Synthesis, structures, and oxo transfer reactivity of bis(dithiolene)tungsten(IV,VI) complexes related to the active sites of tungstoenzymes

Article abstract of DOI:10.1021/ja981015o

A series of bis(dithiolene)tungsten(IV,VI) complexes derived from benzene-1,2-dithiolate (bdt) has been prepared as an synthetic approach to pterin dithiolene-bound active sites of tungstoenzymes, one example of which, a archaeal oxidoreductase, has been established crystallographically (Chan et al. Science 1995, 267, 1463). With [W(IV)O(bdt)₂]^2- (2) as the starting compound, silylation with RR'₂SiCl afforded [W(IV)(bdt)₂(OSiRR'₂)]^1- (4). Oxidation of 4 with Me₃NO gave [W(VI)O(bdt)₂(OSiRR'₂)]^1- (5), also accessible by silylation of [W(VI)O₂(bdt)₂]^2- (3). Reaction of 3 or 5 with Me₃SiCl resulted in [W(VI)O(bdt)₂Cl]^1- (6), from which the unstable species [W(VI)O(bdt)₂L]^1- (L = Bu(t)O^-, PhS^-) were generated in solution. Reductive oxo transfer of 6 with L' = P(OEt)₃ or Bu(t)NC/P(OEt)₃ gave [W(IV)(bdt)₂L'₂] (8 and 9). Sulfido complex [W(VI)S(bdt)₂(OSiRR'₂)]^1- (12) was obtained in the reaction systems 4/(PhCH₂S)₂S and 5/(Me₃Si)₂S. Structures of [WO(SPh)₄]^1- and [W(bdt)₃]^2- and eight complexes of types 4-6, 8, 9, and 12 were determined by X-ray crystallography. Complexes 4 and 5 are tungsten analogues of the desoxo Mo(IV) and monooxo Mo(VI) states of Rhodobacter sphaeroides DMSO reductase. Six types of reactivity, including oxygen atom transfer, are recognized by the synthesis and interconversion of the set of complexes. The potential biological relevance of these complexes to the structure and function of active sites in two families of tungstoenzymes is considered (RR'₂ = Me₃ (4); Bu(t)Me₂ (4 and 5), Bu(t)Ph₂ (4, 5, and 12)).

Full text of DOI:10.1021/ja981015o

8102
J. Am. Chem. Soc. 1998, 120, 8102-8112
Synthesis, Structures, and Oxo Transfer Reactivity of
Bis(dithiolene)tungsten(IV,VI) Complexes Related to the Active Sites
of Tungstoenzymes
Christian Lorber,† James P. Donahue,† Christine A. Goddard,† Ebbe Nordlander,‡ and
R. H. Holm*,†
Contribution from the Department of Chemistry and Chemical Biology, HarVard UniVersity,
Cambridge, Massachusetts 02138, and Inorganic Chemistry I, Chemical Center, Lund UniVersity,
S-2210 Lund, Sweden
ReceiVed March 25, 1998
Abstract: A series of bis(dithiolene)tungsten(IV,VI) complexes derived from benzene-1,2-dithiolate (bdt) has
been prepared as an synthetic approach to pterin dithiolene-bound active sites of tungstoenzymes, one example
of which, a archaeal oxidoreductase, has been established crystallographically (Chan et al. Science 1995, 267,
1463). With [WIVO(bdt)2]2- (2) as the starting compound, silylation with RR′2SiCl afforded [WIV(bdt)2(OSiRR′2)]1-
(4). Oxidation of 4 with Me3NO gave [WVIO(bdt)2(OSiRR′2)]1- (5), also accessible by silylation of
[WVIO2(bdt)2]2- (3). Reaction of 3 or 5 with Me3SiCl resulted in [WVIO(bdt)2Cl]1- (6), from which the unstable
species [WVIO(bdt)2L]1- (L ) ButO-, PhS-) were generated in solution. Reductive oxo transfer of 6 with L′
) P(OEt)3 or ButNC/P(OEt)3 gave [WIV(bdt)2L′2] (8 and 9). Sulfido complex [WVIS(bdt)2(OSiRR′2)]1- (12)
was obtained in the reaction systems 4/(PhCH2S)2S and 5/(Me3Si)2S. Structures of [WO(SPh)4]1- and
[W(bdt)3]2- and eight complexes of types 4-6, 8, 9, and 12 were determined by X-ray crystallography.
Complexes 4 and 5 are tungsten analogues of the desoxo Mo(IV) and monooxo Mo(VI) states of Rhodobacter
sphaeroides DMSO reductase. Six types of reactivity, including oxygen atom transfer, are recognized by the
synthesis and interconversion of the set of complexes. The potential biological relevance of these complexes
to the structure and function of active sites in two families of tungstoenzymes is considered (RR′2 ) Me3 (4);
ButMe2 (4 and 5), ButPh2 (4, 5, and 12)).
Introduction
at 1.74 Å, about three W-S bonds at 2.41 Å, and a possible
W-O/N bond at 1.97 Å.6 A second EXAFS study revealed
one WdO (1.74 Å), four to five W-S (2.40 Å), and perhaps
one W-O/N (1.97 Å) bond,2 in improved agreement with the
X-ray results. It is probable that the WO2 form of the enzyme
is inactive. The active enzyme has been examined in detail by
MCD and EPR spectroscopies.5
Recently, more than a dozen tungsten-containing enzymes
have been isolated from hyperthermophilic archaea and bacte-
ria1,2 and have been classified into two major families.2
Members of the aldehyde oxidoreductase (AOR) family catalyze
-
the reaction RCHO + H2O h RCO2 + 3H+ + 2e-. The
enzyme from Pyrococcus furiosus (Pf, Mr 136 kDa, R2) is the
most thoroughly studied. It contains one tungsten atom and
one [Fe4S4]2+/1+ redox center per cluster and is the only tungsten
enzyme for which an X-ray structure is currently available.3,4
The tungsten atom is coordinated by two pterin dithiolene
cofactor ligands in a distorted square pyramidal arrangement,
and perhaps also by two oxygen ligands. However, oxygen
ligation is not definitely established, owing to the heterogeneous
nature of the tungsten center5 and crystallographic difficulties
in locating light atoms in the presence of a heavy scatterer.4
The initial EXAFS analysis of dithionite-reduced Pf AOR,
preceding the crystallographic results, revealed two WdO units
The second family of tungstoenzymes consists of formate
dehydrogenase (FDH) and N-formylmethanofuran dehydroge-
nase (FMDH). These enzymes catalyze the first step in the
conversion of CO2 to acetate and to methane in acetogens and
methanogens, respectively.2 On the basis of sequence data,
F(M)DH enzymes have similarities to molybdoenzymes, includ-
ing Mo-FDH, biotin S-oxide reductase, and DMSO reductase.2
It has been suggested that their tungsten coordination units may
be structurally similar to those found for DMSO reductase but
with cysteinate or selenocysteinate in place of serinate.2 X-ray
crystallography of the Rhodobacter sphaeroides enzyme has
established monooxo MoVIO and desoxo MoIV site structures
with one dithiolene ligand tightly bound, another asymmetrically
coordinated (MoVIO) or virtually unbound (MoIV), and Mo-
O‚Ser ligation in both states.7 EXAFS8 and resonance Raman
† Harvard University.
‡ Lund University.
(1) Kletzin, A.; Adams, M. W. W. FEMS Microbiol. ReV. 1996, 18, 5.
(2) Johnson, M. K.; Rees, D. C.; Adams, M. W. W. Chem. ReV. 1996,
96, 2817.
(3) Chan, M. K.; Mukund, S.; Kletzin, A.; Adams, M. W. W.; Rees, D.
C. Science 1995, 267, 1463.
(4) (a) Schindelin, H.; Kisker, C.; Rees, D. C. JBIC 1997, 2, 773. (b)
Rees, D. C.; Hu, Y.; Kisker, C.; Schindelin, H. J. Chem. Soc., Dalton Trans.
1997, 3909.
(6) George, G. N.; Prince, R. C.; Mukund, S.; Adams, M. W. W. J. Am.
Chem. Soc. 1992, 114, 3521.
(7) Schindelin, H.; Kisker, C.; Hilton, J.; Rajagopalan, K. V.; Rees, D.
C. Science 1996, 272, 1615.
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R.; Adams, M. W. W.; Johnson, M. K. J. Am. Chem. Soc. 1996, 118, 12391.
(8) George, G. N.; Hilton, J.; Rajagopalan, K. V. J. Am. Chem. Soc.
1996, 118, 1113.
S0002-7863(98)01015-4 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/30/1998

Bis(dithiolene)tungsten(IV,VI) Complexes
J. Am. Chem. Soc., Vol. 120, No. 32, 1998 8103
ally, we are addressing on a broader basis the synthesis of bis-
(dithiolene)molybdenum and -tungsten systems with the intent
of approaching or attaining biological coordination units and
accurate structural definition thereof, providing structural and
spectroscopic calibrant molecules for native sites, and probing
reactivity. Certain results have been briefly described.15
Excluding organometallic compounds, about 20 tungsten dithi-
olenes have been previously prepared, the large majority being
tris-complexes.16 Some of these date from the discovery of
dithiolene complexes and accompanying recognition of their
noninnocent behavior in certain molecular oxidation states.16a-d,17
Three monodithiolene species have been prepared.18,19 Several
sets of bis(dithiolene) complexes have been synthesized.18,20,21
Indeed, preparation of [WO(bdt)2]2-,1- and [WO2(bdt)2]2- (bdt
) benzene-1,2-dithiolate(2-)) by Nakamura and co-workers,20
and [WO(mnt)2]2- and [WO2(mnt)2]2- by Sarkar and co-
workers,21 was stimulated by the discovery of tungstoenzymes.
We have found the bdt complexes to be tractable precursors
for further development of bis(dithiolene)tungsten chemistry
relevant to the enzyme active site problem. The results of our
investigation in this area are presented here.
Figure 1. Schematic structures of the MoIV and MoVIO sites of R.
sphaeroides DMSO reductase depicted with tightly bound dithiolene
chelate rings, possible structures of W-FM(D)H enzymes in two
oxidation states, and the structure of the pterin dithiolene cofactor
(nucleotide omitted).
spectroscopy9 of this enzyme support the structures shown in
Figure 1, in which two dithiolenes form tight chelate rings.10 It
might be conjectured that the tungsten coordination sites in
F(M)DH resemble those depicted (Figure 1) in which cysteinate
or selenocysteinate replaces serinate binding. Recently, bis-
(dithiolene) selenocysteinate coordination has been established
for Escherichia coli Mo-FDH by crystallography11a and EX-
AFS analysis.11b
Experimental Section
Preparation of Compounds. All reactions and manipulations were
performed under a pure dinitrogen atmosphere using either modified
Schlenk techniques or an inert atmosphere box. The compounds
PhIO,22 PhI18O,23 and Ph2SeO24 were prepared by literature methods.
Other reagents were of commercial origin and were used as received.
Acetonitrile was freshly distilled from CaH2 and methanol from
magnesium. Diethyl ether and THF were distilled from sodium and
stored over 4 Å molecular sieves.
(Et4N)[WO(SPh)4]. A solution of 2.84 mL (27.7 mmol) of
benzenethiol and 2.80 g (27.7 mmol) of Et3N in 20 mL of acetonitrile
was slowly added to a stirred solution of 2.49 g (5.53 mmol) of
WOCl3(THF)225 in 20 mL of THF at -40 °C. The reaction was allowed
to warm to room temperature and stirring was continued for 20 min.
The violet solution was filtered and reduced in vacuo to a volume of
15 mL. To this solution was added a solution of 1.78 g (6.92 mmol)
of Et4NI in 80 mL of methanol, resulting in the precipitation of a dark
solid. This material was collected by filtration, washed with methanol
(3 × 10 mL), and dried in vacuo. The product was obtained as 3.70
g (87%) of a dark violet solid. Absorption spectrum (acetonitrile): λmax
All molybdenum12 and tungsten2 enzymes of the hydroxylase
or oxotransferase type contain at least one pterin dithiolene
cofactor, sometimes with a nucleotide appended to the phosphate
group. The cofactor structure is set out in Figure 1. The
indicated dithiolene chelation mode has been established crys-
tallographically for Pf AOR.3,4 Although no bond distances
were quoted, the depictions of the cofactor imply tight binding
of the metal. In other tungstoenzymes, the number of cofactors
bound to the metal has not been determined.
The existence of native metal-dithiolene coordination raises
a new imperative for the examination of molybdenum and
tungsten dithiolene complexes, particularly those with physi-
ologically relevant coordination units. In this context, we have
undertaken several investigations. In one study, the kinetics
of oxygen atom transfer from [MoO2(mnt)2]2- (mnt ) male-
onitriledithiolate(2-)) to tertiary phosphine substrates as de-
pendent on the stereoelectronic properties of the phosphines have
been determined.13 In another, the relative kinetics of oxo
transfer from [MO2(mnt)2]2- (M ) Mo, W) to tertiary phosphine
and phosphite acceptors have been established, showing that
transfer from the MoVIO2 complex is more facile.14 Addition-
(14) Tucci, G. C.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 1998, 37,
1602.
(15) Donahue, J. P.; Lorber, C.; Nordlander, E.; Holm, R. H. J. Am.
Chem. Soc. 1998, 120, 3259.
(16) (a) Davison, A.; Edelstein, N.; Holm, R. H.; Maki, A. H. J. Am.
Chem. Soc. 1964, 86, 2799. (b) Stiefel, E. I.; Eisenberg, R.; Rosenberg, R.
C.; Gray, H. B. J. Am. Chem. Soc. 1966, 88, 2956. (c) McCleverty, J. A.;
Locke, J.; Wharton, E. J.; Gerloch, M. J. Chem. Soc. (A) 1968, 816. (d)
Wharton, E. J.; McCleverty, J. A. J. Chem. Soc. (A) 1969, 2258. (e) Stiefel,
E. I.; Bennett, L. E.; Dori, Z.; Crawford, T. H.; Simo, C.; Gray, H. B.
Inorg. Chem. 1970, 9, 281. (f) Brown, G. F.; Stiefel, E. I. Inorg. Chem.
1973, 12, 2140. (g) Yang, X.; Freeman, G. K. W.; Rauchfuss, T. B.; Wilson,
S. R. Inorg. Chem. 1991, 30, 3034. (h) Sellmann, D.; Kern, W.; Moll, M.
J. Chem. Soc., Dalton Trans. 1991, 1733. (i) Knoch, F.; Sellmann, D.; Kern,
W. Z. Kristallogr. 1993, 205, 300. (j) Burrow, T. E.; Morris, R. H.; Hills,
A.; Hughes, D. L.; Richards, R. L. Acta Crystallogr. 1993, C49, 1591. (k)
Matsubayashi, G.; Douki, K.; Tamura, H.; Nakano, M.; Mori, W. Inorg.
Chem. 1993, 32, 5990.
(17) McCleverty, J. A. Prog. Inorg. Chem. 1968, 10, 49.
(18) Schrauzer, G. N.; Mayweg, V. P.; Heinrich, W. J. Am. Chem. Soc.
1966, 88, 5174.
(19) Eagle, A. A.; Harben, S. M.; Tiekink, E. R. T.; Young, C. G. J.
Am. Chem. Soc. 1994, 116, 9749.
(20) Ueyama, N.; Oku, H.; Nakamura, A. J. Am. Chem. Soc. 1992, 114,
7310.
(21) Das, S. K.; Biswas, D.; Maiti, R.; Sarkar, S. J. Am. Chem. Soc.
1996, 118, 1387.
(9) Garton, S. D.; Hilton, J.; Oku, H.; Crouse, B. R.; Rajagopalan, K.
V.; Johnson, M. K. J. Am. Chem. Soc. 1997, 119, 12906.
(10) Independent crystal structures of Rhodobacter capsulatus DMSO
reductase do not give the same Mo site structures nor do they agree with
that found in the R. sphaeroides enzyme: (a) Schneider, F.; Lo¨we, J.; Huber,
R.; Schindelin, H.; Kisker, C.; Kna¨blein, J. J. Mol. Biol. 1996, 263, 53. (b)
McAlpine, A. S.; McEwan, A. G.; Shaw, A. L.; Bailey, S. JBIC 1997, 2,
690. See also: (c) McAlpine, A. S.; McEwan, A. G.; Bailey, S. J. Mol.
Biol. 1998, 275, 613. Because the origin of these discrepancies is not clear,
we display the sites of the R. sphaeroides enzyme in Figure 1; these bear
a closer relationship to the tungsten coordination units prepared in this
investigation.
(11) (a) Boyington, J. C.; Gladyshev, V. N.; Khangulov, S. V.; Stadtman,
T. C.; Sun, P. D. Science 1997, 275, 1305. (b) George, G. N.; Colangelo,
C. M.; Dong, J.; Scott, R. A.; Khangulov, S. V.; Gladyshev, V. N.; Stadtman,
T. C. J. Am. Chem. Soc. 1998, 120, 0, 1267.
(22) Saltzman, H.; Sharefkin, J. G. Organic Syntheses; Wiley: New York,
1973; Collect. Vol. V, p 658.
(23) Schardt, B. C.; Hill, C. L. Inorg. Chem. 1983, 22, 1563.
(24) Krafft, F.; Vorster, W. Chem. Ber. 1893, 26, 2813.
(12) Hille, R. Chem. ReV. 1996, 96, 2757.
(13) Lorber, C.; Plutino, M. R.; Elding, L. I.; Nordlander, E. J. Chem.
Soc., Dalton Trans. 1997, 3997.

8104 J. Am. Chem. Soc., Vol. 120, No. 32, 1998
Lorber et al.
(ꢀM) 520 (3300) nm. IR (KBr): 948 cm-1 (νWO). FAB-MS-: m/z
636 (M-). Anal. Calcd for C32H40NOS4W: C, 50.13; H, 5.26; N, 1.83;
S, 16.72. Found: C, 50.21; H, 5.22; N, 1.86; S, 16.79. This compound
has been previously reported,26 but no explicit preparation was given.
The Ph4P+ salt was prepared in 73% yield by the same procedure as
for the Et4N+ salt.
Celite, and ether was introduced into the filtrate by vapor diffusion.
The solid was separated and was collected by filtration, washed with
ether (3 × 3 mL), and dried in vacuo to afford the product as 99 mg
(90%) of red crystals. IR (KBr): 1250 (m), 1171 (m), 909 (vs, νSiO),
844 (s), 750 (s). MS-ES: m/z 553 (M-). 1H NMR (anion, CD3CN):
δ 7.96 (dd, 4), 6.98 (dd, 4), -0.21 (s, 9). Anal. Calcd for C23H37-
NOS4SiW: C, 40.40; H, 5.45; N, 2.05; S. 18.76. Found: C, 40.26;
H, 5.48; N, 2.01; S, 18.89.
(Et4N)[W(bdt)2(OSiButMe2)]. A solution of 50 mg (0.067 mmol)
of (Et4N)2[WO(bdt)2] in 10 mL of acetonitrile was treated with 10 mg
(0.066 mmol) of ButMe2SiCl, producing a red color. The reaction
mixture was stirred for 1 h, and solvent was removed in vacuo. The
residue was dissolved in 2 mL of THF, the solution was filtered through
Celite, and the volume of the filtrate reduced to 1 mL. Ether (18 mL)
was added very slowly to the filtrate, and the solution was allowed to
stand overnight. Red crystals were collected by filtration, washed with
ether (2 × 5 mL), and dried in vacuo to afford 35 mg (71%) of product.
IR (KBr): 1250 (s), 1170 (m), 923 (vs, νSiO), 833 (m), 819 (m), 782
(s), 745 (s) cm-1. FAB-MS-: m/z 595 (M-). 1H NMR (anion, CD3-
CN): δ 7.95 (dd, 4), 6.98 (dd, 4). 0.61 (s, 9), -0.26 (s, 6). Anal.
Calcd for C26H43NOS4SiW: C, 43.03; H, 5.97; N, 1.93; S. 17.67.
Found: C, 43.19; H, 6.07; N, 1.87; S, 17.50.
(Et4N)[WO(bdt)2]. A solution of 0.500 g (3.52 mmol) of benzene-
1,2-dithiol27 and 0.712 g (7.04 mmol) of Et3N in 10 mL of acetonitrile
was added slowly to a stirred solution of 0.792 g (1.76 mmol) of WOCl3-
(THF)2 in 10 mL of acetonitrile at -40 °C. The reaction mixture was
allowed to warm to room temperature and was stirred for 30 min. The
solution was filtered and reduced in vacuo to a volume of 6 mL. The
deep blue-green solution was treated dropwise with a solution of 0.565
g (2.20 mmol) of Et4NI in 20 mL of methanol. The mixture was stirred
for 30 min, and the black solid was collected by filtration. This material
was washed with methanol (3 × 4 mL), and dried in vacuo to give
0.850 g (79%) of product as a black solid. Absorption spectrum
(acetonitrile): λmax (ꢀM) 354 (sh), 455 (1000), 613 (3000) nm. IR
(KBr): 949 cm-1 (νWO). FAB-MS-: m/z 480 (M-). Anal. Calcd for
C20H28NOS4W: C, 39.35; H, 4.62; N, 2.29; S, 21.00. Found: C, 39.22;
H, 4.62; N, 2.36; S, 20.83. This compound has been prepared
previously by a different method.20
(Et4N)[W(bdt)2(OSiButPh2)]. A suspension of 0.400 g (0.540
mmol) of (Et4N)2[WO(bdt)2] in 5 mL of acetonitrile was treated
dropwise with 0.153 g (0.557 mmol) of ButPh2SiCl. The reaction
mixture was stirred for 1 h, at which point it consisted of a red solution
and a red-purple solid. The solid was separated by filtration, washed
with acetonitrile (2 × 2 mL) and ether (2 × 5 mL), and dried in vacuo
to give the product as 0.380 g (83%) of a red-purple solid. An analytical
sample was recrystallized from acetonitrile/ether. Absorption spectrum
(acetonitrile): λmax (ꢀM) 307 (21 100), 345 (6740), 420 (420), 553 (85)
nm. IR (KBr): 1587 (m), 1554 (m), 1112 (s), 963 (vs, νSiO), 751 (s),
707 (s), 506 (s) cm-1. ES-MS-: m/z 595 (M-). 1H NMR (anion, CD3-
CN): δ 8.00 (dd, 4), 7.36 (d, 4), 7.25 (t, 2), 7.08 (t, 4), 7.02 (dd, 4),
0.73 (s, 9). Anal. Calcd for C36H47NOSiS4W: C, 50.87; H, 5.57; N,
1.65; S, 15.09. Found: C, 50.72; H, 5.61; N, 1.69; S, 15.18.
(Et4N)[WO(bdt)2(OSiButPh2)]. (a) Method 1. A stirred solution
of 0.200 g (0.235 mmol) of (Et4N)[W(bdt)2(OSiButPh2)] in 5 mL of
acetonitrile was treated with 36 mg (0.48 mmol) of Me3NO, resulting
in an instantaneous color change from red to brown-green. The mixture
was stirred for 1 h, the solvent was removed in vacuo, and the solid
residue was extracted with 40 mL of THF. The green extract was
filtered through Celite, evaporated to dryness, washed with ether (3 ×
10 mL), and dried in vacuo to yield the product as 0.155 g (76%) of
brown powder. An analytical sample as red crystals was obtained by
vapor diffusion of ether into an acetonitrile/THF solution (1:5 v/v).
Absorption spectrum (acetonitrile): λmax (ꢀM) 294 (14 300), 339 (sh,
7620), 375 (sh, 5250), 455 (3720), 600 (1610) nm. IR (KBr): 1109
(s), 933 (vs, νSiO), 888 (vs, νWO), 748 (s), 704 (s), 611 (s), 505 (s)
cm-1. FAB-MS-: m/z 735 (M-). 1H NMR (anion, CD3CN): δ 7.91
(dd, 4), 7.36 (m, 6), 7.23 (dd, 4), 6.87 (dd, 4), 1.06 (s, 9). Anal. Calcd
for C36H47NO2SiS4W: C, 49.93; H, 5.47; N, 1.62; S, 14.81. Found:
C, 50.11; H, 5.59; N, 1.73; S, 14.66.
(b) Method 2. A stirred solution of 0.200 g (0.264 mmol) of (Et4N)2-
[WO2(bdt)2] in 2 mL of acetonitrile was treated with 80 mg (0.29 mmol)
of ButPh2SiCl. The orange solution turned brown-green within a few
seconds; stirring was continued for 1 h. The reaction mixture was
worked up as in method 1 to afford 0.195 g (85%) of product. The
spectroscopic properties were identical to those of the product of method
1. Anal. Found: C, 50.06; H, 5.55; N, 1.63; S, 14.69.
(Et4N)[WO(bdt)2(OSiButMe2)]. A solution of 50 mg (0.066 mmol)
of (Et4N)2WO2(bdt)2] in 0.5 mL of acetonitrile was treated with 10 mg
(0.066 mmol) of ButMe2SiCl, resulting in an orange to brown-green
color change. The solution was stirred for 30 min, the solvent was
removed in vacuo, and the residue extracted with 2 mL of THF. The
solution was filtered through Celite, and ether was added dropwise to
the filtrate. The dark crystals that separated from the filtrate solution
overnight were collected, washed with ether (2 × 5 mL), and dried in
vacuo to give 45 mg (92%) of product as a dark brown-green solid. IR
(KBr): 1244 (m), 1171 (m), 930 (vs, νSiO), 890 (vs, νWO), 835 (m),
821 (m), 778 (m), 752 (s) cm-1. FAB-MS-: m/z 611 (M-). 1H NMR
(Et4N)2[WO(bdt)2]. A solution of sodium acenaphthylenide was
prepared from 0.110 g (4.78 mmol) of sodium and 0.750 g (4.93 mmol)
of acenaphthylene in 75 mL of THF; the mixture was stirred until all
of the sodium dissolved. A portion of this solution (60 mL) was added
dropwise to a stirred solution of 2.00 g (3.28 mmol) of (Et4N)[WO-
(bdt)2] in 30 mL of acetonitrile, resulting in a brown solution. The
solution was allowed to warm to room temperature and was stirred for
1 h. The solution was reduced in vacuo to a volume of 15 mL, and
was treated with a solution of 1.10 g (4.28 mmol) of Et4NI in 80 mL
of methanol. The resulting suspension was filtered to separate an
orange-brown solid, which was washed with methanol (3 × 20 mL),
acetonitrile (2 × 10 mL), and ether (2 × 10 mL), and dried in vacuo
to give 1.60 g (66%) of product as an ochre solid. Absorption spectrum
(acetonitrile): λmax 326, 394, 466 nm. IR (KBr): 905 cm-1 (νWO).
ES-MS-: m/z 480 (M-). 1H NMR (anion + Cp2Co, CD3CN): δ 7.70
(d, 1), 6.70 (d, 1). Cobaltocene was added to reduce line broadening
by electron transfer with [WO(bdt)2]1- impurity. Anal. Calcd for
C28H48N2OS4W: C, 45.40; H, 6.53; N, 3.78; S, 17.31. Found: C, 45.18;
H, 6.44; N, 3.66; S, 16.99. This compound has been prepared
previously by another method.20
(Et4N)2[WO2(bdt)2]. This compound was prepared by a published
procedure, but few characterization details were given.20 It was isolated
in 75% yield as a light red-orange crystalline solid. Absorption
spectrum (acetonitrile): λmax 286 (sh), 324 (sh), 423, 482 nm. IR
(KBr): 847, 887 cm-1 (νWO). FAB-MS-: m/z 496 (M-). 1H NMR
(anion, CD3CN): δ 6.99 (d, 1), 6.52 (d, 1).
(Et4N)2[W(bdt)3]. This compound was isolated as a byproduct in
the synthesis of (Et4N)2[WO(bdt)2] and was extracted from it by washing
the solid products with acetonitrile to give a red solution. Slow addition
of ether by vapor diffusion to this solution afforded the compound as
red crystals. Yields of up to 70% have been obtained, which apparently
depend on the water content of the solvent. FAB-MS-: m/z 604 (M-).
1H NMR (anion, CD3CN): δ 7.57 (d, 1), 6.58 (d, 1). Anal. Calcd for
C34H52N2S6W: C, 47.21; H, 6.06; N, 3.24; S, 22.24. Found: C, 47.09;
H, 6.02; N, 3.30; S, 22.18.
(Et4N)[W(bdt)2(OSiMe3)]. To a stirred solution of 100 mg (0.135
mmol) of (Et4N)2[WO(bdt)2] in 2 mL of acetonitrile was added 18.0
mg (0.170 mmol) of Me3SiCl. The reaction mixture turned red and a
red precipitate appeared. Stirring was continued for 2 h, the solvent
was removed in vacuo, and the solid residue was washed with ether (3
× 3 mL). This material was dissolved in the minimum volume (∼6
mL) of THF/acetonitrile (3:1 v/v), the solution was filtered through
(25) Persson, C.; Andersson, C. Inorg. Chim. Acta 1993, 203, 235.
(26) Hanson, G. R.; Brunette, A. A.; McDonell, A. C.; Murray, K. S.;
Wedd, A. G. J. Am. Chem. Soc. 1981, 103, 1953.
(27) (a) Adams, R.; Reifschneider, W.; Ferretti, A. Organic Syntheses;
Wiley: New York, 1973; Collect. Vol. V, p 107. (b) Ferretti, A. Organic
Syntheses, Wiley: New York, 1973; Collect. Vol. V, p 419. (c) Giolando,
D. M.; Kirschbaum, K. Synthesis 1992, 451.

Bis(dithiolene)tungsten(IV,VI) Complexes
J. Am. Chem. Soc., Vol. 120, No. 32, 1998 8105
(anion, CD3CN): δ 7.22 (dd, 4), 6.85 (dd, 4), 0.93 (s, 9), 0.19 (s, 6).
Anal. Calcd for C26H43NO2SiS4W: C, 42.10; H, 5.84; N, 1.89; S, 17.29.
Found: C, 42.24; H, 5.88; N, 1.88; S, 17.44.
Chart 1. Designation of Tungsten-Dithiolene Complexes
(Et4N)[WO(bdt)2Cl]. (a) Method 1. (Et4N)[WO(bdt)2(OSiButPh2)]
(0.250 g, 0.289 mmol) was dissolved in 15 mL of acetonitrile to form
a dark green-black solution, to which was added 63 mg (0.58 mmol)
of Me3SiCl. The reaction mixture was stirred until it became deep
purple (3 h), and 60 mL of ether was added. The black microcrystalline
product that separated was collected by filtration, washed with ether
(3 × 10 mL), and dried in vacuo to yield the product as 0.138 g (74%)
of black solid. Absorption spectrum (acetonitrile): λmax (ꢀM) 290
(18 100), 351 (12 500), 499 (5100), 600 (3130) nm. IR (KBr): 1170
(m), 997 (m), 915 (vs, νWO), 835 (m), 765 (s) cm-1. ES-MS: m/z 515
(M-). 1H NMR (anion, CD3CN): δ 7.36 (dd, 1). 7.00 (dd, 1). Anal.
Calcd for C20H28ClNOS4W: C, 37.19; H, 4.37; Cl, 5.49; N, 2.17; S,
19.85. Found: C, 36.94; H, 4.33; Cl, 5.56; N, 2.20; S, 19.64. This
procedure was also applied to (Et4N)[WO(bdt)2(OSiButMe2)] on a 0.12
mmol scale; the product was obtained as 51 mg (66%) of red crystals.
(b) Method 2. To a stirred solution of 200 mg (0.585 mmol) of
The red solution turned brown and was stirred for 6 h; method 1 was
then followed. The desired compound was obtained in a mixture of
similar proportion to that of method 1. Although this compound could
not be obtained pure in bulk quantity, dark violet crystals suitable for
X-ray diffraction were grown from a DMF-ether solution.
Ph2Se18O. To a solution of 70 mg of NaOH in 0.100 mL of H218O
(Icon, 98.7% 18O) cooled in an ice bath was added 100 mg of Ph2-
SeCl2. The reaction mixture was stirred vigorously for 30 min in the
ice bath and overnight at room temperature. The liquid was decanted,
and the solid was washed with distilled water (2 × 1 mL) and hexane
(2 × 1 mL) and dried in vacuo. Mass spectrometry showed the product
to contain 62(3)% 18O.
28
WOCl4 in 5 mL of acetonitrile was added 50.0 mg (0.585 mmol) of
LiOBut in portions. Within 1 min, the orange solution turned yellow
and a white precipitate formed. Et4NCl (100 mg, 0.585 mmol) was
added to the reaction mixture followed by a solution of 90.0 mg (1.17
mmol) of Li2(bdt) in 1 mL of acetonitrile. The mixture was stirred for
5 min and filtered through Celite, and the filtrate taken to dryness in
vacuo. The residue of black powder was washed with ether (4 × 4
mL) and 14 mL of THF/ether (2:5 v/v) and dried in vacuo, giving the
product as 230 mg (60%) of a black solid. Spectroscopic properties
were identical to those of the product of method 1.
Oxo Transfer Reactions.
These reactions, involving
(Et4N)[W(bdt)2(OSiButPh2)] (δ 0.73) as an oxo acceptor and
(Et4N)[WO(bdt)2(OSiButPh2)] (δ 1.06) as an oxo donor, were monitored
1
in CD3CN solutions by H NMR. The mole percents of initial and
final complexes are based on integration of But signals with the
indicated chemical shifts and that of ButPh2SiOH (δ 0.98), which
appeared in nearly all reaction systems owing to partial hydrolysis of
the tungsten complexes by trace amounts of water.
[W(bdt)2(P(OEt)3)2]. To a solution of 50 mg (0.077 mmol) of
(Et4N)[WO(bdt)2Cl] in 5 mL of acetonitrile was added 50 mg (0.30
mmol) of P(OEt)3. The reaction mixture was stirred for 12 h, the
solvent was removed in vacuo, and the dark residue was extracted with
ether (2 × 10 mL). The yellow-orange extract was filtered, and the
filtrate was reduced to dryness in vacuo, affording the product as 24
mg (39%) of orange crystalline solid. Absorption spectrum (acetoni-
trile): λmax (ꢀM) 339 (10 000), 411 (14 700) nm. 1H NMR (CD3CN):
δ 8.20 (dd, 4), 7.20 (dd, 4), 3.81 (q, 12), 1.18 (t, 18). Anal. Calcd for
C24H38O6P2S4W: C, 36.19; H, 4.81; P, 7.78; S, 16.10. Found: C, 36.26;
H, 4.88; P, 7.86; S, 16.19.
18O Transfer Reactions. (a) (Et4N)[W(bdt)2(OSiButPh2)] (5.0 mg,
5.8 µmol) and PhI18O (5.0 mg, 23 µmol) were stirred in 0.5 mL of
acetonitrile for 3 h. The solvent was removed in vacuo and the residue
dried in vacuo. IR (KBr): 931 (Si-O), 895 (Wd16O), 848 (Wd18O).
The 1H NMR spectrum of the product is identical to that of
[WO(bdt)2(OSiButPh2)]1-
.
In two experiments the 18O product
incorporation was 60(3<)% and 68(5)% by FAB-MS. (b)
(Et4N)[W(bdt)2(OSiButPh2)] (5.0 mg, 5.8 µmol) and Ph2Se18O (3.0 mg,
12 µmol) were stirred in 0.5 mL of acetonitrile for 10 h. The previous
procedure was followed, leading to 60(3)% 18O product incorporation.
X-ray Structure Determinations. Reference is made to the
numerical designation of complexes in Chart 1. The structures of the
10 compounds in Tables 1 and 2 were determined. Crystals of
(Ph4P)[WO(SPh)4]‚3/2DMF (black blocks), (Et4N)[4a] (red plates),
(Et4N)[4c] (red-black blocks), (Et4N)[5a]‚1/2MeCN (orange-red plates),
and (Et4N)2[7] (red plates) were obtained by slow diffusion of But-
OMe into saturated DMF ((Ph4P)[WO(SPh)4]‚3/2DMF) or acetonitrile
solutions ((Et4N)[4a], (Et4N)[4c], (Et4N)[5a]‚1/2MeCN), and (Et4N)2[7].
A similar procedure using Et2O gave (Et4N)[6] (red needles). Diffusion
of Et2O in 1:1 acetonitrile/THF solution gave (Et4N)[5b] (black plates)
and into a DMF solution afforded (Et4N)[12] (violet elongated plates).
Slow evaporation of an ether/methanol solution (2:1 v/v) produced 8
(orange needles), while 9 (red blocks) was obtained directly from the
reaction mixture upon standing.
Diffraction data for (Ph4P)[WO(SPh)4]‚3/2DMF, (Et4N)[4c],
(Et4N)[5a]‚1/2MeCN, (Et4N)[5b], (Et4N)[6], and 9 were collected on a
Nicolet P3 diffractometer. Crystals were coated in grease, mounted
on glass fibers, and cooled in a nitrogen stream. Refined cell parameters
were obtained by least-squares fits of 30-50 machine-centered reflec-
tions (10° e 2θ° e 20°). Two check reflections were monitored during
the data collections and showed no significant decay. Data reduction
and corrections for scan speed, background, and Lorentz and polariza-
tion effects were applied by the program XDISK of the SHELXTL
PLUS program suite. Empirical absorption corrections were applied
with XPREP using variations in intensity in azimuthal (Ψ) data for
7-10 reflections with 2θ evenly spaced between 10° and 45°. The
compounds (Et4N)[4a], (Et4N)2[7], 8, and (Et4N)[12] were examined
with a Siemens (Bruker) SMART CCD area detector instrument. Data
[W(bdt)2(ButNC)2]. To a solution of 50 mg (0.077 mmol) of
(Et4N)[WO(bdt)2Cl] in 5 mL of acetonitrile was added 25 mg (0.30
mmol) of ButNC followed by 15 mg (0.090 mmol) of P(OEt)3. The
reaction mixture was stirred for 1 h, during which time the color
changed from purple to orange-brown and a dark microcrystalline
product precipitated. Solvent was removed in vacuo and the dark
residue was extracted with ether (10 × 10 mL). The orange-red extract
was filtered and 20 mL of methanol was added to the filtrate. The
volume of the solution was reduced to 3 mL, causing separation of a
solid which was collected by filtration. This material was washed with
methanol (2 × 1 mL) and dried in vacuo, giving the product as 27 mg
(55%) of a red crystalline product. Absorption spectrum (acetoni-
trile): λmax (ꢀM) 352 (9100), 445 (15 100) nm. IR (KBr): 2151, 2128
(sh) cm-1 (νNC). 1H NMR (CD2Cl2): δ 8.20 (dd, 4), 7.20 (dd, 4), 1.56
(s, 18). Anal. Calcd for C22H26N2S4W: C, 41.91; H, 4.16; N, 4.44;
S, 20.34. Found: C, 41.82; H, 4.22; N, 4.36; S, 20.28.
(Et4N)[WS(bdt)2(OSiButPh2)]. This compound could be repro-
ducibly prepared by two methods but was always obtained as a mixture.
(a) Method 1. An acetonitrile solution of 20 mg (0.023 mmol) of
(Et4N)[WO(bdt)2(OSiButPh2)] in 1 mL of acetonitrile was treated with
6.0 µL (0.029 mmol) of (Me3Si)2S (cautionsstench). The reaction
mixture was stirred for 12 h, during which it turned from green to
brown. After 2 d of stirring, the solvent was removed in vacuo,
and the residue was triturated with ether (2 × 5 mL) and dried in
1
vacuo. An H NMR analysis of the solid showed that it contained
60% desired product and 40% [W(bdt)2(OSiButPh2)]1-. The spectrum
of the former in CD3CN closely resembles that of [WO(bdt)2(OSiBut-
Ph2)]: δ 7.88 (dd), 7.35 (m), 7.26 (dd), 6.87 (dd), 1.06 (s). IR (KBr):
915 cm-1 (νSiO). FAB-MS-: m/z 751 (M-). (b) Method 2.
(Et4N)[W(bdt)2(OSiButPh2)] (20 mg, 0.023 mmol) was added to a
solution of 8.0 mg of (PhCH2S)2S (0.029 mmol) in 1 mL of acetonitrile.

8106 J. Am. Chem. Soc., Vol. 120, No. 32, 1998
Lorber et al.
Table 1. Crystallographic Dataa for Compounds Containing [WO(SPh)4]-, 4a, 4c, 5a, and 5b
(PPh4)[WO(SPh)4]‚3/2DMF
(Et4N)[4a]
(Et4N)[4c]
(Et4N)[5a]‚1/2CH3CN
(Et4N)[5b]
formula
fw
crystal system
space group
Z
C48H40OPS4W‚3/2HCONMe2
C23H37NOS4SiW
683.72
monoclinic
P21/c
C36H47NOS4SiW
849.93
monoclinic
Pn
C29H47.5N1.5O2S4SiW
782.85
triclinic
P1h
4
C36H47NO2S4SiW
865.93
orthorhombic
Pbca
1085.50
triclinic
P1h
2
4
2
8
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
10.391(2)
15.430(3)
17.380(4)
63.78(3)
89.75(3)
79.78(3)
2451.6(9)
223
9.9543(1)
25.2280(3)
11.8162(0)
10.616(2)
9.968(2)
17.804(4)
11.030(2)
17.581(4)
17.765(4)
97.23(3)
94.76(3)
95.91(3)
3383.3(12)
223
10.662(2)
22.730(5)
31.414(6)
102.638(1)
96.02(3)
2895.47(5)
213
0.0325 (0.0564)
1873.6(6)
223
0.0279 (0.0635)
7613(3)
223
0.0367 (0.0731)
T, K
Rb (Rw )
0.0352 (0.0852)
0.0672 (0.1633)
c
2
a Obtained with graphite-monochromatized Mo KR (λ ) 0.71073 Å) radiation. b R ) ∑||Fo| - |Fc||/∑|Fo|. c Rw ) {∑[w(|Fo| - |Fc|)2]/∑[w|Fo| ]}1/2
.
Table 2. Crystallographic Dataa for Compounds Containing 6-9 and 12
(Et4N)[6]
(Et4N)2‚[7]d
8
9
(Et4N)[12]
formula
fw
crystal system
space group
Z
C20H28ClNOS4W
645.97
monoclinic
P21/c
C34H52N2S6W
864.99
orthorhombic
Pbca
C24H38O6P2S4W
796.6
monoclinic
P21/c
C22H26N2S4W
630.5
orthorhombic
Pna21
C36H47NOS5SiW
881.99
triclinic
P1h
4
4
8
8
4
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
10.156(2)
11.649(2)
20.055(4)
14.2662(2)
17.5888(1)
30.3401(5)
19.4060(0)
16.7707(3)
21.6413(1)
17.110(3)
16.380(3)
9.466(2)
10.2247(1)
10.2247(1)
39.6961(7)
85.791(1)
84.855(1)
69.668(1)
3871.80(9)
213
90.91(3)
116.514(1)
2372.4(8)
223
0.0419 (0.1017)
7613.1(2)
213
0.0431 (0.0716)
6302.4(1)
213
0.0358 (0.0534)
2653.0(9)
223
0.0281 (0.0653)
T, K
c
Rb (Rw )
0.0910 (0.1822)
2
a Obtained with graphite-monochromatized Mo KR (λ ) 0.71073 Å) radiation. b R ) ∑||Fo| - |Fc||/∑|Fo|. c Rw ) {∑[w(|Fo| - |Fc|)2]/∑[w|Fo| ]}1/2
.
d Crystalline [Et4N]2[WIV(bdt)3] was also obtained in space group C2/c with cell parameters a ) 19.267(2) Å, b ) 27.581(3) Å, c ) 17.852(3) Å,
â ) 114.512(8)° by slow diffusion of 1,2-dimethoxyethane into a DMF solution.
were measured using ω scans of 3°/frame with 30 or 60 s frames such
that 1271 frames were collected for a hemisphere of data. No decay
in intensities was observed over the data collections. Cell parameters
were retrieved using SMART software and refined using SAINT
software on all observed reflections between 2θ of 3° and 56° ((Et4N)-
[4a], (Et4N)2[7], 8) or 45° ((Et4N)[12]). Data reduction was performed
with SAINT software, which corrects for Lorentz polarization and
decay. Absorption corrections were applied using SADABS based on
the method described by Blessing.29
Space groups were assigned on the basis of systematic absences with
use of XPREP ((Et4N)[4a], (Et4N)[4c], (Et4N)[5b], (Et4N)[6], (Et4N)2-
[7], 8, 9). For (Ph4P)[WO(SPh)4]‚3/2DMF, (Et4N)[5a]‚1/2MeCN, and
(Et4N)[12], space groups were assigned on the basis of statistics and
successful structure solution and refinement. All structures were solved
by direct methods using SHELXS and refined by full-matrix least-
squares methods. All non-hydrogen atoms except those of the
disordered DMF molecule in (Ph4P)[WO(SPh)4]‚3/2DMF were refined
anisotropically; hydrogen atoms were added at idealized positions and
refined as riding atoms with a uniform value of Uiso. In the final stages
of refinement of (Et4N)[5a]‚1/2MeCN, (Et4N)[5b], (Et4N)[6], and 9, a
weighting scheme was used that increased the contribution of the lighter
atoms to the structure factor amplitudes such that an improved
goodness-of-fit value was obtained.30 The asymmetric unit of
(Ph4P)[WO(SPh)4]‚3/2DMF contains 1.5 DMF solvate molecules, the
nitrogen atom of one of which resides on an inversion center. The
position requires site occupancy factors of 0.5 for the atoms of DMF
and imposes disorder over the symmetry site. For 8, one methylene
group of a phosphite ligand was disordered over two positions, which
were refined with 0.5 site occupancies. The methylene groups of the
cation of (Et4N)[12] were disordered, and were refined with variable
occupancies of the carbon atoms determined as optimal fits by
SHELXTL. All structures were checked for missing symmetry with
the checking program PLATON (V: 120695). Supporting Information
was prepared with use of XCIF.31
Other Physical Measurements. All measurements were made
under anaerobic conditions. Absorption spectra were recorded on
Perkin-Elmer Lambda 6 or Varian Cary 3 spectrophotometer. 1H and
31P NMR spectra were obtained with a Bruker AM 400 spectrometer.
IR spectra were determined with use of a Nicolet Impact 400 FT-IR
instrument. Mass spectra were recorded on a JEOL AX-505 (EI-MS),
JEOL SX-102 (FAB-MS), and a Micromass Platform II (ES-MS)
spectrometers. The matrix for FAB spectra was 3-nitrobenzyl alcohol.
Results and Discussion
This work constitutes the first systematic investigation of the
synthetic and structural chemistry of tungsten-dithiolene com-
plexes of any type. A synthesis and reactivity scheme is
presented in Figure 2. Structures of 10 complexes are set out
in Figures 3-7, selected metric data are collected in Tables
3-5. Complexes 1-320 and716h have been previously prepared,
but by different methods, and their structures determined.16i,20
Synthesis and Structures of Bis(dithiolene)tungsten(IV,V,-
VI) Complexes. (a) Precursors. Complex 1 was first prepared
by the ligand substitution reaction of bdtH2 with [WO(SPh)4]1-,20
which itself was obtained in unspecified yield from [WOCl4]1-
and Et3N/PhSH.26 In this work, the precursor complex was
synthesized by the reaction of [WOCl3(THF)2] and Et3N/PhSH
(28) Gibson, V. C.; Kee, T. P.; Shaw, A. Polyhedron 1988, 7, 579.
(29) Blessing, R. H. Acta Crystallogr. 1995, A51, 33.
(30) Dunitz, J. D.; Seiler, P. Acta Crystallogr. 1973, B29, 589.
(31) See paragraph at the end of this article concerning Supporting
Information available.

Bis(dithiolene)tungsten(IV,VI) Complexes
J. Am. Chem. Soc., Vol. 120, No. 32, 1998 8107
Figure 2. Scheme for the synthesis and reactions of bis(benzenedithiolato)tungsten complexes 1-12.
in THF/acetonitrile and was isolated as two salts in 87% (Et4N+)
and 73% (Ph4P+) yields. The structure of the Ph4P+ compound
(Figure 3, Table 3) is distorted square pyramidal with an axial
W-O1 bond length of 1.589(5) Å and a 0.765 Å displacement
of the tungsten atom from the S(1-4) mean plane. Severe
distortions from idealized C4V symmetry are particularly evident
in W-S bond distances, which span a range of 0.225 Å with a
mean value of 2.46(9) Å. The phenyl rings are disposed on
the oxo side of the S(1-4) plane with o-H‚‚‚O1 distances of
2.883 Å (S1 ring) and 2.984 Å (S4 ring) suggestive of weak
interactions. In contrast, the structure of [MoO(SPh)4]1- (Ph4-
As+ salt) is regular with Mo-O and mean Mo-S bond lengths
of 1.669(9) Å and 2.403(6) Å.32
We have found that 1 can be more conveniently and
efficiently prepared by a procedure analogous to that for
[WO(SPh)4]1- with use of bdtH2/2Et3N. The compound (Et4N)-
[1] was obtained in 79% yield. When reduced with sodium
acenaphthylenide in THF/acetonitrile, this compound afforded
(Et4N)2[2] in 66% yield. We have been unsuccessful in
reproducing the reported reduction of 1 to 2 (71%) with (Ph4P)-
(BH4).20 Rigorously anhydrous and freshly distilled solvents
and bdtH2 are obligatory to obtaining high yields of 1 and 2,
both of which have square pyramidal stereochemistry.20 Small
amounts of water resulted in the formation of [W(bdt)3]1-,2-
.
Variable amounts of (Et4N)2[7] have been encountered in the
preparation of 2 and can be separated by differential solubility
in acetonitrile. The structure of 7 has been determined (Figure
3, Table 4). Metric parameters are unexceptional; as is the
case for many tris(dithiolene) complexes,16f,g,i,j,k,33 7 closely
Figure 3. Structures of [WO(SPh)4]1- (upper) and [W(bdt)3]2- (7,
lower), showing 50% probability ellipsoids and partial atom-labeling
schemes.
(32) Bradbury, J. R.; Mackay, M. F.; Wedd, A. G. Aust. J. Chem. 1978,
31, 2423.
(33) Cowie, M.; Bennett, M. J. Inorg. Chem. 1976, 15, 1584, 1589, 1595.

8108 J. Am. Chem. Soc., Vol. 120, No. 32, 1998
Lorber et al.
Figure 4. Structures of [W(bdt)2(OSiMe3)]1- (4a, upper) and
[W(bdt)2(OSiButPh2)]1- (4c, lower), showing 50% probability ellipsoids
and partial atom-labeling schemes.
Figure 6. Structures of [WO(bdt)2(OSiButPh2)]1- (5b, upper) and
[WO(bdt)2(OSiButMe2)]1- (5a, lower), showing 50% probability el-
lipsoids and partial atom-labeling schemes.
Figure 5. Structures of [W(bdt)2(ButNC)2] (9, upper) and [W(bdt)2-
(P(OEt)3)2] (8, lower), showing 50% probability ellipsoids and partial
atom-labeling schemes.
Figure 7. Structures of [WO(bdt)2Cl]1- (6, upper, 50%) and
[WS(bdt)2(OSiButPh2)]1- (12, lower, 30%), showing the indicated
probability ellipsoids and partial atom-labeling schemes.
approaches trigonal prismatic geometry, with an average twist
angle of 3.5°.34 The complex exhibits in acetonitrile two
chemically reversible redox steps at -0.48 and 0.34 V vs SCE
corresponding to the formation of [W(bdt)3]1-,0, which have
been prepared earlier.16b,h
(b) Desoxo W(IV) and Monooxo W(VI). (i) Preparations.
We have sought bis(dithiolenes) of these types by silylation of
(34) Calculated from interatomic distances: Larsen, E.; La Mar, G. N.;
Wagner, B. E.; Parks, J. E.; Holm, R. H. Inorg. Chem. 1972, 11, 2652.

Bis(dithiolene)tungsten(IV,VI) Complexes
J. Am. Chem. Soc., Vol. 120, No. 32, 1998 8109
Table 3. Selected Interatomic Distances (Å) and Angles (deg) for Square Pyramidal [WIV,VOS4]1- Complexes
[WVO(SPh)4]1-
[WIV(bdt)2(OSiMe3)]1-
[WIV(bdt)2(OSiButPh2)]1-
W-S1
2.446(2)
2.358(2)
2.437(2)
2.583(2)
2.46(9)
2.341(1)
2.350(1)
2.334(1)
2.331(1)
2.339(8)
1.836(3)
145.3(2)
110.0(1)
109.1(1)
109.0(1)
106.3(1)
129.2
2.334(2)
2.333(2)
2.329(2)
2.335(2)
2.333(3)
1.844(6)
176.0(4)
108.1(2)
107.1(2)
108.5(2)
108.0(2)
131.1
W-S2
W-S3
W-S4
W-Sav
W-O1
1.589(5)
W-O1-Si1
O1-W-S1
O1-W-S2
O1-W-S3
O1-W-S4
100.1(2)
108.2(2)
110.8(2)
111.6(2)
a
θ1
θ2
b
14.7
0.746
17.7
0.717
c
W - Smean plane
0.765
a θ1 ) angle between planes defined by WS2 atoms. b θ2 ) angle between planes defined by WS2 and S2C2 ligand atoms. c W - Smean plane
displacement of W atom from least-squares S4 plane.
)
Table 4. Selected Interatomic Distances (Å) and Angles (deg) for Trigonal Prismatic [WIV(bdt)2L2] Complexes
[WIV(bdt)3]2-
[WIV(bdt)2(ButNC)2]
[WIV(bdt)2(P(OEt)3)2]a
W-S1
2.398(1)
2.375(1)
2.393(1)
2.392(1)
2.396(1)
2.391(1)
80.78(4)
80.90(4)
80.89(4)
2.354(2)
2.353(3)
2.362(3)
2.353(3)
2.086(11)
2.080(12)
80.6(4)
82.02(13)
81.97(10)
129.4
2.363(1)
2.361(1)
2.347(1)
2.374(1)
2.453(1)
2.459(1)
83.35(4)
82.02(4)
82.14(4)
128.3
W-S2
W-S3
W-S4
W-X1b
W-X2b
X1-W-X2b
S1-W-S2
S1-W-S4
c
θ1
θ2
d
4.9
0.759
4.1
0.775
e
W - Smean plane
a Data for one of two molecules in the asymmetric unit. b X ) S, C, or P. c θ1 ) angle between planes defined by WS2 atoms. d θ2 ) angle
between planes defined by WS2 and S2C2 ligand atoms. e W - Smean plane ) displacement of W atom from least squares S4 plane.
Table 5. Selected Interatomic Distances (Å) and Angles (deg) for W(VI) Complexes
[WVIO(bdt)2(OSiButPh2)]1-
[WVIO(bdt)2(OSiButMe2)]1- a
[WVIS(bdt)2(OSiButPh2)]1- a
[WVIO(bdt)2Cl]1-
W-S1
2.489(2)
2.429(2)
2.410(2)
2.427(2)
1.723(5)
1.907(5)
161.5(3)
95.0(3)
145.6(2)
81.1(2)
104.6(2)
103.8(2)
153.8(2)
153.86(8)
2.554(4)
2.388(4)
2.417(4)
2.439(4)
1.729(10)
1.835(12)
163.9(9)
94.8(5)
155.3(3)
81.3(4)
105.4(4)
99.2(4)
2.490(5)
2.371(5)
2.382(5)
2.440(5)
2.163(5)
1.939(11)
158.1(8)
98.0(4)
154.1(2)
82.7(2)
104.4(2)
101.5(2)
155.5(4)
156.3(2)
2.450(2)
2.419(2)
2.416(2)
2.408(2)
1.728(5)
2.436(2)
W-S2
W-S3
W-S4
W-X1b
W-X2c
W-X2-Si1
X1-W-X2
X1-W-S1
X1-W-S2
X1-W-S3
X1-W-S4
X2-W-S4
S2-W-S3
89.0(2)
142.6(2)
83.4(2)
108.7(2)
103.8(2)
155.23(6)
154.24(7)
158.3(4)
158.2(2)
a Data for one of two anions in the asymmetric unit. b X1 ) O or S. c X2 ) O-Si or Cl.
oxo complexes in the corresponding oxidation states. Treatment
of a slurry of 2 with 1.05-1.25 equiv of the chlorosilanes RR′2-
SiCl in acetonitrile resulted in silylation of the oxo ligand and
formation of the red W(IV) complexes 4a, 4b, and 4c (Figure
2), isolated in 71-90% yields as Et4N+ salts. Similarly,
silylation of 3 with 1.03-1.14 equiv of ButR′2SiCl in acetonitrile
afforded the brown-green monooxo W(VI) species 5a and 5b
in 85-92% yield, also as Et4N+ salts. Alternatively, (Et4N)-
[5b] (76%) was prepared by the oxo transfer reaction of 4c and
Me3NO in acetonitrile. The compounds 5 are brown-green
noncrystalline solids giving dark green solutions in acetonitrile
or THF, and light red solids when crystalline. Treatment of 3
with Me3SiCl in acetonitrile did not lead to a mono silyl oxide
product, but instead resulted in chloride substitution and the
formation of black (Et4N)[6] (74%). This compound can be
more simply prepared in procedures not directly requiring 3.
The reaction system WOCl4/LiOBut/2Li(bdt)2 resulted in a 60%
yield;35 silylation of 5b gave 6 in 74% yield.
While silylation of ModO and WdO groups is not an
extensively investigated reaction type, a number of stable MoV-
(OSiR3)/MoVO(OSiR3),36 MoVIO(OSiR3),37 MoVIO2(OSiR3),38
(35) The role of LiOBut in the reaction system is unclear, but 6 is not
formed in its absence.
(36) (a) Wilson, G. L.; Kony, M.; Tiekink, E. R. T.; Pilbrow, J. R.;
Spence, J. T.; Wedd, A. G. J. Am. Chem. Soc. 1988, 110, 6923. (b) Xiao,
Z.; Young, C. G.; Enemark, J. H.; Wedd, A. G. J. Am. Chem. Soc. 1992,
114, 9194. (c) Xiao, Z.; Gable, R. W.; Wedd, A. G.; Young, C. G. J. Am.
Chem. Soc. 1996, 118, 2912. (d) Xiao, Z.; Bruck, M. A.; Enemark, J. H.;
Young, C. G.; Wedd, A. G. JBIC 1996, 1, 415.
(37) Arzoumanian, H.; Corao, C.; Krentzien, H.; Lopez, R.; Teruel, H.
J. Chem. Soc., Chem. Commun. 1992, 856.
(38) Huang, M.; DeKock, C. W. Inorg. Chem. 1993, 32, 2287.

8110 J. Am. Chem. Soc., Vol. 120, No. 32, 1998
Lorber et al.
and MoVIS3(OSiR3)39 species have been formed in this way.
The only examples of silylation of a WdO group of which we
are aware are in the systems [(C5Me5)2WO]/Me3SiCl40a and
[(MeC5H4)2WO/Me3SiX (X ) Cl, I).40b In the first system, the
initial reaction product is [(C5Me5)2W(OSiMe3)Cl], which reacts
with a second equivalent of Me3SiCl to give [(C5Me5)2WCl2]
or slowly disproportionates in the absence of the silyl reagent
to form [(C5Me5)2WO] and [(C5Me5)2WCl2]. In the second
sytem, [(MeC5H4)2W(OSiMe3)Cl] was detected and [(MeC5H4)2-
WI2] was formed rapidly and quantitatively. These reactions
proceed with formation of (Me3Si)2O. The formation of 5ab
proceeds by reaction 1. Steric features are sufficient to prevent
reaction with a second equivalent of ButR′2SiCl (R′ ) Me, Ph),
but not with less hindered Me3SiCl which in reaction 2 forms
6. When reaction 3 is carried out with one equivalent of Me3-
SiCl, the characteristic green-black color of 6 develops instantly,
indicating that reaction of the silyl reagent with bound silyl oxide
is faster than any other process. Complexes 5ab, and also 4abc,
Two other desoxo W(IV) complexes, 8 and 9, were readily
prepared by reduction of chloro complex 6 in reactions 4 and
5 conducted in acetonitrile. Triethyl phosphite is an effective
[WO(bdt)2Cl]1- + 3(EtO)3P f
[W(bdt)2(P(OEt)3)2] + (EtO)3PO + Cl- (4)
[WO(bdt)2Cl]1- + 2ButNC + (EtO)3P f
[W(bdt)2(ButNC)2] + (EtO)3PO + Cl- (5)
oxo acceptor in these reactions at ambient temperature while
Ph3P shows slow reactivity at 60 °C. The associated reaction
system [WOCl4]/Ph3P affords trans-[WCl4(PPh3)2].43 Com-
plexes 8 and 9 are related to the bis(dithiolene) dicarbonyl
[W(S2C2Me2)2(CO)2], prepared by the photochemical reaction
of W(CO)6 and [Ni(S2C2Me2)2].18
(ii) Structures. From the structures of 4a and 4c (Figure 4,
Table 3), it is immediately apparent that these are desoxo W(IV)
complexes. They adopt a square-pyramidal stereochemistry
with the tungsten atoms strongly displaced from the least-squares
S(1-4) planes (by 0.72 Å (4c) and 0.75 Å (4a)) in the direction
of axial silyl oxide ligands. This displacement is further
emphasized by the dihedral angles θ1 between WS2 coordination
planes. As is common with dithiolene complexes, there are
small folds in the chelate ring structures along the S‚‚‚S vectors
that are made evident by the dihedral angles θ2. Mean W-S
bond distances in the two complexes are indistinguishable and
average to 2.336 Å. The W-O-Si angle is 4a is bent (145.3-
(2)°) whereas in 4c it is nearly linear (176.0(4)°), an effect
ascribed to the larger steric bulk of the silyl oxide ligand in the
latter complex. The complexes 8 and 9 approach the trigonal
prismatic stereochemistry of 7 (Figure 5, Table 4). In 9, the
W-C bond distances of 2.08(1) Å and 2.09(1) Å are comparable
to those in other W(IV) isonitrile complexes.44 The nearly linear
C-N-C bond angles of 174(1)° indicate little π back-bonding,
which would result in a bent configuration. Close similarities
in the out-of-plane displacements of the tungsten atom and the
dihedral angles θ1 emphasize the structural relationship between
five-coordinate 4a,b,c and six-coordinate 8 and 9. Structures
of the latter resemble that of the isoelectronic bis(diselenolene)
complex [W(Se2C6H4)2(CO)2].45
The structures of 5a and 5b (Figure 5, Table 5) confirm the
monooxo W(VI) formulation. These complexes are irregularly
distorted from octahedral, although several features normal to
oxo species are present. The WdO bond lengths are in the
range of those in [WO2(bdt)2]2- 20 and [WO2(mnt)2]2- 21 (1.70-
1.74 Å). The trans effect of O1 renders the W-S1 bonds
significantly longer than W-S(2-4), the effect being larger in
5a. The angles O1-W-X where X ) O, S cis to the oxo ligand
are larger than 90° (except for X ) S2), owing to electrostatic
repulsion. Trans bond angles at tungsten are less than 180° by
22-34°, an effect due in part to the restricted bite distance of
the rigid bdt ligand. The structure of 6 (Figure 7, Table 5) is
similar in all respects to those of 5a and 5b except for the
replacement of silyl oxide by chloride in the W-Cl bond of
length 2.436(2) Å. The stereochemistry and metric pattern of
5b extends to its sulfido analogue 12 (Figure 7, Table 5). The
W-S5 bond length of 2.163(5) Å is consistent with other recent
determinations of WVIdS bond lengths.46 Compared to their
[WO2(bdt)2]2- + ButR′2SiCl f
[WO(bdt)2(OSiButR′2)]1- + Cl- (1)
[WO(bdt)2(OSiButR′2)]1- + Me3SiCl f
[WO(bdt)2Cl]1- + Me3SiOSiButR′2 (2)
[WO2(bdt)2]2- + 2Me3SiCl f
[WO(bdt)2Cl]1- + (Me3Si)2O + Cl- (3)
are stable for at least 2-3 days in anaerobic anhydrous
acetonitrile solutions at ambient temperature. While there is
visual indication of a reaction between the WVO complex 1
and Me3SiCl, thus far we have been unable to isolate a pure
silyl oxide or chloride complex. Stabilization of monooxo
W(VI) complexes 5ab appears to require suitably hindered silyl
oxide ligands. There are several prior examples (including
MoVO species) related to reaction 2, in which bound silyl oxide
rather than oxo acts as a nucleophile toward a further equivalent
of Me3SiCl, resulting in a chloride rather a silyl oxide
product.36d,41
Complex 12 was prepared by the reaction of 1.10 equiv of
(Me3Si)2S with 5b in acetonitrile, or by an oxidative addition
reaction of 4c and 1.26 equiv of (PhCH2S)2S. Either method
afforded 12 and 4c as a byproduct or unreacted material.
Increased amounts of either sulfur reagent resulted in increased
amounts of 4c in the mixture, suggesting a reductive decom-
position of 12.42 We have not been able to devise an effective
bulk separation of (Et4N)[4c] and (Et4N)[12], which is the
sulfido analogue of 5b. Indeed, complex 12 is easily recognized
1
by its H NMR similarity to 5b. Although a bulk quantity of
pure (Et4N)[12] was not achieved, a small quantity of single
crystals suitable for structure determination (vide infra) was
obtained by slow crystallization from a DMF/ether solution of
the mixture.
(39) Do, Y.; Simhon, E. D.; Holm, R. H. Inorg. Chem. 1985, 24, 1831.
(40) (a) Parkin, G.; Bercaw, J. E. Polyhedron 1988, 7, 2053. (b) Luo,
L.; Lanza, G.; Fragala`, Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1998,
120, 3111.
(41) Stavropoulos, P.; Bryson, N.; Youinou, M.-T.; Osborn, J. A. Inorg.
Chem. 1990, 29, 1807.
(42) This situation appears related to the outcome of a silylation reaction
of a MoVIO2 complex resulting in reduction to MoVO, possibly according
to the reaction [MoVIO2L] + (Me3Si)2S f [MoVO(OSiMe3)L] + 1/2(Me3-
SiS)2.36a.
(43) Drew, M. G. B.; Page, E. M.; Rice, D. A. J. Chem. Soc., Dalton
Trans. 1983, 61.
(44) Rabinovich, D.; Parkin, G. Inorg. Chem. 1995, 34, 6341.
(45) Heckmann, G.; Wolmersha¨user, G. Chem. Ber. 1993, 126, 1071.

Bis(dithiolene)tungsten(IV,VI) Complexes
J. Am. Chem. Soc., Vol. 120, No. 32, 1998 8111
Figure 8. Summary of the oxo transfer reactivity of [W(bdt)2(OSiButPh2)]1- (4c) and [WO(bdt)2(OSiButPh2)]1- (5b) (NMO ) N-methylmorpholine
N-oxide).
MoVIO counterparts, WVIO complexes are relatively common.
Excluding organometallics and peroxides, the principal classes
are halides,47 alkylidenes,48 and alkoxides/silyl oxides.49 No
WVIO or WVIS dithiolenes have been previously prepared.
Reactivity. The following reactivity types of bis(dithiolene)
complexes have thus far been demonstrated and are summarized
in Figure 2: (i) oxidative oxo transfer of 2 and 4bc with Me3-
NO to give 320 and 5ab, respectively; (ii) oxo ligand silylation
resulting in the conversions 2 f 4abc and 3 f 5ab; (iii)
silylation of coordinated silyl oxide in 3 (in situ) and 5b with
Me3SiCl resulting in chloride complex 6; (iv) oxidative sulfur
transfer of 4c with (PhCH2S)2S to afford sulfido complex 12;
(v) oxo/sulfido replacement in the conversion of 5b to 12 with
(Me3Si)2S;50 (vi) reductive oxo transfer reactions of 6 with
(EtO)3P leading to 8 and 9, respectively. In addition, two other
reactions involving displacement of chloride in 6 have been
observed. Treatment of this complex in acetonitrile with 1.0
equiv of LiOBut resulted in the formation of an intense green
tion, the reaction products are unstable to reduction, in contrast
to the silyl oxide complexes 5ab.
Noting the occurrence of oxo transfer reactions i and vi above,
we examined this type of reactivity using other substrates and
the complexes 4c and 5b. The observed reactivity is sum-
1
marized in Figure 8; reactions were monitored by H NMR.
Complex 5b was tested with six potential oxo acceptors; no
clean reaction was observed in five cases. Only the strongly
basic phosphinite PhP(OMe)2 in large excess (g80 equiv)
afforded demonstrable oxo tranfer. This reagent has been
previously shown to reduce [WO2(mnt)2]2- in a clean oxo
transfer reaction.14 Reaction 6 was monitored by 1H NMR (60
°C) and spectrophotometry (25 °C). The weak band of 5b at
[WO(bdt)2(OSiButPh2)]1- + PhP(OMe)2 f
[W(bdt)2(OSiButPh2)]1- + PhP(O)(OMe)2 (6)
600 nm slowly decreased in intensity as product bands at 345
and 417 nm grew in. These features are analogous to the intense
339 and 411 nm bands of 8. The NMR spectrum was consistent
with the formation of [W(bdt)2(PhP(OMe)2)2], which was further
demonstrated by FAB-MS (m/z 804, M+). The formation of
PhP(O)(OMe)2 was confirmed by 31P NMR. With 80 equiv of
phosphinite at 60 °C after 24 h, 30% of 5b remained unreacted
and 30% was converted to 4c. Amounts were determined by
NMR signal integration. In this and subsequent relatively slow
reaction systems, departures from tungsten complex material
balance, are due to hydrolysis of 5b by trace water before or
during oxo transfer. With the evident lack of reactivity of 5b,
occasioned presumably by the difficulty of the WVI/WIV
reduction,14 attention was directed to the oxo acceptor propensity
of 4c.
1
solution. The H NMR spectrum showed clean formation of
alkoxide complex 10. Attempted isolation of this product led
to (Et4N)2[7], indicating reductive decomposition of 10.51
Similarly, reaction of 6 with 1.0 equiv of NaSPh led to an
immediate color change to red-purple and then blue. When
1
monitored by H NMR, the reaction was found to produce
thiolate complex 11,52 which rapidly decomposed to 1, which
has a characteristic blue chromophore. This compound was
isolated and demonstrated by X-ray crystallography to be (Et4N)-
[1].53 While the chloride ligand in 6 is susceptible to substitu-
(46) (a) Eagle, A. A.; Harben, S. M.; Tiekink, E. R. T.; Young, C. G. J.
Am. Chem. Soc. 1994, 116, 9749. (b) Barnard, K. R.; Gable, R. W.; Wedd,
A. G. JBIC 1997, 2, 623.
(47) (a) Page, E. M.; Rice, D. A.; Hagen, K.; Hedberg, L.; Hedberg, K.
Inorg. Chem. 1987, 26, 467. (b) Arnaudet, L.; Bougon, R.; Ban, B.; Lance,
M.; Nierlich, M.; Vigner, J. Inorg. Chem. 1993, 32, 1142. (c) Lu, Y.-J.;
Beer, R. H. Polyhedron 1996, 15, 1667.
(48) (a) Wengrovious, J. H.; Schrock, R. R.; Churchill, M. R.; Missert,
J. R.; Youngs, W. J. J. Am. Chem. Soc. 1980, 102, 4515. (b) Churchill, M.
R.; Rheingold, A. L. Inorg. Chem. 1982, 21, 1357. (c) Bryan, J. C.; Mayer,
J. M. J. Am. Chem. Soc. 1987, 109, 7213.
Summarized in Table 6 are the oxo transfer properties of 4c
in reaction 7 with some 10 substrates XO covering nearly
[W(bdt)2(OSiButPh2)]1- + XO f
[WO(bdt)2(OSiButPh2)]1- + X (7)
(49) (a) Cotton, F. A.; Schwotzer, W.; Shamshoum, E. S. J. Organomet.
Chem. 1985, 296, 55. (b) Corazza, F.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,
C. Inorg. Chem. 1991, 30, 4465. (c) Chisholm, M. H.; Cook, C. M.; Folting,
K.; Streib, W. E. Inorg. Chim. Acta 1992, 198, 63. (d) Persson, C.;
Oskarsson, A° .; Andersson, C. Polyhedron 1992, 11, 2039. (e) Heppert, J.
A.; Dietz, S. D.; Eilerts, N. W.; Henning, R. W.; Morton, M. D.;
Takusagawa, F. Organometallics 1993, 12, 2565.
entirely the thermodynamic scale of oxo transfer reactivity.54
A broad range of reactivity is encountered. Tertiary amine
oxides, which are near the top of the scale, react quickly and
relatively cleanly. Trimethylamine N-oxide, N-methylmorpho-
line N-oxide, and Ph2SeO gave quantitative conversions. The
slow reactivity of the strong oxo donor PhIO arises from its
sparing solubility in acetonitrile. Using PhI18O and Ph2Se18O,
oxo transfer was demonstrated from isotope shifts of WdO
stretching frequencies and FAB-MS of the products (cf.
Experimental Section). Interestingly, 4c is capable of reducing
Ph3PO, although forcing conditions (60 °C) are required to
achieve an appreciable reaction rate. On the thermodynamic
reactivity scale, the gaseous couples Me3N + 1/2O2 f Me3NO
(50) For the related WVIO2/WVIS2 conversion with the same reagent, cf:
Yu, S.-B.; Holm, R. H. Inorg. Chem. 1989, 28, 4385.
(51) The formation of 7 may result from intramolecular hydrogen
abstraction from the But group with elimination of isobutene and transient
formation of an WV-OH species. The latter itself, or by bimolecular
condensation to form water, could supply the protons necessary for
decoordination of bdt, which can function as a ligand and as a reductant
when bound or free. Use of NaOMe led to a mixture of 2 and 7, again
requiring a reductive pathway.
(52) 1H NMR of 11 (CD3CN): δ 6.90 (4, dd), 7.12 (1, t), 7.32 (2, d),
7.40 (4, dd), 7.75 (2, d).
(53) (Et4N)[1] crystallizes in monoclinic space group P21/n with a )
7.7645(1) Å, b ) 16.5852(3) Å, c ) 27.0389(4) Å, and â ) 94.089(1)° at
213 K. The structure was solved to the point of compound identification
but was not fully refined. The structure of (Ph4P)[1] is available.20
1
(-2 kcal/mol),15 Ph2Se + /2O2 f Ph2SeO (-17 kcal/mol,
(54) Holm, R. H.; Donahue, J. P. Polyhedron 1993, 12, 571.

8112 J. Am. Chem. Soc., Vol. 120, No. 32, 1998
Lorber et al.
Table 6. Oxo Transfer Reactivity of [WIV(bdt)2(OSiButPh2)]1-
representations of bis(dithiolene) desoxo W(IV) five- and six-
coordinate stereochemistry. Complexes 5a,b and 6 serve the
same function for the monooxo W(VI) state. In a stereochem-
ical (but not electronic) sense, silyl oxide or chloride simulate
binding of hydroxide and protein-bound ligands, should the latter
eventuate in either family of enzymes. Complex 12 fulfills a
similar purpose for any site containing the WVIdS group.
Consequently, these molecules may be useful auxiliaries in
X-ray absorption edge and EXAFS studies2,6 and resonance
Raman examination5 of tungsten enzyme sites. Simple oxo
transfer reactivity, as established here and exemplified in biology
by, e.g., molybdenum DMSO reductases,12 is not yet known as
a function of tungstoenzymes. The reaction catalyzed by the
AOR family, minimally RCHO + [O] h RCOOH, as with the
molybdoenzyme xanthine oxidase,12 must have a different
mechanism. Indeed, molybdenum aldehyde oxidases belong to
the xanthine oxidase enzyme family, and in the oxidized state
contain the MoVIOS group.12 While we do not discount an all-
oxygen ligand group such as WVIO(OH), conceivably a WVI-
OS group or a protonated form (e.g., WVIO(SH)) may intervene
in oxidized AOR enzymes. Bis(dithiolene)tungsten species of
these types and the sites shown in Figure 1 that may apply to
the F(M)DH family based on sequence homologies57 represent
attractive objectives for both their structural and functional
properties. Synthesis of such compounds is now in progress
in this laboratory. An account of bis(dithiolene)molybdenum
complexes related to the tungsten group presented here is
forthcoming.58
with Substrates XOa
5b formed 4c remaining
XO
Me3NO
equiv T, °C
time
(%)
(%)
2
20
20
<10 min
<10 min
100
99
0
0
O–
10
+
O
N
Me
(PhCH2)3NO
PhNdN(O)Ph
Ph2SeO
PhIO (insol.)
Ph3AsO
1
3
10
5
20
80
3
60
25
20
60
20
20
60
60
60
60
20
15 h
2 d
<10 min
12 h
15 h
2 d
21 h
5 d
25 h
84
64
100
95
45
60
35
9
9
23
0
0
0
37
55
57
71
Ph3PO
Me2SO
21
40
60
21 h
40
50
S
O
a Conditions: (Et4N)[W(bdt)2(OSiButPh2)] (1 equiv, ∼3 mM) in
1
CD3CN solution; reactions analyzed by H NMR.
estimated),55 and Ph3P + 1/2O2 f Ph3PO (-74 kcal/mol) with
the indicated ∆H values indicate the large spread in oxo donor
ability. Amine oxides are among the more reactive donors while
phosphine oxides are near the bottom of the scale. From these
results, 4c emerges as a strong, albeit sluggish, oxo acceptor in
1
the couple 4c + /2O2 f 5b for which ∆H j -74 kcal/mol.
The oxo transfer chemistry of tungsten is relatively little
developed compared to that of molybdenum, which is the most
extensive of any element. The small body of tungsten-mediated
oxo transfer reactions preceding this work is summarized
elsewhere.14,56
Acknowledgment. This research was supported by National
Science Foundation Grant CHE 95-23830 (to R.H.H.) and by
grants from the Swedish Natural Science Research Council, and
the Swedish Department of Education (to E.N.). X-ray diffrac-
tion equipment was obtained by NIH Grant 1 S10 RR 02247.
Biological Relevance. Because the (partial) coordination unit
of only one tungsten enzyme, Pf AOR, is defined and the
number of pterin cofactors bound in other enzymes is not
generally established, we can at present speak only of the
potential relevance of the complexes studied here. However,
if members of the AOR enzyme family are structurally related,
as seems likely,2 bis(dithiolene) coordination is pervasive and
the species in Figure 2 may be viewed in that context. The
complexes 4a-c and 8/9 provide the initial structural
Supporting Information Available: Crystallographic data
for the 10 compounds in Tables 1 and 2, including intensity
collections, positional, and thermal parameters, interatomic
distances and angles, and calculated hydrogen atom positions
(96 pages, print/PDF). See any current masthead page for
ordering information and Web access instructions.
JA981015O
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(56) (a) Holm, R. H. Chem. ReV. 1987, 87, 1401. (b) Holm, R. H. Coord.
Chem. ReV. 1990, 100, 183. (c) Enemark, J. H.; Young, C. G. AdV. Inorg.
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(58) Donahue, J. P.; Goldsmith, C. R.; Nadiminti, U.; Holm, R. H. Results
to be published.