Thiofunctional vanadium complexes

Article abstract of DOI:10.1021/ic011118z

The neutral tetradentate ligand 1,6-bis(2′-pyridyl) -2,5-dithiahexane (N₂S₂), containing two thioether functions, reacts with [VX₂L₄] (X = Br, L₄ = 2 tmeda (tmeda = Me₂NCH₂CH

Full text of DOI:10.1021/ic011118z

Inorg. Chem. 2002, 41, 2379−2384
Thiofunctional Vanadium Complexes
H. Nekola, D. Wang, C. Gru1ning, J. Ga1tjens, A. Behrens, and D. Rehder*
Institut fu¨r Anorganische und Angewandte Chemie, UniVersita¨t Hamburg,
D-20146 Hamburg, Germany
Received October 30, 2001
The neutral tetradentate ligand 1,6-bis(2′-pyridyl)-2,5-dithiahexane (N S ), containing two thioether functions, reacts
2
2
with [VX L4] (X ) Br, L4 ) 2 tmeda (tmeda ) Me2NCH CH NMe2); X ) I, L ) tetrahydrofuran (THF)) and
2
2
2
[VX (THF)3] (X) Br, I) to form the complexes [VX (N S )] (1) and [VX (N S )]X (2), respectively. [V (µ-Cl)3(THF)6]I
3
2
2
2
2
2
2
2
IV
and N S yield the V complex [VOCl(N S ]I (3). The pentadentate, dianionic ligand 2,6-bis(2′-mercaptophenylthio)-
2
2
2 2
dimethylpyridine, NS S′22-, which contains two thioether (S) and two thiophenolate (S′) functions, reacts with [VBr3-
2
(THF)3] to afford [VBr(NS S′2)] (4). The complex [VO(Cl)S′NS′] (5; H S′NS′ is the Schiff base formed between
2
2
o-mercaptoaniline and o-mercaptobenzaldehyde) is obtained by redox interaction between [VCl3(THF)3] and 2,2′-
dithiodibenzaldehyde in the presence of o-mercaptoaniline.The crystal and molecular structures have been obtained
for 3‚THF, 4‚THF, and 5‚n-C H . The relevance of these compounds and their formation for the interaction between
5
12
vanadium and thiofunctional biomolecules is addressed.
Introduction
site cysteinate,9 a situation which is further of interest in the
context of the insulin-mimetic behavior of VIII, VIV, and VV
coordination compounds:10 The insulin-mimetic efficacy of
vanadium compounds, i.e., their ability to trigger glucose
intake into glucose-metabolizing cells in the case of lacking
insulin supply or insulin tolerance,11 may be due to the
inhibition of a protein tyrosine phosphatase.12 Vanadium
complexes containing thiofunctional ligands have been
shown to be active in the treatment of diabetes in animal
models,13 and intracellular glutathione and its oxidized
disulfide form possibly play a key role for the speciation of
VV and VIII by redox interaction.10,14
A biological role for vanadium1 has been established for
two groups of enzymes: The alternative or vanadium-
nitrogenases (alternative with respect to the more common
molybdenum-nitrogenases) from nitrogen-fixing bacteria of
the genus Azotobacter2,3 contains vanadium in medium
oxidation states as a constituent of a complex iron-sulfur
cluster. Vanadium is linked to three bridging sulfides, a
histidine, and the vicinal carboxylate and alkoxide of
homocitrate. In the second group of enzymes, the vanadate-
dependent haloperoxidases,4 vanadate (H2VO4-) is covalently
linked to the Nꢀ of a histidine; the vanadium center thus
attains the geometry of a trigonal bipyramid.5 This coordina-
tion mode is also realized in the vanadate analogue of a low
molecular weight phosphotyrosyl phosphatase, where the
axial histidine is replaced by active site cysteinate.6 The
redox-7 and nonredox-inhibition8 of phosphate-metabolizing
enzymes has been traced back to vanadate-binding to active
Vanadate-dependent haloperoxidases also enantioselec-
tively catalyze the oxidation of prochiral thioethers to chiral
sulfoxides,15 a behavior which has been mimicked by chiral
vanadium coordination compounds.16 The enantioselective,
(9) Huyer, G.; Liu, S.; Kelly, J.; Moffat, J.; Payette, P.; Kennedy, B.;
Tsaprailis, G.; Gresser, M. J.; Ramachandran, C. J. Biol. Chem. 1997,
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A.; Kabanos, T.; Kiss, T.; Meier, B.; Micera, G.; Pettersson, L., Rangel,
M.; Salifoglou, A.; Turel, I.; Wang, D. J. Biol. Inorg. Chem. 2002, 7,
384-396.
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Zhang-Sun, G.; Fantus, I. G.; Ng, J. B.; Hall, D. A.; Soo Lum, B.;
Shaver, A. J. Biol. Chem. 1994, 269, 4596-4604.
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Takada, J. Inorg. Chim. Acta 1998, 238, 175-183.
(14) (a) Goda, T.; Sakurai, H.; Yashimura, T. Nippon Kagaku Kaishi 1988,
654-661. (b) Degani, H.; Gochin, M.; Karlish, S. J. D.; Shechter, Y.
Biochemistry 1981, 34, 6218-6225.
* Author to whom correspondence should be addressed. E-mail: dieter.
rehder@chemie.uni-hamburg.de.
(1) Rehder, D. Coord. Chem. ReV. 1998, 182, 297-322.
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Schomburg, D. J. Mol. Biol. 1999, 293, 595-611.
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10.1021/ic011118z CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/11/2002
Inorganic Chemistry, Vol. 41, No. 9, 2002 2379

Nekola et al.
Scheme 1
enzymatic reaction, which presupposes coordination of the
substrate thioether to the vanadium center, is reminiscent of
dimethyl sulfoxide (DMSO) reductase, a molybdopterin
containing oxotransferase,17 stressing the similarity of the
chemistry, also on the biological level, of vanadium and
molybdenum.
Investigations of vanadium model compounds containing,
in addition to an imine or aromatic nitrogen function
modeling histidine binding, thiolate and/or thioether ligands
are of interest in this context. Pursuing continuing work on
this theme carried out by us18-21 and others,22-29 we have
now investigated the coordination properties of a neutral
tetradentate ligand, N2S2, containing two aromatic N (pyridyl)
and two thioether functions, a dianionic pentadentate ligand
with one pyridyl-N, two thioether (S) and two thiolate (S′)
groups, viz., NS2S′2, and a dianionic S′NS′ ligand, formed
in situ, and containing an imine-N and two thiolate functions;
cf. Scheme 1.
Experimental Section
Materials and Methods. The following starting materials were
synthesized according to published procedures: [VI2(THF)4] (THF
) tetrahydrofuran),30 [VI3(THF)3],31 [VCl3(THF)3],32 [VBr2-
(tmeda)2] (tmeda ) Me2NCH2CH2NMe2),33 [VBr3(THF)3],34 [V2-
(µ-Cl)3(THF)6]2[Zn2Cl6],35 N2S2,36 H2NS2S′2‚HCl.37 2,2′-Dithio-
dibenzaldehyde and o-mercaptoaniline were purchased.
(15) ten Brink, H. B.; Tuynman, A.; Dekker: H. L.; Hemrika, W.; Izumi,
Y.; Oshiro, T.; Schoemaker, H. E.; Wever, R. Inorg. Chem. 1998, 37,
6780-6784.
(16) Arends, I. W. C. E.; Pellizo Birelle, M.; Sheldon, R. A. Stud. Surf.
Sci. Catal. 1997, 110, 1031-1040.
(17) Rees, D. C. Science 1996, 272, 1615-1621.
(18) Tsagkalidis, W.; Rehder, D. J. Biol. Inorg. Chem. 1996, 1, 507-514.
(19) Farahbakhsh, M.; Nekola, H.; Schmidt, H.; Rehder, D. Chem. Ber./
Recueil 1997, 130, 1129-1133.
IR spectra were obtained in KBr pellets on a Perkin-Elmer FT
1720, and in CsI pellets on a Perkin-Elmer 1700 XFT IR
spectrometer. NMR spectra were measured on a Bruker AM 360
or Varian Gemini 200 instrument with the usual spectrometer
settings. Solution EPR spectra of 3 (in THF and 2-Me-THF) were
scanned at ca. 9.6 GHz (X-band) on a Bruker ESP-300 E
spectrometer at room temperature and 100 K. The X-ray fluores-
cence analysis was performed with a Spectro X-Lab energy-
dispersive spectrometer in the 25 keV range. Conductivity mea-
surements of 2a were carried out with a WTW LF 410 conductivity
cell at room temperature and concentrations between 2 and 3 mM
in DMSO. Cyclovoltammetric measurements of 4 (in DMSO) were
carried out under N2 atmosphere with an EG&G Princeton Applied
Research Potentiostat 273A, using a standard three electrode
assembly (Pt foil as the working and a Pt wire as the counter
electrode, SCE as the reference). Tetra-n-butylammonium perchlo-
rate (TBAP) (0.2 M) was used as supporting electrolyte. Calibration
was carried out against Fc/Fc+.
(20) Maurya, M. R.; Khurana, S.; Schulzke, C.; Rehder, D. Eur. J. Inorg.
Chem. 2001, 779-788.
(21) Wang, D.; Ebel, M.; Schulzke, C.; Gru¨ning, C:; Hazari, S. K. S.;
Rehder, D. Eur. J. Inorg. Chem. 2001, 935-942.
(22) Nanda, K. K.; Sinn, E.; Addison, A. W. Inorg. Chem. 1996, 35, 2-3.
(23) Davies, S. C.; Hughes, D. L.; Janas, Z.; Jerzykiewicz, L. B.; Richards,
R. L.; Sanders, J. R.; Silverston, J. E.; Sabota, P. Inorg. Chem. 2000,
39, 3485-3498.
(24) Klich, P. R.; Daniher, A. T.; Challen, P. R.; McConville, D. B.;
Youngs, W. J. Inorg. Chem. 1996, 35, 347-356.
(25) Maeda, H.; Kanamori, K.; Michibata, H.; Tonno, T.; Okamoto, K.;
Hidaka, J. Bull. Chem. Soc. Jpn. 1993, 66, 790-796.
(26) Sendlinger, S. C.; Nicholson, J. R.; Lobkovsky, E. B.; Huffman, J.
C.; Rehder, D.; Christou, G. Inorg. Chem. 1993, 32, 204-210.
(27) Higgs, T. C.; Ji, D.; Czernuszewicz, R. S.; Matzanke, B. F.;
Schunemann, V.; Trautwein, A. X.; Helliwell, M.; Ramirez, W.;
Carrano, C. J. Inorg. Chem. 1998, 37, 2383-2392.
(28) Durrant, M. C.; Davies, S. C.; Hughes, D. L.; Le Floc’h, C.; Richards,
R. L.; Sanders, J. R.; Champness, N. R.; Pope, S. J. A.; Reid, G. Inorg.
Chim. Acta 1996, 251, 13-14.
(29) Wenzel, B.; Strauch, P. Z. Naturforsch. 1999, 54b, 165-170.
(30) Hitchcock, P. B.; Hughes, D. L.; Leigh, G. J.; Sanders, J. R.; de Souza,
J.; McGarry, C. J.; Larkworthy, L. F. J. Chem. Soc., Dalton Trans.
1994, 3683-3687.
(31) Davies, S. C.; Durrant, M. C.; Huges, D. L.; Le Floc’h, C.; Pope, S.
J. A.; Reid, G.; Richards, R. L.; Sanders, J. R. J. Chem. Soc., Dalton
Trans. 1998, 2191-2198.
(32) Manzer, L. E., Fackler, J. P., Eds. Inorganic Syntheses; Wiley: New
York 1982; Vol. XXI, p 138.
(33) Hitchcock, P. B.; Hughes, D. L.; Larkworthy, L. F.; Leigh, G. J.;
Marmion, C. J.; Sanders, J. R.; Smith, G. W.; de Souza, J. S. J. Chem.
Soc., Dalton Trans. 1997, 1127-1135.
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1967, 29, 2365-2370.
X-ray structure analyses were carried out in the θ/2θ scan mode
using Mo KR irradiation (λ ) 0.710 73 Å: Hilger & Watts Y290,
3‚THF; Sart Apex CCD, 4‚THF and 5‚pentane). In the case of 5,
a slight disorder of the site occupancy of the VdO group (above
(35) Cotton, F. A.; Duraj, S. A.; Extine, M. W.; Lewis, G. E.; Roth, W.
T.; Schmulbach, C. D.; Schwotzer, W. J. J. Chem. Soc., Chem.
Commun. 1983, 1377-1378.
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466.
2380 Inorganic Chemistry, Vol. 41, No. 9, 2002

Thiofunctional Vanadium Complexes
Table 1. Structure and Refinement Data
[VOCl(N2S2)]I‚THF, 3‚THF
[VBr(NS2S′2)]‚THF, 4‚THF
[VO(Cl)S′NS′]‚C5H12, 5‚C5H12
emperical formula
fw, g mol-1
temp, K
cryst syst
space group
a, Å
C14H16ClIN2OS2V‚C4H8O
C19H15BrNS4V‚C4H8O
588.51
153(2)
monoclinic
P2(1)/c
10.5001(4)
13.9969(5)
16.4615(5)
C13H9ClNOS2V‚C5H12
417.87
153(2)
orthorhombic
Pna2(1)
13.5994(4)
9.6053(3)
577.80
173(2)
triclinic
P1h
9.852(5)
10.739(5)
11.748(5)
b, Å
c, Å
16.3449
R, deg
116.09(3)
90.19(4)
100.78(4)
1092.2(9)
â, deg
96.8330(10)
γ, deg
cell vol., Å3
Z
2402.14(15)
5
2.034
3.051
2135.07(11)
4
1.300
0.790
2
density (calcd), g cm-3
abs coeff., mm-1
F(000)
1.760
2.201
574
1490
864
cryst size, mm
θ range, °
index ranges
1.0 × 0.2 × 0.2
0.6 × 0.4 × 0.1
0.7 × 0.15 × 0.05
2.69-30.07
2.44-32.54
2.46-27.49
-1 < h < +13, -14 < k < +14,
-15 < l < +15
7577
6338
0.0519
248
-15 < h < +15, -20 < k < +20,
-24 < l < +24
64 463
8614
0.0531
280
-17 < h < +17, -12 < k < +12,
-21 < l < +21
reflns collected
independent reflns
R(int)
no. of params
final R indices, I > 2σ(I0),
R1; wR2
45 970
4906
0.0597
225
0.0744; 0.188
0,0781; 0.1911
0.0317; 0.0906
0.0400; 0.0949
0.0839; 0.2560
0.1014; 0.2705
R indices, all data,
R1; wR2
or below the tetragonal plane, respectively) was taken into account
by a 86:14 model. Hydrogen atoms were calculated into idealized
positions and included in the last cycles of refinement. Data for
the crystal structure determination and refinement are collated in
Table 1. For deposition see CCDC 167057 (3‚THF), 167058 (4‚
THF), and 172314 (5‚pentane).
Preparation of Complexes. All reactions were carried out under
N2 and in oxygen-free, absolute solvents, using Schlenk techniques.
Products were dried at room temperature under high vacuum and
stored under N2.
4H, S-CH2-CH2-S). Anal. Calcd for C14H16Br3N2S2V (M )
567.08 g mol-1): C, 29.65; H, 2.84; N, 4.94. Found: C, 29.59; H,
3.30; N, 4.54.
Compound 2b was prepared accordingly from [VI3(THF)3] (0.18
g, 0.28 mmol) and N2S2 (0.08 g, 0.29 mmol). The initially black
mixture turned blue in the course of the reaction, and a turquoise
precipitate formed. Yield 0.14 g (70.6%) of turquoise-blue 2b. IR:
ν(CdC, CdN) 1602, 1564, 1534; δ(HC-S) 1481, 1438; δ-
(monosubst. aromatic) 768, 754; ν(V-S, V-I) 429, 373, 353, 303
cm-1 1H NMR (DMSO-d6): δ 8.53, 7.88, 7.50, 7.36 (m, 8H,
.
[VX2(N2S2)], X ) Br (1a) and I (1b). To [VBr2(tmeda)2] (0.35
g, 0.79 mmol) dissolved in 20 mL of THF was added N2S2 (0.22
g, 0.79 mmol). The solution immediately turned red. After 3 h of
stirring, a red powder had formed, which was filtered off, washed
with THF and dried to yield 0.24 g (62%) of solid, red 1a. IR:
ν(CdC, CdN) 1600, 1561; δ(HC-S) 1477, 1436; δ(monosubst.
aromatic) 768, 712; ν(V-S, V-Br) 431, 377, 363, 301, 284, 276
cm-1. Anal. Calcd for C14H16Br2N2S2V (M ) 487.18 g mol-1): C,
34.65; H, 3.33; N, 5.78. Found: C, 34.02; H, 3.47; N 5.61.
Compound 1b was prepared accordingly from [VI2(THF)4] (0.22
g, 0.36 mmol) and N2S2 (0.10 g, 0,36 mmol). Recrystallization from
CH2Cl2 yielded 0.12 g (57%) of dark red, crystalline 1b. IR: ν-
(CdC, CdN) 1599, 1561; δ(HC-S) 1476, 1435; HCS wagging
1321; δ(monosubst. aromatic) 776, 755, 712; ν(V-S, V-I) 428,
aromatic H); 3.88 (s, 4H, ArCH2-S); 2.67 (s, 4H, S-CH2-CH2-S).
Anal. Calcd. for C14H16I3N2S2V‚0.5THF (M ) 744.13 g mol-1):
C, 25.83; H, 2.71; N, 3.76. Found: C, 25.81; H, 2.79; N, 3.96.
In a second preparation, a sample of [VI3(THF)3] was employed
which apparently was contaminated with its precursor compound
[V2(µ-Cl)3(THF)6]Cl (cf. Discussion). In the filtrate of the main
product, green needles suitable for an X-ray structure analysis
formed after several days at 0 °C, which turned out to be 3‚THF.
EPR of the redissolved crystals: (THF, room temperature) g0 )
2.0062, A0 ) 111.4 × 10-4 cm-1; (THF, 100 K) Azz 178.3, Axy
78.3 × 10-4 cm-1, g components not resolved; (2-Me-THF, room
temperature) g0 ) 2.0052, A0 ) 110.8 × 10-4 cm-1; (2-Me-THF,
98 K) gzz ) 1.982, gxy ) 2.016; Azz 177.6, Axy 77.4 × 10-4 cm-1
.
1
380, 362, 311 cm-1. The H NMR (DMSO-d6), corresponded to
[VBr(NS2S′2)] (4). H2N2S2S′2‚HCl (0.552 g, 1 mmol) was
suspended in 30 mL of THF, cooled to -78 °C (dry ice/ethanol)
and treated slowly and dropwise with 3 equiv of butyllithium (1.6
M in pentane). The solution was stirred while warmed to room
temperature within 1.5 h. During this time, a precipitate of
Li2N2S2S′2‚LiCl formed which was used without further purification.
To a suspension of Li2N2S2S′2‚LiCl (0.37 g, 0.83 mmol) in 30 mL
of THF/pentane was added [VBr3(THF)3] (0.42 g, 0.83 mmol). The
mixture was stirred for 4 h. A dark green precipitate formed, which
was filtered off, washed with THF and dried. Yield: 0.33 g (72%)
of dark green 4. IR: ν(C-H) 3042, 2966; ν(CdC, CdN) 1596,
1571, 1534; δ(C-H) and ν(C-S) 1457, 1440, 1421, 1389;
δ(disubst. aromatic) 1094, 959, 746; ν(V-S, V-I) 353, 334, 288
that of the free ligand, broadened by interaction with the paramag-
netic VII center: δ 8.45, 7.74, 7.40, 7.24 (m, 8H, aromatic H); 3.83
(s, 4H, ArCH2-S); 2.67 (s, 4H, S-CH2-CH2-S). Anal. Calcd for
C14H16I2N2S2V (M ) 581.18 g mol-1): C, 28.93; H, 2.77; N, 4.82.
Found: C, 28.70; H, 2.94; N, 4.69.
[VX2(N2S2)]X, X ) Br (2a), I (2b), and [VOCl(N2S2)]I (3).
[VBr3(THF)3] (0.38 g, 0.75 mmol) dissolved in 30 mL of CH2Cl2
was treated with N2S2 (0.21 g, 0.75 mmol) and stirred for 3 h at
room temperature. A gray-blue precipitate formed, which was
filtered off, washed with CH2Cl2, and dried to yield 0.36 g (63.4%)
of gray-blue, microcrystalline 2a. IR: ν(CdC, CdN) 1613, 1534;
δ(HC-S) 1463, 1415; δ(monosubst. aromatic) 780, 747; ν(V-S,
1
cm-1. H NMR (DMSO-d6): δ 7.8-7.0 (m, 11H, aromatic H);
1
V-Br) 429, 376, 356, 295 cm-1. H NMR (DMSO-d6): δ 8.49,
7.83, 7.32 (m, 8H, aromatic H); 3.85 (s, 4H, ArCH2-S); 2.65 (s,
4.24-4.18 (m, 4H, CH2). Anal. Calcd for C19H15BrNS4V (M )
Inorganic Chemistry, Vol. 41, No. 9, 2002 2381

Nekola et al.
516.44 g mol-1): C, 44.19; H, 2.93; N, 2.71. Found: C, 44.23; H,
2.98; N, 2.77.
A corresponding reaction with Na2N2S2S′2‚NaCl yielded 4
contaminated with NaCl and NaBr. The bulk material was filtered
off, and green crystals of 4‚THF suitable for an X-ray diffraction
analysis were obtained from the filtrate after standing at 2 °C for
a couple of weeks.
Efforts to prepare 4 from [V2(µ-Cl)3(THF)6]2[Zn2Cl6] and
Na2N2S2S′2‚NaCl afforded [Zn(NS2S′2)] as the bulk material which,
according to an X-ray fluorescence analysis, contained 10.7% of
the vanadium complex 4.
are slightly soluble in strongly polar solvents only. 1H NMR
spectra of the complexes 1 and 2 in DMSO-d6 essentially
represent the pattern for the ligand. For diamagnetic 2, the
minor coordination shifts for the hydrogens adjacent to the
coordinating groups, 0.04 to 0.13 ppm to low magnetic field,
suggest an equilibrium between complexed and free ligand.
For paramagnetic 1, the resonance signals are broadened,
and coordination shifts have not been determined. Due to
the apparent lability of the complexes in solution, electro-
chemical data have not been obtained.
[VO(Cl)S′NS′] (5). [VCl3(THF)3] (0.635 g, 1.7 mmol), 2,2′-
dithiodibenzaldehyde (0.466 g, 1.7 mmol), and o-mercaptoaniline
(0.463 g, 3.4 mmol) were dissolved in 60 mL of absolute THF.
Triethylamine (0.405 g, 4 mmol) was added, and the solution
refluxed under N2 overnight. The resulting brown precipitate was
filtered off and washed with chloroform and pentane. Yield 0.25 g
(80% calcd for 5 with respect to [VCl3(THF)3]). The bulk material
contained varying admixtures of [Et3NH]Cl, which could not be
removed. IR (KBr): ν(CdN) 1582; ν(VdO) 930; ν(VS) 380; ν-
The precursor compound [VI3(THF)3] employed in the
preparation of 2b was synthesized by reduction of [VCl3-
(THF)3] with AlEt2(OEt), followed by treatment of the
binuclear [V2Cl3(THF)6][AlCl2Et2] thus obtained with Me3-
SiI (f [VI2(THF)4]) and further with I2 (f [VI3(THF)3]).
This reaction sequence also yields small amounts of [VOCl-
(THF)4]I, possibly via [V2Cl3(THF)6]I, in the presence of
contaminants such as O2 and/or H2O. From the filtrate of
the preparation of 2b, green crystals of [VOCl(N2S2)]I‚THF
(3‚THF) were obtained at 0 °C. The VIV oxidation state in 3
was also established by the EPR spectrum of crystals
redissolved in THF. The parallel component of the aniso-
tropic hyperfine coupling constant, Azz, is 178.3 × 10-4 cm-1.
The partial hyperfine coupling relationship38 might be used
to calculate an expected value for Azz. The partial contribution
of the thioether function is not known. If we employ the
corresponding contribution of thiophenolate, 35.3 × 10-4
cm-1, we arrive, in an octahedral array, at a calculated value
of 160 × 10-4 cm-1 as a lower limit (R2S is expected to
have a higher partial contribution than RS-), which is about
what has been found for the nondistorted complex [VOCl2-
([9]aneN2S)] ([9]aneN2S ) 1,4-diaza-7-thiacyclononane, Azz
) 161.1 × 10-4 cm-1).39 There are two possible explanations
for the large found Azz for 3, viz., overall weak coordination
such as might be expected if 3 decomposes with subsequent
predominant coordination of THF to the VO2+ moiety, or
substantial distortions and V-S bond weakening in 3 (vide
infra), diminishing the delocalization of spin density toward
the ligand system. To exclude the former possibility, we have
also obtained the EPR parameter of 3 in the noncoordinating
solvent 2-Me-THF, where a similarly high Azz ) 177.6 ×
10-4 cm-1 is found (for details, see Experimental Section).
1
(VCl) 349 cm-1. H NMR (DMSO-d6): δ 9.45 (CdNH). Dark-
red crystals of 5‚C5H12 suitable for an X-ray structure analysis were
obtained by slow diffusion of n-pentane to the filtrate of the above
reaction.
Results and Discussion
The neutral compounds [VX2(N2S2)] (1) and the formally
ionic compounds [VX2(N2S2)]X (2), X ) Br, I, were prepared
in analogy to the previously reported [VCl2(N2S2)]19 by
ligand exchange, starting from the precursor compounds
[VXnL6-n] (X ) Br, I; n ) 2, 3; Scheme 1). The red VII
complexes are air- and extremely moisture-sensitive. The
structure proposed in Scheme 1 is based on that of the
structurally characterized chloro analogue [VCl2(N2S2)2],19
where the halides and the thioether functions occupy the
equatorial plane. In the case of [VBr2(tmeda)2] as the
precursor compound, rearrangement thus takes place of the
two bromides from the trans (tmeda complex)33 to the cis
position (N2S2 complex 1a), invoked by the steric require-
ment of the tetradentate N2S2. The characteristic CdN and
CdC bands (see Experimental Section) are shifted to larger
wavenumbers by several cm-1 with respect to the free ligand.
In the far IR, there are bands between 300 and 380 cm-1
associated with the V-S and V-Br stretches. The blue VIII
complexes are only moderately air-sensitive. Comparison of
the spectral data with the very air-sensitiveVII complexes
suggests a comparable coordination, i.e., tetradendate coor-
dination of the ligand in an octahedral, formally cationic
complex, and one of the halides acting as counterion.
Bromine L-edge XAS investigations of 1a and 2a (unpub-
lished results) support the assumption of identical coordina-
tion environments for the two series of compounds. Con-
ductivity measurements carried out for 2a dissolved in
DMSO (Λ ) 8.3 S cm2 mol-1, c ) 2.5 mM) indicate a tight
ion-pair interaction between [VBr(N2S2)]+ and Br-. The
hypsochromic shift of the ν(CdC) and ν(CdN) bands is
more pronounced in 2 (10-20 cm-1) than in 1. In the far-
IR, there is a double band at ca. 375 and 355 cm-1, associated
with the ν(V-S), and an additional band at 295 [2a, ν(V-
Br)] and 303 cm-1 [2b, ν(V-I)], respectively. The complexes
In Figure 1, the molecular structure of the cation of 3 and
a unit cell drawing of 3‚THF are represented. Selected
structure parameters are collated in Table 2. The contacts
between the counterion iodide and the CH2 linking the sulfur
to the pyridine ring, I‚‚‚H9A ) 2.985 Å, is at the limit of
the sum of the van der Waals radii (ca. 3.1 Å). Vanadium is
in the center of a strongly distorted octahedron. If, based on
the angle closest to 180° and the main site of occupancy for
the oxo ligand (see below), S2-V-O2/Cl2 is defined as the
predominant axis, the two pyridine nitrogens, S1, O1/Cl1,
and V form the equatorial plane. The positions of the chloro
(38) Tasiopoulos, A. J.; Troganis, A. N.; Evangelou, A.; Raptopoulou, C.
P.; Terzis, A.; Deligiannakis, Y.; Kabanos, T. A. Chem. Eur. J. 1999,
5, 910-921.
(39) Heinzel, U.; Henke, A.; Mattes, R. J. Chem. Soc., Dalton Trans. 1997,
501-508.
2382 Inorganic Chemistry, Vol. 41, No. 9, 2002

Thiofunctional Vanadium Complexes
Figure 2. ORTEP plot (30% probability level) of 4.
of these bond lengths, the occupancy for the oxo group is
35% in the equatorial position 1 and 65% in the apical
position 2. The resulting calculated d(V-Cl) is 2.48 Å, and
hence longer than in [VOCl2([9]aneN2S)] [d(V-Cl) ) 2.34
Å],39 [VOCl2([9]aneS3)] (2.295 Å)40 or in 5 [2.339(2) Å].
Both of the thioether functions in 3 are subjected to the trans
influence exerted by the oxo group. As expected, d(V-S2)
) 2.597 (S2 is the axial sulfur) is longer than d(V-S1) )
2.530 Å. In [VOCl2([9]aneN2S)], where this trans influence
is fully effective, d(V-S) is 2.689(1) Å.39 The respective
bond lengths in [VOCl2([9]aneS3)] are 2.634(5) and 2.470(5)
Å for the sulfur atoms trans and cis to the doubly bonded
oxygen.40 The oxidation state of vanadium does not seem to
have a sizable effect on the d(V-S) bond lengths: In VII,
VIII, and nonoxo-VIV complexes containing thioether ligands,
the d(V-S) vary from 2.48 to 2.51 Å.28,41,42 The pyridine
nitrogens are bonded more strongly to the hard VIV center
of complex 3 [2.124(5) and 2.146(5) Å] than to the soft VII
center in [VCl2(N2S2)] [2.188(2) Å]. An additional interesting
feature is the N1-V-N2 bond angle of 155.2(2)°, which is
sufficiently smaller than in [VCl2(N2S2)] [172.3(1)°].19
The dilithium salt of pentadentate 2,6-bis(2′-mercaptophe-
nylthio)dimethylpyridine, Li2NS2S′2, reacts with [VBr3-
(THF)3] to form green 4 along with LiBr; Scheme 1. Pure
4‚THF was obtained from the filtrate of the bulk material
by crystallization in the cold. In the IR of 4, the typical ν-
(S-H) ) 2513 cm-1 for the free ligand H2NS2S′2‚HCl is
lacking, as expected for coordination of both of the thiolates.
The 1H resonance for Ar-CH2-S, which appears at 4.30 in
H2NS2S′2‚HCl and 4.05 in Na2NS2S′2, is a multiplet at 4.18-
4.24 in 4.
Figure 1. ORTEP plot (30% probability level) of the cation of 3 and a
cell drawing of 3‚THF. The broken lines represent contacts involving the
iodide counterion.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg)
[VOCl(N2S2)]I‚THF, 3‚THF
V-O1/Cl1
V-O2/Cl2
V-N1
2.183(3)
2.1931(3)
2.124(5)
2.146(5)
2.530(2)
2.597(2)
O1/Cl1-V-S1
O2/Cl2-V-S2
O1/Cl1-V-N1
O1/Cl1-V-N2
N1-V-S2
166.78(9)
169.36(12)
97.45(16)
94.20(16)
80.25(15)
78.98(16)
155.2(2)
V-N2
V-S1
V-S2
N2-V-S2
N1-V-N2
[VBr(NS2S′2)]‚THF, 4‚THF
The molecular structure of 4 is shown in Figure 2; selected
bonding parameters are provided in Table 2. The geometry
of 4 is essentially octahedral, with the pyridine N and the
bromo ligand in the axial positions. The angle Br-V-N )
172.49(3)° deviates from linearity, in marked contrast to
ideally octahedral [Fe(CO)NS2S′2].41 The deviation from
linearity gives rise to an inequivalence of the two halves of
the plane spanned by the two mutually trans thiophenolates
(S1 and S4; S′) and thioether functions (S2 and S3, S). This
V-Br
V-N1
V-S1
V-S4
V-S2
V-S3
2.5029(3)
Br-V-N1
S1-V-S2
S1-V-S3
S3-V-S4
S2-V-S4
S1-V-S4
S2-V-S3
172.49(3)
87.363(14)
90.029
86.106(15)
94.035(15)
171.595(17)
162.164(16)
2.1630(11)
2.3557(4)
2.3485(4)
2.4326(4)
2.4566(4)
[VO(Cl)(S′NS′)]‚C5H12, 5‚C5H12
V-O1
V-N1
V-S1
V-S2
V-Cl
1.626(4)
2.114(6)
2.307(3)
2.288(3)
2.3383(15)
S1-V-S2
N1-V-S1
N1-V-S2
Cl-V-S1
Cl-V-S2
Cl-V-N1
135.14(8)
79.08(17)
94.46(18)
84.27(9)
85.39(9)
156.17(17)
(40) Willey, G. R.; Lakin, M. T.; Alcock, N. W. J. Chem. Soc., Chem.
Commun. 1991, 1414-1416.
(41) Sellmann, D.; Utz, J.; Heinemann, F. W. Inorg. Chem. 1999, 38, 5314-
5322.
(42) Tsagkalidis, W.; Rodewald, D.; Rehder, D. J. Chem. Soc., Chem.
Commun. 1995, 165-167.
and the oxo ligands are disordered. The experimental
distances are V-O1/Cl1 ) 2.18 and V-O2/Cl2 ) 1.93 Å.
In [VOCl2([9]aneN2S)], d(VdO) is 1.63 Å.39 On the basis
Inorganic Chemistry, Vol. 41, No. 9, 2002 2383

Nekola et al.
plane is slightly bent toward the pyridine. Vanadium is
0.2706(3) Å above the plane. The d(V-S′) in 4 are 2.352 Å
(average), and thus compare to those of other thiophenolate
complexes,18,24,27,42 with the exception of the VII complex
[V(S2S′2)tmeda] [S2S′2 ) 1,2-bis(2-sulfidophenylsulfanyl)-
ethane(2-)], where the d(V-S) are 2.481 Å and thus about
as long as d(V-S′) ) 2.478 Å.42 The d(V-S) ) 2.4326-
2.4566(4) Å in 4 are comparable to the corresponding bonds
in [V(S2S′2)tmeda]; they are shorter, however, than the d(V-
S) in [VCl3([9]aneS3)] [2.504(1) Å]28 or [V(thiapentane-1,5-
dithiolate)] [2.507(5) Å].43 The V-Br bond length, 2.5209(3)
Å, is between those found in other bromovanadium com-
plexes such as [VBr2(S2CNEt2)], 2.4137(14) and 2.4007(14);44
[VBr2(tmeda)2], 2.565(1);33 [{VBr(tris(2-methylpyridyl)-
amine)}2(µ-O)], 2.5141(7) and 2.5133(7).45 Compound 4
dissolved in DMSO shows a reversible one-electron reduc-
tion/oxidation step at -0.42 V and an irreversible oxidation
step at +0.21 V (vs SCF).
The formation of the VV compound [VO(Cl)S′NS′] (5)
from the VIII precursor [VCl3(THF)3], the disulfide 2,2′-
dithiodibenzaldehyde, and o-mercaptoaniline (Scheme 1) is
remarkable in several aspects: (i) VIII acts as a two-electron
reducing agent for the disulfide and is oxidized to VV; (ii)
oxo transfer to vanadium occurs, possibly from the water
formed through the condensation between o-mercaptoben-
zaldehyde (the reduction product of the disulfide) and
o-mercaptoaniline; (iii) the Schiff base thus obtained is the
tautomeric form of an otherwise oxidation labile thiozoline,
stabilized here by coordination to vanadium, and suggesting
that vanadium acts as a template in its formation. As far as
this latter aspect of thiazoline stabilization is concerned, the
situation is reminiscent of the one-pot reaction between the
VIV complex [VOCl2(THF)2], o-mercaptoaniline, and o-
hydroxynaphthaldehyde,19 where the formation of the nonoxo
VIV Schiff base (thiazoline tautomer) complex [V(S′NO)2]
is observed, a reaction which, however, goes along with a
deoxygenation of vanadium and concomitant oxidation of
part of the thiol to a disulfide (2,2′-dithiodianiline). Com-
pound 5 is square pyramidal (Figure 3); the effective distance
of V from the plane spanned by the chloro ligand, the two
thiolates, and the imine nitrogen is 0.61 Å. Bonding
parameters (Table 2) are similar to those of comparable
complexes, except of the d(V-S′) [2.307(3) and 2.288(3)
Å], which are significantly shorter than in other thiopheno-
latovanadium complexes (see the discussion for compound
4), but compare to d(V-S′) ) 2.306(2) Å in [V(S′NO)2].19
Figure 3. ORTEP plot (30% probability level) of 5‚C5H12.
as vanadium nitrogenase, where vanadium is in the oxidation
state II to IV,2,46,47 vanadate(V)-reconstituted tyrosyl phos-
phatase,6 and redox-inactivated glyceraldehyde 3-phosphate
dehydrogenase.7 As already noted in the Introduction, the
intracellular speciation of vanadium complexes by interaction
with glutathione and other thiolates goes along with the
coordination of the thiolate function to vanadium, and the
oxidation of thiolate to disulfide.14 The possibility of further
intracellular reduction to vanadium(III) has been noted.48,49
The reductive cleavage of the disulfide link in 2,2′-dithio-
dibenzaldehyde by VIII, leading to thiolate and the VV
complex 5, is an interesting model reaction in this context.
Interactions between vanadium and biogenic thioethers have
not yet been established. However, resorting to the diagonal
relationship between vanadium and molybdenum and the
discovery and structural characterization of a molybdenum
enzyme that interacts with dimethyl sulfide,17 such interac-
tions are likely to occur in living organisms, also with the
participation of vanadium centers. This view is corroborated
by the enantioselective oxidation of prochiral sulfides to
sulfoxides, catalyzed by isolated vanadate-dependent per-
oxidases.15,50,51
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Che-
mischen Industrie.
Supporting Information Available: Tables of crystal structure
data, atomic coordinates, bond lengths and angles, displacement
parameters, and hydrogen coordinates and an X-ray crystallographic
file (CIF format) for 3‚THF, 4‚THF, and 5‚C5H12. This material is
available via the Internet at http://pubs.acs.org.
IC011118Z
Conclusion
The structurally characterized complexes 5 (VV), 3 (VIV),
and 4 (VIII) and the related VIII complexes 2 and VII
complexes 1 model the binding of vanadium to thiolate and
sulfide found in naturally occurring vanadium systems such
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J.; Coucouvanis, D.; Cramer, S. P. J. Am. Chem. Soc. 1993, 115,
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(47) Blanchard, C. Z.; Hales, B. J. Biochemistry 1996, 35, 472-478.
(48) Thopson, K. H., Orvig, C. J. Chem. Soc., Dalton Trans. 2000, 2885-
2892.
(49) (a) Stern, A.; Davison, A. J.; Wu, Q.; Moon, J. Arch. Biochem. Biophys.
1992, 299, 125. (b) Kanamori, K.; Kinebuchi, Y.; Michibata, H. Chem.
Lett. 1997, 423.
(43) Kawaguchi, H.; Tatsumi, K.; Nakamura, A. J. Chem. Soc., Chem.
Commun. 1995, 111-112.
(44) Jones, E. L.; Reynolds, J. G.; Huffman, J. C.; Christou, G. Polyhedron
1991, 10, 1817-1825.
(50) Andersson, M. A.; Allenmark, S. G. Tetrahedron 1998, 54, 15293-
15304.
(45) Kanamori, K.; Kameda, E.; Kabetani, T.; Suemoto, T.; Okamoto, K.;
Kaizaki, S. Bull. Chem. Soc. Jpn. 1995, 68, 2581-2589.
(51) ten Brink, H. B.; Holland, H. L.; Schoemaker, H. E.; van Lingen, H.;
Wever, R. Tetrahedron Asymmetry 1999, 10, 4563-4572.
2384 Inorganic Chemistry, Vol. 41, No. 9, 2002