Hybrid metal carbonyl-oxide clusters: Synthesis and structure of [Et4N]2[(OC)5WSbW3(CO)9( μ3-OMe)2(μ3-O)WO2(OR)] (R = Me, H)

Article abstract of DOI:10.1021/om020129c

The synthesis and structure of a novel hybrid metal carbonyl-oxide cluster was presented. The cluster was produced from W(CO)₆ and NaSbO₃. The terminal methoxide was loosely coordinated and was hydrolyzed to produce the hydroxide derivatives. NaSbO₃ and W(CO)₆ were heated in boiling methanol under an atmosphere of nitrogen.

Full text of DOI:10.1021/om020129c

Organometallics 2002, 21, 2581-2583
2581
Hybr id Meta l Ca r bon yl-Oxid e Clu ster s: Syn th esis a n d
Str u ctu r e of
[Et4N]2[(OC)5WSbW3(CO)9(µ3-OMe)2(µ3-O)WO2(OR)]
(R ) Me, H)
Li Xu and Kenton H. Whitmire*
Department of Chemistry, Rice University, 6100 Main Street, Houston, Texas 77005
Received February 19, 2002
Summary: The novel hybrid metal carbonyl-oxide clus-
ter [Et4N]2[(OC)5WSbW3(CO)9(µ3-OMe)2(µ3-O)WO2(OMe)]
produced from W(CO)6 and NaSbO3 contains a SbW3
tetrahedron that is triply bridged by the tungsten trioxide
[WO3(OMe)3]3-. The terminal methoxide is loosely coor-
dinated and can be hydrolyzed to produce the hydroxide
derivatives.
Transition-metal oxides and metal carbonyl cluster
compounds have both been studied as models for
catalytic processes or as catalysts themselves, but it is
rare that both high and low valence states are found in
the same molecule. Some metal carbonyl cluster com-
pounds that contain bridging oxide ligands have been
reported;1-9 the systems studied to date are all homo-
metallic clusters constituted solely of transition metals.
Although main-group-transition-metal carbonyl clus-
ters have been well documented10 and heterometallic
clusters have received attention for attachment to
support materials such as silica and alumina,10 no
studies have yet appeared on supported metal clusters
that also contain the heavy main-group elements. In this
paper, we report the reaction of tungsten hexacarbonyl
with sodium antimonate in methanol that leads to
unusual metal cluster complexes containing tungsten
in its highest oxidation state coupled to a low-valent
tungsten carbonyl unit. These compounds are
[Et4N]2[(OC)5WSbW3(CO)9(µ3-OMe)2(µ3-O)WO2(OR)],
which have been isolated for R ) Me ([Et4N]2[1a ]) and
R ) H ([Et4N]2[1b]). To our knowledge, they represent
the first examples that have the metal trioxide moiety
MO3 incorporated into metal carbonyl cluster units.
Heating NaSbO3 and W(CO)6 in boiling methanol
under an atmosphere of nitrogen after 3 days leads to
a brown-black solution from which [Et4N]2[1a ] was
obtained upon cooling and addition of [Et4N]BF4.11
According to the infrared spectrum of the reaction
solution, in the absence of NaSbO3, about half of the
W(CO)6 (1980 (s) cm-1) reacts in 3 days to produce a
compound with bands at 1926 (s) and 1881 (m) cm-1
.
This compound is believed to be W(CO)5(HOMe). For
comparison, the known anionic compound [Et4N][W(CO)5-
(11) [Et4N]2[1a ]: Using standard air-free techniques, a Schlenk flask
was charged with 1.0 mmol of NaSbO3 (0.19 g) and 5.0 mmol of W(CO)6
(1.8 g). To this were added 60 mL of methanol and 5 mL of n-heptane.
The mixture was further degassed with dry nitrogen for 30 min and
then refluxed for 5 days. The black crude reaction solution was cooled
to room temperature, at which point solid [Et4N]BF4 (2.2 g, 10 mmol)
was added. The resulting solution was evacuated under vacuum. The
resulting black solid was purified by extracting the cluster into THF
and allowing diethyl ether to diffuse slowly into the thf solution to
give [Et4N]2[1a ] (0.54 g, 30%). IR (thf; cm-1): 2070 (m), 1957 (s), 1916
(ms), 1874 (mw), 1850 (mw), 896 (s. 1H NMR (CD3CN; ppm): 4.47 (t-
OCH3, 3H), 4.07 (b-OCH3, 6H), 3.18 ([Et4N]+, q), 1.22 ([Et4N]+, t). Anal.
Calcd for C33H49N2O20SbW5: C, 21.59; H, 2.67; N, 1.53. Found: C,
21.05; H, 2.56; N, 1.54. [Et4N]2[1b]: [Et4N]2[1a ] (0.36 g, 0.2 mmol) was
dissolved in a mixture of acetonitrile (20 mL) and acetic acid (1 mL).
The resulting brown-black solution was refluxed under an atmosphere
of nitrogen for 10 h. The reaction solution was concentrated in vacuo
to half its volume. [Et4N]2[1b] was obtained as needlelike crystals from
slow diffusion of diethyl ether into the CH3CN solution. Yield: 0.20 g,
ca. 60%. IR (thf; cm-1): 2071 (m), 1957, 1918 (ms), 1876 (w), 1848,
896 (s). 1H NMR (CD3CN; ppm): 4.11 (OCH3, 6H), 6.11 (t-OH, 1H),
3.18 ([Et4N]+, q), 1.22 ([Et4N]+). Anal. Calcd for C32H47N2O20SbW5: C,
21.10; H, 2.58; N, 1.54. Found: C, 20.88; H, 2.59; N, 1.61.
(1) Gong, J .-H.; Hwang, D.-K.; Tsay, C.-W.; Chi, Y.; Peng, S.-M.; Lee,
G.-H. Organometallics 1994, 13, 1720-1727.
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Chem. 1984, 23, 1017-1021.
(3) (a) Chi, Y.; Hwang, L.; Lee, G.-H.; Peng, S.-M. J . Chem. Soc.,
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J .; Churchill, M. R. Organometallics 1987, 6, 301-307.
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Whitmire, K. H. J . Chem. Soc., Chem. Commun. 1983, 246-247.
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423-425.
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M.; Sansoni, M. J . Organomet. Chem. 1983, 249, C35-C37.
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10.1021/om020129c CCC: $22.00 © 2002 American Chemical Society
Publication on Web 05/23/2002

2582 Organometallics, Vol. 21, No. 13, 2002
Communications
(OMe)] exhibits bands at 1901 (s) and 1847 (m) cm-1 12
Similar shifts in CO stretching frequencies are exhibited
.
nearly identical CO absorption patterns in their infrared
spectra (2070 (w), 1956 (s), 1916 (ms), 1876 (w), 1848
(w) cm-1). A strong band at 896 cm-1 is attributable to
ν(WdO).
by W(CO)4(HOMe)2 (1864 (s), 1804 (m), 1790 (m) cm-1
)
when converted to (Et4N)2[W(CO)4(OMe)2] (1851 (s),
1808 (m), 1774 (m)).12 Boiling longer than 3 days did
not increase the amount of the hypothetical W(CO)5-
(HOMe) present in solution. In boiling phenol, we found
that W(CO)6 is quantitatively oxidized to the known
compound W(OPh)6, which has previously been pre-
pared by the phenolysis of WOCl4 or the reaction of
W(OCH2CH2O)3 with PhOAc.13 Workup of the reaction
mixture using [Et4N]Br instead of [Et4N]BF4 leads to
the formation of [Et4N][(CO)5WBr] in addition to [Et4N]2-
[1a ]. Presumably this byproduct arises from the reaction
of bromide ion with W(CO)5(HOMe). It is difficult to
The compound [Et4N]2[1a ] is an air-stable crystalline
solid. It is soluble in polar organic solvents such as
tetrahydrofuran, acetone, acetonitrile, and dichlo-
romethane. The solution is stable under an inert
atmosphere, but the compound is converted into [Et4N]2-
[W6O19] when its solutions are exposed to air. In
contrast, [Et4N]2[1b] remains unchanged in solution
even after several days in air. The reaction of [Et4N]2-
[1a ] with [tBu4N]2Mo2O7 in refluxing acetonitrile, which
was designed to replace the WO3 unit with polyoxomo-
lybdate, leads to the formation of [tBu4N]3[Mo3W3O19].14
The related heterometallic compound [tBu4N]3[MoW5O19]
was obtained from eletrochemical reduction of the
corresponding dianion prepared from WO3 and Na2-
MoO4.15 Attempts to prepare derivatives from replace-
ment of the methoxide ligands in [Et4N]2[1a ] with
phenolate or benzoate groups failed even under reflux-
ing conditions. In both cases the observed product was
[Et4N]2[1b].
Both [Et4N]2[1a ] and [Et4N]2[1b] crystallize as iso-
morphous, black, needle-shaped crystals from THF/
hexane.16 Figure 1 shows the structure of the cluster
dianion [(OC)5WSbW3(CO)9(µ3-OMe)2(µ3-O)WO2(OMe)]2-
[1a ]2-. The core structures of [1a ]2- and [1b]2- differ
only in that the former has the terminal MeO- ligand,
while the latter possesses a OH- ligand. The core
structure is characteristic of the SbW3 tetrahedron,
similar to those in the related clusters [Et4N]2-
[(OC)5MoAsMo3(CO)9(µ3-OMe)3Mo(CO)3]17 and [Et4N]2-
[BiMo3(CO)9(µ3-OMe)3Mo(CO)3].18 The Sb atom donates
its external lone pair of electrons to a W(CO)5 fragment,
showing more basic character of the lone pair of
electrons than the Bi atom.10 Like [(OC)5MoAsMo3(CO)9-
(µ3-OMe)3Mo(CO)3],17 [1a ]2- and [1b]2- have 50 cluster
electrons with one more pair of electrons than the
typical count. This counting scheme considers the com-
plex to be composed of [WO3(OMe)3]3- or [WO3(OMe)2-
(OH)]3- groups attached to a [:SbW3(CO)9]+ cluster core.
The [WO3(OMe)3]3- and [WO3(OMe)2(OH)]3- units do-
nate 12 electrons (4 electrons for each bridging meth-
oxide and oxo ligand).
-
separate from [Et4N]2[1a ]; therefore, the use of the BF4
salt is preferred.
When [Et4N]2[1a ] is treated with acetic acid in MeCN,
no change is observed after 1 h, but the cluster is
completely hydrolyzed to form [Et4N]2[1b] after 18 h.
[Et4N]2[1a ] shows two types of methoxy 1H NMR signals
at 4.47 and 4.07 ppm in a ratio of 1:2 attributable to
the terminal and bridging methoxide ligands. The
bridging MeO- and terminal OH- groups in [Et4N]2[1b]
display proton signals at 4.11 and 6.12 ppm, respec-
tively. It is interesting that an additional MeO- proton
signal at 4.25 ppm was observed in the reaction solution
containing [Et4N]2[1a ]. We believe this signal to arise
from the symmetric isomer [Et4N]2[(OC)5WSbW3(CO)9-
(µ3-OMe)3WO3] ([Et4N]2[1c]) with the methoxide ligands
An interesting structural feature is the asymmetry
in the positions of the methoxide and oxide ligands.
Instead of having all oxide ligands in bridging or
terminal modes, two oxide ligands are terminal and one
is bridging. As a consequence, one of the three methoxy
(14) Xu, L.; Whitmire, K. H. Unpublished results. Crystal data: a
) 30.301(3) Å, b ) 18.390(2) Å, c ) 27.411 (2) Å, â ) 112.258(1)°, V )
14136(2) Å3, Z ) 8, R1/wR2 ) 0.048/0.14 for 7115 observed reflections
(I 2σ(I)), GOF ) 1.17.
(15) Sanchez, C.; Livage, J .; Launay, J . P.; Fournier, M.; J eannin,
Y. J . Am. Chem. Soc. 1982, 104, 3194.
in the bridging positions based upon the chemical shift
of the 1H NMR signal. The signal disappears in the
presence of phenol or acetic acid. It appears that this
compound is much less stable than [Et4N]2[1a ] under
acidic conditions, It has eluded isolation to this point.
The compounds [Et4N]2[1a ] and [Et4N][1b] exhibit
(16) Crystal data for [Et4N]2[1a ]: crystal size 0.72 × 0.17 × 0.07
mm, monoclinic, space group C2/c, a ) 38.606(8) Å, b ) 11.595(2) Å, c
) 24.166(5) Å, â ) 112.11(3) Å, V ) 10 022(3) Å3, Z ) 8, µ ) 12.03
cm-1, dcalcd ) 2.432 g/cm3, R1/wR2 ) 0.031/0.074 for 5916 observed
reflections (I ) 2σ(I)), GOF ) 0.8. Crystal data for [Et4N]2[1b]: crystal
size 0.52 × 0.20 × 0.18 mm, monoclinic, space group P21/c, a ) 11.352-
(2) Å, b ) 44.091(9) Å, c ) 19.876(4) Å, â ) 104.11(3)°, V ) 9648(3) Å3,
Z ) 4, µ ) 12.50 cm-1, dcalcd ) 2.507 g/cm3, R1/wR2 ) 0.072/0.168 for
7441 observed reflections (I ) 2σ(I)), GOF ) 0.89.
(17) Van Hal, J . W.; Whitmire, K. H.; Zouchoune, B.; Halet, J .-F.;
Saillard, J .-Y. Inorg. Chem. 1995, 34, 5455-5460.
(18) Shieh, M.; Mia, F.-D.; Peng, S.-M.; Lee, G.-H. Inorg. Chem.
1993, 32, 2785.
(12) Darensbourg, D. J .; Klausmeyer, K. K.; Draper, J . D.; Chojnacki,
J . A.; Reibenspies, J . H. R. Inorg. Chim. Acta 1998, 270, 405.
(13) (a) Mortimer, P. I.; Strong, M. A. Aust. J . Chem. 1965, 18, 1579.
(b) Lehtonen, A.; Sillanp, R. Polyhedron 1999, 18, 175.

Communications
Organometallics, Vol. 21, No. 13, 2002 2583
(1.901(6) Å), whereas the other terminal W-O distances
are considerably shorter, being within the range ob-
served for WdO double bonds: [1a ]2- (W(5)-O(55) )
1.713(6) Å, W(5)-O(56) ) 1.718(6) Å); [1b]2- (1.63(2)-
1.74(2) Å, average 1.67(2) Å). The W(5)-µ3-O bond
lengths (1.931(6) Å in [1a ]2-, 1.87(1) Å in [1b]2-) are
considerably shorter than the [W3]-µ3-O bonds in the
carbonyl cluster unit (average 2.146(6) Å in [1a ]2-, 2.15-
(1) Å in [1b]2-). This may be explained by the Wd(µ3-
O)fW2 bonding mode as shown in the line drawing.
Such a bonding mode is not observed in related orga-
nometallic molybdenum oxide clusters, such as in Cp*3-
Mo5O11 (Mo-µ3-O ) 2.060(7) Å)20 and Cp*6Mo8O16 (Mo-
µ3-O ) 2.144(2) Å),21 although the Wd(µ-O)fOs system
has been discussed previously.3 The W(5)-(µ3-OMe)
bonds (average 2.314(6) Å in [1a ]2- and 2.29(2) Å in
[1b]2-) are longer than the [W3]-(µ3-OMe) bonds (aver-
age 2.210(6) Å in [1a ]2- and 2.21(2) Å in [1b]2-) due to
the trans influence of the terminal oxo atoms. The
dative σ-bonds between the Sb atoms and W(1) are
slightly shorter than those found in Ph3SbW(CO)5
F igu r e 1. ORTEP drawing of [1a ]2- with 30% probability
thermal ellipsoids. Selected bond lengths (Å): Sb(1)-W(1),
2.7338(8); Sb(1)-W(2), 2.732(1); Sb(1)-W(3), 2.7124(7);
Sb(1)-W(4), 2.7390(8); W(2)-W(3), 3.0805(7); W(2)-W(4),
3.0327(10); W(3)-W(4), 3.0942(7); W(2)-O(51), 2.187(5);
W(2)-O(53), 2.148(5); W(3)-O(52), 2.207(5). W(3)-O(53),
2.149(5); W(4)-O(51), 2.191(5); W(4)-O(52), 2.213(5); W(5)-
O(51), 2.190(5); W(5)-O(52), 2.213(5); W(5)-O(53), 1.928(5);
W(5)-O(54), 1.901(6); W(5)-O(55), 1.713(6); W(5)-O(56),
1.718(6). The corresponding values (Å) for one of the
molecules in the asymmetric unit of [1b]2- are as follows:
Sb(1a)-W(1a), 2.732(2); Sb(1a)-W(2a), 2.731(2); Sb(1a)-
W(3a), 2.706(2); Sb(1a)-W(4a), 2.730(2); W(2a)-W(3a),
3.051(2); W(2a)-W(4a), 3.040(2); W(3a)-W(4a), 3.071(2);
W(2a)-O(51a), 2.19(1); W(2a)-O(53a), 2.21(1); W(3a)-
O(52a), 2.20(1), W(3a)-O(53a), 2.08(1); W(4a)-O(51a),
2.19(2); W(4a)-O(52a), 2.22(1); W(5a)-O(51a), 2.18(1);
W(5a)-O(52a), 2.27(2); W(5a)-O(53a), 1.86(1); W(5a)-
O(54a), 1.94(1); W(5a)-O(55a), 1.74(2); W(5a)-O(56a),
1.63(2).
(2.753(0) Å).22 Unlike the case of the As cluster [2]2-
,
the Sb-W bonds are longer than in the open Sb-W
compound W2(CO)10Sb{CH(SiMe3)2} (2.687(1) Å)23 but
considerably shorter than those found in closed species
such as {W2(CO)10}{W(CO)5}SbtBu (2.825(5) Å),24 (F3C)2-
SbW(CO)3MeCp (2.8058(7) Å),25 and CpW(CO)3Sb(Nt-
Bu)2SiMe2 (3.010(1) Å).26 The W-W distances in the W3
triangle (average 3.069(1) Å) are within the range of
formal W-W single bonds, as found in [W3(CO)9(µ-
OC2H5)(µ3-OC2H5)2] (2.939(2), 2.966(2) Å),27 [CpW-
(CO)3]2 (3.222(1) Å),28 and [(µ-Et2P)W(CO)4]2 (3.05(1)
Å).29
Ack n ow led gm en t. This work was supported by the
National Science Foundation (Grant No. CHE9983352)
and the Robert A. Welch Foundation.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordination and isotopic parameters, and bond
lengths and angles for [Et4N]2[1] and [Et4N]2[2] and an ORTEP
drawing of [1b]2-. This material is available free of charge via
the Internet at http://pubs.acs.org.
ligands in [1a ]2- becomes terminal, and it is this
methoxide ligand that is replaced by hydroxide ion. It
is not clear whether selection of this asymmetric struc-
ture is determined by kinetics or thermodynamics, but
the trianionic [WO3(µ3-OMe)3]3- unit in the symmetric
isomer may be highly reactive because of the strong
basicity of the terminal oxo ligands as observed in
Cp*WO3.19 While the proton attached to the hydroxide
ligands could not be located with certainty in the X-ray
structure determination, it is clear from the asymmetry
in the W-O bond distances that this ligand occupies
the same coordination site as the methoxide group. The
W-O bond length assigned to the OH- ligand in [1b]2-
(1.94(2) Å) is similar to the Mo-OMe bond in [1a ]2-
OM020129C
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