Hexa- and triosmium carbonyl clusters bearing bridging dppm and capping sulfido ligands

Article abstract of DOI:10.1016/j.jorganchem.2004.04.038

Treatment of [Os₃(CO)₇(μ₃-S) ₂(μ-dppm)] (1) with Me₃ NO in toluene at 80 °C affords the trinuclear cluster [Os₃(CO), ₆(μ₃-S)₂(NMe₃)(μ-dppm)] (2) and the hexanuclear cluster [Os₆(CO)₁₂(μ-S) ₄(μ-dppm)₂] (3) in 30% and 51% yields, respectively. The reaction of 1 with [Os₃(CO)₁₀ (MeCN)₂] in refluxing benzene at 80 °C gives the hexanuclear cluster [Os₆(CO)₁₄(μ3-S) ₂ (μ-dppm)] (4) in 15% yield. Compound 2 reacts with CO, PPh₃ and P(OMe)₃ at room temperature to give 1 , [Os₃(CO)₆(μ3-S)₂(μ-dppm) (PPh₃)] (5) and [Os₃(CO)₆(μ3-S) ₂(μ-dppm){P(OMe)₃}] (6), respectively; in high yields indicating that the NMe₃ ligand is weakly bound. Compound 1 reacts with PPh₃ in presence of Me₃NO to afford 5, 2 and 3 in 53%, 6% and 18% yields, respectively, whereas with P(OMe)₃ 1 gives only 6 in 84% yield. Compound 3 reacts with CO at 98 °C to regenerate 1 by the cleavage of the three unsupported osmiumosmium bonds. The molecular structures of 4 and 6 have been unambiguously determined by single crystal X-ray diffraction studies. The hexanuclear compound 3 appears to be a64-electron butterfly core with four triply bridging sulfido ligands and two bridging dppm ligands based on the spectroscopic and analytical data. The metal core of 4 can be described as a central tetrahedral array capped on two faces with two additional osmium atoms. The triply bridging sulfido ligands face cap the two tetrahedral arrays formed by metal capping of the two faces of the central tetrahedron. The dppm ligand bridges one edge of one of the external tetrahedral arrays. Compounds 5 and 6 are formed by the displacement of equatorial carbonyl group of 1 by a PPh₃ and P(OMe)₃ ligand respectively and their structures are comparable to that of 1.

Full text of DOI:10.1016/j.jorganchem.2004.04.038

Journal of Organometallic Chemistry 689 (2004) 2571–2580
www.elsevier.com/locate/jorganchem
Hexa- and triosmium carbonyl clusters bearing bridging dppm
and capping sulfido ligands
a
Tahmina Akter , Noorjahan Begum , Daniel T. Haworth , Dennis W. Bennett
a
b
* b
b
,
Shariff E. Kabir * a, Md. Arzu Miah , Nitai C. Sarker , Tasneem A. Siddiquee ,
a
a
c,
*
Edward Rosenberg
a
Department of Chemistry, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh
b
Department of Chemistry, University of Wisconsin-Milwaukee, Wisconsin, WI 53211, USA
c
Department of Chemistry, The University of Montana, Missoula, MT 59812, USA
Received 3 March 2004; accepted 26 April 2004
Available online 2 July 2004
Abstract
Treatment of [Os3(CO)7(l3-S)2(l-dppm)] (1) with Me3NO in toluene at 80 ꢀC affords the trinuclear cluster [Os3(CO)6(l3-
S)2(NMe3)(l-dppm)] (2) and the hexanuclear cluster [Os6(CO)12(l3-S)4(l-dppm)2] (3) in 30% and 51% yields, respectively. The re-
action of 1 with [Os3(CO)10(MeCN)2] in refluxing benzene at 80 ꢀC gives the hexanuclear cluster [Os6(CO)14(l3-S)2(l-dppm)] (4) in
15% yield. Compound 2 reacts with CO, PPh3 and P(OMe)3 at room temperature to give 1, [Os3(CO)6(l3-S)2(l-dppm)(PPh3)] (5)
and [Os3(CO)6(l3-S)2(l-dppm){P(OMe)3}] (6), respectively; in high yields indicating that the NMe3 ligand is weakly bound. Com-
pound 1 reacts with PPh3 in presence of Me3NO to afford 5, 2 and 3 in 53%, 6% and 18% yields, respectively, whereas with P(OMe)3
1 gives only 6 in 84% yield. Compound 3 reacts with CO at 98 ꢀC to regenerate 1 by the cleavage of the three unsupported osmium–
osmium bonds. The molecular structures of 4 and 6 have been unambiguously determined by single crystal X-ray diffraction studies.
The hexanuclear compound 3 appears to be a64-electron butterfly core with four triply bridging sulfido ligands and two bridging
dppm ligands based on the spectroscopic and analytical data. The metal core of 4 can be described as a central tetrahedral array
capped on two faces with two additional osmium atoms. The triply bridging sulfido ligands face cap the two tetrahedral arrays
formed by metal capping of the two faces of the central tetrahedron. The dppm ligand bridges one edge of one of the external tet-
rahedral arrays. Compounds 5 and 6 are formed by the displacement of equatorial carbonyl group of 1 by a PPh3 and P(OMe)3
ligand respectively and their structures are comparable to that of 1.
ꢁ 2004 Elsevier B.V. All rights reserved.
Keywords: Trinuclear; Hexanuclear; Osmium carbonyl clusters; Crystal structures
1. Introduction
pair of electrons to form coordinative interactions to
electron-deficient metal groupings, the sulfido ligand
could also facilitate the entry of metal-containing moie-
ties into the cluster [3]. Thus the triply bridging sulfido
cluster [Os3(CO)9(l3-S)2] has served as an important
precursor for many aggregation and condensation
reactions. For example, Adams et al. [4] reported the
synthesis of the mixed-metal cluster [Os3(CO)9(l4-
S)(l3-S){W(CO)5}] from the photo-induced reaction of
[Os3(CO)9(l3-S)2] with W(CO)6 in which the W(CO)5
The triply bridging sulfido ligand with its lone pair of
electrons would seem to be an ideal species for use in
cluster size-expansion reactions [1,2]. By using the lone
*
Corresponding author. Tel.: +1-406-243-2592; fax: +1-406-243-
4227.
E-mail address: rosen@selway.umt.edu (E. Rosenberg).
0022-328X/$ - see front matter ꢁ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.04.038

2572
T. Akter et al. / Journal of Organometallic Chemistry 689 (2004) 2571–2580
is coordinated through a l4-S atom. They also reported
that when irradiated in presence of [W(CO)5(PMe2Ph)],
the compound [Os3(CO)9(l3-S)2] yields four mixed-
metal clusters [Os3W(CO)12(l3-S)2(PMe2Ph)], [Os3W(CO)12-
(l3-S)2(PMe2Ph)2], [Os3W(CO)11(l3-S)2(PMe2Ph)2] and
[Os3W2(CO)14(l4-S)(l3-S)(PMe2Ph)2] [5]. The cluster
[Os3(CO)9(l3-S)2] was also found to react with Os(CO)5
under UV irradiation to form [Os4(CO)13(l3-S)2]. Ad-
ams and coworkers [6] also reported that when irradiat-
ed under a rapid purge of nitrogen [Os3(CO)9(l3-S)2]
undergoes a self condensation and forms the hexanucle-
ar compound [Os6(CO)16(l3-S)4] through the removal of
two CO ligands. The dimerization is reversed by CO or
the dimer can react with H2 to form [(l-H)2-
Os3(CO)8(l3-S)2]. They also demonstrated [7] that
MeCN)2] to form the hexanuclear cluster [Os6(CO)17-
(l4-S)2]. Our interest in chalcogenide containing clusters
stems from a desire to understand how the incorpora-
tion of main group elements into transition metal clus-
ters would affect their stability, structure and reactivity.
We have recently reported [8] the synthesis of the
hexanuclear selenido cluster [Os6(CO)12(l3-Se)4(l-
dppm)2] from the Me3NO initiated decarbonylation of
[Os3(CO)7(l3-Se)2(l-dppm)] at 80 ꢀC. Predieri et al. [9]
reported the corresponding hexaruthenium compound
[Ru6(CO)12(l3-Se)4(l-dppm)2] from a similar self con-
densation reaction of [Ru3(CO)7(l3-Se)2(l-dppm)]. As
part of our continued interest in cluster expansion reac-
tions, we have been pursuing the chemistry associated
with the reactivity of the triply bridging selenido and
sulfido triosmium clusters [Os3(CO)7(l3-Se)2(l-dppm)]
and [Os3(CO)7(l3-S)2(l-dppm)] (1). In this paper we re-
port the synthesis of [Os3(l3-S)2(CO)6(Me3N)(l-dppm)]
(2) and [Os6(CO)12(l3-S)4(l-dppm)2] (3) by the Me3NO
initiated self condensation reaction of 1. We also de-
scribe the synthesis of the hexanuclear complex [Os6-
(CO)14(l3-S)2(l-dppm)] (4) from the reaction of 1 with
[Os3(CO)10(MeCN)2]. These complexes permit the direct
comparison of the structures of [Os6(CO)12(l3-Se)4(l-
dppm)2] and [Os6(CO)14(l3-S)2(l-dppm)] with those of
the unsubstituted complexes [Os6(CO)16(l3-S)4] and
[Os6(CO)17(l4-S)2]. To further explore the reactivity of
[Os3(CO)7(l3-S)2(l-dppm)] (1) and [Os3(l3-S)2(CO)6-
(Me3N)(l-dppm) (2) we have examined their interac-
tions with CO, PPh3 and P(OMe)3 and the results are
also described in the present paper.
The formation of 2 constitutes an unambiguous
example where oxidation of a cluster bound CO by
Me3NO leads to the corresponding amino derivative.
This observation is similar to that reported by
Braunstein and coworkers [10] who obtained the
NMe3 substituted compounds [(l-H)FeCo3(CO)11-
(NMe3)] and [(l-H)FeCo3(CO)10(PPh2H)(NMe3)] from
the reactions of Me3NO with [(l-H)FeCo3(CO)12] and
[(l-H)FeCo3(CO)11(PPh2H)] respectively. Amine-substi-
tuted clusters are rarely amenable to solid-state charac-
terization since the stability of such complexes is limited
[11]. Thus we were unable to obtain X-ray quality crys-
tals of compound 2, therefore, the characterization is
based on elemental analysis, infrared, 1H NMR, 31P
{1H} NMR and FAB mass spectroscopic data. The in-
frared spectrum of 2 shows m(CO) bands characteristic
of terminal carbonyl groups. In addition to the usual
phenyl proton resonances the 1H NMR spectrum shows
two multiplets at d 4.61 and 3.48 due to the methylene
protons of the dppm ligand and a singlet at d 2.81 due
to the methyl protons of the NMe3 ligand. The 31P
{1H} NMR spectrum shows two doublets at d À13.6
and À14.8 (J=92.4 Hz) for the two magnetically non-
equivalent 31P nuclei. The FAB mass spectrum shows
molecular ion (M+) peak at m/z 1245 and fragment ions
formed by the sequential loss of six carbonyl groups.
The hexanuclear cluster 3 has been characterized by
1
elemental analysis, infrared, H NMR, 31P {1H} NMR
and mass spectroscopic data. The spectroscopic data
of 3 are in accord with the solid-state structure of the se-
lenium analogue [8]. The infrared spectrum exhibits
m(CO) bands characteristic of terminal carbonyl groups
and is exactly the same as the selenium analog. In addi-
tion to the usual phenyl proton resonances the 1H NMR
spectrum in the aliphatic region contains two multiplets
centered at d 3.56 and 3.80 due to the methylene protons
of the dppm ligand. The 31P {1H} NMR spectrum shows
two doublets at d À9.8 (J=17.2 Hz) and À6.4 (J=17. 2
Hz), indicating that the 31P nuclei are magnetically non-
equivalent. These NMR data are identical in pattern
with the selenium analog with only slight variations in
the chemical shifts. The FAB mass spectrum shows a
molecular ion peak at m/z 2374 (M+) corresponding to
the formulation [Os6(CO)12(l3-S)4(l-dppm)2]. Both 3
and its selenium analogue are dark green. The proposed
structure of 3 gives a 96eÀ count, two more than that re-
quired for a hexanuclear cluster with seven metal–metal
bonds. The two extra electrons probably occupy an an-
tibonding molecular orbital and one would expect to see
elongated metal–metal bonds for 3 as reported for the
selenium analog [8] where four elongated metal–metal
2. Results and discussion
Treatment of [Os3(l3-S)2(CO)7(l-dppm)] (1) with
Me3NO in toluene at 80 ꢀC affords a novel trinuclear
cluster [Os3(l3-S)2(CO)6(Me3N)(l-dppm)] (2) and a
hexanuclear cluster [Os6(CO)12(l3-S)4(l-dppm)2] (3) in
30% and 51% yields respectively, after usual chromato-
graphic work-up (Scheme 1).
˚
bonds in the range of 2.982(4)–3.042(5) A are observed
for the osmium–osmium bonds around the periphery
of the central cluster.
The reaction of 1 with [Os3(CO)10(MeCN)2] in reflux-
ing benzene for 3 h followed by usual work up and

T. Akter et al. / Journal of Organometallic Chemistry 689 (2004) 2571–2580
2573
Scheme 1.
chromatographic separation has resulted in the isolation
of a hexanuclear cluster [Os6(l3-S)2(CO)14(l-dppm)] (4)
in 15% yield (Scheme 2). Cluster 4 has been character-
ized by elemental analysis, infrared, 1H NMR, 31P
{1H} NMR and FAB mass spectroscopic data and by
single crystal X-ray diffraction analysis. The molecular
structure of 4 is shown in Fig. 1, crystal data are given
in Table 1 and the selected bond distances and angles
are listed in Table 2. The molecule consists of an extend-
ed array of six osmium atoms and two triply bridging
sulfido ligands. The metal core can be described as a
central tetrahedral array capped on two faces with two
additional osmium atoms. The triply bridging sulfido li-
gands face cap the two tetrahedral arrays formed by
metal capping of the two faces of the central tetrahe-
dron. The dppm ligand bridges one edge {Os(1)–
Os(2)} of one of the external tetrahedral arrays. The
compound contains fourteen linear terminal carbonyl li-
gands. The metal–metal bonding within the cluster is
not uniform with the metal–metal bond distances be-
tween the apical–equatorial and equatorial–equatorial
˚
osmium atoms ranging from 2.701 (1) to 3.058 (1) A.
There are two metal–metal bonds which are significantly
longer
{Os(1)–Os(3)=3.014(1)
˚
and
Os(1)–
Os(4)=3.058(1) A} than the average Os–Os bond dis-
˚
tances in [Os3(CO)12] {2.877(3) A} [12]. Each hinge met-
al contains two linear terminal carbonyl ligands. The
other metal atoms are ligated by three CO ligands. In
cluster 1, all the metal atoms contain 18-electron config-
urations; however, these configurations cannot be main-
tained in the 88eÀ 4 if the newly formed bonds are of a
two-centered two-electron type. Compound 4 has 88
electrons and the effective atomic number rule predicts
86 electrons for a hexanuclear cluster with eleven met-
al–metal bonds. As for 3 this cluster contains two extra
electrons which occupy a low lying anti bonding orbital
Scheme 2.

2574
T. Akter et al. / Journal of Organometallic Chemistry 689 (2004) 2571–2580
low-lying antibonding orbital and also exhibits elongat-
ed metal–metal bonds [7]. The Os–S bond distances in 4
˚
lie within the range {2.316(6)–2.410(5) A} and are com-
parable to those observed for other capping sulfido
˚
bridges (2.35–2.45 A) [13–16]. The details of the nature
of the delocalized bonding in cluster 4 remain to be es-
tablished. This bonding could have an important influ-
ence on the reactivity of compounds 3 and 4 and
could lead to the development of new reaction pathways
that are characteristic of the multinuclear metal centers
containing more than the number of electrons required
by the effective atomic number rule (vide infra).
The spectroscopic data for 4 are in accord with the sol-
id-state structure. The infrared spectrum of 4 in the CO
region exhibits absorption bands characteristic of termi-
nal carbonyl ligands. The 1H NMR spectrum of 4 shows
a series of well-separated multiplets centered at d 7.31 and
two equal intensity pseudo quartets at d 4.37 and 3.99 for
the methylene protons of the dppm ligand. The 31P {1H}
NMR spectrum of 4 shows two doublets at d 5.52
(J=34.0 Hz) and 4.37 (J=34.0 Hz) indicating that the
two 31P nuclei are non-equivalent. The FAB mass spec-
trum exhibits the molecular ion peak at m/z 1980 (M+).
The lability of the Os-amine bond of 2 may be ex-
ploited for the selective preparation of other substituted
Fig. 1. Molecular structure of [Os6(CO)14(l3-S)2(l-dppm)] (4) showing
the crystallographic labeling scheme. Thermal ellipsoids are at the 50%
probability level.
of the central Os4 core which correlates well with the
lengthening of four Os–Os bonds. Electronically, the
cluster [Os6(CO)17(l4-S)2], also contains two electrons
in excess of the requirements of the 18-electron rule
and it was proposed that these electrons also occupy a
Table 1
Crystal data and structure refinement for 4 and 6
4
6
Empirical formula
Formula weight
Temperature
C39H22O14Os6P2S2
1981.86
293 (2)
C34H31O9Os3P3S2
1311.22
293(2)
Wavelength
0.71073
Triclinic
0.71069
Orthorhombic
Pbca
Crystal system
Space group
Unit cell dimensions (A)
ꢀ
P1
˚
˚
a (A)
11.719(5)
12.880(5)
17.0481(5)
69.280(5)
77.500(5)
70.460(5)
2254.1(15)
2
16.767(5)
17.812(5)
28.951(5)
90.00
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
90.00
90.00
3
˚
V (A )
8646(4)
8
2.015
Z
Dcalc (Mg mÀ3
Absorption coefficient (mmÀ1
F (000)
)
2.920
17.071
)
9.049
4896
1772
0.32·0.10·0.07
2.11–20.02
Crystal size (mm)
h range for data collection (ꢀ)
Index ranges
0.33·0.26·0.14
2.18–20.00
À106h611, À116k611, 06l616
4164
4164
Full-matrix least-squares on F2
06h616, 06k617, 06l627
3967
3967
Full-matrix least-squares on F2
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2r(I)]
R indices (all data)
4164/334/569
1.163
3967/224/461
1.049
R1 =0.0504, wR2 =0.1181
R1 =0.0567, wR2 =0.1233
2.028 and À2.796
R1 =0.0567, wR2 =0.1430
R1 =0.0849, wR2 =0.1667
1.602 and À1.460
À3
˚
Largest diff. peak and hole (e A
)

T. Akter et al. / Journal of Organometallic Chemistry 689 (2004) 2571–2580
2575
Table 2
˚
Selected bond lengths (A) and angles (ꢀ) for 4
Bond lengths
Os(1)–Os(5)
Os(1)–Os(3)
Os(2)–Os(3)
Os(3)–Os(5)
Os(3)–Os(6)
Os(5)–Os(6)
Os(2)–S(1)
2.8797(14)
3.0137(12)
2.7569(16)
2.7009(11)
2.8795(14)
2.9326(16)
2.369(4)
Os(1)–Os(2)
Os(1)–Os(4)
Os(2)–Os(5)
Os(3)–Os(4)
Os(4)–Os(6)
Os(1)–S(1)
2.9747(13)
3.0577(17)
2.8864(13)
2.8456(12)
2.8561(16)
2.379(4)
Os(3)–S(1)
Os(5)–S(2)
2.342(5)
2.316(6)
Os(4)–S(2)
Os(6)–S(2)
2.410(5)
2.363(5)
Os(1)–P(1)
Os–C (average)
2.326(5)
1.87(3)
Os(2)–P(2)
C–O (average)
2.289(6)
1.14(2)
Bond angles
P(1)–Os(1)–Os(5)
S(1)–Os(1)–Os(5)
S(1)–Os(1)–Os(2)
P(1)–Os(1)–Os(3)
Os(2)–Os(1)–Os(3)
S(1)–Os(1)–Os(4)
Os(2)–Os(1)–Os(4)
P(2)–Os(2)–S(1)
118.94(10)
98.85(10)
51.06(10)
141.62(12)
54.82(3)
P(1)–Os(1)–S(1)
100.46(17)
88.37(12)
59.06(3)
P(1)–Os(1)–Os(2)
Os(5)–Os(1)–Os(2)
Os(5)–Os(1)–Os(3)
P(1)–Os(1)–Os(4)
Os(5)–Os(1)–Os(4)
Os(3)–Os(1)–Os(4)
P(2)–Os(2)–Os(3)
P(2)–Os(2)–Os(5)
Os(3)–Os(2)–Os(5)
S(1)–Os(2)–Os(1)
Os(5)–Os(2)–Os(1)
S(1)–Os(3)–Os(2)
S(1)–Os(3)–Os(4)
Os(2)–Os(3)–Os(4)
Os(5)–Os(3)–Os(6)
Os(4)–Os(3)–Os(6)
Os(5)–Os(3)–Os(1)
Os(4)–Os(3)–Os(1)
S(2)–Os(4)–Os(3)
S(2)–Os(4)–Os(6)
Os(3)–Os(4)–Os(1)
S(2)–Os(5)–Os(3)
Os(3)–Os(5)–Os(1)
Os(3)–Os(5)–Os(2)
S(2)–Os(5)–Os(6)
Os(1)–Os(5)–Os(6)
S(2)–Os(6)–Os(4)
Os(4)–Os(6)–Os(3)
Os(4)–Os(6)–Os(5)
Os(3)–S(1)–Os(2)
Os(2)–S(1)–Os(1)
Os(5)–S(2)–Os(4)
54.50(3)
162.34(12)
66.30(3)
55.89(3)
95.52(13)
107.68(3)
100.78(16)
53.73(12)
95.89(12)
93.11(12)
63.31(3)
152.32(11)
124.52(12)
57.13(3)
S(1)–Os(2)–Os(3)
S(1)–Os(2)–Os(5)
P(2)–Os(2)–Os(1)
Os(3)–Os(2)–Os(1)
S(1)–Os(3)–Os(5)
Os(5)–Os(3)–Os(2)
Os(5)–Os(3)–Os(4)
S(1)–Os(3)–Os(6)
Os(2)–Os(3)–Os(6)
S(1)–Os(3)–Os(1)
Os(2)–Os(3)–Os(1)
Os(6)–Os(3)–Os(1)
Os(3)–Os(4)–Os(6)
S(2)–Os(4)–Os(1)
Os(6)–Os(4)–Os(1)
S(2)–Os(5)–Os(1)
S(2)–Os(5)–Os(2)
Os(1)–Os(5)–Os(2)
Os(3)–Os(5)–Os(6)
Os(2)–Os(5)–Os(6)
S(2)–Os(6)–Os(3)
S(2)–Os(6)–Os(5)
Os(3)–Os(6)–Os(5)
Os(3)–S(1)–Os(1)
Os(5)–S(2)–Os(6)
Os(6)–S(2)–Os(4)
51.35(11)
58.83(3)
101.70(10)
63.85(3)
71.69(3)
54.64(11)
102.24(12)
120.76(4)
63.31(3)
158.74(11)
122.13(4)
50.87(10)
61.87(3)
59.85(4)
60.22(3)
62.84(4)
108.05(4)
60.67(3)
91.35(13)
52.49(12)
61.27(3)
90.54(14)
107.47(3)
97.05(12)
152.65(11)
62.11(3)
97.20(12)
65.28(2)
59.02(3)
51.90(13)
110.30(3)
54.00(11)
59.49(3)
59.02(3)
115.94(4)
91.49(14)
50.48(14)
55.37(3)
68.30(3)
71.63(12)
77.59(12)
86.88(16)
79.33(14)
77.61(15)
73.51(13)
products. Thus as expected compound 2 reacts with CO,
PPh3 and P(OMe)3 at room temperature to give 1,
[Os3(l3-S)2(CO)6(PPh3)(l-dppm)] (5) and [Os3 (CO)6(l3-S)2-
(l-dppm){P(MeO)3}] (6) in 90%, 77% and 81% yields,
respectively (Scheme 3). Clusters 5 and 6 have been
characterized on the basis of elemental analysis, IR,
1H NMR, 31P NMR and mass spectroscopic data to-
gether with a single crystal X-ray diffraction study for
6. The solid-state structure of 6 is depicted in the Fig.
2, crystal data are provided in Table 1 and selected bond
distances and angles are collected in Table 3. Compound
6 consists of an open triangular cluster having two al-
most equal metal–metal bonds Os(1)–Os(2)=2.8106(14),
˚
Os(1)–Os(3)=2.8122(13) A, a bridging dppm ligand,
two triply bridging sulfido ligands, a trimethylphosphite
ligand and six linear terminal carbonyl ligands two
bonded to each osmium atom. The Os–S bond distances
to the triply bridging sulfido ligands {Os(1)/Os(2)/Os(3)–
S(1)=2.438(6)/2.426(5)/2.419(6) and Os(1)/Os(2)/Os(3)–
˚
S(2)=2.404(6)/2.363(5)/2.354(6) A} are comparable to
the Os–S distances in 1 [15] and [Os3(CO)9(l3-S)2]
[16]. The Os–P bond distances of the dppm ligand

2576
T. Akter et al. / Journal of Organometallic Chemistry 689 (2004) 2571–2580
Ph2
P
(CO)2
CH2
Os
S
PPh2
S
RT
(CO)2Os
PPh
2
PPh3
Os(CO)2
+
CH2Cl2
3
+
5
P(OMe)3
CH2Cl2
RT
Ph2
P
(CO)2
Os
CH2
1
S
PPh2
S
(CO)2Os
P(OMe)3
Os(CO)2
6
Scheme 3.
ilar, indicating that they have a similar distribution of
the carbonyl ligands. The 31P {1H} NMR spectra of 5
and 6 display three sets of equally intense resonances, in-
dicating three different phosphorus atoms in the mole-
cule. For 5, the doublet of doublets at d À9.7 (J=23.0
and J=11.8 Hz) and the doublet at d À16.2 (J=23.0
Hz) are due to the two non-equivalent phosphorous at-
oms of the dppm ligand while the doublet at d 15.4
(J=11.8 Hz) is due to the PPh3 ligand. Similarly for 6,
the doublet at d À16.0 (J=23.5 Hz) and the doublet of
doublets at d À9.2 (J=23, 9.2 Hz) are assigned to the
non-equivalent 31P nuclei of the dppm ligand while the
doublet at 110.5 (J=9.2 Hz) is due to the tri-
methylphosphite ligand. In addition to the usual phenyl
resonances, the 1H NMR spectrum of 5 and 6 shows two
AB multiplets (d 4.83 and 3.72 for 5 and d 4.84 and 3.66
for 6) due to the methylene protons of the dppm ligand
and a doublet at d 3.82 for 6 due to the methyl protons
of the P(OMe)3 ligand. The FAB mass spectra of 5 and 6
show the molecular ion peaks at m/z 1449 and 1310, re-
spectively, and ions due to the sequential loss of six car-
bonyl groups.
Fig. 2. Molecular structure of [Os3(CO)6(l3-S)2(l-dppm){P(OMe)3}]
(6) showing the crystallographic labeling scheme. Thermal ellipsoids
are at the 50% probability level.
˚
{Os(1)–P(1)=2.332(6) and Os(2)–P(2)=2.323(6) A} are
similar to those observed in 1 [15] and the parent com-
pound [Os3(CO)10(l-dppm)] [17]. Overall the structure
of 6 is similar to that of 1 except that a P(OMe)3 has
been substituted for an equatorially positioned carbonyl
ligand. Both complexes 5 and 6 contain 50-valence elec-
trons and are electron precise with two metal–metal
bonds.
The spectroscopic data of 6 are consistent with the
solid-state structure and the spectroscopic data for 5
are consistent with the structure proposed in Scheme
3. The patterns of their m(CO) absorption bands are sim-
We have studied the substitution reaction of the nido
cluster 1 to see if the substitution occurs at apical or basal
metal atoms. The reaction of 1 with PPh3 in the presence
of Me3NO, results in the isolation of the PPh3 substitut-
ed compound 5 in 53% yield in addition to 2 and 3 in 6
and 18% yields respectively. In contrast P(OMe)3 reacts
with 1 in presence of Me3NO to give 6 as the only prod-
uct in 81% yield. The formation of only 6 in the presence

T. Akter et al. / Journal of Organometallic Chemistry 689 (2004) 2571–2580
2577
Table 3
˚
Selected bond distances (A) and angles (ꢀ) for 6
Bond lengths
Os(3)–C(6)
Os(3)–P(3)
Os(3)–S(1)
Os(1)–C(1)
Os(1)–P(1)
Os(1)–S(1)
Os(2)–C(34)
Os(2)–P(2)
Os(2)–S(1)
C–O (average)
1.90(3)
Os(3)–C(7)
Os(3)–S(2)
1.92(3)
2.354(6)
2.237(7)
2.419(6)
1.86(2)
Os(3)–Os(1)
Os(1)–C(2)
Os(1)–S(2)
2.8122(13)
1.890(3)
2.404(6)
2.8106(14)
1.90(3)
2.332(6)
2.438(6)
1.90(3)
Os(1)–Os(2)
Os(2)–C(33)
Os(2)–S(2)
2.323(6)
2.426(5)
1.19 (8)
2.363(5)
1.89(7)
Os–C(CO) (average)
Bond angles
P(3)–Os(3)–S(2)
S(2)–Os(3)–S(1)
S(2)–Os(3)–Os(1)
P(1)–Os(1)–S(2)
S(2)–Os(1)–S(1)
S(2)–Os(1)–Os(2)
P(1)–Os(1)–Os(3)
S(1)–Os(1)–Os(3)
P(2)–Os(2)–S(2)
S(2)–Os(2)–S(1)
S(2)–Os(2)–Os(1)
Os(3)–S(1)–Os(2)
Os(2)–S(1)–Os(1)
Os(3)–S(2)–Os(1)
106.1(2)
P(3)–Os(3)–S(1)
P(3)–Os(3)–Os(1)
S(1)–Os(3)–Os(1)
P(1)–Os(1)–S(1)
P(1)–Os(1)–Os(2)
S(1)–Os(1)–Os(2)
S(2)–Os(1)–Os(3)
Os(2)–Os(1)–Os(3)
P(2)–Os(2)–S(1)
P(2)–Os(2)–Os(1)
S(1)–Os(2)–Os(1)
Os(3)–S(1)–Os(1)
Os(3)–S(2)–Os(2)
Os(2)–S(2)–Os(1)
105.5(2)
77.75(18)
54.61(15)
137.0(2)
152.7(2)
54.94(13)
94.1(2)
76.43(19)
53.20(13)
146.68(15)
54.30(13)
153.2(2)
86.91(16)
54.51(13)
52.95(13)
82.32(4)
90.86(19)
98.95(16)
54.90(14)
70.76(15)
103.3(2)
72.24(16)
77.43(19)
54.56(15)
103.3(2)
70.59(14)
72.44(17)
of trimethyl phosphite but not in the presence of triphe-
nylphosphine is probably due to the lower nucleophilic-
ity of the phosphite relative to the phosphine.
Treatment of 3 with CO at 98 ꢀC results in the forma-
tion of 1 in 83% yield indicating that compound 3 is un-
usually reactive. The relatively mild conditions observed
here for the cleavage of the hexanuclear 3 are most likely
due to the occupation of the antibonding orbital by the
extra two electrons.
from the reaction of [Os3(CO)9(l3-S)2] with [Os3(CO)10-
(MeCN)2] at 128 ꢀC. This complex has a square pyrami-
dal core of osmium atoms with a sixth osmium bridging
one basal edge and has a total of ten metal–metal bonds.
Interestingly, the presence of the dppm ligand results in
a structure with eleven metal–metal bonds but with two
l3-sulfido ligands instead of two l4-sulfido ligands. Thus
the bulky dppm ligand blocks additional closure of the
sulfido caps. In addition, it should be noted that the re-
action of 1 with [Os3(CO)10(MeCN)2] results in a struc-
ture with many more metal–metal bonds than the self
condensation of 1 after treatment with one equivalent
Me3NO. This difference is undoubtedly due to the avail-
ability of two labile sites in the case of [Os3(CO)10-
(MeCN)2] rather than one as in 2 and underlines the
general concept that the formation of higher nuclearity
clusters is very sensitive to reaction pathway and there-
fore under kinetic control.
3. Conclusions
In contrast to the Me3NO initiated self condensation
of [Os6(CO)12(l3-Se)4(l-dppm)2] and [Ru3(CO)7(l3-
S)2(l-dppm)] which afforded only the hexanuclear
compounds [Os6(CO)12(l3-Se)4(l-dppm)2] and [Ru6-
(CO)12(l3-S)4(l-dppm)2] respectively, the reaction of 1
with Me3NO at 80 ꢀC gives the labile trinuclear com-
pound 2 and as well as the hexanuclear compound 3.
The lability of the NMe3 ligand in 2 has been demon-
strated by its reaction with CO, PPh3 and P(OMe)3
which yielded compounds 1, 5 and 6 respectively. Inter-
estingly, 1 has been found to combine with [Os3(CO)10
(MeCN)2] at 80 ꢀC to give the hexanuclear compound
4 containing a bridging dppm and two triply bridging
sulfide ligands. Compound 4 has a different structure
from that of [Os6(CO)17(l4-S)2] which was obtained
4. Experimental
All reactions were routinely performed under a nitro-
gen atmosphere using standard Schlenk techniques al-
though no special precautions were taken to exclude
air during work-up. The solvents were dried and distilled
prior to use by standard methods (CH2Cl2 over CaH2,
toluene and benzene from sodium benzophenone). All

2578
T. Akter et al. / Journal of Organometallic Chemistry 689 (2004) 2571–2580
other solvents were of reagent grade and used as re-
ceived. Infrared spectra were recorded on a Shimadzu
FTIR 8101 spectrophotometer. 1H and 31P {1H}
NMR spectra were recorded on a Varian Unity Plus
400 and a Bruker DPX 400 spectrometers. Chemical
shifts for the 31P {1H} NMR spectra are relative to
85% H3PO4. Mass spectra were recorded on Varian
Mat 312 mass spectrometer. The cluster [Os3(l3-
S)2(CO)7(l-dppm)] (1) was prepared by the literature
procedure [15]. Triphenylphosphine and trimethyl phos-
phite were purchased from Aldrich and used as received.
(Anal. Calc. for C39H22O14Os6P2S2: C, 23.63; H, 1.12.
Found: C, 23.75; H, 1.28%). IR (mCO, CH2Cl2): 2256
1
w, 2127 w, 2081 s, 2052 s, 2019 s, 2008 vs, cmÀ1; H
NMR (CD2Cl2): d 7.31 (m, 20H), 4.37(m, 1H), 3.99
(m, 1H); 31P {1H} NMR (CD2Cl2): d 5.5 (d, J=34.0
Hz), 4.4 (d, J=34.0 Hz); mass spectrum: m/z 1982
(M+). The minor bands were too small for complete
characterization.
4.3. Reaction of [Os3(CO)6(l3-S)2(l-dppm)(NMe3)]
(2) with PPh3
4.1. Reaction of [Os3(l3-S)2(CO)7(l-dppm)] (1) with
Me3NO
A dichloromethane solution (20 ml) of 2 (0.020 g,
0.016 mmol) and PPh3 (0.005 g, 0.019 mmol) was stirred
at room temperature for 2 h. The solvent was removed
under reduced pressure and the residue was separated
by TLC on silica gel. Elution with hexane/CH2Cl2 devel-
oped a single band which afforded [Os3(CO)6(l3-
S)2(PPh3)(l-dppm)] (5) (0.017 g, 77%) as yellow crystals
after recrystallization from hexane/CH2Cl2 at 4 ꢀC
(Anal. Calc. for C49H37O6Os3P3S2: C, 41.49; H, 2.63.
Found: C, 41.68.; H, 2.75%). IR (mCO, CH2Cl2): 2016
A toluene solution (30 ml) of 1 (0.105 g, 0.086 mmol)
and Me3NO (0.009 g, 0.120 mmol) was heated to 80 ꢀC
for 15 min, during this time the color changed from or-
ange to green. The reaction mixture was filtered through
a short silica column to remove excess Me3NO. The sol-
vent was removed under reduced pressure and the resi-
due was chromatographed by TLC on silica gel.
Elution with hexane/CH2Cl2 (1:1, v/v) developed four
bands. The first band gave unconsumed starting materi-
al 1 (0.004 g). The second band gave [Os3(CO)6(l3-S)2(l-
dppm)(NMe3)] (2) (0.032 g, 30%) as yellow crystals after
recrystallization from hexane/CH2Cl2 at À4 ꢀC (Anal.
Calc. for C34H31NO6Os3P2S2: C, 32.76; H, 2.51; N,
1.12. Found: C, 32.98; H, 2.82; N, 1.25%). IR (mCO,
1
s, 1991 vs, 1943 vs, 1935 m cmÀ1; H NMR (CD2Cl2):
d 7.67 (m, 35 H), 4.83 (m, 1H), 3.72 (m, 1H); 31P {1H}
NMR (CD2Cl2): d 15.4 (J=11.8), À16.2 (J=23.0) and
d À9.7 (dd, J=23.0 and J=11.8); mass spectrum: m/z
1417 (M+).
4.4. Reaction of 2 with P(OMe)3
1
CH2Cl2): 2006 vw, 1983 vs, 1975 vs, 1927 s; H NMR
(CDCl3): d 7.32 (m, 20H) 4.61(m, 1H), 3.48 (m, 1H),
2.81 (s, 9H); 31P {1H} NMR (CDCl3): d À13.6 (d,
J=92.4 Hz), À14.8 (J=92.4 Hz); mass spectrum: m/z
1245 (M+). The third band was too small for complete
characterization. The fourth band gave [Os6(CO)12(l3-
S)4(l-dppm)2] (3) (0.053 g, 51%) as green crystals after
recrystallization from heptane/CH2Cl2 at 25 ꢀC (Anal.
Calc. for C62H44O12Os6P4S4: C, 31.36; H, 1.87. Found:
C, 31.60; H, 2.02%). IR (mCO, CH2Cl2): 2035 vw, 2020
A similar reaction of 2 (0.025 g, 0.020 mmol) with
P(OMe)3 (0.008 g, 0.064 mmol) for 1 h followed by sim-
ilar workup and chromatographic separation gave 6
(0.021 g, 81%) as yellow crystals after recrystallization
from hexane/CH2Cl2 at
C34H31O9Os3P3S2: C, 31.09; H, 2.53. Found: C, 31.32.;
4
ꢀC (Anal. Calc. for
H, 2.63%). IR (mCO, CH2Cl2): 2026 vs, 1993 vs, 1950
vs, 1931, 1869 vw cmÀ1 1H NMR (CD2Cl2): d 7.41
;
(m, 20H), 4.84 (m, 1H), 3.89 (s, 9H), 3.66 (m, 1H); 31P
{1H} NMR (CD2Cl2): d 110.5 (d, J=9.2 Hz), À9.2 (t,
J=23.5 and 9.2 Hz) and À16.0 (d. J=23.5 Hz); mass
spectrum: m/z 1312 (M+).
1
vs, 1985s, 1954 m, 1898 vw cmÀ1; H NMR (CDCl3):
7.49 (m, 40H), 3.80 (m, 2H), 3.56 (m, 2H); 31P {1H}
NMR (CDCl3): d À9.8 (J=17.2 Hz), À6.4 (J=17. 2
Hz); mass spectrum: m/z 2374 (M+).
4.5. Reaction of 2 with CO
4.2. Reaction of 1 with [Os3(CO)10(MeCN)2]
Carbon monoxide gas was bubbled through a
CH2Cl2 solution (20 ml) of 2 (0.025 g, 0.020 mmol) for
5 min. IR spectrum indicated quantitative formation
of compound 1.
A benzene solution (100 ml) of 1 (0.075 g, 0.062
mmol) and [Os3(CO)10(MeCN)2] 4 (0.230 g, 0.246
mmol) was refluxed for 4 h, during this time the color
changed from yellow to red. The solvent was removed
under reduced pressure and the residue was chromato-
graphed by TLC on silica gel. Elution with hexane/
CH2Cl2 (7:3, v/v) developed one major and two very mi-
nor bands. The slower moving major band gave [Os6-
(CO)14(l3-S)2(l-dppm)] 4 (0.018 g, 15%) as red crystals
after recrystallization from hexane/CH2Cl2 at À20 ꢀC
4.6. Reaction of 1 with PPh3
To a dichloromethane solution (20 ml) of 1 (0.050 g,
0.041 mmol) and PPh3 (0.011 g, 0.042 mmol) was added
dropwise a solution of Me3NO (0.005 g, 0.066 mmol) in
the same solvent (10 ml) over a period of 20 min. The

T. Akter et al. / Journal of Organometallic Chemistry 689 (2004) 2571–2580
2579
resulting mixture was stirred at room temperature for 3
5. Supplementary material
h during which time analytical TLC indicated complete
consumption of 1. The solvent was removed under re-
duced pressure and the resulting residue was separated
by TLC on silica gel. Elution with hexane/CH2Cl2
(1:1, v/v) developed three bands which afforded the fol-
lowing compounds in order of elution: 5 (0.031 g, 53%)
2, (0.003 g, 6%) as yellow crystals after recrystallization
from hexane/CH2Cl2 at 4 ꢀC 3 (0.009 g, 18%).
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 226811 for compound 4,
and 226812 for compound 6. Copies of this information
may be obtained free of charge from the Director,
CCDC, 12 Union Road Cambridge, CB2 1EZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk).
4.7. Reaction of 1 with P(OMe)3
To a dichloromethane solution (20 ml) of 1 (0.040
g, 0.033 mmol) and P(OMe)3 (0.009 g, 0.073 mmol)
was added dropwise a solution of Me3NO (0.006 g,
0.080 mmol) in a methanolic solution (2 ml) of
CH2Cl2 (10 ml) over a period of 10 min. The resulting
mixture was stirred at room temperature for 3 h, dur-
ing which time analytical TLC indicated complete con-
sumption of 1. The solvent was removed under
reduced pressure and the resulting residue was separat-
ed by TLC on silica gel. Elution with hexane/CH2Cl2
(3:2, v/v) developed a single band, which afforded 6
(0.036 g, 84%).
Acknowledgement
We gratefully acknowledge the Ministry of Science
and Technology, Government of the peoples Republic
of Bangladesh for financial assistance. NB acknowledges
the Sher-E-Bangla Agricultural University, Dhaka for
study leave.
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