Nucleophilic addition reactions of the osmium-antimony cluster (μ-H)Os3(CO)9(μ3-C6H4 ) (μ-SbPh2): Orthometalation of triphenylphosphine at ambient temperature

Article abstract of DOI:10.1021/om010959a

At ambient temperatures, the reaction of Os₃(μ-H)(μ-SbPh₂)(μ₃,η² -C₆H₄)(CO)₉, 1, with PPh₃ proceeded via a nucleophilic addition product, Os₃(μ-H)(μ-SbPh₂)(μ₂,η² -C₆H₄)(CO)₉(PPh₃), 2a.This can lose CO to give Os₃(μ-H)(μ-SbPh₂)(μ₃,η² -C₆H₄)(CO)₃(PPh₃), 3a, isomerize, deorthometalate to Os₃(μ-SbPh₂)(C₆H₅)(CO)₉ (PPh₃), 5a, or react with excess PPh₃ to give an orthometalated product, Os₃(μ-SbPh₂)(CO)₈(PPh₂C₆ H₄)(PPh₃)₂, 6a. The origin of the orthometalated phenyl ring in 6a has been established via the reaction of a p-tolyl analogue of 2a, viz., Os₃(μ-H)(μ-SbPh₂)(μ₂,η² -C₆H₄)(CO)₉{(p-tolyl)₃P}, 2b, with PPh₃.

Full text of DOI:10.1021/om010959a

Organometallics 2002, 21, 1227-1234
1227
Nu cleop h ilic Ad d ition Rea ction s of th e
Osm iu m -An tim on y Clu ster
(µ-H)Os3(CO)9(µ3-C6H4)(µ-SbP h 2): Or th om eta la tion of
Tr ip h en ylp h osp h in e a t Am bien t Tem p er a tu r e
Guizhu Chen, Mingli Deng, Chee Keong Lee, and Weng Kee Leong*
Department of Chemistry, National University of Singapore, Kent Ridge, Singapore 119260
Received November 6, 2001
At ambient temperatures, the reaction of Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)9, 1, with PPh3
proceeded via a nucleophilic addition product, Os3(µ-H)(µ-SbPh2)(µ2,η2-C6H4)(CO)9(PPh3), 2a .
This can lose CO to give Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)8(PPh3), 3a , isomerize, deortho-
metalate to Os3(µ-SbPh2)(C6H5)(CO)9(PPh3), 5a , or react with excess PPh3 to give an
orthometalated product, Os3(µ-SbPh2)(CO)8(PPh2C6H4)(PPh3)2, 6a . The origin of the ortho-
metalated phenyl ring in 6a has been established via the reaction of a p-tolyl analogue of
2a , viz., Os3(µ-H)(µ-SbPh2)(µ2,η2-C6H4)(CO)9{(p-tolyl)3P}, 2b, with PPh3.
Sch em e 1
In tr od u ction
There is an extensive triosmium cluster chemistry
associated with µ3-phenylene ligands. A common method
of synthesis is by P-C,1 As-C,2 or S-C3 bond cleavage
via thermolysis of clusters containing ligands with
P-Ph, As-Ph, or S-Ph units. The mode of coordination
of the µ3-phenylene group to the metal framework often
depends on other ligands on the cluster, and the most
common is the µ3,η2 mode, in which the phenylene acts
as a four-electron donor.4 The reactivity of these clusters
has also been investigated and generally results in sub-
stitution at the metal core, for example, with phosphines
or alkynes.5 Reactivity involving the phenylene ring has
been less well investigated, one rare example being the
Friedel-Crafts acylation and alkylation of the phe-
nylene complexes Os3(µ-H)2(CO)9(arylene) (Scheme 1).6
We have recently reported that the thermolysis of the
cluster Os3(CO)11(SbPh3) led initially to Sb-C cleavage
to afford the cluster Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)9,
1,7 and that it displayed interesting reactivity with
alkenes and alkynes, including C-C coupling and
deorthometalation of the phenylene.8 We were thus
intrigued if it may react in a novel manner even with
apparently simple two-electron donor ligands such as
phosphines and isocyanides. Herein we would like to
report our investigations of the reactivity of 1 with
phosphines, particularly triphenylphosphine.
Resu lts a n d Discu ssion
The reaction of 1 with excess PPh3 in hexane gave a
yellow suspension, from which three bands were ob-
tained after TLC separation. Fractional crystallization
of the first band gave yellow crystals of Os3(µ-H)(µ-
SbPh2)(µ3,η2-C6H4)(CO)9(PPh3), 2a , and orange crystals
of Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)8(PPh3), 3a . Fur-
ther crystallization of the supernatant afforded crystals
of yet another cluster, 4, which has the same molecular
formula as 2a , but from which a pure sample could not
be obtained. All three novel clusters were characterized
by single-crystal X-ray crystallographic studies; the
ORTEP diagrams showing their molecular structures
are given in Figures 1-3, respectively.
(1) (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. (d) Cullen, W. R.; Chacon,
S. T.; Bruce, M. I.; Einstein, F. W. B.; J ones, R. H. Organometallics
1988, 7, 2273. (e) Cullen, W. R.; Rettig, S. T.; Zhang, H. Organome-
tallics 1991, 10, 2965. (f) Cullen, W. R.; Rettig, S. T.; Zhang, H.
Organometallics 1992, 11, 928. (g) Cullen, W. R.; Rettig, S. T.; Zhang,
H. Organometallics 1992, 11, 1000.
(2) (a) Arce, A. J .; Deeming, A. J . J . Chem., Soc., Dalton Trans. 1982,
1155. (b) Cullen, W. R.; Rettig, S. T.; Zhang, H. Organometallics 1993,
12, 1964. (c) J ohnson, B. F. G.; Lewis, J .; Massey, A. D.; Braga, D.;
Grepioni, F. J . Organomet. Chem. 1983, 251, 261. (d) J ackson, P. A.;
et al. J . Organomet. Chem. 1990, 391, 225.
(3) Adams, R. D.; Katahira, D. A.; Yang, L. W. Organometallics 1982,
1, 235.
(4) J ohnson, B. F. G.; Lewis, J .; Whitton, A. J .; Bott, S. J . J .
Organomet. Chem. 1990, 389, 129.
(5) (a) Chen, H.; J ohnson, B. F. G.; Lewis, J .; Raithby, P. R. J .
Organomet. Chem. 1991, 406, 219. (b) Chen, H.; J ohnson, B. F. G.;
Lewis, J .; Raithby, P. R. J . Organomet. Chem. 1991, 376, C7.
(6) Chen, H.; J ohnson, B. F. G.; Lewis, J . Organometallics 1989, 8,
2965.
The second band from the TLC separation gave a
yellow solid in very low yield and hence was not fully
characterized. However, the solution IR spectrum in the
(7) Leong, W. K.; Chen, G. Organometallics 2001, 20, 2280.
(8) (a) Deng, M.; Leong, W. K. Organometallics, in press. (b) Deng,
M.; Leong, W. K. J . Chem. Soc., Dalton Trans., in press.
10.1021/om010959a CCC: $22.00 © 2002 American Chemical Society
Publication on Web 02/20/2002

1228 Organometallics, Vol. 21, No. 6, 2002
Chen et al.
F igu r e 4. ORTEP diagram (organic hydrogens omitted,
50% probability thermal ellipsoids) and selected bond
parameters for 5c: Os(1)-Os(2) ) 3.0018(5) Å; Os(1)-
Os(3) ) 2.8215(4) Å; Os(2)-Os(3) ) 2.9943(5) Å; Os(2)-
Sb(4) ) 2.6756(6) Å; Os(3)-Sb(7) ) 2.5667(6) Å; Os(1)-
P(1) ) 2.319(2) Å; Os(2)-C(101) ) 2.165(9) Å; Os(2)-
Os(1)Os(3) ) 61.795(11)°; Os(1)Os(2)Os(3) ) 56.141(10)°;
Os(1)Os(3)Os(2) ) 62.064(11)°; Os(2)Sb(4)Os(3) )
69.630(16)°.
F igu r e 1. ORTEP diagram (organic hydrogens omitted,
50% probability thermal ellipsoids) for 2a .
F igu r e 2. ORTEP diagram (organic hydrogens omitted,
50% probability thermal ellipsoids) for 3a .
F igu r e 5. ORTEP diagram for molecule A (organic
hydrogens omitted, 50% probability thermal ellipsoids) of
6a . Selected bond parameters, Molecule A: Os(1)-
Os(3) ) 3.0315(10) Å; Os(2)-Os(3) ) 2.9648(10) Å;
Os(2)-Sb(7) ) 2.6720(13) Å; Os(1)-Sb(7) ) 2.7051(13) Å;
Os(1)-P(1) ) 2.429(5) Å; Os(2)-P(2) ) 2.318(5) Å; Os(3)-
P(3) ) 2.331(5) Å; Os(2)-C(302) ) 2.157(15) Å; Os(1)Os-
(3)Os(2) ) 92.73(3)°; Os(1)Sb(7)Os(2) ) 107.64(4)°. Mol-
ecule B: Os(4)-Os(6) ) 3.0488(9) Å; Os(5)-Os(6) )
2.9749(9) Å; Os(5)-Sb(8) ) 2.6597(13) Å; Os(4)-Sb(8) )
2.7011(13) Å; Os(4)-P(4) ) 2.416(5) Å; Os(5)-P(5) ) 2.328-
(5) Å; Os(6)-P(6) ) 2.332(4) Å; Os(5)-C(602) ) 2.151(16)
Å; Os(4)Os(6)Os(5) ) 91.96(2)°; Os(4)Sb(8)Os(5) )
107.82(4)°.
F igu r e 3. ORTEP diagram (organic hydrogens omitted,
50% probability thermal ellipsoids) for 4.
(PPh2C6H4)(PPh3)2, 6a ; the structure was established
by a single-crystal X-ray crystallographic study and is
shown in Figure 5, together with selected bond param-
eters. The structure of 6a comprises an orthometalated
triphenylphosphine. This structural feature is not sur-
prising per se as there are a number of examples of such
orthometalation of arylphosphines known. However, the
formation of 6a is exceptional, as such orthometalation
of coordinated arylphosphines by osmium clusters nor-
mally occurs only under thermolytic conditions.
carbonyl region of this product was similar to that of
Os3(µ-SbPh2)(Ph)(CO)9(PMe2Ph), 5c, which was ob-
tained from the analogous reaction of 1 with PMe2Ph.
Thus the compound was assigned as Os3(µ-SbPh2)(Ph)-
(CO)9(PPh3), 5a ; the ORTEP diagram showing the
molecular structure of 5c is given in Figure 4, together
with selected bond parameters. The reaction with PMe2-
Ph also afforded analogues of 2a and 3a , viz., Os3(µ-
H)(µ-SbPh2)(µ2,η2-C6H4)(CO)9(PMe2Ph), 2c, and Os3 (µ-
H)(µ-SbPh2)(µ3,η2-C6H4)(CO)8(PMe2Ph), 3c.
That clusters 2a , 3a , and 4 were obtained from the
same TLC band suggested that they were related via a
decomposition process. Indeed, when a CDCl3 solution
The third TLC band afforded a yellow solid, which
was identified as the novel cluster Os3(µ-SbPh2)(CO)8-

Orthometalation of Triphenylphosphine
Organometallics, Vol. 21, No. 6, 2002 1229
Sch em e 2
F igu r e 6. ORTEP diagram (organic hydrogens omitted,
50% probability thermal ellipsoids) and selected bond
parameters for 7.
by TLC; 6a was obtained in high yield instead. This
suggested that 6a was formed from the decomposition
of the intermediate A during TLC workup. In contrast,
we have also found that cluster 3a reacted with PPh3
to give 6a in quantitative yield. The reaction was
1
of 2a was monitored by 1H NMR spectroscopy over
several days, the spectrum showed the emergence of two
sets of doublets at -16.40 and -18.60 ppm, which was
indicative of the formation of 3a and 4. Furthermore,
the intensities of the latter signals increased at the
expense of that for 2a . A similar monitoring by 31P{1H}
NMR spectroscopy also showed the emergence of a very
weak resonance ascribable to 5a after several days of
standing, suggesting that 5a was also derived from 2a .
Scheme 2 shows the possible relationship among these
clusters.
Cluster 3a may be considered as being derived from
2a by loss of one CO and a change in the bonding mode
of the C6H4 moiety. By stirring 2a in a CH2Cl2 solution
together with silica gel, we have found that the color of
the solution changed from yellow to orange gradually,
and TLC separation gave cluster 3a as the only cluster
compound present. Furthermore, UV photolysis of a
hexane solution of 2a also gave 3a in quantitative yield.
All these suggested that 2a should be rather unstable,
and indeed it is very difficult to obtain a sample of 2a
that is relatively free of 3a ; a similar situation was
observed for the P(p-tolyl)3 and PMe2Ph analogues 2b
and 2c, respectively.
We have found that the yield of 6a increased at the
expense of that of 2a . We therefore hypothesized that
6a was the result of further reaction of 2a with excess
PPh3. Indeed, 2a did react with PPh3 to afford 6a in
high yield after TLC separation. However, when the
reaction between 1 and 3 equiv of PPh3 was monitored
by IR and NMR spectroscopy, it was observed that only
2a was formed directly in the reaction; 6a was not
detected. Thus the 1H NMR spectrum of the reaction
mixture showed a singlet at -17.18 ppm (assignable to
1) and a doublet at -18.41 ppm (assignable to 2a ), but
no resonances ascribable to 4, 3a , or 6a . The 31P{1H}
NMR spectrum of the reaction mixture showed three
sets of resonances at 29.1, 5.4, and -5.2 ppm. The latter
two resonances were assignable to 2a and free PPh3,
respectively. The resonance at 29.1 ppm was therefore
assigned to an intermediate, A. However, this interme-
diate was not observed among the products separated
monitored by H and 31P{1H} NMR spectroscopy; the
31P{1H} NMR spectrum of the reaction mixture showed
the presence of an intermediate, B, with a resonance
at 29.6 ppm. Resonances attributable to 6a were also
found, indicating that 6a was readily formed from the
reaction of 3a with excess PPh3, unlike the case for 2a .
The formation of 6a from 2a or 3a required the
accommodation of two additional PPh3 ligands, loss of
the o-phenylene, and orthometalation of one of the
phenyl rings of a PPh3. The sequence of these events is
not known, and whether the last two events were as
described or involved loss of a phenyl from a PPh3 and
coupling of the o-phenylene ligand with phosphorus was
also uncertain. There was no spectroscopic evidence for
any reaction intermediate or product containing two
phosphine ligands in the reactions leading to 6a . We
could synthesize a cluster with two phosphine ligands
via chemical activation of 1 or 3a with Me3NO, viz., Os3-
(µ-H)2(µ-SbPh2)(µ3,η2-C6H4)(CO)7(PPh3)2, 7; the ORTEP
diagram is given in Figure 6. However, as is readily
observed, cluster 7 has seven carbonyl ligands while 6a
has eight. It is therefore unlikely that 7 was an
intermediate for the formation of 6a .
To establish whether the formation of 6a involved
orthometalation or P-C coupling, and also which of the
phosphine ligands was orthometalated or dephenylated,
Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)9{P(p-tolyl)3}, 2b, was
prepared from the reaction of 1 with P(p-tolyl)3; the
molecular structure of 2b has been confirmed by a
single-crystal X-ray crystallographic study. Cluster 2b
was then reacted with PPh3; if the arene that was lost
originated from the o-phenylene, then orthometalation
of a p-tolyl group will occur (Scheme 3, route a), and if
it is from the P(p-tolyl)3, then the orthometalated group
will still be an o-phenylene (Scheme 3, route b).
The product so obtained was formulated as Os3(µ-
SbPh2)(CO)8{µ-P(p-tolyl)2(C6H3CH3)}(PPh3)2, 8, which
was characterized spectroscopically and analytically.
1
The H NMR spectrum of 8 exhibited two resonances
at 1.73 and 2.39 ppm with a 1:2 relative intensity. These
were assignable to CH3 groups of the p-tolyl moiety and
indicated that one of the tolyl groups on the P(p-tolyl)3

1230 Organometallics, Vol. 21, No. 6, 2002
Chen et al.
Ta ble 1. Com m on Atom ic Nu m ber in g Sch em e a n d Selected Bon d P a r a m eter s for 2a , 2b, a n d 4
2a
2b
4
Bond Lengths (Å)
3.2308(3)
Os(1)-Os(2)
Os(1)-Os(3)
Os(2)-Sb
3.2332(12)
3.0298(13)
2.6554(15)
2.6717(11)
2.365(2)
3.2025(8)
2.9999(8)
2.6431(9)
3.0454(4)
2.6706(5)
2.6663(5)
2.3593(17)
Os(3)-Sb
2.6773(11)
Os(1)-P(1)
Os(2)-P(2)
Os(1)-C(1)
Os(2)-C(2)
C(1)-C(2)
2.382(3)
2.159(9)
2.145(6)
2.133(7)
1.408(9)
3.02-3.09
2.167(14)
2.160(13)
1.383(18)
3.00-3.09
2.123(10)
1.437(12)
3.02-3.12
Os-C + C-O
Bond Angle (deg)
Os(2)-Os(1)-Os(3)
Os(2)-Sb-Os(3)
Os-C-O
88.88(3)
110.90(5)
173.3(8)-178.9(10)
88.406(9)
110.228(7)
171.6(7)-178.3(9)
88.75(2)
109.31(4)
173.8(14)-179.8(16)
in two dinuclear o-phenylene complexes, Cp2Ir2(µ-η2-
C6H4)(CO)2 and Fe2(µ-η2-C6F4)(CO)8,9 and one trinuclear
derivative, Os3(µ-H)3(µ-η2-C6H4)(CO)8(HCdNC6H5).10 The
presence of the metal hydride in these clusters is
indicated by a doublet at about -18 ppm in the 1H NMR
spectrum. The positions of the hydrides were predicted
by potential energy calculations, except in 2b, for which
the hydride was located by a low-angle difference map.
It is a common observation that the hydride tends to
bridge the most electron-rich metal-metal bond, which
is that cis to the phosphine ligand, even though this is
the most sterically hindered metal-metal bond.11 Both
the Os(1)-Os(2) and Os(1)-Os(3) bonds are very long;
the latter especially so, exceeding 3.2 Å in the three
clusters. This is much longer than the maximum Os-
Os bonded distance of 3.05 Å proposed by Deeming,12
and they are the longest Os-Os bond lengths reported
to date. This is probably a combination of the lengthen-
ing due to a hydride bridge, further enhanced by the
geometrical constraints of an η2-phenylene, and coor-
dination of a phosphine ligand cis to the Os-Os bond.
Selected bond parameters for the clusters 3a , 3c, and
7 are given in Table 2. These clusters contain the µ3,η2-
C6H4 ligand, and unlike those above, the Os-Os bond
lengths are more typical. The presence of the metal
Sch em e 3
ligand of 2b has indeed undergone orthometalation,
thus supporting pathway a.
Cr ysta llogr a p h ic Stu d ies
(9) (a) Rausch, M. D.; Gastinger, R. G.; Gardner, S. A.; Brown, R.
K.; Wood, J . S. J . Am. Chem. Soc. 1977, 99, 7870. (b) Bernett, M. J .;
Graham, W. A. G.; Stewart, R. P; Tuggle, R. M. Inorg. Chem. 1973,
12, 2944.
(10) Adams, R. D.; Golembeski, N. M. J . Organomet. Chem. 1979,
172, 239.
(11) (a) Churchill, M. R.; Lashewycz, R. A. Inorg. Chem. 1978, 17,
1950. (b) Adams, R. D.; Golembeski, N. M.; Selegue, J . P. J . Am. Chem.
Soc. 1981, 103, 546.
Clusters 2a , 2b, and 4 are structurally similar, and
4 is a positional isomer of 2a differing in the location of
the phosphine ligand; selected bond parameters are
tabulated in Table 1. These clusters contain an o-
phenylene ligand, and the clusters are electron-precise
if the phenylene is regarded as a two-electron donor.
Such a bonding mode has been observed previously only
(12) Deeming, A. J . Adv. Organomet. Chem. 1986, 26, 6.

Orthometalation of Triphenylphosphine
Organometallics, Vol. 21, No. 6, 2002 1231
Ta ble 2. Com m on Atom ic Nu m ber in g Sch em e a n d Selected Bon d P a r a m eter s for 3a , 3c, a n d 7
3a
2.9065(4)
2.9626(4)
2.6496(6)
2.6565(6)
2.3566(19)
3c
2.8871(3)
3.0014(4)
2.6403(5)
2.6574(5)
2.3194(17)
7
Bond Lengths (Å)
Os(1)-Os(3)
Os(2)-Os(3)
Os(1)-Sb
2.8706(3)
3.0152(3)
2.6545(4)
2.6763(4)
Os(2)-Sb
Os(3)-P(1)
Os(2)-P(2)
Os(3)-P(3)
Os(1)-C(1)
Os(2)-C(2)
Os(3)-C(1)
Os(3)-C(2)
C(1)-C(2)
2.3817(13)
2.3896(15)
2.149(5)
2.165(7)
2.176(8)
2.333(8)
2.342(7)
1.448(10)
3.03-3.08
2.168(6)
2.187(7)
2.350(6)
2.339(6)
1.451(9)
3.05-3.08
2.197(5)
2.366(5)
2.365(5)
1.446(7)
Os-C + C-O
3.02-3.08
Bond Angles (deg)
Os(1)-Os(3)-Os(2)
Os(1)-Sb-Os(2)
Os-C-O
87.502(11)
99.806(18)
170.8(9)-177.0(9)
87.576(9)
100.586(16)
175.4(8)-178.6(7)
87.547(8)
99.652(13)
175.4(6)-179.0(5)
hydrides is indicated by doublets in the -16 ppm region
Os-Os edge that is bridged by the SbPh2 moiety is
somewhat elongated. Contrary to what may be expected,
however, the Os-Os bond cis to the phosphine ligand
is shortest among the Os-Os bonds. Indeed, the Os(1)-
Os(2) bond that is trans to the phenyl ring is very long
at 3.0018(5) Å and suggests that the phenyl competes
strongly for π back-donation from the metal. On the
other hand, the Os(3)-Sb(4) length at 2.5665(6) Å is the
shortest among the simple triosmium-antimony clus-
ters observed to date, possibly to compensate for the
steric repulsion between the phenyl ligand on Os(2) and
those on Sb(4).
There are two crystallographically distinct molecules
in the crystal structure of 6a . The differences between
their bond parameters are mainly those associated with
the heavy atoms, the largest being the Os(1)-Os(3) bond
lengths, which differ by 18σ. The Os(1)-P(1) bond
length is unusually long at ∼2.42 Å and is barely within
the sum of the atomic radii for Os and P (2.45 Å).15
Although the orthometalated phosphine lies more or less
in the equatorial plane, it is noticed that the carbonyl
ligands on Os(2) are staggered with respect to those on
Os(3), adopting what Pomeroy et al. have termed the S
conformation.16 In more highly substituted clusters,
such as Os3(CO)6[P(OMe)3]6, the S geometry is more
common. We have earlier suggested that in the mono-
substituted triosmium clusters Os3(CO)11(PR3) steric
effects from the PR3 ligand led to a propensity toward
greater twisting of the Os(CO)3(PR3) group.17 Thus the
distortion in cluster 6a may be attributed to the same
1
of their H NMR spectra, and potential energy calcula-
tions suggested that they bridge the longer Os-Os
bonds. The Os-C bond lengths associated with the
phenylene ligand are similar to those in the µ,η2 cases
above. However, it is noteworthy that the C(1)-C(2)
lengths are generally longer in the µ3,η2-C6H4 ligands
than in the µ,η2-C6H4 ligands; ranges are 1.446(7)-
1.451(9) and 1.383(18)-1.437(12) Å, respectively. These
values can be compared to the 1.40 Å in benzene13 and
may be indicative of a greater loss of aromaticity in the
former ligand bonding mode. The change in the bonding
mode from µ,η2 to µ3,η2 is also manifested in the smaller
OsOsOs and OsSbOs angles; ∼100° and ∼87.5°, respec-
tively, for the clusters with the µ,η2 phenylene bonding
mode and ∼88° and ∼110°, respectively, for clusters
with the µ3,η2 bonding mode.
An outstanding structural feature of the clusters 3a
and 3c is that the phosphine occupies an axial position
with respect to the metal framework. There is only one
other example of a triosmium cluster with an axially
bound phosphorus ligand, viz., Os3(µ-H)2(C4H3N)(CO)7-
[P(OMe)3]2.5a The reason for the unusual stereochem-
istry adopted is not clear, since an axially bound
phosphine is not observed for cluster 7.
Cluster 5 comprises an almost planar Os3Sb “kite”;
the dihedral angle between the Os3 and Os2Sb trian-
gular planes is 2.9°. It is the first example of such an
Os3Sb geometry, the closest relation being the Os3Sb2
cluster Os3(µ-SbPh2)2(CO)10 that we have reported
earlier.14 As was also observed in that compound, the
(15) Shriver, D. F.; Atkins, P. W. Inorganic Chemistry, 3rd ed.;
OUP: Oxford, 1999.
(16) Hansen, V. M.; Ma, A. K.; Biradha, K.; Pomeroy, R. K.;
Zaworotko, M. J . Organometallics 1998, 17, 5267.
(17) Leong, W. K.; Liu, Y. J . Organomet. Chem. 1999, 584, 5267.
(13) (a) Bastiansen, O.; Fernholt, L.; Seip, H. M.; Kambara, H.;
Kuchitsu, K. J . Mol. Struct. 1973, 18, 163. (b) Tamagawa, K.; Iijima,
T.; Kimura, M. J . Mol. Struct. 1976, 30, 243.
(14) Leong, W. K.; Chen, G. J . Chem. Soc., Dalton Trans. 2000, 4442.

Ta ble 3. Cr ysta l a n d Refin em en t Da ta for 2a , 2b, 3a , 3c, 4, 5c, 6a , a n d 7
2a
2b
3a
3c
4
5c
6a
7
empirical formula
C
45H30O9Os3PSb
C48H36O9Os3PSb
C44H30O8Os3PSb
C34H26O8Os3PSb
C45H30O9Os3PSb‚
CH2Cl2
1522.94
triclinic
P1h
12.9772(2)
13.3713(3)
15.7753(3)
92.310(1)
109.491(1)
114.119(1)
2305.04(8)
5364
C35H26O9Os3PSb
2C74H54O8Os3P3Sb‚
3/4CH2Cl2
3776.56
triclinic
P1h
13.4047(1)
23.8087(3)
26.2516(1)
64.522(1)
82.590(1)
89.910(1)
7486.61(11)
7996
C61H45O7Os3P2Sb‚
CH2Cl2
1729.19
triclinic
P1h
12.0001(2)
12.7351(1)
20.6397(2)
75.511(1)
82.520(1)
71.545(1)
2892.38(6)
7927
fw
1438.01
monoclinic
P21/c
13.1280(2)
18.9541(2)
18.5330(1)
90
106.427(1)
90
4423.41(8)
7021
1480.09
monoclinic
P21/n
13.7183(2)
17.4565(3)
20.1485(2)
90
102.507(1)
90
4710.53(12)
6881
1410.00
monoclinic
P21/c
9.7194(2)
10.7339(3)
40.2425(10)
90
95.578(1)
90
4178.50(18)
7519
1285.87
triclinic
P1h
1313.88
monoclinic
P21/c
18.6644(1)
10.3866(2)
19.8068(3)
90
102.103(1)
90
3754.39(9)
8192
cryst syst
space group
a, Å
b, Å
c, Å
10.4650(2)
10.5676(2)
18.7774(3)
76.960(1)
76.443(1)
61.982(1)
1765.94(6)
5631
R, deg
â, deg
γ, deg
volume, Å3
no. of reflns for unit
cell determination
Z
4
4
4
2
2
4
2
2
density (calcd), g/cm3
abs coeff, mm-1
F(000)
2.159
9.283
2664
2.087
8.721
2760
2.241
9.823
2608
2.418
11.608
1176
2.194
9.026
1416
2.324
10.925
2408
1.675
5.573
3607
1.985
7.230
1636
cryst size, mm3
0.430 × 0.390 ×
0.240 × 0.220 ×
0.260 × 0.120 ×
0.38 × 0.38 ×
0.16 × 0.10 ×
0.26 × 0.10 ×
0.24 × 0.14 ×
0.28 × 0.15 ×
0.160
0.180
0.110
0.24
0.04
0.05
0.06
0.10
θ range for data
collection, deg
index ranges
2.01 to 29.31
2.02 to 29.39
2.11 to 29.37
2.20 to 29.24
2.11 to 29.31
2.10 to 29.29
2.04 to 29.37
2.01 to 29.30
-18 e h e 17,
0 e k e 25,
0 e l e 24
28 891
10920 [R(int) )
0.0360]
-18 e h e 18,
0 e k e 22,
0 e l e 27
30 987
11660 [R(int) )
0.0380]
-12 e h e 12,
0 e k e 14,
0 e l e 52
31 484
10411 [R(int) )
0.0386]
-13 e h e 13,
-13 e k e 14,
0 e l e 25
14 981
8373 [R(int) )
0.0298]
-17 e h e 16,
-18 e k e 18,
0 e l e 21
19 571
10931 [R(int) )
0.0685]
-25 e h e 24,
0 e k e 14,
0 e l e 26
24 444
9318 [R(int) )
0.0423]
-17 e h e 17,
-28 e k e 31,0 e l e 36 -16 e k e 17,
-15 e h e 16,
0 e l e 28
21 980
13670 [R(int) )
0.0226]
no. of reflns collected
no. of ind reflns
55 114
34796 [R(int) )
0.0616]
max. and min.
transmn
0.189284, 0.100457 0.297276, 0.195012 0.432052, 0.269139 0.121436, 0.057538 0.526835, 0.347287 0.461175, 0.311235 0.603987, 0.455841
0.583495, 0.321392
no. of data/restraints/ 10 920/6/548
11 660/0/563
10 411/2/517
8373/2/427
10 931/2/562
9318/0/442
24 945/4/522
13 670/2/698
params
goodness-of-fit on F2
final R indices
[I>2σ(I)]
1.149
1.074
1.251
1.125
0.967
1.132
1.039
1.186
R1 ) 0.0457,
wR2 ) 0.0986
R1 ) 0.0716,
wR2 ) 0.1110
1.722 and -1.572
R1 ) 0.0394,
wR2 ) 0.0698
R1 ) 0.0689,
wR2 ) 0.0810
1.374 and -1.422
R1 ) 0.0436,
wR2 ) 0.0877
R1 ) 0.0628,
wR2 ) 0.0936
0.985 and -1.868
R1 ) 0.0352,
wR2 ) 0.0821
R1 ) 0.0425,
wR2 ) 0.0867
1.377 and -2.150
R1 ) 0.0646,
wR2 ) 0.1130
R1 ) 0.1620,
wR2 ) 0.1472
2.146 and -2.461
R1 ) 0.0456,
wR2 ) 0.0691
R1 ) 0.0869,
wR2 ) 0.0822
0.765 and -1.024
R1 ) 0.0715,
wR2 ) 0.1657
R1 ) 0.1335,
wR2 ) 0.1996
2.318 and -2.334
R1 ) 0.0330,
wR2 ) 0.0781
R1 ) 0.0443,
wR2 ) 0.0855
0.960 and -1.418
R indices (all data)
largest diff peak and
hole, e Å-3

Orthometalation of Triphenylphosphine
Organometallics, Vol. 21, No. 6, 2002 1233
presence of CH2Cl2 solvent in the crystalline sample used for
the X-ray diffraction study was confirmed by 1H NMR spec-
troscopy.
minimization of steric interactions between the bulky
phosphine ligands.
Rea ction of 2a w ith P P h 3. To a hexane solution of 2a (20
mg, 0.014 mmol) was added PPh3 (10 mg, 0.038 mmol). The
mixture was stirred overnight to give a precipitate and a light
yellow supernatant. Removal of the solvent and volatile
materials in vacuo followed by TLC separation with CH2Cl2/
hexane (30:70, v/v) as eluant gave, besides unreacted starting
material (5 mg), cluster 6a (21 mg, 71%).
Rea ction of 3a w ith P P h 3. To a CH2Cl2 solution of 3a (10
mg, 0.0071 mmol) was added PPh3 (5 mg, 0.019 mmol). The
mixture was stirred at room temperature for 20 h, when the
IR spectrum of the solution showed that the starting material
was consumed. TLC separation of the mixture using CH2Cl2/
hexane (30:70, v/v) gave 6a (13 mg, 99%).
P h otolysis of 2a . A hexane solution (15 mL) of 2a (21 mg,
0.015 mmol) was photolyzed under a UV lamp (15W, 360 nm)
for 1 h. The color of the solution changed from yellow to orange,
and an orange solid was precipitated. TLC separation using
CH2Cl2/hexane (20:80, v/v) as eluant afforded 3a (19 mg, 92%).
Decom p osition of 2a on Silica Gel. A dichloromethane
(15 mL) solution of 2a (25.5 mg, 0.018 mmol) was stirred
together with silica gel for 2 h. The color of the supernatant
changed from yellow to orange. Filtration of the solution
followed by TLC separation using CH2Cl2/hexane (20:80, v/v)
gave 3a (24 mg, 95%).
Con clu d in g Rem a r k s
We have found that the osmium-antimony cluster
Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)9 is very reactive, its
reaction with PPh3 proceeding even under ambient
conditions to initially afford a nucleophilic addition
product which can rapidly isomerize, decarbonylate,
deorthometalate, or react further with excess PPh3 to
give an orthometalated product, Os3(µ-SbPh2)(CO)8-
(PPh2C6H4)(PPh3)2. The origin of the orthometalated
phenyl ring in this product has been established via the
reaction of a p-tolyl derivative, Os3(µ-H)(µ-SbPh2)(µ2,η2-
C6H4)(CO)9{(p-tolyl)3P}, with PPh3. Many of the new
clusters isolated exhibit interesting structural features
and ligand bonding modes. It is therefore apparent that
there is potential for much more interesting chemistry
associated with this and other osmium-antimony clus-
ters.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions and manipulations
were performed under a nitrogen atmosphere by using stan-
dard Schlenk techniques. Solvents were purified, dried, dis-
tilled, and kept under nitrogen prior to use. NMR spectra were
recorded on a Bruker 300 MHz NMR spectrometer in CDCl3
unless otherwise stated. FTIR spectra were recorded as
solutions in CH2Cl2 unless otherwise stated. Microanalyses
were carried out by the microanalytical laboratory at the
National University of Singapore. The cluster Os3(µ-H)(µ-
SbPh2)(µ3,η2-C6H4)(CO)9, 1, was prepared according to the
published method;7 all other reagents were from commercial
sources and used as supplied.
Rea ction of 1 w ith (p-tolyl)3P . To a hexane solution (15
mL) of 1 (21.6 mg, 0.018 mmol) was added (p-tolyl)3P (5 mg,
0.025 mmol). A similar workup as for the PPh3 reaction above
gave two chromatographic bands. Recrystallization of the first
yellow band gave yellow crystals of Os3(µ-H)(µ-SbPh2)(µ2,η2-
C6H4)(CO)9{(p-tolyl)3P}, 2b (5.3 mg, 20%), as well as orange
crystals of Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)8{P(p-tolyl)3}, 3b
(9.1 mg, 35%). Mechanical separation of 2b and recrystalliza-
tion from a CH2Cl2/hexane solution again afforded 3b. 2b: IR
1
ν(CO) 2092m, 2073vs, 2011vs, 2007vs, 1932w cm-1; H NMR
2
δ -18.60 (d, J PH ) 8.3 Hz, OsHOs); 31P{1H} NMR δ -2.10
(s). Anal. Calcd for C48H36O9Os3PSb: C, 38.94; H, 2.43; P, 2.10.
Found: C, 38.87; H, 2.65; P, 1.85. 3b: IR ν(CO) 2080s, 2036s,
2009vs, 1957m, 1948m cm-1; 1H NMR δ -16.22 (d, 2J PH ) 10.7
Hz, OsHOs); 31P{1H} NMR δ 3.99 (s). Anal. Calcd for C47H36O8-
Os3PSb‚1/4hexane: C, 39.53; H, 2.70. Found: C, 39.29; H, 2.66.
Rea ction of 1 w ith P P h 3. To a solution of 1 (44 mg, 0.037
mmol) in hexane (10 mL) was added PPh3 (15 mg, 0.057 mmol).
The mixture was stirred for 20 h, upon which the initial color
of the solution turned from bright yellow to light yellow. The
solvent was removed on the vacuum line and the residue
subjected to TLC separation to give three bands. Recrystalli-
zation of the first band gave yellow crystals of Os3(µ-H)(µ-
SbPh2)(µ2,η2-C6H4)(CO)9(PPh3), 2a , and orange crystals of
Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)8(PPh3), 3a . Further crystal-
lization from the supernatant afforded more crystalline samples,
which contained Os3(µ-H)(µ-SbPh2)(µ2,η2-C6H4)(CO)9(PPh3), 4,
an isomer of 2a . However, 4 could not be obtained free from
contamination by 2a . Mechanical separation of the yellow
crystals of 2a from 3a and recrystallization of it from CH2Cl2/
hexane again gave orange crystals of 3a . 2a (27 mg, 50%): IR
ν(CO) 2093m, 2075s, 2013vs, 1992m, 1933w cm-1; 1H NMR δ
1
The presence of hexane was confirmed by H NMR spectros-
copy.
The second band gave Os3(µ-SbPh2)(CO)8{µ-P(p-tolyl)2(C6H3-
CH3)}{P(p-tolyl)3}2, 6b (9.3 mg, 26%): IR ν(CO) 2050w, 2008m,
1987s, 1969s, 1941m,br cm-1 31P{1H} NMR δ 12.47 (s), 0.91
;
(s), -8.04 (s). Anal. Calcd for C83H72O8Os3P3Sb: C, 50.27; H,
3.63. Found: C, 50.52; H, 3.80.
Rea ction of 2b w ith P P h 3. To a CH2Cl2 solution of 2b (20
mg, 0.014 mmol) was added PPh3 (10.6 mg, 0.040 mmol). The
mixture was stirred overnight, whereupon the solution turned
to a light yellow. TLC separation using CH2Cl2/hexane (30:
70, v/v) as eluant gave only one product, Os3(µ-SbPh2)(CO)8-
{µ-P(p-tolyl)2(C6H3CH3)}(PPh3)2, 8 (23.6 mg, 90%): IR ν(CO)
2
-18.41 (d, J PH ) 5.8 Hz, OsHOs); 31P{1H} NMR δ 5.46 (s).
Anal. Calcd for C45H30O9Os3PSb: C, 37.57; H, 2.09. Found: C,
2052w, 2011m, 1988s, 1968s, 1941m cm-1 31P{1H} NMR δ
;
37.59; H, 2.21. 3a : IR ν(CO) 2081m, 2037s, 2011vs, 1950m
1
2
cm-1; H NMR δ -16.40 (d, J PH ) 12.4 Hz, OsHOs); 31P{1H}
NMR δ 6.75 (s). Anal. Calcd for C44H30O8Os3PSb: C, 37.46;
H, 2.12; P, 2.20. Found: C, 37.69; H, 2.29; P, 1.84. 4: IR ν-
(CO) 2098m, 2071w, 2055m, 2031m, 2019s, 1979mw,br,
1952mw,br cm-1; 1H NMR δ -18.62 (d, 2J PH ) 7.4 Hz, OsHOs);
31P{1H} NMR δ 0.13 (s).
12.28 (s), 1.63 (s), -5.71 (s). Anal. Calcd for C77H60O8Os3P3Sb:
C, 48.70; H, 3.16. Found: C, 48.80; H, 3.42.
Rea ction of 1 w ith P P h 3 a n d TMNO. To a solution of 1
(32 mg, 0.027 mmol) in CH2Cl2 (15 mL) was added Me3NO‚
2H2O (7 mg, 0.063 mmol), followed by PPh3 (15 mg, 0.057
mmol). The solution turned to an orange color within 15 min.
Solvent and volatiles were removed under vacuum, and TLC
separation of the residue using CH2Cl2/hexane (20:80, v/v) as
eluant gave a major orange band. Recrystallization of this
orange band from CH2Cl2/hexane gave red blocks of the cluster
Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)7(PPh3)2, 7 (37 mg, 82%): IR
The second band gave a very low yield of a yellow solid that
has been identified as Os3(µ-SbPh2)(Ph)(CO)9(PPh3), 5a : IR
ν(CO) 2070w, 2039m, 2003m, 1990s, 1943w cm-1. The third
band gave a pale yellow crystalline sample of Os3(µ-SbPh2)-
(CO)8(PPh2C6H4)(PPh3)2, 6a (17 mg, 25%): IR ν(CO) 2053w,
1
2012m, 1988s, 1970s, 1943m, 1930m, 1908w cm-1
;
31P{1H}
ν(CO) 2070w, 2040s, 2012s, 1993m, 1966m, 1948m cm-1; H
NMR δ 14.35 (s), 1.41 (s), -6.03(s). Anal. Calcd for C74H54O8-
Os3P3Sb: C, 47.86; H, 2.91. Found: C, 48.02; H, 3.13. The
NMR δ -16.64 (dd, 2J PH ) 9.1, 10.0 Hz, OsHOs); 31P{1H} NMR
δ 1.60 (s), 0.75 (s). Anal. Calcd for C61H45O7Os3P2Sb‚CH2Cl2:

1234 Organometallics, Vol. 21, No. 6, 2002
Chen et al.
C, 43.06; H, 2.74; P, 3.58. Found: C, 43.17; H, 2.92; P, 3.13.
The presence of CH2Cl2 was verified by 1H NMR spectroscopy.
for absorption effects with SADABS.18 The final unit cell
parameters were obtained by least squares on a number of
strong reflections. Structural solution and refinement were
carried out with the SHELXTL suite of programs.19 The
structure was solved by direct methods to locate the heavy
atoms, followed by difference maps for the light, non-hydrogen
atoms. The phenyl hydrogens were placed in calculated
positions. Metal hydride positions were calculated with XHY-
DEX20 (except for 2b, in which the hydrides were located in
the difference map) and allowed to ride on one of the osmium
atoms that they are attached to, and given a fixed isotropic
thermal parameter. All non-hydrogen atoms were given aniso-
tropic displacement parameters in the final refinement, except
for 6a (see below).
Compound 2a exhibited large residues close to the heavy
atoms in the difference map; this was interpreted as disorder
of the metal core. Thus the metal atom positions were modeled
with two alternative sites. Appropriate restraints were placed
on the occupancies, anisotropic thermal parameters, and the
Os-Os and Os-Sb distances. Compound 6a had two molecules
in the asymmetric unit. The phenyl rings (but not the phe-
nylenes) were regularized. All the carbon atoms were given
isotropic thermal parameters; all phenyl carbon atoms were
given one common thermal parameter. Two partial molecules
of dichloromethane were found, and they were given occupan-
cies of 0.5 and 0.25, the chlorine and carbon atoms were given
fixed isotropic thermal paramters, and restraints were placed
on the C-Cl distances.
Rea ction of 3a w ith P P h 3 a n d TMNO. To a CH2Cl2
solution of 3a (15 mg, 0.011 mmol) was added PPh3 (5 mg,
0.019 mmol), followed by Me3NO‚2H2O (3 mg, 0.027 mmol).
The mixture was stirred at room temperature for 1 h. TLC
separation using CH2Cl2/hexane (20:80, v/v) as eluant afforded
only one product, identified by IR spectroscopy as 7 (17 mg,
98%).
Rea ction of 1 w ith P Me2P h . To a solution of 1 (101.4 mg,
0.086 mmol) in hexane (10 mL) was added PMe2Ph (13.8 mg,
0.10 mmol). The mixture was stirred at room temperature
until the IR spectrum of the solution showed that 1 was
consumed (15 h). Removal of the solvent followed by chro-
matographic separation on silica gel using dichloromethane/
hexane (1:4, v/v) as eluant gave a major yellow band, from
which Os3(µ-H)(µ-SbPh2)(µ2,η2-C6H4)(CO)9(PMe2Ph), 2c, was
obtained (65.5 mg, 58.0%). Cluster 2c was not stable and
quickly decomposed, as shown by the change of color from
yellow to orange and the change in its IR spectrum. After
allowing it to stand for 1 day at room temperature, the mixture
was chromatographed on silica TLC plates to give two yellow
bands and an orange band. The first yellow band was found
to be 2c (10.2 mg). The second band gave yellow crystals of
Os3(µ-H)(µ-SbPh2)(µ3,η2-C6H4)(CO)8(PMe2Ph), 3c (15.6 mg,
24.3%), while the third band gave orange crystals of Os3(µ-
SbPh2)(Ph)(CO)9(PMe2Ph), 5c (34.7 mg, 52.8%). 2c: IR ν(CO)
2090w, 2073s, 2008vs,br, and 1933w,br cm-1; 1H NMR δ 7.7-
2
7.0 (m, aromatic), 2.41 (d, J PH ) 9.9 Hz, PMe2Ph), -18.88 (d,
Ack n ow led gm en t. This work was supported by the
National University of Singapore (Research Grant No.
RP 982751), and two of us (G.C. and M.D.) thank the
University for a Research Scholarship.
2J PH ) 7.4 Hz, OsHOs). Anal. Calcd for C35H26O9Os3SbP: C,
31.99; H, 1.99. Found: C, 31.81; H, 2.22. 3c: IR (hexane) ν-
(CO) 2080m, 2034s, 2011s,br, 1960w,br, and 1942m,br cm-1
;
1H NMR δ 7.7-7.0 (m, aromatic), 2.41 (d, 2J PH ) 10.7 Hz, PMe2-
2
Ph), -16.44 (d, J PH ) 12.4 Hz, OsHOs); 31P{1H} NMR δ
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.
-32.43 (s). Anal. Calcd for C34H26O8Os3PSb: C, 31.75; H, 2.04.
Found: C, 31.91; H, 1.99. 5c: IR (hexane) ν(CO) 2083w,
2036w, 2014m, 1999s, and 1942w,br cm-1; 1H NMR δ 7.6-7.2
(m, aromatic), 2.30 (d, 2J PH ) 10.7 Hz, PMe2Ph); 31P{1H} NMR
δ -31.80 (s). Anal. Calcd for C35H26O9Os3PSb: C, 31.99; H,
1.99. Found: C, 31.94; H, 1.88.
Cr ysta l Str u ctu r e Deter m in a tion of 2a , 2b, 3a , 3c, 4,
5c, 6a , a n d 7. The crystals were mounted on quartz fibers.
Crystal data and structure refinement details are given in
Table 3. The data were measured on a Bruker APEX AXS
diffractometer, equipped with a CCD detector, using Mo KR
radiation (λ ) 0.71073 Å), at 293(2) K. The data were corrected
OM010959A
(18) Sheldrick, G. M. SADABS; University of Go¨ttingen, 1996.
(19) SHELXTL, version 5.03; Siemens Energy and Automation
Inc.: Madison, WI, 1995.
(20) Orpen, A. G. XHYDEX: A Program for Locating Hydrides in
Metal Complexes; School of Chemistry, University of Bristol, UK, 1997.