Osmium-antimony higher nuclearity clusters

Article abstract of DOI:10.1021/om010039s

Thermolysis of Os₃(CO)₁₁(SbPh₃), 1, in refluxing octane gave initially the clusters Os₃(μ-SbPh₂)(μ-H)(μ₃,η² -C₆H₄)(CO₉), 2, and Os₆(μ₃-SbPh)(μ₃,η²-C₆ H₄)(CO)₂₀, 3. Prolonged heating gave the cluster Os₆(μ₄-Sb)(μ-H)(μ₃ η⁴-C₁₂H₈) (μ₃,η²-C₆H₄)(CO)₁₆ , 4, as the major product. In contrast, thermolysis in hexane at 115 °C in a Carius tube gave Os₆(μ₄-Sb)(μ-SbPh₂)(μ-H)₂ -(μ₃,η⁴-C₁₂H₈) (μ₃,η²-C₆H₄)(CO)₁₅ , 5, Os₆(μ₄-Sb)(μ-SbPh₂)(μ-H) (μ₃,η²-C₆H₄)₂ (C₆H₅)(CO)₁₆, 6, and Os₆(μ₄-Sb)(μ-SbPh₂)(μ-H) (μ₃,η⁶-C₆H₄) (μ₃,η²-C₆H₄) (C₆H₅)(CO)₁₅, 7, besides 2 and 3. It has been demonstrated that cluster 6 was formed from 2, while clusters 5 and 7 were formed from the further decomposition of 6. The reaction of 5 with SbPh₃ afforded a monosubstituted derivative, Os₆(μ₄-Sb)(μ-H)₂(μ-SbPh₂) (μ₃,η²-C₆H₄)(μ₃ ,η⁴-C₁₂H₈)(CO)₁₄ (SbPh₃), 8. The clusters 2-8 were all shown by single-crystal X-ray crystallographic studies to have a benzyne moiety acting as a four-electron donor to a triosmium fragment. In addition, 4 and 8 contain a novel μ₃,η⁴-biphenylene moiety bound to a triosmium framework, while 7 was found to have a μ₃,η¹:η¹:η⁶ -C₆H₄ ring.

Full text of DOI:10.1021/om010039s

2
280
Organometallics 2001, 20, 2280-2287
Osm iu m -An tim on y High er Nu clea r ity Clu ster s
Weng Kee Leong* and Guizhu Chen
Department of Chemistry, National University of Singapore, Kent Ridge, Singapore 119260
Received J anuary 19, 2001
Thermolysis of Os
3
(CO)11(SbPh
)(CO) , 2, and Os
-Sb)(µ-H)(µ
3
), 1, in refluxing octane gave initially the clusters Os
3
(µ-
)(CO)20, 3. Prolonged heating
)(CO)16, 4, as the major product. In
(µ -Sb)(µ-SbPh )(µ-H)
(C )(CO)16, 6, and
)(CO)15, 7, besides 2 and 3. It has been
demonstrated that cluster 6 was formed from 2, while clusters 5 and 7 were formed from
2
2
SbPh
gave the cluster Os
2
)(µ-H)(µ
3
,η -C
6
H
(µ
4
9
6
(µ
,η -C12
3
-SbPh)(µ
3
6 4
,η -C H
4
2
6
4
3
H
8
)(µ
3
6 4
,η -C H
contrast, thermolysis in hexane at 115 °C in a Carius tube gave Os
6
4
2
2
-
4
2
2
(µ
3
,η -C12
H
8
)(µ
3
,η -C
6
H
4
)(CO)15, 5, Os
6
(µ
4
-Sb)(µ-SbPh
2
)(µ-H)(µ
3
,η -C
6
H
4
)
2
6 5
H
6
2
Os
6
(µ
4
-Sb)(µ-SbPh
2
)(µ-H)(µ
3
,η -C
6
H
4
)(µ
3
6 4 6 5
,η -C H )(C H
the further decomposition of 6. The reaction of 5 with SbPh
3
afforded a monosubstituted
2
4
derivative, Os
6
(µ
4
-Sb)(µ-H)
2
(µ-SbPh
2
)(µ
3
,η -C
6
H
4
)(µ
3
,η -C12
H
8
)(CO)14(SbPh ), 8. The clusters
3
2
-8 were all shown by single-crystal X-ray crystallographic studies to have a benzyne moiety
acting as a four-electron donor to a triosmium fragment. In addition, 4 and 8 contain a
novel µ ,η -biphenylene moiety bound to a triosmium framework, while 7 was found to have
4
3
1
1
6
a µ
3
6 4
,η :η :η -C H ring.
2
In tr od u ction
Despite the increasing trend toward rational synthe-
(CO)9(PPh3), and Os3(µ-PPh2)(µ-H)(µ3,η -C6H4)(CO)7-
PPh3); and three complexes obtained from loss of
(
phenyl rings, viz., Os3(µ-PPh2)(µ-PPhC6H4)(Ph)(CO)8,
Os3(µ-PPh2)2(µ3,η -C6H4)(CO)7, and Os3(µ-PPh2)(CO)8-
PPh3) (Scheme 1). Later work on this reaction and
related systems by Deeming’s group has led to clarifica-
tion of much of the reaction pathway; he has demon-
strated that the clusters resulting from loss of phenyls
and/or orthometalation were formed from thermal de-
composition of the substituted products, and it was clear
that the nature of the ligand was important in deter-
sis, much of the discoveries in higher nuclearity carbonyl
clusters are still based on pyrolytic and redox condensa-
tion reactions. Careful control of pyrolytic conditions can
lead to useful stepwise decarbonylation as, for example,
in the vacuum pyrolysis of Os3(CO)12, which afforded a
large number of clusters ranging in nuclearity from 5
2
7
(
1
to 11, but the conditions can be optimized to give Os6-
2
(
CO)18 in up to 80% yield. Heteroatoms of the main
group can also play an important role in cluster forma-
tion. The main group elements may be incorporated into
the pyrolysis products via the splitting of organic ligands
as, for example, in the thermolysis of Os3(µ-SR)(µ-H)-
8
,9
mining the product distribution.
In all these thermal decomposition reactions, there
were no reports of cluster aggregation to form higher
nuclearity clusters. In fact, low yields of dimeric species
such as Os2(µ-AsMe)2(µ,η -C6H4)(CO)6 were obtained
from the AsMe2Ph complexes, indicating cluster frag-
(
(
CO)10 (R ) CH2C6H5) to give two isomers of Os6(µ4-S)-
µ3-S)(µ-H)2(CO)17 through homolysis of the C-S bond
2
3
,4
and formation of dibenzyl. The condensation of Os3-
CO)10(NCCH3)2 with Os3(µ3-S)2(CO)9 or Os4(µ3-S)(CO)12
8
mentation. We have also recently reported that the
(
thermolysis of Os3(CO)11(AsPh3) gave rise to four major
products, which contained Os3As or Os3As2 cores.10 Our
past experience with antimony-containing clusters has
been that they can behave very differently from the
phosphine and arsine analogues. We were therefore
interested to determine if thermolysis of antimony-
containing derivatives of osmium would afford structur-
gave Os6(µ4-S)(µ3-S)(CO)17 or Os7(µ4-S)(CO)19, respec-
5
tively, and it is believed that the sulfur atoms played
a key role in linking the low-nuclearity cluster units and
6
directing the formation of the new clusters.
1
1
Among osmium clusters containing group 15 ele-
ments, the classic reaction is that of Os3(CO)12 with
excess PPh3 in refluxing xylene to give a mixture of
nine compounds: the substitution derivatives Os3(CO)12-
n(PPh3)n (n ) 1-3); three hydride-bridged species Os3-
(
7) (a) Bradford, C. W.; Nyholm, R. S. J . Chem. Soc., Dalton Trans.
973, 5, 529. (b) Gainsford, G. J .; Guss, J . M.; Ireland, P. R.; Mason,
R.; Bradford, C. W.; Nyholm, R. S. J . Organomet. Chem. 1972, 40, C70.
c) Bradford, C. W.; Nyholm, R. S.; Gainsford, G. J .; Guss, J . M.;
1
(
µ-PPh2C6H4)(µ-H)(CO)8(PPh3), Os3(PPh2C6H4)(µ-H)-
(
Ireland, P. R.; Mason, R. J . Chem. Soc., Chem. Commun. 1972, 87.
(8) (a) Arce, A. J .; Deeming, A. J . J . Chem., Soc., Dalton Trans. 1982,
1155. (b) Deeming, A. J .; Kimber, R. E.; Underhill, M. J . Chem., Soc.,
Dalton Trans. 1973, 2589.
(9) (a) Deeming, A. J .; Kabir, S. E.; Powell, N. I.; Bates, P. A.;
Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1987, 1529. (b) Brown,
S. C.; Evans, J .; Smart, L. E. J . Chem. Soc., Chem. Commun. 1980,
1021. (c) Deeming, A. J .; Marshall, J . E.; Nuel, D.; O’Brien, G.; Powell,
N. I. J . Organomet. Chem. 1990, 384, 347.
(10) Tay, C. T.; Leong, W. K. J . Organomet. Chem., in press.
(11) (a) Chen, G.; Leong, W. K. J . Chem. Soc., Dalton Trans. 1998,
2489. (b) Chen, G.; Leong, W. K. J . Organomet. Chem. 1999, 574, 276.
(c) Leong, W. K.; Chen, G. J . Chem. Soc., Dalton Trans. 2000, 4442.
(
1) Braga, D.; Henrick, K.; J ohnson, B. F. G.; Lewis, J .; McPartlin,
M.; Nelson, W. J . H.; Sironi, A.; Vargas, M. D. J . Chem. Soc., Chem.
Commun. 1983, 1132.
(
2) Eady, C. R.; J ohnson, B. F. G.; Lewis, J . J . Chem. Soc., Dalton
Trans. 1975, 2606.
3) Adams, R. D.; Horvath, I. T.; Segmuller, B. E.; Yang, L. W.
Organometallics 1983, 2, 1301.
(
(
(
4) Adams, R. D.; Yang, L. W. J . Am. Chem. Soc. 1982, 104, 4115.
5) Adams, R. D.; Horvath, I. T.; Yang, L. W. J . Am. Chem. Soc.
1
983, 105, 1533.
6) Adams, R. D.; Foust, D. F.; Mathur, P. Organometallics 1983,
, 990.
(
2
1
0.1021/om010039s CCC: $20.00 © 2001 American Chemical Society
Publication on Web 05/01/2001

Osmium-Antimony Higher Nuclearity Clusters
Organometallics, Vol. 20, No. 11, 2001 2281
Sch em e 1
ally different complexes. In this paper, we report on our
work with the monosubstituted triphenylstibine deriva-
tive Os3(CO)11(SbPh3), 1.
Resu lts a n d Discu ssion
When a suspension of 1 was heated under reflux in
octane, the color of the solution changed from yellow to
orange. When the reflux was halted after half an hour,
and the mixture separated by TLC, two other major
bands besides unreacted 1 were obtained. The first of
2
these afforded Os3(µ-SbPh2)(µ-H)(µ3,η -C6H4)(CO)9, 2,
as a yellow solid. Cluster 2 is closely related to the
2
known arsenic analogues Os3(µ-AsR2)(µ-H)(µ3,η -C6H4)-
(
CO)9, products from the pyrolysis of the arsine-
1
2
substituted clusters Os3(CO)11(AsR2Ph) (R ) Me,
F igu r e 1. ORTEP diagram (organic hydrogens omitted,
50% probability thermal ellipsoids) and selected bond
parameters for the ordered molecule of 2. Os(7)-Os(8) )
1
0
Ph ); they have similar patterns in their IR spectrum
for the carbonyl stretching region. The structure of 2
has been confirmed by a single-crystal X-ray crystal-
logaphic study (Figure 1). The second TLC band gave a
red solid, the identity of which was determined by X-ray
2
2
.8538(6) Å; Os(8)-Os(9) ) 2.9788(6) Å; Os(7)-Sb(12) )
.6473(9) Å; Os(9)-Sb(12) ) 2.6481(9) Å; ∠ Os(7)Os(8)Os-
(
9) ) 87.838(17)°; ∠ Os(7)Sb(12)Os(9) ) 99.67(3)°; ∠ Sb-
(12)Os(7)Os(8) ) 84.64(2)°; ∠ Sb(12)Os(9)Os(8) ) 82.18(2)°.
2
crystallography as the novel cluster Os6(µ3-SbPh)(µ3,η -
C6H4)(CO)20, 3 (Figure 2). Cluster 3 comprises two
discrete Os3 triangles that are linked via a µ3-SbPh
moiety; one of the triosmium units carries a µ3,η -
C-C bond formation, and oxidative addition of C-H
bonds. Thus in contrast to the phosphine and arsine
analogues, the thermolysis of 1 in octane resulted in
condensation reactions to higher nuclearity clusters.
The mechanism by which cluster expansion occurs is
thought to involve formation of coordinatively unsatur-
ated species by dissociation of ligands or cleavage of
M-M bonds; these coordinatively unsaturated frag-
ments are apparently the key intermediates that con-
2
benzyne ligand.
The prolonged reflux of 1 in octane (5 h) gave a dark
red solution and a brown precipitate. Chromatographic
separation of the reaction mixture gave many products
in low yields, one of which was a red crystalline material
2
identified as the novel cluster Os6(µ4-Sb)(µ-H)(µ3,η -
4
C6H4)(µ3,η -C12H8)(CO)16, 4 (Figure 3). The structure of
13
dense to give high nuclearity clusters. We believe that
4
exhibits two triosmium units that are linked via a µ4-
the initial decarbonylation compound, 2, obtained from
Sb-C and Os-Os bond cleavages and ortho C-H bond
activation from 1, played an important role in the
antimony atom. Another novel feature is the presence
of a biphenylene ligand, the formation of which must
involve a multistep process, including Sb-C cleavage,
(
13) (a) J ohnson, B. F. G.; Lewis, J . Adv. Inorg. Chem. Radiochem.
(
12) Deeming, A. J .; Rothwell, I. P.; Hursthouse, M. B.; Backer-
1981, 24, 225. (b) Vargas, M. D.; Nicholls, J . N. Adv. Inorg. Chem.
Radiochem. 1986, 30, 123.
Dirks, J . D. J . J . Chem. Soc., Dalton Trans. 1981, 1879.

2
282 Organometallics, Vol. 20, No. 11, 2001
Leong and Chen
F igu r e 2. ORTEP diagram (organic hydrogens omitted,
0% probability thermal ellipsoids) for molecule 1 of 3.
F igu r e 4. ORTEP diagram (organic hydrogens omitted,
50% probability thermal ellipsoids) for 8.
5
presence of benzene; the added benzene could conceiv-
ably act as a source of phenyl for the formation of the
biphenylene moiety. As it turned out, there was no
change in the IR spectrum of the reaction mixture even
after 5 h of heating. In contrast, in the absence of
benzene, refluxing 3 in octane led to a rapid change in
the color of the solution from pink-red to dark red; TLC
separation afforded several bands but no 4. These
reactions demonstrated that 3 probably decomposed via
loss of benzene and that 4 was not derived from 2 via 3
but via some other intermediate.
In an attempt to control the thermal decomposition,
we also carried out a thermolysis of 1 in hexane at 115
°
C in a Carius tube. After 20 h of heating, an orange-
red solution and a brown precipitate were obtained,
from which five clusters (besides unreacted 1) were
isolated (Scheme 2).
F igu r e 3. ORTEP diagram (organic hydrogens omitted,
0% probability thermal ellipsoids) for 4.
5
2
The new clusters Os6(µ4-Sb)(µ-SbPh2)(µ-H)2(µ3,η -
formation of 3 and 4. Cluster 3 may conceivably be
formed by the attack of an “Os3(CO)11” moiety on 2. It
has been suggested that in the reactions of Os3(CO)11-
4
C6H4)(µ3,η -C12H8)(C6H5)(CO)15, 5, Os6(µ4-Sb)(µ-SbPh2)-
2
(
µ-H)(µ3,η -C6H4)2(CO)16, 6, and Os6(µ4-Sb)(µ-SbPh2)(µ-
2
6
H)(µ3,η -C6H4)(µ3,η -C6H4)(C6H5)(CO)15, 7, were char-
acterized by IR and NMR spectroscopy, elemental
analyses, and single-crystal X-ray crystallographic stud-
ies. Despite numerous attempts at growing a suitable
crystal of 5, however, we invariably ended up with
extremely thin plates, which afforded data sets that
were of a quality that was sufficient to establish the
heavy atom positions, but not enough to provide reliable
data on the light atoms. We thus attempted to obtain a
substitution derivative that would afford good diffrac-
tion quality crystals, which would then allow corrobora-
tion of the proposed structure of 5. We were fortunate
in that the reaction of 5 at room temperature with
SbPh3 proceeded smoothly to give a red solution, from
which one product was obtained after TLC separation.
The molecular structure of this compound has been
determined by a single-crystal X-ray crystallographic
(
PMe2Ph) a CO group initially dissociates, whereas in
the AsMe2Ph analogue, the arsine ligand, which is more
weakly bound than the phosphine, could dissociate in
competition with CO.14 We therefore conjectured that
dissociation of SbPh3 from 1 may have occurred during
the reaction to afford the “Os3(CO)11” moiety. We
initially attempted to verify this by refluxing 2 with Os3-
(
CO)11(NCCH3) or Os3(CO)12 in octane, but no 3 was
observed. We thought that perhaps this may be due to
the poor solubility of Os3(CO)11(NCCH3) and Os3(CO)12
in octane. We then tried reacting 2 with 1 equiv of 1;
this gave cluster 3 in higher yield than the direct
thermolysis of 1 (40% vs 10%); the reaction was also
more facile (shorter reaction time and lower tempera-
ture). Also consistent with this, we have found that
thermolysis of 1 under a CO atmosphere gave mainly
Os3(CO)12, pointing to dissociation of the SbPh3 ligand.
That 2 was not observed in the reaction mixture on
prolonged reflux indicated that 2 was likely also the
precursor to 4, possibly via 3 as an intermediate; the
latter possibility was suggested by the structural simi-
larities between 3 and 4. We conjectured that 3 may
decarbonylate and undergo an Sb-C bond cleavage and
a C-C coupling to afford 4. We thus heated 3 in the
2
4
study as Os6(µ4-Sb)(µ-H)2(µ-SbPh2)(µ3,η -C6H4)(µ3,η -
C12H8)(CO)14(SbPh3), 8 (Figure 4).
The structures of 5, 6, and 7 are closely related
(Figures 5 and 6, Scheme 2). All three clusters have
similar metal skeletons; the main differences lie in their
ligand sets. The route for the formation of cluster 6 was
suggested by the structure of the compound itself; 6 may
be considered as being derived from the condensation
of two molecules of 2. Indeed, thermolysis of 2 did afford
a high yield of cluster 6.
(14) Deeming, A. J .; Kimber, R. E.; Underhill, M. J . Chem., Soc.,
Dalton Trans. 1973, 2589.

Osmium-Antimony Higher Nuclearity Clusters
Organometallics, Vol. 20, No. 11, 2001 2283
Sch em e 2
quite robust. Heating a solution of 6 in hexane at 110
C for 2 h gave 5 (70%) and 7 (10%) as the major
°
products, thus indicating that both 5 and 7 were derived
from 6 by further competitive decomposition (Scheme
3
). The formation of 5 from 6 should be a multistep
process, involving the elimination and migration of CO
ligands, C-H and Os-C bond cleavage, and C-C bond
formation, but the sequence of these processes remains
unknown. Although the elimination of only one carbonyl
and cleavage of an Os-Os bond in 6 could stoichiomet-
rically lead to 7, the yield was much lower than
expected. This suggested that the Os3(µ-SbPh2)(µ-H)-
2
(
µ3,η -C6H4)(CO)8 subunit in 6 is more robust than its
other subunit.
F igu r e 5. ORTEP diagram (organic hydrogens omitted,
Cr ysta llogr a p h ic Stu d ies
5
0% probability thermal ellipsoids) for 6.
Cluster 2 has three crystallographically distinct mol-
ecules in the asymmetric unit, two of which showed
disorder about the Os3Sb core; the ordered molecule,
together with its selected bond parameters, is shown
in Figure 1. The SbPh2 fragment forms a symmetrical
bridge across the Os(7)‚‚‚Os(9) edge; at 4.05 Å this is
clearly nonbonding, and electron count requires that the
2
µ3,η -C6H4 ligand acts as a four-electron donor. The
metal hydride was not located in the X-ray crystal
structure; its position was calculated with the program
1
5
XHYDEX as bridging the longer Os(8)-Os(9) edge, in
accord with general observations in triosmium cluster
chemistry.
Selected bond parameters involving the heavy atoms
for clusters 3, 4, 6, 7, and 8 are given in Table 1; there
are two crystallographically distinct molecules in 3.
With the exception of 3, all the other clusters are
characterized by the presence of a µ4-Sb moiety joining
two triosmium units, and bridging metal hydrides. The
presence of the bridging hydrides were indicated in their
F igu r e 6. ORTEP diagram (organic hydrogens omitted,
5
0% probability thermal ellipsoids for 7.
The similarity of the structures of 5, 6, and 7 sug-
gested that they may be related mechanistically. For
example, 5 may be formed from 6 by an intracluster
oxidative addition of the benzyne into the â C-H bond
of the terminal phenyl ligand. UV irradiation (15 W,
1
H NMR spectra, and their positions were determined
(15) Orpen, A. G. XHYDEX: A Program for Locating Hydrides in
3
60 nm) of a CH2Cl2 solution of 6 was monitored by IR
Metal Complexes; School of Chemistry, University of Bristol: UK,
1997.
spectroscopy and indicated that 6 was photochemically

2
284 Organometallics, Vol. 20, No. 11, 2001
Leong and Chen
Sch em e 3
Ta ble 1. Selected Bon d P a r a m eter s for Clu ster s 3, 4, 6, 7, a n d 8
bond parameter
3
4
6
7
8
Os(1)-Os(2)
2.7939(12); 2.8024(10)
2.9095(11); 2.9101(11)
2.7739(10); 2.7659(12)
2.9133(12); 2.9174(10)
2.8704(11); 2.8794(10)
2.8910(12); 2.8824(11)
2.7170(14); 2.7201(15)
2.7240(16); 2.7263(13)
2.6327(15); 2.6344(14)
2.7778(6)
2.9368(6)
2.7907(6)
2.9022(6)
2.8875(6)
2.8812(6)
2.6960(8)
2.6911(8)
2.5504(8)
2.5529(8)
2.9113(9)
2.9422(8)
2.9547(9)
3.0037(9)
Os(1)-Os(3)
3.0165(10)
Os(2)-Os(3)
Os(4)-Os(5)
2.8943(9)
2.8466(9)
2.8188(9)
2.5376(11)
2.7664(11)
2.6306(11)
2.6474(12)
2.6310(11)
2.6621(12)
2.8716(11)
2.7962(12)
2.8089(10)
2.6762(15)
2.5929(15)
2.6583(14)
2.6452(15)
2.6447(15)
2.6125(16)
2.9241(11)
2.8869(11)
2.8741(11)
2.5713(12)
2.7763(12)
2.5589(13)
2.5663(13)
2.6235(13)
2.6912(14)
2.6695(13)
68.22(3)
Os(4)-Os(6)
Os(5)-Os(6)
Os(1)-Sb(7)
Os(3)-Sb(7)
Os(4)-Sb(7)
Os(5)-Sb(7)
Os(2)-Sb(8)
Os(3)-Sb(8)
Os(2)-Sb(9)
Os(1)-Sb(7)-Os(3)
Os(4)-Sb(7)-Os(5)
Os(2)-Sb(8)-Os(3)
64.65(4); 64.59(3)
66.07(2)
69.32(2)
67.22(3)
66.51(3)
101.04(4)
69.83(4)
65.57(4)
93.97(5)
69.57(4)
102.13(4)
by potential energy calculations using XHYDEX, with
the exception of 7, in which the hydride was located in
a low-angle difference map.
This structural feature of a spirocyclic µ4-Sb has been
observed in one instance for iron,16 but the clusters
presented here are the first examples from osmium
cluster chemistry. An interesting observation here is
that there is a large Os-Os bond lengthening effect of
a bridging Sb: the Os-Os edges bridged by the µ4-Sb
The Os-Sb bond lengths vary from 2.5376(11) Å in 6
to 2.7763(12) Å in 8; in fact, the upper limit is longer
than the Os(2)-Os(3) bond in 3 (2.7728(10) and 2.7657-
(11) Å). On the other hand, ∠ Os-Sb-Os angles can vary
from 64.59(3)° to 69.83(4)° over a “closed” Os-Os edge
and from 93.97(5)° to 102.13(4)° over an “open” Os‚‚‚Os
edge. It is therefore quite apparent that the bond
parameters associated with the antimony atoms vary
over a wide range, indicating that antimony can accom-
modate a large amount of molecular distortions.
(
4
Os(1)-Os(3) for 3, 4, 6, 7, and 8 and Os(4)-Os(5) for
, 6, 7, and 8) are invariably the longest of the Os-Os
Cluster 3 comprises two discrete Os3 triangles that
are linked via a µ3-SbPh moiety; one of the triosmium
edges in a given triosmium unit; this effect is even
greater than that of a bridging hydride,17 as is most
readily discerned in 4, 6, and 8.
(17) (a) Leong, W. K. M.Sc. Thesis, National University of Singapore,
1
992. (b) Churchill, M. R.; DeBoer, B. G.; Rotella, F. J . Inorg. Chem.
(
16) Rheingold, A. L.; Geib, S. J .; Shieh, M.; Whitmire, K. H. Inorg.
1976, 15, 1843. (c) Bau, R.; Teller, R. G.; Kirtley, S. W.; Koetzle, T. F.
Acc. Chem. Res. 1979, 12, 176.
Chem. 1987, 26, 463.

Osmium-Antimony Higher Nuclearity Clusters
Organometallics, Vol. 20, No. 11, 2001 2285
Sch em e 4
contributing two electrons to the Os3(µ-SbPh)(µ-H)-
2
(CO)8(µ3,η -C6H4) fragment; this satisfies the EAN rule
for the fragment. The µ4-Sb can then be considered to
contribute three electrons to the Os3 fragment carrying
the biphenylene ligand, and hence the latter should be
regarded as a six-electron donor in order to satisfy the
EAN rule.
Cluster 7 also possesses an interesting structural
feature; there is a C6H4 unit that appears to be σ-bonded
6
to two osmium atoms (Os(1) and Os(3)) and η -
coordinated to Os(2). This would imply that the C6H4
unit is acting as an eight-electron donor ligand; consis-
tent with this is the presence of only one Os-Os bond,
as required by the electron count. There is no analogue
to 7 known in osmium cluster chemistry, although the
6
feature of a µ3,η -C6H4 unit has been observed in some
triruthenium-chromium clusters that were obtained
6
from the reaction of Ru3(CO)12 with some η -C6H5Cr-
2
units carries a µ3,η -benzyne ligand, while the other is
containing precursor like P[C6H5Cr(CO3)]2Ph or P[C6H5-
an “Os3(CO)11” unit. The Os-Os edge on this “Os3-
CO)11” unit that is cis to the Os-Sb bond (Os(1)-Os-
2) and Os(4)-Os(5)) is elongated with respect to the
t
Cr(CO3)]2Bu and from the pyrolysis of Ru3(CO)11-
(
(
AsMe2C6H5Cr(CO)3];21 all these have η -coordination
6
[
to a Cr atom.
other Os-Os edges (2.9137(11) and 2.9175(9) Å, respec-
tively, for the two crystallographically distinct mol-
ecules, compared to 2.8708(11)-2.8912(11) Å for the
other edges); this is consistent with the observation that
the substitution of a CO group by a σ-donating ligand
at an equatorial position in a triosmium unit usually
Con clu sion
In this paper, we have reported that the thermolysis
of 1 at ∼120 °C gave initially the trinuclear cluster 2.
Over a longer reaction time, and depending on the
control of CO loss, higher nuclearity clusters 3-7 were
formed in varying amounts. All of these higher nucle-
arity clusters represent new structural types in os-
mium-antimony cluster chemistry and are the first
examples of higher nuclearity clusters of osmium and
1
8
results in the lengthening of the M-M bond cis to it.
2
In other words, the (µ-SbPh)Os3(CO)9(µ3,η -C6H4) group
may be regarded as a very bulky stibine toward the “Os3-
(CO)11” unit.
A novel feature in 4, 5, and 8 is the presence of a
biphenylene ligand. One of the osmium atoms (Os(6))
lies in the plane of the biphenylene ligand, and the
ligand is tilted toward the other two osmiums; the
dihedral angles between the Os(4)Os(5)Os(6) and bi-
phenylene planes are 66.2° and 66.4° for 4 and 8,
respectively. Thus the bonding situation can be de-
scribed as comprising two σ interactions to the unique
antimony containing a µ -Sb moiety. The structural
details show that there is capacity for a wide variation
4
in bond parameters involving antimony. The relation-
ship among these clusters is depicted in Scheme 3.
Formation of the higher nuclearity clusters found neces-
sarily involves Os-Sb and C-C bond formation and
Sb-C and C-H bond cleavage. Thus compared to
osmium-phosphorus or -arsenic clusters, osmium-
antimony clusters exhibit a greater tendency to form
higher nuclearity clusters via condensation at an anti-
mony atom.
2
osmium atom and an η interaction each to the two
osmium atoms that are bridged by the antimony atom;
the Os‚‚‚C distances involved in such a bonding situa-
tion range from about 2.16 Å to 2.74 Å (Scheme 4), while
the other Os‚‚‚C distances are all > 3.0 Å. This is a novel
bonding mode for biphenyl; a closely related example
Exp er im en ta l Section
4
is that found in the dinuclear clusters M2(CO)6(µ,η -
Gen er a l Exp er im en ta l P r oced u r es. Manipulations were
carried out using standard Schlenk techniques under a
nitrogen atmosphere.22 Cluster 1 was prepared from the
C12H8) (M ) Fe, Ru, Os), in which the biphenylene
exhibits two σ interactions to one metal atom and an
4
19
η
interaction to the other. Other bonding modes
reaction of SbPh
CN).23 NMR spectra were recorded on a Bruker ACF-300FT-
NMR spectrometer as CDCl solutions. Microanalyses were
3 3 3
(commercial source) and Os (CO)11(CH -
observed involve only one of the aromatic rings, either
2
19
6
via an η interaction (to a triosmium cluster) or an η
3
interaction (in ruthenium clusters).20 In assigning elec-
tron count, it has been found convenient to consider the
two Os3 units in the Os3(µ4-Sb)Os3 clusters separately.
For instance, in 4, the µ4-Sb may be regarded as
carried out by the microanalytical laboratory at the National
University of Singapore. The presence of solvent molecules in
samples used for elemental analyses or X-ray crystallographic
1
studies was confirmed by H NMR spectroscopy.
Th er m olysis of 1 in Reflu xin g Octa n e. A sample of 1
(110 mg, 0.089 mmol) in octane (20 mL) was refluxed until
the color of the solution changed from bright yellow to orange
(
18) (a) Beringhelli, T.; D’Alfonso, G.; Minojia, A. P. Organometallics
1
991, 10, 394. (b) Andreu, P. L.; Cabeza, J . A.; Pellinghelli, M. A.; Riera,
V.; Tiripicchio, A. Inorg. Chem. 1991, 30, 4611. (c) Farrugia, L. J .; Rae,
S. E.; Organometallics 1991, 10, 3919. (d) Bruce, M. I.; Liddell, M. J .;
Hughes, C. A.; Skelton, B. W.; White, A. H. J . Organomet. Chem. 1988,
(21) (a) Cullen, W. R.; Rettig, S. T.; Zhang, H. Organometallics 1991,
10, 2965. (b) Cullen, W. R.; Rettig, S. T.; Zhang, H. Organometallics
1992, 11, 1000. (c) Cullen, W. R.; Rettig, S. T.; Zhang, H. Organome-
tallics 1993, 12, 1964.
(22) Shriver, D. F.; Drzedzon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley: New York, 1986.
(23) Nicholls, J . N.; Vargas, M. D. Inorg. Synth. 1989, 28, 232.
3
47, 157. (e) Sappa, E.; Tiripicchio, A.; Carty, A. J .; Toogood, G. E.
Prog. Inorg. Chem. 1987, 35, 437, and references therein.
19) Yeh, W.-Y.; Hsu, S. C. N.; Peng, S.-M.; Lee, G.-H. Organome-
tallics 1998, 17, 2477.
20) J ohnson, B. F. G.; Shephard, D. S.; Braga, D.; Grepioni, F.;
Parsons, S. J . Chem., Soc., Dalton Trans. 1997, 3563.
(
(

2
286 Organometallics, Vol. 20, No. 11, 2001
Leong and Chen

Osmium-Antimony Higher Nuclearity Clusters
30 min). Removal of the solvent followed by TLC separation
Organometallics, Vol. 20, No. 11, 2001 2287
(
of the mixture using dichloromethane/hexane (1:1, v/v) gave
using hexane as eluant gave three bands.
5 (21 mg, 70%) and 7 (3 mg, 10%).
2
Band 1 gave Os
3
(µ-H)(µ-SbPh
2
)(µ
3
,η -C
6
H
4
)(CO)
9
, 2 (45 mg,
Rea ction of 5 w ith SbP h
mg, 0.015 mmol) in dichloromethane (15 mL) was added SbPh
(10 mg, 0.026 mmol). The solution was then stirred for 20 h.
Removal of the solvent followed by TLC separation using CH
Cl /hexane (40:60, v/v) as eluant gave two bands.
Band 1 gave unreacted 5 (3 mg).
Band 2 gave Os (µ -Sb)(µ-H) (µ-SbPh
)(CO)14(SbPh ), 8 (28 mg, 76%): IR (CH
3
. To a solution of cluster 5 (32
4
2
3%): IR (hexane) ν(CO) 2091w, 2071vs, 2043vs, 2018m,
3
-
1
1
004m, 1988w, 1971w cm ; H NMR δ -17.81 (s, OsHOs).
Os Sb.1/2C 14: C, 29.55; H, 1.80.
Found: C, 29.94; H, 1.50.
Band 2 gave unreacted 1 (40 mg, 36%).
Band 3 gave red crystals of Os (µ -SbPh)(µ
(9 mg, 10%): IR (CH Cl ) ν(CO) 2108w, 2094vs, 2058vs,
028vs, 1987w, 1973w cm- . Anal. Calcd for C32
Anal. Cald for C27
H
15
O
9
3
6
H
2
-
2
2
2
,η4-
Cl2) ν(CO)
6
3
3
,η -C
6
H
4
)(CO)20
,
6
4
2
2
)(µ
3
,η -C
6
H
4
)(µ
3
3
2
2
2
C
12
H
8
3
2
1
-1 1
H
9
O
20Os
6
Sb:
2080m, 2056s, 2023vs, 1995s, 1969w, 1940m cm ; H NMR δ
-12.65 (s, OsHOs), -13.26 (s, OsHOs). Anal. Calcd for
C, 19.43; H, 0.46. Found: C, 19.69; H, 0.25.
Prolonged heating of 1 (∼5 h) gave a dark red solution and
C
62
H
39
O
14Os
6
Sb
3
6
‚1/4C H14: C, 30.07; H, 1.69. Found: C, 30.04;
a brown precipitate. TLC separation of the reaction mixture
H, 1.88.
using CH
2
2
Cl
2
/hexane (30:70, v/v) as eluant gave Os
6
(µ
)(CO)16, 4, as the major product
17 mg, 20%): IR (hexane) ν(CO) 2098m, 2067m, 2057s, 2025s,
4
-Sb)-
Rea ction of 1 w ith CO. A suspension of 1 (104 mg, 0.084
mmol) in hexane (15 mL) was pressurized with CO (10 atm)
and heated at 125 °C for 20 h. A yellow precipitate was
4
(
µ-H)(µ
3
,η -C
6
H
4
)(µ ,η -C12H
8
3
(
-
1
1
2
008m, 2000m, 1986w,1948w cm
;
H NMR δ -13.66 (s,
Sb: C, 21.03; H, 0.67.
obtained, which was confirmed by IR spectroscopy to be Os
(CO)12. TLC separation of the reaction mixture with CH Cl
(CO)12 as the major
3
-
OsHOs). Anal. Calcd for C34
Found: C, 21.15; H, 0.93. No 2 or 3 was observed among the
products.
H
13
O
16Os
6
2
2
/
hexane (10:90, v/v) as eluant gave Os
3
compound (total yield ) 69 mg, 90%).
Th er m olysis of 1 in a Ca r iu s Tu be. A sample of 1 (110
mg, 0.089 mmol) was placed in a Carius tube with hexane (15
mL), and the reaction mixture degassed by three freeze-
pump-thaw cycles. The suspension was then heated at 115
Rea ction of 1 a n d 2 in Octa n e. Clusters 1 (50 mg, 0.041
mmol) and 2 (47 mg, 0.040 mmol) were dissolved in octane
(10 mL), degassed by three freeze-pump-thaw cycles, and
heated at 105 °C for 1 h. The color of the solution changed
from yellow to orange. TLC separation of the reaction mixture
°
C for 17 h, upon which the color of the solution changed from
yellow to red. TLC separation of the mixture with CH
hexane (30:70, v/v) as eluant gave the following bands.
2
Cl
2
/
2
using CH Cl2/hexane (10:90,v/v) gave unconsumed reactants
(60 mg) and 3 (32 mg, 40%).
Band 1 gave a mixture containing both 1 and 2 (14 mg).
Band 2 gave 3 (8 mg, 9%).
X-r a y Cr ysta llogr a p h ic Stu d ies. Diffraction-quality crys-
tals were grown by slow cooling of solutions of the compounds
in the appropriate solvent, and the crystals selected were
mounted on quartz fibers or in glass capillaries. Crystal data
were collected on a Siemens SMART diffractometer, equipped
with a CCD detector, using Mo KR radition (λ ) 0.71073 Å) at
293 K. The data were corrected for absorption effects with
Band 3 gave red crystals of Os
6
(µ
4
-Sb)(µ-H)
2
(µ-SbPh
2
)(µ
) ν(CO)
096m, 2080s, 2057s, 2027vs, 1998s, 1942m cm ; H NMR δ
12.97 (s, OsHOs), -13.83 (s, OsHOs). Anal. Calcd for
Sb : C, 24.67; H, 1.10. Found: C, 24.88; H, 0.66.
3
,η2-
4
C
2
-
C
6
H
4
)(µ
3
,η -C12
H
8
)(CO)15, 5 (27 mg, 28%): IR (CH
2
1 1
Cl
2
-
45
H
24
O
15Os
6
2
2
24
Band 3 gave red crystals of Os
6
(µ
4
-Sb)(µ-H)
2
(µ-SbPh
2
)(µ
3
,η -
SADABS. Structural solution and refinement were carried
4
15
25
C
6
H
4
)(µ
3
,η -C12
H
8
)(CO) , 5 (27 mg, 28%): IR (CH
2
1 1
C
l2) ν(CO)
out with the SHELXTL suite of programs. The structure was
-
2
096m, 2080s, 2057s, 2027vs, 1998s, 1942m cm ; H NMR δ
12.97 (s, OsHOs), -13.83 (s, OsHOs). Anal. Calcd for
Sb : C, 24.67; H, 1.10. Found: C, 24.88; H, 0.66.
Band 4 gave red crystals of Os (µ -Sb)(µ-H)(C )(µ-SbPh )-
(CO)16, 6 (37 mg, 40%): IR (hexane) ν(CO) 2098w,
solved by a combination of direct methods, followed by differ-
ence maps. The phenyl hydrogens and metal hydrides not
located by difference maps were placed in calculated positions
with the program XHYDEX.15 All non-hydrogen atoms were
given anisotropic displacement parameters in the final refine-
-
C
45
H
24
O
15Os
6
2
6
4
6
H
5
2
2
(
2
µ
3
,η -C
6 4 2
H )
-1
1
2
2 2
086vs, 2060m, 2042vs, 2031s, 2016s, 1991w, 1962m cm ; H
ment. Refinements were on ∑[w(F
tabulated in Table 2.
o
c
- F ) ]. Crystal data are
NMR δ -14.63 (s, OsHOs). Anal. Calcd for C46
C, 24.90; H, 1.08. Found: C, 25.30; H, 1.44.
H
24
O
16Os
6
Sb
2
:
Band 5 gave orange crystals of Os
6
(µ
)(CO)15, 7 (5 mg, 5%): IR (CH
) ν(CO) 2086m, 2053s, 2032s, 2008s, 1988m, 1954m cm-1;
H NMR δ -11.93 (s, OsHOs). Anal. Calcd for C45
Sb : C, 24.67; H, 1.10. Found: C, 25.01; H, 0.86.
Th er m olysis of 2. A sample of 2 (30 mg, 0.026 mmol) was
4
-Sb)(µ-H)(C
6
H
5
)(µ-
2
-
Ack n ow led gm en t. This work was supported by the
National University of Singapore (Research Grant No.
RP 982751), and one of us (G.C.) thanks the University
for a Research Scholarship.
6
SbPh
Cl
2
)(µ
3
,η
2
-C
6
H
4
))(µ
3
,η -C
6
H
4
2
1
24 6
H O15Os -
2
Su p p or tin g In for m a tion Ava ila ble: Experimental and
refinement details for the crystallographic studies, tables of
crystal data and structure refinement, atomic coordinates,
isotropic and anisotropic thermal parameters, complete bond
parameters, and hydrogen coordinates. Crystallographic data
in CIF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
placed in a Carius tube with hexane (10 mL), and the reaction
mixture degassed by three freeze-pump-thaw cycles. The
suspension was then heated at 115 °C for 15 h, upon which
the color of the solution changed from yellow to orange. TLC
separation of the mixture using CH Cl /hexane (30:70, v/v) as
2 2
eluant gave 6 as the major compound, which was identified
by its IR spectroscopic characteristics (20 mg, 73%).
Th er m olysis of 6. A sample of 6 (30 mg, 0.014 mmol) was
placed in a Carius tube with hexane (10 mL), and the reaction
mixture degassed by three freeze-pump-thaw cycles. The
suspension was then heated at 110 °C for 3 h. TLC separation
OM010039S
(
(
24) Sheldrick, G. M. SADABS, University of G o¨ ttingen, 1996.
25) SHELXTL, version 5.03; Siemens Energy and Automation
Inc.: Madison, WI, 1995.