Synthesis and reactivity of (pyrazol-1-yl)acyl iron complexes

Article abstract of DOI:10.1016/j.jorganchem.2015.06.008

Abstract Treatment of 1-methyl-3,5-dialkylpyrazoles with n-BuLi, and subsequently with iron carbonyl and iodine yielded (pyrazol-1-yl)acyl iron complexes CH₂(CO) (3,5-R₂Pz)Fe(CO)₃I (R = Me or Prⁱ, Pz = pyrazol-1-yl). Reaction of CH₂(CO) (3,5-Me₂Pz)Fe(CO)₃I with PhSNa gave a dimeric complex [CH₂(CO) (3,5-Me₂Pz)Fe(CO)₂(SPh)]₂, while similar reactions of CH₂(CO) (3,5-R₂Pz)Fe(CO)₃I with PySNa (Py = 2-pyridyl) gave mononuclear complexes CH₂(CO) (3,5-R₂Pz)Fe(CO)₂(SPy), which exhibited an isomerization in solution. Treatment of the dimeric complex with PPh₃ at room temperature resulted in the decomposition of the starting material. Furthermore, this dimeric complex readily underwent reductive elimination to generate CH₂(COSPh) (3,5-Me₂Pz) when heated at relatively low temperature, and thermal decomposition reaction to give PhSSPh in refluxing toluene solution. Reaction of mononuclear complexes with PPh₃ caused one carbonyl to be replaced by phosphine ligand to give complexes CH₂(CO) (3,5-R₂Pz)Fe(CO) (PPh₃) (SPy). All these acyl iron complexes were fully characterized by IR and NMR spectroscopy, and their structures were unambiguously determined by X-ray crystallography.

Full text of DOI:10.1016/j.jorganchem.2015.06.008

Journal of Organometallic Chemistry 791 (2015) 303e310
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and reactivity of (pyrazol-1-yl)acyl iron complexes
Da-Wei Zhao, Yi Xu, Yao-Wei Guo, Hai-Bin Song, Liang-Fu Tang*
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering,
Nankai University, Tianjin 300071, People's Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Treatment of 1-methyl-3,5-dialkylpyrazoles with n-BuLi, and subsequently with iron carbonyl and iodine
yielded (pyrazol-1-yl)acyl iron complexes CH2(CO) (3,5-R2Pz)Fe(CO)3I (R ¼ Me or Pri, Pz ¼ pyrazol-1-yl).
Reaction of CH2(CO) (3,5-Me2Pz)Fe(CO)3I with PhSNa gave a dimeric complex [CH2(CO) (3,5-Me2Pz)
Fe(CO)2(SPh)]2, while similar reactions of CH2(CO) (3,5-R2Pz)Fe(CO)3I with PySNa (Py ¼ 2-pyridyl) gave
mononuclear complexes CH2(CO) (3,5-R2Pz)Fe(CO)2(SPy), which exhibited an isomerization in solution.
Treatment of the dimeric complex with PPh3 at room temperature resulted in the decomposition of the
starting material. Furthermore, this dimeric complex readily underwent reductive elimination to
generate CH2(COSPh) (3,5-Me2Pz) when heated at relatively low temperature, and thermal decompo-
sition reaction to give PhSSPh in refluxing toluene solution. Reaction of mononuclear complexes with
PPh3 caused one carbonyl to be replaced by phosphine ligand to give complexes CH2(CO) (3,5-R2Pz)
Fe(CO) (PPh3) (SPy). All these acyl iron complexes were fully characterized by IR and NMR spectroscopy,
and their structures were unambiguously determined by X-ray crystallography.
Received 1 April 2015
Received in revised form
4 June 2015
Accepted 6 June 2015
Available online 10 June 2015
Keywords:
Pyrazole
Pyridine
Iron carbonyl
Metal-acyl complex
Thiolate
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
polydentate ligands not only plays an important role in stabilizing
metal-acyl complexes during their formation [29e31], but also
The metal-acyl complexes are of great importance since they
have proven to be excellent homogenous catalysts or crucial active
intermediates in many important organic transformations [1e5],
especially such as catalytic carbonylation reactions [6e9].
Furthermore, the metal-acyl unit has been introduced into the
main chain of polymers to form potential functional organometallic
materials [10,11], which develops the new application fields of
metal-acyl complexes. In addition, since the successful elucidation
of the structure of [Fe]-hydrogenase [12] indicated that an acyl-iron
ligates to the active site of [Fe]-hydrogenase [13e15], many acyl
iron complexes have been synthesized as biomimetic models for
the active site of [Fe]-hydrogenase [16e25], which greatly pro-
motes the development of metal-acyl complexes and widely
broadens the potential application areas of metal-acyl complexes.
Our recent investigations showed that polydentate pyrazolyl-based
ligands could potentially be used to stabilize metal-acyl complexes
[26e28]. These interesting results encouraged us to explore other
related metal-acyl complexes based on pyrazolyl-based ligands. On
the other hand, it is known that the chelation-assisted effect of
significantly affects their reactivity [3]. As a part of our in-
vestigations on the metal-acyl complexes, in order to deeply un-
derstand the effect of the chelation-assisting roles of polydentate
ligands on the reactivity and properties of the corresponding
metal-acyl complexes, in this paper we describe the synthesis and
reactivity of new pyrazolyl-based iron complexes containing
bidentate (pyrazol-1-yl)acyl ligands.
2. Results and discussion
2.1. Synthesis of (pyrazol-1-yl)acyl iron complexes
It is known that N-alkyl-3,5-dialkylpyrazoles underwent lith-
iation exclusively at the a-position of the N-alkyl groups [32], and
the resulting lithium salts could react with various electrophiles,
leading to the corresponding carbanions as important synthetic
intermediates. Herein we find that treatment of the 1-lithio de-
rivatives
of
1,3,5-trimethylpyrazole
and
1-methyl-3,5-
diisopropylpyrazole with Fe(CO)5 followed by I2 yields (pyrazol-1-
yl)acyl iron complexes 1 and 2 (Scheme 1). These two complexes
were air-stable in the solid state and their solution could be
manipulated in air for a short time without notable decomposition.
They were fully characterized by IR and NMR spectroscopy.
* Corresponding author.
E-mail address: lftang@nankai.edu.cn (L.-F. Tang).
http://dx.doi.org/10.1016/j.jorganchem.2015.06.008
0022-328X/© 2015 Elsevier B.V. All rights reserved.

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D.-W. Zhao et al. / Journal of Organometallic Chemistry 791 (2015) 303e310
Scheme 1. Synthesis and reactivity of (pyrazol-1-yl)acyl iron complexes.
The IR spectra of 1 and 2 showed that the characteristic acyl
by 2-pyridinethiolate caused the characteristic acyl carbonyl peaks
of 5 (1650 cmꢀ1) and 6 (1655 cmꢀ1) in their IR spectra to signifi-
cantly shift toward lower wave numbers compared to those of 1
and 2, which should be attributed to the stronger donor ability of 2-
pyridinethiolate than iodide strengthening metal to carbonyl back
bonding. The 1H and 13C NMR spectra of 5 and 6 displayed two sets
of proton and carbon signals, indicating the presence of isomers
(Scheme 2). The assignment of isomers was based on the NOE ex-
periments and the X-ray crystal structure determination of isomer
5A (Fig. 2). Though the high similarity in the properties of 5A and
5B complicated the spectra, two sets of signals with a ratio of ca. 4/1
in CDCl3 were clearly integrated for the two isomers respectively.
For the signal set with larger integrals, strong correlation was
observed in the NOESY spectrum between the methyl signal at
1.68 ppm and the aromatic proton at 8.10 ppm which should be the
carbonyl (C]O) peak occurred at 1667 and 1676 cmꢀ1, respectively,
lower than those in tridentate acyl ligated iron complexes, but
higher than those in monodentate acyl ligated iron complexes [26].
The corresponding acyl carbons resonated at 254.0 ppm (1) and
254.2 ppm (2) in their 13C NMR spectra, which were comparable to
those in monodentate and tridentate acyl ligated iron complexes
[26]. In addition, the protons of the methylene group of these two
complexes displayed an AB system in their 1H NMR spectra, indi-
cating that the five-membered metallacyclic structure was reserved
in solution, which resulted in these two diastereotopic protons.
Furthermore, four sets of proton and carbon signals of the isopropyl
methyl groups were observed in the 1H and 13C NMR spectra of 2,
reflecting that their free rotation was hindered possibly due to the
repulsion among the bulky isopropyl groups.
2.2. Reaction of (pyrazol-1-yl)acyl iron complexes with ArSNa (Ar ¼
Ph or 2-pyridyl)
Reaction of 1 with PhSNa gave a dimeric complex (3) (Scheme
1). The oxidative addition of thioesters to iron(0) to afford acyl
thiolato iron complexes is known [16,17], but the dimeric complex
readily underwent reductive elimination to generate S-phenyl (3,5-
dimethylpyrazol-1-yl)thioacetate (4) when heated at relatively low
temperature (45 ꢁC), and thermal decomposition reaction to give
PhSSPh in refluxing toluene solution. Additionally, compound 4
was easily decomposed to afford PhSSPh with other uncharacter-
izable products when heated in refluxing toluene. Some analogous
spectroscopic features were observed in complexes 1e3. For
example, their IR spectra showed a resembling acyl carbonyl ab-
sorption peak. The 1H NMR spectrum of 3 also displayed the
inequivalent methylene protons, similar to those in 1 and 2. The
structure of 3 was further confirmed by X-ray crystallography, and
is shown in Fig.1. The (pyrazol-1-yl)acyl group is bonded to the iron
atom in a bidentate
distances (2.347e2.408 Å) are unequal, but comparable to those
reported in other acyl diiron complexes with the -SPh group, such
k
2-[N,C] chelating fashion. The FeeS bond
m
as 2.3102e2.3972 Å in Fe2(SPh)2[Ph2PC6H4C(O)]2(CO)3 [16]. The
FeꢀCacyl and FeeN bond distances are similar to the corresponding
values reported for tridentate chelating bis(pyrazol-1-yl)acyl iron
derivatives [26]. The CꢀCacyl bond distance is 1.544(6) Å, close to
those in monodentate acyl iron complexes, but slightly shorter than
those in tridentate acyl iron complexes [26].
Fig. 1. The molecular structure of 3. The thermal ellipsoids are drawn at the 30%
probability level. Selected bond distances (Å) and angles (ꢁ): Fe(1)eS(1) 2.347(2),
Fe(1)eS(2) 2.408(1), Fe(1)eN(1) 2.033(4), Fe(1)eC(5) 1.938(5), Fe(2)eS(1) 2.402(1),
Fe(2)eS(2) 2.347(2), Fe(2)eN(4) 2.039(3), Fe(2)eC(6) 1.945(5), C(5)eO(5) 1.213(5),
C(6)eO(6) 1.217(5), C(5)eC(7) 1.544(6) Å; C(5)eFe(1)eS(2) 166.6(2), C(5)eFe(1)eN(1)
84.1(2), C(6)eFe(2)eS(1) 171.4(2), C(6)eFe(2)eN(4) 82.1(2), Fe(1)eS(1)eFe(2) 98.19(5),
Fe(1)eS(2)eFe(2) 98.05(5), Fe(1)eC(5)eO(5) 130.5(4), Fe(1)eC(5)eC(7) 112.9(3),
Fe(2)eC(6)eC(13) 111.0(3), Fe(2)eC(6)eO(6) 131.9(4), C(6)eC(13)eN(3) 108.6(4), C(5)e
C(7)eN(2) 110.4(4)ꢁ.
Reaction of 1 and 2 with PySNa (Py ¼ 2-pyridyl) gave mono-
nuclear complexes 5 and 6, respectively. The substitution of iodide

D.-W. Zhao et al. / Journal of Organometallic Chemistry 791 (2015) 303e310
305
Scheme 2. The isomerization of complexes 5 and 6 as well as the NOE of complexes 5, 6 and 8.
H6 of pyridyl, indicating the proximity of the 3-methyl of pyrazolyl
to the pyridyl ring. This spatial arrangement fitted the three-
dimensional description of the isomer with the pyridyl ring trans
to the bridging acyl and thus assigned the signal set with larger
integrals to 5A. The NOE signals were attenuated for 5B due to the
relatively small amount of the isomer but still recognizable. A
correlation between the methylene proton at 4.39 ppm and the
aromatic proton at 7.51 ppm was consistent with the structure of
5B, corroborating the above NMR assignment of 5A and differen-
tiated the methylene proton Ha with Hb as well, since only one of
the methylene protons could spatially approach the pyridyl ring.
The structural difference of isomers A and B mainly originates from
the relative location between 2-pyridinethiolate and (pyrazol-1-yl)
acyl. It is also interesting that the relative ratio of isomers 5A and 5B
is different in the CDCl3 and acetone-d6 solutions, reflecting that
the conversion between isomer A and isomer B is possible in so-
lution. Moreover, this conversion can be explained by a plausible
pathway through the partial dissociation of the nitrogen ligands
and succedent association process with the help of solvent [33,34].
The structure of isomer 5A has been confirmed by X-ray crystal
structural analyses, and is presented in Fig. 2, which shows the
pyridyl nitrogen atom occupies the position trans to the acyl group
with the angle C(3)ꢀFe(1)ꢀN(1) of 160.51(9)ꢁ. The shortest distance
between H6 of pyridyl and 3-methyl protons of pyrazolyl is 2.771 Å,
suggesting the NOE correlation between these protons as shown by
the NOE experiments. Other structural parameters such as FeeN,
FeeS and FeꢀCacyl bond distances are analogous to those in 3.
decomposition of the starting material, which was significantly
different from the reactivity of the related thiolate diiron de-
rivatives with the
m-SR groups [19,35,36]. The reason for this
dissimilarity is not completely clear at present, which may be
attributed to the instability of the resulting products as well as the
easy reductive elimination from 3. Although the decomposition
reaction occurred upon treatment of 3 with PPh3, complexes 7e9
were successfully obtained by the substitution of carbonyl in 1, 5
and 6 by PPh3, and characterized by IR and NMR spectroscopy. Their
acyl carbonyl absorption frequencies (1641ꢀ1655 cmꢀ1) were close
to those of 5 and 6. Their 1H, 13C and 31P NMR showed only one set
of proton, carbon and phosphorous signals, which unanimously
confirmed that these three complexes had no isomers in solution,
unlike complexes 5 and 6. Moreover, like that in 5B, the obvious
NOE correlation between H6 of pyridyl and one methylene proton
Ha was also observed in 8 (Scheme 2), suggesting that 2-
pyridinethiolate and (pyrazol-1-yl)acyl should be in the same
relative location in these two complexes.
A computational
modeling suggested that 8 is more stable by 3.0 kcal/mol than its
potential isomer that has a structure analogous to 5A, explaining
the exclusive existence of 8, while in the case of 5 the two isomers
have an energy difference of only 0.2 kcal/mol (see the
Supplementary materials). This clear energy difference in the case
of 8 most probably comes from the preference of aligning the
electronegative ligands, namely the triphenylphosphine and the
pyridyl ring, in trans positions. While two same carbonyl ligands in
5 minimized this effect and radically reduced the energy difference.
The structures of 7e9 were confirmed by X-ray crystallography,
and are shown in Figs. 3e5, respectively. Fig. 3 shows that the iron
atom adopts a six-coordinate distorted octahedral geometry with
the iodine and phosphorous atoms in a trans configuration. The
2.3. Reaction of (pyrazol-1-yl)acyl iron complexes with PPh3
Treatment of 3 with PPh3 at room temperature rendered the
Fig. 2. The molecular structure of 5A. The thermal ellipsoids are drawn at the 30% probability level. Selected bond distances (Å) and angles (ꢁ): Fe(1)eS(1) 2.3764(7), Fe(1)eN(1)
2.053(2), Fe(1)eN(2) 1.989(2), Fe(1)eC(3) 1.935(3), C(3)eO(3) 1.214(3), C(3)eC(4) 1.538(3) Å; N(1)eFe(1)eS(1) 69.82(6), C(3)eFe(1)eN(2) 82.9(1), C(1)eFe(1)eN(2) 172.3(1), N(2)e
Fe(1)eS(1) 90.62(6), C(3)eFe(1)eN(1) 160.51(9), Fe(1)eC(3)eO(3) 130.7(2), Fe(1)eC(3)eC(4) 111.5(2), Fe(1)eS(1)eC(10) 78.91(8), C(3)eC(4)eN(3) 108.5(2)ꢁ.

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D.-W. Zhao et al. / Journal of Organometallic Chemistry 791 (2015) 303e310
angle P(1)ꢀFe(1)ꢀI(1) is 170.34(2)ꢁ. Figs. 4 and 5 show that the
fundamental frameworks in complexes 8 and 9 are similar to each
other. In these two complexes, the sulfur atom instead of the pyr-
idyl nitrogen occupies the position trans to the acyl group with the
angle C(2)ꢀFe(1)ꢀS(1) of 161.9(1)ꢁ for 8 and 160.91(7)ꢁ for 9,
respectively. The shortest distance between H6 of pyridyl and the
methylene protons is 2.737 Å, in the range of the NOE correlation
between these protons. The structural features of 8 and 9 also
indirectly support the suggested structures of isomers 5B and 6B,
since the resembling NOE between H6 of pyridyl and one of the
methylene protons was observed in 5B and 8. Complexes 7e9
possess analogous FeeN, FeꢀCacyl and CꢀCacyl bond distances,
which are also comparable to those in 1 and 5A, as well as the
corresponding values in some model complexes for the active site
of [Fe]-hydrogenase [16e20].
In summary, (pyrazol-1-yl)acyl iron complexes are readily ob-
tained through the reaction of 1-lithio derivatives of 1-methyl-3,5-
dialkylpyrazoles with Fe(CO)5 followed by I2, which can be good
starting materials for new acyl iron species with interesting
structural features because of their high chemical reactivity.
Although several kinds of mimics of the [Fe]-hydrogenase active
site bearing acyl [20], acylphosphine [16], carbamoylpyridine [18]
and acylmethylpyridine [21,25] ligands have appeared in litera-
ture, other structural models should be welcome to gain deeply
understanding of the structure and catalytic function of [Fe]-
hydrogenase. These newly synthesized acylmethylpyrazole iron
complexes may be used as potential models for the active site of
[Fe]-hydrogenase, which is in progress.
Fig. 4. The molecular structure of 8. The thermal ellipsoids are drawn at the 30%
probability level. Selected bond distances (Å) and angles (ꢁ): Fe(1)eP(1) 2.239(1),
Fe(1)eS(1) 2.471(1), Fe(1)eN(2) 2.011(2), Fe(1)eN(3) 2.001(3), Fe(1)eC(2) 1.901(3),
C(2)eO(2) 1.224(4), C(2)eC(3) 1.549(5) Å; N(3)eFe(1)eP(1) 173.0(1), C(1)eFe(1)eN(2)
176.0(1), N(3)eFe(1)eS(1) 68.7(1), C(2)eFe(1)eN(2) 84.5(1), C(2)eFe(1)eS(1) 161.9(1),
Fe(1)eS(1)eC(13) 76.5(1), Fe(1)eC(2)eO(2) 131.1(3), Fe(1)eC(2)eC(3) 113.7(2), Fe(1)e
P(1)eC(26) 116.5(1), C(20)eP(1)eC(26) 100.8(1), C(2)eC(3)eN(1) 109.7(3)ꢁ.
the chemical shifts were reported in ppm with respect to the
reference (internal SiMe4 for 1H and 13C NMR spectra, external 85%
H3PO4 aqueous solution for 31P NMR spectra). IR spectra were
recorded as KBr pellets on a Nicolet 380 spectrometer. Elemental
analyses were carried out on an Elementar Vairo EL analyzer. HR
mass spectra were obtained on a Varian QFT-ESI spectrometer.
Melting points were measured with an X-4 digital micro melting-
point apparatus and were uncorrected.
3. Experimental
All reactions were carried out under an atmosphere of argon.
Solvents were dried and freshly distilled prior to use according to
standard procedures. NMR spectra were recorded on a Bruker 400
spectrometer using CDCl3 as solvent unless otherwise noted, and
Fig. 5. The molecular structure of 9. The thermal ellipsoids are drawn at the 30%
probability level. Selected bond distances (Å) and angles (ꢁ): Fe(1)eP(1) 2.2620(7),
Fe(1)eS(1) 2.4935(7), Fe(1)eN(1) 2.024(2), Fe(1)eN(3) 2.007(2), Fe(1)eC(2) 1.894(2),
C(2)eO(2) 1.232(3), C(2)eC(3) 1.539(3) Å; N(3)eFe(1)eP(1) 174.04(6), C(1)eFe(1)e
N(1) 175.6(1), N(3)eFe(1)eS(1) 68.33(6), C(2)eFe(1)eN(1) 84.74(9), C(2)eFe(1)eS(1)
160.91(7), Fe(1)eC(2)eO(2) 130.9(2), Fe(1)eC(2)eC(3) 114.1(2), Fe(1)eP(1)eC(18)
116.92(8), C(18)eP(1)eC(30) 101.8(1), C(13)eC(12)eC(14) 111.1(2), C(16)eC(15)eC(17)
113.1(3), C(2)eC(3)eN(2) 110.4(2)ꢁ.
Fig. 3. The molecular structure of 7. The thermal ellipsoids are drawn at the 30%
probability level. Selected bond distances (Å) and angles (ꢁ): Fe(1)eI(1) 2.676(1),
Fe(1)eC(3) 1.973(3), Fe(1)eN(2) 1.984(2), Fe(1)eP(1) 2.273(1), C3eO(3) 1.211(3),
C3eC(4) 1.543(4) Å; P(1)eFe(1)eI(1) 170.34(2), N(2)eFe(1)eC(3) 83.5(1), Fe(1)eC(3)e
O(3) 129.9(2), Fe(1)eC(3)eC(4) 112.8(2), Fe(1)eP(1)eC(22) 119.93(9), C(10)eP(1)e
C(22) 101.8(2), C(3)eC(4)eN(1) 110.1(2)ꢁ.

D.-W. Zhao et al. / Journal of Organometallic Chemistry 791 (2015) 303e310
307
3.1. Synthesis of 1,3,5-trimethylpyrazole and 1-methyl-3,5-
diisopropylpyrazole
mixture was continuously stirred for 6 h. The solvent was removed
under reduced pressure, and the residue was purified by column
chromatography on silica with ethyl acetate/hexane (1:1, v/v) as the
eluent. The yellow eluate was concentrated to dryness to afford
NaH (60 mmol) was added to the solution of 3,5-
dimethylpyrazole or 3,5-diisopropylpyrazole (50 mmol) in THF
(40 ml) at room temperature. The resulting mixture was stirred for
1 h, and then CH3I (50 mmol) was added. After the reaction mixture
was continuously stirred overnight at room temperature, water
(100 ml) was added slowly. The solution was extracted with ethyl
acetate (3 ꢂ 50 ml). The organic layers were combined, washed
with saturated brine and dried over anhydrous MgSO4. The solvent
was removed in vacuo to give the expected products.
90 mg (66%) of 3. Mp 66e70 ꢁC (dec.). 1H NMR:
d 2.30 (s, 6H), 2.31
(s, 6H) (CH3), 3.92 (d, J ¼ 15.4 Hz, 2H), 4.48 (d, J ¼ 15.4 Hz, 2H) (CH2),
6.04 (s, 2H, H4 of pyrazole), 7.15 (t, J ¼ 7.3 Hz, 2H), 7.25 (t, J ¼ 7.9 Hz,
4H), 7.68 (d, J ¼ 7.7 Hz, 4H) (C6H5) ppm. 13C NMR:
d 12.2, 15.5 (CH3),
64.4 (CH2), 109.1 (C4 of pyrazole), 125.5, 128.8, 131.4, 138.6 (C6H5),
140.6, 154.2 (C3 and C5 of pyrazole), 207.1, 213.4 (C^O), 262.2 (C]
O) ppm. IR: nC^O ¼ 2087 (vs), 2037 (vs, br), 1977 (vs); nC]O ¼ 1678
(s) cmꢀ1. Anal. Calc. for C30H28Fe2N4O6S2: C, 50.30; H, 3.94; N, 7.82.
Found: C, 50.12; H, 3.63; N, 7.95%.
1,3,5-Trimethylpyrazole, yield: 46%. 1H NMR:
d 2.18 (s, 3H), 2.19
(s, 3H) (CH3), 3.67 (s, 3H, NCH3), 5.76 (s, 1H, H4 of pyrazole) ppm. 13
C
NMR:
d
11.0, 13.4 (CH3), 35.6 (NCH3), 104.8 (C4 of pyrazole), 139.0,
3.5. Reaction of 3 with PPh3
147.0 (C3 and C5 of pyrazole) ppm.
1-Methyl-3,5-diisopropylpyrazole, yield: 43%. 1H NMR:
d
1.23 (d,
PPh3 (51 mg, 0.19 mmol) was added to the solution of 3 (70 mg,
0.098 mmol) in CH2Cl2 (15 ml), the resulting reaction mixture was
stirred overnight at room temperature. After the solvent was
removed under reduced pressure, the residue was separated by
column chromatography on silica. This reaction yielded no char-
acterizable products.
J ¼ 1.8 Hz, 6H), 1.25 (d, J ¼ 1.9 Hz, 6H) (CH3), 2.85e2.95 (m, 2H, CH),
3.75 (s, 3H, NCH3), 5.82 (s, 1H, H4 of pyrazole) ppm. 13C NMR:
d 22.3,
23.0 (CH3), 25.5, 27.9 (CH), 35.7 (NCH3), 98.1 (C4 of pyrazole), 149.6,
157.8 (C3 and C5 of pyrazole) ppm.
3.2. Synthesis of CH2(CO) (3,5-Me2Pz)Fe(CO)3I (1)
3.6. Thermal decomposition reaction of 3
A hexane solution of n-BuLi (1.6 M, 0.63 ml, 1 mmol) was added
to the solution of 1,3,5-trimethylpyrazole (0.11 g, 1 mmol) in THF
(30 ml) at ꢀ78 ꢁC. The resulting mixture was stirred for 1 h at that
temperature, and then Fe(CO)5 (0.13 ml, 1 mmol) was added. The
reaction mixture was continuously stirred at ꢀ78 ꢁC for 0.5 h,
allowed to reach room temperature slowly and stirred for 2 h. Then,
a solution of I2 (0.25 g, 1 mmol) in THF (10 ml) was added dropwise.
After completion of addition, the reaction mixture was stirred
overnight. The solvent was removed under reduced pressure, and
the residue was purified by column chromatography on silica with
CH2Cl2 as the eluent. The red eluate was concentrated to dryness to
give 1 as a red solid. Yield: 0.12 g (30%), mp 43e50 ꢁC (dec.). 1H
The solution of 3 (86 mg, 0.12 mmol) in toluene (10 ml) was
stirred and heated at 45 ꢁC for 6 h. The solvent was removed under
reduced pressure, and the residue was purified by column chro-
matography on silica with ethyl acetate as the eluent. The eluate
was concentrated to dryness to give compound 4 as a slightly yel-
low liquid. Yield: 18 mg (31%). 1H NMR:
d
2.21 (s, 6H, CH3), 4.88 (s,
2H, CH2), 5.87 (s, 1H, H4 of pyrazole), 7.32e7.35 (m, 5H, C6H5) ppm.
13C NMR: 11.2, 13.6 (CH3), 57.6 (CH2), 106.5 (C4 of pyrazole), 126.2,
d
129.3, 129.7, 134.6 (C6H5), 140.7, 149.3 (C3 and C5 of pyrazole), 195.0
(C]O) ppm. HRMSeESI (m/z): 269.0722 (Calc. for C13H14N2NaOS:
269.0725, [MþNa]þ, 100%).
NMR:
d
2.36 (s, 3H), 2.49 (s, 3H) (CH3), 4.52 (d, J ¼ 16.2 Hz, 1H), 5.08
When the toluene solution of 3 was stirred and heated at reflux
for 3 h, PhSSPh was obtained in 52% yield after column chroma-
tography on silica with hexane as the eluent, and confirmed by
comparison of NMR spectroscopic data with those of the authentic
sample of PhSSPh. In addition, PhSSPh was obtained in ca. 25% yield
with other uncharacterizable products when heating 4 in refluxing
toluene.
(d, J ¼ 16.2 Hz, 1H) (CH2), 6.10 (s, 1H, H4 of pyrazole) ppm. 13C NMR:
d
12.5, 15.6 (CH3), 67.2 (CH2), 109.9 (C4 of pyrazole), 141.7, 152.1 (C3
and C5 of pyrazole), 200.5, 206.7, 207.5 (C^O), 254.0 (C]O) ppm.
IR: nC^O ¼ 2087 (vs), 2041 (vs), 2014 (vs), 1979 (sh); nC]O ¼ 1667
(s) cmꢀ1. Anal. Calc. for C10H9FeIN2O4: C, 29.73; H, 2.25; N, 6.94.
Found: C, 29.47; H, 2.50; N, 6.73%.
3.3. Synthesis of CH2(CO) (3,5-Pri2Pz)Fe(CO)3I (2)
3.7. Synthesis of CH2(CO) (3,5-Me2Pz)Fe(CO)2(SPy) (5)
This complex was similarly obtained as above-mentioned for 1,
while 1,3,5-trimethylpyrazole was replaced by 1-methyl-3,5-
diisopropylpyrazole. Yield: 26%, mp 41e44 ꢁC (dec.). 1H NMR:
This complex was similarly obtained as above-mentioned for 3,
but PhSH was replaced by 2-mercaptopyridine. Yield: 57%, mp
70e77 ꢁC (dec.). Complex 5 displayed two isomers (5A/5B) in so-
lution. The relative ratio of isomers 5A/5B was ca. 4/1 in CDCl3 and
3/1 in acetone-d6, respectively, according to the integration of the
corresponding protons of the methylene group. 1H NMR of isomer
d
1.30 (d, J ¼ 3.8 Hz, 3H), 1.32 (d, J ¼ 3.8 Hz, 3H), 1.38 (d, J ¼ 6.8 Hz,
3H), 1.43 (d, J ¼ 6.8 Hz, 3H) (CH3), 2.88e2.98 (m, 1H), 3.18e3.29 (m,
1H) (CH), 4.58 (d, J ¼ 16.1 Hz, 1H), 5.17 (d, J ¼ 16.1 Hz, 1H) (CH2), 6.15
(s, 1H, H4 of pyrazole) ppm. 13C NMR:
d
21.5, 21.8, 22.9 (2 ꢂ C) (CH3),
of 5A: d 1.68 (s, 3-CH3 of pyrazole), 2.30 (s, 5-CH3 of pyrazole), 4.24
27.1, 29.4 (CH), 66.6 (CH2), 102.6 (C4 of pyrazole), 152.6, 162.4 (C3
and C5 of pyrazole), 200.6, 207.0, 207.6 (C^O), 254.2 (C]O) ppm.
IR: nC^O ¼ 2087 (vs), 2047 (vs), 2008 (vs), 1975 (sh); nC]O ¼ 1676
(s) cmꢀ1. Anal. Calc. for C14H17FeIN2O4: C, 36.55; H, 3.72; N, 6.09.
Found: C, 36.72; H, 3.53; N, 6.35%.
(d, J ¼ 15.8 Hz), 4.51 (d, J ¼ 15.8 Hz) (CH2), 5.94 (s, H4 of pyrazole),
6.67 (d, J ¼ 8.1 Hz, H3 of pyridyl), 6.81 (t, J ¼ 6.0 Hz, H5 of pyridyl),
7.36 (t, J ¼ 7.5 Hz, H4 of pyridyl), 8.10 (d, J ¼ 4.6 Hz, H6 of pyridyl)
ppm. 1H NMR of isomer of 5B:
d 2.30 (s, 5-CH3 of pyrazole), 2.62 (s,
3-CH3 of pyrazole), 4.30 (d, J ¼ 16.7 Hz, Hb of CH2), 4.39 (d,
J ¼ 16.7 Hz, Ha of CH2), 5.96 (s, H4 of pyrazole), 6.66 (t, J ¼ 5.8 Hz, H5
of pyridyl), 7.51 (d, J ¼ 4.5 Hz, H6 of pyridyl), 7.26 (t, J ¼ 7.4 Hz, H4 of
pyridyl), 7.63 (s, br, H3 of pyridyl) ppm. These assignments were
confirmed by standard Bruker gradient enhanced NOE pulse se-
3.4. Synthesis of [CH2(CO) (3,5-Me2Pz)Fe(CO)2(SPh)]2 (3)
NaH (9.1 mg, 0.38 mmol) was added to a solution of PhSH
(39.5
m
l, 0.38 mmol) in CH2Cl2 (15 ml). The reaction mixture was
quences. 1H NMR of isomer of 5A (acetone-d6):
d 1.70 (s, 3-CH3 of
stirred for 2 h at room temperature, followed by the addition of a
solution of 1 (154 mg, 0.38 mmol) in CH2Cl2 (10 ml). The resulting
pyrazole), 2.37 (s, 5-CH3 of pyrazole), 4.39 (d, J ¼ 16.1 Hz), 4.53 (d,
J ¼ 16.1 Hz) (CH2), 6.08 (s, H4 of pyrazole), 6.77 (d, J ¼ 8.3 Hz, H3 of

308
D.-W. Zhao et al. / Journal of Organometallic Chemistry 791 (2015) 303e310
pyridyl), 6.95e6.99 (m, H5 of pyridyl), 7.51 (t, J ¼ 8.0 Hz, H4 of
pyridyl), 8.35 (d, J ¼ 4.8 Hz, H6 of pyridyl) ppm. 1H NMR of isomer of
C27H24FeIN2O3P: C, 50.81; H, 3.79; N, 4.39. Found: C, 50.98; H, 3.92;
N, 4.17%.
5B (acetone-d6):
d 2.33 (s, 5-CH3 of pyrazole), 2.61 (s, 3-CH3 of
pyrazole), 4.51 (d, J ¼ 16.8 Hz), 4.76 (d, J ¼ 16.8 Hz) (CH2), 6.09 (s, H4
of pyrazole), 7.40 (t, J ¼ 8.0 Hz), 7.72 (d, J ¼ 5.8 Hz) (protons of
pyridyl) ppm. The other two protons of the pyridyl group over-
lapped with those of the pyridyl group of isomer 5A. 13C NMR of
3.10. Synthesis of CH2(CO) (3,5-Me2Pz)Fe(CO) (PPh3) (SPy) (8)
This complex was similarly obtained as above-mentioned for 7,
while 1 was replaced by 5. After the solvent was removed under
reduced pressure, the residue was purified by column chromatog-
raphy on silica with ethyl acetate/hexane (1:3, v/v) as the eluent
firstly to remove the starting materials, then with ethyl acetate/
hexane (1:1, v/v) as the eluent to give a yellow eluate, which was
concentrated to dryness to afford 20 mg (31%) of 8 as a yellow solid.
isomer of 5A (acetone-d6): d
12.1, 13.5 (CH3), 64.9 (CH2), 109.0 (C4 of
pyrazole), 117.2, 125.7, 135.6, 150.4, 178.0 (carbons of pyridyl), 140.0,
151.7 (C3 and C5 of pyrazole), 208.6, 211.7 (C^O), 265.2 (C]O) ppm.
13C NMR of isomer of 5B (acetone-d6):
d 12.2, 15.9 (CH3), 64.8 (CH2),
109.3 (C4 of pyrazole), 116.8, 127.0, 135.7, 148.0, 181.3 (carbons of
pyridyl), 140.5, 154.2 (C3 and C5 of pyrazole), 210.2, 211.1 (C^O),
269.1 (C]O) ppm. IR: nC^O ¼ 2030 (vs), 1967 (vs); nC]O ¼ 1650
(s) cmꢀ1. Anal. Calc. for C14H13FeN3O3S: C, 46.81; H, 3.65; N, 11.70.
Found: C, 46.58; H, 3.74; N, 11.94%.
Mp 50e66 ꢁC (dec.). 1H NMR:
d 1.99 (s, 3H), 2.20 (s, 3H) (CH3), 3.01
(d, J ¼ 16.3 Hz, 1H), 3.94 (d, J ¼ 16.3 Hz, 1H) (CH2), 5.81 (s, 1H, H4 of
pyrazole), 6.48 (t, J ¼ 6.3 Hz, 1H), 6.71 (d, J ¼ 8.2 Hz, 1H), 7.09e7.14
(m, 1H), 7.28e7.39 (m, 16H) (C5H4N and C6H5) ppm. The obvious
NOE correlations between the methylene protons and the pyridyl
as well as phenyl protons were observed, although these two
methylene protons were barely distinguishable owing to the
serious overlap among the signals of the pyridyl and phenyl pro-
3.8. Synthesis of CH2(CO) (3,5-Pri2Pz)Fe(CO)2(SPy) (6)
This complex was similarly obtained by the reaction of 2 with 2-
mercaptopyridine as above-mentioned reaction of 1 with PhSH.
Yield: 53%, mp 66e76 ꢁC (dec.). Complex 6 also displayed two
isomers (6A/6B) in CDCl3 solution. The relative ratio of isomers 6A/
6B was ca. 3/1 according to the integration of the corresponding
tons. 13C NMR:
d
12.0, 15.6 (CH3), 64.2 (d, JP-C ¼ 5.6 Hz, CH2), 109.4
(C4 of pyrazole),116.2,125.6 (d, JP-C ¼ 3.6 Hz),128.0 (d, JP-C ¼ 9.4 Hz),
129.7 (d, JP-C ¼ 2.1 Hz), 132.9, 133.5 (d, JP-C ¼ 9.8 Hz), 134.5, 139.3,
148.9, 153.6, 179.5 (C6H5, C5H4N as well as C3 and C5 of pyrazole)
ppm. The carbonyl carbon signals were not observed possibly
owing to low solubility and low sensitivity of carbonyl carbon. 31P
protons of one methyl group. 1H NMR of isomer of 6A:
d 0.54 (d,
J ¼ 6.8 Hz, CH3),1.19 (d, J ¼ 6.9 Hz, CH3),1.21e1.30 (m, CH3 of 6A/6B),
2.47e2.57 (m, CH), 2.82e2.92 (m, CH), 4.27 (d, J ¼ 15.6 Hz), 4.57 (d,
J ¼ 15.6 Hz) (CH2), 6.01 (s, H4 of pyrazole), 6.75 (d, J ¼ 8.2 Hz),
6.84e6.87 (m), 7.33 (dt, J ¼ 1.6 and 8.3 Hz), 8.11 (d, J ¼ 5.1 Hz)
NMR:
d
56.6 ppm. IR: nC^O ¼ 1952 (vs); nC]O ¼ 1648 (s) cmꢀ1. Anal.
Calc. for C31H28FeN3O2PS: C, 62.74; H, 4.76; N, 7.08. Found: C, 62.94;
H, 4.51; N, 7.23%.
(protons of pyridyl) ppm. 1H NMR of isomer of 6B:
d 1.09 (d,
J ¼ 6.8 Hz, CH3), 4.34 (d, J ¼ 16.6 Hz), 4.42 (d, J ¼ 16.6 Hz) (CH2), 6.03
(s, H4 of pyrazole), 6.62e6.66 (m), 6.81e6.83 (m), 7.50 (d,
J ¼ 5.3 Hz), 8.47 (d, J ¼ 4.7 Hz) (protons of pyridyl) ppm. The
methine proton and part of methyl proton signals overlapped each
3.11. Synthesis of CH2(CO) (3,5-Pri2Pz)Fe(CO) (PPh3) (SPy) (9)
This complex was similarly obtained as above-mentioned for 7,
while 1 was replaced by 6. The workup was carried out according to
other in isomers 6A/6B. 13C NMR of isomer 6A:
d 21.5, 21.8, 22.5,
the synthesis of 8. Yield: 32%, mp 52e61 ꢁC (dec.). 1H NMR:
d 0.71
23.3 (CH3), 26.8, 27.3 (CH), 64.6 (CH2), 101.2 (C4 of pyrazole), 117.6,
125.8, 135.4, 150.9, 177.9 (carbons of pyridyl), 147.9, 151.1 (C3 and C5
of pyrazole), 208.8, 211.7 (C^O), 265.1 (C]O) ppm. 13C NMR of
(d, J ¼ 6.9 Hz, 3H, CH3), 0.88 (d, J ¼ 6.7 Hz, 3H, CH3), 1.12 (d,
J ¼ 6.8 Hz, 3H, CH3), 1.18 (d, J ¼ 6.9 Hz, 3H, CH3), 2.54e2.61 (m, 1H,
CH), 3.09 (d, J ¼ 16.3 Hz, 1H, CH2), 4.00e4.06 (m, 2H, CH2 and CH),
5.96 (s, 1H, H4 of pyrazole), 6.47 (t, J ¼ 6.3 Hz,1H), 6.73 (d, J ¼ 8.1 Hz,
1H), 7.12 (t, J ¼ 7.6 Hz, 1H) (C5H4N), 7.28e7.41 (m, 16H, C5H4N and
isomer 6B:
d 21.4, 21.9, 23.5, 23.6 (CH3), 26.8, 27.4 (CH), 64.4 (CH2),
102.0 (C4 of pyrazole), 116.8, 127.1, 135.7, 149.6, 181.2 (carbons of
pyridyl), 137.4, 151.5 (C3 and C5 of pyrazole), 210.2, 211.2 (C^O)
ppm. The acyl carbon signal (C]O) was not observed owing to the
relatively low contents of isomer 6B and low sensitivity of the
carbonyl carbon. IR: nC^O ¼ 2031 (vs), 1968 (vs); nC]O ¼ 1655
(s) cmꢀ1. Anal. Calc. for C18H21FeN3O3S: C, 52.06; H, 5.10; N, 10.12.
Found: C,52.36; H, 4.87; N, 10.45%.
C6H5) ppm. 13C NMR:
d 21.6, 21.7, 22.5, 25.4 (CH3), 26.5, 27.6 (CH),
63.8 (d, JP-C ¼ 4.3 Hz, CH2), 101.9 (C4 of pyrazole), 116.1, 125.8, 128.0
(d, JP-C ¼ 9.1 Hz), 128.5 (d, JP-C ¼ 11.6 Hz), 129.7, 132.1 (d, JP-
¼ 9.8 Hz), 133.5 (d, JP-C ¼ 9.7 Hz), 134.4, 148.6, 150.8, 180.0 (C6H5,
C
C5H4N as well as C3 and C5 of pyrazole), 218.4 (d, JP-C ¼ 30.0 Hz,
C^O), 291.7 (d, JP-C ¼ 22.6 Hz, C]O) ppm. 31P NMR:
d 54.9 ppm. IR:
nC^O ¼ 1957 (vs); nC]O ¼ 1655 (s) cmꢀ1. Anal. Calc. for C35H36Fe-
3.9. Synthesis of CH2(CO) (3,5-Me2Pz)Fe(CO)2(PPh3)I (7)
N3O2PS: C, 64.72; H, 5.59; N, 6.47. Found: C, 64.56; H, 5.62; N, 6.74%.
PPh3 (97 mg, 0.37 mmol) was added to a solution of 1 (0.15 g,
0.37 mmol) in CH2Cl2 (15 ml). The resulting mixture was stirred
overnight at room temperature. The solvent was removed under
reduced pressure, and the residue was purified by column chro-
matography on silica with hexane as the eluent firstly to remove
the starting materials, then with CH2Cl2 as the eluent to give a red
eluate, which was concentrated to dryness to afford 80 mg (34%) of
3.12. Crystal structure determinations
Crystals of 3, 5A and 7e9 suitable for X-ray analyses were ob-
tained by slow diffusion of hexane into their CH2Cl2 solutions
at ꢀ18 ꢁC. All intensity data were collected on a SuperNova Eos
detector for 3, 5A and 9 as well as Rigaku Saturn CCD detector for 7
7 as a red solid. Mp 56e58 ꢁC. 1H NMR:
d
2.09 (s, 6H, CH3), 2.98 (d,
and
8
using graphite monochromated Mo-K
a
radiation
J ¼ 16.1 Hz, 1H), 4.53 (d, J ¼ 16.1 Hz, 1H) (CH2), 6.01 (s, 1H, H4 of
(l
¼ 0.71073 Å). Semi-empirical absorption corrections were
pyrazole), 7.21e7.23 (m, 6H), 7.33e7.37 (m, 6H), 7.44e7.47 (m, 3H)
applied using the Crystalclear program [37]. The structures were
solved by direct methods and difference Fourier map using SHELXS
of the SHELXTL package and refined with SHELXL [38] by full-
matrix least-squares on F2. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were added geometrically and
refined with riding model position parameters. A summary of the
fundamental crystal data for 3, 5A and 7e9 is listed in Table 1.
(C6H5). 13C NMR:
d
12.5, 15.2 (CH3), 66.1 (d, JP-C ¼ 2.0 Hz, CH2), 109.7
(C4 of pyrazole), 128.5 (d, JP-C ¼ 9.8 Hz), 130.7 (d, JP-C ¼ 2.0 Hz), 131.8
(d, JP-C ¼ 42.3 Hz), 133.4 (d, JP-C ¼ 9.6 Hz) (C6H5), 140.6, 151.9 (C3 and
C5 of pyrazole), 210.7 (d, JP-C ¼ 8.7 Hz), 215.4 (d, JP-C ¼ 25 Hz) (C^O),
275.4 (d, JP-C ¼ 25.2 Hz, C]O). 31P NMR:
d
61.8. IR (cmꢀ1):
nC^O ¼ 2016 (vs), 1969 (vs); nC]O ¼ 1641 (s). Anal. Calc. for

D.-W. Zhao et al. / Journal of Organometallic Chemistry 791 (2015) 303e310
309
Table 1
Crystal data and refinement parameters for complexes 3, 5A and 7e9.
Complex
3
5A
7
8
9
Formula
C30H28Fe2N4O6S2
716.38
0.04 ꢂ 0.02 ꢂ 0.01
Monoclinic
P21/c
10.5881(4)
19.3808(9)
17.9126(9)
90
122.356(3)
90
293(2)
3105.1(2)
4
1.532
1472
C14H13FeN3O3S
355.20
0.30 ꢂ 0.30 ꢂ 0.20
Monoclinic
C2/c
23.776(2
8.3422(7)
15.7464(13)
90
100.58(1)
90
125(2)
3070.2(5)
8
1.554
1472
C27H24FeIN2O3P
638.20
C31H28FeN3O2PS
593.44
0.20 ꢂ 0.18 ꢂ 0.10
Monoclinic
P21/n
9.615(3)
21.278(6)
13.632(4)
90
91.292(6)
90
113(2)
2788.3(14)
4
1.414
1232
C35H36FeN3O2PS
649.55
0.50 ꢂ 0.30 ꢂ 0.15
Monoclinic
P21/n
10.6604(3)
21.8759(9)
13.8367(5)
90
95.097(3)
90
129(2)
3214.0(2)
4
1.342
1360
Formula weight
Crystal size (mm)
Crystal system
Space group
a (Å)
0.20 ꢂ 0.18 ꢂ 0.12
Triclinic
ꢁ
Pı
8.923(4)
9.026(4)
16.059(7)
78.759(17)
80.70(2)
88.36(2)
113(2)
1251.9(10)
2
1.693
636
1.932
1.30e27.93
16131
5955 (0.1214)
5517
b (Å)
C (Å)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
T (K)
V (Å)3
Z
Dc (g.cmꢀ3
F (000)
)
m
(mmꢀ1
Range (ꢁ)
)
1.118
2.42e25.01
11556
5471 (0.0752)
3445
1.133
2.83e26.50
6860
3177 (0.0390)
2574
0.707
1.77e27.88
25577
6636 (0.0487)
5608
0.620
2.96e25.01
12944
5656 (0.0351)
4716
q
No. of measured reflections
No. of unique reflections (Rint
No. of observed reflections
)
with (I > 2s(I))
No. of parameters
GOF
401
0.959
201
1.043
318
1.063
354
1.160
392
1.056
Residuals R, Rw
0.0596, 0.0724
0.0422, 0.0804
0.0384, 0.0981
0.0601, 0.1064
0.0389, 0.0829
mutated [Fe]-hydrogenase suggests an acyl-iron ligation in the active site iron
complex, FEBS Lett. 583 (2009) 585e590.
Acknowledgments
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(2013) 42e63.
[14] M.J. Corr, J.A. Murphy, Evolution in the understanding of [Fe]-hydrogenase,
Chem. Soc. Rev. 40 (2011) 2279e2292.
This work is supported by the National Natural Science Foun-
dation of China (No. 21372124) and NFFTBS (No. J1103306).
[15] J.A. Wright, P.J. Turrell, C.J. Pickett, The third hydrogenase: More natural or-
ganometallics, Organometallics 29 (2010) 6146e6156.
[16] A.M. Royer, T.B. Rauchfuss, D.L. Gray, Oxidative addition of thioesters to
iron(0): Active-site models for hmd, nature's third hydrogenase, Organome-
tallics 28 (2009) 3618e3620.
[17] A.M. Royer, M. Salomone-Stagni, T.B. Rauchfuss, W. Meyer-Klaucke, Iron acyl
thiolato carbonyls: structural models for the active site of the [Fe]-
Hydrogenase (Hmd), J. Am. Chem. Soc. 132 (2010) 16997e17003.
[18] P.J. Turrell, J.A. Wright, J.M.T. Peck, V.S. Oganesyan, C.J. Pickett, The third hy-
drogenase: A ferracyclic carbamoyl with close structural analogy to the active
site of Hmd, Angew. Chem. Int. Ed. 49 (2010) 7508e7511.
[19] P.J. Turrell, A.D. Hill, S.K. Ibrahim, J.A. Wright, C.J. Pickett, Ferracyclic carba-
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42 (2013) 8140e8146.
[20] D. Chen, R. Scopelliti, X. Hu, Synthesis and reactivity of iron acyl complexes
modeling the active site of [Fe]-Hydrogenase, J. Am. Chem. Soc. 132 (2010)
928e929.
[21] D. Chen, R. Scopelliti, X. Hu, [Fe]-Hydrogenase models featuring acylme-
thylpyridinyl ligands, Angew. Chem. Int. Ed. 49 (2010) 7512e7515.
[22] D. Chen, R. Scopelliti, X. Hu, Reversible protonation of a thiolate ligand in an
[Fe]-Hydrogenase model complex, Angew. Chem. Int. Ed. 51 (2012)
1919e1921.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2015.06.008.
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