An Expanded Set of Functional Groups in Bis(dithiolene)tungsten(IV,VI) Complexes Related to the Active Sites of Tungstoenzymes, Including W- IV-SR and WVI-O(SR)

Article abstract of DOI:10.1021/ic030301k

The active sites of tungstoenzymes have the formulations W ^IV,VL(S₂pd)₂ and W^VILL′(S ₂pd)₂, in which two pyranopterindithiolene cofactor ligands (S₂pd) are chelated to a tungsten atom. Ligands L and/or L′ are not fully defined in any wild-type enzyme. The feasibility of various coordination fragments (functional groups) in potential bis(dithiolene)tungsten site analogues has been examined in previous work by exploratory synthesis. This investigation expands the range of accessible functional groups. The synthetic scheme originates with [W(CO) ₂(S₂C₂Me₂)₂], whose carbonyl groups are labile to substitution. Complexes [W ^IV,VILL′(S₂C₂Me₂) ₂]^1- are described in terms of their functional groups W^IV,VILL′. Reaction of the dicarbonyl with formate in acetonitrile/THF affords W^IV(CO)(η¹-HCO₂) (4) and in Me₂SO W^VIO(η¹-HCO₂) (7) by an oxo transfer reaction. Carboxylates yield six-coordinate W ^IV(η²-O₂CR) (1-3, R = Ph, Me, Bu ^t with C_2v symmetry. Reaction of 3 (R = Bu^t with Me₃SiSR (R = C₆H₂-2,4,6-Pr ₃ⁱ) gives W^IV(SR) (5), which undergoes oxo and sulfido atom transfer to form W^VIO(SR) (8) and W^VIS(SR) (9), respectively. Attempts to prepare corresponding selenolate complexes, pertinent to the active site of formate dehydrogenase, were unsuccessful, including reactions of W^VIOCI (10) with RSe^-. Structure proofs of 2-10 were obtained by X-ray structure determinations. Some 26 functional group types in bis(dithiolene)W(IV,V,VI) molecules have now been achieved by synthesis. It remains to be seen which are incorporated in an enzyme site. A number of them (e.g., 5) are directly analogous to molybdoenzyme sites, and may possess corresponding reactivity with biological substrates, as do W^IV(OR)/W^VIO(OR) (prepared earlier) in the reduction of N- and S-oxides by atom transfer.

Full text of DOI:10.1021/ic030301k

Inorg. Chem. 2004, 43, 1302−1310
An Expanded Set of Functional Groups in Bis(dithiolene)tungsten(IV,VI)
Complexes Related to the Active Sites of Tungstoenzymes, Including
IV
VI
W −SR and W −O(SR)
Jianfeng Jiang and R. H. Holm*
Department of Chemistry and Chemical Biology, HarVard UniVersity,
Cambridge, Massachusetts 02138
Received October 24, 2003
IV,V
VI
The active sites of tungstoenzymes have the formulations W L(S pd)2 and W LL′(S pd)2, in which two
2
2
pyranopterindithiolene cofactor ligands (S pd) are chelated to a tungsten atom. Ligands L and/or L′ are not fully
2
defined in any wild-type enzyme. The feasibility of various coordination fragments (functional groups) in potential
bis(dithiolene)tungsten site analogues has been examined in previous work by exploratory synthesis. This investigation
expands the range of accessible functional groups. The synthetic scheme originates with [W(CO)2(S C Me2)2],
2
2
whose carbonyl groups are labile to substitution. Complexes [WIV,VILL′(S C Me2)2]1- are described in terms of their
2
2
IV
functional groups WIV,VILL′. Reaction of the dicarbonyl with formate in acetonitrile/THF affords W (CO)(η1-HCO )
2
(4) and in Me2SO W O(η1-HCO ) (7) by an oxo transfer reaction. Carboxylates yield six-coordinate W (η2-O CR)
(1−3, R ) Ph, Me, Bu) with C symmetry. Reaction of 3 (R ) Bu) with Me3SiSR (R ) C H -2,4,6-Pr3) gives
VI
IV
2
2
t
t
i
2v
6 2
IV
VI
VI
W (SR) (5), which undergoes oxo and sulfido atom transfer to form W O(SR) (8) and W S(SR) (9), respectively.
Attempts to prepare corresponding selenolate complexes, pertinent to the active site of formate dehydrogenase,
VI
were unsuccessful, including reactions of W OCl (10) with RSe-. Structure proofs of 2−10 were obtained by X-ray
structure determinations. Some 26 functional group types in bis(dithiolene)W(IV,V,VI) molecules have now been
achieved by synthesis. It remains to be seen which are incorporated in an enzyme site. A number of them (e.g.,
5) are directly analogous to molybdoenzyme sites, and may possess corresponding reactivity with biological substrates,
IV
VI
as do W (OR)/W O(OR) (prepared earlier) in the reduction of N- and S-oxides by atom transfer.
Introduction
physiological oxidation state (WVI,V,IV) remains undefined.
The most significant structural feature is the presence of two
pyranopterindithiolene cofactor ligands bound in the oxidized
mononuclear unit WVI(S2pd)2 of all enzymes that have been
crystallographically examined (1.85-2.3 Å resolution). The
geometry of this unit places additional ligands in a cis
arrangement. Structural data together with other consider-
ations and conjectures have led to the putative oxidized active
sites a-f set out in Figure 1.2,5
The site in Pyrococcus furiosus AOR contains two
probable oxygen ligands, neither of which is derived from
the protein.7 Tungsten EXAFS analysis has detected two
WdO distances at 1.74 Å.8 In formaldehyde oxidoreductase
from the same organism, an apparent oxygen ligand is
The discovery and characterization of tungsten-containing
enzymes1-5 provides an unanticipated opportunity for the
development of synthetic systems that can potentially
disclose intrinsic structural and reactivity aspects of active
sites. These enzymes derive from bacterial or archaeal
sources and have been classified into two major groups, the
AOR and F(M)DH families.1,2,6 While these enzymes as a
class are undergoing continuing delineation, the complete
active site structure of any wild-type enzyme in any
* To whom correspondence should be addressed. E-mail: holm@
chemistry.harvard.edu.
(1) Johnson, M. K.; Rees, D. C.; Adams, M. W. W. Chem. ReV. 1996,
96, 2817-2839.
(2) Hille, R. Trends Biochem. Sci. 2002, 27, 360-367.
(3) Garner, C. D.; Stewart, L. J. Met. Ions Biol. Syst. 2002, 39, 699-726.
(4) Roy, R.; Adams, M. W. W. Met. Ions Biol. Syst. 2002, 39, 673-697.
(5) Vorholt, J. A.; Thauer, R. K. Met. Ions Biol. Syst. 2002, 39, 571-
619.
(7) Chan, M. K.; Mukund, S.; Kletzin, A.; Adams, M. W. W.; Rees, D.
C. Science 1995, 267, 1463-1469.
(8) George, G. N.; Prince, R. C.; Mukund, S.; Adams, M. W. W. J. Am.
Chem. Soc. 1992, 114, 3521-3523.
(6) Abbreviations are given in Chart 1.
1302 Inorganic Chemistry, Vol. 43, No. 4, 2004
10.1021/ic030301k CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/30/2004

Bis(dithiolene)tungsten(IV,VI) Complexes
tallographically determined to contain the monoprotonated
site [MoVI(OH)(Se‚Cys)(S2pd)2].14,15
The sites in Figure 1 are all plausible objectives for
synthesis and structural and reactivity examination. Several
site analogues have already been prepared. The complexes
[WO2(bdt)2]2-,16 [WO2(ndt)2]2-,17 [WO2(mnt)2]2-,18 and
[WO2(S2C2Me2)2]2- 19 are suitable structural analogues of site
a. Their reactivity, however, has not been fully investigated
in the enzymatic context. The complexes [WO(OR)-
(S2C2Me2)2]1- (R ) Ph, Pri) are excellent structural and
reactivity analogues of site b. Functional reaction systems
based on the reduction of S-oxides (DMSOR activity) and
N-oxides (TMAOR activity) have been amply demon-
strated.20,21 No analogues exist for sites c-f. The chemistry
of bis(dithiolene)tungsten species having been largely un-
revealed, we have in recent investigations utilized exploratory
synthesis to determine what coordination fragments (equiva-
lently, functional groups) WIV,VL and WVILL′ are capable
of existence in bis(dithiolene) species.19-24 Certain of these
then become candidates for functionalities in enzyme sites.
Much of this research is summarized elsewhere.25 We
continue that line of inquiry here, directed at unknown
functional groups and also, given our interest in FDH, bis-
(dithiolene)tungsten complexes of formate.
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
following ligand salts were prepared from equimolar reactants and
were isolated as colorless crystalline solids from the indicated
recrystallization medium: (Et4N)(ButCO2), from ButCO2H and 25%
Et4NOH in methanol, acetonitrile/ether; (Et4N)(MeCO2), from Et4-
NCl and NaO2CMe in acetonitrile, acetonitrile/THF/ether; (Et4N)-
(HCO2), from HCO2Ag and Et4NCl in methanol. The compound
Me3SiSC6H2-2,4,6-Pri3 was prepared by a procedure similar to that
for Me3SiSPh.26 Representative compounds were analyzed. All
compounds were identified by X-ray structure determinations.
(a) WIV Complexes. (Et4N)[W(O2CMe)(S2C2Me2)2]. To a
solution of 95.5 mg (0.505 mmol) of (Et4N)(MeCO2) in 2 mL of
acetonitrile was added a dark purple solution of 226 mg (0.475
mmol) of [W(CO)2(S2C2Me2)2]23 in 5 mL of THF. The solution
became red-brown immediately with accompanying vigorous gas
Figure 1. Possible oxidized active sites in tungstoenzymes grouped by
family, except for DMSO reductase (see text), and the pyranopterindithiolene
cofactor ligand (R absent or a nucleotide).
reported at -2.1 Å.9 A reasonable proposal is dioxo site a
or its monoprotonated form [WVIO(OH)(S2pd)2], in which
case the situation would be analogous to that in molybdenum-
containing arsenite oxidase.10 Site b is that of W-DMSOR,
an isoenzyme of Mo-DMSOR from Rhodobacter capsula-
tus.11 While W-DMSOR is not known as a wild-type enzyme
and thus is not classified in the foregoing families, it is the
only tungstoenzyme for which the complete active site
coordination unit is established. Some or all of sites c-f may
apply to members of the F(M)DH family. The only structural
information available is for DesulfoVibrio gigas W-FDH,
whose site contains a selenocysteinate and one additional
oxygen or sulfur ligand.12,13 Site d is an attractive possibility
inasmuch as two E. coli Mo-FDH isoenzymes were crys-
(14) Boyington, J. C.; Gladyshev, V. N.; Khangulov, S. V.; Stadtman, T.
C.; Sun, P. D. Science 1997, 275, 1305-1308.
(15) Jormakka, M.; To¨rnroth, S.; Byrne, B.; Iwata, S. Science 2002, 295,
1863-1868.
(16) Ueyama, N.; Oku, H.; Nakamura, A. J. Am. Chem. Soc. 1992, 114,
7310-7311.
(17) Oku, H.; Ueyama, N.; Nakamura, A. Bull. Chem. Soc. Jpn. 1996, 69,
3139-3150.
(18) Das, S. K.; Biswas, D.; Maiti, R.; Sarkar, S. J. Am. Chem. Soc. 1996,
118, 1387-1397.
(9) Hu, Y.; Faham, S.; Roy, R.; Adams, M. W. W.; Rees, D. C. J. Mol.
Biol. 1999, 286, 899-914.
(19) Sung, K.-M.; Holm, R. H. Inorg. Chem. 2001, 40, 4518-4525.
(20) Sung, K.-M.; Holm, R. H. J. Am. Chem. Soc. 2001, 123, 1931-1943.
(21) Sung, K.-M.; Holm, R. H. J. Am. Chem. Soc. 2002, 124, 4312-4320.
(22) Lorber, C.; Donahue, J. P.; Goddard, C. A.; Nordlander, E.; Holm, R.
H. J. Am. Chem. Soc. 1998, 120, 8102-8112.
(10) Ellis, P. J.; Conrads, T.; Hille, R.; Kuhn, P. Structure 2001, 9, 125-
132.
(11) Stewart, L. J.; Bailey, S.; Bennett, B.; Charnock, J. M.; Garner, C.
D.; McAlpine, A. S. J. Mol. Biol. 2000, 299, 593-600.
(12) Raaijmakers, H.; Teixeira, S.; Dias, J. M.; Almendra, M. J.; Brondino,
C. D.; Moura, I.; Moura, J. J. G.; Romno, M. J. J. Biol. Inorg. Chem.
2001, 6, 398-404.
(13) Raaijmakers, H.; Macieira, S.; Dias, J. M.; Texeira, S.; Bursakov, S.;
Huber, R.; Moura, J. J. G.; Moura, I.; Romno, M. J. Structure 2002,
10, 1261-1272.
(23) Goddard, C. A.; Holm, R. H. Inorg. Chem. 1999, 38, 5389-5398.
(24) Sung, K.-M.; Holm, R. H. Inorg. Chem. 2000, 39, 1275-1281.
(25) Enemark, J. H.; Cooney, J. J. A.; Wang, J.-J.; Holm, R. H. Chem.
ReV. 2004, 104, 1175-1200.
(26) Davis, F. A.; Rizvi, S. Q. A.; Ardecky, R.; Gosciniak, D. J.; Friedman,
A. J.; Yocklovich, S. G. J. Org. Chem. 1980, 45, 1650-1653.
Inorganic Chemistry, Vol. 43, No. 4, 2004 1303

Jiang and Holm
evolution, and was stirred for 35 min. Ether (15 mL) was layered
on the reaction mixture. The solid that separated was washed with
ether (3 × 2 mL) and dried to afford the product as 189 mg (63%)
of a red-brown microcrystalline solid. Absorption spectrum
(acetonitrile): λmax (ꢀM) 330 (4200), 381 (2900), 408 (2900) nm.
IR (KBr): νCOO 1439 cm-1. 1H NMR (CD3CN, anion): δ 1.48 (s,
3), 2.68 (s, 12).
(Et4N)[W(O2CBut)(S2C2Me2)2]. To a solution of 101 mg (0.437
mmol) of (Et4N)(ButCO2) in 1 mL of acetonitrile was added a
solution of 201 mg (0.422 mmol) of [W(CO)2(S2C2Me2)2] in 3 mL
of THF. The solution was stirred for 1 h. Ether (25 mL) was layered
on the reaction mixture. The solid that separated was washed with
ether (3 × 3 mL) and dried to afford the product as 203 mg (74%)
of a red-brown microcrystalline solid. Absorption spectrum
(acetonitrile): λmax (ꢀM) 333 (3900), 384 (3300), 403 (3300), 474
(1100), 670 (620) nm. IR (KBr): νCOO 1438 cm-1. 1H NMR (CD3-
CN, anion): δ 0.87 (s, 9), 2.68 (s, 12). Anal. Calcd for C21H41-
NO2S4W: C, 38.71; H, 6.34; N, 2.15; S, 19.68. Found: C, 38.55;
H, 6.41; N, 2.14; S, 19.49.
(Et4N)[W(CO)(O2CH)(S2C2Me2)2]. A solution of 21 mg (0.12
mmol) of (Et4N)(HCO2) in 0.5 mL of acetonitrile was treated with
a solution of 52 mg (0.11 mmol) of [W(CO)2(S2C2Me2)2] in 1.5
mL of THF at -40 °C. The same color change and gas evolution
occurred as in the preceding preparations. The reaction mixture
was stirred for 5 min at -40 °C, and cold ether (40 mL) was layered
on. The solid that separated was washed with ether (3 × 2 mL)
and dried to give the product as 21 mg (32%) of a red microcrys-
talline solid. 1H NMR (CD3CN, anion): δ 2.59 (s, 12), 7.95 (s, 1).
The compound is unstable in solution at ambient temperature;
analytical data could not be obtained.
The black reaction mixture was stirred for 8 min and cooled to
-40 °C. Cold ether (20 mL, -40 °C) was layered on, causing
separation of 17 mg (41%) of a dark red crystalline solid whose
1H NMR spectrum was identical to the product of method A.
(Et4N)[WO(O2CH)(S2C2Me2)2]. To a purple suspension of 30
mg (0.063 mmol) of [W(CO)2(S2C2Me2)2] in 0.8 mL of Me2SO
was added 12 mg (0.069 mmol) of (Et4N)(HCO2). The reaction
mixture was stirred for 10 min during which the solid dissolved
and a dark red solution developed. Addition of 20 mL of cold ether
(0 °C) caused immediate formation of an oily precipitate, which
was washed with ether (3 × 3 mL) and dissolved in 3:7 acetonitrile/
THF (v/v). The solution was layered with cold ether/pentane (1:1
v/v, -40 °C) and stored at -40 °C. The solid that separated was
washed with ether (3 × 2 mL) and dried, giving the product as 11
mg (29%) of a dark red microcrystalline solid. Absorption spectrum
(acetonitrile): λmax (ꢀM) 294 (6300), 358 (2200), 512 (1300), 620
(2000), 687 (1900) nm. IR (KBr): νWO 887 cm-1, νCOO 1653 cm-1
1H NMR (CD3CN, anion): δ 2.23 (s, 12), 8.44 (s, 1).
.
(Et4N)[WO(SC6H2-2,4,6-Pri3)(S2C2Me2)2]. To a solution of 62
mg (0.079 mmol) of (Et4N)[W(SC6H2-2,4,6-Pri3)(S2C2Me2)2] in 1
mL of acetonitrile/THF (1:4 v/v) was added a solution of 27 mg
(0.081 mmol) of Ph3AsO in 1 mL of THF. The red solution
immediately changed to purple. The reaction mixture was stirred
for 5 min, cold ether (20 mL, -40 °C) was layered on, and the
mixture was maintained at -40 °C. The solid that separated was
washed with cold ether (3 × 2 mL) and dried. The product was
obtained as 43 mg (68%) of a purple microcrystalline solid.
Absorption spectrum (acetonitrile): λmax (ꢀM) 340 (5100), 411
(3600), 556 (3800) nm. IR (KBr): νWO 902 cm-1. 1H NMR (CD3-
CN, anion): δ 1.19 (d, 12), 1.22 (d, 6), 2.23 (s, 12), 2.86 (m, 1),
4.23 (m, 2), 6.97 (s, 2). Anal. Calcd for C31H55NOS5W: C, 46.49;
H, 6.92; N, 1.75; S, 20.02. Found: C, 46.58; H, 7.03; N, 1.79; S,
20.08.
(Et4N)[WS(SC6H2-2,4,6-Pri3)(S2C2Me2)2]. A solution of 62 mg
(0.079 mmol) of (Et4N)[W(SC6H2-2,4,6-Pri3)(S2C2Me2)2] in 1 mL
of acetonitrile/THF (1:4 v/v) was treated with a solution of 22 mg
(0.079 mmol) of (PhCH2S)2S in 1 mL of THF. The red solution
turned to red-purple immediately. The reaction mixture was stirred
for 5 min, and cold ether (20 mL, -40 °C) was layered on. The
mixture was maintained at -40 °C. The solid that separated was
washed with ether (3 × 2 mL) and dried. The product was obtained
as 27 mg (42%) of a red microcrytalline solid. Absorption spectrum
(acetonitrile): λmax (ꢀM) 274 (9700), 335 (6500), 391 (5200), 524
(4100) nm. 1H NMR (CD3CN, anion): δ 1.19 (d, 12), 1.24 (d, 6),
2.32 (s, 12), 2.87 (m, 1), 4.17 (m, 2), 6.92 (s, 2). Anal. Calcd for
C31H55NS6W: C 45.52; H, 6.78; N, 1.71; S, 23.52. Found: C, 45.46;
H, 6.84; N, 1.68; S, 23.14.
(Et4N)[WOCl(S2C2Me2)2]. A red solution of 30 mg (0.042
mmol) of (Et4N)2[WO2(S2C2Me2)2]19 in 0.8 mL of acetonitrile was
treated with 10 mg (0.092 mmol) of Me3SiCl. The reaction mixture
immediately assumed a purple color and was stirred for 5 min.
Solvent was removed in vacuo, and the residue was extracted with
4 mL of acetonitrile/THF (1:4 v/v). Cold ether (20 mL, -40 °C)
was layered onto the extract, and the mixture was maintained at
-40 °C for 2 days. The solid was collected, washed with ether (3
× 2 mL), and dried to afford the product as 8.0 mg (29%) of purple-
black microcrystalline solid. 1H NMR (CD3CN, anion): δ 2.26 (s).
In the sections which follow, tungsten complexes are referred
to by the numerical designations in Chart 1.
(Et4N)[W(SC6H2-2,4,6-Pri3)(S2C2Me2)2]. A solution of 84 mg
(0.13 mmol) of (Et4N)[W(O2CBut)(S2C2Me2)2] in 1 mL of aceto-
nitrile was treated with 44 mg (0.14 mmol) of Me3SiSC6H2-2,4,6-
Pri3. The red-brown solution became red immediately. The reaction
mixture was stirred for 10 min, and the solvent was removed in
vacuo. The residue was washed with ether (3 × 2 mL) and dissolved
in 2.5 mL of THF/acetonitrile (4:1 v/v). The solution was filtered
through Celite, and ether (40 mL) was layered on the filtrate. The
solid which formed was washed with ether (3 × 2 mL) and dried.
The product was obtained as 61 mg (60%) of a red microcrystalline
solid. Absorption spectrum (acetonitrile): λmax (ꢀM) 294 (13 600),
1
313 (sh, 11 700), 345 (sh, 7800), 430 (3500), 517 (1300) nm. H
NMR (CD3CN, anion): δ 1.08 (d, 12), 1.17 (d, 6), 2.77 (s, 12),
2.80 (m, 1), 3.72 (m, 2), 6.76 (s, 2). Anal. Calcd for C31H55NS5W:
C, 47.44; H, 7.06; N, 1.78; S, 20.43. Found: C, 47.37; H, 6.95; N,
1.74; S, 20.37.
(b) WVI Complexes. (Et4N)[WO(O2CPh)(S2C2Me2)2]. Method
A. To a suspension of 33 mg (0.058 mmol) of (Et4N)[WO(S2C2-
Me2)2]19 in 1 mL of acetonitrile was added a solution of 8.0 mg
(0.033 mmol) of dibenzoyl peroxide in 0.5 mL of acetonitrile. The
reaction mixture immediately became black and was stirred for 5
min. Cold ether/pentane (25 mL, 1:1 v/v, -40 °C) was layered on
the reaction mixture, which was maintained at -40 °C. The solid
that separated was washed with ether (3 × 2 mL) and dried to
yield the product as 29 mg (73%) of a dark red microcrystalline
solid. Absorption spectrum (acetonitrile): λmax (ꢀM) 381 (sh, 2500),
509 (1300), 610 (1900) nm. IR (KBr): νCOO 1648 cm-1, νWO 905
cm-1. 1H NMR (CD3CN, anion): δ 2.26 (s, 12), 7.41 (m, 2), 7.51
(m, 1), 8.01 (m, 2). Anal. Calcd for C23H37NO3S4W: C 40.17; H,
5.42; N, 2.04; S, 18.65. Found: C, 40.04; H, 5.41; N, 2.06; S, 18.76.
Method B. To a suspension of 41 mg (0.061 mmol) of
(Et4N)[W(O2CPh)(S2C2Me2)2] in 1 mL of acetonitrile was added a
solution of 20 mg (0.060 mmol) of Ph3AsO in 1 mL of acetonitrile.
X-ray Structure Determinations. The nine compounds in Table
1 were structurally identified. Suitable crystals of (Et4N)[2, 4] (red-
brown plates), (Et4N)[3, 5] (red-brown blocks), (Et4N)[6, 7, 10]
(dark purple blocks), and (Et4N)[8, 9] (thin purple plates) were
1304 Inorganic Chemistry, Vol. 43, No. 4, 2004

Bis(dithiolene)tungsten(IV,VI) Complexes
Table 1. Crystallographic Dataa for Bis(dithiolene)W(IV,VI) Complexes
(Et4N)[2]
(Et4N)[3]
(Et4N)[4]
(Et4N)[5]
(Et4N)[6]
(Et4N)[7]
(Et4N)[8]
(Et4N)[9]
(Et4N)[10]
formula
C18H35N-
O2S4W
609.56
monoclinic
C2
C21H41N-
O2S4W
651.64
orthorhombic monoclinic
Pnma
C18H33N-
O3S4W
623.54
C31H55N-
S5W
785.91
monoclinic
P21/n
C23H37N-
O3S4W
687.63
monoclinic
P21/c
C17H33N-
O3S4W
611.53
monoclinic
P21/c
C31H55N-
OS5W
801.91
monoclinic
P21/c
C31H55N-
OS6W
817.98
monoclinic
P21/c
C16ClH32N-
OS4W
601.97
monoclinic
P21/n
213
fw
cryst syst
space group
T, K
P21/n
193
213
213
193
193
193
193
193
Z
2
4
4
4
4
4
4
4
4
a, Å
b, Å
c, Å
15.725(3)
7.949(2)
9.710(2)
97.093(4)
1204.4(4)
1.681
17.734(1)
16.533(1)
9.4002(7)
10.009(7)
18.64(1)
13.668(9)
108.99(2)
2411(3)
1.718
11.397(2)
11.463(2)
19.149(2)
109.853(2)
3591.7(7)
1.453
14.183(2)
11.792(2)
17.008(2)
97.735(2)
2818.7(6)
1.620
8.974(1)
15.043(2)
17.928(3)
97.576(3)
2399.1(6)
1.693
10.71(1)
18.05(2)
18.79(2)
93.86(2)
3625(6)
1.468
20.84(3)
10.91(2)
16.38(3)
93.73(2)
3713(10)
1.454
8.960(1)
16.507(2)
15.718(2)
91.828(2)
2323.6(4)
1.721
â, deg
V, Å3
2756.1(4)
1.570
4.509
d
calcd, g/cm3
µ, mm-1
5.154
5.516
3.527
4.418
5.179
3.498
3.469
5.450
θ range, deg
2.11-22.50 2.30-22.50
1.152
1.92-22.50 1.37-22.50 2.11-22.50 1.77-25.00 1.57-22.50 2.11-22.50 1.79-28.32
1.096
3.56(9.56)
GOF (F2)
1.1561
2.67(7.61)
0.958
2.28(5.09)
1.013
2.32(5.80)
0.854
2.41/4.38
0.885
3.71(7.78)
0.643
6.58(13.61)
1.019
7.80(14.27)
c
R1b (wR2 ), % 2.91(7.22)
a Mo KR radiation. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
2
2
2
Chart 1. Designation of Complexes and Abbreviations
figure of merit. Structures were solved by direct methods with
SHELXL-97 and refined against all data in the 2θ ranges by full-
matrix least-squares on F2 using SHELXL-97. All non-hydrogen
atoms, including those of disordered cations, were refined aniso-
tropically. Hydrogen atoms at idealized positions were included in
final refinements. Cell parameters and final agreement factors are
given in Table 1. (See paragraph at the end of this article for
Supporting Information available.)
Other Physical Measurements. All measurements were per-
formed under anaerobic conditions. Absorption spectra were
1
recorded with a Varian Cary 50 Bio spectrophotometer. H NMR
spectra were obtained with Varian Mercury 300/400 spectrometers.
IR spectra were measured in KBr pellets with a Nicolet 5PC FT-
IR instrument.
Results and Discussion
We seek molecules that are analogous to the putative bis-
(dithiolene)tungsten sites c-f in Figure 1 and examples of
formate binding to tungsten centers that are possibly pertinent
to one or more reaction stages of FDH. The synthetic scheme
is set out in Figure 2. As in previous synthetic studies,19-21,23,24
we utilize [W(CO)2(S2C2Me2)2],23,28 whose carbonyl groups
are labile to substitution, as a starting material. Isolated yields
are indicated below. All new complexes were characterized
by X-ray structure determinations; structures are shown in
Figures 3-6, and leading structural parameters are collected
in Tables 2 and 3. For the most part, these parameters are in
good agreement with closely related molybdenum29,30 and
tungsten19,20,23,24 bis(dithiolenes), and do not require further
discussion. The ranges of mean C-C and S-C bond
distances are 1.33-1.34 Å and 1.73-1.79 Å, respectively.
These values are sufficiently close to the typical bond lengths
(sp2)CdC(sp2) ) 1.331(9) Å and S-C(sp2) ) 1.75(2) Å31
to warrant description of the ligand as a classical ene-1,2-
dithiolate, as is the case for all bis(dithiolene)tungsten
obtained either by layering ether onto or ether vapor diffusion into
acetonitrile solutions. These mixtures were allowed to stand 2-3
days at room temperature ((Et4N)[2, 3, 5]) or at -40 °C (others).
Crystals were coated in grease and mounted on a Siemens (Bruker)
SMART CCD area detector instrument with Mo KR radiation. Data
were collected at 213 or 193 K with ω scans of 0.3° per frame,
with 10, 20, or 30 s frames, such that 1271 frames were collected
for a hemisphere of data.
The first 50 frames were recollected at the end of the data
collection to monitor intensity decay; no significant decay was
observed for any compound. Data out to 2θ of 50° and 56° were
used for (Et4N)[7] and (Et4N)[10], respectively, but for the other
compounds data out to 2θ of 45° were employed because of the
low quality of the high-angle data. Cell parameters were retrieved
using SMART software and refined using SAINT software on all
observed reflections between 2θ of 3° and the upper thresholds.
Data reduction was performed with SAINT, which corrects for
Lorentz polarization and decay. Absorption corrections were applied
with SADABS, as described by Blessing.27 All space groups were
assigned by analysis of symmetry and systematic absences deter-
mined by XPREP. The space group for (Et4N)[2] was selected from
noncentrosymmetric choices of the basis of the lowest combined
(28) Fomitchev, D.; Lim, B. S.; Holm, R. H. Inorg. Chem. 2001, 40, 645-
654.
(29) Lim, B. S.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 2000, 39, 263-
273.
(30) Lim, B. S.; Holm, R. H. J. Am. Chem. Soc. 2001, 123, 1920-1930.
(31) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.
G.; Taylor, R. In International Tables of Crystallography; Wilson, A.
J. C., Ed.; Kluwer Academic Publishers: Boston, 1995; section 9.5.
(27) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38.
Inorganic Chemistry, Vol. 43, No. 4, 2004 1305

Jiang and Holm
Figure 2. Synthetic scheme for bis(dithiolene)tungsten complexes based on [W(CO)2(S2C2Me2)2] and affording WIV (1-5) and WVI (6-10) complexes.
Table 2. Selected Bond Distances (Å) and Angles (deg) of
Table 3. Selected Bond Distances (Å) and Angles (deg) of
Bis(dithiolene)W(IV) Complexes
Bis(dithiolene)W(VI) Complexes
2
3
4
5
6
7
8
9
10
W-Sa
W-Sax
W-Oa
W-C
S-Ca
C-Ca
δc
2.328(6)
2.301(1)
2.37(2)
2.313(5)
2.319(1)
W-Sa,b
W-Strans
WdO/S
2.406(5) 2.392(7) 2.39(2)
2.374(8) 2.381(9)
b
c
2.445(1) 2.420(1) 2.499(3) 2.436(7) 2.465(4)
1.721(3) 1.717(3) 1.749(6) 2.120(7) 1.824(8)
2.066(3) 2.087(3) 2.436(3) 2.447(8) 2.402(4)
2.178(6)
2.167(3)
2.132(7)
2.018(9)
1.744(9)
1.334(1)
0.784
W-O/S/Cl
1.77(1)
1.34(2)
0.799
1.75(2)
1.33(1)
0.805
1.79(1)
1.325(1)
0.696
S-Ca
1.75(1)
1.34(1)
1.75(1)
1.33(2)
1.74(2)
1.34(2)
1.75(2)
1.34(1)
1.73(4)
1.33(3)
C-Ca
O/S-W-Strans
143.5(1) 138.7(1) 153.4(2) 153.0(3) 149.0(3)
88.7(1) 91.4(2) 96.4(2) 91.5(3)
153.3(4) 151.8(1) 158.5(1) 156.1(2) 156.9(2)
103.0 108.0 96.9 94.4 84.2(1)
d
θd
126.0
124.7
128.1
132.7
O/S-W-O/S/Cl 94.0(1)
S-W-Sd
a Mean values with standard deviation from the mean. b Axial ligand.
c Perpendicular displacement of W atom from S4 least-squares plane.
d Dihedral angle between WS2 planes.
e
θd
a Mean values with standard deviation from the mean. b Mean of 3.
c Trans to oxo or sulfido. d Transoid angle. e Dihedral angle between WS2
chelate planes.
complexes previously prepared. Consequently, the oxidation
state designations WIV,VI are appropriate (Chart, Figure 2).
Formate and Other Carboxylate Complexes. Reaction
of the dicarbonyl with 1 equiv of formate in reaction 1 at
low temperature affords the monocarbonyl formate complex
4 (32%). This species is prone to decomposition at room
temperature. In a second experiment, the dicarbonyl was
treated with 1 equiv of formate in Me2SO, presumably
generating 4. Thereafter, oxo transfer reaction 2 ensues,
affording the WVIO complex 7 (29%) in reaction 2 which is
analogous to the reduction of N- and S-oxides with
[W(OR)(S2C2Me2)2]1-.20,21 The structures of the two com-
plexes (Figure 3) reveal different shapes. Complex 4 shows
a dihedral angle θd ) 128.1° (Table 2) which approaches
that (120°) for idealized trigonal prismatic (C2V) geometry.
[W(CO)2(S2C2Me2)2] + HCO2- f
[W(CO)(HCO2)(S2C2Me2)2]1- + CO (1)
[W(CO)(HCO2)(S2C2Me2)2]1- + Me2SO f
[WO(HCO2)(S2C2Me2)2]1- + CO + Me2S (2)
Very similar values are found for the monocarbonyls
[MIV(CO)L(S2C2Me2)2]1- (M ) Mo,29 W24). Complex 7 has
θd ) 108.0° and an S-W-S transoid angle of 151.8°
1306 Inorganic Chemistry, Vol. 43, No. 4, 2004

Bis(dithiolene)tungsten(IV,VI) Complexes
Figure 3. Structures of [W(CO)(HCO2)(S2C2Me2)2]1- (4, upper) and
[WO(HCO2)(S2C2Me2)2]1- (7, lower). In this and succeeding figures, 50%
probability ellipsoids and partial atom labeling schemes are shown.
Figure 4. Structures of [W(MeCO2)(S2C2Me2)2]1- (2, upper) and
[WO(PhCO2)(S2C2Me2)2]1- (6, lower). In the acetate structure, atoms n and
nA are related by a crystallographically imposed 2-fold axis.
(involving sulfur atoms of different chelate rings). For an
octahedron, θd ) 90° and the transoid angle is 180° (136°
for a trigonal prism). Consequently, oxo transfer product 7
possesses a distorted octahedral stereochemistry similar to
that observed for complexes such as [WO(OPh)(S2C2Me2)2]1-
(θd ) 99.8°, transoid angle 153.5°).20 A sufficient body of
information now exists to demonstrate the generality of the
structural changes in oxo transfer reaction 3 of bis(dithiolene)
complexes with M ) Mo and W, including those reported
here (compare the WIV and WVIO structures in Figures 3-5).
With square pyramidal MIV, this is the presumed intrinsic
change in proteins, a matter supported by the structural
correspondence between [WO(OPh)(S2C2Me2)2]1- and the
oxidized site in the W-DMSOR isoenzyme from Rhodo-
bacter capsulatus.20
of both η1 and η2 interactions.36 Complexes 4 and 7 are the
first structurally proven examples of formate binding to
mononuclear WIV or WVI. They presumably simulate η1
substrate binding, should this occur in enzymes, but the
complexes lack the selenocysteinate ligand present in the
active site of D. gigas W-FDH.
Carboxylate complexes 119, 2 (63%), and 3 (74%) are
readily prepared by displacement of both carbonyl groups
in reaction 4. The carboxylate groups exhibit essentially
symmetric η2 coordination such that the molecules approach
C2V symmetry (Figures 4 and 6). In acetate complex 2, an
imposed 2-fold axis bisects the carboxylate chelate ring.
Benzoate complex 1 undergoes oxo transfer with Ph3AsO
to afford 6 (41%). The complex may be obtained more
efficiently (73%) by reaction 5 in which WV reduces
dibenzoyl peroxide to benzoate, which is captured as an η1
ligand by WVI. Complexes 6 and 7 have the same distorted
octahedral structure and are nearly isometric (Table 3).
[MIVL(S2C2R2)2]1- (sq pyramidal),
[MIVLL′(S2C2R2)2]1- (trigonal prismatic) + XO f
[MVIOL(S2C2R2)2]1- (distorted oct) + X (3)
Formate complexes of tungsten are uncommon and are
primarily confined to low-valent mononuclear species with
η1 coordination.32-34 Recently, [MIV3O4]4+ and [MIV3S4]4+
clusters (M ) Mo, W) have been shown to bind formate as
η1 terminal ligands.35 Examples exist with other elements
[W(CO)2(S2C2Me2)2] + RCO2- f
[W(O2CR)(S2C2Me2)2]1- + 2CO (4)
[WO(S2C2Me2)2]1- + PhC(O)OOC(O)Ph f
(32) Kundel, P.; Berke, H. J. Organomet.Chem. 1986, 314, C31-C33.
(33) Tso, C. C.; Cutler, A. R. Inorg. Chem. 1990, 29, 471-475.
•
[WO(O2CPh)(S2C2Me2)2]1- + PhCO2 (5)
Inorganic Chemistry, Vol. 43, No. 4, 2004 1307

Jiang and Holm
Figure 5. Structures of [W(SC6H2-2,4,6-Pri3)(S2C2Me2)2]1- (5, upper) and
[WO(SC6H2-2,4,6-Pri3)(S2C2Me2)2]1- (8, lower).
Thiolate Complexes. The most obvious route to analogues
of the five-coordinate reduced enzyme sites [MIV(S/Se‚Cys)(S2-
pd)2] is by displacement of both carbonyls in [M(CO)2(S2C2-
Me2)2]. Such species are potentially subject to oxo or sulfido
atom transfer, affording analogues of c-f (Figure 1). The
displacement route has been previously investigated in detail
for M ) Mo29,30 and W.19,24 The complexes [Mo(QR)-
(S2C2Me2)2]1- (Q ) S, Se) are accessible by displacement
with extremely bulky thiolates (R ) 2-adamantyl). Less
hindered thiolates and selenolates form the monocarbonyl
products [Mo(CO)(QR)(S2C2Me2)2]1-. However, with tung-
sten the same thiolates and selenolates, including the
2-adamantyl derivatives, afford only the monocarbonyls
[W(CO)(QR)(S2C2Me2)2]1-. Attempts at decarbonylation
have not been successful. The relative stabilities of the
molybdenum and tungsten monocarbonyls are discussed
elsewhere.24
Figure 6. Structures of [W(ButCO2)(S2C2Me2)2]1- (3, upper), [WS(SC6H2-
2,4,6-Pri3)(S2C2Me2)2]1- (9, middle), and [WOCl(S2C2Me2)2]1- (10, lower).
exhaustively explored, less hindered reactants (including Me3-
SiSPh) do not yield tractable products. Complex 5 (Figure
5, Table 2) is isostructural with [Mo(SC6H2-2,4,6-Pri3)(S2C2-
Me2)2]1- (Mo-Sax ) 2.31 Å, δ ) 0.706 Å, θd ) 132.1°),
which is accessible by a carbonyl displacement reaction.29
[W(O2CBut)(S2C2Me2)2]1- + Me3SiSC6H2-2,4,6-Pri3 f
[W(SC6H2-2,4,6-Pri3)(S2C2Me2)2]1- + Me3SiOCOBut (6)
Reaction 6 provides the first route to complexes of the
type [W(SR)(S2C2Me2)2]1-, and utilizes the enthalpic change
in forming a Si-O versus a Si-S bond. Treatment of 3 with
1 equiv of the hindered silylthiolate affords complex 5 (60%)
as a red microcrystalline solid. While the matter has not been
The near-identity of the structural parameters indicates that
the inability to displace both carbonyls from [W(CO)2(S2C2-
Me2)2] versus [Mo(CO)2(S2C2Me2)2] is not steric in origin
but in intrinsically stronger carbonyl binding in the tungsten
complex.
The availability of complex 5 has permitted the investiga-
tion of atom transfer reactions. Oxo transfer reaction 7 leads
to the purple WVIO species 8 (68%) while sulfur transfer
reaction 8 affords the red WVIS complex 9 (42%), whose
(34) Baur, J.; Jacobsen, H.; Burger, P.; Artus, G.; Berke, H.; Dahlenberg,
L. Eur. J. Inorg. Chem. 2000, 1411-1422.
(35) Brorson, M.; Hazell, A.; Jacobsen, C. J. H.; Schmidt, I.; Villadsen, J.
Inorg. Chem. 2000, 39, 1346-1350.
(36) Gibson, D. H. Coord. Chem. ReV. 1999, 185-186, 335-355.
1308 Inorganic Chemistry, Vol. 43, No. 4, 2004

Bis(dithiolene)tungsten(IV,VI) Complexes
Table 4. Functional Groups in Bis(dithiolene)W(IV, V, VI) Complexes
a This work. b Not proven by a structure determination. c Ambiguous oxidation state. d References to a given group delimited by a semicolon.
stability to isolation is noteworthy given the strongly reducing
ligand environment. Reaction 7 is the first example of oxo
transfer of a dithiolene molybdenum or tungsten complex
with an axial thiolate ligand.
complex is analogous to [WOCl(bdt)2]1-, which undergoes
chloride substitution by benzenethiolate.22 Reaction systems
based on 10 and selenolates also failed to produce stable
products. The inability to isolate the selenolate counterparts
of thiolate complex 5 is unexpected and, at present, not
readily explained.
[W(SC6H2-2,4,6-Pri3)(S2C2Me2)2]1- + Ph3AsO f
[WO(SC6H2-2,4,6-Pri3)(S2C2Me2)2]1- + Ph3As (7)
Tungsten Functional Groups. The completion of the
scheme of Figure 2 provides an expanded array of functional
groups in bis(dithiolene)tungsten(IV,V,VI) complexes. The
currently available set of these groups is summarized in Table
4,37,38 which supplants several earlier versions.19,25 Previously
unknown groups include WVIO(SR) (c), WVIS(SR) (e),
WVIO(O2CR), (R ) H, Ph), WIVSR, and WIV(CO)(O2CH).
Additional examples of WIV(O2CR) and WVIOCl have been
prepared. There are now analogue complexes for all sites in
Figure 1 except the two involving selenocysteinate ligation
(d, f). The biological relevance of these molecules as
structural and functional analogues requires a more complete
specificiation of enzyme sites. In the meantime, we note the
relation to defined molybdoenzyme sites and the possibility
of corresponding reactivity. The WVIO(OR)/WIV(OR) com-
plexes are meaningful reactivity analogues of DMSOR and
TMAOR enzymes and of tungsten isoenzymes,20,21 and may
appertain to selenate reductase.39 The pair WVIO2/WIVO is
[W(SC6H2-2,4,6-Pri3)(S2C2Me2)2]1- + (PhCH2S)2S f
[WS(SC6H2-2,4,6-Pri3)(S2C2Me2)2]1- + (PhCH2S)2 (8)
Reaction 8 is precedented only by the formation of
[WS(OSiR3)(bdt)2]1- from [W(OSiR3)(bdt)2]1- and dibenz-
yltrisulfide.22 Complexes 8 and 9 are essentially isostructural
(Figures 5 and 6, Table 3) with distorted octahedral stereo-
chemistry and exert a substantial trans influence of ca. 0.07-
0.10 Å on the bond length of an opposite chelate ring sulfur
atom.
Extensive attempts were made to prepare the WIV com-
plexes [W(SeR)(S2C2Me2)2]1-, related to 5 and [Mo(Se-2-
adamantyl)(S2C2Me2)2]1-.30 Among the reactions investigated
were those analogous to 6 with different Me3SiSeR reagents,
including R ) 2,4,6-C6H2R′3 (R′ ) Pri, But, Ph) at room
1
temperature and -40 °C. While H NMR spectra indicated
a slight amount of product formation, no tractable materials
were isolated. Silylation of [WO2(S2C2Me2)2]2- resulted in
the synthesis of chloride complex 10 (Figure 1) with a
distorted octahedral structure (Figure 6, Table 3). This
(37) Lim, B. S.; Sung, K.-M.; Holm, R. H. J. Am. Chem. Soc. 2000, 122,
7410-7411.
(38) Davies, E. S.; Aston, G. M.; Beddoes, R. L.; Collison, D.; Dinsmore,
A.; Docrat, A.; Joule, J. A.; Wilson, C. R.; Garner, C. D. J. Chem.
Soc., Dalton Trans. 1998, 3647-3656.
Inorganic Chemistry, Vol. 43, No. 4, 2004 1309

Jiang and Holm
related to the active sites of arsenite oxidase, which has two
pyranopterindithiolene ligands and no polypeptide ligand,10,40
and possibly to assimilatory nitrate reductases41,42 and AOR
(vide supra) which apparently share these properties. The
pair WVIO(SR)/WIV(SR) is related to the sites of a dissimila-
tory nitrate reductase, which features cysteinate ligation.43
As noted, FDH analogue sites are currently missing. The
substitution of Cys‚S for Cys‚Se in E. coli FDHH results in
a ∼300-fold decrease in kcat,44 implying a direct role of the
selenocysteinate residue in catalysis. Possibly the preceding
pair of complexes may be useful in determining whether
formate can be bound and oxidized in the absence of
selenolate ligation. While there is as yet no evidence for
carboxylate ligation in tungstoenzymes, unsymmetrical
Mo(O2CAsp) coordination has been found in a nitrate reduc-
tase of E. coli.45 Our present research investigates certain
complexes in Table 4 as atom transfer reactants in the
transformation of biological substrates of molybdo- and
tungstoenzymes.
Acknowledgment. This research was supported by NSF
Grant CHE 0237419. We thank D. V. Partyka for the
synthesis and structure of complex 10.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of the nine
compounds in Table 1. This material is available free of charge
via the Internet at http://pubs.acs.org.
(39) Maher, M. J.; Macy, J. M. Acta Crystallogr. 2002, D58, 706-708.
(40) Conrads, T.; Hemann, C.; George, G. N.; Pickering, I. J.; Prince, R.
C.; Hille, R. J. Am. Chem. Soc. 2002, 124, 11276-11277.
(41) Dias, J. M.; Than, M. E.; Humm, A.; Huber, R.; Bourenkov, G. P.;
Bartunik, H. D.; Bursakov, S.; Calvete, J.; Caldeira, J.; Carneiro, C.;
Moura, J. J. G.; Moura, I.; Romno, M. J. Structure 1999, 7, 65-79.
(42) Axley, M. J.; Bo¨ck, A.; Stadtman, T. C. Proc. Natl. Acad. Sci. U.S.A.
1991, 88, 8450-8454.
IC030301K
(44) Axley, M. J.; Bo¨ck, A.; Stadtman, T. C. Proc. Natl. Acad. Sci. U.S.A.
1991, 88, 8450-8454.
(45) Bertero, M. G.; Rothery, R. A.; Palak, M.; Hou, C.; Lim, D.; Blasco,
F.; Weiner, J. H.; Strynadka, N. J. C. Nat. Struct. Biol. 2003, 10, 681-
687.
(43) Dias, J. M.; Than, M. E.; Humm, A.; Huber, R.; Bourenko, G. P.;
Bartunik, H. D.; Bursakov, S.; Calvete, J.; Carneiro, C.; Moura, J. J.
G.; Moura, I.; Romno, M. J. Structure 1999, 7, 65-79.
1310 Inorganic Chemistry, Vol. 43, No. 4, 2004