Reactions of monodithiolene tungsten(VI) sulfido complexes with copper(I) in relation to the structure of the active site of carbon monoxide dehydrogenase

Article abstract of DOI:10.1021/ic902066m

Reactions directed at the synthesis of structural analogues of the active site of molybdenum-containing carbon monoxide dehydrogenase have been investigated utilizing [WO₂S(bdt)]^2- (1) and [WOS ₂(bdt)]^2-(2) and sterically hindered [Cu(R)L] or [Cu(SSiR′₃)₂]^- as reactants. All successful reactions of 2 afford the binuclear W^VI/Cu^I products [WO(bdt)(μ₂-S)₂Cu(L)]^2-/- with L = carbene (3), Ar*S (4), Ar* (7), SSiR₃ (R = Ph (5), Prⁱ (6)). Similarly, [W(bdt)(OSiPh₃)S₂] ^- leads to [W(bdt)(OSiPh₃)(μ₂·S) ₂Cu(SAr*)] (8). These complexes, with apical oxo and basal dithiolato and sulfido coordination (excluding 8), terminal thiolate ligation at Cu^I (4-6, 8), and W-(μ₂-S)-Cu bridging, bear a structural resemblance to the enzyme site. Differences include two bridges instead of one and the absence of basal oxo/hydroxo ligation. Complex 8 differs from the others by utilizing apical and basal sulfido ligands in bridge formation. Related reaction systems based on 1 gave 4 in small yield or product mixtures in which the desired monobridged complex [WO₂(bdt) (μ₂-S)Cu(R)]^2- was not detected. Mass spectrometric analysis of the reaction system with L = carbene suggests that any monobridged species forms may converted to the dibridged form by disproportionation. In these experiments, the use of W^VI preserves the structural integrity of Mo^VI, whose analogues of 1 and 2 have not been isolated. (Ar* = 2,6-bis(2,4,6-triisopropylphenyl)phenyl, bdt = benzene-1,2- dithiolate(2-)).

Full text of DOI:10.1021/ic902066m

1082 Inorg. Chem. 2010, 49, 1082–1089
DOI: 10.1021/ic902066m
Reactions of Monodithiolene Tungsten(VI) Sulfido Complexes with Copper(I) in
Relation to the Structure of the Active Site of Carbon Monoxide Dehydrogenase
Stanislav Groysman, Amit Majumdar, Shao-Liang Zheng, and R. H. Holm*
Department of Chemisty and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
Received October 19, 2009
Reactions directed at the synthesis of structural analogues of the active site of molybdenum-containing carbon
monoxide dehydrogenase have been investigated utilizing [WO2S(bdt)]2- (1) and [WOS2(bdt)]2- (2) and sterically
hindered [Cu(R)L] or [Cu(SSiR03)2]- as reactants. All successful reactions of 2 afford the binuclear WVI/CuI products
[WO(bdt)(μ2-S)2Cu(L)]2-/- with L = carbene (3), Ar*S (4), Ar* (7), SSiR3 (R = Ph (5), Pri (6)). Similarly,
[W(bdt)(OSiPh3)S2]- leads to [W(bdt)(OSiPh3)(μ2-S)2Cu(SAr*)]- (8). These complexes, with apical oxo and basal
dithiolato and sulfido coordination (excluding 8), terminal thiolate ligation at CuI (4-6, 8), and W-(μ2-S)-Cu bridging,
bear a structural resemblance to the enzyme site. Differences include two bridges instead of one and the absence of
basal oxo/hydroxo ligation. Complex 8 differs from the others by utilizing apical and basal sulfido ligands in bridge
formation. Related reaction systems based on 1 gave 4 in small yield or product mixtures in which the desired
monobridged complex [WO2(bdt)(μ2-S)Cu(R)]2- was not detected. Mass spectrometric analysis of the reaction
system with L = carbene suggests that any monobridged species forms may converted to the dibridged form by
disproportionation. In these experiments, the use of WVI preserves the structural integrity of MoVI, whose analogues of
1 and 2 have not been isolated. (Ar* = 2,6-bis(2,4,6-triisopropylphenyl)phenyl, bdt = benzene-1,2-dithiolate(2-)).
Introduction
is linked an exo FeII atom.4-6 The latter is bound to the cluster
by one μ3-S atom which, however, is part of a Fe-S-
Fe-S-Ni bond sequence with four bonds intervening be-
tween the nickel and external iron atom.
The single-atom unsupported bridge M-S-M0 between
heterometals is an uncommon structural element in synthetic
molecules and metalloprotein sites, and has been recognized in
only one enzyme type. Carbon monoxide dehydrogenases in
aerobic carboxidotrophic bacteria are Mo-Cu-Fe-S en-
zymes that utilize carbon monoxide as the sole source of
carbon and energy and catalyze the reaction CO þ H2O h
CO2 þ 2Hþ þ 2e-. The most thoroughly studied Mo-
CODH1 is that from O. carboxidovorans. Crystallographic
Mo-CODH is classified in the xanthine oxidoreductase
family,7,8 all members of which manifest one pyranopterin-
dithiolene, two oxo/hydroxo, and one sulfido ligand(s), with
the latter in the equatorial plane of an idealized square pyra-
mid. The structures and dimensions of quinoline 2-oxidoreduc-
tase9 and bovine xanthine oxidoreductase10 and its reaction
intermediates with substrates,11,12 among other information,
substantiate this arrangement. Mo-CODH is a derivative of
this structure motif, the essential features of which have been
˚
results at 1.1 A resolution for the oxidized form of the enzyme
disclose the active site structure in Figure 1.2 Here the MoVI
atom is coordinated in an approximate square pyramidal
configuration with axial oxo and basal dithiolene, hydroxo,
and sulfido ligation. A nearly linear Mo-S-Cu bridge is
evident, terminated by cysteinate binding to two-coordinate
CuI. Crystallographic bond lengths are in good agreement
with EXAFS results.3 These enzymes are to be distinguished
from Ni-Fe-S CODHs of anaerobic organisms whose
catalytic site consists of a NiFe3S4 cuboidal cluster to which
reproduced in the structural analogue [WO2S(bdt)]2- 13,14
.
(5) Gong, W.; Hao, B.; Wei, Z.; Ferguson, D. J.; Tallant, T.; Krzycki,
J. A.; Chan, M. K. Proc. Natl.Acad. Sci. U.S.A. 2008, 105, 9558–9563.
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Biochemistry 2009, 48, 7432–7440.
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~
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Dobbek, H. Structure 2004, 12, 1425–1435.
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Soc. 2005, 127, 4518–4522.
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4818–4824.
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2007, 129, 7512–7513.
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J. Am. Chem. Soc. 2008, 130, 12794–12807.
*To whom correspondence should be addressed. E-mail: holm@
chemistry.harvard.edu.
(1) Abbreviations are given in Chart 1.
(2) Dobbek, H.; Gremer, L.; Kiefersauer, R.; Huber, R.; Meyer, O. Proc.
Natl. Acad. Sci. U.S.A. 2002, 99, 15971–15976.
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r
pubs.acs.org/IC
Published on Web 12/23/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1083
Chart 1. Designation of Compounds and Abbreviationsa
Figure 1. Structure of the oxidized active site of O. carboxidovorans
carbon monoxide dehydrogenase with bond distances (A); the ene-1,2-
dithiolate fragment represents the pyranopterindithiolene ligand found in
all mononuclear enzyme sites containing molybdenum and tungsten.
This complex is a member of the series [WO3-nSn(bdt)]2- (n =
0-2) prepared in this laboratory.14,15 While MoVI(O)-
S-CuI fragments are known, they are often derived from
[MoOS3]2- with consequent tetrahedral MoVI geometry and
nuclearities higher than two (e.g., [MoOS3(CuCl3)3]2-16). In
metallobiomolecules, the MoVI-IV-S-CuI connectivity is
unique to Mo-CODH and provides a synthetic challenge in
biomimetic chemistry. Two interesting approaches to this
problem have been reported. The six-coordinate complex
[(TpiPr)MoVO(OAr)(μ2-S)CuI(Me3tacn)] contains the elusive
unsupported Mo-S-Cu bridge but without dithiolene co-
ordination to molybdenum and thiolate bound to copper.17
a Ad = adamantyl, Ar* = 2,6-bis(2,4,6-triisopropylphenyl)phenyl,
bdt = benzene-1,2- dithiolate(2-), CODH = carbon monoxide dehy-
drogenase, lut = 2,6-lutidine, mnt = 3 maleonitriledithiolate(2-), Me
tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, Pri2NHCMe2 = 1,3-
diisopropyl-4,5-dimethylimidazol-2-ylidene, tht
= tetrahydrothio-
phene, TpiPr = hydrotris(3-isopropylpyrazol-1-yl)borate(1-).
Vapor diffusion of ether caused separation of the product as
red-orange crystals (31 mg, 91%). Absorption spectrum
(acetonitrile): λmax (εM) 285 (sh, 15200), 315 (9500), 462 (1500)
nm. ES-MS-: m/z 404.9 {[WOS2(bdt)H]-}, 466.8 {[WO(bdt)S2-
Cu]-}, 647.0 {[(WO(bdt)S2Cu(Pri2NHCMe2)]-}. 1H NMR
(CD3CN, anion): δ 1.46 (d, 12), 2.22 (s, 6), 4.52 (sept, 2), 6.82
(m, 2), 7.39 (m, 2). Anal. Calcd for C25H45CuN3OS4W: C, 38.53;
H, 5.82; N, 5.39; S, 16.46. Found: C, 38.61; H, 5.92; N, 5.11; S,
15.90.
In [MoVIO(bdt)(μ2-S)2CuI(SPh)]2- 18
, the molybdenum atom
is square-pyramidal with an apical oxo ligand, bdt simu-
lates pyranopterindithiolene chelation, and copper carries a
thiolate ligand; however, there are two sulfido bridges instead
of one.
(Et4N)2[WO(bdt)(μ2-S)2Cu(SAr*)]. A solution of [Cu(SAr*)-
(2,6-lut)]19 (34 mg, 0.049 mmol) in THF (2 mL) was added
dropwise to a bright red stirred solution of (Et4N)2[WOS2-
(bdt)]14 (32 mg, 0.048 mmol) in THF (2 mL). The dark red-
brown reaction mixture was stirred for 20 min, and volatiles
were removed. The solid residue was recrystallized from THF/
ether to give the product as a dark red-brown solid (20 mg,
50%). Absorption spectrum (acetonitrile): λmax (εM) 303
(18200), 378 (8200), 488 (1100) nm. ES-MS-: m/z 404.2
{[WOS2(bdt)]-}, 466.8 {{WOS2(bdt)Cu]-}, 513.8 {[Ar*S]-}.
1H NMR (CD3CN, anion): δ 0.99 (d, 12), 1.18 (d, 12), 1.28 (d,
12), 2.90 (sept, 6), 6.75 (m, 2), 6.84 (d, 2), 6.96 (t, 1), 7.08 (s, 4),
7.30 (m, 2).
In this work, we have explored the possibility of stabi-
lizing one or more sulfido bridge interactions in com-
plexes that resemble the CODH catalytic site. The complexes
[WO3-nSn(bdt)]2- (n = 1,2) and sterically encumbered species
of the type [Cu(SAr*)L],19 only recently available, provide
one potential entry to the problem. To avoid internal reduc-
tion, reactants containing WVI rather than MoVI are em-
ployed without structural compromise inasmuch as isoligated
molecules in these two oxidation states are always isostruc-
tural and nearly isometric.
(Et4N)2[WO(bdt)(μ2-S)2Cu(SSiPh3)]. A solution of (Et4N)-
[Cu(SSiPh3)2] (39 mg, 0.050 mmol) in acetonitrile (10 mL) was
added dropwise to a solution of (Et4N)[WO2(bdt)(OSiMe3)]21
(29 mg, 0.050 mmol) in acetonitrile (2 mL). The solution was
stirred for 12 h. Solvent was removed from the reddish-pink
solution, and the residue was washed with THF and ether. The
pink solid was dissolved in a minimum volume of acetonitrile,
the solution was maintained at -30 °C, and ether was diffused in
overnight to afford the product as thin needle-shaped pink
crystals (16 mg, 31%). Alternatively, 2 equiv of (Et4N)[Cu-
(SSiPh3)2] resulted in a 60% yield after a reaction time of 2 h.
Absorption spectrum (acetonitrile): λmax (εM) 244 (16,500), 300
Experimental Section
Preparation of Compounds. All operations were carried out
under a pure dinitrogen atmosphere using standard Schlenk
techniques or an inert atmosphere box. Solvents were passed
through an MBraun or Innovative Technology solvent purifica-
tion system prior to use. All volume reduction steps were
performed in vacuo. Compounds were identified from combi-
nations of spectroscopic data, analytical results (selected com-
€
pounds, H. Kolbe, Mulheim, Germany), and X-ray structure
determinations.
(Et4N)2[WO(bdt)(μ2-S)2Cu(Pri2NHCMe2)]. A solution of the
(6760), 318 (sh), 5800), 508 (540) nm. IR (KBr): vWO 917 cm-1
.
ESMS: m/z 379.7 ({WO(bdt)S2Cu(SSiPh3)]2-), 890.0 ({(Et4N)-
[WO(bdt)S2Cu(SSiPh3)]}-). 1H NMR (CD3CN, anion): δ 6.71
(dd, 2), 7.23 (m, 9), 7.27 (dd, 2), 7.72 (m, 6). Anal. Calcd for
C42H62CuN3OS5SiW: C, 47.11; H, 5.83; N, 2.75. Found: C,
45.98; H, 5.46; N, 2.69.
carbene Pri2NHCMe2 (8.0 mg, 0.044 mmol) in THF (1 mL)
20
was added dropwise to a solution of [Cu(MeCN)4](PF6) (17 mg,
0.045 mmol) in acetonitrile (1 mL). This solution was added to a
solution of (Et4N)2[WOS2(bdt)] (29 mg, 0.044 mmol) in aceto-
nitrile (1 mL). The reaction mixture was stirred for 20 min,
volatiles were removed, and the residue was dissolved in a mix-
ture of tetrahydrofuran (THF, 1 mL) and acetonitrile (0.3 mL).
(Et4N)2[WO(bdt)(μ2-S)2Cu(SSiPri3)]. A solution of [Cu-
(MeCN)4](PF6) (26 mg, 0.070 mmol) in acetonitrile (2 mL)
was added dropwise to a solution of (Et4N)(SSiPri3) (45 mg,
0.14 mmol) in an equal volume of acetonitrile. The colorless
solution was stirred for 10 min and added to a solution of
(Et4N)[WO2(bdt)(OSiMe3)] (40 mg, 0.070 mmol) in acetonitrile
(2 mL). The reaction mixture was stirred for 12 h, solvent was
removed, and the residue was thoroughly washed with THF and
(15) Partyka, D. V.; Holm, R. H. Inorg. Chem. 2004, 43, 8609–8616.
(16) Clegg, W.; Garner, C. D.; Nicholson, J. R.; Raithby, P. R. Acta
Crystallogr. 1983, C39, 1007–1009.
(17) Gourlay, C.; Nielsen, D. J.; White, J. M.; Knottenbelt, S. Z.; Kirk,
M. L.; Young, C. G. J. Am. Chem. Soc. 2006, 128, 2164–2165.
(18) Takuma, M.; Ohki, Y.; Tatsumi, K. Inorg. Chem. 2005, 44,
6034–6043.
(19) Groysman, S.; Holm, R. H. Inorg. Chem. 2009, 48, 621–627.
(20) Kuhn, N.; Kratz, T. Synthesis 1993, 561562.
(21) Wang, J.-J.; Holm, R. H. Inorg. Chem. 2007, 46, 11156–11164.

1084 Inorganic Chemistry, Vol. 49, No. 3, 2010
Groysman et al.
Table 1. Crystallographic Dataa for WVI-(μ2S)-CuI Complexes
complexes
3
4
5
6
8
formula
C
778.30
triclinic
P1
193
25H44CuN3OS4W
C58H95CuN2O2S5W
1260.10
monoclinic
P21/c
193
4
19.040(2)
15.949(1)
21.698(3)
90.00
107.470(2)
90.00
C42H62CuN3OS5SiW
1060.73
triclinic
P1
100
C31H65CuN2OS5SiW
917.68
monoclinic
P21/c
100
C70H92CuNO1.50S5SiW
1407.23
monoclinic
P21/c
193
4
23.782(6)
18.684(5)
18.789(5)
90.00
104.684(6)
90.00
8076(4)
formula weight
crystal system
space group
T, K
Z
a, A
2
2
4
˚
˚
12.061(7)
12.413(7)
12.699(7)
117.797(8)
104.023(9)
96.789(9)
1571.48(1)
1.645
9.223(3)
15.324(6)
17.019(6)
97.540(8)
105.259(8)
101.085(8)
2234.9(1)
1.576
14.551(5)
15.531(5)
17.680(5)
90.00
91.693(5)
90.00
3994(2)
1.526
3.728
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
6285.0(1)
1.332
2.372
dcalcd, g/cm3
1.157
1.866
μ, mm-1
4.622
3.344
2θ range, deg
3.80-52.0
0.0235(0.0575)
1.043
3.58-50.0
0.0616(0.1386)
1.003
3.36-52.0
0.0603(0.1070)
1.041
2.80-52.44
0.0448(0.0914)
1.018
2.80-50.0
0.0653(0.1859)
1.083
c
R1b (wR2 )
GOF (F2)
P
P
P
P
a Mo KR radiation (λ = 0.71073). b R1 = ||Fo| - |Fc||/ |Fo|. c wR2 = { w(Fo2 - Fc2)2/ w(Fo2)2}1/2
.
Table 2. Crystallographic dataa for Cu(I) complexes and [Et4N][SSiPri3]
complexes
formula
formula weight
crystal system
space group
T, K
9
10
11
12
[Et4N][SSiPri3]
C
776.72
triclinic
P1
193
44H50CuNS2Si2
C38H55CuN4-S3Si
755.71
monoclinic
P21
100
C29H61CuN4-S3Si
653.63
monoclinic
P21/c
100
C23H40CuN5S2
514.29
monoclinic
P21/n
100
C17H41NSSi
319.67
monoclinic
P21
100
Z
a, A
b, A
˚
c, A
1
2
4
4
4
˚
˚
9.448(3)
9.582(3)
12.742(4)
94.349(4)
96.600(5)
117.022(4)
1010.0(5)
1.277
9.024(5)
24.784(5)
9.108(5)
90.00
106.965(5)
90.00
1948.4(1)
1.288
0.784
18.372(4)
15.257(3)
13.661(3)
90.00
106.746(3)
90.00
3666.8(1)
1.184
0.822
9.346(3)
18.693(6)
15.338(5)
90.00
90.982(6)
90.00
2679.2(1)
1.275
0.990
12.840(1)
11.762(1)
14.337(1)
90.00
106.866(2)
90.00
2072.2(4)
1.025
0.209
R, deg
β, deg
γ, deg
3
˚
V, A
dcalcd, g/cm3
μ, mm-1
0.735
2θ range, deg
3.26-55.78
0.0401(0.1098)
1.011
3.28-59.70
0.0509(0.0808)
1.060
3.54-57.78
0.0578(0.1332)
1.029
3.44-56.64
0.0572(0.1531)
1.007
2.96-52.0
0.0421(0.0895)
1.046
c
R1b (wR2 )
GOF (F2)
P
P
P
P
a Mo KR radiation (λ = 0.71073). b R1 = ||Fo| - |Fc||/ |Fo|. c wR2 = { w(Fo2 - Fc2)2/ w(Fo2)2}1/2
.
ether . The solid was dissolved in a minimal volume of aceto-
nitrile, ether was diffused in, and the mixture was maintained
at -30 °C overnight. The product was obtained as thin needle-
shaped, reddish-pink crystals (20 mg, 31%). Alternatively,
2 equiv of [Cu(MeCN)4](PF6) and 4 equiv of (Et4N)(SSiPri3)
afforded a 60% yield after a reaction time of 2 h. Absorption
spectrum (acetonitrile): λmax (εM) 242 (11500), 302 (6880), 336
(sh, 5300), 500 (sh, 580) nm. IR (KBr): vWO 923 cm-1. ES-MS:
m/z 466.5 {[WOS2(bdt)Cu]-}. 1H NMR (CD3CN, anion): δ 1.06
(18), 6.74 (dd, 2), 7.30 (dd, 2).
(Et4N)[W(bdt)(OSiPh3)(μ2-S)2Cu(SAr*)]. A solution of [Cu-
(SAr*)(2,6-lut)] (20 mg, 0.029 mmol) in THF (1 mL) was added
dropwise to a red-brown solution of (Et4N)[WS2(bdt)(OSiPh3)].21
The reaction mixture was stirred for 10 min, and volatiles were
removed. The solid residue was recrystallized from THF/ether to
1
give the product as a red-brown solid (20 mg, 58%). H NMR
(C6D6): δ 1.23 (d, 12), 1.26 (d, 12), 1.43 (d, 12), 2.84 (sept, 4), 3.32
(sept, 4), 6.72 (dd, 2), 6.84 (d, 2), 6.98 (t, 1), 7.15 (m, 15), 7.32 (dd,
2), 7.82 (m, 6).ES-MS: m/z 513 {[SAr*]-}.
(Et4N)[Cu(SSiPh3)2]. A solution of Ph3SiSH (23 mg, 0.079
mmol) in THF (0.5 mL) was added to a solution of (Et4N)[Cu(S-
1-Ad)2]22 (21 mg, 0.040 mmol) in acetonitrile 0.5 mL). The
reaction mixture was stirred for 40 min and filtered. Vapor
diffusion of ether into the mixture resulted in separation of the
product as colorless needle-like crystals (16 mg, 52%).ES-MS:
m/z 644.7 {[Cu(SSiPh3)2]-}. 1H NMR (CD3CN, anion): δ 7.27
(m, 12), 7.31 (m, 6), 7.66 (m, 12).
(Et4N)2[WO(bdt)(μ2-S)2Cu(Ar*)]. A solution of [Cu(Ar*)-
(tht)]19 (19 mg, 0.030 mmol) in THF (2 mL) was added dropwise
to a stirred solution of (Et4N)2[WOS2(bdt)]14 (19 mg, 0.029
mmol). The dark red solution was stirred for 30 min, and
volatiles were removed. The solid residue was washed with
hexanes, dissolved in a miminal volume of THF, and the solu-
tion was filtered. Addition of ether to the filtrate gave the
product as a dark red solid (20 mg, 59%). Absorption spectrum
(acetonitrile): λmax (εM) 297 (11050), 374 (4700), 499 (900) nm.
ES-MS: m/z 466.8 {[WOS2(bdt)Cu]-}, 1063.8 {[Et4N(WO(bdt)-
S2Cu)2]-}, 1660.7 {((Et4N)2[WO(bdt)S2Cu]3)-}. 1H NMR
(CD3CN, anion): δ 1.01 (d, 12), 1.22 (d, 12), 1.28 (d, 12), 2.90
(sept, 2), 3.26 (sept, 4), 6.67 (m, 2H), 6.69 (d, 2), 6.87 (s, 4), 6.90
(m, 1), 7.25 (m, 2).
(Et4N)2[Cu(mnt)(SSiPh3)]. A solution of (Et4N)(SSiPh3)
(21 mg, 0.050 mmol) in acetonitrile (3 mL) was added dropwise
to a light yellow solution of (Et4N)[Cu(mnt)(PPh3)]23 (30 mg,
(22) Fujisawa, K.; Imai, S.; Kitajima, N.; Moro-oka, Y. Inorg. Chem.
1998, 37, 168–169.
(23) Maiti, B. K.; Pal, K.; Sarkar, S. Eur. J. Inorg. Chem. 2008, 2407–2420.

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1085
Figure 2. Synthetic scheme affording complexes 2-8 containing the core bridge unit WVI(μ2-S)2CuI. Structures of two CuI reactants are shown in the
boxes.
0.050 mmol) in acetonitrile (2 mL). The solution was stirred for
1 h to give a light orange solution. Solvent was removed and the
light orange residue was washed with benzene and dried. The
solid was dissolved in acetonitrile (1 mL), ether was added by
vapor diffusion, and the mixture maintained at -30 °C over-
night. The product was isolated as a yellow-orange crystalline
solid (29 mg, 77%). Absorption spectrum (acetonitrile): λmax
(εM) 245 (sh, 3830), 293 (1790), 381 (970), 408 (1170) nm. IR
(KBr): vCN 2178 cm-1. 1H NMR (CD3CN, anion): δ 7.21 (m, 3),
7.71 (m, 2). Anal. Calcd for C38H55CuN4S3Si: C, 60.40; H, 7.34;
N, 7.41. Found: C, 60.16; H, 7.11; N, 7.39.
IR (KBr): vCN 2178 cm-1
1.06 (d).
.
1H NMR (CD3CN, anion): δ
(Et4N)[Cu(mnt)(Pri2NHCMe2)]. A solution of Pri2NHCMe2
(18 mg, 0.010 mmol) in THF (2 mL) was added dropwise to a
solution of (Et4N)[Cu(mnt)(PPh3)] (30 mg, 0.050 mmol) in
acetonitrile (2 mL). The reaction mixture was stirred for 1 h to
give a yellow-orange solution, solvent was removed, and the
light orange residue was washed with benzene and dried. The
residue was dissolved in acetonitrile (1 mL), and ether was
diffused in at -30 °C overnight. The product was obtained as
yellow-orange needles (20 mg, 77%). Absorption spectrum
(acetonitrile): λmax (εM) 240 (sh, 2360), 296 (2240), 392 (1550)
(Et4N)2[Cu(mnt)(SSiPri3)]. The preceding preparation
but with use of (Et4N)(SSiPri3) was followed on the same
scale. The product was isolated as a yellow-orange crystal-
line solid (24 mg, 73%). Absorption spectrum (acetonitrile):
nm. IR (KBr): vCN 2178 cm-1 1H NMR (CD3CN, anion):
.
δ 1.52 (d, 6), 2.10 (s, 3), 4.52 (sept, 1). Anal. Calcd for C23H41-
CuN5: C, 53.61; H, 8.02; N, 13.59; S, 12.45. Found: C, 53.84; H,
8.01; N, 13.41; S, 12.25.
λ
max (εM) 236 (6260), 321 (2560), 386 (sh, 950), 414 (1550) nm.

1086 Inorganic Chemistry, Vol. 49, No. 3, 2010
Groysman et al.
Figure 3. Structures of complexes 3, 5, and 6 (left) and 4 and 8 (right) showing 50% probability ellipsoids and partial atom labeling schemes.
(Et4N)(SSiPh3). NaOMe (108 mg, 2.00 mmol) was added to a
mixture of Ph3SiSH (585 mg, 2.00 mmol) and Et4NCl (331 mg,
2.00 mmol) in acetonitrile (30 mL). The mixture was stirred for 12 h
and filtered. The filtrate was reduced to obtain a pale yellow solid,
which was dissolved in acetonitrile (80 mL) and diluted with ether
(100 mL) producing a white solid. This material was dissolved in a
minimum volume (∼60 mL) of acetonitrile, ether was added by
diffusion, and the mixture was maintained at -30 °C for 1 d. The
product was obtained as colorless block-shaped crystals (674 mg,
80%). 1H NMR (CD3CN, anion): δ 7.18 (m, 3), 7.64 (m, 2).
(Et4N)(SSiPri3). The preceding preparation but with use of
Pri3SiSH was followed on the same scale. The product was
isolated as colorless crystals (575 mg, 90%). 1H NMR (CD3CN,
anion): δ 0.97 (d).
((Et4N)2[5,6], (Et4N)2[9, 10, 11], (Et4N)(SSiPri3)), aceto-
nitrile/THF (((Et4N)[3, 8], (Et4N)2[4]) and THF ((Et4N)[7])
solutions. Crystal mounting and data collections were per-
formed as described24 on a Siemens (Bruker) SMART CCD
diffractometer using Mo KR radiation. Data reductions were
performed with SAINT, which corrects for Lorentz polariza-
tion and decay. Space groups were assigned by analysis of
symmetry, and systematic absences determined by XPREP. Struc-
tures were solved by direct methods and refined against all data in
the 2θ ranges by full-matrix least-squares on F2 using SHELXS-97
and SHELXL-97. Hydrogen atoms at idealized positions were
included in final refinements. Refinement details and explanations
(wherever necessary) are included in the individual CIF files. Oak
Ridge Thermal Ellipsoid Plot Program (ORTEP) plots were
produced using the Mercury 2.2 program. Crystallographic data
and final agreement factors are given in Table 1.25
In the following sections, complexes and reactants are desig-
nated according to Chart 1.
X-ray Structure Determinations. The structures of the 10
compounds in Tables 1 and 2 were determined. Diffraction-
quality crystals were obtained by ether diffusion into acetonitrile
(24) Groysman, S.; Holm, R. H. Inorg. Chem. 2007, 46, 4090–4102.
(25) See paragraph at the end of this article for Supporting Information
available.

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1087
Table 3. Selected Bond Distances (A) and Angles (degree) for WVI-(μ2-S)2-CuI
Complexes
Unlike the successful reaction of disulfido 2 and [Cu-
(SAr*)(2,6-lut)], multiple attempts to obtain a product from
the reaction of this reagent and monosulfido 1 led to complex
product mixtures. The only pure product isolated from such
mixtures was crystalline (Et4N)2[4] in low yield. The desired
product [WO2(bdt)(μ2-S)Cu(SAr*)]2- was never detected.
Copper(I) binding was investigated further in the reaction
between [Cu(SAr*)(2,6-lut)] and [W(bdt)(OSiPh3)S2]-,14
which presents apical and basal sulfido ligands with a some-
what larger S-W-S bond angle of 107.8° than in 2 (102.1°)
˚
complexes
parameters
3
4
5
6
8
W-Sbdt
W-S
2.430(8)
2.450(8)
2.298(8)
2.299(8)
1.709(2)
2.618(4)
0.607
2.409(3)
2.461(3)
2.282(2)
2.286(3)
1.748(6)
2.630(1)
0.587
2.189(3)
2.198(3)
2.188(2)
71.87(8)
71.95(8)
2.395(3)
2.437(2)
2.248(3)
2.282(3)
1.765(1)
2.585(1)
0.579
2.400(1)
2.438(2)
2.260(1)
2.283(1)
1.733(4)
2.594(1)
0.586
2.381(5)
2.428(5)
2.185(4)
2.193(4)
1.867(1)
2.642(2)
W-O
W-Cu
δa
˚
and with W-S bond lengths 0.07 A shorter. This reaction
afforded 8 (58%), which retains the stereochemistry of
the starting complex with a mean W-S bond distance
Cu-S
2.196(9)
2.200(9)
1.926(3)
2.155(3)
2.187(3)
2.169(3)
71.24(1)
71.30(1)
2.170(1)
2.191(2)
2.180(2)
71.22(5)
71.29(6)
2.212(4)
2.217(5)
2.156(5)
73.72(1)
73.76(1)
˚
Cu-C/S
W-S-Cu 71.12(3)
71.21(3)
(2.189(6) A) and S-W-S bond angle 106.98(1)° intermediate
between 2 and the starting complex. The small dimensional
differences and different orientation of sulfido ligands com-
pared to 2 did not retard formation of the WS2Cu bridge
rhomb. In contrast, the reaction between monosulfido
[W(bdt)(OSiPh3)OS]- and [Cu(SAr*)(2,6-lut)] did not lead
to a tractable product.
S-W-S
S-Cu-S
θb
fold angle
τc
104.80(3) 104.23(9) 104.58(1) 104.82(6) 106.98(1)
111.89(3) 110.55(1) 111.24(1) 111.33(7) 105.20(1)
135.13
23.6
0.11
133.84
20.5
0.29
135.81
16.74
0.08
135.52
15.8
0.13
101.97
14.6
0.14
Further reactions involved CuI complexes with large
aryl or carbene ligands instead of thiolate. The premise
was that these ligands, upon binding to CuI without
an intervening sulfur atom, might lead to a different
bridging mode and/or stereochemical outcome. [Cu(Ar*)-
(tht)] reacts cleanly with 2 to yield sterically crowded aryl-
ligated complex 7 (59%). Diffraction-quality crystals
were not obtained; however, mass spectroscopic data
a W perpendicular displacement from [S1S2S3S4] basal plane. b Di-
hedral angle between WS1S2 and WS3S4 planes, τc: The shape para-
meter τ14 is defined as (R-β)/60, where R and β are the largest and next
largest interligand bond angles, respectively. For idealized SP geometry
τ = 0, for idealized TBP geometry τ = 1.
Other Physical Measurements. All measurements were
performed under anaerobic conditions. 1H NMR spectra
were recorded with Varian Mercury 300/400/500 spectro-
meters. Absorption spectra were obtained with a Cary 50
Bio spectrophotometer and infrared spectra on a Nicolet 5PC
FT-IR instrument. Electrospray mass spectra were measured
on acetonitrile solutions directed infused into a LCT mass
spectrometer.
1
and the H NMR spectrum (very similar to 4) are con-
sistent with the double-bridged formulation. The reaction
of 1 with [Cu(Ar*)(tht)] failed to yield an identifiable
product.
We initially sought as a reactant the complex [Cu(Pri2-
NHCMe2)(MeCN)x]þ having N-isopropyl groups proximal
to the bound carbon atom (Figure 2). However, the reac-
tion of 1 equiv each of [Cu(MeCN)4]þ and the carbene
proceeded by reaction 2. Formation of the bis(carbene)
complex was demonstrated by isolation of its PF6- salt and
an X-ray structure determination.26 Increasing the bulk of
the carbene with N-2,6-Pri2C6H3 substituents did not
prevent formation of a bis(carbene) as shown by the cell
parameters of the reaction product.27 However, reaction 3
readily affords in high yield (Et4N)[3] (91%). The reactivity
Results and Discussion
In this work, we seek monosulfido or disulfido WVI-CuI
species related to the active site of Mo-CODH (Figure 1)
by containing a W-S-Cu bridge, dithiolene coordina-
tion simulating that of the native pyranopterindithio-
lene ligand, and square pyramidal stereochemistry with
apical oxo and basal dithiolene and sulfido ligation.
The reaction scheme developed is presented in Figure 2.
Structures of binuclear product complexes 3-6 and 8 are
set out in Figure 3 and selected metric parameters are
collected in Table 3.
½CuðMeCNÞ4ꢀþ þ 2Pri2NHCMe2 f
Two synthetic approaches have been explored. In the
first, the reactions 1 (n = 1,2) of complexes 1 and 2 with di-
coordinate CuI have been examined. This approach utilizes
½CuðPri2NHCMe2Þ2ꢀþ þ 4MeCN
ð2Þ
2 -
½WOS2ðbdtÞꢀ þ ½CuðMeCNÞ4ꢀþ þ Pri2NHCMe2 f
2 -
½WO3 -nSnðbdtÞꢀ þ ½CuðRÞLꢀ f
-
½WOðbdtÞðμ2-SÞ2CuðPri2NHCMe2Þꢀ þ 4MeCN ð3Þ
-=2 -
½WO3 -nðμ2-SÞnðbdtÞCuðRÞꢀ
þ L
ð1Þ
of monosulfido 1 was then investigated in a system analo-
gous to reaction 3. The outcome was examined by electro-
spray mass spectrometry, as seen in Figure 4. The spectrum
in the higher mass region corresponds exactly to 3 whereas
in the lower mass region the spectrum is indicative of the
copper complexes with neutral ligands L such as thiourea
Ph3P, 2,6-lut, tht, and the N-heterocyclic carbene Pri2NH-
CMe2 as well as the sterically encumbering R ligands ArS*
and Ar*19 intended to minimize coordination at CuI. Of the
three sulfur-containing potential precursors, only [Cu(SAr*)-
(2,6-lut)] reacted cleanly with 2, yielding red-brown binuclear
complex 4 (50%) This species, like all other binuclear com-
plexes isolated in this work, approximates square pyramidal
stereochemistry and contains two W-(μ2-S)-Cu bridges in the
form of a WS2Cu rhombic core.
(26) [Cu(Pri2NHCMe2)2](PF6) crystallizes in orthorhombic space group
˚
˚
˚
Fddd with a = 14.262(8) A, b = 18.295 A, c = 20.59(1) A, and Z = 8 (R1 =
0.0679, T = 193 K).
ꢀ
(27) Dıez-Gonzalez, S.; Stevens, E. D.; Scott, N. M.; Petersen, J. L.;
Nolan, S. P. Eur. J. Inorg. Chem. 2008, 14, 158–168.

1088 Inorganic Chemistry, Vol. 49, No. 3, 2010
Groysman et al.
Figure 4. Electrospray mass spectroscopic data for the reaction products of 2 and [Cu(MeCN)4]þ/Pri2NHCMe2 in acetonitrile/THF. The experimental
spectrum in the region m/z 640-660 is shown together with features at lower m/z values centered at 373 corresponding to [WO3(bdt)H]- (left box). The
spectrum of an authentic sample of 3 (right box) is also presented.
the tentative stoichiometry of reaction 4, doubtless driven
by the stability of the WS2Cu core unit.
-
2½WO2ðbdtÞðμ2-SÞCuðPri2NHCMe2Þꢀ
f
-
½WOðbdtÞðμ2-SÞ2CuðPri2NHCMe2Þꢀ
þ ½WO3ðbdtÞꢀ þ ½CuðPri2NHCMe2ÞðsolvÞxꢀþ ð4Þ
2 -
A second approach utilizes CuI silylthiolate reactants and
is based on the difference of 25-40 kcal/mol between Si-O
and Si-S bond dissociation energies.28-30 Preparations and
structures of possible reactants are contained in Figure 5.
That of immediate interest is 9, isolated from the reaction of
Ph3SiSH and [Cu(S-1-Ad)2]- (52%). Like the other three
examples of mononuclear homoleptic two-coordinate CuI
thiolates,22,31,32 complex 9 has linear coordination (Cu-S
˚
2.148(1) A).
Reaction 5 is readily conceived with the desired mono-
sulfido-bridged complex and a siloxane as products.
However, the reaction takes a different course, and the
only isolable tungsten-copper product is the disulfido-
bridged complex 5 (31%, Figure 3). When the reactant
mol ratio is 2:1, the yield of 5 is increased to 60%.
Apparently, any monosulfido-bridged product formed is
subjected to a further reaction to form doubly bridged 5.
This reaction is described as 6, under which stoichiometry
a CuI-sulfide species is required. Any such species is likely
Figure 5. (a) Synthetic scheme leading to CuI silylthiolate complexes
9-12, three of which contain dithiolene chelate rings. Note the use of 9 in
the formation of 5 (Figure 2). (b) Structures of CuI complexes 9 (imposed
centrosymmetry) and 12 and Pri3SiS- (two independent anions) as the
Et4Nþ salt. Selected bond distances (A) and angles (deg): 9, Cu-S
2.1477(8), Si-S 2.094(1); 12, Cu-S1 2.259(1), Cu-S2 2.266(1), Cu-C
1.932(23), S1-Cu-S2 94.71(4), S1-Cu-C 132.4(1), S2-Cu-C 132.7(1);
Pri3SiS-, Si-S 2.071(8), 2.072(8).
(28) Luo, Y.-R. Handbook of Bond Dissociation Energies in Organic
Compounds; CRC Press: New York, 2003.
(29) Basch, H. Inorg. Chim. Acta 1996, 252, 265–279.
(30) Leroy, G.; Temsamani, D. R.; Wilante, C. J. Mol. Struct. (Theochem)
1994, 306, 21–39.
(31) Koch, S. A.; Fikar, R.; Millar, M.; O’Sullivan, T. Inorg. Chem. 1984,
23, 121–124.
(32) Zeevi, S.; Tshuva, E. Y. Eur. J. Inorg. Chem. 2007, 5369–5376.
formation of [WO3(bdt)H]-. Evidently any monosulfido
bridged species formed undergoes disproportionation with

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1089
to be insoluble in acetonitrile and would be removed in the
contains apical and basal sulfur atoms with consequent
differences in structure parameters, most notably θ =102°.
The MVI(μ2-S)2CuI bridge rhomb is a ubiquitous structural
element in the cluster chemistry of molybdenum and
tungsten,34-36 and is also present in recent dinuclear
Mo-Cu complexes relevant to the CODH site.18 In tungsten
chemistry, individual WVI(μ2-S)2CuI rhombs are most un-
common. These rhombs tend to be bridged to other such
units either through metal atom or through sulfido atoms
leading to μ3-S structures.37-40 As a result, the rhombs are
dimensionally somewhat variable; metric features of 3-6
and 8, occurring within known limits, are not exceptional.
-
-
½WO2ðbdtÞðOSiMe3Þꢀ þ ½CuðSSiPh3Þ2ꢀ
f
2 -
½WO2ðbdtÞðμ2-SÞCuðSSiPh3Þꢀ þ Ph3SiOSiMe3 ð5Þ
-
-
½WO2ðbdtÞðOSiMe3Þꢀ þ 2½CuðSSiPh3Þ2ꢀ
f
2 -
½WOðbdtÞðμ2-SÞ2CuðSSiPh3Þꢀ þ Ph3SiOSiMe3
-
þ ðPh3SiÞ2O þ ½CuSꢀ
ð6Þ
workup procedure. A second reaction system with differ-
ent silyl substituents was also investigated. Because
the compound (Et4N)[Cu(SSiPri3)2] could not be isolated,
the reaction was performed with a 1:1 mol ratio of
[Cu(MeCN)4](PF6) and (Et4N)(SSiPri3), which was sepa-
rately prepared and structurally characterized (Figure 5).
The use of 1 and 2 equiv of the silylthiolate afforded
doubly bridged 6 in 31% and 60% yields, respec-
tively. Again, no monosulfido bridged species could be
identified.
Summary
Reactions of the disulfido complex 2 with a set of CuI
reactants affords previously unknown square pyramidal
complexes of the type [WO(bdt)S2Cu(R)]2-/- with R =
Ar*S, Ar*, carbene, and R03SiS, a WVI(μ2-S)2CuI bridge
rhomb core, and trigonal planar CuI. The thiolate-ligated
complexes, with apical oxo and basal dithiolato and sulfido
coordination (excluding 8), terminal ligation at CuI, and
W-S-Cu bridging, bear a structural relation to the CODH
site (Figure 1). The presence of two such bridges and the
absence of a basal oxo or hydroxo ligand are significant
departures from the desired structure. All attempts thus far to
obtain molecules with the latter two features have not been
successful. Our conjecture, underscored by the formulation
of reaction 4, is that disproportion of an initially formed
monobridged species, minimally represented as 2O2W-
S-Cu f OWS2Cu þ WO3 þ Cu, is a reasonable rationaliza-
tion of the double-bridged structure. The driving force would
be the stability of the WS2Cu bridge rhomb abetted by the
formation of Si-O bonds in reaction 6. Suppression of this
reaction by steric means would require considerable frontside
hindrance, possibly attainable in the precursor [WOS(bdt)-
(OSiR3)]- with exceptionally capacious R substituents. The
stability of the only known molecule with an unsupported
Mo-S-Cu bridge17 may derive from coordinative satura-
tion and steric congestion at the MoV center. While the
desired structure was not realized, the present results should
be of use in the design of future experiments based on
monodithiolene complexes intended to eliminate double-
bridged products.
Dithiolate complexes 10-12 are prepared by reaction of
silylthiolates R3SiS- or the carbene with [Cu(mnt)(PPh3)]-
(Figure 5). The CuS3 and CuS2C coordination units are
˚
planar; Si-S bond distances are increased by about 0.02 A
upon binding. Metric features are unexceptional. The inten-
tion was to utilize 10 and 11 in place of 9 in reaction 5, leading
to complexes with one W-S-Cu bridge and a CuS3 unit.
Unfortunately, the CuI silylthiolates are somewhat unstable
in solution and did not yield pure products in multiple
attempts. Complexes 10-12 are initial examples of a three-
coordinate CuI dithiolate with silylthiolate or carbene
ligands, prompting their report here. Of the set, 12 and
the parent phosphine complex are stable in anaerobic
solution.
Structural Features. Complexes 3-6 exhibit the com-
mon features of distorted square pyramidal stereochem-
istry, planar WVI(μ2-S)2CuI bridge rhombs, displace-
˚
ments δ = 0.58-0.61 A of the tungsten atom above the
S4 basal plane, angles θ = 134-136° between coordina-
tion planes, τ = 0.08-0.29, and WS2/bdt dihedral or fold
angles of 15-24° (Table 3). The latter has been implicated
in stabilization of multiple redox states in molybdo- and
tungstoenzymes.33 Reduced metal centers form nearly
planar chelate rings (fold angle ∼0°) whereas oxidized
centers as in the present set of complexes cause folded
rings. The effect enables overlap of filled sulfur p-orbitals
with the metal in-plane vacant d-orbital. Copper(I) co-
ordination to sulfido bridge ligands removes some elec-
tron density such that the fold angles of 3 (23.6°) and 4
(20.5°) are larger than in precursor 2 (13.6°), and in 8
(14.6°) compared to [WS2(bdt)(OSiPh3)]-. Complex 8
differs from the others because the bridge rhomb
Acknowledgment. This research was supported by NSF
Grants CHE 0547734 and 0846397. We thank Drs. L.
Deng and W. Lo for experimental assistance.
Supporting Information Available: ESMS for complex 5, 1H
NMR for the complexes 3-12, (Et4N){SSiPh3] and (Et4N)-
{SSiPri3]. X-ray crystallographic files in CIF format for the 10
compounds in Tables 1 and 2. This material is available free of
charge via the Internet at http://pubs.acs.org.
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