Oxo/sulfidotungstate(VI) as precursors to W(VI)O2, W(VI)OS, and W(VI)S2 complexes and W(IV) - Dithiolene chelate rings

Article abstract of DOI:10.1021/ic000047l

Synthetic models leading to oxosulfidotungsten(VI) groups and dithiolene chelate rings have been investigated. The heterogeneous reaction systems [WO(4-n)S(n)]^2-/2Ph₃SiCl/Me₄phen (n = 0-2) in acetonitrile afford the complexes [WQ₂(OSiPh₃)₂(Me₄phen)] (1-3) in the indicated yields containing the groups W(VI)O₂ (1; 86%), W(VI)OS (2; 45%), and W(VI)S₂ (3; 83%). In the crystalline state these complexes have imposed C₂ symmetry, with cis-oxo/sulfido and trans-silyloxide ligands. ¹H NMR spectra indicate that this stereochemistry is retained in solution. The colors of 2 (yellow, 367 nm) and 3 (orange, 451 nm) arise from LMCT absorptions at the indicated wavelengths. These results demonstrate that the silylation procedure previously introduced for the preparation of molecules with the Mo(VI)OS group (Thapper, et al. Inorg. Chem. 1999, 38, 4104) extends to tungsten. Methods for the formation of dithiolene chelate rings MS₂C₂R₂ in reactions with sulfide-bound M = Mo or W precursors are summarized. In a known reaction-type, 3 and activated acetylenes rapidly form [W(IV)(OSiPh₃)₂(Me₄phen)(S₂C₂R₂)] (R = CO₂Me, 4, 83%, and Ph, 5, 98%). In a new reaction type not requiring the isolation of an intermediate, the systems [MO₂S₂]^2-/2Ph₃SiCl/Me₄phen/PhC≡CPh in acetonitrile afford 5 (68%) and [Mo(IV)(OSiPh₃)₂(Me₄phen)(S₂C₂Ph₂)] (6; 61%). Complexes 5 and 6 are isostructural, maintain the trans-silyloxide stereochemistry, and exhibit chelate ring dimensions indicative of ene-1,2-dithiolate coordination. Reductions in the -1.4 to -1.7 V range are described as metal-centered. It remains to be seen whether the oxo/sulfidotungsten(VI) groups in 1-3 eventuate in the active sites of tungstoenzymes. (Me₄phen = 3,4,7,8-tetramethyl-1,10-phenanthroline).

Full text of DOI:10.1021/ic000047l

Inorg. Chem. 2000, 39, 2843-2849
2843
Oxo/Sulfidotungstate(VI) as Precursors to WVIO2, WVIOS, and WVIS2 Complexes and
WIV-Dithiolene Chelate Rings
Mingming Miao, Michael W. Willer, and R. H. Holm*
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
ReceiVed January 11, 2000
Synthetic models leading to oxosulfidotungsten(VI) groups and dithiolene chelate rings have been investigated.
The heterogeneous reaction systems [WO4-nSn]2-/2Ph3SiCl/Me4phen (n ) 0-2) in acetonitrile afford the complexes
[WQ2(OSiPh3)2(Me4phen)] (1-3) in the indicated yields containing the groups WVIO2 (1; 86%), WVIOS (2; 45%),
and WVIS2 (3; 83%). In the crystalline state these complexes have imposed C2 symmetry, with cis-oxo/sulfido
and trans-silyloxide ligands. 1H NMR spectra indicate that this stereochemistry is retained in solution. The colors
of 2 (yellow, 367 nm) and 3 (orange, 451 nm) arise from LMCT absorptions at the indicated wavelengths. These
results demonstrate that the silylation procedure previously introduced for the preparation of molecules with the
MoVIOS group (Thapper, et al. Inorg. Chem. 1999, 38, 4104) extends to tungsten. Methods for the formation of
dithiolene chelate rings MS2C2R2 in reactions with sulfide-bound M ) Mo or W precursors are summarized. In
a known reaction type, 3 and activated acetylenes rapidly form [WIV(OSiPh3)2(Me4phen)(S2C2R2)] (R ) CO2Me,
4, 83%, and Ph, 5, 98%). In a new reaction type not requiring the isolation of an intermediate, the systems
[MO2S2]2-/2Ph3SiCl/Me4phen/PhCtCPh in acetonitrile afford 5 (68%) and [MoIV(OSiPh3)2(Me4phen)(S2C2Ph2)]
(6; 61%). Complexes 5 and 6 are isostructural, maintain the trans-silyloxide stereochemistry, and exhibit chelate
ring dimensions indicative of ene-1,2-dithiolate coordination. Reductions in the -1.4 to -1.7 V range are described
as metal-centered. It remains to be seen whether the oxo/sulfidotungsten(VI) groups in 1-3 eventuate in the
active sites of tungstoenzymes. (Me4phen ) 3,4,7,8-tetramethyl-1,10-phenanthroline.)
Introduction
X-ray absorption spectroscopy4,11 indicates bis(dithiolene) co-
ordination and one or two presumably oxygenous ligands. In
Coordination of the one or two pterin dithiolene cofactor
ligands at the active sites of enzymes containing molybdenum1-3
(excluding nitrogenase) and tungsten4,5 necessitates the synthesis
of new types of dithiolene complexes, if the properties of these
sites are to be investigated using analogue molecules. Two issues
in synthesis are immediately apparent: (i) development of routes
to complexes whose dithiolene ligand(s) resemble the cofactor
and are not necessarily available in the free form; (ii) introduc-
tion of the functionalities and other ligands present in enzyme
sites, including MoIVQR and and MoVIO(QR) (Q ) O, S, Se),
MoVIO2, and MoVIOS inter alia, in complexes with the ap-
propriate number of dithiolene ligands. Our recent research has
emphasized synthesis of bis(dithiolene)molybdenum species
with the foregoing functional units6,7 and incorporation of the
MoVIOS group in six-coordinate (non-dithiolene) complexes.8
The structural nature of tungsten sites is much less clear at this
stage. Collective evidence from protein crystallography9,10 and
our development of molybdenum analogues, we have considered
it advisable to prepare where possible related tungsten
complexes,12-14 should their coordination units eventuate as
biologically relevant. Toward that end, we have recently reported
a detailed X-ray absorption spectroscopic study of congeneric
structurally defined bis(dithiolene)molybdenum and -tungsten
complexes.15 These results should be useful in identifying
structural features of enzyme sites.
Closely associated with the preparation of dithiolene com-
plexes is the synthesis of dithiolene ligands themselves, for
which a number of methods are available.16-19 One approach,
summarized in Table 1, results in the closure of chelate rings
in sulfide-bound precursors,20-30 nearly always by reaction with
(10) Hu, Y.; Faham, S.; Roy, R.; Adams, M. W. W.; Rees, D. C. J. Mol.
Biol. 1999, 286, 899-914.
(11) George, G. N.; Prince, R. C.; Mukund, S.; Adams, M. W. W. J. Am.
Chem. Soc. 1992, 114, 3521-3523.
(12) Lorber, C.; Donahue, J. P.; Goddard, C. A.; Nordlander, E.; Holm, R.
H. J. Am. Chem. Soc. 1998, 120, 8102-8112.
(1) Hille, R. Chem. ReV. 1996, 96, 2757-2816.
(2) Roma˜o, M. J.; Kna¨blein, J.; Huber, R.; Moura, J. J. G. Prog. Biophys.
Mol. Biol. 1997, 68, 121-144.
(13) Goddard, C. A.; Holm, R. H. Inorg. Chem. 1999, 38, 5389-5398.
(14) Sung, K.-M.; Holm, R. H. Inorg. Chem. 2000, 39, 1275-1281.
(15) Musgrave, K. B.; Donahue, J. P.; Lorber, C.; Holm, R. H.; Hedman,
B.; Hodgson, K. O. J. Am. Chem. Soc. 1999, 121, 10297-10307.
(16) Mueller-Westerhoff, U. T.; Vance, B. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1987; pp 595-
631.
(3) Roma˜o, M. J.; Huber, R. Struct. Bonding 1998, 90, 69-95.
(4) Johnson, M. K.; Rees, D. C.; Adams, M. W. W. Chem. ReV. 1996,
96, 2817-2839.
(5) Hagen, W. R.; Arendsen, A. F. Struct. Bonding 1998, 90, 161-192.
(6) Donahue, J. P.; Goldsmith, C. R.; Nadiminti, U.; Holm, R. H. J. Am.
Chem. Soc. 1998, 120, 12869-12881.
(17) Mueller-Westerhoff, U. T.; Vance, B.; Yoon, D. I. Tetrahedron 1991,
47, 909-932.
(18) Tian, Z.-Q.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 1995, 34,
5567-5572.
(19) Hsu, J. K.; Bonangelino, C. J.; Kaiwar, S. P.; Boggs, C. M.; Fettinger,
J. C.; Pilato, R. S. Inorg. Chem. 1996, 35, 4743-4751.
(20) Ansari, M. A.; Chandrasekaran, J.; Sarkar, S. Inorg. Chim. Acta 1987,
133, 133-136.
(7) Lim, B. S.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 2000, 39, 263-
273.
(8) Thapper, A.; Donahue, J. P.; Musgrave, K. B.; Willer, M. W.;
Nordlander, E.; Hedman, B.; Hodgson, K. O.; Holm, R. H. Inorg.
Chem. 1999, 38, 4104-4114.
(9) Chan, M. K.; Mukund, S.; Kletzin, A.; Adams, M. W. W.; Rees, D.
C. Science 1995, 267, 1463-1469.
10.1021/ic000047l CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/27/2000

2844 Inorganic Chemistry, Vol. 39, No. 13, 2000
Miao et al.
Table 1. Formation of Dithiolene Chelate Rings MS2C2R2 (M )
Mo, W) from Sulfido-Bound Precursors and Activated Acetylenes
[WO2(OSiPh3)2(Me4phen)]. A suspension of 0.163 g (0.500 mmol)
of K2[WO4] and 0.165 g (0.698 mmol) of 3,4,7,8-tetramethyl-1,10-
phenanthroline (Me4phen) in 15 mL of acetonitrile was stirred for 30
min, and 0.266 g (0.902 mmol) of Ph3SiCl was added. The reaction
mixture was refluxed for 4 h and reduced to dryness. The residue was
washed with acetonitrile (2 × 10 mL) and redissolved in 150 mL of
dichloromethane. The solution was filtered, and the filtrate was reduced
to dryness. The residue was washed with acetonitrile (2 × 10 mL) and
ether (2 × 10 mL), and dried to afford the product as 0.431 g (86%)
of a white solid. An analytical sample was obtained by recrystallization
from dichloromethane/acetone. IR (KBr): νSiO 949 (br), νWO 928, 905
cm-1. Absorption spectrum (CH2Cl2): λmax (ꢀM) 285 (28 000), 307 (sh,
1
9000), 334 (1600) nm. FAB-MS: m/z 1002 (M+). H NMR (CDCl3):
δ 9.12 (s, 2,9-H, 1), 7.76 (s, 5,6-H, 1), 7.12 (t, Ph, 3), 7.07 (d, Ph, 6),
6.97 (t, Ph, 6), 2.52, 2.28 (2 s, Me, 3, 3). Anal. Calcd for C52H46N2O4-
Si2W: C, 62.27; H, 4.62; N, 2.79. Found: C, 62.41; H, 4.71; N, 2.84.
[WOS(OSiPh3)2(Me4phen)]. A suspension of 0.328 g (0.959 mmol)
of K2[WO3S] and 0.319 g (1.35 mmol) of Me4phen in 20 mL of
acetonitrile was stirred for 20 min. To the mixture was added 0.513 g
(1.74 mmol) of Ph3SiCl, resulting in a red-brown solution and a light
orange precipitate within 10 min. The reaction mixture was stirred for
2 h. The solid was collected, washed with acetonitrile (3 × 10 mL)
and ether (2 × 10 mL), and dissolved in 200 mL of THF. The orange
solution was filtered, and the filtrate was reduced to dryness. The orange
residue was redissolved in 10 mL of dichloromethane and loaded onto
a silica gel column (3 × 10 cm) packed as a slurry in a 3:2
dichloromethane/hexanes (v/v) mixture, which was also used as the
eluant. The first band, an orange compound identified as [WS2-
(OSiPh3)2(Me4phen)], was dried and collected (0.144 g, 15%). A higher
yield preparation of this compound has been developed (vide infra).
The second band was dried and collected to give the desired product
as 0.438 g (45%) of a yellow solid. IR (KBr): νSiO 933 cm-1 (br), νWS
480 cm-1. Absorption spectrum (CH2Cl2): λmax (ꢀM) 285 (33 000), 307
(sh, 11 000), 335 (2100), 367 (560) nm. FAB-MS: m/z 1018 (M+). 1H
NMR (CDCl3): δ 9.73, 8.92 (2 s, 2,9-H, 1, 1), 7.79 (dd, 5,6-H, 2),
7.13 (t, Ph, 6), 7.06 (d, Ph, 12), 6.97 (t, Ph, 12), 2.55, 2.52, 2.35, 2.24
(4 s, 3,4,7,8-Me, 3, 3, 3, 3). Anal. Calcd for C52H46N2O3SSi2W: C,
61.29; H, 4.55; N, 2.75; S, 3.15. Found: C, 61.46; H, 4.45; N, 2.77; S,
3.19.
a Reactant is ArC(O)CH(X)R (X ) Br, tosyl). b Not derived from
an oxosulfidotungstate in two cases.28,30 c This work.
an activated alkyne. In these procedures, bound sulfur as sulfide,
hydrosulfide, or tetrasulfide is directly incorporated into product
chelate rings. This general method is useful for the formation
of certain coordinated dithiolenes that are not available in free
form. Here we report synthetic procedures leading to the
introduction of the uncommon WVIOS and WVIS2 groups in six-
coordinate molecules and dithiolene ring closure using the
simple precursors [MoO2S2]2- and [WO2S2]2-
.
Experimental Section
[WS2(OSiPh3)2(Me4phen)]. A suspension of 0.158 g (0.500 mmol)
of (NH4)2[WO2S2] and 0.165 g (0.698 mmol) of Me4phen in 20 mL of
acetonitrile was stirred for 20 min, and 0.266 g (0.902 mmol) of Ph3-
SiCl was added. The reaction mixture was stirred for 2 h; the orange
solid was collected and washed with acetonitrile (2 × 10 mL). The
solid was dissolved in 150 mL of dichloromethane, and the solution
was filtered. The filtrate was reduced to dryness. The residue was
washed with acetonitrile (2 × 10 mL) and ether (2 × 10 mL), and
dried to afford the product as 0.428 g (83%) of an orange solid. IR
(KBr): νSiO 928 (br), νWS 473 cm-1. Absorption spectrum (CH2Cl2):
λmax (ꢀM) 285 (38 000), 307 (sh, 14 000), 334 (5300), 451 (910) nm.
1H NMR (CDCl3): δ 9.42 (s, 2,9-H, 1), 7.82 (s, 5,6-H, 1), 7.14 (t, Ph,
3), 7.08 (d, Ph, 6), 6.98 (t, Ph, 6), 2.55, 2.28 (2 s, Me, 3, 3). Anal.
Calcd for C52H46N2O2S2Si2W: C, 60.34; H, 4.48; N, 2.71; S, 6.20.
Found: C, 60.35; H, 4.41; N, 2.69; S, 6.16.
Preparation of Compounds. K2[WO3S]31 and (NH4)2[MO2S2] (M
) Mo, W)32 were prepared as described. Other reagents were of
commercial origin and were used as received. Tetrahydrofuran, diethyl
ether, and hexanes were distilled from sodium, and acetonitrile and
dichloromethane were distilled from CaH2. These compounds were
stored over 4 Å molecular sieves. In the preparations below, solvent
removal and drying steps were performed in vacuo, and solids were
separated by filtration.
(21) Coucouvanis, D.; Hadjikyriacou, A.; Draganjac, M.; Kanatzidis, M.;
Ileperuma, O. Polyhedron 1986, 5, 349-356.
(22) Coucouvanis, D.; Hadjikyriacou, A.; Toupadakis, A.; Koo, S.-M.;
Ileperuma, O.; Draganjac, M.; Salifoglou, A. Inorg. Chem. 1991, 30,
754-767.
(23) Eagle, A. A.; Young, C. G.; Tiekink, E. R. T. Polyhedron 1990, 9,
2965-2969.
[W(OSiPh3)2(Me4phen)(S2C2(CO2Me)2)]. To a solution of 0.206
g (0.199 mmol) of [WS2(OSiPh3)2(Me4phen)] in 10 mL of dichloro-
methane was added 0.043 g (0.302 mmol) of dicarbomethoxyacetylene,
causing an immediate color change from orange to green-brown. The
mixture was stirred for 1 h, and the solvent was removed. The residue
was washed with ether (4 × 20 mL) and redissolved in 3 mL of
dichloromethane. Addition of ether (20 mL) caused the product to
crystallize as brown needles, which were collected, washed with ether
(2 × 10 mL), and dried to afford the product as 0.195 g (83%) of a
(24) Draganjac, M.; Coucouvanis, D. J. Am. Chem. Soc. 1983, 105, 5, 139-
140.
(25) Soricelli, C. L.; Szalai, V. A.; Burgmayer, S. J. N. J. Am. Chem. Soc.
1991, 113, 9877-9878.
(26) Kawaguchi, H.; Tatsumi, K. J. Am. Chem. Soc. 1995, 117, 3885-
3886.
(27) Kawaguchi, H.; Yamada, K.; Lang, J.-P.; Tatsumi, K. J. Am. Chem.
Soc. 1997, 119, 10346-10358.
(28) Eagle, A. A.; Harben, S. M.; Tiekink, E. R. T.; Young, C. G. J. Am.
Chem. Soc. 1994, 116, 9749-9750.
green-brown microcrystalline solid. IR (KBr): νSiO 904 (br) cm-1
.
(29) Oku, H.; Ueyama, N.; Nakamura, A. Inorg. Chem. 1997, 36, 1504-
Absorption spectrum (CH2Cl2): λmax (ꢀM) 286 (33 000), 307 (sh,
15 100), 334 (sh, 3 500), 393 (650), 485 (320) nm. FAB-MS: m/z 1176
(M+). 1H NMR (CDCl3): δ 9.13 (s, 2,9-H, 1), 7.97 (s, 5,6-H, 1), 7.10
(t, Ph, 3), 6.92 (t, Ph, 6), 6.74 (d, Ph, 6), 4.06 (s, CO2Me, 3), 2.65,
2.27 (2 s, 3,4,7,8-Me, 3, 3). Anal. Calcd for C58H52N2O6S2Si2W: C,
59.18; H, 4.45; N, 2.38. Found: C, 59.21; H, 4.41; N, 2.26.
1516.
(30) Eagle, A. A.; George, G. N.; Tiekink, E. R. T.; Young, C. G. J. Inorg.
Biochem. 1999, 76, 39-45.
(31) Corleis, E. Justus Liebig’s Ann. Chem. 1886, 232, 244-270.
(32) McDonald, J. W.; Friesen, G. D.; Rosenhein, L. D.; Newton, W. E.
Inorg. Chim. Acta 1983, 72, 205-210.

Oxosulfidotungsten(VI) Groups and Dithiolene Rings
Inorganic Chemistry, Vol. 39, No. 13, 2000 2845
Table 2. Crystal Dataa for WVIQ2 (Q ) O, S) and WIV- and MoIV-Monodithiolene Complexes
b
1
2
3
5‚MeCN
6‚C5H12
empirical formula
fw
cryst syst
space group
Z
C52H46N2O4Si2W
1002.94
monoclinic
C2/c
C52H46N2O3SSi2W
1019.00
monoclinic
C2/c
C52H46N2O2S2Si2W
1035.06
monoclinic
C2/c
C68H59N3O2S2Si2W
1254.33
triclinic
P1h
2
C71H56MoN2O2S2Si2
1185.42
monoclinic
C2/c
4
4
4
4
a, Å
b, Å
c, Å
27.119(4)
10.017(1)
16.547(1)
16.710(2)
10.3575(6)
27.002(3)
16.9351(1)
10.4963(1)
26.8896(2)
13.305(2)
14.959(1)
17.549(1)
109.330(7)
103.81(1)
106.667(8)
2934.4(5)
0.0291, 0.0612
19.068(1)
19.316(1)
17.7183(9)
R, deg
â, deg
96.65(1)
103.518(9)
104.517(1)
112.442(1)
γ, deg
V, Å3
4465(1)
0.0309, 0.0767
4543.8(7)
0.0305, 0.0760
4627.18(6)
0.0506, 0.1272
6032.0(5)
0.0485, 0.1342
R1,c wR2d
a Obtained with graphite-monochromatized Mo KR (λ ) 0.710 73 Å) radiation at 213 K. b Solvate modeled as a disordered pentane molecule.
c R1 ) ∑|Fo| - |Fc|/∑|Fo|. d wR2 ) {Σ[w(Fo - Fc2)2]/∑[w(Fo )2]}1/2
.
2
2
[W(OSiPh3)2(Me4phen)(S2C2Ph2)]. Method A. To a solution of
0.206 g (0.199 mmol) of [WS2(OSiPh3)2(Me4phen)] in 10 mL of
dichloromethane was added dropwise a solution of 0.0534 g (0.300
mmol) of diphenylacetylene in 5 mL of dichloromethane, causing an
immediate color change from orange to deep red-brown. The mixture
was stirred for 1 h, and the solvent was removed. The residue was
washed with ether (4 × 20 mL) and dissolved in 3 mL of dichloro-
methane. Addition of ether (20 mL) induced crystallization of the
product, which was collected, washed with ether (2 × 10 mL), and
dried to afford the product as 0.237 g (98%) of a deep red-brown
microcrystalline solid. IR (KBr): νSiO 918 (br) cm-1. Absorption
spectrum (CH2Cl2): λmax (ꢀM) 285 (39 300), 306 (22 800), 332 (sh,
Chart 1. Compound Designations and Abbreviations
1
9640), 350 (sh, 4150), 504 (835) nm. FAB-MS: m/z 1212 (M+). H
NMR (CDCl3): δ 9.16 (s, 2,9-H, 1), 7.99 (s, 5,6-H, 1), 7.60-6.84 (m,
Ph, 20), 2.65, 2.27 (2 s, Me, 3, 3). Anal. Calcd for C66H56N2O2S2-
Si2W: C, 65.33; H, 4.65; N, 2.31; S, 5.29. Found: C, 65.18; H, 4.58;
N, 2.24; S, 5.35.
Method B. A suspension of 0.064 g (0.203 mmol) of (NH4)2-
[WO2S2], 0.143 g (0.800 mmol) of diphenylacetylene, and 0.066 g
(0.279 mmol) of Me4phen in 10 mL of acetonitrile was stirred for 4 h.
To the reaction mixture was added 0.106 g (0.359 mmol) of Ph3SiCl,
resulting in a red-brown solution and a deep brown precipitate within
30 min. The mixture was stirred for 4 h, and the solid was collected.
This material was washed with acetonitrile and toluene (both 2 × 6
mL) and was dissolved in 30 mL of dichloromethane. The solution
was filtered, and the filtrate was reduced to dryness. The residue was
washed with acetonitrile and ether (both 2 × 6 mL) and dried to afford
the product as 0.167 g (68%) of a deep red-brown solid, whose
spectroscopic properties are identical with those of the product of
method A.
[Mo(OSiPh3)2(Me4phen)(S2C2Ph2)]. A suspension of 0.115 g (0.504
mmol) of (NH4)2[MoO2S2], 0.356 g (2.00 mmol) of diphenylacetylene,
and 0.165 g (0.698 mmol) of Me4phen in 10 mL of acetonitrile was
stirred for 4 h. Addition of 0.265 g (0.899 mmol) of Ph3SiCl caused
formation of a red-brown solution and a purple-brown precipitate within
30 min. The reaction mixture was stirred for 4 h, and the solid was
collected, washed with acetonitrile (2 × 8 mL), and dissolved in 40
mL of dichloromethane. The solution was filtered, and the filtrate was
reduced to dryness. The residue was washed with acetonitrile, toluene,
and ether (all 2 × 8 mL) and dried to yield the product as 0.346 g
(61%) of purple-brown solid. IR (KBr): νSiO 904 cm-1. Absorption
spectrum (CH2Cl2): λmax (ꢀM) 285 (39 200), 306 (sh, 21 100), 332 (sh,
9830), 360 (8670), 504 (2080) nm. 1H NMR (CDCl3): δ 8.76 (s, 2,9-
H, 1), 8.07 (s, 5,6-H, 1), 7.69-6.80 (m, Ph, 20), 2.67, 2.26 (2 s, Me,
3, 3). Anal. Calcd for C66H56MoN2O2S2Si2: C, 70.46; H, 4.98; N, 2.49;
S, 5.70. Found: C, 70.28; H, 5.10; N, 2.37; S, 5.56.
Crystals were coated in oil and mounted on a Bruker CCD area detector
instrument operated by the SMART software package. For each crystal,
a hemisphere of data was collected at 213 K in 30 s frames and with
ω scans of 0.3 deg/frame. The first 50 frames were recollected at the
end of the data collection to monitor for significant decay, which was
not detected for any compound. For all five structures, all data out to
2θ of 56° were used, allowing for a final resolution of 0.76 Å. Data
reduction was performed with SAINT, which corrects for Lorentz
polarization and decay. Absorption corrections were applied using
SABABS. For compounds 1, 2, 3, and 6‚C5H12, the space group was
identified as C2/c on the basis of systematic absence analysis by the
program XPREP and the successful structure solution and refinement.
The space group of 5‚MeCN was selected as P1h on the basis of
anomalous scattering effects, as determined by the program XPREP,
and by successful solution and refinement of the structure. Crystal
parameters are collected in Table 2.
All structures were solved by Patterson methods with SHELXTL
and subsequently refined against all data by full-matrix least-squares
on F2. In the structure of 2, the oxo and sulfido ligands as well as the
Me4phen ligand were disordered and refined with site occupancy factors
of 0.5 for all atoms. The solvate in 6 was modeled as a disordered
pentane molecule, and hydrogen atoms were not added. All non-
hydrogen atoms were refined anisotropically, with the exception of the
Me4phen ligand in 2 and the pentane solvate in 6. Hydrogen atoms
were attached at idealized positions on carbon atoms and were refined
as riding atoms with uniform isotropic thermal parameters. All structures
converged in the final stages of refinement, showing no movement in
atom positions. No residual electron density >1 e-/Å3 was observed
upon convergence, with the exception of two electron density peaks
of opposite sign symmetrically disposed around the tungsten atoms.
These peaks, which were located within 1 Å of the tungsten and did
not exceed 2e-/Å3, are due to the X-ray absorption properties of
tungsten and could not be adequately corrected using SADABS. Bond
distances and angles were not constrained in refinements. Use of the
checking program PLATON did not identify any missing or higher
In the sections which follow, complexes are designated as shown in
Chart 1.
X-ray Structure Determinations. Crystals of 1 (colorless blocks),
2 (yellow blocks), and 3 (red-orange blocks) were grown by slow
evaporation of dichloromethane solutions. Crystals of 5‚MeCN (red-
brown blocks) and 6‚C5H12 (deep red blocks) were produced by layering
concentrated dichloromethane solutions with acetonitrile or pentane.

2846 Inorganic Chemistry, Vol. 39, No. 13, 2000
Miao et al.
Figure 1. Scheme depicting the synthesis of oxo/sulfidotungstate(VI)
complexes 1-3.
symmetry. Final agreement factors are given in Table 2. (See the
Supporting Information.)
Other Physical Measurements. Absorption spectra were obtained
1
with a Varian Cary 50 Bio spectrophotometer. H NMR spectra were
obtained with Bruker AM 400N/500N spectrometers. Cyclic voltam-
mograms were recorded at 100 mV/s with a PAR model 263
potentiostat/galvanostat using a platinum disk working electrode and
0.1 M (Bu4N)(PF6) supporting electrolyte. Potentials are referenced to
the saturated calomel electrode (SCE).
Figure 2. 1H NMR spectra of the Me4phen ligand in [WO2-
(OSiPh3)2(Me4phen)] (top), [WOS(OSiPh3)2(Me4phen)] (middle), and
[WS2(OSiPh3)2(Me4phen)] (bottom) in CDCl3 solutions. Chemical shifts
are indicated.
Results and Discussion
Oxo/Sulfido Tungsten(VI) Complexes. (a) Synthesis and
Properties. We have sought the tungsten analogues of the MoVI
complexes [MoO2(OSiPh3)2(Me4phen)] and [MoOS(OSiPh3)2-
(Me4phen)] recently prepared in this laboratory.8 The preparation
of the dioxo compound was based on the observation that Ag2-
MoO4 could be silylated to form coordinatively unsaturated
[MoO2(OSiPh3)2].33 The compound K2[MoO3S] undergoes an
analogous reaction which in the presence of Me4phen affords a
product containing the cis-MoOS group. This group in unper-
turbed form has proven to be synthetically elusive in five- and
six-coordinate molecules, and is of significance because of its
presence in the xanthine oxidase family of enzymes where it is
obligatory to function.1,2 We have verified the unexpected lack
of reactivity of Ag2WO4 with Ph3SiCl under forcing condi-
tions.33 However, as indicated in Figure 1, tungstate itself and
oxosulfidotungstates can be silylated in reaction mixtures in
acetonitrile at room temperature in the presence of a ligand
which stabilizes a six-coordinate structure. The starting materials
are K2[WO4], K2[WO3S], and (NH4)2[WO2S2], all of which are
insoluble but reactive as acetonitrile suspensions to give products
1, 2, and 3, respectively, in overall reaction 1. The lower yield
Figure 3. Observed and calculated FAB+ mass spectra of [WOS-
(OSiPh3)2(Me4phen)] in the parent ion region.
with the separate loss of one oxygen atom and one sulfur atom.
Absorption spectra of the three complexes are shown in Figure
4. Complex 1 is a white solid with no visible absorption.
Complex 2 is yellow and absorbs at λmax (ꢀM) ) 367 (560) nm,
while 3 is orange with λmax (ꢀM) ) 451 (910) nm. The
corresponding feature for orange [MoOS(OSiPh3)2(Me4phen)]
is at 434 nm. This is the expected trend for LMCT bands, owing
to the higher optical electronegativity of MoVI vs WVI.34
[WO4-nSn]2- + 2Ph3SiCl + Me4phen f
[WO2-nSn(OSiPh3)2(Me4phen)] + 2Cl- (n ) 0-2) (1)
of 2 is associated with difficulty in obtaining highly pure K2-
[WO3S]. We are aware of only one prior example of silylation
of a WVIdO group.12 The compounds were identified by
analytical, spectroscopic, and X-ray structural results.
The 1H NMR spectra of the Me4phen portion of 1-3 in Figure
2 are characterized by downfield-shifted 2,9-H resonances owing
to the inductive effect of the metal. The spectra of 1 and 3 are
consistent with C2 symmetry whereas the spectrum of 2 clearly
reflects the absence of symmetry. This is particularly evident
in the splitting of the 2,9-H signals by 0.81 ppm, larger than
that observed in [MoOS(OSiPh3)2(Me4phen)] (0.66 ppm).8 The
mass spectrum of 2 in the parent ion region, shown in Figure
3, reveals a prominent parent ion peak and features consistent
(b) X-ray Structures. Complexes 1-3 crystallize in mono-
clinic space group C2/c (Table 2). Structures are set out in Figure
5, from which it is seen that all three have the same overall
stereochemistry and considerable similarity in metric details.
Oxo/sulfido ligands are mutually cis and cis to the silyloxide
ligands, which are mutually trans. Each molecule has imposed
C2 symmetry at the tungsten special position. Selected dimen-
sions of these molecules are collected in Table 3. Taking 3 as
(34) Lever, A. B. P. Electronic Absorption Spectroscopy; Elsevier: New
(33) Huang, M.; DeKock, C. W. Inorg. Chem. 1993, 32, 2287-2291.
York, 1986; Chapter 5.

Oxosulfidotungsten(VI) Groups and Dithiolene Rings
Inorganic Chemistry, Vol. 39, No. 13, 2000 2847
Figure 4. UV-vis spectra of [WO2(OSiPh3)2(Me4phen)], [WOS(OSiPh3)2(Me4phen)], and [WS2(OSiPh3)2(Me4phen)] in dichloromethane solutions.
Band maxima are indicated.
Figure 5. Structures of [WO2(OSiPh3)2(Me4phen)], [WOS(OSiPh3)2(Me4phen)], and [WS2(OSiPh3)2(Me4phen)], showing 50% probability ellipsoids
and atom-labeling schemes. Primed and unprimed atoms are related by a 2-fold axis.
Table 3. Selected Distances (Å) and Angles (deg) for Oxo/Sulfido
Complexes 1-3
Me4phen ligands. Comparable distortions from octahedral
coordination are observed in 1 and 2, in the corresponding
molybdenum complexes,8 and in numerous five- and six-
coordinate complexes containing the cis-MVIO2 group.
1
2a
3
WdO
WdS
WsOSi
WsNO
WsNS
SisO
1.733(2)
1.689(6)
2.222(2)
1.924(2)
2.37(3)
2.160(1)
1.923(3)
The imposed symmetry requires that a crystal of 2 contain a
1:1 mixture of identical molecules that differ only in the relative
disposition of the WVIOS group. The disorder problem is the
same as that described at length for [MoOS(OSiPh3)2(phen)]
and [MoOS(OSiPh3)2(Me4phen)]8 and was treated in the same
way. The two MoVIOS compounds are isomorphous, and the
latter is nearly isometric, with 2. To obtain accurate bond
distances, free of disorder, in the two molybdenum compounds,
Mo EXAFS analyses were carried out. The results were the same
for both compounds (ModO, 1.71-1.72 Å; ModS, 2.19 Å).8
We have not carried out a similar analysis for 2. Here our
primary aim was the preparation of a WVIOS complex by the
silylation method.
1.926(2)
2.322(3)
2.32(4)
2.345(4)
1.625(4)
106.16(9)
1.609(2)
106.3(2)
98.1(1)
1.625(4)
103.7(3)
97.0(2)
QsWsQ′
OoxosWsOSi
SsWsOSi
OSisWsOSi
NsWsN′
WsOsSi
94.99(9)
153.0(1)
68.6(2)
99.1(1)
152.7(2)
69.4(2)
153.3(2)
152.9(1)
70.0(1)
158.7(2)
153.6(1)
a Disordered structure; see the text.
an example, sulfido ligands form a S-W-S angle of 106.2°
owing to charge repulsion. For the same reason, the silyloxide
groups are bent back from the sulfido ligands such that the
O-W-S angle is 99.1°; the W-O-Si angle is 153.3(2)°. The
displacement of the silyloxide groups is in the direction of the
Whereas five- and six-coordinate complexes containing the
WVIO2 group are unexceptional, those containing the WVIOS
and WVIS2 groups are less common. Complexes with the WVI-

2848 Inorganic Chemistry, Vol. 39, No. 13, 2000
OS group include [WOS(NCS)4]2- 35
[(C5Me5)WOS(R)]
Miao et al.
,
(R ) Me, CH2SiMe3),36 [(HB(Me2pz)3)WOS(L)] (L ) Cl,37
(-)mentholate28), and [WOS(L-N2S2)].38 Of these, [WOS(L-
N2S2)] is described as disordered; accurate structures are
available for [WOS(NCS)4]2- and [(HB(Me2pz)3)WOS((-)-
mentholate)]. Those with the WVIS2 group include three Schiff
base complexes,39 [(HB(Me2pz)3WS2(L)] (L ) Cl,37 OPh28),
[WS2(PMe3)2(η2-OCHPh)],40 [(C5Me5)WS2(SR)],26,27 and [WS2-
(L-N2S2)].38 Given that the WdS bond distance range defined
by these complexes and [WVIS(OSiButPh2)(bdt)2]12 is 2.11-
2.19 Å, it is probable that the value from the refinement of
disordered 2 (Table 3) is artifactually long.
Dithiolene Ring Closure. While a number of dithiolene
ligands are available in uncomplexed form as ene-1,2-dithiolate
salts, such as Na2(S2C2(CN)2), Na2(S2C2H2), and Li2(bdt), and
can be used as such in synthesis, others are not available in
this condition. Dithiolenes protected as, e.g., thiophosphate41
and 1,3-dithiolium or 1,3-dithiol-2-one derivatives,42 can be
deprotected under reaction conditions leading to complex
formation. Summarized in Table 1 is a different general method
with eight reaction types for chelate ring formation in molyb-
denum and tungsten dithiolenes. Here one or more ene-1,2-
dithiolate rings are closed in reactions of sulfide-bound precur-
sors with suitably activated alkynes RCtCR, usually with R
) aryl, COAr, CONH2, or CO2R′. Reaction type 5 employs a
different closure reagent. Although the matter has not been
proven by isotope labeling, it is entirely probable that the sulfur
atoms in the product chelate ring are those present in the
reactant. Two other procedures, involving the reactions of
[MS4]2- with the thiocarbonates C2S4(CO)(CQ) (Q ) O, S),43
and [MS4-nOn]2- (n ) 0-2) with the dithiete (CF3)2C2S2,44 are
not included in Table 1 because the origin of all chelate ring
sulfur atoms is less certain.
The eight reaction types are represented generally, ancillary
ligands usually being omitted, to emphasize chelate ring
formation. The first demonstration that a dithiolene ring could
be closed in this manner was the reaction of (RC5H4)2TiS5 with
dicarbomethoxyacetylene.45 This was followed by formation of
bis- and tris(dithiolene)molybdenum complexes by reaction
types 1-3. Five procedures start with readily accessible
tetrasulfido- or oxosulfidometalates(VI). In reaction type 1, for
example, [MoOS3]2- is converted to [MoO(S4)2]2-, which reacts
with bis(phenacyl)acetylene to afford [MoO(S2C2(COPh)2)2]2-
(39%).20 The general method has been applied much less
frequently to the synthesis of tungsten complexes. Reaction type
6 with dicarbomethoxyacetylene gives [W(S2C2(CO2Me)2)3]2-
(43%).20 In procedure 7, the WVIS2 group reacts with alkynes
to afford products in yields as high as 86%.30 In these cases,
Figure 6. Scheme depicting the formation of dithiolene chelate rings
in WIV and MoIV complexes 4-6 using precursors with coordinated
sulfide.
Figure 7. Structure of [WIV(OSiPh3)2(Me4phen)(S2C2Ph2)] showing
50% probability ellipsoids and the atom-labeling scheme. The structure
of the corresponding molybdenum complex is essentially identical.
the group was not derived from an oxosulfidotungstate(VI)
starting material. Evidently, MoIV(S4) and WVIS2 are functionally
equivalent groups in reactions with activated alkynes. Reactions
involving the former group do not change the oxidation state,
whereas those of the latter result in reduction to WIV.
We provide here several examples of the formation of
dithiolene rings using [MO2S2]2- starting materials and the
reactions in Figure 6. Complex 3, derived from [WO2S2]2-
(Figure 1), reacts instantly with dicarbomethoxyacetylene or
diphenylacetylene in reactions 2 and 3 to afford monodithiolene
complexes 4 and 5, respectively, in high yield. These reactions
are new examples of type 7, first demonstrated by Young and
co-workers.28,30 Even more convenient are reactions 4 and 5,
in which intermediate species need not be isolated. These
reactions lead to complexes 5 and 6 in good yield; they
constitute the current examples of reaction type 8.
The structures of both 5 and 6 have been determined. Because
the complexes are isostructural and virtually isometric, only the
structure of 5, presented in Figure 7, is reported. Selected bond
angles and distances are given in Table 4. Comparison with
precursor 3 (Figure 2) reveals a closely related stereochemistry,
which includes the direction of bending of the trans-silyloxide
groups toward the Me4phen ligand. Using average values where
appropriate, the largest dimensional changes upon formation of
5 are a 0.15 Å increase in the W-S distance and a 22.2°
decrease in the S-W-S angle as a consequence of chelate ring
formation. Removal of the trans influence of the sulfido ligand
results in a 0.09 Å decrease in the W-N distance. Other changes
(35) Potvin, C.; Manoli, J. M.; Marzak, S.; Secheresse, F. Acta Crystallogr.
1988, C44, 369-370.
(36) Faller, J. W.; Ma, Y. Organometallics 1989, 8, 609-612.
(37) Eagle, A. A.; Tiekink, E. R. T.; Young, C. G. J. Chem. Soc., Chem.
Commun. 1991, 1746-1748.
(38) Barnard, K. R.; Gable, R. W.; Wedd, A. G. J. Biol. Inorg. Chem.
1997, 2, 623-633.
(39) Yu, S.-B.; Holm, R. H. Inorg. Chem. 1989, 28, 4385-4391.
(40) Rabinovich, D.; Parkin, G. Inorg. Chem. 1995, 34, 6341-6361.
(41) Schrauzer, G. N.; Mayweg, V. P. J. Am. Chem. Soc. 1965, 87, 1483-
1489.
(42) Davies, E. S.; Beddoes, R. L.; Collison, D.; Dinsmore, A.; Docrat,
A.; Joule, J. A.; Wilson, C. R.; Garner, C. D. J. Chem. Soc., Dalton
Trans. 1997, 3985-3995.
(43) Yang, X.; Freeman, G. K. W.; Rauchfuss, T. B.; Wilson, S. R. Inorg.
Chem. 1991, 30, 3034-3038.
(44) Wang, K.; McConnachie, J. M.; Stiefel, E. I. Inorg. Chem. 1999, 38,
4334-4341.
(45) Bolinger, C. M.; Rauchfuss, T. B. Inorg. Chem. 1982, 21, 3947-
3954.

Oxosulfidotungsten(VI) Groups and Dithiolene Rings
Inorganic Chemistry, Vol. 39, No. 13, 2000 2849
Table 4. Selected Bond Distances (Å) and Angles (deg) for
[W(OSiPh3)2(Me4Phen)(S2C2Ph2)
(3) The complex [WS2(OSiPh)2(Me4phen)] reacts immedi-
ately with two activated alkynes, resulting in dithiolene ring
closure and formation of [WIV(OSiPh)2(Me4phen)(S2C2R2)] (R
) CO2Me, Ph; reaction type 7). The product retains the trans-
silyloxide stereochemistry. Localization of significant structural
changes to the WS2 fragment presumably contributes to the
facility of these reactions.
(4) Dithiolene ring closure occurs in the reaction systems
[MO2S2]2-/2Ph3SiCl/Me4phen/PhCtCPh to afford the products
[MIV(OSiPh)2(Me4phen)(S2C2Ph2)] (M ) Mo, W; reaction type
8). These are the same as or analogous to those in (3), and are
obtained in high yield without requiring the isolation of an
intermediate.
W-S1
2.306(1)
2.253(2)
1.905(2)
1.627(2)
1.341(4)
1.807(3)
83.99(3)
100.05(6)
97.35(6)
80.99(8)
82.19(8)
163.4(1)
157.63(8)
W-S2
2.308(1)
2.257(2)
1.893(2)
1.630(2)
1.804(3)
73.73(8)
97.92(6)
97.79(6)
80.99(8)
80.20(8)
161.7(1)
W-N1
W-N2
W-O1
W-O2
Si1-O1
Si2-O2
C1-C2
C2-S2
C1-S1
N1-W-N2
O1-W-S2
O2-W-S2
N2-W-O1
N2-W-O2
W-O2-Si2
S1-W-S2
O1-W-S1
O2-W-S1
N1-W-O1
N1-W-O2
W-O1-Si1
O1-W-O2
These results are part of an ongoing investigation of the
synthesis of new types of mono- and bis(dithiolene) complexes
of molybdenum6-8 and tungsten12,13 with functional units the
same as, or analogous to, those present in enzymes.1-4 They
demonstrate the viability of the silylation method, introduced
earlier for molybdenum complexes,8 in the formation of oxo/
sulfidotungsten(VI) groups. The procedures in (1) and (3)/(4)
are potentially extendable to the formation of complexes with
different ancillary ligands and variously substituted dithiolene
rings, respectively. Owing to the absence of five- or six-
coordinate complexes containing the MoVIS2 group, reaction
type 7 is currently restricted to the formation of monodithi-
olene-W(IV) complexes. It remains to be seen whether the
active sites of tungstoenzymes contain the oxo/sulfido groups
in Figure 1 and other ligation modes recently achieved in this
laboratory,12-14 including WIVOR and WVIO(OR).
of bond angles at tungsten are <5°. The localization of
significant structural changes to the WS2 fragment presumably
contributes to the rapidity of reactions 2 and 3. The chelate ring
C-C and C-S distances are very close to the expected values
for double (1.33 Å) and single (1.82 Å) bonds, respectively,
indicating that the ligand is best formulated as an enedithiolate.
The corresponding distances in 6 are 1.344(5) and 1.784(3) Å.
Therefore, the chemically reversible reductions (ipc/ipa ≈ 1) at
-1.45 V (6) and -1.62 V (5) in dichloromethane are interpreted
as metal-centered MIV/III processes. The order E(W) < E(Mo)
is consistent with this assignment.
Summary
The following are the principal results and conclusions of
this investigation.
(1) The readily available oxo/sulfidotungstates [WVIO4-nSn]2-
(n ) 0-2) in the presence of a chelating ligand are effective
precursors in a silylation method for the formation of the six-
coordinate complexes [WQ2(OSiPh3)2(Me4phen)], containing the
WVIO2, WVIOS, and WVIS2 groups.
(2) The complexes in (1) have crystallographically imposed
C2 symmetry, with cis-oxo/sulfido and trans-silyloxide ligands,
and are isostructural with their molybdenum analogues, includ-
ing the S/O and Me4phen positional disorder encountered in
the structure of [WOS(OSiPh3)2(Me4phen)].
Acknowledgment. This research was supported by NIH
Grant CHE-9876457. M.M. is the recipient of grants from the
China Scholarship Council and the Yunnan Committee of
Science and Technology.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of the five compounds
in Table 2. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC000047L