Substitution and oxidation reactions of bis(dithiolene)tungsten complexes of potential relevance to enzyme sites

Article abstract of DOI:10.1021/ic010421x

Structurally characterized tungstoenzymes contain mononuclear active sites in which tungsten is coordinated by two pterin-dithiolene ligands and one or two additional ligands that have not been identified. In this and prior investigations (Sung, K.-M.; Ho

Full text of DOI:10.1021/ic010421x

4518
Inorg. Chem. 2001, 40, 4518-4525
Ar ticles
Substitution and Oxidation Reactions of Bis(dithiolene)tungsten Complexes of Potential
Relevance to Enzyme Sites
Kie-Moon Sung and R. H. Holm*
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
ReceiVed April 20, 2001
Structurally characterized tungstoenzymes contain mononuclear active sites in which tungsten is coordinated by
two pterin-dithiolene ligands and one or two additional ligands that have not been identified. In this and prior
investigations (Sung, K.-M.; Holm, R. H. Inorg. Chem. 2000, 39, 1275; J. Am. Chem. Soc. 2001, 123, 1931),
stable coordination units of bis(dithiolene)tungsten(IV,V,VI) complexes potentially related to enzyme sites have
been sought by exploratory synthesis. In this work, additional members of the sets [WL(S2C2Me2)2]2-,- and
[WLL′(S2C2Me2)2]2-,- have been prepared and structurally characterized. Tungsten(IV) complexes obtained by
substitution are carbonyl displacement products of [W(CO)2(S2C2Me2)2] and include those with the groups WIVS
(4), WIV(O2CPh) (5), and WIV(2-AdQ)(CO) (Q ) S (6), Se (7); Ad ) adamantyl). Those obtained by oxidation
reactions contain the groups WVO (9), WV(QPh)2 (Q ) S (10), Se (11)), WVIS(OPh) (12), and WVIO2 (14). The
latter two complexes were obtained from W(IV) precursors using sulfur and oxygen atom transfer reactions,
respectively. Complexes 4 and 9 are square pyramidal; 6, 7, 10, and 11 are distorted trigonal prismatic with cis
ligands LL′; and 12 and 14 are distorted octahedral. Complexes 4, 10, and 11 support three-membered electron
transfer series. Attempts to oxidize 4 to the WVS complex results in the formation of binuclear [W2(µ2-S)2(S2C2-
Me2)4]2- having distorted octahedral coordination. The 21 known functional groups WL and WLL′ in mononuclear
bis(dithiolene) complexes prepared in this and prior investigations are tabulated. Of those with physiological-
type ligands, it remains to be seen which (if any) of these ligation modes are displayed by enzyme sites.
Introduction
Tungstoenzymes may be organized into two major families,
AOR (aldehyde oxidoreductases) and F(M)DH (formate dehy-
drogenase, N-formylmethanofuran dehydrogenases).11 In two
members of the AOR family, the tungsten atoms are bound by
two pterin-dithiolene cofactor ligands (S2pd) and one or two
light, presumably oxygen-donor, ligands as determined by
crystallography.12,13 Because of site heterogeneity and/or the
difficulty of identifying light scatterers in the presence of
tungsten, these ligands and the full coordination geometry have
not been determined. Nothing is known concerning active site
structures in the F(M)DH family. The best defined site at present
is that in the tungsten isoenzyme of Rhodobacter capsulatus
DMSO reductase, where the site formulation [WO(O‚Ser)(S2-
pd)2] in the oxidized enzyme is consistent with crystallographic
and EXAFS results.10 In view of the absence of fully defined
binding sites in tungstoenzymes, we have continued exploratory
synthesis in order to determine accessible coordination units of
bis(dithiolene)tungsten complexes. Some of these may be
relevant to enzymes, and others contribute to the further
disclosure of tungsten-dithiolene chemistry,3-5,14-18 a little-
We have demonstrated recently that the trigonal prismatic
dicarbonyl-bis(dithiolene) complexes [M(CO)2(S2C2R2)2] (M
) Mo, W; R ) Me, Ph) are effective synthetic precursors to
five- and six-coordinate bis(dithiolene) complexes of molyb-
denum1,2 and tungsten.3-5 One or, usually, two carbonyl groups
are displaced under mild conditions in substitution reactions that
afford a variety of previously unknown bis(dithiolene) com-
plexes. In the case of tungsten, the complexes can be described
as containing the mononuclear fragments WIV,VdQ, WIV(OR),
WIV(CO)(QR), WVIdO(OR) (Q ) O, S; R ) alkyl, aryl), and
binuclear WV2(µ2-S)2. Certain of these complexes serve as
structural6,7 and functional2,5,8 representations of the catalytic
sites of oxotransferase enzymes, especially members of the
molybdenum DMSO reductase enzyme family9 and the corre-
sponding tungsten isoenzymes.5,10
(1) Lim, B. S.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 2000, 39, 263-
273.
(2) Lim, B. S.; Holm, R. H. J. Am. Chem. Soc. 2001, 123, 1920-1930.
(3) Goddard, C. A.; Holm, R. H. Inorg. Chem. 1999, 38, 5389-5398.
(4) Sung, K.-M.; Holm, R. H. Inorg. Chem. 2000, 39, 1275-1281.
(5) Sung, K.-M.; Holm, R. H. J. Am. Chem. Soc. 2001, 123, 1931-1943.
(6) Musgrave, K. B.; Donahue, J. P.; Lorber, C.; Holm, R. H.; Hedman,
B.; Hodgson, K. O. J. Am. Chem. Soc. 1999, 121, 10297-10307.
(7) Musgrave, K. B.; Lim, B. S.; Sung, K.-M.; Holm, R. H.; Hedman,
B.; Hodgson, K. O. Inorg. Chem. 2000, 39, 5238-5247.
(8) Lim, B. S.; Sung, K.-M.; Holm, R. H. J. Am. Chem. Soc. 2000, 122,
7410-7411.
(10) Stewart, L. J.; Bailey, S.; Bennett, B.; Charnock, J. M.; Garner, C.
D.; McAlpine, A. S. J. Mol. Biol. 2000, 299, 593-600.
(11) Johnson, M. K.; Rees, D. C.; Adams, M. W. W. Chem. ReV. 1996,
96, 2817-2839.
(12) Chan, M. K.; Mukund, S.; Kletzin, A.; Adams, M. W. W.; Rees, D.
C. Science 1995, 267, 1463-1469.
(13) Hu, Y.; Faham, S.; Roy, R.; Adams, M. W. W.; Rees, D. C. J. Mol.
Biol. 1999, 286, 899-914.
(9) Hille, R. Chem. ReV. 1996, 96, 2757-2816.
10.1021/ic010421x CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/28/2001

Reactions of Bis(dithiolene)tungsten Complexes
Inorganic Chemistry, Vol. 40, No. 18, 2001 4519
1
as 185 mg (63%) of dark brown plates. IR (KBr): νWS 468 cm-1. H
Chart 1. Designation of Tungsten Complexes and
NMR (CD3CN, anion): δ 2.66 (s, br, 12). Absorption spectrum
(acetonitrile): λmax (ꢀM) 359 (6100), 400 (sh, 2000), 470 (700), 600
(400) nm. Anal. Calcd for C24H52N2S5W: C, 40.44; H, 7.35; N, 3.93;
S, 22.49. Found: C, 40.32; H, 7,26; N, 3.84; S, 22.58.
Abbreviations
(Et4N)[W(O2CPh)(S2C2Me2)2]. To a suspension of 38.2 mg (0.152
mmol) of (Et4N)(O2CPh) in 1 mL of acetonitrile was added a dark
violet solution of 72.1 mg (0.151 mmol) of [W(CO)2(S2C2Me2)2] in 3
mL of THF. The solution color changed to orange-brown immediately.
After 1 h of stirring, the solution was filtered to remove an orange
solid. Ether (60 mL) was layered on the filtrate. The solid that separated
was collected, washed with ether (3 × 1 mL), and dried. The product
was obtained as 38 mg (38%) of brown microcrystalline solid. IR
1
(KBr): νCOO 1444 cm-1. H NMR (CD3CN, anion): δ 2.69 (s, 12),
7.36 (t, 2), 7.44 (t, 1), 7.71 (d, 2). Absorption spectrum (acetonitrile):
λmax (ꢀM) 336 (4300), 394 (4000), 419 (sh, 3800), 491 (1000), 686 (510)
nm. Anal. Calcd for C23H37NO2S4W: C, 41.13, H, 5.55; N, 2.09; S,
19.10. Found: C, 41.28; H, 5.43; N, 1.96; S, 19.16.
(Et4N)[W(CO)(2-AdS)(S2C2Me2)2]. To a suspension of 15.6 mg
(89.5 µmol) of 2-AdSLi and 16.4 mg (99.0 µmol) of Et4NCl in 1.5 mL
of acetonitrile was added a dark violet solution of 41.0 mg (86.1 µmol)
of [W(CO)2(S2C2Me2)2] in 2 mL of THF. An intense green color
developed immediately. The solution was stirred for 10 min, and the
solvents were removed. The dark green solid was dissolved in 2 mL
of acetonitrile and filtered. Ether (60 mL) was added to the green filtrate,
and the mixture was allowed to stand for 2 days. The solid was isolated,
washed with ether (10 × l mL), and dried to afford the product as 37
mg (58%) of black blocklike crystals. IR (KBr): νCO 1931 cm-1.1H
NMR (CD3CN, anion): δ 1.41-2.14 (m, 14), 2.44 (s, 12), 4.91 (s, 1).
Absorption spectrum (acetonitrile): λmax (ꢀM) 272 (10000), 342 (6600),
431 (8100), 607 (2900) nm. Anal. Calcd for C27H47NOS5W: C, 43.48;
H, 6.35; N, 1.88; S, 21.40. Found: C, 43.63; H, 6.46; N, 1.94; S, 21.56.
(Et4N)[W(CO)(2-AdSe)(S2C2Me2)2]. To a dark violet solution of
55.0 mg (0.116 mmol) of [W(CO)2(S2C2Me2)2] in 2 mL of THF was
added a solution of 2-AdSeLi, which was generated in situ from the
reaction of 24.9 mg (0.0581 mmol) of (2-AdSe)2 and 0.12 mL of a 1.0
M solution of LiEt3BH in THF. An intense green color developed
immediately. The reaction mixture was stirred for 10 min and then
treated with 22.4 mg (0.135 mmol) of Et4NCl in 1 mL of acetonitrile,
and the solvent was removed. The dark-green solid was dissolved in 2
mL of acetonitrile, and the solution was filtered. Ether (60 mL) was
added to the green filtrate, causing the separation of a solid over 1
day. This material was isolated, washed with ether (3 × 1 mL), and
dried to yield the product as 43 mg (47%) of black block-shaped
crystals. IR (KBr): νCO 1923 cm-1. 1H NMR (CD3CN, anion): δ 1.47-
2.18 (m, 14), 2.46 (s, 12), 5.09 (s, 1). Absorption spectrum (acetoni-
trile): λmax (ꢀM) 280 (10000), 332 (6300), 359 (sh, 5900), 438 (7900),
625 (3300) nm. Anal. Calcd for C27H47NOS4SeW: C, 40.91; H, 5.98;
N, 1.77; S, 16.18; Se, 9.96. Found: C, 40.76; H, 6.46; N, 1.69; S,
16.25; Se, 10.06.
explored area prior to the imperative provided by the discovery
of tungstoenzymes.11 As noted elsewhere,4 we utilize the
dimethyldithiolene ligand 1,2-Me2C2S2 because, like the
2-
pterin-dithiolene cofactor ligand, it is a dialkyldithiolene.
Experimental Section
Preparation of Compounds. All operations were carried out under
a pure dinitrogen atmosphere using an inert atmosphere box or standard
Schlenk techniques. Solvents were passed through the Innovative
Technology solvent purification system prior to use. Lithium 2-ada-
mantylthiolate was obtained from adamantane-2-thiol19 by reaction with
BunLi at -78 °C. Bis(2-adamantyl)diselenide was obtained as de-
scribed.2 (Et4N)(SH) was recrystallized from acetonitrile/ether, and
benzenethiol and benzeneselenol were distilled prior to use. Other
reagents were commercial samples used as received. Solvent removal
was performed in vacuo. Filtrations were through Celite; compounds
were isolated by filtration unless otherwise stated. Abbreviations are
given in Chart 1.
(1) W(IV) Complexes. (Et4N)2[WS(S2C2Me2)2]. To a dark violet
solution of 198 mg (0.415 mmol) of [W(CO)2(S2C2Me2)2]3 in 1.5 mL
of THF was added a solution of 135 mg (0.829 mmol) of (Et4N)(SH)
in 1 mL of acetonitrile. An immediate reaction occurred, and the
solution color changed from violet to green to brown. The solution
was stirred for 1 h, and the solvents were removed. The resulting dark
brown solid was dissolved in 2 mL of acetonitrile and filtered. THF
(30 mL) was layered on the filtrate. The solid which separated was
collected, washed with THF (3 × 3 mL), and dried to give the product
(2) W(V) Complexes. (Et4N)[WO(S2C2Me2)2]. To an orange-yellow
solution of 59.8 mg (85.8 µmol) of (Et4N)2[WO(S2C2Me2)2]3 in 3 mL
of acetonitrile was added dropwise a solution of 12.2 mg (48.1 µmol)
of I2 in 1 mL of THF. The solution color changed to blue immediately.
The solution was stirred for 10 min, and the solvents were removed.
The dark residue was dissolved in a minimal volume of THF, and the
solution was filtered. Addition of ether to the filtrate gave the product
as 19 mg (39%) of black crystalline solid. IR (KBr): νWO 896 cm-1
.
Absorption spectrum (acetonitrile): λmax (ꢀM) 283 (sh, 1900), 312 (sh,
1500), 400 (3100), 505 (1300), 607 (5100) nm. EPR (DMF/acetoni-
trile): br, isotropic, gav ) 1.995. This compound was identified by its
spectroscopic similarity to [WO(S2C2Ph2)2]-,3 and by an X-ray structure
determination.
(Et4N)[W(SPh)2(S2C2Me2)2]. To a green-brown solution of 26.4 mg
(41.0 µmol) of (Et4N)[W(OPh)(S2C2Me2)2]4 in 1.5 mL of acetonitrile
was added 8.4 µL (81.8 µmol) of benzenethiol. Upon stirring of the
reaction mixture, the solution changed to red-brown in 10 min. Solvent
was removed, the dark brown oily residue was redissolved in 1 mL of
acetonitrile, and the mixture was filtered. Ether (30 mL) was layered
on the top of the filtrate. The solid which separated was collected,
washed with ether, and dried to afford the product as 21 mg (67%) of
(14) Ueyama, N.; Oku, H.; Nakamura, A. J. Am. Chem. Soc. 1992, 114,
7310-7311.
(15) Das, S. K.; Biswas, D.; Maiti, R.; Sarkar, S. J. Am. Chem. Soc. 1996,
118, 1387-1397.
(16) Davies, E. S.; Aston, G. M.; Beddoes, R. L.; Collison, D.; Dinsmore,
A.; Docrat, A.; Joule, J. A.; Wilson, C. R.; Garner, C. D. J. Chem.
Soc., Dalton Trans. 1998, 3647-3656.
(17) Tucci, G. C.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 1998, 37,
1602-1608.
(18) Lorber, C.; Donahue, J. P.; Goddard, C. A.; Nordlander, E.; Holm, R.
H. J. Am. Chem. Soc. 1998, 120, 8102-8112.
(19) Greidanus, J. W. Can. J. Chem. 1970, 48, 3593-3597.

4520 Inorganic Chemistry, Vol. 40, No. 18, 2001
Table 1. Crystallographic Dataa
Sung and Holm
(Et4N)[5]
(Et4N)[6]
(Et4N)[7]
(Et4N)2[8]‚CH3CN
(Et4N)[9]
formula
fw
cryst syst
space group
Z
C23H37NO2S4W
671.63
monoclinic
P21/n
C27H47NOS5W
745.81
trigonal
R3h
18
C27H47NOS4SeW
792.71
trigonal
R3h
18
C34H67N3S10W2
1206.21
triclinic
P1h
C16H32NOS4W
566.52
tetragonal
I4h2d
8
4
2
a, Å
b, Å
c, Å
8.934(1)
23.801(2)
12.980(2)
39.2057(1)
39.2057(1)
10.4603(1)
39.466(2)
39.466(2)
10.4482(8)
11.516(7)
14.901(9)
14.952(8)
88.86(1)
67.88(1)
87.36(1)
2375(2)
1.687
12.8552(2)
12.8552(2)
27.3574(4)
R, deg
â, deg
γ, deg
V, Å3
105.33(1)
2662.0(5)
1.676
13924.3(1)
1.601
14094(1)
1.681
4521.0(1)
1.665
d
calc, g/cm3
2θ range, deg
3.4-56.6
2.1-56.6
2.1-56.6
2.7-50
3.5-55.3
GOF (F2)
1.030
1.039
1.048
1.010
1.088
R1b (wR2c)
0.0520 (0.1421)
0.0421 (0.0863)
0.0224 (0.0592)
0.0256 (0.0499)
0.0256 (0.0781)
a Obtained with graphite-monochromatized Mo KR (λ ) 0.71073 Å) radiation at 213 K. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo
-
2
Fc2)2]/∑[w(Fo )2]}1/2
.
2
black rodlike crystals. Absorption spectrum (acetonitrile): λmax (ꢀM)
294 (sh, 12000), 397 (8300), 513 (6700), 608 (sh, 3900) nm. EPR
(DMF/acetonitrile): v br, gav ∼ 1.990. Anal. Calcd for C28H42NS6W:
C, 43.74; H, 5.51; N, 1.82; S, 25.02. Found: C, 43.73; H, 5.45; N,
1.77; S, 25.11.
3 mL of acetonitrile was added a solution of 9.7 mg (0.129 mmol) of
Me3NO in 1 mL of acetonitrile dropwise with stirring. An intense
orange-red color developed in 3 min; the solution was stirred for 10
min. The solvent was removed, the red oily residue was dissolved in
a minimal amount of acetonitrile/THF (1:3 v/v), and the mixture was
filtered. Ether (60 mL) was layered on the filtrate. Over 1 day a
crystalline solid separated and was collected, washed with ether (3 ×
1 mL), and dried. The product was obtained as 40.2 mg (69%) of
orange-red thin needles. IR (KBr): νWO 876, 833 cm-1. 1H NMR (CD3-
CN, anion): δ 1.87 (s, 12). Absorption spectrum (acetonitrile): λmax
(ꢀM) 370 (4300), 457 (2500) nm. Anal. Calcd for C24H52N2O2S4W: C,
40.44; H, 7.35; N, 3.93; S, 17.99. Found: C, 40.27; H, 7.26; N, 3.84;
S, 17.85.
(Et4N)[W(SePh)2(S2C2Me2)2]. The preceding procedure was fol-
lowed with use of benzeneselenol on a 97 µmol scale and gave the
product as a black microcrystalline product (45%). Absorption spectrum
(acetonitrile): λmax (ꢀM) 294 (sh, 12000), 397 (8300), 513 (6700), 608
(sh, 3900) nm. EPR (DMF/acetonitrile): br, g1 ) 2.068, g2 ) 1.988,
g3 ) 1.949. This compound is isomorphous with the preceding
compound and was identified by an X-ray structure determination.
(Et4N)2[W2(µ-S)2(S2C2Me2)4]. Method a. To a green-brown solution
of 32.5 mg (50.5 µmol) of (Et4N)[W(OPh)(S2C2Me2)2] in 1.5 mL of
acetonitrile was added a solution of 14.5 mg (52.5 µmol) of Ph3CSH
in 1 mL of acetonitrile with stirring. The solution color turned dark
brown over 1 h, after which the solvent was removed. The dark brown
residue was dissolved in a minimal volume of acetonitrile, and the
solution was filtered. Ether (60 mL) was added to precipitate a solid,
which was isolated, washed with ether (3 × 1 mL), and dried to give
the product as 24.0 mg (79%) of black microcrystalline solid.
Absorption spectrum (acetonitrile): λmax (ꢀM) 337 (8900), 403 (7400),
490 (6700), 568 (5400) nm. Anal. Calcd for C32H64N2S10W2‚CH3CN:
C, 33.85; H, 5.60; N, 3.48; S, 26.58. Found: C, 33.94; H, 5.54; N,
3.41; S, 26.46.
Method b. A green-brown solution of 58.7 mg (82.3 µmol) of
(Et4N)2[WS(S2C2Me2)2] in 2 mL of acetonitrile was treated with a
solution of 10.1 mg (39.6 µmol) of I2 in 1 mL of THF. The reaction
mixture was stirred for 10 min, and solvent was removed. The dark
brown residue was dissolved in a minimum volume of acetonitrile, and
the mixture was filtered. Vapor diffusion of ether into the filtrate
produced 18 mg (36%) of black solid. This material was contaminated
with a slight amount of (Et4N)2[W2S2(µ-S)2(S2C2Me2)2] (identified by
an X-ray structure determination), which can be removed by washing
with a minimal amount of acetonitrile/ether (1:3 v/v).
(Et4N)[WS(OPh)(S2C2Me2)2]. To a solution of 31.0 mg (48.2 µmol)
of (Et4N)[W(OPh)(S2C2Me2)2] in 1 mL of acetonitrile was added a
solution of 18.7 mg (67.2 µmol) of dibenzyl trisulfide in 1 mL of
acetonitrile. The initial green-brown solution immediately turned red-
brown. The reaction mixture was stirred for 10 min, and solvents were
removed. The residual dark brown oil was dissolved in 1.5 mL of
acetonitrile, and the solution was filtered. Ether (50 mL) was added to
the dark red-brown filtrate. The solid which separated over 1 day was
collected, washed with ether (3 × 1 mL), and dried, affording the
product as 13 mg (40%) of black microcrystalline solid. IR (KBr): νWS
1
470 cm-1. H NMR (CD3CN, anion): δ 2.29 (s, 12), 6.80 (t, 1), 6.94
(d, 2), 7.18 (t, 2). Absorption spectrum (acetonitrile): λmax (ꢀM) 290
(sh, 10000), 341 (11000), 370 (sh, 9500), 474 (5500) nm. Anal. Calcd
for C22H37NOS5W: C, 39.11; H, 5.52; N, 2.07; S, 23.73. Found: C,
38.97; H, 5.46; N, 2.03; S, 23.87.
In the sections which follow, tungsten complexes are referred to by
the numerical designations in Chart 1.
X-ray Structure Determinations. The nine compounds listed in
Tables 1 and 2 were structurally identified by X-ray crystallography.
Single crystals were obtained by layering ether on the corresponding
acetonitrile solutions at ambient temperature over a period of at least
1 day. Selected crystals were coated in silicone grease and mounted
on a Siemens (Bruker) SMART CCD-based diffractometer equipped
with an LT-2 low-temperature apparatus operating at 213 K. Mo KR
radiation (λ ) 0.71073 A) was used for all data collection. Data were
collected with ω scans of 0.3°/frame for 30 s, such that 1271 frames
were collected for a hemisphere of data. The first 50 frames were re-
collected at the end of the data collection to monitor for decay; no
significant decay was detected for any compounds. Data only out to
2θ of 50° for (Et4N)[8]‚CH3CN were used because of the low-quality
high-angle data while data out to 2θ of 55.9-56.6° was collected for
the other compounds. Cell parameters were retrieved using SMART
software and refined using SAINT software on all reflections. Data
reduction was performed with SAINT software, which corrects for
Lorentz polarization and decay. Absorption corrections were applied
using SADABS. The space groups for all compounds were assigned
unambiguously by analysis of symmetry and systematic absences
Method c. To a green-yellow suspension of the mixture of 18.3 mg
(0.166 mmol) of Na2S2 and 51.8 mg (0.313 mmol) of Et4NCl in 1 mL
of acetonitrile was added a dark violet solution of 78.6 mg (0.165 µmol)
of [W(CO)2(S2C2Me2)2] in 3 mL of THF. The color of the reaction
mixture immediately changed to green, and became brown in 5 min.
The mixture was stirred for 2 h, and solvent was removed. The resulting
brown solid was redissolved in a minimal amount of acetonitrile and
filtered. Ether (60 mL) was layered on the filtrate to yield a brown
solid and pale blue supernatant over 2 days. The brown solid was
recrystallized by vapor diffusion of ether into an acetonitrile solution.
The solid was washed with ether (3 × 1 mL), and dried to afford the
product as 63.3 mg (64%) of thin black plates.
The products from the three methods are spectroscopically identical.
(3) W(VI) Complexes. (Et4N)2[WO2(S2C2Me2)2]. To an orange-
yellow solution of 59.6 mg (85.5 µmol) of (Et4N)2[WO(S2C2Me2)2] in

Reactions of Bis(dithiolene)tungsten Complexes
Inorganic Chemistry, Vol. 40, No. 18, 2001 4521
Table 2. Crystallographic Dataa
(Et4N)[10]
(Et4N)[11]
(Et4N)[12]
(Et4N)2[14]
formula
fw
cryst syst
space group
Z
C28H42NS6W
768.84
orthorhombic
Pbca
C28H42NS4Se2W
862.64
orthorhombic
Pbca
C22H37NOS5W
675.68
orthorhombic
Fdd2
C24H52N2O2S4W
712.77
monoclinic
P21/n
8
8
16
4
a, Å
b, Å
c, Å
13.2822(5)
20.1469(7)
23.9424(9)
13.326(2)
20.196(3)
24.352(4)
24.309(4)
20.528(4)
21.720(4)
11.1622(9)
21.897(3)
13.169(2)
102.891(9)
3137.6(6)
1.509
â, deg
V, Å3
6406.9(4)
1.594
6554(1)
1.749
10838(3)
1.656
d
calc, g/cm3
2θ range, deg
3.4-56.6
3.3-56.5
3.2-55.9
3.7-56.5
GOF (F2)
1.001
1.044
0.953
1.131
R1b (wR2c)
0.0453 (0.0912)
0.0459 (0.0916)
0.0311 (0.0798)
0.0630 (0.1200)
a Obtained with graphite-monochromatized Mo KR (λ ) 0.71073 Å) radiation at 213 K. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo
-
2
Fc2)2]/∑[w(Fo )2]}1/2
.
2
Table 3. Selected Bond Distances (Å) and Angles (deg)
5
6
7
8a
9b
10
11
12c
14
W-O1
2.177(4)d
2.172(4)d
2.329(2)
2.324(2)
2.335(2)
2.322(2)
1.724(6)e
1.967(5)f
1.741(5)e
1.757(6)e
2.581(2)g
2.422(2)
2.586(2)g
2.419(2)
W-O2
W-S1
2.372(2)
2.381(2)
2.400(2)
2.342(2)
2.405(2)f
2.376(1)
2.381(1)
2.400(1)
2.341(1)
2.382(2)
2.453(2)
2.432(2)
2.391(2)
2.346(2)h
2.330(2)h,i
2.377(2)
2.381(2)
2.367(2)
2.368(2)
2.368(2)
2.374(2)
2.429(2)f
2.430(2)f
2.366(2)
2.375(2)
2.367(2)
2.370(2)
2.456(2)g
2.408(2)
2.394(2)
2.400(2)
2.151(2)j
W-S2
W-S3
W-S4
W-S5
W-S6
W-Se1
W-Se2
W‚‚‚W
2.532(1)
2.550(1)
2.550(1)
3.000(1)
W-C1
2.024(6)
1.129(7)
1.741(7)
1.337(9)
2.009(3)
1.145(4)
1.748(3)
1.340(5)
C1-O1
S-Ck
1.737(7)
1.330(9)
100.16(5)
79.84(5)
1.773(6)
1.326(8)
1.742(2)
1.34(1)
86.00(6)
1.745(7)
1.34(1)
86.48(2)
1.745(8)
1.34(1)
96.6(2)
1.745(8)
1.34(1)
100.2(3)
C-Ck,l
Q-W-Q′ m
W-S-W
W-Q-Cf
S1-W-S2n
S3-W-S4n
S1-W-S4p
S2-W-S3p
δs
59.4(2)d
118.4(2)
79.26(2)
81.18(5)
137.96(6)
140.96(6)
0.822
114.89(8)
81.26(3)
79.51(3)
138.93(3)
140.81(3)
0.814
113.3(2)
80.48(6)
80.09(6)
122.68(7)
150.51(6)
0.870
110.5(2)
80.29(6)
80.54(6)
124.21(7)
151.24(6)
0.849
136.4(4)
77.36(6)
79.09(7)
92.13(7)
155.48(9)
81.71(6)
82.15(6)
138.05(6)
141.04(6)
0.805
79.07(7)
78.92(6)
158.92(5)
94.08(6)
82.62(6)o
78.06(7)
78.40(7)
85.51(7)
90.83(7)
141.5(1)q
144.5(1)r
0.755
t
θd
125.5
126.1
126.7
94.0
130.0
118.6
120.2
95.0
92.8
a-c One of the two anions in asymmetric unit; symmetry transformations used to generate equivalent atoms: a-x + 2, -y + 1, z. b-x + 1, -y,
1
1
c
z (anion); -x + /2, y, -z - /4 (cation). -x + 3, -y + 2, z. d Bidentate benzoate ligand. e Terminal oxo ligand. f Unidentate ligand. g Trans to
terminal oxo or sulfido ligand. h Bridging sulfido ligand. i S5A. j Terminal sulfido ligand. k Mean value. l Dithiolene chelate ring. m Angle between
unidentate or bridging ligands; Q ) O, S, Se. n Chelate ring bite angle. o S1-W-S2 and S1A-W-S2A are identical. p Transoid angle. q S1-
W-S1A. r S2-W-S2A. s Perpendicular displacement of W atom from S4 least-squares plane. t Dihedral angle between WS2 planes.
determined by the program XPREP. Missing symmetry was checked
by the program PLATON. Crystal parameters are given in Tables 1
and 2.
Nicolet Nexus 470 FT-IR instruments. Cyclic voltammograms and
differential potential voltammograms were recorded with a PAR model
263 potentiostat/galvanostat using Pt disk working electrode and 0.1
M Bu4NPF6 supporting electrolyte in MeCN solution. Potentials were
directly measured with and referenced to the saturated calomel electrode
(SCE). EPR spectra were recorded at ∼4 K in DMF/acetonitrile (1:1
v/v) with a Bruker ESP 300 spectrometer. Spectral simulations were
performed with WIN-EPR SimFonia v. 1.25 software.
All structures were solved by direct methods with SHELXS-97 and
subsequently refined against all data by full-matrix least squares on F2
using SHELXL-97. Disorder in the cations was frequently encountered.
All methylene groups and one methyl group of (Et4N)[12], all methylene
groups of one of the two cations in (Et4N)2[13], and all methylene
groups of (Et4N)[5,9] were disordered over two positions and were
refined with a site occupancy factor of 0.5. All non-hydrogen atoms
including the disordered cations were refined anisotropically. Hydrogen
atoms were attached at idealized positions on carbon atoms in the final
stages of refinement. All residual peaks near the highly absorbing
tungsten atoms are within acceptable distances. Selected bond distances
and angles are listed in Table 3.
Other Physical Measurements. All measurements were performed
under anaerobic conditions. Absorption spectra were recorded with a
Varian Cary 50 Bio spectrophotometer. 1H NMR spectra were obtained
with a Bruker AM500N or a Varian Mercury 400 spectrometers. IR
spectra were measured with KBr pellets in a Nicolet Impact 400 or a
Results and Discussion
In this investigation, we have sought to expand the basis set
of stable coordination units in bis(dithiolene)W(IV,V,VI) com-
plexes beyond those containing the foregoing mononuclear
fragments WLL′ prepared in this laboratory.3-5,18 The synthetic
schemes in Figures 1 and 2 summarize reactions developed in
this and in prior investigations. The structural data in Table 3
reveal the ranges of 1.33-1.34 and 1.74-1.77 Å for chelate
ring C-C and S-C distances. These values are sufficiently close

4522 Inorganic Chemistry, Vol. 40, No. 18, 2001
Sung and Holm
Figure 1. Scheme for the synthesis of bis(dithiolene)W(IV,V) complexes 2-8 by partial or complete substitution of the carbonyl ligands of 1.
Figure 2. Scheme for the synthesis of bis(dithiolene)W(V,VI) complexes 9-14 by oxidation reactions of W(IV) complexes 2, 3, and 4. [O] )
Me3NO; [S] ) (PhCH2S)2S.
to the typical distances (sp2)CdC(sp2) ) 1.331(9) Å and
S-C(sp2) ) 1.751(17) Å20 to allow description of the ligand
as an ene-1,2-dithiolate and assignment of tungsten oxidation
states in the sections that follow. This is the case for all bis-
(dithiolene)molybdenum and -tungsten complexes thus far
examined with the exception of dicarbonyls.21 In considering
the structures of reaction products, nearly all metric parameters
(20) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.
G.; Taylor, R. In International Tables of Crystallography; Wilson, A.
J. C., Ed.; Kluwer Academic Publishers: Boston, 1995; Sect. 9.5.
(21) Fomitchev, D. V.; Lim, B. S.; Holm, R. H. Inorg. Chem. 2001, 40,
645-654.

Reactions of Bis(dithiolene)tungsten Complexes
Inorganic Chemistry, Vol. 40, No. 18, 2001 4523
Table 4. Redox Potentials for W(VI/V), W(V/IV), and W(IV/III)
Couples in Acetonitrile
E1/2, Va (∆Ep, mV)
complex
W(VI/V)
W(V/IV)
W(IV/III)
[W(CO)(2-AdS)(S2C2Me2)2]-
[W(CO)(2-AdSe)(S2C2Me2)2]-
[WO(S2C2Me2)2]2- b
-1.53 (100)
-1.55 (110)
-0.05 (80) -0.91 (80)
-0.13 (80)c -0.89 (90)
-0.18 (80) -0.93 (70)
-0.21 (80) -0.93 (150)
[WS(S2C2Me2)2]2-
[W(SPh)2(S2C2Me2)2]-
[W(SePh)2(S2C2Me2)2]-
a E1/2 ) (Epc + Epa)/2, scan rate 100 mV/s, vs SCE. b Reference 3.
c Quasi-reversible.
genase (Q ) Se).2 In our parallel development of molybdenum
and tungsten dithiolene chemistry, we are interested in obtaining
an analogous tungsten series. The square pyramidal complex
[W(2-AdO)(S2C2Me2)2]- is readily prepared.5 Reaction of 1 with
1-5 equiv of 2-adamantylthiolate or 2-adamantylselenolate gave
only the monocarbonyl 6 or 7. These results are consistent with
that obtained in the reaction of 1 with highly hindered 2,4,6-tri-
isopropylbenzenethiolate, from which the monocarbonyl com-
plex was obtained.4 Complexes 6 and 7 are isostructural (Figure
3). From θd and transoid S-W-S angles (Table 3), they are
described as trigonal prismatic. We consider the W-S (2.405-
(2) Å) and W-Se (2.532(1) Å) bond lengths, much longer than
the W-O distance in [W(2-AdO)(S2C2Me2)2]- (1.826(4) Å),5
to reduce steric interactions between the adamantyl and carbonyl
groups to the point where the monocarbonyls are stable. This
aspect, together with higher W-CO than Mo-CO bond disso-
ciation energies,22 leads to the relative stability of the tungsten
monocarbonyls, a matter discussed in more detail elsewhere.4
Tungsten(V). Complexes in this oxidation state have been
prepared by oxidation of W(IV) species with iodine (Figure 2).
Redox potentials for four complexes are given in Table 4, and
two cyclic voltammograms showing the existence of three-
member electron transfer series based on 4 and 10 are presented
in Figure 4. The low-potential oxo complex 3 is readily
converted to 9 by treatment with iodine. It has the standard
square pyramidal structure in Figure 5, observed for 33 and
related complexes such as [WO(bdt)2]-.14 The redox potentials
for 3 and sulfido complex 4 are nearly identical, as is the case
with [WQ(S2C2Ph2)2]2- (Q ) O, S).3 When an analogous
oxidation reaction was attempted with 4, binuclear sulfide-
bridged 8 was obtained instead of the desired mononuclear
product. The complex can also be prepared in two other ways:
oxidation of 1 with Na2S2 (Figure 1) and the reaction of 2 with
Ph3CSH, where we assume that the incipient triphenylmethyl
carbocation is the likely oxidant as a W-S bond is developed
and a S-C bond is compromised. This complex is characterized
by a W‚‚‚W interaction at 3.000(1) Å and distorted octahedral
coordination (Figure 5). It is isostructural with [Mo2(µ2-S)2-
(S2C2R2)4]2- (R ) Me,1 CO2Me23) and [W2(µ2-S)2(S2C2R2)4]2-
(R ) Ph,3 CO2Et24). [W2(µ2-S)2(S2C2Ph2)4]2- was obtained by
the oxidation of [WS(S2C2Ph2)2]2- with tropylium ion.3 We are
unaware of any mononuclear dithiolene species containing either
the MoVdS or the WVdS group, the stability of bridged
structures being prevalent.
Figure 3. Structures of the W(IV) complexes 5 (upper) and 6/7 (lower;
Q ) S, Se) showing 50% probability ellipsoids and a partial atom-
labeling scheme; 6 and 7 are isostructural.
(Table 3) are normal and are not explicitly discussed. Attention
is directed toward molecular stereochemistry.
Tungsten(IV). All complexes have been prepared by dis-
placement of one or two carbonyl groups from the readily
prepared dicarbonyl precursor 1 (Figure 1). While depicted for
simplicity as a bis(ene-1,2-dithiolate) complex, our recent
experimental and theoretical work shows that 1 and its
molybdenum analogue are highly delocalized, noninnocent
species without clear-cut metal and ligand oxidation levels.21
Both carbonyls are readily displaced by alkoxide or phenolate
to afford 2, by hydroxide to form oxo complex 3, by hydro-
sulfide to form sulfido complex 4, and by benzoate to yield 5.
Structures of square pyramidal 2,4 3,3 and [WS(S2C2Ph2)2]2- 3
,
closely related to 4, are available elsewhere. As seen in Figure
3, benzoate complex 5 is six-coordinate. The tungsten atom is
displaced by 0.805 Å from the S4 mean plane toward the
benzoate ligand which is bound by two equivalent W-O
interactions at 2.175 Å with a O-W-O angle of 59.4(2)°. The
dihedral angle θd ) 125.5° between WS2 planes and the transoid
S-W-S angles of 138° and 141° (involving sulfur atoms in
different chelate rings) are close to the values of 120° and 136°,
respectively, for trigonal prismatic geometry. In this sense, 5
closely resembles precursor 13 and is the first example of a
tungsten dithiolene carboxylate.
In reactions intended to effect substitution of the phenolate
ligand in 2 by proton transfer, this complex was treated with
(22) Lewis, K. E.; Golden, D. M.; Smith, G. P. J. Am. Chem. Soc. 1984,
106, 3905-3912.
(23) Coucouvanis, D.; Hadjikyriacou, A.; Toupadakis, A.; Koo, S.-M.;
Ileperuma, O.; Draganjac, M.; Salifoglou, A. Inorg. Chem. 1991, 30,
754-767.
Earlier we reported the synthesis and structures of the set of
complexes [Mo(2-AdQ)(S2C2Me2)2]-, intended as representa-
tions of the Mo(IV) sites in DMSO reductase (Q ) O),
assimilatory nitrate reductase (Q ) S), and formate dehydro-
(24) Umakoshi, K.; Nishimoto, E.; Sokolov, M.; Kawano, H.; Sasaki, Y.;
Onishi, M. J. Organomet. Chem. 2000, 611, 370-375.

4524 Inorganic Chemistry, Vol. 40, No. 18, 2001
Sung and Holm
Figure 6. Structures of the W(VI) complexes 14 (upper) and 12 (lower)
showing 50% probability ellipsoids and a partial atom-labeling scheme.
Table 5. Functional Groups in Mononuclear
Bis(dithiolene)W(IV,V,VI) Complexes
Figure 4. Cyclic voltammograms (100 mV/s) for complexes 4 (upper)
and 10 (lower) in acetonitrile at ∼25 °C. Peak potentials are indicated.
a This work. b Not proven by a structure determination. c Ambiguous
oxidation state.
compounds are isostructural (Figure 5) and represent a new type
of tungsten dithiolene complex. From transoid angles and θd
values (Table 3), the complexes exhibit a distorted trigonal
prismatic stereochemistry with the thiolate or selenolate ligands
in cis positions. The overall stereochemistry is quite similar to
that of 1, 6, and 7. When compared with distances in PhQQPh
(Q ) S, 2.03 Å;25,26 Q ) Se, 2.29 Å27), the corresponding
separations in 10 (3.31 Å) and 11 (3.49 Å) and Q-W-Q angles
(Table 3) make clear that the ligands are monoanions, leading
Figure 5. Structures of the W(V) complexes 9 and 8 (upper) and 10/
11 (lower; Q ) S, Se) showing 50% probability ellipsoids and a partial
atom-labeling scheme; 10 and 11 are isostructural.
benzenethiol or benzeneselenol. With 1 equiv of either com-
pound in acetonitrile, the methyl resonance of 2 (δ 2.61)
decreased in intensity by one-half; with 2 equiv, the resonance
was abolished. On a preparative scale, 10 was obtained in 67%
yield and 11 in 45% yield using 2 equiv of the reagents. These
(25) Lee, J. D.; Bryant, M. W. R. Acta Crystallogr. 1969, B25, 2094-
2101.
(26) Sacerdoti, M.; Gilli, G. Acta Crystallogr. 2001, B31, 327-329.
(27) Marsh, R. E. Acta Crystallogr. 1952, 5, 458-462.

Reactions of Bis(dithiolene)tungsten Complexes
Inorganic Chemistry, Vol. 40, No. 18, 2001 4525
to a W(V) formulation. As shown by the results in Table 4 and
Figure 4, complexes 10 and 11 reducible to W(IV) and
oxidizable to W(VI) in reversible reactions at essentially
identical potentials. EPR spectra of 9-11 at 4 K were broad
and uninformative (Experimental Section).
to obtain a pure salt of [WOS(S2C2Me2)2]2-. It remains to be
seen which (if any) of the groups in Table 5 with physiological-
type ligands eventuate in tungstoenzymes. Among the candidates
are WIVO, WVO, and WVIO2, which appear in 3, 9, and 14,
respectively. We are continuing synthetic and reactivity studies,
with current emphasis on the latter three species whose Et4N+
salts are water-soluble, an unusual property for bis(dithiolene)-
tungsten complexes.
Tungsten(VI). This oxidation state was achieved by the atom
transfer reactions in Figure 2. Reaction of oxo complex 3 with
Me3NO affords dioxo complex 14. Treatment of 2 with dibenzyl
trisulfide affords sulfido complex 12. The structures of 14 and
12 are set out in Figure 6. Complex 14 has a distorted octahedral
stereochemistry and is essentially isostructural with [WO2-
Acknowledgment. This research was supported by NSF
Grant CHE 95-23830.
(bdt)2]2- 14,28 and[WO2(mnt)2]2- 15
Complex 12 is congeneric
.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of the nine compounds
in Tables 1 and 2. This material is available free of charge via the
Internet at http://pubs.acs.org.
with 13 and isostructural with it and [WS(OSiButPh2)(bdt)2]-.18
Neither 12 nor 13 shows reversible reduction to W(V).
Summary. The research has afforded, by a combination of
substitution and oxidation reactions, a new set of bis(dithiolene)-
tungsten complexes composed of 4-12 and 14, some of which
are precedented structural types. The results of this and prior
exploratory synthetic investigations are summarized in Table
5, which enumerates the 21 functional groups WL and WLL′
thus far stabilized in mononuclear bis(dithiolene) complexes and
supplants an earlier version.4 Conspicuously absent is the group
WVIOS, which has been stabilized in complexes with other
ligands.29-34 Despite multiple attempts, we have not been able
IC010421X
(29) Potvin, C.; Manoli, J. M.; Marzak, S.; Secheresse, F. Acta Crystallogr.
1988, C44, 369-370.
(30) Eagle, A. A.; Tiekink, E. R. T.; Young, C. G. J. Chem. Soc., Chem.
Commun. 1991, 1746-1748.
(31) Faller, J. W.; Ma, Y. Organometallics 1989, 8, 609-612.
(32) Eagle, A. A.; Harben, S. M.; Tiekink, E. R. T.; Young, C. G. J. Am.
Chem. Soc. 1994, 116, 9749-9750.
(33) Barnard, K. R.; Gable, R. W.; Wedd, A. G. J. Biol. Inorg. Chem.
1997, 2, 623-633.
(28) Oku, H.; Ueyama, N.; Nakamura, A. Bull. Chem. Soc. Jpn. 1996, 69,
3139-3150.
(34) Miao, M.; Willer, M. W.; Holm, R. H. Inorg. Chem. 2000, 39, 2843-
2849.