suitable for X-ray diffraction analyses were grown by
a slow diffusion of CH2Cl2 into their hexane solutions at room
temperature or at –5 °C. Single crystal of 2, 6, or 8 were mounted
on a Rigaku MM-007 (rotating anode) diffractometer equipped
1458 (s), 1432 (m), 1287 (m), 1132 (s), 1047 (s, B–O), 763 (m), 741
(s) cm–1. UV/Vis (THF): λmax (logε) 562 (5.03), 507 (4.47), 306
(4.81) nm. C47H28BFe2N7O9S4 (1085.6): calcd. C 52.00, H 2.60, N
9.03; found C 52.30, H 2.74, N 9.00.
[{(μ-SCH2)2NC6H4OH-4}Fe2(CO)6] (6): The same procedure as with a Saturn 724 CCD. Data were collected at 113 K by using a
that for the preparation of diiron complex 4 was followed. 4-Ami-
nophenol (0.273 g, 2.50 mmol) was added to the in-situ-prepared
solution containing [(μ-HOCH2S)2Fe2(CO)6]. Diiron complex 6
(0.730 g, 61%) was isolated as a red solid; m.p. 139–141 °C. 1H
NMR (400 MHz, CDCl3): δ = 4.25 [br. s, 4 H, (CH2S)2N], 4.58 (br.
s, 1 H, OH), 6.67 (br. s, 2 H, 2m-H of NC6H4), 6.82 (br. s, 2 H,
2o-H of NC6H4) ppm. 13C NMR (100 MHz, CDCl3): δ = 50.6
(SCH2N), 116.7, 118.0 (4 o,m-C of C6H4), 139.4, 149.9 (2 ipso-C
confocal monochromator with Mo-Kα radiation (λ = 0.71070 Å) in
the ω–θ scanning mode. Data collection, reduction, and absorption
correction were performed with the CRYSTALCLEAR pro-
gram.[54] A single crystal of 4 was mounted on a Bruker SMART
1000 automated diffractometer. Data were collected at room tem-
perature with graphite-monochromated Mo-Kα radiation
(0.71073 Å) in the ω–θ scanning mode. Absorption correction was
performed by the SADABS program.[55] All structures were solved
by direct methods by using the SHELXS-97 program[56] and refined
by full-matrix least-squares techniques (SHELXL-97)[57] on F2. Hy-
drogen atoms were located by using the geometric method. Details
of crystal data, data collections, and structure refinements are sum-
marized in Table 3.
of C H ), 207.0 (CϵO) ppm. IR (KBr disk): ν = 3690 (m, O–H),
˜
6
4
2074 (s), 2031 (vs), 1964 (vs, CϵO) cm–1. C14H9Fe2NO7S2 (479.1):
calcd. C 35.16, H 1.89, N 2.92; found C 35.00, H 2.09, N 2.95.
[{(μ-SCH2)2NC6H4-4-O(SubPc)}Fe2(CO)6] (8): Method (i): A mix-
ture of SubPc-Cl (0.172 g, 0.40 mmol) and 7 (0.382 g, 0.80 mmol)
in toluene (30 mL) was heated to reflux for 16 h. The solvent was
removed under reduced pressure, and the residue was subjected to
TLC separation with CHCl3/ethyl acetate (v/v = 30:1) as eluent to
give 8 (0.046 g, 13%) as a pink solid. Method (ii): A mixture of
SubPc-Cl (0.344 g, 0.80 mmol) and AgOTf (0.256 g, 1.00 mmol)
CCDC-916878 (for 2), -916879 (for 4), -916880 (for 6), and -916881
(for 8) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data-request/cif.
Eur. J. Inorg. Chem. 2013, 2549–2557
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FULL PAPER
Table 3. Crystal data and structure refinements details for 2, 4, 6, and 8.
2
4
6
8
Formula
C36H21BN6O2S2
644.52
orthorhombic
113(2)
C11H9Fe2NO8S2
459.01
monoclinic
113(2)
C14H9Fe2NO7S2·0.5H2O C38H20BFe2N7O7S2·2CH2Cl2·0.5H2O
Mr [gmol–1]
488.05
triclinic
113(2)
1052.10
triclinic
113(2)
Crystal system
T [K]
Space group
¯
P1
¯
Pca21
P21/c
P1
a [Å]
b [Å]
c [Å]
α [°]
19.699(3)
12.198(2)
25.266(4)
90
90
90
6071.4(18)
8
1.410
12.627(3)
22.817(5)
17.139(3)
90
95.45(3)
90
4915.5(17)
12
1.861
6.886(2)
13.812(5)
18.402(7)
90.385(8)
93.514(8)
90.282(12)
1746.8(11)
4
10.994(2)
11.4951(18)
17.310(3)
80.198(8)
84.881(9)
75.519(9)
2084.7(6)
2
β [°]
γ [°]
V [Å3]
Z
ρcalcd. [gcm–3]
1.856
1.941
1.676
1.115
μ [mm–1]
0.221
2.064
Crystal size [mm]
F(000)
Reflections collected
Independent reflections
2θmax [°]
R
Rw
0.20ϫ0.18ϫ0.12 0.18ϫ0.16ϫ0.12 0.20ϫ0.18ϫ0.10
0.20ϫ0.18ϫ0.10
1062
21372
9768
55.76
0.0349
0.0891
1.011
1.026/–0.628
2656
2760
33150
8648
980
17859
6129
51722
12787
54.18
0.0524
0.0970
1.092
50.04
50.04
0.0577
0.1207
1.074
0.0309
0.0564
0.912
Goodness-of-fit
Largest diff. peak and hole [eÅ–3] 0.209/–0.278
0.592/–0.626
0.386/–0.458
J. Yan, H.-T. Wang, X.-F. Liu, Q.-M. Hu, Organometallics
2006, 25, 1544–1547.
Acknowledgments
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The authors are grateful to the State Key Project of Fundamental
Research for Nanoscience and Nanotechnology (973) (grant
number 2011CB935902), the National Natural Science Foundation
of China (NSFC) (grant numbers 21132001 and 21272122), and
the Tianjin Natural Science Foundation (grant number
09JCZDJC27900) for financial support.
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Published Online: March 26, 2013
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim