Synthesis, characterisation and crystal structures of new nickel complexes in S4 coordination spheres; An unprecedented rearrangement during ligand synthesis

Article abstract of DOI:10.1039/b110332f

Two new nickel(II) complexes were synthesized with an S₄ coordination environment. These complexes were synthesized by in situ deprotection of thiouronium salts in the presence of nickel(II). The ligands used are 4-mercapto-3,3-methyl-1-phenyl-

Full text of DOI:10.1039/b110332f

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Synthesis, characterisation and crystal structures of new nickel
complexes in S4 coordination spheres; an unprecedented
rearrangement during ligand synthesis
Johanna A. W. Verhagen,a Dianne D. Ellis,b Martin Lutz,b Anthony L. Spekb and
Elisabeth Bouwman*a
a Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502,
2300 RA Leiden, The Netherlands. E-mail: bouwman@chem.leidenuniv.nl
b Bijvoet Center for Biomolecular Research, Crystal and Structural Chemistry,
Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
Received 13th November 2001, Accepted 23rd January 2002
First published as an Advance Article on the web 7th March 2002
Two new nickel() complexes were synthesized with an S4 coordination environment. These complexes were
synthesized by in situ deprotection of thiouronium salts in the presence of nickel(). The ligands used are
4-mercapto-3,3-methyl-1-phenyl-2-thiabutane (Hbsms) and α,αЈ-bis(4-mercapto-3,3-methyl-2-thiabutyl)-o-xylene
(H2xbsms). The former is a didentate ligand containing one thioether and one thiolate group and the latter is a
dithioether dithiolate tetradentate ligand. The differences between these ligands upon coordination to nickel have
been investigated. During the synthesis of these ligands, an unprecedented spontaneous rearrangement occurs, which
is very fast and selective to a single product. The complexes were characterized by analytical, spectroscopic and
electrochemical methods. The geometry of the nickel complexes is square planar according to the single-crystal X-ray
structures. In [Ni(bsms)2] the two ligands are coordinated with the thiolates in trans positions towards each other; in
¯
[Ni(xbsms)] the thiolates are in enforced cis positions. [Ni(bsms)2] crystallizes in the triclinic space group P1 and has
one centrosymmetric molecule in the unit cell. [Ni(xbsms)] crystallizes in the monoclinic space group P21/c with two
independent molecules in the asymmetric unit, however, the differences between these two molecules are very small.
The Ni–S distances are 2.1730(4)–2.1909(6) Å and in the common range for thiolates and chelating thioethers.
Introduction
Hydrogenases are widespread among several classes of anaer-
obic and occasionally aerobic bacteria.1 These enzymes catalyse
the reversible oxidation of dihydrogen. Furthermore, in vitro
they have been shown to catalyse the Hϩ/D2 exchange. Exten-
sive studies and characterizations, including single-crystal X-
Fig. 1 Schematic drawing of the target ligands.
ray diffraction, have revealed the structure of several Fe-only
and [NiFe]-hydrogenases.2–6 The X-ray studies have shown
that the active sites of the [NiFe] enzymes isolated from
Desulfovibrio gigas and Desulfovibrio vulgaris contain the hetero-
dinuclear site [(Cys–S)2Ni(µ-S–Cys)2Fe(CN)2(CO)]. In the last
few years, considerable interest has been shown in the [NiFe]-
hydrogenases and their structural modelling.7–16 Most of the
synthetic models contain a mixed-donor environment and only
a few square-planar nickel complexes have been synthesized
which contain only sulfur donors in the coordination environ-
ment.17–21 With this information, it was decided to synthesize
nickel complexes with an S4-donor environment, incorporating
two thiolate sulfur donors and two thioether sulfur donors.
With Ni() this results in a neutral complex, with the thiolate
sulfurs being available to bridge to e.g. an iron centre. The
present paper describes two new nickel complexes with new
chelating ligands. The ligands designed for this study are 4-
mercapto-4-methyl-1-phenyl-2-thiapentane and α,αЈ-bis(3-mer-
capto-3-methyl-1-thiabutyl)-o-xylene. A schematic drawing of
the intended ligands is shown in Fig. 1. The methyl groups on
the carbon α to the thiolate groups are intended to prevent
oligomerisation of the nickel complexes.
all yield of 70% for both ligands. A schematic drawing of the
synthesis of the ligands is shown in Scheme 1. During the ligand
synthesis a spontaneous rearrangement takes place, by which
the methyl groups on the α carbon end up at the β positions.
This rearrangement clearly takes place during the reaction
of the hydroxyl group with thionyl chloride, via a proposed
mechanism shown in Scheme 2, which includes episulfonium
salt (2A) as a possible intermediate. After the formation of the
episulfonium salt, the chloride will attack the least sterically
hindered carbon,22 thus selectively opening the ring to form
2 and 7. As this reaction is very fast 2 and 7 are the kinetically
most favourable products.
To the best of our knowledge this spontaneous rearrange-
ment is unprecedented. In fact a few reports on the deliberate
synthesis of episulfonium salts have been published. One of
these describes the use of a silver salt to abstract chloride ions
to facilitate the formation of the episulfonium salt;23 another
report describes the use of very low temperatures to isolate the
episulfonium salt.24 The spontaneous rearrangement described
here takes place under ambient conditions without the use of
silver salts. The reaction apparently is very rapid, only the final
products 2 and 7 are obtained and the intermediate episulf-
onium salts are not observed. The chlorides in 2 and 7 are not
strongly bound, which has been confirmed by the reaction of
2 with AgNO3, yielding an immediate precipitate of AgCl.
Results and discussion
Synthesis
The new ligands reported here were synthesized in a good over-
DOI: 10.1039/b110332f
J. Chem. Soc., Dalton Trans., 2002, 1275–1280
This journal is © The Royal Society of Chemistry 2002
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Scheme 1 Synthesis of the thiouronium salt ligands.
Fig. 2 Displacement ellipsoid plot of Ni(bsms)2, drawn at the 50%
probability level. Symmetry operation a: Ϫx, 1 Ϫ y, 1 Ϫ z.
Scheme 2 Proposed rearrangement mechanism of the ligands.
NOESY NMR has been used to confirm the description of 2
and 7 as the rearranged products with the methyl groups on the
β carbon atom.
Although the thiol ligands are quite stable in an oxygen
atmosphere and only oxidize after several days, during depro-
tection some disulfide is also formed. This is probably due to
the basic conditions used during the deprotection of the thio-
urea derivatives.
The nickel complexes were synthesized by reactions of
[Ni(acac)2] with the thiouronium precursor salts of the ligands,
3 and 8 respectively, in ethanol in the presence of the base
tetramethylammonium hydroxide. The hydroxide ion attacks at
the thiouronium carbon atom resulting in urea and a thiolate
ligand, which then coordinates to the nickel centre. The
[Ni(acac)2] does not dissolve well in ethanol, but after refluxing
the complex is formed. The complex [Ni(xbsms)] was formed
directly in pure form. The complex [Ni(bsms)2] needs recrystal-
lisation from ethanol to remove the tetramethylammonium salt
impurities. By the use of the thiouronium salts of the ligands
and the in situ formation of the thiolate ligand, the isolation of
the oxidation sensitive thiol-ligands is circumvented. The com-
plexes were synthesized and handled in an inert atmosphere,
but were found to be stable in the solid state in air for several
days.
Fig. 3 Displacement ellipsoid plot of molecule 1 of Ni(xbsms), drawn
at the 50% probability level.
The thiolates are coordinated trans to each other. The bond
distances of thiolate sulfur to nickel are 2.1903(4) Å and the
bond distances of the thioether sulfur to nickel are 2.1730(4) Å.
The bite-angle of the ligand, S6–Ni–S9 is 88.127(16)Њ, which is
only slightly less than the ideal 90Њ. Due to the inversion centre
at the nickel ion, the environment around nickel is perfectly
planar. Stacking of aromatic rings or hydrogen bonding is not
observed between the molecules in the lattice.
[Ni(xbsms)] crystallizes in the space group P21/c and has two
independent molecules in the asymmetric unit. However, the
differences between the two molecules are very small, so only
one of them is discussed here. The complex contains a Ni()
centre which is in square-planar surroundings with an S2SЈ2
coordination sphere. Two thiolate donors and two thioether
groups are coordinated to the nickel centre, and are in enforced
cis positions. The bond distances of the thiolate sulfurs to
nickel are 2.1802(6) and 2.1869(6) Å. The bond distances of the
thioether sulfurs to nickel are 2.1909(6) and 2.1756(5) Å. The
angles in this complex differ from the ideal angles 90 and 180Њ.
The angle of S6–Ni–S9 and S16–Ni–S19 are 87.92(2)Њ and
87.11(2)Њ. These angles are slightly less than the ideal 90Њ, due
to the limitations of the 5-membered rings. However, the 7-
Structures of [Ni(xbsms)] and [Ni(bsms)2]
Projections of the structures of the complexes [Ni(bsms)2] and
[Ni(xbsms)] are shown in Figs. 2 and 3 respectively. Crystal data
are given in Table 1 and selected bond distances and angles are
given in Table 2.
¯
[Ni(bsms)2] crystallizes in the space group P1 with one
molecule in the unit cell, the nickel ion residing on an inversion
center. The complex contains a Ni() centre in square-planar
surroundings. The nickel ion has a coordination environment
which consists of two thiolate donors and two thioether groups.
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Table 1 Crystal and structure refinement data for the nickel complexes [Ni(bsms)2] and [Ni(xbsms)]
[Ni(bsms)2]
[Ni(xbsms)]
Empirical formula
Molecular weight
C22H30NiS4
481.43
C16H24NiS4
403.30
Crystal dimensions/mm
Crystal system
Space group
0.24 × 0.24 × 0.18
Triclinic
P1 (no. 2)
0.32 × 0.12 × 0.12
Monoclinic
P21/c
¯
a/Å
b/Å
c/Å
α/Њ
7.1006(2)
8.3936(2)
10.4298(4)
108.6417(16)
105.6636(17)
89.9694(19)
564.61(3)
1
13.2008(2)
17.3926(2)
20.6855(2)
90
129.5047(7)
90
3664.44(9)
8
1.462
β/Њ
γ/Њ
V/Å3
Z
Dcalc/Mg mϪ3
1.416
12.3
µ/cmϪ1
15.06
Reflections measured
Reflections collected
Reflections observed [I > 2σ(I )]
Ra
6230
2670
2283
0.0308
0.0679
1.056
65338
8398
6460
0.0311
0.0685
1.010
b
Rw
Sc
No. of refined parameters
126
387
a R = Σ( Fo| Ϫ |Fc )/Σ|Fo|. b Rw = [Σw(|Fo| Ϫ |Fc|)2/Σw|Fo|2]1/2 with w = σϪ2F Ϫ1 c S = [Σ(|Fo| Ϫ |Fc|)2/(No Ϫ Nv)]1/2
. .
Table 2 Selected bond lengths (Å) and angles (Њ) for [Ni(xbsms)] and
[Ni(bsms)2]
Table 3 Electronic absorption maxima for the Ni() complexes
ν/cmϪ1 (ε/molϪ1 l cmϪ1
)
[Ni(bsms)2]
[Ni(xbsms)] (molecule 1)
Solid state
Chloroform
Acetonitrile
Ni1–S6
Ni1–S9
Ni1–S16
Ni1–S19
2.1903(4)
2.1730(4)
2.1802(6)
2.1909(6)
2.1869(6)
2.1756(5)
[Ni(bsms)2]
[Ni(xbsms)]
14 400 (96)
22 000 (sh)
14 800 (sh)
22 000 (sh)
28 200 (6500)
32 400 (sh)
35 000 (13000)
38 000 (16000)
15 700 (67)
19 700 (sh)
30 200 (6300)
34 400 (16000)
21 500
S6–Ni1–S9
88.127(16)
180
91.874(16)
87.92(2)
84.05(2)
170.72(2)
171.45(2)
100.75(2)
87.11(2)
S6–Ni1–S16(S6a)
S6–Ni1–S19(S9a)
S9–Ni1–S16
S9–Ni1–S19(S9a)
S16–Ni1–S19
39 300
15 300
23 200
29 400
35 500
15 600 (69)
19 800 (sh)
25 600 (sh)
180
are found between 14 000 cmϪ1 and 24 000 cmϪ1, which are
characteristic of square-planar nickel complexes with a NiS4
chromophore. Only small differences are observed between the
chloroform and acetonitrile solutions, indicating that MeCN
membered ring enforces an angle of 100.75(2)Њ for S9–Ni–S19
and therefore pushes the thiolates together, resulting in an angle
of only 84.05(2)Њ for S6–Ni–S16. Also due to this tetradentate
coordination mode, the [Ni(xbsms)] complex has a small tetra-
hedral distortion with a dihedral angle of 4.31(4)Њ as defined
by the planes S6–Ni1–S9 and S16–Ni1–S19. No stacking
or hydrogen bonding is observed between the molecules in the
lattice.
Both complexes show no remarkable differences in bond dis-
tances and angles compared to complexes from the literature.25
The bond distances of the thioether sulfur and the thiolate
sulfur to the nickel ion are unexceptional.19
does not coordinate to the nickel centres. Around 15 000 cmϪ1
,
[Ni(bsms)2] shows an absorption maximum at lower energy
than [Ni(xbsms)], while around 22 000 cmϪ1 the former shows
an absorption maximum at higher energy than the latter. In
[Ni(bsms)2] no absorption maximum is found around 25 000
cmϪ1. The absorption maxima at 25 000 cmϪ1 and higher are
due to LMCT transitions. In chloroform, these absorption
maxima are hidden underneath the strong absorptions from the
solvent.
NMR and UV–Visible–NIR spectroscopy of [Ni(bsms)2] and
[Ni(xbsms)]
Electrochemical results
The electrochemical behaviour of both nickel complexes was
investigated using cyclic voltammetry. The experiments were
performed in acetonitrile between 1.7 and Ϫ1.8 V vs. an Ag/
AgCl reference electrode. At a scan rate of 0.20 V sϪ1 only
irreversible reduction and oxidation waves are observed for
both [Ni(xbsms)] and [Ni(bsms)2]. [Ni(xbsms)] shows irre-
versible oxidation waves at 1406 and 508 mV. [Ni(bsms)2]
shows irreversible oxidation waves at 1030 and 522 mV. This
implies that the Ni() state is inaccessible for both complexes,
although it is generally accepted that thiolate ligands stabilize
higher oxidation states. Furthermore, both complexes only
show irreversible reduction waves at Ϫ508 and Ϫ1572 mV for
[Ni(xbsms)] and Ϫ762 and Ϫ1465 mV for [Ni(bsms)2]. Because
of the presence of non-innocent thiolate and thioether donors,
The square-planar surroundings of both nickel centres is also
shown in their ligand field spectra. Both complexes remain
square planar in solution with at best a slight tetrahedral dis-
tortion, which is also shown by NMR spectroscopy. Because of
this tetrahedral distortion, the NMR signals of the complexes
dissolved in chloroform are slightly broadened.
Electronic spectra of the complexes were recorded using
diffuse reflection methods and as solutions in chloroform
and acetonitrile. The data are presented in Table 3. The com-
plex [Ni(bsms)2] is a brown solid and yields orange solutions in
chloroform and acetonitrile, whereas the [Ni(xbsms)] complex
is a dark green solid and yields green solutions in chloroform
and acetonitrile. Two absorption bands due to d–d transitions
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the exact nature of the redox sites cannot be established using
these data. However, this was not investigated further. Other
techniques would be needed.
After evaporating the ethanol under reduced pressure, water
was added and the product was extracted with chloroform.
The combined chloroform layers were dried with MgSO4 and
evaporated and a yellow oil was obtained in a yield of 14.46 g
(74%). δH [199.56 MHz, CDCl3, 298 K] 7.31 (m, 5H, phenyl
ring), 3.78 (s, 2H, Ph–CH2–S–), 2.58 (s, 2H, –S–CH2–C(CH3)2–
OH), 2.25 (s, 1H, –OH ), 1.25 (s, 6H, CH3). δC [50.18 MHz,
CDCl3, 298 K] 138.00 (Ph–C1), 128.75 (Ph–C2), 128.34 (Ph–
C3), 126.91 (Ph–C4), 70.49 –C(CH3)2–), 45.39 (–S–CH2–C-
(CH3)2–OH), 38.00 (Ph–CH2–S–), 28.57 (CH3).
Conclusions
Two new nickel complexes were synthesized both in an S4
coordination environment. These complexes are promising for
new structural models for [NiFe]-hydrogenases. The thiolates
can form a bridge between nickel and iron upon coordinating to
an iron complex. The [Ni(xbsms)] complex has the advantage
that only one side of the molecule is available for a reaction
with an iron complex, while the thiolates are in a cis orientation
and are ideal to bridge to an iron centre. Two new ligands
were synthesized. During the synthesis of these ligands, an
unprecedented spontaneous rearrangement occurred, which
is very fast and selective to one product. Further studies will
deal with the synthesis of nickel–iron complexes for better
understanding of [NiFe]-hydrogenases.
4-Chloro-3,3-dimethyl-1-phenyl-2-thiabutane (2). To a solu-
tion of 1 (14.46 g, 0.074 mol) in 20 ml chloroform was slowly
added a solution of excess thionyl chloride (20 g, 0.17 mol)
in 30 ml chloroform. After an hour stirring the chloroform
and excess thionyl chloride were evaporated under reduced
pressure, to yield 15.83 g of a yellow oil (100%). δH [199.56
MHz, CDCl3, 298 K] 7.33 (m, 5H, phenyl ring), 3.83 (s, 2H, Ph–
CH2–S–), 2.86 (s, 2H, S–C(CH3)2–CH2–Cl), 1.63 (s, 6H, CH3).
δC [50.18 MHz, CDCl3, 298 K] 137.80 (Ph–C1), 128.84 (Ph–
C2), 128.34 (Ph–C3), 126.97 (Ph–C4), 70.14 (–C(CH3)2–) 46.53
(–S–C(CH3)2–CH2–Cl), 38.03 (Ph–CH2–S–), 31.35 (CH3).
Experimental
Chemicals
4-Thiouronium-3,3-dimethyl-1-phenyl-2-thiabutane
hydro-
All preparations were carried out in reagent grade solvents. All
chemicals used in the syntheses were obtained from Acros
or Aldrich and were used without further purification unless
mentioned otherwise. The nickel complexes were synthesized
in an argon atmosphere using standard Schlenk techniques.
Solvents were deoxygenated by bubbling through a stream of
argon or by the freeze–pump–thaw methods and were dried
over molecular sieves. The complex [Ni(acac)2] was synthesized
according to published methods.26
chloride (3). To a solution of 2 (15.83 g, 0.074 mol) in 30 ml
ethanol was added a solution of thiourea (5.61 g, 0.074 mol)
in 60 ml ethanol. After 5 hours of reflux the solvent was
evaporated under reduced pressure, which resulted in a solid.
This solid was washed with a small amount of ethanol and
diethyl ether to obtain a white product in a yield of 18.41 g
(95%). δH [199.56 MHz, DMSO-d6, 298 K] 9.35 (s, 4H, –S–
C(NH2)2ϩClϪ), 7.30 (m, 5H, phenyl ring), 3.81 (s, 2H, Ph–CH2–
S–), 3.58 (s, 2H, –S–C(CH3)2–CH2–), 1.33 (s, 6H, CH3).
δC [50.18 MHz, [d6]-DMSO, 298 K] 170.30 (–S–C(NH2)2ϩClϪ),
137.66 (Ph–C1), 129.02 (Ph–C2), 128.41 (Ph–C3), 126.89
(Ph–C4), 45.83 (–C(CH3)2–CH2–), 42.33 (–S–C(CH3)2–CH2–),
32.32 (Ph–CH2–S–), 27.50 (CH3).
Physical measurements
IR spectra were recorded on a Perkin-Elmer FT-IR Paragon
1000 spectrophotometer equipped with a golden gate ATR
device, using the reflectance technique (4000–300 cmϪ1, reso-
lution 4 cmϪ1). Elemental analyses were carried out on a Perkin-
Elmer series II CHNS/O analyser 2400. Ligand field spectra
were obtained on a Perkin-Elmer Lambda 900 spectro-
photometer. The diffuse reflectance technique, with MgO as
a reference was used for the solid compounds. Ligand field
spectra of the solutions were obtained with the used solvent
in the reference beam. NMR spectra were taken on a Bruker
WM 300 MHz spectrometer and on a JEOL FX-200 Teqmac.
Chemical shifts are indicated in ppm relative to tetramethyl-
silane (TMS). The electrochemistry measurements were per-
formed with an Autolab PGstat10 potentiostat controlled by
GPES4 software. A three-electrode system was used, consisting
of a platinum working electrode, a platinum auxiliary electrode
and an Ag/AgCl reference electrode. The experiments were
carried out in acetonitrile at room temperature in an argon
atmosphere with tetrabutylammonium hexafluorophosphate
(0.10 M) as electrolyte. Under these conditions the ferro-
cenium–ferrocene couple is located at ϩ430 mV with a peak-to-
peak separation of 59 mV. All potentials are reported relative
to Ag/AgCl. Mass experiments were performed on a Finnigan
MAT 900 equipped with an electrospray interface. Spectra
were collected by constant infusion of the sample dissolved in
methanol/water with 1% HOAc.
4-Mercapto-3,3-methyl-1-phenyl-2-thiabutane (Hbsms). One
equivalent NaOH was added to a solution of 3 (0.38 g,
1.33 mmol) in 50 ml water. After 15 minutes stirring at room
temperature, the mixture was acidified with a concentrated
HCl solution to pH 7. The product was then extracted with
3 portions of 20 ml chloroform. The combined extracts were
dried over MgSO4. After filtration the solvent was evaporated
under reduced pressure resulting in a yellow oil. δH [199.56
MHz, CDCl3, 298 K] 7.33 (m, 5H, Ph), 3.73 (s, 2H, Ph–CH2–
3
3
S–), 2.71 (d, J = 8.4 Hz, 2H, C(CH3)2–CH2–SH), 1.62 (t, J =
8.4 Hz, 1H, –SH ), 1.39 (s, 6H, CH3). δC [50.18 MHz, CDCl3,
298 K] 137.77 (Ph–C1), 128.72 (Ph–C2), 128.32 (Ph–C3),
126.77 (Ph–C4), 46.91 (–S–C(CH3)2–), 37.01 (–C(CH3)2–CH2–
SH), 32.98 (Ph–CH2–S–), 27.03 (CH3). The product contained
varying amounts of the disulfide as characterized with δH
[199.56 MHz, CDCl3, 298 K] 7.33 (m, 5H Ph), 3.78 (s, 2H, Ph–
CH2–S–), 3.10 (s, 2H, C(CH3)2–CH2–S–S–), 1.41 (s, 6H, CH3).
δC [50.18 MHz, CDCl3, 298 K] 54.17 (–C(CH3)2–CH2–S–S–),
46.20 (–C(CH3)2–), 33.22 (Ph–CH2–S–), 27.67 (CH3).
ꢀ,ꢀЈ-Dithiouronium-o-xylene dihydrochloride (4). To a solu-
tion of α,αЈ-dichloro-o-xylene (5.0 g, 28.5 mmol) in 25 ml
ethanol was added a solution of thiourea (4.34 g, 57.1 mmol)
in 50 ml ethanol. After 30 min refluxing a white product was
formed. After filtration and washing with ethanol and diethyl
ether the yield was 8.48 g (91%). δH [199.56 MHz, D2O, 298 K]
7.54 (m, 4H, phenyl ring), 4.80 (s, –S–C(NH2)2ϩClϪ and H2O),
4.59 (s, 4H, Ph–CH2–S–).
Syntheses
4-Hydroxy-4-methyl-1-phenyl-2-thiapentane (1). Benzylmer-
captan (12.40 g, 0.1 mol) and 1-chloro-2-methyl-2-propanol
(10.85 g, 0.1 mol) were dissolved in 15 ml ethanol. While
cooling the mixture on ice, a solution of NaOH (4.05 g, 0.1 mol
in 6 ml H2O) was slowly added. After two hours stirring at
room temperature, the formed NaCl was removed by filtration.
ꢀ,ꢀЈ-Dimercapto-o-xylene (5). To a solution of 4 (8.48 g,
25.9 mmol) in 50 ml water was added a solution of NaOH
(3.11 g, 78.0 mmol) in 20 ml water. After 3 hours refluxing the
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mixture was neutralized with a concentrated HCl solution. The
product was extracted with dichloromethane. The combined
organic layers were dried with MgSO4 and evaporated under
vacuum to yield 4.03 g of a solid off-white product (91%).
δH [199.56 MHz, CDCl3, 298 K] 7.31 (m, 4H, phenyl ring), 3.88
(d, 3J = 7.2 Hz, 4H, –CH2–), 1.89 (t, 3J = 7.2 Hz, 2H, –SH ). δC
[50.18 MHz, CDCl3, 298 K] 138.50 (Ph–C1, Ph–C2), 129.54
(Ph–C3, Ph–C6), 127.70 (Ph–C4, Ph–C5), 25.95 (–CH2–).
1.18 mmol). The mixture was refluxed for 1 hour, then the
unreacted [Ni(acac)2] was removed by filtration and the volume
of the filtrate was reduced in vacuo to 10 ml. The dark green
product was collected in a yield of 0.170 g (71%). Crystals suit-
able for X-ray diffraction were obtained from CHCl3/Et2O.
δH [300.13 MHz, CDCl3, 300 K] 7.28 (m, 2H, Ph–H3, Ph–H6),
7.19 (m, 2H, Ph–H4, Ph–H5), 3.83 (s, 4H, Ph–CH2–S–), 2.22
(s, 4H, –C(CH3)2–CH2–S–), 1.69 (s, 12H, CH3). νmax/cmϪ1
2954m, 2887m, 2820m, 1433m, 1455s, 1362s, 1248m, 1133s,
1074s, 949m, 788s, 771s, 702s, 605m, 492s, 465s, 390m, 360s,
341s cmϪ1 (Found: C, 47.33; H, 6.13; S, 30.82. C16H24NiS4
requires C, 47.65; H, 6.00; S, 31.80%). ESI-MS: 404 = [M ϩ
H]ϩ.
ꢀ,ꢀЈ-Bis(3-hydroxy-3-methyl-1-thiabutyl)-o-xylene (6). In
80 ml ethanol 5 (3.59 g, 21.1 mmol) and 1-chloro-2-methyl-2-
propanol (4.58 g, 42.2 mmol) were dissolved. While cooling on
ice, a solution of NaOH (1.68 g, 42.2 mmol) in 10 ml water was
added. After one hour stirring, the product was worked up in a
similar way as described for 1, resulting in a yellow oil in a yield
of 6.62 g (100%). δH [199.56 MHz, CDCl3, 298 K] 7.26 (m, 4H,
phenyl ring), 3.98 (s, 4H, Ph–CH2–S–), 2.66 (s, 4H, –S–CH2–
C(CH3)2–), 2.38 (s, 2H, OH ), 1.28 (s, 12 H, CH3). δC [50.18
MHz, CDCl3, 298 K] 135.96 (Ph–C1, Ph–C2), 130.30 (Ph–C3,
Ph–C6), 127.03 (Ph–C4, Ph–C5), 70.52 (–CH2–C(CH3)2–OH),
45.59 (–S–CH2–C(CH3)2–OH), 35.17 (Ph–CH2–S–), 28.37
(CH3).
Crystal structure determinations
X-Ray intensities were measured on a Nonius KappaCCD
diffractometer with rotating anode (λ = 0.71073 Å) at a
temperature of 150(2) K. The structures were solved with
automated Patterson methods (DIRDIF9727) and refined with
SHELXL-9728 against F 2 of all reflections. Molecular illus-
tration, structure checking and calculations were performed
with the PLATON29 package.
ꢀ,ꢀЈ-Bis(3-chloro-2,2-methyl-1-thiapropyl)-o-xylene (7). The
product was synthesized in the same way as 2, resulting in a
yellow oil in a yield of 7.40 g (100%). δH [199.56 MHz, CDCl3,
298 K] 7.26 (m, 4H, phenyl ring), 4.02 (s, 4H, Ph–CH2–S–), 2.90
(s, 4H, –S–C(CH3)2–CH2–Cl), 1.62 (s, 12 H, CH3). δC [50.18
MHz, CDCl3, 298 K] 136.02 (Ph–C1, Ph–C2), 130.71 (Ph–C3,
Ph–C6), 127.44 (Ph–C4, Ph–C5), 70.23 (–S–C(CH3)2–CH2–Cl),
47.34 (–S–C(CH3)2–CH2–Cl), 35.64 (Ph–CH2–S–), 31.41
(CH3).
Ni(bsms)2. The crystals were obtained as brown hexagons.
The absorption correction was based on multiple measured
reflections (program PLATON29 routine MULABS, 0.76–0.81
transmission). Non-hydrogen atoms were refined freely with
anisotropic displacement parameters. Hydrogen atoms were
refined as rigid groups.
Ni(xbsms). The crystals were obtained as dark red blocks.
The absorption correction was based on multiple measured
reflections (program PLATON29 routine MULABS, 0.75–0.83
transmission). Non-hydrogen atoms were refined freely with
anisotropic displacement parameters. Hydrogen atoms were
refined as rigid groups.
CCDC reference numbers 174229 and 174230.
See http://www.rsc.org/suppdata/dt/b1/b110332f/ for crystal-
lographic data in CIF or other electronc format.
ꢀ,ꢀЈ-Bis(3-thiouronium-2,2-methyl-1-thiapropyl)-o-xylene
dihydrochloride (8). The product was synthesized in the same
way as 4, resulting in a white solid in a yield of 9.05 g (85%).
δH [199.56 MHz, D2O, 298 K] 7.36 (m, 4H, phenyl ring), 4.80
(s, –S–C(NH2)2ϩClϪ and H2O), 4.05 (s, 4H, Ph–CH2–S–), 3.48
(s, 4H, –S–C(CH3)2–CH2–), 1.54 (s, 12 H, CH3).
ꢀ,ꢀЈ-Bis(3-mercapto-2,2-methyl-1-thiapropyl)-o-xylene
(H2xbsms). This reaction was performed in a similar manner
to that of Hbsms, except that this reaction was performed in
an inert atmosphere preventing thiol oxidation to disulfide.
δH [199.56 MHz, CDCl3, 298 K] 7.23 (m, 4H, phenyl ring), 3.86
(s, 4H, Ph–CH2–S–), 2.79 (d, 3J = 8.2 Hz, 4H, –C(CH3)2–CH2–
SH), 1.66 (t, 3J = 8.2 Hz, 2H, –SH ), 1.42 (s, 12H, CH3).
Acknowledgements
Professor Jan Reedijk is gratefully acknowledged for fruitful
discussions. Dr G.A. van der Marel and Dr D.V. Fillippov
are gratefully acknowledged for discussions concerning the
mechanism of rearrangement.
References
[Ni(bsms)2]. To a suspension of [Ni(acac)2] (0.52 g, 2.02
mmol) in 35 ml ethanol was added two equivalents of 3 (1.18 g,
4.05 mmol). After the addition of two equivalents of NMe4OH
(0.73 g, 4.05 mmol), the solution was refluxed for 2 hours.
The formed crude brown product was collected by filtration and
purified by refluxing for 1 hour in 15 ml ethanol to remove
additional amounts of impurities. The product was isolated and
dried under vacuum to yield 0.58 g (60%) of a brown powder.
Crystals suitable for X-ray diffraction were obtained from the
filtrate upon standing. δH [300.13 MHz, CDCl3, 300 K] 7.36 (d
3J = 6.9 Hz, 4H, Ph–C2, Ph–C6), 7.20 (m, 6H, Ph–C3, Ph–C4,
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391s, 326w cmϪ1 (Found: C, 55.17; H, 6.66; S, 26.29; Ni, 12.68.
C22H30NiS4 requires C, 54.88; H, 6.28; S, 26.64; Ni, 12.21%).
ESI-MS: 481 = [M ϩ H]ϩ.
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