Two heterodinuclear NiFe-based sulfenate complexes mimicking an S-oxygenated intermediate of an O2-tolerant [NiFe]-H2ase: Synthesis, structures, and reactivity

Article abstract of DOI:10.1039/d0nj02586k

The synthetic modelling of the S-oxygenated intermediate of an O2-tolerant [NiFe]-H2ase has proven to be greatly challenging. Treatment of 1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptane with Ni(acac)2 gave dithiolate complex [1,4-bis(2-mercapto-

Full text of DOI:10.1039/d0nj02586k

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Two heterodinuclear NiFe-based sulfenate complexes mimicking
an S-oxygenated intermediate of an O
2
-tolerant [NiFe]-H ase:
2
synthesis, structures, and reactivity†
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ab
a
a
Li-Cheng Song,* Wei Chen, and Li Feng
The synthetic modelling of the S-oxygenated intermediate of an O
2
-tolerant
[
NiFe]-H ase has proven to be great challenging. Treatment of
2
1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptane with Ni(acac)
dithiolate
2
gave the
complex
or
[
(
1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptanato]nickel(II)
bmmp-dach)Ni (1), further treatment of complex 1 with 37% aqueous H
2
O
2
afforded
complex
sulfenate
[1-(2-mercapto-2-methylpropyl)-4-(2-sulfeno-2-methylpropyl)-1,4-diazacycloheptana
to]nickel(II) or (mmp-sulfeno-dach)Ni (2) and sulfinate complex
1-(2-mercapto-2-methylpropyl)-4-(2-sulfino-2-methylpropyl)-1,4-diazacycloheptanat
o]nickel(II) or (mmp-sulfino-dach)Ni (3). More interestingly, treatment of complex 2
with FeI afforded the unexpected dithiolate/diiodine complex [(bmmp-dach)Ni][2I
(4), while complex 2 reacted with Fe (CO) or CpFe(CO) (BF ) to give the dinuclear
Ni(II)Fe(0) and Ni(II)Fe(II) complexes[(mmp-sulfeno-dach)Ni][Fe(CO) ] (5) and
[
2
2
]
2
9
2
4
4
aDepartment of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai
University, Tianjin 300071, China. E-mail: lcsong@nankai.edu.cn
b
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300072, China
†
Eelectronic supplementary information (ESI) available: The IR and NMR spectra of complexes 17 (Fig.
S1S21). CCDC 1997887-1997891 for complexes 2-5 and 7. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b000000x/.
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[(mmp-sulfeno-dach)Ni][Fe(CO)
demonstrated that (i) reaction of complex 5 or 6 with decarbonylating agent Me
produced complex 2; and (ii) reaction of complex 5 with organometallic oxidant
FcBF afforded the trinuclear Ni dithiolate complex [(bmmp-dach)Ni] [Ni(BF ] (7),
2
Cp(BF
4
)] (6), respectively. Further reactivity studies
3
NO
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unexpectedly. All the new complexes 17 were fully characterized by elemental
analysis and various spectroscopic methods, and particularly the molecular structures
of complexes 25 and 7 were further confirmed by X-ray crystallography.
Introduction
[
NiFe]-Hydrogenases (H
reversible H conversion into two protons and two electrons in various
microorganisms under aerobic or anaerobic conditions.1-4 However, most of the
2
ases) are a class of metalloenzymes that catalyze the
2
[
NiFe]-H
2
2
ases are O
ases from the “Knallgas” bacterium R. eutropha (Re), are O
.5,6 According to the experimental and theoretical
-tolerance of the R. Eutropha SH [NiFe]-H ase was
2
-sensitive, while only a few of [NiFe]-H
2
ases, such as the four
[NiFe]-H
2
-tolerant for the
H
2
cycling in the presence of O
2
studies, a mechanism for the O
2
2
proposed, which involves the reversible S-oxygenation of one bridging cysteinyl
ligand in the [NiFe] active site upon formal tautomerization of an hydroperoxide
7
species to give an S-oxygenated intermediate (Fig. 1a).
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Fig. 1 (a) The proposed S-oxygenated NiFe intermediate. (b) Driess's model. (c)
Darensbourg's model. (d) Two models for the S-oxygenated NiFe intermediate
reported in this work.
To gain a better understanding of the structure and catalytic function of the
S-oxygenated intermediate and to synthesize the ideal O
oxidation and/or H production, synthetic chemists decided to design and prepare
biomimetic models for the S-oxygenated intermediate in the O -tolerant H cycling.
However, although synthetic chemists have prepared a large number of models for the
-sensitive [NiFe]-H
ase active site,8-26 only two models for the S-oxygenated
2
-tolerant catalysts used for
H
2
2
2
2
O
2
2
intermediate have been prepared, so far. Recently, Driess and coworkers reported the
first heterodinuclear NiFe-based S-oxygenated model (with mixed Ni(µ-S)Fe and
Ni(µ-SO)Fe bridging moieties) for the S-oxygenated intermediate of an O
2
-tolerant
H
2
ase (Fig. 1b).27 In addition, Darensbourg and coworkers reported another
heterodinuclear NiFe model complex (with mixed Ni(µ-S)Fe and Ni(µ-OSPh)Fe
bridging moieties), in which the O atom of its bridging moiety Ni(µ-OSPh)Fe, in
contrast to the bridging moiety Ni-S-O-Fe in the S-oxygenated intermediate, is
attached to Ni atom rather than Fe atom (Fig. 1c).28
In this article, we report the synthesis, structural characterization, and reactivity
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of the two NiFe-based sulfenate complexes as models for the S-oxygenated NiFe
intermediate (Fig. 1d). In addition, some related new mononuclear and trinuclear Ni(II)
complexes prepared in this study are also described.
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Results and discussion
Synthesis and structural characterization of mononuclear Ni(II) dithiolate
complex 1, sulfenate complex 2, and sulfinate complex 3
According to our designed synthetic route for preparation of the heterodinuclear NiFe
sulfenate complexes, we should first prepare complexes 1 and 2. By using the
previously published methods with some modifications,29,30 dithiolate complex 1 was
prepared in 44% yield by mercaptolysis of nickel(II) acetylacetonate with
1
,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptane (A)31 in toluene at room
temperature, while sulfenate complex 2 along with sulfinate complex 3 were prepared
by oxygenation of one of the two S atoms in dithiolate complex 1 with 37% aqueous
solution of hydrogen peroxide in MeOH from 78 C to room temperature in 67%
and 20% yields, respectively; in addition, it was found that sulfenate complex 2 could
be converted into dithiolate complex 1 in 54% yield under the action of PPh
3
in
CH Cl at reflux (Scheme 1).
2
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Scheme 1 Synthesis of complexes 13.
Dithiolate complex 1 is an air-stable purple solid, whereas sulfenate and sulfinate
complexes 2 and 3 are air-stable yellow solids. Complexes 13 are new and were
characterized by elemental analysis and various spectroscopic methods. All the
characterization data are in good agreement with their structures shown in Scheme 1.
For example, the IR spectrum of sulfenate complex 2 showed one absorption band at
1
9
28 cm for its S=O group, whereas sulfinate complex 3 displayed two absorption

1
bands at 1184 and 1049 cm for its SO group. All these IR data of 2 and 3 are
2
comparable with those of the previously reported mononuclear Ni(II) complexes.32,33
Particularly worth noting is that the molecular structures of 2 and 3 were
unambiguously confirmed by X-ray crystallography. As shown in Fig. 2/3 and Table
S1 (see Supporting Information), the Ni1 atom in molecule 2 or 3 adopts a slightly
distorted square-planar geometry with a dihedral angle 1.492  for 2 and 2.308  for 3
between the two Ni1N1N2 and Ni1S1S2 planes.32,33 In addition, the double bond
length S1=O1 in 2 is 1.521 (3) Å, while the bond lengths S1=O1 and S1=O2 in 3 are
1
.483(2) and 1.467(2) Å, respectively. These double bond lengths are very close to
those of the corresponding mononuclear Ni(II) complexes.32,33
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Fig. 2 Molecular structure of 2 with ellipsoids at a 30% probability level. All
hydrogen atoms are omitted for clarity.
Fig. 3 Molecular structure of 3 with ellipsoids at a 30% probability level. All
hydrogen atoms are omitted for clarity.
Synthesis and structural characterization of mononuclear Ni(II)
dithiolate/diiodine complex 4
As indicated in Introduction, Driess and coworkers prepared the first heterodinuclear
NiFe-based model for the S-oxygenate intermediate of an O
2
-tolerant [NiFe]-H
2
ase by
.27 To see the
reaction of a mononuclear Ni(II) sulfenate complex with FeBr
2
generality of this reaction and to prepare a new analogue of the first S-oxygenated
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model reported by Driess group, we carried out the reaction of our mononuclear Ni(II)
sulfenate complex 2 with FeI in MeCN at room temperature. As a result, to our
2
surprise, the expected heterodinuclear NiFe-based model complex was not produced;
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instead, the dithiolate/diiodine complex 4 was produced in 54% yield, unexpectedly
(
Scheme 2). Interestingly, complex 4 is the first charge-transfer complex consisting of
one molecule of mononuclear Ni(II) dithiolate complex and two molecules of
diiodine.34,35
In order to account for the unexpected formation of complex 4, we propose a
possible pathway that includes the following three elementary reaction steps. The first
step involves the oxygen atom elimination from sulfenate complex 2 to give dithiolate
complex 1 in the presence of ferrous iodide FeI
2
. The second step involves release of
I
2
from FeI under the action of the eliminated O atom from complex 2. The third step
2
involves formation of the charge-transfer complex 4 from one molecule of the in situ
formed complex 1 with two molecules of the in situ released iodine. This proposed
pathway appears to be plausible. This is because (i) we found that similar oxygen
atom elimination from 2 to give 1 occurred in the presence of PPh
release of I from other transition-metal iodide ZrI was previously observed by
Cotton and coworkers;36 and (iii) an analogue of the charge-transfer complex 4,
namely Ni(bme-daco)I , was previously reported to be prepared by reaction of
dithiolate complex Ni(bme-daco) with I
3
(see Scheme 1); (ii)
2
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Scheme 2 Synthesis of dithiolate/diiodine complex 4.
Complex 4 is an air-stable red solid and was characterized by elemental analysis
1
13
1
and IR, H NMR and C{ H} NMR spectroscopy. The X-ray crystallographic study
(Fig. 4 and Table S1) revealed that the Ni1 atom in complex 4, like that of 2 or 3,
adopts also a slightly distorted square-planar geometry with a dihedral angle (6.889 )
between the two N1Ni1N1a and S1Ni1S1a planes. Interestingly, complex 4 has a
plane of symmetry that bisects this molecule through its metal atom into two halves in
mirror images. Both iodine molecules set on the two sulfur atoms to form two bond
angles S1I1I2 = SlaI1aI2a = 173.28 (3) . The two bond lengths I1I2 =
I1aI2a = 2.9457 (6) Å are considerably longer than the bond lengths of free iodine
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molecule in the gaseous state (2.6667(2) Å) and in the solid state (2.715 (6) Å).
Fig. 4. Molecular structure of 4 with ellipsoids at a 30% probability level. All
hydrogen atoms are omitted for clarity.
Synthesis and structural characterization of dinuclear Ni(II)Fe(0) and
Ni(II)Fe(II) sulfenate complexes 5 and 6
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After the attempted preparation failed to give the NiFe-based model for the
S-oxygenated intermediate of an O
complex 2 with FeI , we further studied the reactions of complex 2 with other Fe
reagents. Fortunately, it was found that when sulfenate complex 2 was treated with
Fe (CO) in CH Cl at room temperature, the dinuclear Ni(II)Fe(0) sulfenate model
2
-tolerant [NiFe]-H
2
ase by reaction of sulfenate
2
1
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complex 5 was obtained in 41% yield; in addition, when complex 2 was treated with
I and AgBF 3
9,40
in CH
Cl in the
the in situ formed CpFe(CO)
2
(BF
4
) from CpFe(CO)
2
4
2
2
dark, the dinuclear Ni(II)Fe(II) sulfenate model complex 6 was obtained in 73% yield
(Scheme 3).
Scheme 3 Synthesis of dinuclear sulfenate complexes 5 and 6.
While the Ni(II)Fe(0) sulfenate complex 5 is an air-sensitive purple solid, the
Ni(II)Fe(II) sulfenate complex 6 is an air-stable yellow solid. Both of them were
characterized by elemental analysis and various spectroscopic techniques. For
1
3
1
example, the C{ H} NMR spectrum of 5 displayed one singlet at 219.6 ppm for its

1
terminal carbonyls, while its IR spectrum showed one absorption band at 914 cm for
its S=O group32,33 and two bands at 2030 and 1926 cm for its terminal carbonyls.
1
1
The H NMR spectrum of 6 displayed three singlets in the range 5.445.53 ppm for
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the magnetically different H atoms in its Cp ring. In addition, the 13C{ H} NMR
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DOI: 10.1039/D0NJ02586K
spectrum of 6 displayed two singlets at 211.5 and 212.6 ppm for its two terminal
carbonyls, whereas its IR spectrum showed one strong absorption band at 937 cm1
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9
0
for its S=O group32,33 and two absorption bands at 2036 and 1986 cm for its two
1
terminal carbonyls.
The single-crystal X-ray diffraction analysis (Fig. 5, Table S1) confirmed that
complex 5 indeed consists of one molecule of sulfenate complex 2 that is coordinated
via its S atom to Fe atom of the iron tetracarbonyl moiety. While the Ni1 atom
possesses a slightly distorted square-planar geometry, the Fe atom takes a square
pyramidal geometry. The distance between Ni1 and Fe1 (3.959 Å) is much longer
than the sum of their atomic radii (2.56 Å), indicating that no metal-metal bond exists.
The S1=O1 double bond length (1.5211 (15) Å) is actually the same as that in the
uncoordinated sulfenate complex 2. It follows that our sulfenate model complex 5 is
structurally very similar to that S-oxygenated NiFe-based model reported by Driess
group, albeit the S1=O1 bond in our model complex 5 is not bridged between its Ni1
and Fe1 centers.
Fig. 5 Molecular structure of 5 with ellipsoids at a 30% probability level. All
10

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hydrogen atoms are omitted for clarity.
Studies on reactivity of dinuclear NiFe sulfenate complexes 5/6 or complex 5.
Synthesis and characterization of trinuclear Ni(II) dithiolate complex 7
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Having prepared dinuclear NiFe complexes 5 and 6, we decided to study their
chemical reactivity towards decarbonylating agent Me
NO41,42 in order to see if they
3
could undergo the intramolecular CO substitution reactions to give the expected
sulfenate NiFe complexes with mixed thiolato and sulfenato bridging moieties.
However, unfortunately, the attempted intramolecular CO substitution reactions of 5
and 6 in the presence of Me
3
NO in CH
2
Cl at room temperature did not occur, instead,
2
the ligand dissociation reactions of 5 and 6 took place to give their precursor sulfenate
complex 2 in 72% and 69% yields, respectively (Scheme 4). In addition, we further
found that treatment of dinuclear NiFe complex 5 with O-abstracting agent PPh 28
refluxing CH Cl , mononuclear Ni dithiolate complex 1 and the known compounds
and Fe(CO)
respectively.
in
3
2
2
4
3
44
O=PPh
3
3
(PPh
3
)
2
were isolated in 56%, 87% and 79% yields,
Scheme 4 Ligand dissociation of complexes 5 and 6 to give precursor 2.
To further study the chemical reactivity of the Ni(II)Fe(0) complex 5 towards
organometallic oxidant FcBF 4
5
in order to get its Ni(II)Fe(II) derivative, we carried
in CH Cl at room temperature. As a result,
4
out the reaction of complex 5 with FcBF
4
2
2
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1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
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the expected Ni(II)Fe(II) derivative was not produced, but interestingly, a trinuclear
Ni(II) cationic complex 7 was isolated in 43% yield, unexpectedly (Scheme 5).
According to the related experimental facts regarding the ligand dissociation of 5
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
under the action of oxidant Me NO shown in Scheme 4 and the feasible oxygen atom
3
elimination from complex 2 shown in Scheme 1 as well as the basic principles of
coordination chemistry, we might propose a possible pathway to account for the
formation of complex 7. The proposed pathway involves the following two major
reaction steps: (i) the initial ligand dissociation from dinuclear complex 5 followed by
the oxygen atom elimination from the resulting selfenate complex 2 to give dithiolate
complex 1; and (ii) the coordination of the four S atoms in two molecules of complex
2
+
1 to the naked Ni ion derived in situ from further decomposition of complex 1 to
form complex 7. It should be noted that this proposed pathway is mainly speculative
and the detailed mechanism for formation of complex 7 needs to be further studied.
Scheme 5 Synthesis of trinuclear Ni(II) dithiolate complex 7.
Complex 7 is an air-stable yellow solid, which has been characterized by various
spectroscopic methods (note that its elemental analysis was not qualified due to
incomplete combustion) and X-ray crystallographic study (Fig. 6, Table S1). Fig. 6
shows that complex 7 is composed of one trinuclear Ni(II) dication and two BF 
4
monoanions. All the three Ni1, Ni2 and Ni1a adopt a square-planar geometry and the
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three square-planar planes N1N2S1S2, S1S2S1aS2a and S1aS2aN1aN2a forms a
stepladder-like structure with average NiS bond length (2.2593 Å) in the central
NiS
folding angles between the NiS
Å above the N plane) are all 140 . Interestingly, complex 7 is a centrosymmetric
4
plane significantly longer than that (2.1528 Å) in the two NiS
2
N
2
planes. The
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4
square plane and the two NiN planes (Ni is 0.093
S
2 2
S
2 2
molecule with respect to Ni2 atom. The distances Ni1Ni2 = Ni1aNi2 are 3.025
Å. It follows that the structure of complex 7 is very similar to that of the previously
reported trinuclear Ni(II) complex.29
Fig. 6 Molecular structure of 7 with ellipsoids at a 30% probability level. All

hydrogen atoms and two BF
4
anions are omitted for clarity.
Conclusion
On the basis of preparation of mononuclear Ni(II) dithiolate, sulfenate and sulfinate
complexes 13, we further investigated the reactions of sulfenate complex 2 with
some inorganic and organometallic Fe reagents in order to prepare the sulfenato S=O
moiety-containing dinuclear NiFe-based mimics for the S-oxygenated intermediate of
an O
2
-tolerant [NiFe]-H
2
ase. As a result, while the reaction of complex 2 with FeI
2
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1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
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gives the unexpected mononuclear Ni(II) thiolate/diiodine charge-transfer complex 4,
the expected dinuclear NiFe sulfenate complexes 5 and 6 are prepared by reactions of
complex 2 with Fe
2
(CO)
9
and CpFe(CO)
2
(BF ), respectively. The spectroscopic study
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
on complexes 5 and 6, and particularly X-ray crystallographic study on their
representative complex 5 demonstrate that they are structurally very similar to the first
NiFe-based model for the S-oxygenated intermediate reported by Driess group.
However, it should be noted that although the sulfenato S=O moieties in 5 and 6 are
not bridged between their two metal centers, the Fe subsites in 5 and 6 (like the Fe
subsite Fe(CO)(CN)
2
in the S-oxygenated intermediate) are organometallic Fe(CO)
4
+
and [Cp(CO)
2
Fe] moieties. In addition, the Fe subsite in the NiFe-based model
reported by Driess group is an inorganic FeBr moiety, although its sulfenato SO
2
moiety is bridged between the two metal centers. Further reactivity study on
complexes 5 and 6 indicates that they undergo the ligand dissociation reactions in the
presence of Me
3
NO to give their precursor complex 2, while complex 5 undergoes a
to
complicated sequential reaction in the presence of organometallic oxidant FcBF
4
afford the trinuclear Ni(II) complex 7, unexpectedly. It is believed that the successful
synthesis of the heterodinuclear NiFe-based sulfenate model complexes 5 and 6 as
well as the studied results regarding their structures and reactivity should promote
further development of the synthetic and functional modelling study on the proposed
S-oxygenated intermediate in the H
[NiFe]-H ase.
2
cycling catalyzed by an O -tolerant
2
2
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Experimental
Materials and techniques
All reactions were carried out using standard Schlenk and vacuum-line techniques
under an atmosphere of argon. While MeCN and CH Cl were distilled under Ar from
CaH , toluene and THF were distilled from sodium benzophenone ketyl. While
CpFe(CO) was prepared from [CpFe(CO) and
iodine46
,4-bis(2-mercapto-2-methylpropyl-1,4-diazacycloheptane31 was prepared from
homopiperazine and isobutylene sulfide.47 Nickel(II) acetylacetonate (Ni(acac)
),
hydrogen peroxide (30% w/v aqueous solution), FeI , Fe (CO) , AgBF
Cp FeBF (FcBF ) and other materials are available commercially and used without
further purification. The solid state IR spectra were recorded on a Bio-Rad FTS 135
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
2
2
I
2 2
]
1
2
2
2
9
4
,
2
4
4
1
13
1
infrared spectrophotometer, while the H and C{ H} NMR spectra in solution were
obtained on a Bruker Avance 400 NMR spectrometer. Elemental analyses were
performed on an Elementar Vario EL analyzer. Melting points were determined on a
SGW X-4 microscopic melting point apparatus and are uncorrected.
Synthesis
of
[
(
1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptanato]nickel(II)
or
bmmp-dach)Ni (1). A 250 mL three necked flask fitted with a magnetic stir-bar, two
caps, and an Ar inlet tube was charged with
1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptane (3.32 g, 12.0 mmol),
Ni(acac) (3.08 g, 12.0 mmol), and toluene (200 mL). The resulting green suspension
was stirred at room temperature for 10 h to give a purple solution with a dark purple
serum
2
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9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
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5
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DOI: 10.1039/D0NJ02586K
precipitate. The solution was filtered out and the precipitate was subjected to column
chromatography (silica gel). After elution with CH Cl /MeOH (v/v = 50:1) removed
some impurities, the elution with CH Cl /MeOH (v/v = 10:1) developed a major
purple band, from which 1 (1.76 g, 44%) was obtained as a purple solid, mp 261 C
dec). Elemental analysis calcd (%) for C13 NiS : C 46.86, H 7.87, N 8.41; found:
C 46.60, H 7.77, N 8.59. IR (KBr disk): v 1589 (s), 1444 (vs), 1358 (s), 1255 (s),
2
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
H
26
N
2
2

1
1
1
051 (s) cm . H NMR (400 MHz, CDCl
.002.24 (m, 2H, NCH CH CH N), 2.462.84 (m, 8H, NCH
CH N), 3.493.81, 4.514.68 (2m, 4H, 2NCH
MHz, CDCl ):  = 23.8 (s, NCH CH CH N), 30.1 (s, CH
NCH ) ppm.
3
):  = 1.251.68 (m, 12H, 4CH
CH CH N,
CMe) ppm. C{ H} NMR (100
3
),
2
2
2
2
2
2
2
1
3
1
NCH
2
2
2
3
2
2
2
3
), 58.7, 59.2, 61.3 (3s, CMe,
2
Synthesis
of
[
1-(2-mercapto-2-methylpropyl)-4-(2-sulfeno-2-methylpropyl)-1,4-diazacyclohept
anato]nickel(II) or (mmp-sulfeno-dach)Ni (2) and
1-(2-mercapto-2-methylpropyl)-4-(2-sulfino-2-methylpropyl)-1,4-diazacyclohept
[
anato]nickel(II) or (mmp-sulfino-dach)Ni (3). While stirring, a suspension of 1
(0.150 g, 0.45 mmol) in MeOH (100 mL) was cooled 78 C and then a dilute
solution of H
2
O (30% w/v aqueous solution) (34 μL, 0.30 mmol) in MeOH (20 mL)
2
was slowly added over a period of 2 h. The resulting mixture was warmed to room
temperature and stirred at this temperature for additional 6 h. Volatiles were removed
at reduced pressure to leave a residue, which was subjected to column
chromatography (silica gel). After elution with CH
2
Cl /MeOH (v/v = 10:1) removed
2
some impurities, elution with CH Cl /MeOH (v/v = 1:1) developed a yellow band,
2
2
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from which 2 (0.070 g, 67 %) was obtained as a yellow solid. The second yellow band
was eluted with methanol, from which 3 (0.022 g, 20%) was obtained as a yellow
solid. For compound 2, mp 271 C (dec). Elemental analysis calcd (%) for
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
C
13
H
26
N
2
NiOS
2
: C 44.72, H 7.51, N 8.02; found: C 44.56, H 7.33, N 8.23. IR (KBr

1
1
disk): vS=O 928 (vs) cm . H NMR (400 MHz, CD
3
OD):  =1.19 (s, 2H,
N); 1.411.46, 1.852.09 (2m, 12H, 4CH ), 2.473.04 (m, 8H,
N, NCH CH N), 3.443.67, 3.994.21 (2m, 4H, 2NCH CMe) ppm.
OD):  = 22.035.1 (m, NCH CH CH N, CH ), 52.5
) ppm. For compound 3, mp 278 C (dec). Elemental
NiO : C 42.76, H 7.18, N 7.67; found: C 42.41, H
.26, N 7.53. IR (KBr disk): vO=S=O 1184 (m), 1049 (s) cm . H NMR (400 MHz,
CD OD):  = 1.06 (s, 2H, NCH CH CH N), 1.48, 1.52, 1.98, 2.19 (4s, 12H, 4CH ),
.433.09 (m, 8H, NCH CH CH N, NCH CH N), 3.633.71, 3.994.25 (2m, 4H,
CMe) ppm. C{ H} NMR (100 MHz, CD OD):  = 15.8 (s, NCH CH CH N),
2.9, 23.6, 34.2, 34.4 (4s, CH ), 51.0 (s, CMe), 58.380.6 (m, NCH ).
NCH
2
CH
2
CH
2
3
NCH
2
CH
2
CH
2
2
2
2
1
3
1
C{ H} NMR (100 MHz, CD
3
2
2
2
3
(
s, CMe), 57.879.8 (m, NCH
2
analysis calcd (%) for C13
H
26
N
2
S
2 2
1
1
7
3
2
2
2
3
2
2
2
2
2
2
2
2
1
3
1
NCH
2
3
2
2
2
3
2
Conversion of sulfenate complex 2 into dithiolate complex 1 under the action
of PPh . A solution consisting of 2 (0.035 g, 0.10 mmol), PPh (0.131 g, 0.50 mmol),
and CH Cl (15 mL) was stirred and refluxed for 6 h. Solvent was removed at reduced
pressure and the residue was subjected to column chromatography (silica gel). After
3
3
2
2
some impurities (including the excess starting material PPh
triphenylphosphine oxide) were removed by elution with CH Cl
00:1), the elution with CH Cl
which 1 (0.018 g, 54%) was obtained.
3
and by-product
/MeOH (v/v =
2
2
1
2
2
/MeOH (v/v = 1:1) developed a purple band, from
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4
5
6
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8
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
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Synthesis
[1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptanato]nickel(II)}[2I
(bmmp-dach)Ni][2I ] (4). A suspension of 2 (0.035 g, 0.10 mmol) and anhydrous
(0.062 g, 0.20 mmol) in 10 mL of MeCN was stirred at room temperature for 2 h.
of
{
2
] or
[
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
FeI
2
After solvent was removed at reduced pressure, the residue was subjected to silica gel
column chromatography. Elution with CH Cl /MeOH (v/v = 50:1) developed a red
band, from which 4 (0.045 g, 54%) was obtained as a red solid, mp 277 C (dec).
Elemental analysis calcd (%) for C13 NiS : C 18.57, H 3.12, N 3.33; found: C
18.22, H 3.51, N 3.29. IR (KBr disk): v 1261 (s), 1093 (s), 1020 (s), 780 (s) cm . H
NMR (400 MHz, acetone-d ):  = 1.29 (s, 2H, NCH CH CH N), 1.58, 2.00 (2s, 12H,
), 2.152.61, 2.983.25 (2m, 8H, NCH CH CH N, NCH CH N), 4.084.10,
CMe) ppm. C{ H} NMR (100 MHz, CD OD):  = 17.2
N); 21.9, 22.5, 23.1 (3s, CH ), 56.474.9 (m, CMe, NCH ) ppm.
2
2
H
26
I
4
N
2
2

1 1
6
2
2
2
4
CH
.354.42 (2m, 4H, 2NCH
CH CH
3
2
2
2
2
2
1
3
1
4
2
3
(
s, NCH
2
2
2
3
2
Synthesis
{[1-(2-mercapto-2-methylpropyl)-4-(2-sulfeno-2-methylpropyl)-1,4-diazacyclohe-
ptanato]nickel(II)}[Fe(CO) ] or [(mmp-sulfeno-dach)Ni][Fe(CO) ] (5). A mixture
of 2 (0.035 g, 0.10 mmol), Fe (CO) (0.036 g, 0.10 mmol), and 10 mL of CH Cl was
of
4
4
2
9
2
2
stirred at room temperature for 4 h. After solvent was removed, the residue was
subjected to no air column chromatography (silica gel). After elution with
CH
v/v = 1:1) developed a purple band, from which 5 (0.021 g, 41%) was obtained as a
purple solid, mp 262 C (dec). Elemental analysis calcd (%) for C17 NiO S :
2
Cl
2
/MeOH (v/v = 10:1) removed some impurities, the elution with CH
2
Cl
2
/MeOH
(
H
26FeN
2
5
2
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C 39.49, H 5.07, N 5.42; found: C 39.52, H 4.99, N 5.33. IR (KBr disk): vC≡O 2030 (s),

1 1
1
926 (vs); vS=O 914 (s) cm . H NMR (400 MHz, CD
2m, 14H, NCH CH CH N, 4CH ), 2.523.20 (m, 8H, NCH
3.493.74, 3.994.17 (2m, 4H, 2NCH
CD OD):  = 21.7 (s, NCH CH CH
CMe, NCH ), 219.6 (s, C≡O) ppm.
3
OD):  = 1.251.68, 1.882.16
(
2
2
2
3
2
CH
2
CH
2
N, NCH
2
CH N),
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
3
1
2
CMe) ppm. C{ H} NMR (100 MHz,
3
2
2
2
N), 23.1, 30.2, 32.7 (3s,, CH
3
), 55.974.9 (m,
2
Synthesis
of
[
1-(2-mercapto-2-methylpropyl)-4-(2-sulfeno-2-methylpropyl)-1,4-diazacyclohept
anato]nickel(II)][Fe(CO) Cp(BF )] or [(mmp-sulfeno-dach)Ni][Fe(CO) Cp(BF )]
(6). In a 50 mL three-necked flask, a solution consisting of CpFe(CO) I (0.030 g, 0.10
mmol), AgBF (0.019 g, 0.10 mmol), and CH Cl (10 mL) was stirred at room
temperature for 1 h in the dark. After the resulting mixture was filtered to remove AgI,
the filtrate that contained the in situ formed intermediate CpFe(CO) (BF ) was
2
4
2
4
2
4
2
2
2
4
transferred to another 50 mL flask that contained 2 (0.035 g, 0.10 mmol). The new
mixture was stirred at room temperature for 4 h in the dark and then it was filtered to
give a filtrate. Removal of solvent from the filtrate, 6 (0.045 g, 73%) was obtained as
a yellow solid, mp 258 C (dec). Elemental analysis calcd (%) for
C
20
H
31BF
4
FeN
KBr disk): vC≡O 2036 (s), 1986 (s); vS=O 937 (m) cm . H NMR (400 MHz, CD
 = 1.271.50, 1.802.22 (2m, 14H, NCH CH CH N, 4CH ), 2.503.03 (m, 8H,
NCH CH CH N, NCH CH N), 3.654.01 (m, 4H, 2NCH CMe), 5.44, 5.49, 5.53 (3s,
H, C ) ppm. C{ H} NMR (100 MHz, CD OD):  = 15.2 (s, NCH CH CH N),
2
NiO
3
S
2
: C 39.19, H 5.10, N 4.57; found: C 39.05, H 5.33, N 4.44. IR
1
1
(
3
OD):
2
2
2
3
2
2
2
2
2
2
1
3
1
5
5
H
5
3
2
2
2
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
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View Article Online
DOI: 10.1039/D0NJ02586K
H ), 211.5, 212.6 (2s, C≡O)
21.5, 26.9, 33.0 (3s, CH
3
), 53.587.9 (m, CMe, NCH
2
, C
5
5
ppm.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Dissociation reactions of dinuclear NiFe complexes 5 and 6 in the presence of
NO to give sulfenate complex 2. To a stirred purple solution of 5 (0.052 g, 0.10
mmol) in CH Cl (10 mL) was added a solution of Me NO (0.008 g, 0.10 mmol) in 5
mL of CH Cl to give a brown-yellow solution, immediately. After the resulting
Me
3
2
2
3
2
2
brown-yellow solution was continuously stirred at room temperature for 0.5 h, solvent
was removed at reduced pressure to leave a residue, which was subjected to column
chromatography (silica gel). Elution with CH
yellow band, from which 2 (0.025 g, 72 %) was produced. In addition, 2 (0.024 g,
9%) was also produced by the same procedure except that 5 was replaced by 6
2
Cl
2
/MeOH (v/v = 1:1) developed a
6
(
0.061 g, 0.10 mmol).
Reaction of dinuclear NiFe complex 5 with O-abstracting agent PPh to give
3
dithiolate complex 1, O=PPh
3
and Fe(CO)
3
(PPh
3
)
2
. A solution consisting of 5
Cl (10 mL) was stirred
(
0.103 g, 0.20 mmol), PPh (0.157 g, 0.60 mmol), and CH
3
2
2
and refluxed for 6 h. The solution changed from purple to yellow. After removal of
volatiles at reduced pressure, the residue was subjected to column chromatography
(
silica gel). Elution with ethyl acetate/petroleum ether (v:v = 1:20) developed a
colorless band (that was monitored by fluorescent TLC analysis to be a purple band),
from which the known compound O=PPh 43
3
(0.048 g, 87 %) was obtained as a white
solid. The developed yellow band was eluted with CH
2
Cl , from which the known
2
44
mononuclear Fe complex Fe(CO)
3
(PPh
3
)
2
(0.105 g, 79%) was obtained as a yellow
solid. The developed purple band was eluted with CH
2
Cl /MeOH (v/v = 10:1), from
2
which complex 1 (0.037g, 56%) was obtained.
20

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Synthesis
[1,4-bis(2-mercapto-2-methylpropyl)-1,4-diazacycloheptanato]nickel(II)}
] or [(bmmp-dach)Ni] [Ni(BF ] (7). A solution of 5 (0.052 g, 0.10 mmol),
FcBF (0.055 g, 0.20 mmol), and 10 mL of CH Cl was stirred at room temperature
of
{
2
[Ni(B
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
F
4
)
2
2
4 2
)
4
2
2
for 8 h. The resulting mixture was filtered over a Celite pad to give a filtrate. After
solvent was removed from the filtrate, the residue was washed with a mixed solvent
(2 mL of CH
2
Cl
2
and 20 mL of Et
2
O) three times and then dried under vacuum to give
complex 7 (0.013 g, 43%) as a yellow solid, mp 285 C (dec). IR (KBr disk): v 1445

1 1
(
vs), 1159 (s), 1044 (vs), 763 (s), 731 (s) cm . H NMR (400 MHz, CD
3
OD):  =
N), 3.523.57,
CMe) ppm. C{ H} NMR (100 MHz, DMSO-d ):  =
N); 45.9, 46.2, 48.7, 50.8 (4s, CMe, NCH ) ppm.
0
.971.33, 2.092.82 (2m, 44H, 8CH
.964.03 (2m, 8H, 4NCH
CH CH
3
, 2NCH
2
CH
2
CH
2
N, 2NCH
2
CH
2
1
3
1
3
2
6
13.8 (s, NCH
2
2
2
2
Crystal structure determinations of 25 and 7
While single crystals of 2 suitable for X-ray diffraction analysis were grown by slow
diffusion of hexane into its CH Cl solution at 18 ℃, those of 3, 4 and 7 were grown
by slow diffusion of hexane into their CH Cl solutions at room temperature, and
2
2
2
2
those of 5 were grown by slow diffusion of hexane into its THF solution at 10 ℃
under nitrogen atmosphere, respectively. A single crystal of 2, 3, 4 or 7 was mounted
on a Rigaku MM-007 (rotating anode) diffractometer equipped with a Bruker P4
accessory. A single crystal of 5 was mounted on a Rigaku MM-007 (rotating anode)
diffractometer equipped with a SuperNova, Single source at offset/far, Eos accessory.
While the data of 2, 3, 4 and 7 were collected using a confocal monochromator with
21

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1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
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DOI: 10.1039/D0NJ02586K
Mo Kα radiation (λ = 0.71073 Å) in the ω scanning mode at 113 K, data of 5 were
collected using a confocal monochromator with Mo Kα radiation (λ = 0.71073 Å) in
the ω scanning mode at 117 K. Data collection, reduction, and absorption correction
4
8
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
were performed by the CRYSTALCLEAR program. The structures were solved by
4
9
direct methods using the SHELXS program and refined by full-matrix least-squares
5
0
2
techniques (SHELXL) on F . Hydrogen atoms were located by using the geometric
method. Details of crystal data, data collections, and structure refinements are
summarized in Tables 1 and 2.
Table 1 Crystal data and structure refinements details for 2 and 3
2
3
Formula
13
C H
26
N
2
NiOS
2
CH
2
Cl
2
0.5H
2
O
13
C H
26
N
2
NiO
2
2
S 1.5CH
2
Cl
2
Formula weight
Cryst system
Space group
a (Å)
443.12
492.58
triclinic
P-1
monoclinic
C12/c1
24.079(5)
14.047(3)
12.304(3)
90
12.423(3)
12.854(3)
14.255(3)
83.97(3)
89.15(3)
74.77(3)
2183.9(8)
4
b (Å)
c (Å)



(°)
(°)
(°)
105.83(3)
90
3
V (Å )
4003.9(15)
8
Z
Crystal size (mm)
0.12  0.11  0.10
1.470
0.05  0.04  0.03
1.498

3
D (g cm )
c
μ (mm1)
1.450
1.457
F(000)
1864
1028
Reflns collected
Reflns unique
23673
25894
4766
10287

min/max (°)
2.238/27.871
0.0568
1.699/27.836
0.0460
Final R
Final R
W
0.1656
0.1224
GOF on F2
1.091
1.019

3
Δρmax/min (e Å )
1.137/-1.315
0.652/-0.945
22

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Table 2 Crystal data and structure refinements details for 4, 5 and 7
4
5
7
Formula
13
C H
26
4
I N
2
NiS
2
17
C H
26FeN
2
NiO
5
S
2
26
C H
52
B
2
F
8
N
4 3 4
Ni S
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Formula weight
Cryst system
Space group
a (Å)
840.79
517.08
898.70
orthorhombic
Pnma
monoclinic
I12/a1
monoclinic
P121/c1
6.4220(13)
27.134(5)
10.320(2)
90
14.938(3)
19.323(4)
8.0820(16)
90
14.9746(3)
14.4363(2)
26.1448(4)
90
b (Å)
c (Å)


(°)
(°)
90
96.359(2)
90
97.03(3)
90
 (°)
90
3
V (Å )
2332.8(8)
4
5617.15(16)
8
1784.8(6)
2
Z
Crystal size (mm)
D
(g cm3)
0.05  0.04  0.03
2.394
0.12  0.11  0.10
1.223
0.12  0.11  0.10
1.672
c

1
μ (mm )
6.303
1.358
1.868
F(000)
1560
2144
932
Reflns collected
Reflns unique
24929
22432
20403
2858
6641
4246

min/max (°)
2.108/27.866
0.0372
3.136/29.039
0.0326
2.125/27.926
0.0858
Final R
Final R
W
0.0808
0.0831
0.1537
GOF on F2
1.170
1.044
1.210

3
Δρmax/min (e Å )
1.086/-1.387
0.892/-0.486
0.635/-0.808
Conflicts of interests
There are no conflicts to declare.
Acknowledgements
We are grateful to the National Natural Science Foundation of China (21772106) and
the Ministry of Science and Technology of China (973 program 2014CB845604) for
financial support.
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A table of contents entry
Two heterodinuclear NiFe-based sulfenate complexes mimicking
an S-oxygenated intermediate of an O -tolerant [NiFe]-H ase:
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2
synthesis, structures, and reactivity
Li-Cheng Song,* Wei Chen, and Li Feng
Two biomimetic models for an O -tolerant [NiFe]-H ase is successfully prepared by
2
2
reactions of sulfenate complex 2 with Fe (CO) and CpFe(CO) BF .
2
9
2
4
Fe (CO)
2
9
N
S
S O
Ni
CH2Cl2
N
2
Model 5
1