Synthesis, characterization, and novel fluxional mechanisms of triosmium clusters containing the highly flexible ligand Ph2PC 2H4SC2H4SC2H 4PPh2 (PSSP)

Article abstract of DOI:10.1021/om900966c

Treatment of Ph₂PC₂H₄SC₂H ₄SC₂H₄PPh₂ (PSSP) with [Os ₃(CO)₁₁(NCMe)] under mild conditions yields [{Os ₃(CO)₁₁}₂(μ-PSSP)], 1, and [Os ₃(CO)₁₁(PSSP)], 2. In cluster 1 the ligand links two trinuclear cluster subunits, coordinating via its phosphine moieties. In cluster 2, the ligand is coordinated through one of the phosphine groups, while the remaining part of the PSSP ligand is oriented in a dangling mode. Treatment of [Os₃(CO)₁₀(NCMe)₂] with PSSP yields 1,2-[Os₃(CO)₁₀(PSSP)], 3. NMR data presented in this paper indicate that a concerted cis/trans isomerism with respect to the phosphines operates in the cluster. This type of process has not been observed previously for a bridging ligand, but has been detected in the case of corresponding triosmium clusters with bis-monodentate phosphine ligands. Oxidative decarbonylation of [{Os₃(CO)₁₁}₂(μ-PSSP)], 1, with Me₃NO yields cluster [{Os₃(CO)₁₀} ₂(μ-PSSP)], 4. This cluster consists of two P,S-bridged cluster units. In solution at room temperature, 4 undergoes a slow rearrangement from a 1,2-bridging to a 1,1-chelating coordination mode. The crystal structures of clusters 1, 3, and 4 are reported.

Full text of DOI:10.1021/om900966c

Organometallics 2010, 29, 2223–2233 2223
DOI: 10.1021/om900966c
Synthesis, Characterization, and Novel Fluxional Mechanisms of
Triosmium Clusters Containing the Highly Flexible Ligand
Ph2PC2H4SC2H4SC2H4PPh2 (PSSP)
Roger Persson,† Marc J. Stchedroff,† Bettina Uebersezig,† Roberto Gobetto,‡
Jonathan W. Steed,§ Paul D. Prince,§ Magda Monari,^ and Ebbe Nordlander*,†
†Inorganic Chemistry Research Group, Chemical Physics, Center for Chemistry and Chemical Engineering,
Lund University, Box 124, SE-221 Lund, Sweden, ‡Dipartimento di Chimica Inorganica,
Chimica Fisica e de Chimica dei Materiali, Universitaꢀ degli Studi di Torino, Via Pietro Giuria 7, 10125
Torino, Italy, §Department of Chemistry, University of Durham, U.K., and ^Dipartimento di Chimica “G.
Ciamician”, Universita degli Studi di Bologna, Via Selmi 2, I-40126 Bologna, Italy
Received November 4, 2009
Treatment of Ph2PC2H4SC2H4SC2H4PPh2 (PSSP) with [Os3(CO)11(NCMe)] under mild condi-
tions yields [{Os3(CO)11}2(μ-PSSP)], 1, and [Os3(CO)11(PSSP)], 2. In cluster 1 the ligand links two
trinuclear cluster subunits, coordinating via its phosphine moieties. In cluster 2, the ligand is
coordinated through one of the phosphine groups, while the remaining part of the PSSP ligand is
oriented in a dangling mode. Treatment of [Os3(CO)10(NCMe)2] with PSSP yields 1,2-[Os3(CO)10-
(PSSP)], 3. NMR data presented in this paper indicate that a concerted cis/trans isomerism with
respect to the phosphines operates in the cluster. This type of process has not been observed
previously for a bridging ligand, but has been detected in the case of corresponding triosmium
clusters with bis-monodentate phosphine ligands. Oxidative decarbonylation of [{Os3(CO)11}2(μ-
PSSP)], 1, with Me3NO yields cluster [{Os3(CO)10}2(μ-PSSP)], 4. This cluster consists of two P,S-
bridged cluster units. In solution at room temperature, 4 undergoes a slow rearrangement from a 1,2-
bridging to a 1,1-chelating coordination mode. The crystal structures of clusters 1, 3, and 4 are
reported.
Introduction
over, the correlation of coordination modes of such ligands
with the reactivity of the specific clusters is of general interest
and is also central to different applications, e.g. develop-
ment of new catalysts and potentially useful synthons in
preparative chemistry.7 In recent studies on the coordination
properties of the PS [PPh2(CH2)2SMe]8 and PSP [PPh2-
(CH2)2S(CH2)2PPh2] ligands,9 we have found that the thio-
ether moiety of the phosphine-thioether ligands can coordi-
nate to a metal center only when the phosphine is already
coordinated. On the other hand, prior coordination of the
phosphine moiety (moieties) of these ligands may favor
thioether coordination via the chelate effect. This is a useful
way to coordinate inactive sulfur (or other donor atoms) to
metal centers under mild conditions. For example, thienyl-
phosphines may be used as “Trojan horses” to introduce
Multidentate phosphine-thiol or phosphine-thioether (P,S)
ligands are of considerable interest since they are intrinsically
asymmetric and potentially hemilabile.1-4 Such ligands have
been shown to be potentially useful in catalytic alkylation,
carbonylation, and coupling reactions.5,6 We are currently
investigating the reactivity of phosphine-thioether ligands
with polynuclear transition metal complexes. In particular,
we want to determine to what extent the thioether moiety
may compete with the phosphines as a ligand to one or
several transition metal(s) in a low oxidation state. More-
*Corresponding author. E-mail: Ebbe.Nordlander@chemphys.lu.se.
Fax: þ46 46 222 4439.
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r
2010 American Chemical Society
Published on Web 04/29/2010
pubs.acs.org/Organometallics

2224 Organometallics, Vol. 29, No. 10, 2010
Scheme 1. Preparation of Compounds 1-4
Persson et al.
yielded [Os3(CO)10(μ-PSSP)] (3) (Scheme 1). On treatment of
1 with two equivalents of the oxo-transfer reagent trimethy-
lamine N-oxide, [{Os3(CO)10}2(μ-PSSP)] (4) is obtained as an
orange solid in ca. 60% yield (Scheme 1). All the products are
air and thermally stable and can be separated on silica.
1
Characterization of [{Os3(CO)11}2(μ-PSSP)] (1). The H
NMR spectrum of compound 1 showed the methylene
signals as three complex multiplets at δ 2.27, 2.49, and
2.82. The 31P{1H} NMR spectrum exhibits a singlet at δ
-10.9, indicating that the phosphorus atoms are equivalent
and that the solution structure of the cluster is symmetric.
This is consistent with two cluster subunits linked by a
bridging ligand. The mass spectrum shows an isotopic
envelope at 2276 amu, in agreement with the values obtained
in the simulated spectrum, and the IR spectrum is similar to
that previously observed for [{Os3(CO)11}2(L)] (where L
is a bidentate phosphine ligand).13 We have been unable to
freeze out any conformers (173 K, 500 MHz) of 1; it is
possible that the interactions between phenyl moieties of the
ligand (vide infra) are responsible for this. Another possibi-
lity that cannot be ruled out with such a flexible ligand is that
the ligand chain is highly mobile even at very low tempera-
tures, thus averaging any potential conformers on the NMR
time scale.
Crystal and Molecular Structure of [{Os3(CO)11}2(μ-
PSSP)] (1). A single-crystal X-ray study was carried out on
1 in order to confirm the proposed structure for the cluster.
The molecular structure of 1 (Figure 1, relevant bond lengths
and angles in Table 1) confirms that the diphosphine ligand is
bridging two triosmium subunits, being coordinated in a
κ1(P)-mode. Similar diphosphine-bridged dimers have been
prepared by us9 and by other groups.14-18,25-27 The phos-
phine moieties coordinate to equatorial sites on each trios-
mium unit, as has been previously found in related
[Os3(CO)11(PR3)] species.17-19,21-24 The two triosmium tri-
angles are oriented approximately at 90ꢀ to each other. The
thienyl moieties in low-valent metal complexes;10,11 initial
coordination by the phosphine moiety of a thienylphosphine
permits, in some cases, subsequent coordination via the
thienyl sulfur.11
The ligand bis(diphenylphosphinodiethylene)ethylenedi-
sulfide (PSSP) is closely related to the above-mentioned P,
S-donor ligands. It has considerable flexibility, an unusual
chain length, and four potential donor atoms. We were
interested in investigating whether PSSP exhibits coordina-
tive behavior similar to that of PS and PSP. Here, we report
the results of the reaction of PSSP with the mono- and bis-
acetonitrile derivatives of [Os3(CO)12]12 as well as some
further reactions of the resultant products.
Results and Discussion
(13) Kabir, S. E. Ph.D. Thesis, University of London, 1986.
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Synthesis of [{Os3(CO)11}2(μ-PSSP)] (1),[Os3(CO)11(PSSP)]
(2), [Os3(CO)10(μ-PSSP)] (3), and [{Os3(CO)10}2(μ-PSSP)]
(4). Treatment of [Os3(CO)11(NCMe)] with PSSP at room
temperature in dichloromethane gave [{Os3(CO)11}2(μ-
PSSP)], 1, and [Os3(CO)11(PSSP)], 2 (Scheme 1). The pre-
dominant species was dependent on the stoichiometric ratios
of the reactants. Thus, cluster 1 is obtained in high yield as a
yellow crystalline compound by reacting PSSP with two
equivalents of [Os3(CO)11(NCMe)]. On the other hand, the
room-temperature reaction of [Os3(CO)11(NCMe)] with one
equivalent of PSSP gave a relatively low yield (9%, after
separation) of 2 as an orange oil. Treatment of [Os3(CO)10-
(NCMe)2] withPSSP at room temperature in dichloromethane
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Article
Organometallics, Vol. 29, No. 10, 2010 2225
Figure 1. ORTEP drawing of the molecular structure of [{Os3(CO)11}2(μ-PSSP)], 1. Hydrogen atoms have been omitted for clarity.
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for
[{Os3(CO)11}2(μ-PSSP)], 1
Scheme 2. Proposed Classical Merry-go-Round Fluxional Pro-
cess for [Os3(CO)11(PSSP)] Involving Sites a, f, b, and ga
Os(1)-Os(2)
2.8752(9)
2.8982(9)
2.889(1)
2.883(1)
2.908(1)
2.890(1)
2.351(4)
2.355(5)
1.85(2)
Os(4)-C(44)
1.91(2)
1.94(2)
1.92(2)
1.92(2)
1.92(2)
1.96(2)
1.96(2)
1.90(2)
1.95(2)
1.95(2)
1.77(2)
1.88(2)
1.83(2)
1.84(2)
1.86(2)
1.83(2)
1.92(2)
1.82(2)
1.83(2)
1.87(2)
117.7(7)
112.7(7)
97.3(9)
100(1)
Os(1)-Os(3)
Os(4)-C(42)
Os(2)-Os(3)
Os(5)-C(48)
Os(4)-Os(6)
Os(5)-C(47)
Os(4)-Os(5)
Os(5)-C(46)
Os(5)-Os(6)
Os(5)-C(45)
Os(1)-P(1)
Os(6)-C(50)
a Signals with shifts 193.1, 185.4, 176.3, and 170.2; see Figure 2.
P(2)-Os(4)
Os(6)-C(52)
Os(1)-C(2)
Os(6)-C(51)
˚
Os(5) 2.9077(11) A. The Os(1)-Os(3) and Os(4)-Os(5) sepa-
Os(1)-C(1)
1.96(2)
Os(6)-C(49)
Os(1)-C(3)
1.970(19)
1.896(19)
1.926(19)
1.98(2)
1.986(19)
1.890(17)
1.922(17)
1.94(2)
S(1)-C(25)
rations are also longer than the Os-Os separations in the
28
Os(2)-C(6)
S(1)-C(26)
˚
parent cluster [Os3(CO)12] [2.877(3) A]. The Os-P dis-
Os(2)-C(7)
P(1)-C(18)
˚
˚
tances [Os(1)-P(1) 2.351(4) A and Os(4)-P(2) 2.355(5) A]
Os(2)-C(4)
P(1)-C(12)
˚
fall in the range 2.285-2.399 A, which is typical for these
bonds.
Os(2)-C(5)
P(1)-C(24)
Os(3)-C(9)
S(2)-C(27)
Os(3)-C(11)
S(2)-C(28)
Characterization of [Os3(CO)11(PSSP)] (2). The mass
spectrum of cluster 2 shows an isotopic envelope at 1426
amu, consistent with the simulated spectrum. The IR spec-
trum of 2 is similar to that previously observed for 1 and
[Os3(CO)11(L)] (P = PPh3, P(OMe)3) clusters.21 The 31P{1H}
NMR shows two singlets at δ -17.3 and -10.2 attributable
to free and coordinated phosphine moieties, respectively.
The 13CO{1H} variable-temperature spectra show the expe-
cted fluxional behavior and confirm a simple κ1(P) co-
ordination mode. The low-temperature limiting spectrum
(500 MHz, 213 K, CDCl3) shows eight carbonyl signals
representing 11 carbonyls in a 2:2:2:1:1:1:1:1 pattern at δ
193.1(2JP-C ≈ 8 Hz) a, 185.4 f, 183.9 c, 176.8 b, 176.7 d,
172.8 h, 172.4 e, and 170.2 g (the letters refer to assignments
according to Scheme 2); see Figure 2.21 The three high-
frequency signals are assigned to the axial carbonyls on the
basis of chemical shifts and integral values (2H). The CO
signal at highest frequency (δ 193.1) shows phosphorus
coupling (2JC-P 7.9 Hz), whereas the five singlets (integral
1) are assigned to equatorial carbonyl ligands. On raising the
temperature to 273 K, the signals originating from the six
carbonyls along one edge of the cluster coalesce in a classical
merry-go-round process, involving sites a, f, b, and g (see
Scheme 2). The remaining carbonyl signals are assigned in
accordance with assignments of similar [Os3(CO)11(L)]
(L = phosphine or phosphite) compounds;21a see Scheme 2.
Line-shape analysis confirms the presence of the merry-go-
round process involving carbonyls a, f, b, and g and affords
a value for the carbonyl exchange activation energy of 49.3 (
2.0 kJ/mol.
Os(3)-C(8)
P(2)-C(36)
Os(3)-C(10)
1.95(2)
1.86(2)
P(2)-C(29)
Os(4)-C(43)
P(2)-C(30)
C(18)-P(1)-C(12)
C(18)-P(1)-C(24)
C(12)-P(1)-C(24)
C(18)-P(1)-Os(1)
C(12)-P(1)-Os(1)
C(24)-P(1)-Os(1)
C(36)-P(2)-C(29)
C(36)-P(2)-C(30)
C(29)-P(2)-C(30)
C(36)-P(2)-Os(4)
104.5(8)
102.7(9)
104.1(9)
113.8(6)
114.9(7)
115.5(6)
105.3(10)
106.9(10)
99.7(11)
113.1(7)
C(29)-P(2)-Os(4)
C(3)0-P(2)-Os(4)
C(25)-S(1)-C(26)
C(27)-S(2)-C(28)
C(8)-Os(3)-C(10)
C(44)-Os(4)-C(42)
C(46)-Os(5)-C(45)
C(49)-Os(6)-C(50)
C(52)-Os(6)-Os(4)
C(4)-Os(2)-C(5)
174.9(8)
174.0(9)
177.4(9)
178.2(8)
162.9(7)
175.7(7)
arrangement of the phenyl groups appears to stabilize the
structure and lock it into the conformation detected in the
crystal structure. The two pairs of phenyl groups are oriented
roughly edge-to-face to each other. The aliphatic part of the
ligand is oriented in a symmetric way. The sulfur atoms are
not within bonding distance to any osmium atom. As is
frequently observed in [Os3(CO)11(PR3)] clusters,20,22 the cis
bonds relative to the phosphorus-donor ligands are longer
than remaining metal-metal bonds due to the steric bulk of
˚
the phosphine ligands, i.e. Os(1)-Os(3) 2.8982(9) A, Os(4)-
(27) (a) Watson, W. H.; Wu, G.; Richmond, M. G. Organometallics
2006, 25, 930–945. (b) Watson, W. H.; Wu, G.; Richmond, M. G. Organo-
metallics 2005, 24, 5431–5439. (c) Watson, W. H.; Poola, B.; Richmond, M.
G. J. Organomet. Chem. 2006, 691, 4676–4685.
(28) (a) Churchill, M. R.; Lashewycz, R. A.; Richter, S. I.; Shapley,
J. R. Inorg. Chem. 1980, 19, 1277. (b) Puga, J.; Arce, A. J.; Braga, D.;
Centritto, N.; Grepioni, F.; Castillo, R.; Ascanio, J. Inorg. Chem. 1987, 26,
867. (c) Homanen, P.; Persson, R.; Haukka, M.; Pakkanen, T. A.; Nordlander,
E. Organometallics 2000, 19, 5568–5574.

2226 Organometallics, Vol. 29, No. 10, 2010
Persson et al.
Figure 2. Low-temperature-limiting 13C NMR spectrum
(125 MHz, 213 K, CDCl3) for [Os3(CO)11(PSSP)], 2, shows eight
signals representing 11 carbonyl ligands in a 2:2:2:1:1:1:1:1 pattern:
δ193.1(2), 185.4(2), 183.9(2), 176.8(1), 176.7(1), 172.8(1), 172.4(1),
170.2(1) (figures in parentheses refer to the relative intensities).
Figure 3. Variable-temperature 31P{1H} NMR of 1,2-[Os3(CO)10-
(PSSP)], 3.
Characterization of [Os3(CO)10(μ-PSSP)] (3). The mass
spectrum of 3 shows an isotopic envelope at 1369 amu
consistent with the value of 1370 amu for a cluster of
principal formula [Os3(CO)10(μ-PSSP)]. The IR spectrum
of 3 in CH2Cl2 is slightly different from those of [Os3(CO)10-
(μ-PSP)]9 and [Os3(CO)10(μ-P-P)] (P-P = dppe or dppp),13
suggesting that the solution structure of 3 differs from those
of the above-mentioned clusters, where the two phosphine
moieties are coordinated in equatorial cis positions (1,2-cis,
cis) relative to each other.
The 31P{1H} NMR spectrum of 3 recorded at room
temperature shows a broad resonance at δ -8 (and a minor
resonance at δ -10) indicating ligand fluxionality on the
NMR time scale (Figure 3). This fluxional process can be
frozen out at low temperature (213 K), and the static
spectrum shows three resonances at δ -5.5, -9.4, and
-10.1. The three 31P chemical shifts demonstrate that the
two phosphorus atoms are nonequivalent (vide infra). It is
reasonable to assume that both coordinate to the osmium
triangle22 in equatorial positions. There are then four possi-
ble isomers that may, in principle, be observed for an
[Os3(CO)10(L)2] system (see Figure 4). Disubstituted clusters
of formula [Os3(CO)10(PR3)2] (PR3 = phosphine or phos-
phite) are known to exist as interconverting trans,trans and
cis,trans isomers, but for bidentate phosphines, only the
bridged cis,cis and chelating cis,cis coordination modes have
been observed.13,17-19,23 Recently, the crystal structure of
cis,trans [Os3(CO)10(PPh3)2], known for some time from
NMR data, was published.24 In [Os3(CO)10(PSSP)] the
Figure 4. Four possible isomers that may, in principle, be
observed for an [Os3(CO)10(L)2] system.
bridging PSSP ligand forms an unusual 12-membered ring
incorporating also the two phosphorus-coordinated osmium
atoms. Such a large ring may in principle permit the ligand to
coordinate in the 1,2-cis,trans mode and/or even in the 1,2-
trans,trans mode. In order to identify the coordination mode
of the PSSP ligand in 3 in the solid state, a single-crystal X-
ray study was undertaken.
Crystal and Molecular Structure of [Os3(CO)10(μ-PSSP)]
(3). The molecular structure of 3 is shown in Figure 5, and
selected bond lengths and angles are listed in Table 2. Two
independent chiral molecules are present in the asymmetric
unit. They are related by quasi-reflection through a plane
orthogonal to the Os3P2 plane and therefore can be a pair of
enantiomers. The chirality originates from the tilting in

Article
Organometallics, Vol. 29, No. 10, 2010 2227
because of their pronounced conformational flexibility and
therefore can be described as deformation isomers of en-
antiomers. The discussion below is focused on one of the two
molecules [Os(4) to Os(6) (molecule 2)] since the main
structural features are similar. Cluster 3 consists of a trian-
gular triosmium cluster with 10 terminal carbonyl ligands
and one PSSP ligand. The two phosphine moieties occupy
equatorial sites on different osmium atoms with the phos-
phorus atoms coordinated in a cis,trans mode to the bridged
metal atoms [Os(1)-Os(2) and Os(4)-Os(5) for molecules 1
and 2, respectively]. The interconnecting aliphatic chain,
including the two thioether moieties, is oriented in a zigzag
form away from the metal plane. The sulfur atoms are not at
bonding distance to any osmium atom. The two Os-Os
bonds cis to Os(5)-P(4) and Os(4)-P(3) [Os(4)-Os(5)
˚
˚
2.9051(6) A, Os(4)-Os(6) 2.9087(6) A] are slightly longer
than the Os-Os bond trans to the Os(5)-P(4) bond
˚
[Os(5)-Os(6) 2.8889(6) A], which is similar to the average
Os-Os distance in [Os3(CO)12] [Os-Osav 2.877 A]. An
28
˚
Figure 5. ORTEP drawing of one of the two conformers of 1,2-
[Os3(CO)10(PSSP)], 3. Hydrogen atoms have been omitted for
clarity.
analogous trend has been observed for the cis,trans isomer of
[Os3(CO)10(PPh3)2].24 In the latter molecule, the two bonds
in cis position to the phosphines are internally different,
while in 3 there is no significant difference between these
bonds. It should be noted that also the bridged Os-Os bonds
in the compounds [Os3(CO)10(μ-Ph2P(CH2)nPPh2)] (n = 2, 4,
5)24,25 and [Os3(CO)10(μ-PSP)] (PSP = {Ph2PCH2CH2}2S)9
are longer than the other two Os-Os bonds.
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for
[Os3(CO)10(μ-PSSP)], 3
molecule 1
Os(1)-Os(2)
molecule 2
2.9046(6)
2.8770(6)
2.9019(6)
1.864(12)
1.886(14)
1.947(13)
2.358(3)
1.89(1)
1.91(1)
1.86(1)
2.338(3)
1.88(1)
1.88(1)
Os(4)-Os(5)
2.9051(6)
2.9087(6)
2.8889(6)
1.87(1)
1.95(1)
1.92(1)
2.336(3)
1.87(1)
1.99(1)
Os(1)-Os(3)
Os(2)-Os(3)
Os(1)-C(1)
Os(1)-C(2)
Os(1)-C(3)
Os(1)-P(1)
Os(2)-C(4)
Os(2)-C(5)
Os(2)-C(6)
Os(2)-P(2)
Os(3)-C(7)
Os(3)-C(8)
Os(3)-C(9)
Os(3)-C(10)
P(1)-C(11)
P(1)-C(17)
P(1)-C(23)
P(2)-C(28)
P(2)-C(35)
P(2)-C(29)
S(1)-C(24)
S(1)-C(25)
S(2)-C(26)
S(2)-C(27)
Os(4)-Os(6)
Os(5)-Os(6)
Os(4)-C(41)
Os(4)-C(42)
Os(4)-C(43)
Os(4)-P(3)
Os(5)-C(44)
Os(5)-C(45)
Os(5)-C(46)
Os(5)-P(4)
Os(6)-C(47)
Os(6)-C(48)
Os(6)-C(49)
Os(6)-C(50)
P(4)-C(69)
P(4)-C(75)
P(4)-C(68)
P(3)-C(57)
P(3)-C(51)
P(3)-C(63)
S(4)-C(66)
S(4)-C(67)
S(3)-C(65)
S(3)-C(64)
The osmium-phosphorus distances in 3 [Os(1)-P(1)
˚
˚
2.358(3) A, Os(2)-P(2) 2.338(3) A] fall in the range 2.28-
˚
2.40 A, which is typical for Os3(CO)12-x(L)x (x = 1-3, L =
phosphine) species.20 The Os-P bond cis to the bridged
metal-metal bond is slightly longer than the other phos-
phorus-osmium bond. This difference in bond length may
be explained as the combined effect of steric repulsions
between the interconnecting {(CH2)2S(CH2)2S(CH2)2} moi-
ety and the asymmetric coordination of the phosphine
groups. The Os-P distances in the cis,trans isomer of
[Os3(CO)10(PPh3)2]24 are also slightly different. Both phos-
phorus atoms are slightly displaced out of the Os3 planes
1.91(1)
2.361(3)
1.96(1)
1.90(2)
1.93(2)
1.92(2)
1.830(6)
1.834(6)
1.86(1)
1.788(6)
1.839(6)
1.88(1)
1.81(1)
1.80(1)
1.75(1)
1.82(1)
4.417(5)
112.4(3)
118.1(3)
119.8(4)
102.4(6)
96.4(3)
95.8 (3)
107.95(7)
90.0(4)
1.91(1)
1.87(1)
1.821(6)
1.841(6)
1.83(1)
˚
˚
˚
[P(1) ca. þ0.272 A, P(2) ca. þ0.592 A, P(3) ca. þ0.693 A, and
˚
1.81(1)
P(4) ca. þ0.144 A].
1.814(6)
1.831(6)
1.78(1)
1.80(1)
1.80(1)
1.81(1)
4.433(5)
117.7(3)
119.8(4)
113.2(3)
104.6(6)
94.4(3)
98.7(3)
107.85(7)
97.9(3)
101.5(5)
97.6(3)
112.93(7)
102.7(3)
100.4(5)
93.2(3)
112.8(3)
119.7(3)
112.8(3)
In Figure 7, the relative orientation of the equatorial
ligands of 3 is compared to that in [Os3(CO)10(PPh3)2]. In
3, the equatorial substituents at Os(4) are twisted toward
Os(5) when compared to the corresponding orientation in
[Os3(CO)10(PPh3)2]. This twist may be caused by steric
restrictions of the interconnecting chain in the PSSP ligand.
Thus, in 3 the phosphorus atom trans to the bridged metal-
metal bond assumes an almost linear position relative to the
bridged osmium atoms [P(3)-Os(4)-Os(5) = 162.15(7)ꢀ].
The distortion is also accompanied by a narrowing of the
C(41)-Os(4)-Os(5) angle [C(41)-Os(4)-Os(5) 91.6(4)ꢀ
compared to 99.65(16)ꢀ for cis,trans-[Os3(CO)10(PPh3)2]].
The average cis torsion angle derived from the six A(ax)-
Os-Os-A(ax) (A = axially coordinated C and S atoms)
dihedral intersections is less than the corresponding average
cis torsion angle for [Os3(CO)10(μ-PSP)] but near the value
for [Os3(CO)10(PPh3)2] [26.5ꢀ vs 32.3ꢀ and 24.4ꢀ]. The differ-
ence in the twisting of the cluster ligand spheres in 3
and [Os3(CO)10(μ-PSP)] may be explained by the fact that
in 3 the phosphines are coordinated in a cis,trans mode, while
in cluster [Os3(CO)10(μ-PSP)] the two phosphine groups
coordinate in a cis mode. The coordination that results in
the least steric interactions between the ligands is when the
S(1) S(2)
S(3) S(4)
3 3 3
3 3 3
C(11)-P(1)-Os(1)
C(23)-P(1)-Os(1)
C(17)-P(1)-Os(1)
C(24)-S(1)-C(25)
C(1)-Os(1)-Os(3)
C(1)-Os(1)-P(1)
P(1)-Os(1)-Os(2)
C(9)-Os(3)-Os(1)
C(26)-S(2)-C(27)
C(6)-Os(2)-P(2)
P(2)-Os(2)-Os(3)
C(7)-Os(3)-Os(2)
C(7)-Os(3)-C(9)
C(6)-Os(2)-Os(1)
C(35)-P(2)-Os(2)
C(29)-P(2)-Os(2)
C(28)-P(2)-Os(2)
C(69)-P(4)-Os(5)
C(75)-P(4)-Os(5)
C(68)-P(4)-Os(5)
C(67)-S(4)-C(66)
C(44)-Os(5)-Os(6)
C(44)-Os(5)-P(4)
P(4)-Os(5)-Os(4)
C(50)-Os(6)-Os(5)
C(65)-S(3)-C(64)
C(41)-Os(4)-P(3)
P(3)-Os(4)-Os(6)
C(48)-Os(6)-Os(4)
C(48)-Os(6)-C(50)
C(41)-Os(4)-Os(5)
C(57)-P(3)-Os(4)
C(51)-P(3)-Os(4)
C(63)-P(3)-Os(4)
100.7(6)
98.7 (4)
114.57 (7)
111.3(5)
99.6(6)
91.6(4)
116.9(3)
119.8(3)
112.2(3)
opposite directions of the axial CO ligands and out of plane
positioning of the CCSCCSCC ring atoms (Figure 6). The
two molecules are not related by crystallographic symmetry

2228 Organometallics, Vol. 29, No. 10, 2010
Persson et al.
Figure 6. Side view of the two independent molecules in the crystal structure of 1,2-[Os3(CO)10(PSSP)], 3, showing the conformation of
the 12-membered metallacycle and the tilting of the carbonyl ligands relative to the triangular metal plane.
Figure 7. Comparison of the framework structures of [{Os3-
(CO)10}2(μ-PSSP)], 4, and cis,trans-[Os3(CO)10(PPh3)2]. Dotted
lines show the principal position of the stereorelated PPh3 ligand
and the geminal equatorial carbonyl group in cis,trans-[Os3-
(CO)10(PPh3)2]. Values within square brackets are correspond-
ing angles in cis,trans-[Os3(CO)10(PPh3)2].
phosphines are coordinated in trans position (see Figure 4).
The cis,trans coordination found in 3 is also more sterically
favored than the cis,cis mode. The carbon-osmium dis-
˚
tances for the axial carbonyl ligands (Os-C(av) = 1.94 A
˚
[1.90 A for molecule 2]) are slightly longer than the carbon-
osmium distances for carbonyl ligands in equatorial posi-
˚
˚
tions (Os-C(av) = 1.89 A [1.88 A for molecule 2]) as
commonly found in triosmium clusters.
Ligand Fluxionality in [Os3(CO)10(μ-PSSP)] (3). As men-
tioned above, the fluxional process in 3 that was detected by
31P NMR could be frozen out at low temperature (Figure 3),
and the static spectrum shows three resonances at δ -5.5,
-9.4, and -10.1. By taking into account their relative
intensity, it is straightforward to conclude that the peaks at
δ -5.5 and -9.4 are associated with the main isomer,
whereas the resonance at δ -10.1 is associated with a minor
isomer. The resonances of the main isomer start to broaden
at 233 K and coalesce at about 285 K with an activation
energy of 51.6 kJ/mol. In order to gain a better understand-
ing of this fluxional process, we undertook a 13C{1H} vari-
able-temperature study of 3. The low-temperature limiting
natural abundance 13C{1H} spectrum of 3 (400 MHz, 213 K,
Figure 8. Low-temperature limiting natural abundance 13C{1H}
spectrum of 1,2-[Os3(CO)10(PSSP)], 3 (400 MHz, 213 K, CDCl3).
carbonyls, and the four signals at highest frequency are
unambiguously assigned as the axial carbonyl ligands of
the two phosphine-coordinated osmium atoms, on the basis
of the large observed 2JP-C couplings. The X-ray structure of
3 (vide supra) shows that the aliphatic chain is oriented away
from the metal plane in the solid state, and this is the reason
for a significant chemical shift difference of the pairs of axial
carbonyls bound to the same osmium atoms. The unusual
high frequency of the carbonyl resonance at δ 200.5 suggests
that there may be some interaction between the ligand and
this CO. We tentatively propose the presence of a steric
CDCl3) shows 10 distinct CO resonances at δ200.5 h/i (2JP-C
≈
8 Hz), 195.4 i/h (2JP-C ≈ 8 Hz), 192.5 a/b (2JP-C ≈ 9 Hz),
192.0 b/a (2JP-C ≈ 6 Hz), 185.8 d/e, 185.4 e/d, 183.5 j/f,
178.7 c/g, 174.0 g/c, and 172.1 f/j (see Figure 8). The four low-
frequency resonances may be assigned to the equatorial

Article
Organometallics, Vol. 29, No. 10, 2010 2229
Scheme 3. Proposed Fluxional Process for 3
sulfur-CO interaction that affects the energy barrier for the
fluxional process.
perature 31P{1H} NMR shows a sharp resonance at δ -0.06,
indicating a single phosphorus environment and that no
fluxional process involving phosphorus is present at this
temperature. The 31P{1H} NMR chemical shift δ -0.057 is
very similar to that of the compound 1,2-[Os3(CO)10(μ-Ph2-
PCH2CH2SMe)]8 (δ = -0.597), indicating a similar mag-
netic environment for the P atoms in 4 to that in 1,2-[Os3-
(CO)10(μ-Ph2PCH2CH2SMe)]. Furthermore, the presence of
only one resonance in the spectrum indicates that the ligand
On increasing the temperature to 253 K, eight of the 10
signals broaden. However, two equatorial carbonyls (δ 178.7
and 174.0) remain sharp. A value of 50.6 ( 2.0 kJ/mol for the
carbonyl exchange activation energy has been estimated
from line-shape analysis, in reasonable agreement with the
activation energy found for phosphorus exchange (see below).
The observed mutual exchange of the phosphorus and the
behavior of the VT 13C spectra in the temperature range
213-253 K can be explained as follows (see Scheme 3): a
rapid switch forward and backward of the two phosphorus
atoms leads to a restricted and concerted motion of the
carbonyl ligands in the equatorial plane of the metal triangle,
probably through a higher energy intermediate state having
bridging CO ligands. This motion is responsible for the
mutual exchange of the phosphorus atoms and for the
pairwise exchange of equatorial carbonyls f and j. It is worth
noting that carbonyls c and g appear static on the NMR time
scale, since they are moving between chemically equivalent
positions. Moreover, the PSSP chain is expected to possess
considerable flexibility, and large-amplitude conformational
changes in the 12-membered ring/“dimetallacycle” “may
remove the asymmetry of the metal plane, causing also pair-
wise exchange of the axial carbonyls a/b, h/i, d/e. These two
concomitant motions fully explain the line broadening of all
carbonyl resonances, except c and g, observed at 253 K. A
classical terminal/bridge exchange process in the vertical
plane is unlikely to occur since that would induce consider-
able steric interactions of the R groups (in this case phenyl
rings) of the phosphines with the two axial carbonyls on the
same side of the osmium plane.
1
is symmetrically coordinated. In the H NMR spectrum,
three multiplets are present at δ 2.3, 2.5, and 2.8 and a broad
envelope in the region between δ 7.3 and 7.4. These signals
were assigned to the aliphatic (δ 2.3-2.8) and aromatic (δ
7.3-7.4) protons of PSSP, with relative ratios of 20:12,
indicating that the ligand is intact in the cluster. The com-
pound is stable at room temperature and on heating in
refluxing dichloromethane for one hour. Considering the
similarity of the spectroscopic data of 4 and 1,2-[Os3(CO)10-
(μ-Ph2PCH2CH2SMe)],8 compound 4 is expected to consist
of two P,S-bridged cluster units as shown in Figure 9.
We have previously observed that P,S-ligands initially
coordinate in a bridging coordination mode along one edge
of an Os3 cluster unit but rearrange under mild conditions to
a chelating coordination mode, with the ligands remaining
intact throughout the rearrangement process.8 A similar
rearrangement from a 1,2-bridging to a 1,1-chelating coor-
dination mode has been observed for the triosmium carbonyl
derivatives of the unsaturated symmetrical diphosphine
ligands 4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione
(bpcd), (Z)-Ph2PCHdCHPPh2, and 2,3-bis(diphenylphos-
phino)-N-p-tolylmaleimide (bmi).27 Both phosphine donor
atoms occupy equatorial coordination sites in the thermo-
dynamic products of these reactions. Furthermore, similar
rearrangements have been detected for [H4Ru4(CO)10(P-P)]
(P-P = diphosphine) clusters.28 Upon storage in dichloro-
methane solution for several days, a singlet at δ 40.2 ppm
could be observed in the 31P NMR spectrum of 4, but the
conversion never went to completion in our experiments. The
singlet is close in chemical shift to that at δ 41.5 found for the
cluster 1,1-[Os3(CO)10(μ-Ph2PCH2CH2SMe)], and we suggest
that the new resonance is better explained as an effect of the
presence of one or both of the isomers depicted in Figure 10.
Spectroscopic data for the cluster 1,1-[{Os3(13CO)11}(μ-PSP)-
{Os3(CO)10}]9 indicate that the P,S-chelated {Os3(CO)10} unit
is sterically restricted in its movement relative to the phos-
phorus-coordinated {Os3(13CO)11} unit. Considering that
At 303 K, the resonances c and g are also broad, revealing
further dynamic processes. It is interesting to observe that at
303 K the broad peak in the higher frequency region repre-
sents the average value of the six axial carbonyls. This rather
unexpected result can be rationalized only with a migration
of the PSSP ligand in the equatorial plane that involves all
three osmium atoms. The small peak at δ -10.1 in the 31P
spectra (and the occurrence of several small resonances in the
13C spectra) are related to the presence of the trans,trans or
the cis,cis isomer.
Properties of [{Os3(CO)10}2(μ-PSSP)] (4). The IR spec-
trum of [{Os3(CO)10}2(μ-PSSP)], 4, is similar to that ob-
served for P,S-bridged triosmium clusters,8,9 indicating
similar symmetry of the carbonyl ligands. The room-tem-

2230 Organometallics, Vol. 29, No. 10, 2010
Persson et al.
Figure 9. Proposed structure for [{Os3(CO)10}2(PSSP)], 4.
Figure 11. ORTEP drawing of the molecular structure of
[{Os3(CO)10}2(PSSP)], 4. Hydrogen atoms have been omitted
for clarity.
Figure 10. Proposed isomers of [{Os3(CO)10}2(PSSP)], 4, in
which one or both of the phosphine thioether pairs are chelating
one of the osmium atoms in each of the triosmium triangles.
˚
Table 3. Selected Bond Lengths (A) and Angles (deg) for
[{Os3(CO)10}2(PSSP)], 4
cluster 4 consists of two bridged {Os3(CO)10} units, it is thus
likely that the {Os3(CO)10} units of this compound are also
restricted in their movements. In contrast to the cluster
1,2-[Os3(CO)10(μ-Ph2PCH2CH2SMe)], 4 is relatively stable.
This may be explained by steric hindrance increasing the
barrier for the 1,2-bridging to 1,1-chelating rearrangement
in 4. In spite of repeated attempts, we were unable to get pure
samples of the chelated cluster isomer(s), and therefore no
complete characterization of this compound(s) could be
achieved.
Crystal and Molecular Structure of [{Os3(CO)10}2(μ-
PSSP)] (4). The molecular structure of 4 is shown in Fig-
ure 11, and relevant bond lengths and angles are reported in
Table 3. In cluster 4 the PSSP ligand coordinates to two
different triosmium units. In each of the triosmium units, one
phosphorus and one sulfur atom of the PSSP ligand are
coordinated to different metals in a 1,2-bridging mode with
the phosphine and the thioether groups residing cis to each
other, thus generating two equivalent six-membered rings.
All donor atoms are coordinated in equatorial sites, but lie
slightly out of the two triangular metal planes [distance from
Os(1)-Os(2)
2.8803(6)
2.8317(6)
2.8699(5)
2.339(3)
1.86(1)
1.96(1)
1.96(1)
1.94(1)
1.95(1)
1.88(1)
2.371(2)
1.95(1)
1.90(1)
1.96(1)
1.96(1)
1.817(9)
1.82(1)
1.83(1)
P(2)-C(28)
1.803(1)
1.82(1)
1.84(1)
1.82(1)
1.83(1)
2.8804(6)
2.8422(6)
2.8581(5)
2.338(3)
1.87(1)
1.95(1)
1.95(1)
1.95(1)
1.94(1)
1.88(1)
2.390(2)
1.99(1)
2.02(1)
1.89(2)
1.92(1)
Os(2)-Os(3)
P(2)-C(29)
Os(3)-Os(1)
P(2)-C(35)
Os(1)-P(1)
S(2)-C(26)
Os(1)-C(1)
S(2)-C(27)
Os(1)-C(2)
Os(5)-Os(4)
Os(1)-C(3)
Os(6)-Os(4)
Os(2)-C(4)
Os(5)-Os(6)
Os(2)-C(5)
Os(5)-P(2)
Os(2)-C(6)
Os(4)-C(43)
Os(2)-S(1)
Os(4)-C(42)
Os(3)-C(7)
Os(4)-C(41)
Os(3)-C(8)
Os(5)-C(51)
Os(3)-C(9)
Os(5)-C(52)
Os(3)-C(10)
Os(5)-C(53)
S(1)-C(25)
Os(4)-S(2)
S(1)-C(24)
Os(6)-C(61)
P(1)-C(23)
Os(6)-C(63)
P(1)-C(17)
1.83(1)
Os(6)-C(64)
P(1)-C(11)
1.834(9)
115.6(3)
113.6(3)
118.0(4)
117.9(3)
110.7(3)
103.5(5)
59.923(14)
99.2(4)
Os(6)-C(62)
C(28)-P(2)-Os(5)
C(29)-P(2)-Os(5)
C(35)-P(2)-Os(5)
C(23)-P(1)-Os(1)
C(25)-S(1)-Os(2)
C(28)-P(2)-C(35)
Os(6)-Os(4)-Os(5)
C(25)-S(1)-C(24)
S(1)-Os(2)-Os(1)
S(1)-Os(2)-Os(3)
C(24)-S(1)-Os(2)
C(26)-S(2)-C(27)
C(26)-S(2)-Os(4)
C(27)-S(2)-Os(4)
C(28)-P(2)-C(29)
C(17)-P(1)-Os(1)
C(11)-P(1)-Os(1)
C(43)-Os(4)-Os(6)
S(2)-Os(4)-Os(6)
S(2)-Os(4)-Os(5)
112.5(3)
98.8(5)
110.4(3)
113.3(3)
102.6(5)
111.9(4)
118.6(3)
96.9(4)
˚
˚
the Os(1)-Os(3) plane: S(1) -0.12 A, P(1) þ0.65 A; dis-
˚
tances from the Os(4)-Os(6) triangle: S(2) -0.65 A, P(2)
˚
þ0.49 A].
˚
103.11(6)
163.11(6)
156.76(6)
102.32(6)
The Os-P distances [Os(1)-P(1) 2.339(3) A, Os(5)-P(2)
2.3388(3) A] are slightly longer than the Os-P distance in
˚
˚
1,2-[Os3(CO)10(μ-Ph2PCH2CH2SMe)] [Os-P 2.322(3) A]
but still within the range that is typical for compounds of
Os(5)Os(6)] are similar to each other and to Os-Os sepa-
rations found in the parent binary carbonyl [Os3(CO)12]29
formula [Os3(CO)12-x(L)x] (x = 1, 2, 3; L = phosphine).20
˚
(2.877(3) A) and in the other clusters reported here. The
˚
˚
The Os-S [Os(2)-S(1) 2.371(2) A, Os(4)-S(2) 2.390(2) A]
separations are slightly different. The shorter Os(2)-S(1)
interaction is similar to the Os-S separation in the cluster
˚
longest Os-Os separations [2.8803(6) A for Os(1)-Os(2)
˚
and 2.8804(6) A for Os(4)-Os(5)] are the P,S-bridged metal
8
˚
bonds, in agreement with the trend observed for the related
clusters1,2-[Os3(CO)10(μ-Ph2PCH2CH2SMe)]8 and [Os3(CO)10-
(μ-PSP)]9 and the clusters [Os3(CO)10(μ-Ph2P(CH2)xPPh2)]
(x = 2, 4, 5),19,25 where the bridged Os-Os bonds are gene-
rally slightly longer than the nonbridged ones. The increase in
bond length has been credited to conformational needs of the
interconnecting chain of the ligand spanning an osmium-
osmium bond.17-19,23-25 There may also be an electronic
1,2-[Os3(CO)10(μ-Ph2PCH2CH2SMe)] [Os-S = 2.376(3) A)].
The difference in Os-S bond lengths between Os(4)-S(2) and
Os(2)-S(1) may be the result of the fact that the sulfur atom
S(2) is much more displaced out of the metal plane. Spectro-
scopic data for compound 4 indicate that the cluster is
symmetric (vide supra), and therefore it is likely that the
difference in bond lengths is a solid-state phenomenon that
may be related to crystal packing effects.
The average Os-Os distances in the M3 triangles [Os-
Os(av) = 2.861 A for Os(1)Os(2)Os(3) and 2.860 A for Os(4)-
˚
˚
(29) Churchill, M. R.; DeBoer, B. G. Inorg. Chem. 1977, 878.

Article
Organometallics, Vol. 29, No. 10, 2010 2231
source of this effect, as the two out-of-phase combinations of
lone pairs on the sulfur and the phosphorus require an
antibonding combination of Os orbitals, resulting in a desta-
bilization of the bridged Os-Os bond. The Os-Os bonds
trans to the sulfur in each of the M3 units of 4 are the shortest
PCH2CH2SMe)],8 but prolonged standing in solution leads to
the formation of a new cluster, which is suggested to be a stable
isomer of 4 in which the PSSP ligand is chelating an osmium
atom in each of the triosmium triangles.
˚
ones [Os(2)-Os(3) 2.8317(6) A and Os(4)-Os(6) 2.8422(6)
Experimental Section
˚
A], while the metal-metal bonds trans to the phosphorus
General Procedures. The clusters [Os3(CO)12],32 [Os3(CO)11-
(NCMe)],33 and [Os3(CO)10(NCMe)2]34 were synthesized by
published methods. The ligand PSSP was synthesized, as re-
ported previously.35 All reactions were carried out under an
atmosphere of dry nitrogen using standard Schlenk and vacuum-
line techniques. Solvents were dried by standard methods
prior to use. Infrared spectra were recorded as solutions in
0.5 mm NaCl cells on Nicolet 20SXC and Avatar 360 FT-IR
spectrometers with carbon dioxide as calibrant. Fast atom
bombardment (FAB) mass spectra were obtained on a JEOL
SX-102 spectrometer using 3-nitrobenzyl alcohol as matrix and
CsI as calibrant. 1H NMR spectra (299.87 MHz) were acquired
atoms are slightly longer. A contraction of the metal-metal
bondtrans tothe sulfur has beenobserved inrelated clusters.30
The structure of cluster 4 is closer to D3 symmetry than
that of the related compound 1,2-[Os3(CO)10(μ-Ph2PCH2-
CH2SMe)].8 The average cis torsion angle derived from the
six A(ax)-Os-Os-A(ax) (A = axially coordinated C atoms)
dihedral intersections is considerably larger than for 1,2-[Os3-
(CO)10(μ-Ph2PCH2CH2SMe)] but slightly narrower than for
the bridged isomer [Os3(CO)10(μ-PSP)]9 [26.7ꢀ for Os(1)-Os-
(3), 27.5ꢀ for Os(4)-Os(6) vs 11.7ꢀ for 1,2-[Os3(CO)10(μ-
Ph2PCH2CH2SMe)] and 32.3ꢀ for [Os3(CO)10(μ-PSP)]]. Both
4 and 1,2-[Os3(CO)10(μ-Ph2PCH2CH2SMe)] have verysimilar
coordination motifs. The reason for the twist of the cluster
ligand spheres in both M3 units of 4 may be ascribed to the
combined effect of conformational requirements due to mu-
tual interactions between the sterically demanding {Os3-
(CO)10PPh2(CH2)2SCH2} moieties of 4 and packing effects
in the solid state. Conformational isomerism in the solid state
has been observed for the compound [Os3(CO)11(PR3)] (R =
p-C6H4F), which exists in a red and yellow form in the solid
state.31 The yellow isomer has a typical D3h-like structure as
for Os3(CO)11(L) (L = phosphine or phosphite) species, whereas
in the red form the neighboring carbonyls on adjacent Os
atoms are in a staggered configuration, resulting in a D3-like
structure. The close similarities between 4 and the cluster
1,2-[Os3(CO)10(μ-Ph2PCH2CH2SMe)] indicate that only a
subtle change of structure may change the ligand polyhedron
from D3h to D3 and vice versa. The interchange between D3h
and D3 may also be controlled by thermodynamics of the
crystallization process.
1
on a Varian Unity 300 WB spectrometer; H (500.13 MHz),
31P{1H} (200.25 MHz), and 13C{1H} NMR (125 MHz) spectra
were acquired on a Bruker DRX 500 spectrometer. Routine
separations of products were performed by thin-layer chroma-
tography using commercially prepared glass plates, precoated
with 0.25 mm Merck silica gel 60. Column chromatography was
carried out using silica gel (Merck silica gel 60, 0.040-0.063 mm,
230-400 mesh, ASTM) columns, initially packed in CH2Cl2.
Synthesis of [{Os3(CO)11}2(μ-PSSP)] (1). In a typical reac-
tion, 194 mg (0.107 mmol) of [Os3(CO)11(NCMe)] and 56 mg
(0.057 mmol) of PSSP were dissolved in 20 mL of CH2Cl2 and
stirred at room temperature until no νC-O resonances due to the
starting material could be detected (2h). The solvent was then
removed under reduced pressure, and residual solid was sepa-
rated by TLC using thf/hexane (3:7 v/v) as eluent, yielding two
bands, in order of decreasing Rf: [{Os3(CO)11}2(μ-PSSP)] (1),
yellow, 108 mg (0.0623 mmol, 43%), and traces of 2. Cluster 1:
IR ν(CO), cm-1 (cyclohexane): 2108m, 2069m, 2056s, 2036s,
1
2021vs, 2004m, 1992m, 1980m. H NMR (CDCl3, 303 K): δ
2.27m, 2.49m, 2.82m. 13P{1H} NMR (CDCl3, 303 K) (H3PO4:
δ = 0; positive shift at higher frequency): δ -10.92. Anal. Calcd
(found) for 1: H 1.42 (1.54), C 27.44 (29.09), P 2.72 (2.67). FABþ
MS (m/z): 2276 (Mþ).
Conclusions. We have found that the mixed ligand PSSP
easily coordinates to activated triosmium clusters. We have
prepared and structurally characterized four new clusters; in
three of these (clusters 1-3), the PSSP ligand coordinates
only via its phosphine donor atoms. The molecular structure
of 3 shows that the two phosphine moieties occupy equator-
ial sites on different osmium atoms with the phosphorus
atoms coordinated in a cis,trans mode to the bridged metal
atoms. To our knowledge, this is the first example of bridging
coordination of a bi- or polydentate ligand to a [M3(CO)12]
cluster (M = Ru, Os) where the ligand is bridging in a cis,
trans mode. The cluster [Os3(CO)10(μ-PSSP)], 3, is fluxional
on the NMR time scale; this fluxionality involves movement
of the phosphine moieties in the equatorial plane, coupled
with carbonyl exchange in the equatorial plane and a “flip”
of the ligand backbone.
Synthesis of [Os3(CO)11(PSSP)] (2). In a typical reaction,
100 mg (0.100 mmol) of [Os3(CO)11(NCMe)] was dissolved in
20 mL of dichloromethane. A 113 mg (0.218 mmol) amount of
PSSP was added to the solution. The solution was stirred at
room temperature for 1.5 h under nitrogen. The solvent was
removed under vacuum, and the crude product was separated by
thin-layer chromatography using a 7:3 hexane/CH2Cl2 mixture
as eluent. Two bands were recovered, in order of decreasing Rf:
[{Os3(CO)11}2(μ-PSSP)] (1) (minor trace); [Os3(CO)11(PSSP)]
(2), yellow, 20 mg (0.009 mmol, 9%). Cluster 2: IR (cyclo-
hexane), ν(CO)/cm-1: 2108m, 2055s, 2018vs, 1988m. 1H NMR
(CDCl3, 303 K): 2.30 (m, 4H), 2.53 (m, 4H), 2.84 (m, 4H),
7.25-7.46 (m, 20H). 13C{1H} NMR (125 MHz MHz, 213 K,
CDCl3): 193.1 (d, 2JP-C = 7.9 Hz, 2C), 185.4 (s, 2C), 183.9 (s,
2C), 176.8 (s, 1C), 176.7 (s, 1C), 172.8 (s, 1C), 172.4 (s, 1C), 170.2
(s, 1C). 13P{1H} NMR (CDCl3, 303 K) (H3PO4: δ = 0): δ -17.3
(s, 1P), -10.2 (s, 1P). FABþ MS (m/z): 1426 (Mþ) Anal. Calcd
(found) for 2: H 2.31 (2.26), C 35.24 (35.40), P 4.43 (4.84).
Synthesis of [Os3(CO)10(μ-PSSP)] (3). A 100 mg (0.107 mmol)
amount of [Os3(CO)10(NCMe)2] and 139 mg (0.268 mmol) of
The solid-state structure of 4 reveals that the compound
consists of two P,S-coordinated {Os3(CO)10} subunits linked
by a PSSP ligand. Cluster 4 is relatively stable, in contrast to
what has been observed for the analogous compounds 1,2-[-
{Os3(CO)11}(μ-PSP){Os3(CO)10}]9 and 1,2-[Os3(CO)10(μ-Ph2-
(32) Johnson, B. F. G.; Lewis, J. Inorg. Synth. 1972, 13, 93.
(33) Johnson, B. F. G.; Lewis, J.; Pippard, D. A. J. Chem. Soc.,
Dalton Trans. 1978, C4, 407.
(34) Nicholls, J. N.; Vargas, M. D. Inorg. Synth. 1989, 26, 289.
(35) (a) Degischer, G.; Schwarzenbach, G. Helv. Chim. Acta 1966, 49,
1927. (b) Hsiao, Y.-M.; Chojnacki, S. S.; Hinton, P.; Reibenspies, J. H.;
Darensbourg, M. Y. Organometallics 1993, 12, 870.
€
(30) (a) Adams, R. D.; Horvath, I. T.; Segmuller, B. E.; Yang, L. Y.
Organometallics 1983, 2, 144. (b) Kiriakidou-Kazemifar, N. K.; Kretzschmar,
E.; Carlsson, H.; Monari, M.; Selva, S.; Nordlander, E. J. Organomet. Chem.
2001, 623, 191.
(31) Hansen, V. M.; Ma, A. K.; Biradha, K.; Pomeroy, R. K.;
Zaworotko, M. J. Organometallics 1998, 17, 5267.

2232 Organometallics, Vol. 29, No. 10, 2010
Persson et al.
Table 4. Crystal Data and Experimental Details for [{Os3(CO)11}2(μ-PSSP)] (1), [Os3(CO)10(μ-PSSP)] (3), and [{Os3(CO)10}2(μ-
PSSP)] 2CHCl3 (4 2CHCl3)
3
3
1
3
4.
formula
C
52H32O22Os6P2S2
C40H32O10Os3P2S2
C50H32O20Os6P2S2
2CHCl3
2458.75
293(2)
0.71073
3
M
temp, K
2276.04
100(2)
0.71073
triclinic
P1
13.5001(15)
16.0441(16)
16.7391(16)
112.960(3)
103.163(3)
105.503(3)
2983.1 (5)
2
1369.35
293(2)
0.71073
monoclinic
P21
11.8958(5)
18.4288(7)
19.8714(8)
90
100.883(1)
90
4278.0(3)
4
2.126
9.115
2568
˚
wavelength, A
cryst symmetry
space group
triclinic
P1
˚
a, A
13.9222(6)
15.5954(7)
17.5669(8)
109.624(1)
99.645(2)
104.675(2)
3339.2(3)
2
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
cell volume, A
Z
Dc, Mg m-3
μ(Mo KR), mm-1
F(000)
2.534
12.93
2076
2, 2.445
11.789
2252
cryst size, mm
θ limits, deg
reflns collected
unique obsd reflns
[Fo > 4σ(Fo)]
absolute struct param
goodness of fit on F2
R1(F)a,
0.30 ꢀ 0.10 ꢀ 0.08
1.8-25.0
16 593
0.30 ꢀ 0.25 ꢀ 0.20
1.04-30.03
58 470
0.28 ꢀ 0.25 ꢀ 0.23
2.56-29.99
45 638
10 441
24 914
19 363
-0.035(6)
0.820
0.0422, 0.0670
1.10
0.0960, 0.2543
0.901
0.0471, 0.1002
wR2(F2)b
largest diff peak
6.52 and -7.33
1.479 and -1.286
3.336 and -1.762
-3
˚
and hole, e A
P
P
P
P
a R1 =
Fo| - |Fc /
|Fo|. b wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2 where w = 1/[σ2(Fo2) þ (aP)2 þ bP] where P = (Fo þ Fc2)/3.
2
PSSP were dissolved in ca. 100 mL of CH2Cl2. The solution was
stirred under nitrogen for 1.5 h. The solvent was then removed
under reduced pressure, and the crude product was separated
by thin-layer chromatography using a 3:7 thf/n-hexane mixture
as eluent. Two bands were recovered, in order of decreasing Rf:
[Os3(CO)10(μ-PSSP)] (3), red 51.9 mg (0.02 mmol, 35%), and
a yellow, uncharacterized compound. Cluster 3: IR (CH2Cl2),
ν(CO)/cm-1: 2086m, 2021sh, 2000vs, 1973w, 1950w-m. 1H NMR
(CDCl3, 303 K): 2.18m, 2.6-3.2m, 3.74m, 7.45-7.71m. 13C{1H}
CHCl3 solution. Crystal data and experimental details of the
data collections and structure refinements for 1, 3, and 4 are
summarized in Table 4.
X-ray Data Collection and Structure Determination of 1.
Suitable crystals were mounted in inert oil droplets, which
solidified at the data collection temperature of 100(2) K on a
Nonius Kappa CCD diffractometer. The crystals were indexed
and the data collection strategy was determined by the Nonius
Collect program.36 Data were integrated, merged, and corrected
for Lorentz and polarization effects and for the effects of
absorption using the programs DENZO-SMN and Scalepack.37
The structurewas solvedbydirectmethods, andallnon-hydrogen
atoms of the clusters were refined anisotropically (SHELXL-
97),38 while hydrogen atoms were included in calculated posi-
tions and allowed to ride on the atoms to which they were
attached, with thermal parameters tied to those of the parent
atom. Details of the crystal data and of the data collection for 1
are reported in Table 4.
2
NMR (CDCl3, 213 K): 200.5 (d, JP-C ≈ 8 Hz, 1C), 195.4 (d,
2JP-C C ≈ 8 Hz, 1C), 192.5 (2JP-C ≈ 9 Hz, 1C), 192.0 (2JP-C ≈ 6
Hz, 1C), 185.8 (s, 1C), 185.4 (s, 1C), 183.5 (s, 1C), 178.7 (s, 1C),
174.0 (s, 1C), and 172.1 (s, 1C). 13P{1H} NMR (500 MHz, CDCl3,
213 K) (H3PO4: δ = 0): -5.5 (s), -9.4 (s), -10.1 (s). Anal. Calcd
(found) for 3: H 2.36 (2.59), C 35.09 (37.04). FABþ MS (m/z):
1369, calculated from the parent molecular ion 1370.
Synthesis of [{Os3(CO)10}2(μ-PSSP)] (4). In a typical reaction
a solution of 3.7 equiv of Me3NO (6.4 mg, 0.058 mmol) dissolved
in dry CH2Cl2 was added dropwise to a stirred dichloromethane
solution (50 mL) of [{Os3(CO)11}2(μ-PSSP)] (50 mg, 0.023
mmol) at room temperature. The reaction was monitored by
IR spectroscopy. The solvent was removed under reduced
pressure, and the residual solid was separated by preparative
TLC (0.5 mm, Merck 1045) eluting with a thf/hexane mixture
(3:7 by volume). The orange, major product 4 (60 mg, 0.03
mmol, 60%) was recovered and identified as [{Os3(CO)10}2(μ-
PSSP)]. A minor, orange-red product 5 was also recovered and
identified as [{Os3(CO)10}(μ-PSSP)]. Cluster 4: IR (CH2Cl2),
ν(CO)/cm-1: 2090vs, 2029w, 2007vs, 1975m, 1954m. 1H NMR
(CDCl3, 293 K): 2.23-2.28 (m, 4H), 2.47-2.53 (m, 4H), 2.7-2.9
(m, 4H), 7.29-7.44 (m, 20H). 31P{1H} NMR (CDCl3, 293 K):
-0.057 s. FABþ MS (m/z): 1097 (Mþ).
X-ray Data Collection and Structure Determination of 3 and 4.
Crystal data and other experimental details for 3 and 4 are
reported in Table 4. The X-ray intensity data for 3 and 4 were
measured on a Bruker AXS SMART 2000 diffractometer,
equipped with a CCD detector, using Mo KR radiation (λ =
˚
0.71073 A) at room temperature. Cell dimensions and the
orientation matrix were initially determined from least-squares
refinement on reflections measured in three sets of 20 exposures
collected in three different ω regions and eventually refined
against 5905 reflections. A full sphere of reciprocal space was
scanned by 0.3ꢀ ω steps with the detector kept at 5.0 cm from the
sample. Intensity decay was monitored by re-collecting the
initial 50 frames at the end of the data collection and analyzing
the duplicate reflections. The collected frames were processed
Crystallography. Yellow crystals of [{Os3(CO)11}2(μ-PSSP)],
1, were grown by slow evaporation from a CHCl3 solution. Red
crystals of [Os3(CO)10(μ-PSSP)], 3, were obtained by slow
evaporation from a dichloromethane/N-hexane solution. Yel-
low crystals of [{Os3(CO)10}2(μ-PSSP)], 4, were grown from a
(36) “Collect” data collection software; B.V. Nonius: Delft, 1998.
(37) Otwinowski, Z.; Minor, W. Methods in Enzymology; Carter, C.
W.; Sweet, R. M., Eds.; Academic Press: New York, 1996; p 276.
(38) Sheldrick, G. M. SHELXL-97; University of G€ottingen, 1997.

Article
Organometallics, Vol. 29, No. 10, 2010 2233
for integration by using the program SAINT, and an empirical
absorption correction was applied using SADABS39 on the basis
of the Laue symmetry of the reciprocal space. The structures
were solved by direct methods (SIR 97)40 and subsequent Four-
ier syntheses and refined by full-matrix least-squares on F2
(SHELXTL)41 using anisotropic thermal parameters for all
non-hydrogen atoms. The phenyl and methylene hydrogen
atoms were added in calculated positions and refined using
isotropic thermal parameter 1.5 and 1.2 times Ueq of the carrier
carbons. The final refinement on F2 proceeded by full-matrix
least-squares calculations (SHELXL 97) using anisotropic ther-
mal parameters for all the non-hydrogen atoms. For cluster 3
the absolute structure was determined [Flack parameter =
-0.035(6)]. In cluster 4, two CHCl3 molecules are present in
the asymmetric unit. Interestingly one of the two Os3 units
[Os(1)Os(2)Os(3)] in 4 showed some disorder between Os(1)Os-
(2)Os(3) and Os(1A)Os(2A)Os(3A), giving rise to a “star of
David” arrangement, and the occupancy factors were refined to
0.95 for the major component [Os(1)Os(2)Os(3)] and to 0.05 for
the minor one [Os(1A)Os(2A)Os(3A)].
Acknowledgment. This research was supported by grants
from the Swedish Research Council (VR) and the European
Union (TMR network Metal Clusters in Catalysis and
Organic Synthesis, MECATSYN). B.U. was supported by
the Socrates exchange program. M.M. thanks the University
of Bologna and MIUR (PRIN2006) for financial support.
We would like to thank Dr. Karl-Erik Bergquist for the use
of a Bruker DRX500 NMR spectrometer, Prof. Carlaxel
Andersson for a generous gift of the PSSP ligand, and Prof.
A. J. Deeming for helpful discussions.
(39) Sheldrick, G. M. SADABS, program for empirical absorption
€
correction; University of Gottingen: Germany, 1996.
(40) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. SIR97: a new tool for crystal structure determination and
refinement. J. Appl. Crystallogr. 1999, 32, 115.
(41) Sheldrick, G. M. SHELXTLplus Version 5.1 (Windows NT
version)-Structure Determination Package; Bruker Analytical X-ray In-
struments Inc.: Madison, WI, 1998.
Supporting Information Available: Supplementary crystal-
lographic data for compounds 1, 3, and 4 (CCDC 717582,
717583, and 717584). This material is available free of charge
via the Internet at http://pubs.acs.org.