N-Derivatives of peri-Substituted Dichalcogenide [FeFe]-Hydrogenase Mimics: Towards Photocatalytic Dyads for Hydrogen Production

Article abstract of DOI:10.1002/ejic.201500355

Synthetic strategies towards molecular dyads based on peri-substituted dichalcogenide (S,Se) [FeFe]-hydrogenase synthetic mimics covalently linked to a ZnTPP photosensitizer are described. Dithiolate and diselenolate model systems 2-5 are prepared through

Full text of DOI:10.1002/ejic.201500355

FULL PAPER
DOI:10.1002/ejic.201500355
N-Derivatives of peri-Substituted Dichalcogenide
[FeFe]-Hydrogenase Mimics: Towards Photocatalytic
Dyads for Hydrogen Production
Carlotta Figliola,[a] Louise Male,[a] Sarah L. Horswell,*[a] and
Richard S. Grainger*[a]
Keywords: Photocatalysis / Electrocatalysis / Cyclic voltammetry / Porphyrinoids / Carbonyl ligands
Synthetic strategies towards molecular dyads based on peri-
substituted dichalcogenide (S,Se) [FeFe]-hydrogenase syn-
thetic mimics covalently linked to a ZnTPP photosensitizer
are described. Dithiolate and diselenolate model systems 2–
5 are prepared through condensation of 2-naphthaldehydes
with p-methoxyaniline, reduction of the resulting Schiff base
and oxidative insertion of Fe2(CO)6 into the dichalcogen
bond of the imine or amine. Diselenolate-based [FeFe] com-
plexes (imine 3 and amine 5) are more efficient in electrocat-
alysis of proton reduction than their sulfur analogues 2 and
4 with increasing concentrations of pTsOH. Molecular dyad
1
containing a peri-substituted naphthalene dithiolate
Fe2(CO)6 cluster covalently linked via an amine to ZnTPP is
prepared through sequential zinc insertion into the porphyrin
followed by iron insertion into the disulfide bond.
the contribution of aromatic backbones and chalcogens
(SS, SeSe and SSe) to the redox properties of the [FeFe]-
cluster.[12] As previously suggested,[13] the use of peri-substi-
tuted naphthalene and phenanthrene dichalcogen ligands
allowed stabilisation of the catalytic intermediates and
hence promoted hydrogen production. Furthermore,
[FeFe]-hydrogenase analogues containing selenium[14] were
confirmed to be more active towards proton reduction ca-
talysis than their sulfur-based counterparts.
[FeFe]-hydrogenase synthetic mimics as catalysts for
hydrogen production have also been investigated in photo-
chemical systems.[15] Molecular dyads/triads, self-assemblies
and bimolecular systems are the main strategies applied to
design active catalysts for light-induced hydrogen produc-
tion.[15e] Related to the current work, Wasielewski reported
molecular dyads and triads containing peri-substituted
[FeFe] complexes covalently attached to the photosensitiser
ZnTPP, via an imide at the 4- and 5-positions of the
naphthalene, for light-induced hydrogen production.[16] The
turnover number of hydrogen generated was 0.56, along
with decomposition of the [FeFe]-cluster.
Following our interest in the chemistry of peri-substi-
tuted dichalcogenides[17,18] and in the development of new
and efficient [FeFe]-hydrogenase analogues,[12] we herein re-
port the synthesis of ZnTTP-containing molecular dyad 1
and related imine/amine-substituted naphthalene-based
[FeFe] complexes 2–5 (Figure 1). As for the enzyme’s active
site,[19] nitrogen-containing linkers, proximal to the [FeFe]-
cluster, have been chosen since they are protonated upon
acid addition and, hence, provide the metallic centre with
Introduction
In the effort of developing renewable energy sources,
great interest has been directed towards hydrogen[1] pro-
duction by electrochemical and photochemical splitting of
water.[2] Platinum complexes and colloids are commonly
used to catalyse this reaction;[3] alternatively, complexes of
cobalt,[4] nickel,[5] molybdenum[6] and, particularly, iron,[7]
have been intensively studied.
Dithiolate-based [FeFe] complexes, (μ-SR)2Fe2CO6–xLx,
are biomimics of the active site of the [FeFe]-hydrogenase
enzyme, for which the rate of hydrogen production is the
highest
(6,000–9,000 s–1)[8]
among
the
known
hydrogenases.[9] Since the first crystal structures of [FeFe]-
hydrogenase,[10] variation of the organic backbone (R) and
the use of electron-donating ligands (L) allowed achieve-
ment of remarkable progress in reproducing the enzyme’s
catalytic activity.[11] Recently we have reported a study on
[a] School of Chemistry, University of Birmingham,
Edgbaston, Birmingham B15 2TT, United Kingdom
E-mail: s.l.horswell@bham.ac.uk
r.s.grainger@bham.ac.uk
http://www.birmingham.ac.uk/staff/profiles/chemistry/
horswell-sarah.aspx
http://www.birmingham.ac.uk/staff/profiles/chemistry/
grainger-richard.aspx
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201500355.
© 2015 The Autors. Published by Wiley-VCH Verlag GmbH &
Co. KGaA. This is an open access article under the terms of
the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the
original work is properly cited.
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protons.[11e] Spectroscopic and electrochemical properties of
Based on the synthesis of 2 and 3, we attempted to syn-
simple model systems 2–5 are reported and used for the thesise molecular dyads containing an imine-linker between
initial studies into the synthesis of 1 as a potential catalyst the photosensitizer (porphyrin) and the catalyst ([FeFe]
for photocatalytic hydrogen production.
complex).
Reaction
of
tetraphenylporphyrin-amine
(TPPNH2) 10[24–26] with Zn(OAc)2 in refluxing pyridine fol-
[27]
lowed by further reaction of the resulting ZnTPPNH2
with aldehyde 6 or 7, using a further excess of Zn-
(OAc)2,[16a] gave the zinc-containing Schiff bases 11 and 12
in good to excellent yields. Following the synthetic sequence
described for [FeFe] complexes 2 and 3, 11 and 12 were
treated with Fe3(CO)12 in refluxing toluene to afford the
corresponding [FeFe] complexes (not shown); however,
these were prone to degradation upon attempted column
chromatography, with 1H NMR spectroscopy and mass
spectrometry showing both the formation of the expected
[FeFe] complexes and the presence of the starting aldehyde
(6 or 7) and ZnTPPNH2.
Reduction of the imine double bond in 11 and 12 could
not be achieved in an analogous manner to 8 and 9.[21] Con-
sequently, aldehydes 6 and 7 were treated with 10 in re-
[28]
fluxing toluene in the presence of catalytic La(OTf)3
to
Figure 1. Molecular dyad 1 and imine/amine-substituted naphthal-
ene-based [FeFe] complexes 2–5.
afford imines 13 and 14 in high yields. Reduction of imine
13 to amine 15 was successfully achieved using NaBH3CN
and catalytic amounts of AcOH.[29] Metallation of the por-
phyrin core with Zn(OAc)2 followed by oxidative insertion
into the S–S bond of the naphthalene-1,8-dithiole gave the
target [FeFe] complex 1 (Scheme 2). In contrast, attempts to
Results and Discussion
Synthesis
reduce the double bond of diselenole 14 were unsuccessful.
[21]
The syntheses of model systems 2–5 are shown in
Scheme 1. Refluxing 2-formyl-naphthalene 1,8-dithiole 6[20]
with a large excess of p-methoxyaniline in dry CH3CN gave
the Schiff base 8 in excellent yield.[21] The known diselenole
7[21] was converted to imine 9 using TiCl4 as a catalyst and
an excess of NEt3.[22] [FeFe] complexes 2 and 3 were pre-
pared through oxidative insertion of Fe0 into the dichalco-
gen bond by treating 8 or 9 with Fe3(CO)12 in refluxing
toluene and were sufficiently stable for isolation by column
chromatography. Reduction of the imine double bond of 8
NaBH4
caused degradation
of 14, whereas
[30]
NaBH3CN,[29] NaBH(OAc)3 as well as hydrogenation[31]
only resulted in recovered starting material. Consequently,
the synthesis of the selenium-containing molecular dyad
corresponding to 1 could not be achieved.
[21]
and 9 with a large excess of NaBH4 generated the corre-
sponding amines which were reacted directly with Fe3-
(CO)12 to yield the novel [FeFe] complexes 4 and 5.[12,23]
Scheme 1. Synthesis of [FeFe] complexes 2–5.
Scheme 2. Synthesis of molecular dyad 1.
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Spectroscopic and Electrochemical Analysis of [FeFe]
Complexes 2–5
[FeFe] complexes 2–5 were characterised by 1H, 13C
NMR, IR and UV/Vis spectroscopy. Molecular structures
of [FeFe] complexes 2 and 4 were also confirmed by X-ray
diffraction.
1H NMR spectra of 2–5 displayed the expected down-
field shift of the aromatic protons compared with those of
the corresponding ligands 8 and 9 associated with the inser-
tion of the [FeFe]-cluster into the dichalcogen bond.[12] 13
C
NMR spectra showed one single peak at 207 or 208 ppm,
assigned to the carbonyl ligands binding the iron centre in
the dithiolate and diselenolate-bridged complexes, respec-
tively.[12]
The IR stretching wavenumbers of the carbonyl ligands
are listed in Table 1. As previously observed for related
Fe2CO6 complexes with aromatic dichalcogen li-
gands,[12,13a,13b,13f,13m] the absorption bands are all in the
range 2070–1950 cm–1. [FeFe] complexes 3 and 5 display a
bathochromic shift of the carbonyl stretching compared
with the analogous dithiolate-based 2 and 4, confirming
what has been previously observed.[12]
Table 1. Carbonyl IR stretches of [FeFe] complexes 2–5.
ν (CO) [cm–1]
˜
2 (SS)
2066, 2024, 1977, 1959
2061, 2024, 1978, 1953
2064, 2026, 2005, 1988, 1963
2057, 2020, 1997, 1981, 1958
3 (SeSe)
4 (SS)
5 (SeSe)
The UV/Vis spectra of the [FeFe] complexes and the cor-
responding values for the extinction coefficient are reported
in Figure S1 and Table S2, respectively (Supporting Infor-
mation).
The UV/Vis spectra of amine-substituted [FeFe] com-
plexes 4 and 5 display intense bands in the range 210–
260 nm, which are assigned to the naphthalene π-π* transi-
Figure 2. Molecular structures of [FeFe] complexes 2 (top) and 4
(bottom) with ellipsoids drawn at the 50% probability level. The
structure of 2 contains two crystallographically-independent mo-
lecules of which only one (molecule 1) is shown.
tion. The iron-carbonyls metal-ligand charge transfer hydrogenase (2.6 Å), as is the bond length between each
(MLCT) or ligand-metal charge transfer (LMCT) absorbs iron and sulfur (Fe1–S1 = Fe1–S2 = Fe2–S2 = Fe2–S2 =
in the range 310–410 nm, consistent with previous measure- 2.3 Å in the enzyme).[10]
ments.[12,13g,13m,32] Additionally, a weak absorption band is
The presence of an imino- or amino-group in position 2
observed in the range 410–510 nm, which corresponds to on the naphthalene ring of 2 and 4 does not change the
the metal d-d transition.[12,13g,13m,32] Imine-substituted general structure of the complexes, which are comparable in
[FeFe] complexes 2 and 3 display a continuous absorption bond lengths and angles with the data reported for similar
in the range 250–400 nm, due to the highly conjugated sys- compounds.[12,13f] The crystal structure of 2 contains two
tem. The iron d-d transitions of 2 and 3 are stronger than crystallographically-independent molecules, which are com-
those recorded for the corresponding 4 and 5.
parable in geometry. In both molecules the structure dis-
Molecular structures of [FeFe] complexes 2 and 4 were plays a trans geometry of the imine double bond. The
confirmed by X-ray analysis.[33] Crystal structures of 2 and phenyl substituent on the nitrogen is outside of the plane
4 are shown in Figure 2; bond lengths and angles are listed of the conjugated system by rotation around the N(1)–
in Table 2. Crystal data and structure refinement details are C(18) bond [torsion angles: C(23)–C(18)–N(1)–C(17) =
described in Table S4 (Supporting Information).
–25.7(14)° and C(19)–C(18)–N(1)–C(17) = 155.4(9)°] in
Both amine and imine-substituted complexes possess a molecule 1 and C(123)–C(118)–N(101)–C(117) = 35(2)° and
dithiolate-bridged [FeFe]-core which assumes the typical C(119)–C(118)–N(101)–C(117) = –146.3(14)° in molecule 2,
butterfly architecture with two iron centres linked to three Table 2 and Table S3 in Supporting Information.
carbonyl ligands in a distorted square-pyramidal geome-
The electrochemical properties of the amine and imine-
try.[12,13f] The Fe–Fe bond length for each complex is com- substituted [FeFe] complexes 2–5 were investigated by cyclic
parable with those reported for the active site of [FeFe]- voltammetry. Based on our previous studies,[12] all the mea-
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Table 2. Selected bond lengths [Å] and angles [°] for compounds 2
(molecule 1 only) and 4. For geometry of molecule 2 of compound
2 see Supplorting Information, Table S3.
2
4
Fe(1)–Fe(2)
Fe(1)–S(1)
Fe(1)–S(2)
Fe(2)–S(1)
Fe(2)–S(2)
Fe(1)–C(11)
Fe(1)–C(12)
Fe(1)–C(13)
Fe(2)–C(14)
Fe(2)–C(15)
Fe(2)–C(16)
S(1)–C(1)
2.5094(16)
2.249(2)
2.243(2)
2.245(2)
2.239(2)
1.798(9)
1.810(9)
1.806(9)
1.804(10)
1.796(9)
1.816(10)
1.769(8)
1.773(8)
83.84(8)
84.00(8)
123.8(6)
126.3(6)
124.9(7)
179.0(8)
0.8 (13)
155.4(9)
–25.7(14)
2.545(4)
2.261(6)
2.236(6)
2.271(6)
2.241(5)
1.83(2)
1.79(2)
1.83(2)
1.81(2)
1.820(19)
1.81(2)
1.754(18)
1.77(2)
84.3(2)
S(2)–C(8)
S(1)–Fe(1)–S(2)
S(1)–Fe(2)–S(2)
S(1)–C(1)–C(9)
S(2)–C(8)–C(9)
C(8)–C(9)–C(1)
C(1)–C(2)–C(17)–N(1)
C(3)–C(2)–C(17)–N(1)
C(19)–C(18)–N(1)–C(17)
C(23)–C(18)–N(1)–C(17)
84.0(2)
124.3(15)
128.1(14)
122.8(16)
–146.0(18)
33(2)
–2(2)
177.9(16)
Figure 3. Cyclic voltammograms for [FeFe] complexes 2–5 (1 mm)
in 0.1 m NBu4PF6/CH3CN at 0.01 Vs–1 scan rate.
similar to that observed for the Fc/Fc+ internal redox cou-
ple, indicating reversible behaviour (fast electron transfer
kinetics). In contrast, [FeFe] complexes 2, 3 and 5 displayed
a weak oxidation peak on the return sweep, presumably
meaning decomposition of the reduced product. The same
observation can be made for the oxidation processes (except
for the first oxidation of 4 and 5).
surements were recorded in CH3CN at room temperature,
using a three electrode-cell with glassy carbon as working
electrode, Ag/AgNO3 as reference electrode, and platinum
as counter electrode. All the potentials were measured with
respect to the ferrocene redox couple (Fc/Fc+), which was
used as internal reference. All the peak potentials and the
corresponding half-wave potentials (E1/2) are listed in
Table 3 and cyclic voltammograms are shown in Figure 3.
The first reduction wave of selenium-based [FeFe] com-
plexes 3 and 5 occurs at less negative potential than the
corresponding sulfur counterpart 2 and 4 (3 and 5: E1/2
=
–1.41 V vs. 2 and 4: E1/2 = –1.44 V and –1.62 V, respec-
tively) (Table 3), consistent with previous analyses.[12] How-
ever, the presence of selenium might affect the stability of
both reduced products, compared with the analogous
sulfur-based complex. The amine-substituted dithiolate 4 is
shown to be the most thermodynamically stable among the
reported complexes, since both reductions are reversible
(Figure 3).
[FeFe] complexes 2–5 were investigated as proton re-
duction catalysts by monitoring their electrochemical prop-
erties upon addition of pTsOH (concentration 0.5 mm to
10 mm).[12] Cyclic voltammograms are shown in Figure 4
and Figure S5 (Supporting Information).
Table 3. Electrochemical reduction potentials (vs. Fc/Fc+) of [FeFe]
complexes 2–5 (1 mm) in 0.1 m NBu4PF6/CH3CN at 0.01 Vs–1 scan
rate.
2 (SS)
3 (SeSe)
4 (SS)
5 (SeSe)
EЈpc (V)
–1.51
–1.44
–1.74
–
–1.45
–1.41
–1.86
–1.81
0.96
–1.51
–1.62
–1.85
–1.78
0.46
0.76
0.96
–1.51
–1.41
–1.90
–
0.52
0.68
0.76
EЈ1/2 (V)[a]
EЈЈ (V)
pc
EЈЈ (V)[b]
1/2
Epa (V)
1.00
[c]
E1/2–E°HA (V)
0.80
0.76
Imines 2 and 3 show the first reduction process shifted
at less negative potentials than those recorded in the ab-
sence of acid (Table 3). Notably, the first reduction wave
[a] FeIFeIǞFeIFe0. [b] FeIFe0ǞFe0Fe0. [c] E°pTsOH = –0.65 V (vs.
Fc/Fc+) in CH3CN at room temperature.[34]
All complexes undergo two one-electron reductions, moves cathodically from –0.7 V to –1.1 V (2) and from
which are assigned to FeIFeI–Fe0FeI and Fe0FeI–Fe0Fe0, by –0.5 V to –1.17 V (3), upon increasing the acid concentra-
analogy with previously reported [FeFe] complexes.[12] In tion from 0.5 mm to 5 mm. At higher concentration of acid
addition, each [FeFe] complex shows one or two one-elec- (7.5 mm and 10 mm) this reduction wave becomes negligible.
tron oxidations, corresponding to FeIFeI–FeIIFeI and The shift in peak position of this first reduction process is
FeIIFeI–FeIIFeII, respectively.[12] The first and the second re- independent of the acid concentration; however, the peak
duction event result in a chemical decomposition (EC reac- current increases linearly with the acid concentration. Upon
tion), which reduces the amplitude of the return wave. This increasing the concentration of pTsOH (from 0.5 to 2 mm),
rearrangement is unlikely to involve fragmentation of the the second and the third reduction waves are slightly shifted
backbone because an oxidation peak is observed on the re- towards more negative potentials. At higher concentration
turn sweep.[13f,13g] In the case of [FeFe] complex 4, the peak of acid, they are notably shifted towards more negative po-
separation of the first and the second reduction waves is tentials and the peak current is significantly increased.[12]
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Scheme 3. Proposed mechanism for the proton reduction catalysis
by [FeFe] complexes 2 and 3 in the presence of pTsOH.
ture[14] and with previous results.[12] The catalytic efficiency
of [FeFe] complexes 2–5 was also estimated in terms of peak
current increase (Figure S8, Supporting Information).[12]
Only high concentrations of acid were considered, since the
peak height is more markedly affected than at low concen-
tration. Diselenolate-based [FeFe] complexes 3 and 5 give a
bigger peak current increase than the equivalent dithiolates
2 and 4, but this effect is less predictable than that observed
for previously reported complexes.[12]
Figure 4. Cyclic voltammograms for [FeFe] complexes 2 and 3
(1 mm) in 0.1 m NBu4PF6/CH3CN at 0.01 Vs–1 scan rate with in-
creasing concentrations of pTsOH from 0.5 mm to 2 mm (upper
graphs) and from 2.5 mm to 10 mm (lower graphs).
The first reduction peak of the amines 4 and 5 is shifted
in the range from –0.5 V to –0.6 V only upon addition of
0.5 and 1 mm of pTsOH. This process is less defined than
in the imine-substituted 2 and 3. At high concentration of
acid, the second and the third reduction process follow what
has been described previously for complexes 2 and 3.
As previously observed,[35–37] the first process may in-
volve the reduction of the protonated [FeFe] complexes 2–
5 upon addition of pTsOH. The introduction of a positive
Spectroscopic and Electrochemical Analysis of Molecular
Dyad 1
Following spectroscopic and electrochemical analysis of
1
charge could explain the shift towards more positive poten- [FeFe] complex 4, molecular dyad 1 was analysed by H
tial compared with that recorded in the absence of acid. and 13C NMR, IR, UV/Vis and emission spectroscopy. The
Protonation of the amino/imino substituent, proximal to 1H NMR spectrum displayed a significant downfield shift
the [FeFe]-cluster, is thought to decrease the activation en- of naphthalene and amino-linker peaks of 1 compared with
ergy of the Fe–H bond formation; hence, it favours proton those of the ligand 15, associated with the insertion of the
reduction catalysis.[35–37] Protonation of complexes 2 and 3 [FeFe]-cluster. The 13C NMR spectrum showed the charac-
is shown to occur at both low and high acid concentration, teristic peak for the carbonyls of the [FeFe]-cluster at δ =
while for the amine equivalent 4 and 5 only at low concen- 207 ppm.
tration of pTsOH.
IR spectroscopy displayed three stretching bands at 2072,
The proposed mechanism for the proton reduction catal- 2032 and 1982 cm–1, which are assigned to the iron-bound
ysis of [FeFe] complexes 2 and 3 is shown in Scheme 3. carbonyl ligands.[16] [FeFe] complexes 4 (Table 1) and 1
Upon addition of pTsOH, [FeIFeIN] is protonated to showed comparable wavenumbers for the carbonyl stretch-
[FeIFeINH]+, which could explain the anodic shift of the ing, suggesting that ZnTPP in the ground state does not
first reduction potential and give [Fe0FeINH]+. This species significantly affect the [FeFe]-cluster.[16a]
reacts again with acid to generate [HFeIIFeINH]+, which,
The UV/Vis absorption spectrum of 1 in Figure S3 (Sup-
after two more one-electron reductions, liberates hydrogen porting Information) shows one intense Soret band at
and regenerates the initial [FeIFeIN].[35,37] Amine-substi- 422 nm and two weak Q bands at 550 nm and 593 nm,
tuted [FeFe] complexes 4 and 5 follow the above mechanism respectively.[38] By analogy with the model system 4 (Table
at low acid concentration. At high concentration of acid, S2 and Figure S1 in Supporting Information), the absorp-
they follow the proton reduction mechanism described for tion band at 254 nm is assigned to the first naphthalene π-
similar naphthalene-based [FeFe] complexes.[12,13f]
The efficiency of proton reduction catalysis of [FeFe] to the iron-carbonyls MLTC or LMCT.
π* transition and those at 308 nm and 355 nm are assigned
[12]
complexes 2–5 was evaluated in terms of E1/2-E°HA
,
In order to establish if the electron transfer is a thermo-
which gives a measure of the overpotential for the acid re- dynamically feasible process, a cyclic voltammogram of 1
duction to occur in the presence of the catalyst. Table 3 re- was recorded in CH2Cl2/CH3CN (7:3) using the same sys-
ports the values of 2–5 for pTsOH reduction. Diselenolate- tem set up for the analysis of 4 (Figure 5). It displays two
bridged [FeFe] complexes show lower values than their sul- reduction waves at –1.72 V and –2.05 V (EЈ1/2 = –1.65 V
fur counterparts, suggesting they are more efficient catalysts and EЈЈ1/2 = –1.94 V), which are assigned to FeIFeI–Fe0FeI
towards proton reduction. This is consistent with the litera- and Fe0FeI–Fe0Fe0, respectively, by analogy with [FeFe]
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mined using open glass capillaries on a Gallenkamp melting point
apparatus and are uncorrected. Analytical TLC was carried out on
Merck 60 F245 aluminium-backed silica gel plates. Short wave UV
(245 nm) and KMnO4 were used to visualise components. Com-
pounds were purified by flash column chromatography using
Merck silica gel 60.
complex 4. Two oxidation waves are also shown at 0.4 V
and 0.7 V, which are attributed to FeIFeI–FeIIFeI and
FeIIFeI–FeIIFeII, respectively.
Naphtho[1,8-cd][1,2]dithiole-3-carbaldehyde[20] (6), naphtho[1,8-
cd][1,2]diselenole-3-carbaldehyde[21] (7), 5,10,15-triphenyl-20-(4-
amino)phenylporphyrin[24–26] (10), zinc 5,10,15-triphenyl-20-(4-
amino)phenylporphyrin[27] (16) were prepared according to litera-
ture procedures.
1H and 13C NMR spectroscopic data were recorded on a Bruker
1
AVIII300 (300 MHz H, T = 293 K), Bruker AVIII400 (400 MHz
1H, 101 MHz 13C, T = 293 K) or on a Bruker AV400 (400 MHz
1H, 101 MHz 13C, T = 293 K) spectrometer. Spectra were recorded
in CD2Cl2 referenced to residual CH2Cl2 (1H, 5.33 ppm; 13C,
53.84 ppm), [D6]DMSO referenced to residual DMSO (1H,
2.50 ppm; 13C, 39.52 ppm) and CDCl3 referenced to residual
CHCl3 (1H, 7.26 ppm; 13C, 77.16 ppm).[41] Chemical shifts (δ) are
reported in ppm and coupling constants (J) are reported in Hz.
The following abbreviations are used to describe multiplicity: s-
singlet, d-doublet, t-triplet, q-quartet, m-multiplet, br-broad. All
the reported coupling constants are averaged, when the coupling
constants are close in value. Mass spectra (MS) were recorded on
a Microwaters LCT TOF with a mixture (2:1) of MeOH and
CHCl3 as mobile phase, Microwaters SynaptG26 with mixture (2:1)
of CHCl3 and MeOH as mobile phase or on a Microwaters GCT
Premier Probe, utilising electrospray ionisation (recorded in the
positive mode), or electron impact ionisation, and both are re-
ported as m/z (%) and they are given as [M + H]+ and M+. High
resolution mass spectra (HRMS) were recorded on a Microwaters
LCT TOF, Microwaters SynaptG26 or on Microwaters GCT Prem-
ier Probe using a leucine enkephalin-lock mass incorporated into
the mobile phase. IR spectra were recorded neat on a Perkin–Elmer
100 FT-IR spectrometer.
Figure 5. Cyclic voltammogram of complex 1 (1 mm) in 0.1 m
NBu4PF6/CH2Cl2/CH3CN (7:3) at 0.01 Vs–1 scan rate.
The first reduction of molecular dyad 1 occurs at less
negative potential (EЈ1/2 = –1.65 V) than the oxidation of
the excited species ZnTPP* (= –1.74 V).[15c] This suggests
that the oxidative quenching of excited species ZnTPP* by
the [FeFe]-cluster is thermodynamically favoured.[15]
Furthermore, previous results on the catalytic proton re-
duction properties of 4, along with the spectroscopic and
electrochemical similarities between 4 and 1, suggest that
the reduced species of the [FeFe]-cluster in 1 is suitable for
catalysing proton reduction and producing hydrogen.
Conclusions
In this report we describe a new strategy to obtain
[FeFe]-hydrogenase synthetic mimics stabilised by peri-sub-
stituted naphthalene dithiolate or diselenolate ligands
which also contain basic nitrogen functionality in close
proximity to the catalytically active site. [FeFe] complexes
2–5 have been shown to catalyse proton reduction. Proton-
ation of the amino and imino groups under acidic condi-
tions was detected with cyclic voltammetry. The synthetic
strategy was extended to the preparation of a molecular
dyad containing a tetraphenylporphyrinatozinc as a poten-
tial photosensitizer. Electrochemical studies indicate that
electron transfer between the two moieties of 1 is thermody-
namically feasible and consistent with the oxidative quench-
ing of the excited ZnTPP* by the [FeFe]-cluster.
UV/Vis spectra were recorded in a 1 mL quartz cuvette of 1 cm
pathlength at 298 K on a CARY50 spectrometer. Wavelengths are
given in nm, and extinction coefficients in m–1 cm–1. Emission spec-
tra were recorded on a Shimadzu RF-5301PC spectrophotometer
with excitation and emission slit width both set at 10 nm and using
1 mL quartz cuvette of 1 cm pathlength; wavelengths are given in
nm.
[Fe2(CO)6(1,8-S2-2-CH2-N-(ZnTPP)-C10H5)] (1): To a solution of
amine 15 (0.02 g, 0.02 mmol) in CHCl3 (11 mL) Zn(OAc)2·2H2O
(0.01 g, 0.06 mmol) was added in one portion at room temperature
and the reaction mixture was heated under reflux for 1 h. After this
time TLC analysis (7:3, CH2Cl2/hexane) indicated total consump-
tion of 15. The reaction mixture was cooled down to room tem-
perature and the solvent evaporated under reduced pressure. The
residue was dissolved in toluene (11 mL) and Fe3(CO)12 (0.01 g,
0.03 mmol) was added in one portion at room temperature and the
reaction mixture was refluxed for 3 h under argon atmosphere. The
solvent was removed under reduced pressure and the residue puri-
fied by column chromatography (CH2Cl2) to give complex 1 as a
bright purple opaque solid (0.008 g, 33%). Rf = 0.90 (CH2Cl2); m.p.
Ͼ 300 °C. λnm (CH2Cl2) = 254 (ε = 5.8ϫ104 M–1 cm–1), 308 (ε =
3.3ϫ104 M–1 cm–1), 355 (ε = 3.5ϫ104 M–1 cm–1), 422 (ε = 4.5ϫ105
M–1 cm–1), 550 (ε = 2.6ϫ104 M–1 cm–1), 593 (ε = 7.3ϫ103
Experimental Section
General Experimental: Solvents and reagents were purified as fol-
lows. p-Toluenesulfonic acid monohydrate was purchased from Al-
drich, dehydrated by heating at 100 °C for 4 h under vacuum and
recrystallised from CHCl3.[40] Dry solvents were obtained and puri-
fied using a Pure Solv-MD solvent purification system and were
transferred under argon. All other reagents and solvents were pur-
chased and used as received from commercial sources. The follow-
ing cooling baths were used: 0 °C (ice/water) and –78 °C (dry ice/
acetone). All reactions in non-aqueous solvents were carried out
under argon in oven-dried glassware. Melting points were deter-
M–1 cm–1). IR (solid neat, ATR): ν
= 3413, 3051, 3021, 2922,
˜
max
2852, 2072 (CO), 2032 (CO), 1982 (CO), 1596, 1519, 1485, 1440,
1339, 1205, 1179, 1069, 993, 831, 795, 749, 718, 699 cm–1. 1H NMR
(400 MHz, CDCl3): δ = 4.83 (s, 2 H, CH2), 6.67 (d, J = 7.7 Hz, 2
Eur. J. Inorg. Chem. 2015, 3146–3156
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H, ArH), 7.39 (t, J = 7.6 Hz, 1 H, ArH), 7.69 (d, J = 8.6 Hz, 1 H,
under argon atmosphere. The resulting bright yellow solution was
ArH), 7.71–7.79 (m, 9 H, ArH), 7.94 (d, J = 7.7 Hz, 2 H, ArH), poured into H2O (51 mL) and the two layers were then separated.
7.99 (d, J = 7.8 Hz, 2 H, ArH), 8.22 (d, J = 6.3 Hz, 6 H, ArH),
8.27 (d, J = 7.2 Hz, 1 H, ArH), 8.85–9.03 (m, 8 H, ArH); 13C NMR
(101 MHz, CDCl3): 48.4 (CH2), 111.5 (2ϫ CH), 120.9 (C), 121.1
(2ϫ C), 121.9 (C), 123.3 (C), 124.8 (C), 125.2 (CH), 126.7 (6ϫ
CH), 127.1 (CH), 127.6 (3ϫ CH), 131.4 (CH), 131.9 (2ϫ CH),
The aqueous layer was extracted with CH2Cl2 (3ϫ20 mL). The
combined organic layers were washed with brine (20 mL), dried
with MgSO4 and concentrated under reduced pressure to give the
amine (0.10 g, 99%) as a pale yellow solid, which was used without
further purification. A solution of the amine (0.10 g, 0.32 mmol)
132.0 (4ϫ CH), 132.0 (2ϫ CH), 132.4 (CH), 132.8 (C), 133.3 (CH), and Fe3(CO)12 (0.16 g, 0.32 mmol) in toluene (8.2 mL) was refluxed
133.9 (2ϫ C), 134.6 (6ϫ CH), 135.6 (2ϫ CH), 143.1 (3ϫ C), 143.3
for 4 h under argon atmosphere. The mixture was cooled down to
room temperature, filtered and concentrated under reduced pres-
sure. The residue was purified by column chromatography (8:2,
hexane/EtOAc) to afford complex 4 as a red solid (0.08 g, 39%).
Rf = 0.35 (8:2, hexane/EtOAc); m.p. decomp. above 150 °C. λnm
(CH3CN) = 351 (ε = 1.7ϫ104 M–1 cm–1), 253 (ε = 3.0ϫ104
(C), 146.6 (C), 150.2 (2ϫ C), 150.3 (4ϫ C), 150.9 (2ϫ C), 207.7
(6ϫ C) ppm. MS (ES+): m/z = 1173.0010 (M+, C61H35N5O6S2
-
56
Fe264Zn requires 1173.0019), 1175 (100%), 1171 (10), 1172 (14),
1173 (84), 1174 (98), 1176 (80), 1177 (69), 1178 (49), 1179 (26),
1180 (13), 1181 (6). C61H35N5O6S2Fe2Zn (1175.16): calcd. C 62.34,
H 3.00, N 5.96; found C 62.45, H 3.70, N 5.72.
M–1 cm–1). IR (solid neat, ATR): ν
= 2064 (CO), 2026 (CO),
˜
max
2005 (CO), 1988 (CO), 1963 (CO) cm–1. 1H NMR (400 MHz,
CDCl3): 3.72 (s, 3 H, OCH3), 4.94 (2 H, CH2), 6.61 (d, J = 8.1 Hz,
2 H, ArH), 6.76 (d, J = 8.1 Hz, 2 H, ArH), 7.37 (t, J = 7.8 Hz, 1
H, ArH), 7.65 (d, J = 8.2 Hz, 1 H, ArH), 7.91 (d, J = 8.2 Hz, 1 H,
ArH), 7.95 (d, J = 7.8 Hz, 1 H, ArH), 8.25 (d, J = 7.8 Hz, 1 H,
ArH); 13C NMR: δ = (101 MHz, CDCl3): 49.3 (CH2), 55.9 (CH3),
114.7 (2ϫ CH), 115.1 (2ϫ CH), 122.8 (C), 124.7 (C), 125.0 (CH),
126.8 (CH), 127.4 (C), 131.4 (CH), 132.3 (CH), 133.2 (CH), 133.7
(C), 141.7 (C), 143.9 (C), 152.7 (C), 207.7 (6ϫ C) ppm. m/z (EI+)
604.8994 (M+, C24H15NO756Fe2S2 requires 604.8989), 605 (100%),
606 (14). C24H15NO7Fe2S2 (605.20): calcd. C 47.63, H 2.50, N 2.31;
found C 47.75, H 2.44, N 2.45.
[Fe2(CO)6(1,8-S2-2-CH=N-(4-methoxyphenyl)-C10H5)] (2): A solu-
tion of imine
8 (0.10 g, 0.31 mmol) and Fe3(CO)12 (0.16 g,
0.31 mmol) in toluene (8.0 mL) was refluxed for 2 h under argon
atmosphere. The mixture was cooled down to room temperature,
filtered and concentrated under reduced pressure. The residue was
purified by column chromatography (8:2, hexane/EtOAc) to afford
complex 2 as a bright orange solid (0.14 g, 76%). Rf = 0.75 (8:2,
hexane/EtOAc); mp: decomp. above 140 °C; λnm (CH3CN) 288 (ε
= 2.4ϫ104 M–1 cm–1), 242 (ε = 2.2ϫ104 M–1 cm–1). IR (solid neat,
ATR): ν
= 2066 (CO), 2024 (CO), 1977 (CO), 1959 (CO) cm–1.
˜
max
1H NMR (400 MHz, CDCl3): δ = 3.88 (s, 3 H, OCH3), 7.02 (d, J
= 8.7 Hz, 2 H, ArH), 7.41–7.46 (m, 3 H, ArH), 8.00 (app d, J =
8.5 Hz, 2 H, ArH), 8.27 (d, J = 7.3 Hz, 1 H, ArH), 8.41 (d, J =
8.5 Hz, 1 H, ArH), 9.79 (s, 1 H, HC=N); 13C NMR (101 MHz,
CDCl3): 55.7 (CH3), 114.7 (2ϫ CH), 123.0 (2ϫ CH), 125.2 (CH),
125.8 (C), 126.3 (CH), 126.6 (C), 127.5 (C), 131.3 (CH), 132.3
(CH), 133.6 (CH), 135.5 (C), 139.1 (C), 144.7 (C), 156.4 (CH),
159.2 (C), 207.5 (6ϫ C) ppm. m/z (EI+) 602.8836 (M+,
C24H13NO7S256Fe2 requires 602.8832), 323 (100%), 308 (36), 435
(93, M+ – 6 CO), 519 (72, M+ – 3 CO), 603 (24) [M+].
C24H13NO7S2Fe2 (603.18): calcd. C 47.79, H 2.17, N, 2.32; found
C 47.92, H 2.13, N 2.49.
[Fe2(CO)6(1,8-Se2-2-CH2-N-(4-methoxyphenyl)-C10H5)] (5): NaBH4
(0.18 g, 4.79 mmol) was added in one portion to a solution of imine
9 (0.10 g, 0.24 mmol) in a mixture of MeOH/CHCl3 (5:1, 11 mL)
and the reaction was then stirred for 3 h at room temperature under
argon atmosphere. The resulting bright orange precipitate was
poured into H2O (51 mL) and the two layers were then separated.
The aqueous layer was extracted with CH2Cl2 (3ϫ 20 mL). The
combined organic layers were washed with brine (20 mL), dried
with MgSO4 and concentrated under reduced pressure to give the
amine (0.10 g, 99%) as a pale orange solid, which was used without
further purification. A solution of the amine (0.10 g, 0.25 mmol)
and Fe3(CO)12 (0.13 g, 0.24 mmol) in toluene (6.5 mL) was refluxed
for 2.5 h under argon atmosphere. The mixture was cooled down
to room temperature, filtered and concentrated under reduced pres-
sure. The residue was purified by column chromatography (8:2,
hexane/EtOAc) to afford complex 5 as a red crystalline solid
(0.09 g, 52%). Rf = 0.73 (8:2, hexane/EtOAc); m.p. decomp. above
150 °C. λnm (CH3CN) = 346 (ε = 1.6ϫ104 M–1 cm–1), 305 (ε =
1.4ϫ104 M–1 cm–1), 250 (ε = 3.4ϫ104 M–1 cm–1); IR (solid neat,
[Fe2(CO)6(1,8-Se2-2-CH=N-(4-methoxyphenyl)-C10H5)] (3): A solu-
tion of imine
9 (0.10 g, 0.24 mmol) and Fe3(CO)12 (0.12 g,
0.24 mmol) in toluene (6.2 mL) was refluxed for 1.5 h under argon
atmosphere. The mixture was cooled down to room temperature,
filtered and concentrated under reduced pressure. The residue was
purified by column chromatography (8:2, hexane/EtOAc) to afford
complex 3 as a red solid (0.10 g, 58%). Rf = 0.86 (8:2, hexane/
EtOAc); m.p. decomp. above 140 °C; λnm (CH3CN) 290 (ε =
2.5ϫ104 M–1 cm–1), 242 (ε = 2.7ϫ104 M–1 cm–1). IR (solid neat,
ATR): ν
= 2057 (CO), 2020 (CO), 1997 (CO), 1981 (CO), 1958
˜
max
ATR): ν
= 2061 (CO), 2024 (CO), 1978 (CO), 1953 (CO) cm–1.
(CO) cm–1. 1H NMR (500 MHz, CDCl3): 3.73 (s, 3 H, OCH3), 4.03
(1 H, N-H), 4.95 (2 H, CH2), 6.61 (d, J = 8.8 Hz, 2 H, ArH), 6.78
(d, J = 8.8 Hz, 2 H, ArH), 7.34 (t, J = 7.6 Hz, 1 H, ArH), 7.66 (d,
J = 8.4 Hz, 1 H, ArH), 7.86 (d, J = 8.4 Hz, 1 H, ArH), 7.93 (d, J
= 7.6 Hz, 1 H, ArH), 8.29 (d, J = 7.6 Hz, 1 H, ArH); 13C NMR =
(125 MHz, CDCl3): 51.3 (CH2), 56.0 (CH3), 114.6 (2ϫ CH), 115.2
(2ϫ CH), 118.2 (C), 118.9 (C), 124.9 (CH), 126.8 (CH), 129.7 (C),
131.9 (CH), 132.9 (CH), 133.5 (C), 134.8 (CH), 141.9 (C), 144.3
(C), 152.8 (C), 208.5 (6ϫ C) ppm. MS (ES+): m/z = 699.7958 ([M
+ H]+, C24H16NO756Fe278Se80Se requires 699.7964), 702 (100%),
696 (14), 687 (10), 698 (50), 699 (28), 700 (99), 701 (20), 703 (16),
704 (19). C24H15NO7Fe2Se2 (698.99): calcd. C 41.24, H 2.16, N
2.00; found C 39.49, H 2.00, N 2.30.
˜
max
1H NMR (400 MHz, CDCl3): δ = 3.88 (s, 3 H, OCH3), 7.03 (d, J
= 8.0 Hz, 2 H, ArH), 7.38–7.43 (m, 3 H, ArH), 7.97 (app d, J =
8.5 Hz, 2 H, ArH), 8.32 (d, J = 6.8 Hz, 1 H, ArH), 8.38 (d, J =
8.5 Hz, 1 H, ArH), 9.77 (s, 1 H, HC=N); 13C NMR (101 MHz,
CDCl3): 55.6 (CH3), 114.6 (2ϫ CH), 119.5 (C), 121.0 (C), 122.9
(2ϫ CH), 125.3 (CH), 126.0 (CH), 129.5 (C), 131.7 (CH), 132.9
(CH), 135.0 (CH), 135.1 (C), 140.2 (C), 144.4 (C), 157.4 (CH),
159.1 (C), 208.2 (6ϫ C) ppm. m/z (EI+) 696.7180 (M+, C24H13NO7-
56Fe278Se80Se requires 696.7149), 557 (100%), 559 (78), 611 (9), 613
(35), 615 (35). C24H13NO7Fe2Se2 (696.97): calcd. C 41.36, H 1.88,
N 2.01; found C 39.09, H 2.14, N 2.11.
[Fe2(CO)6(1,8-S2-2-CH2-N-(4-methoxyphenyl)-C10H5)] (4): NaBH4
(0.23 g, 6.20 mmol) was added in one portion to a solution of imine
8 (0.10 g, 0.31 mmol) in a mixture of MeOH/CHCl3 (5:1, 15 mL)
(E)-N-(4-Methoxyphenyl)-1-(naphtho[1,8-cd][1,2]dithiol-3-yl)-
methanimine (8): A solution of aldehyde 6 (0.10 g, 0.46 mmol) and
and the reaction was then stirred for 3 h at room temperature and 4-methoxyaniline (1.10 g, 9.20 mmol) in dry CH3CN (10 mL) was
Eur. J. Inorg. Chem. 2015, 3146–3156
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FULL PAPER
refluxed for 22 h under argon atmosphere. The reaction mixture
was cooled down to room temperature and the solvent was re-
moved under reduced pressure. Purification by column chromatog-
raphy (toluene) gave imine 8 (0.15 g, 96%) as a bright orange crys-
talline solid. Rf = 0.52 (toluene); m.p. 125–126 °C. IR (solid neat,
DMSO) 117.7 (CH), 119.7 (2ϫ C), 119.9 (2ϫ CH), 120.4 (2ϫ C),
120.7 (CH), 122.6 (CH), 126.4 (C), 126.6 (6ϫ CH), 127.5 (3ϫ CH),
129.1 (CH), 129.2 (CH), 131.7 (4ϫ CH), 131.7 (4ϫ CH), 134.2
(6ϫ CH), 134.9 (2ϫ C), 135.4 (2ϫ CH), 141.2 (C), 142.8 (3ϫ C),
145.8 (C), 146.8 (C), 147.8 (C), 149.3 (8ϫ C), 155.4 (CH) ppm.
MS (ES+): m/z = 892.1575 ([M + H]+, C55H34N5S264Zn requires
892.1547), 893 (100%), 891 (84), 892 (96), 894 (87), 895 (80), 896
(63), 897 (51), 898 (30), 900 (24).
ATR): νmax = 3050, 2996, 2951, 2832, 1600, 1572, 1520, 1503, 1494,
˜
1430, 1316, 1289, 1243, 1205, 1183, 1144, 1105, 1058, 1031, 966,
908, 823, 811, 777, 754, 733 cm–1. 1H NMR (400 MHz, CDCl3):
3.85 (s, 3 H, OCH3), 6.97 (d, J = 8.5 Hz, 2 H, ArH), 7.38 (d, J =
8.5 Hz, 2 H, ArH), 7.41–7.47 (m, 3 H, ArH), 7.49 (d, J = 8.3 Hz,
1 H, ArH), 7.57 (d, J = 8.3 Hz, 1 H, ArH), 8.78 (s, 1 H, HC=N);
13C NMR = (101 MHz, CDCl3): 55.7 (CH3), 114.8 (2ϫ CH), 117.3
(CH), 120.4 (CH), 122.3 (2ϫ CH), 126.4 (C), 128.1 (CH), 128.6
(CH), 135.7 (C), 135.8 (C), 141.5 (C), 146.7 (C), 148.6 (C), 151.8
(CH), 158.7 (C) ppm. MS (ES+): m/z = 323.0441 (M+, C18H13NOS2
requires 323.0439), 323 (100 %), 324 (34), 325 (7). C18H13NOS2
(323.43): calcd. C 66.84, H 4.05, N 4.33; found C 67.07, H 3.86, N
4.49.
Zinc (E)-N-(TPP)-Naphtho[1,8-cd][1,2]diselenol-3-ylmethanimine
(12): Zn(OAc)2·2H2O (0.07 g, 0.33 mmol) was added in one portion
to a solution of amine 16 (0.05 g, 0.07 mmol) and aldehyde 7
(0.02 g, 0.07 mmol) in pyridine (10 mL) at room temperature and
under argon atmosphere and the reaction mixture was refluxed for
2 d. The reaction mixture was cooled down to room temperature
and the solvent was evaporated under reduced pressure. The resi-
due was purified by column chromatography (CH2Cl2) to give im-
ine 12 as a bright purple opaque solid (0.04 g, 61%). Rf = 0.94
(CH Cl ); m.p. decomp. above 230 °C. IR (solid neat, ATR): ν
˜
max
2
2
= 3658, 2988, 2971, 2920, 2902, 1596, 1561, 1507, 1483, 1430, 1416,
1394, 1338, 1229, 1204, 1184, 1171, 1141, 1067, 1001, 993, 955,
814, 750, 728, 698 cm–1. 1H NMR (400 MHz, [D6]DMSO): δ =
7.54 (t, J = 8.0 Hz, 1 H, ArH), 7.70 (d, J = 8.0 Hz, 1 H, ArH),
7.80–7.82 (m, 9 H, ArH), 7.93–7.97 (m, 2 H, ArH), 8.02 (d, J =
8.0 Hz, 1 H, ArH), 8.05 (d, J = 8.2 Hz, 2 H, ArH), 8.18–8.21 (m,
6 H, ArH), 8.32 (d, J = 8.2 Hz, 2 H, ArH), 8.79 (s, 4 H, ArH),
8.82 (d, J = 4.6 Hz, 2 H, ArH), 8.91 (d, J = 4.6 Hz, 2 H, ArH),
9.81 (s, 1 H, HC=N) ppm. 13C NMR (101 MHz, [D6]DMSO): δ =
119.5 (C), 120.2 (2ϫ CH), 120.4 (2ϫ C), 122.0 (CH), 123.9 (C),
124.3 (CH), 124.9 (CH), 126.6 (6ϫ CH), 127.5 (3ϫ CH), 128.5
(CH), 128.7 (CH), 130.3 (C), 131.5 (2ϫ CH), 131.6 (4ϫ CH), 131.7
(2ϫ CH), 134.1 (6ϫ CH), 135.6 (2ϫ CH), 136.8 (C), 137.8 (C),
141.6 (C), 142.7 (3ϫ C), 145.2 (C), 145.3 (C), 149.2 (2ϫ C), 149.3
(4ϫ C), 149.5 (2ϫ C), 150.7 (C), 155.3 (CH) ppm. MS (ES+): m/z
= 988.0437 ([M + H]+, C55H34N564Zn 80Se2 requires 988.0436), 988
(100%), 983 (31), 984 (48), 985 (66), 986 (82), 987 (86), 989 (78),
990 (73), 991 (56), 992 (43), 993 (24).
(E)-N-(4-Methoxyphenyl)-1-(naphtho[1,8-cd][1,2]diselenol-3-yl)-
methanimine (9): A solution of TiCl4 (0.04 mL, 0.39 mmol) in dry
CH2Cl2 (0.9 mL) was added dropwise over 10 min to a solution of
aldehyde 7 (0.30 g, 0.96 mmol), 4-methoxyaniline (0.14 g,
1.15 mmol) and NEt3 (0.27 mL, 1.92 mmol) in dry CH2Cl2
(7.9 mL) at 0 °C and under argon atmosphere. After 30 min the
reaction mixture was warmed to room temperature and stirred for
an additional 16 h. The solvent was removed under reduced pres-
sure and the crude product was then purified by column
chromatography (8:2, hexane/EtOAc) to give imine 9 (0.38 g, 94%)
as a bright red crystalline solid. Rf = 0.71 (8:2, hexane/EtOAc);
mp: 124–125 °C. IR (solid neat, ATR): ν
= 1598, 1562, 1504,
˜
max
1432, 1419, 1288, 1243, 1182, 1108, 1029, 830, 813, 796, 756, 737
cm–1. 1H NMR (400 MHz, CDCl3): δ = 3.86 (s, 3 H, OCH3), 6.96–
7.01 (m, 2 H, ArH), 7.39 (d, J = 7.7 Hz, 1 H, ArH), 7.41–7.46 (m,
2 H, ArH), 7.57 (d, J = 7.7 Hz, 1 H, ArH), 7.61 (d, J = 8.4 Hz, 1
H, ArH), 7.70 (d, J = 8.4 Hz, 1 H, ArH), 7.82 (d, J = 7.7 Hz, 1 H,
ArH), 8.93 (s, 1 H, HC=N); 13C NMR (101 MHz, CDCl3): 55.7
(CH3), 115.0 (2ϫ CH), 121.9 (CH), 122.9 (2ϫ CH), 124.6 (CH),
125.0 (CH), 127.6 (CH), 128.1 (CH), 129.9 (C), 137.0 (C), 138.5
(C), 139.8 (C), 145.8 (C), 151.4 (C), 151.8 (CH), 159.0 (C) ppm.
MS (ES+): m/z = 417.9413 ([M + H]+, C18H14NO 78Se80Se requires
417.9414), 420 (100%), 413 (7), 414 (16), 415 (29), 416 (50), 417
(73), 418 (84), 419 (64), 421, (22), 422 (19).
(E)-N-(TPP)-Naphtho[1,8-cd][1,2]dithiol-3-ylmethanimine (13):
La(OTf)3 (0.04 g, 0.06 mmol) was added in one portion to a solu-
tion of amine 10 (0.10 g, 0.16 mmol) and aldehyde 6 (0.05 g,
0.24 mmol) in dry toluene (20 mL) at room temperature and under
argon atmosphere. The reaction mixture was refluxed for 8 h. Tolu-
ene was evaporated under reduced pressure and the residue purified
by column chromatography (CH2Cl2) to give imine 13 as a purple
crystalline solid (0.12 g, 87%). Rf = 0.96 (CH2Cl2); m.p. Ͼ300 °C.
Zinc (E)-N-(TPP)-Naphtho[1,8-cd][1,2]dithiol-3-ylmethanimine (11):
Zn(OAc)2·2H2O (0.04 g, 0.17 mmol) was added in one portion to
a solution of amine 10 (0.06 g, 0.09 mmol) in pyridine (13 mL) at
room temperature and under argon atmosphere and the reaction
mixture was refluxed for 1 h and after this time TLC analysis
(CH2Cl2) indicated total consumption of 10 and formation of zinc
amine 16. The reaction mixture was cooled down to room tempera-
ture, added with aldehyde 6 (0.02 g, 0.09 mmol) and more Zn-
(OAc)2·2H2O (0.08 g, 0.35 mmol) and refluxed for 2 d. Pyridine
was evaporated under reduced pressure and the residue purified by
column chromatography (CH2Cl2) to give zinc imine 11 as a bright
purple opaque solid (0.08 g, 96%). Rf = 0.93 (CH2Cl2); m.p. de-
IR (solid neat, ATR): ν
= 3315, 1595, 1568, 1517, 1471, 1435,
˜
max
1401, 1348, 1315, 1209, 1185, 1169, 1155, 1145, 1072, 1058, 981,
964, 905, 876, 795, 749, 720, 698 cm–1 1H NMR (400 MHz,
.
CDCl3): δ = –2.73 (s, 2 H, inner HN), 7.16–7.22 (m, 1 H, ArH),
7.25–7.29 (m, 1 H, ArH), 7.50–7.54 (m, 3 H, ArH), 7.56 (d, J =
8.4 Hz, 2 H, ArH), 7.71 (d, J = 8.4 Hz, 2 H, ArH), 7.73 (m, 9 H,
ArH), 8.22–8.27 (m, 4 H, ArH), 8.27–8.32 (m, 2 H, ArH), 8.87 (s,
4 H, ArH), 8.89 (d, J = 4.8 Hz, 2 H, ArH), 8.95 (d, J = 4.8 Hz, 2
H, ArH), 9.15 (s, 1 H, HC=N); 13C NMR (101 MHz, CDCl3):
117.5 (CH), 119.7 (C), 120.0 (2ϫ CH), 120.4 (3ϫ C), 120.5 (CH),
122.5 (CH), 126.2 (C), 126.8 (6ϫ CH), 127.9 (3ϫ CH), 129.5 (CH),
129.0 (CH), 130.0–132.0 (br. peak, 8ϫ CH), 134.7 (6ϫ CH), 135.8
(2ϫ CH), 136.0 (2ϫ C), 140.6 (C), 142.3 (3ϫ C), 146.9 (C), 148.0
(C), 149.5 (C), 154.3 (CH) ppm. C-α did not appear in the recorded
13C NMR spectrum. MS (ES+): m/z = 830.2416 ([M + H]+,
C55H36N5S2 requires 830.2412), 830 (100%), 831 (64), 832 (26), 833
(9).
comp. above 200 °C. IR (solid neat, ATR): νmax = 3051, 3020, 2988,
˜
2970, 2921, 1596, 1569, 1518, 1485, 1438, 1339, 1316, 1206, 1170,
1069, 994, 967, 907, 814, 750, 729, 715, 701 cm–1 1H NMR
.
(400 MHz, [D6]DMSO): δ = 7.58–7.63 (m, 1 H, ArH), 7.69 (t, J =
7.6 Hz, 2 H, ArH), 7.77 (d, J = 8.4 Hz, 1 H, ArH), 7.79–7.92 (m,
9 H, ArH), 7.93 (d, J = 8.2 Hz, 2 H, ArH), 8.00 (J = 8.5 Hz, 1 H,
ArH), 8.17–8.23 (m, 6 H, ArH), 8.29 (d, J = 8.2 Hz, 2 H, ArH),
8.78 (s, 4 H, ArH), 8.81 (d, J = 4.6 Hz, 2 H, ArH), 8.90 (d, J = (E)-N-(TPP)-Naphtho[1,8-cd][1,2]diselenol-3-ylmethanimine (14):
4.6 Hz, 2 H, ArH), 9.55 (s, 1 H, ArH); 13C NMR (101 MHz [D6]- La(OTf)3 (0.01 g, 0.01 mmol) was added in one portion to a solu-
Eur. J. Inorg. Chem. 2015, 3146–3156
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tion of amine 10 (0.03 g, 0.05 mmol) and aldehyde 7 (0.03 g,
0.08 mmol) in toluene (6.7 mL) at room temperature and under correction based on gaussian integration over a multifaceted crystal
tion was applied using CrysAlisPro[42] using a numerical absorption
argon atmosphere. The reaction mixture was heated under reflux
and stirred for an additional 8 h. Toluene was removed under re-
duced pressure and the residue purified by column chromatography
(CH2Cl2) to give imine 14 as a purple crystalline solid (0.04 g,
75%). Rf = 0.95 (CH2Cl2); m.p. Ͼ 300 °C. IR (solid neat, ATR):
model for 2. An empirical absorption correction was applied using
CrystalClear-SM Expert[43] for 4. Both structures were solved by
direct methods in SHELXS-2014[44] and were refined by a full-ma-
trix least-squares procedure on F2 in SHELXL-2014.[44] All non-
hydrogen atoms were refined with anisotropic displacement param-
eters. The hydrogen atoms were added at calculated positions and
refined by use of a riding model with isotropic displacement pa-
ν
= 3318, 2921, 2852, 1561, 1509, 1472, 1418, 1348, 1319, 1205,
˜
max
1185, 1171, 1000, 982, 965, 847, 794, 763, 752, 719 cm–1. H NMR
1
(400 MHz, CDCl3): δ = –2.74 (s, 2 H, inner HN), 7.48 (t, J = rameters based on the equivalent isotropic displacement parameter
7.7 Hz, 1 H, ArH), 7.65 (d, J = 7.7 Hz, 1 H, ArH), 7.73–7.82 (m,
11 H, ArH), 7.87 (d, J = 8.2 Hz, 2 H, ArH), 7.90 (d, J = 7.5 Hz,
1 H, ArH), 8.20–8.26 (m, 6 H, ArH), 8.32 (d, J = 8.2 Hz, 2 H,
ArH), 8.86 (s, 4 H, ArH), 8.89 (d, J = 4.8 Hz, 2 H, ArH), 8.94 (d,
J = 4.8 Hz, 2 H, ArH), 9.33 (s, 1 H, HC=N); 13C NMR (101 MHz,
CDCl3): 120.3 (2ϫ CH), 120.4 (4ϫ C), 122.1 (CH), 124.7 (CH),
125.3 (CH), 126.9 (6ϫ CH), 127.9 (3ϫ CH), 128.0 (CH), 128.4
(C), 128.5 (CH), 129.2 (C), 130.0 (C), 131.0–132.0 (br. peak, 8ϫ
CH), 136.7 (6ϫ CH), 136.0 (2ϫ CH), 137.4 (C), 141.1 (C), 142.3
(3ϫ C), 146.2 (C), 146.3 (C), 154.0 (CH) ppm. C-α Pyrrole did
not appear in the recorded 13C NMR spectrum. MS (ES+): m/z
= 924.1331 ([M + H]+, C55H36N578Se80Se requires 924.1309), 926
(100%), 920 (15), 921 (21), 922 (52), 923 (57), 924 (82), 927 (54),
928 (37), 929 (12). C55H35N5Se2 (923.82): calcd. C 71.51, H 3.82,
N 7.58; found C 70.38, H 4.01, N 7.09.
(Ueq) of the parent atom. Figures were produced and some struc-
tural analysis was carried out using OLEX2.[45]
2: The structure contains two crystallographically-independent
molecules. These are connected via a π-π stacking interaction be-
tween the naphthalene groups C(1)–C(10) and C(101)–C(110), with
the angle between the least-squares planes through the atoms being
2.6 (2)° and the perpendicular distance between the plane through
C(1)–C(10) and the centroid of the plane through C(101)–C(110)
being 3.264 (7) Å (see Figure S4).
4: The crystal was the best quality that could be grown but the
diffraction pattern was subject to streaking and as such the refine-
ment is somewhat poor.
X-ray Crystal Data for 2: C24H13Fe2NO7S2, M = 603.17, crystal
dimensions: 0.234ϫ0.067ϫ0.020 mm, triclinic, a = 7.5048(3), b =
16.4362(8), c = 20.4236(14) Å, α = 92.017(5), β = 94.220(5), γ =
TPP-N-(Naphtho[1,8-cd][1,2]dithiol-3-ylmethyl)aniline (15):
NaBH3CN (0.36 mL of a 1 m solution in THF, 0.36 mmol) was
added dropwise to a solution of imine 13 (0.05 g, 0.06 mmol) in a
mixture of THF/MeOH (1:1, 19 mL) at room temperature, fol-
lowed by glacial AcOH (1 drop). The reaction mixture was heated
under reflux for 8.5 h under argon atmosphere. The mixture was
cooled down to room temperature, the solvent evaporated under
reduced pressure and the residue purified by column chromatog-
raphy (8:2, CH2Cl2/hexane to CH2Cl2) to give amine 15 as a purple
crystalline solid (0.03 g, 65 %). Rf = 0.95 (CH2Cl2); mp: 183–
3
¯
95.982(4)°, U = 2496.4(2) Å , space group P1, Z = 4, ρcalcd.
=
1.605 g cm–3, 2θmax = 50.7°, μ = 1.374 mm–1, max./min. trans-
mission factors: 0.993/0.963. 23664 reflections measured, 9108
unique (Rint = 0.0674) which were used in all calculations, 651 pa-
rameters. The final R1 was 0.0834 [I Ͼ 2σ(I)] and wR(F2) was
0.2490 (all data), max./min. residual electron density: 1.189/
–1.349 eÅ3.
X-ray Crystal Data for 4: C24H15Fe2NO7S2, M = 605.19, crystal
dimensions: 0.09 ϫ 0.01 ϫ 0.01 mm, triclinic, a = 7.4381(6), b =
12.1808(9), c = 13.5281(10) Å, α = 96.12(3), β = 101.11(3), γ =
184 °C. IR (solid neat, ATR): νmax = 3316, 3051, 2954, 2921, 2853,
˜
3
¯
91.80(3)°, U = 1194.1(2) Å , space group P1, Z = 2, ρcalcd.
=
1607, 1543, 1519, 1470, 1440, 1402, 1349, 1326, 1298, 1254, 1221,
1183, 1156, 1072, 1054, 1032, 965, 877, 840, 815, 797, 723, 700
1.683gcm–3, 2θmax = 50.056°, μ = 1.436 mm–1, max./min. trans-
mission factors: 1.000/0.545, 8368 reflections measured, 4050
unique (Rint = 0.1722) which were used in all calculations, 325 pa-
rameters. The final R1 was 0.1459 [I Ͼ 2σ(I)] and wR(F2) was
0.4021 (all data), max./min. residual electron density: 2.386/
–0.805 eÅ3.
1
cm–1. H NMR (400 MHz, CDCl3): δ = –2.74 (s, 2 H, inner HN),
4.44 (s, 1 H, HN), 4.58 (s, 2 H, CH2), 7.01 (d, J = 8.4 Hz, 2 H,
ArH), 7.23 (dd, J = 7.3, 0.3 Hz, 1 H, ArH), 7.31 (t, J = 7.7 Hz, 1
H, ArH), 7.40 (dd, J = 8.0, 0.5 Hz, 1 H, ArH), 7.43 (d, J = 8.4 Hz,
1 H, ArH), 7.46 (d, J = 8.4 Hz, 1 H, ArH), 7.69–7.82 (m, 9 H,
ArH), 8.01 (d, J = 8.4 Hz, 2 H, ArH), 8.22 (dd, J = 7.5, 1.5 Hz, 6
H, ArH), 8.83 (s, 6 H, ArH), 8.93 (d, J = 4.4 Hz, 2 H, ArH); 13C
NMR (101 MHz, CDCl3): 48.5 (CH2), 111.9 (2ϫ CH), 116.3 (CH),
119.7 (C), 120.1 (2ϫ C), 120.9 (C), 121.5 (CH), 122.7 (CH), 126.8
(9 ϫ CH), 127.7 (CH), 127.8 (CH), 128.5 (C), 130.0–132.5 (br.
peak, 8ϫ CH), 132.8 (C), 134.7 (6ϫ CH), 135.3 (C), 135.9 (2ϫ
CH), 136.0 (C), 142.1 (C), 142.4 (C), 142.4 (2ϫC), 143.9 (C), 147.1
(C) ppm, C-α Pyrrole did not appear in the recorded 13C NMR
spectrum. MS (ES+): m/z = 832.2565 ([M + H]+, C55H38N5S2 re-
quires 832.2569), 830 (100%), 831 (70), 832 (93), 833 (47), 834 (17).
Electrochemistry: Electrochemical studies were performed with a
CHI601B Electrochemical Analyzer. All measurements were car-
ried out under argon at room temperature in dry CH3CN, with the
exception of 1, where a mixed solvent system of CH2Cl2/CH3CN
(7:3) was used because complex 1 is not soluble in acetonitrile,
while AgNO3 (the reference electrode) is not soluble in CH2Cl2.
Tetrabutylammoniun hexafluorophosphate (NBu4PF6, 0.1 m in
CH3CN) was used as supporting electrolyte. A conventional 3-elec-
trode system was employed. The working electrode was a glassy
carbon electrode (diameter: 1.0 mm). Silver/silver nitrate (Ag/
AgNO3, 10 mm solution in CH3CN) was used as an external refer-
ence electrode and a platinum wire was used as auxiliary electrode.
Ferrocene was used as an internal reference. All potentials reported
in this work are with reference to the Fc/Fc+ couple. Cyclic voltam-
mograms were recorded at a scan rate of 0.01 V s–1. The range
–0.8 V to –2.5 V, focusing on the wave, was also recorded at sweep
rates between 0.01 Vs–1 to 0.2 Vs–1, although the capacitive current
of the carbon substrate was rather high at the higher sweep rates.
X-ray Crystallography: Suitable crystals were selected and datasets
were measured on an Agilent SuperNova diffractometer equipped
with an Atlas detector for 2 (λMo–Kα = 0.71073 Å) and by the
EPSRC UK National Crystallography Service[39] on a Rigaku
AFC12 goniometer equipped with an enhanced sensitivity (HG)
Saturn724+ detector mounted at the window of an FR-E+ Su-
perBright molybdenum rotating anode generator (λ = 0.71075 Å,
Mo-Kα) with HF Varimax optics for 4. Both instruments were
equipped with an Oxford Cryosystems Cryostream device with dif-
fraction data collected at 100 K in all cases. An absorption correc-
All glassware was cleaned using a 1:1 mixture of ammonia and
hydrogen peroxide followed by thorough rinsing with pure water.
Eur. J. Inorg. Chem. 2015, 3146–3156
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FULL PAPER
grand, C. E. Hatchikian, J.-C. Fontecilla-Camps, Structure
1999, 7, 13–23.
Glassware was soaked in pure water for 12 h and then rinsed and
oven-dried overnight. Water used throughout (including solution
preparation and rinsing) was purified by a Millipore™ system (res-
istivity 18.2 MΩ cm, TOC Յ 5 ppb). The working electrode was
prepared by polishing with aqueous slurries of successively finer
grades of alumina powder (1 μm, 0.3 μm and 0.05 μm, Buehler),
followed by rinsing and placing in pure water in an ultrasonic bath
for several minutes, then dried in a stream of argon.
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The authors thank the Engineering and Physical Sciences Research
Council (EPSRC) and the University of Birmingham for funding.
The NMR spectrometers used in this research were obtained
through Birmingham Science City: Innovative Uses for Advanced
Materials in the Modern World (West Midlands Centre for Ad-
vanced Materials Project 2), with financial support from the Ad-
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Received: April 8, 2015
Published Online: June 12, 2015
Eur. J. Inorg. Chem. 2015, 3146–3156
3156
© 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim