Chelate and bridge diphosphine isomerization: Triosmium and triruthenium clusters containing 1,1′-bis(diphenylphosphino)ferrocene (dppf)

Article abstract of DOI:10.1021/om700759z

The coordination mode of dppf {dppf = 1,1′-bis(diphenylphosphino) ferrocene} at triosmium and triruthenium carbonyl clusters has been studied. Heating [Os₃(CO)₁₂] with dppf in the presence of Me ₃-NO in benzene at 60°C furnishes three triosmium compounds, [Os₃(CO)₁₁(κ¹-dppf)] (1), [Os ₃(CO)₁₀-(κ²-dppf)] (2), and [Os ₃(CO)₁₀(μ-dppf)] (3) in 10, 20, and 30% yields, respectively. Reaction of the labile cluster [Os₃(CO) ₁₀(MeCN)₂] with dppf at room temperature also gives 1,2, and 3 (5, 10, and 35% yields). Treatment of 1, which contains a pendant diphosphine, with Me₃NO at room temperature affords 2 via a ring closure reaction, whereas heating 2, in which the dppf ligand is chelating, at 110°C affords the thermodynamically stable bridging isomer 3, in which phosphorus atoms are bound at equatorial positions. Reaction of the unsaturated cluster [Os₃(CO)₁₀(μ-H)₂] (4) with dppf in refluxing THF affords the bridging complex [Os₃(CO) ₈(μ-dppf)(μ-H)₂] (6) in high yield as the sole product. Hydrogenation of 3 with H₂ at 110°C at 1 atm also yields 6. Reactions of both the saturated [Os₃(CO)₁₀(μ-dppm)] (7) and electrondeficient [Os₃(CO)₈[μ₃- Ph₂PCH₂P(Ph)C₆H₄)(M-H)] (8) with dppf at 110°C and at room temperature respectively yield [Os ₃(CO)₉(μ-dppm)(κ¹-dppf)] (9) and [Os2(CO)₈(μ-dppm)(κ²-dppf)] (10). Compound 9 converts to 10 at 110°C via CO loss and phosphorus coordination. Reaction of [Ru3(CO)12] with dppf in the presence of Me₃NO affords the dihydroxy-bridged complex, [Ru₃(CO)₈(μ-dppf)(- OH)2] (13), together with the previously reported compounds [Ru ₃(CO)₁₀(M-dppf)] (11) and [Ru₃(CO) ₈(μ-dppf)₂] (12).

Full text of DOI:10.1021/om700759z

6462
Organometallics 2007, 26, 6462-6472
Chelate and Bridge Diphosphine Isomerization: Triosmium and
Triruthenium Clusters Containing
1,1′-Bis(diphenylphosphino)ferrocene (dppf)
Noorjahan Begum,† Uttam K. Das,† Manzur Hassan,† Graeme Hogarth,*,‡
Shariff E. Kabir,*,† Ebbe Nordlander,§ Mohammad A. Rahman,† and Derek A. Tocher*,‡
Department of Chemistry, Jahangirnagar UniVersity, SaVar, Dhaka-1342, Bangladesh, Department of
Chemistry, UniVersity College London, 20 Gordon Street, London WC1H OAJ, UK, and Inorganic
Chemistry Research Group, Chemical Physics, Center for Chemistry and Chemical Engineering, Lund
UniVersity, Box 124, SE-221 00 Lund, Sweden
ReceiVed July 26, 2007
The coordination mode of dppf {dppf ) 1,1′-bis(diphenylphosphino)ferrocene} at triosmium and
triruthenium carbonyl clusters has been studied. Heating [Os3(CO)12] with dppf in the presence of Me3-
NO in benzene at 60 °C furnishes three triosmium compounds, [Os3(CO)11(κ1-dppf)] (1), [Os3(CO)10-
(κ2-dppf)] (2), and [Os3(CO)10(µ-dppf)] (3) in 10, 20, and 30% yields, respectively. Reaction of the labile
cluster [Os3(CO)10(MeCN)2] with dppf at room temperature also gives 1, 2, and 3 (5, 10, and 35% yields).
Treatment of 1, which contains a pendant diphosphine, with Me3NO at room temperature affords 2 via
a ring closure reaction, whereas heating 2, in which the dppf ligand is chelating, at 110 °C affords the
thermodynamically stable bridging isomer 3, in which phosphorus atoms are bound at equatorial positions.
Reaction of the unsaturated cluster [Os3(CO)10(µ-H)2] (4) with dppf in refluxing THF affords the bridging
complex [Os3(CO)8(µ-dppf)(µ-H)2] (6) in high yield as the sole product. Hydrogenation of 3 with H2 at
110 °C at 1 atm also yields 6. Reactions of both the saturated [Os3(CO)10(µ-dppm)] (7) and electron-
deficient [Os3(CO)8{µ3-Ph2PCH2P(Ph)C6H4}(µ-H)] (8) with dppf at 110 °C and at room temperature
respectively yield [Os3(CO)9(µ-dppm)(κ1-dppf)] (9) and [Os3(CO)8(µ-dppm)(κ2-dppf)] (10). Compound
9 converts to 10 at 110 °C via CO loss and phosphorus coordination. Reaction of [Ru3(CO)12] with dppf
in the presence of Me3NO affords the dihydroxy-bridged complex, [Ru3(CO)8(µ-dppf)(µ-OH)2] (13),
together with the previously reported compounds [Ru3(CO)10(µ-dppf)] (11) and [Ru3(CO)8(µ-dppf)2] (12).
backbone or in co-ligands bound to the metal center(s).12
Chelate-bridge isomerization of diphosphine ligands on metal
complexes that are not accompanied by the addition and
elimination of other ligands is a property that may be associated
with homogeneous catalysis. In polynuclear complexes, the
small bite-angle diphosphine, bis(diphenylphosphino)methane
(dppm), can act as a chelate ligand, but the four-membered rings
generated are strained, and thus it has a greater tendency to act
in either a monodentate or a bridging bidentate mode,13 the latter
giving dinuclear complexes that can provide suitable reactive
sites to facilitate the simultaneous activation of substrate
molecules.1 In contrast, 1,2-bis(diphenylphosphino)ethane (dppe)
is an excellent chelating ligand, although less commonly it is
known to bridge metal-metal bonds.13
Introduction
In the past two decades, there has been considerable advances
in the synthesis and reactivity of transition metal complexes
bearing diphosphine ligands due to their potential applicability
to effect organic transformations,1 their ability to act as templates
for the synthesis of metal-metal bonds by bridge-assisted
reactions,2-6 and their widespread application in homogeneous
catalysis.7-11 When metal bound, diphosphines can coordinate
in monodentate, chelating, or bridging modes, and interconver-
sions between these often result from slight changes in the ligand
* To whom correspondence should be addressed. E-mail: g.hogarth@
ucl.ac.uk.
† Jahangirnagar University.
‡ University College London.
§ Lund University.
The reactions of [Os3(CO)12] and activated derivatives [Os3-
(CO)11(MeCN)], [Os3(CO)10(MeCN)2], and [Os3(CO)10(cis-
C4H6)] with diphosphines were first investigated in the mid-
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10.1021/om700759z CCC: $37.00 © 2007 American Chemical Society
Publication on Web 10/31/2007

Chelate and Bridge Diphosphine Isomerization
Organometallics, Vol. 26, No. 25, 2007 6463
Scheme 1
1980s. Poe¨ and Sekhar14 reported the formation of [Os3(CO)11-
(κ1-dppm)], obtained from the room-temperature reaction of
[Os3(CO)11(MeCN)] with dppm, which subsequently undergoes
ring-closure at 60-70 °C to afford the bridging diphosphine
complex [Os3(CO)10(µ-dppm)]. In related work, Smith et al.15
also reported the synthesis of [Os3(CO)10(µ-dppm)] from the
Me3NO initiated reaction of [Os3(CO)12] with dppm. We have
also prepared this product from the reaction of dppm and [Os3-
(CO)10(cis-C4H6)] at 68 °C.16 In the latter, the butadiene is bound
to a single metal atom, and this is important since it suggests
that the anticipated chelate isomer is either too strained to be
stable or rearranges rapidly to the favored bridging conforma-
tion. This prompted us to explore the effect of the length of
diphosphine backbone as well as the structure of starting clusters
on the formation of chelating versus bridging isomers of [Os3-
(CO)10{Ph2P(CH2)nPPh2}] (n ) 1-5).16 Thus, whereas dppm
exclusively bridges a metal-metal vector, dppe predominantly
forms the chelating complex, the bridging isomer being only a
minor product. Interestingly, we observed that the chelating
tendency decreases as the chain length increases, so for 1,5-
bis(diphenylphosphino)pentane (dpppe), only the bridging iso-
mer was obtained (Scheme 1).16-18 It is likely that steric effects
will have a major influence on the bridging versus chelating
behavior of these ligands.
(diphenylphosphinomethyl)-N-p-tolylmaleimide (bmi).21 For
example, with dppv, chelate and bridge isomers are in
equilibrium, the former being favored by ca. 7:1 at room
temperature,19 a process that has been shown to be nondisso-
ciative in nature.
The flexible diphosphine, 1,1′-bis(diphenylphosphino)fer-
rocene (dppf), is an important member of the ferrocenylphos-
phine family that has found widespread use in a range of
homogeneous catalytic processes.22 These stem from its ability
to adopt various coordination modes that can match the steric
requirements of the existing molecular environment.23-30 Most
commonly, dppf chelates to a single metal atom, but it can also
act as a monodentate ligand, as a bridge between disparate metal
centers, or as a bridge across a metal-metal bond. Importantly
for catalytic applications, when acting as a chelating ligand, it
is tolerant to bite-angles ranging from 90° to over 120°, and
this allows low-energy pathways for metal-centered transforma-
tions.31 Dppf displays two types of conformational flexibility:
a tilting motion of the two cyclopentadienyl ring planes thus
changing their dihedral angle, and a torsional rotation around
the axis passing through the two ring centroids, and these allow
a wide range of bite-angles of dppf when bound to molecular
clusters.32-38
(21) Watson, W. H.; Poola, B.; Richmond, M. G. J. Organomet. Chem.
2006, 691, 4676.
Suitable ligand choice is clearly an important factor when
constructing a desired multinuclear skeleton with bridge/chelate
diphosphine. Recently, Richmond’s group have carried out
intensive studies, on bridge-chelate isomerization of diphos-
phines at the triosmium center, detailing kinetic aspects of the
process as well as subsequent carbon-hydrogen and phosphorus-
carbon bond cleavage reactions of the rigid and unsaturated
diphosphines cis-Ph2PCHdCHPPh2 (dppv),19 4,5-bis(diphe-
nylphosphino)-4-cyclopentene-1,3-dione (bpcd),20 and 2,3-bis-
(22) For recent examples, see: (a) Fairlamb, I. J. S.; Grant, S.
McCormack, P.; Whittall, J. Dalton Trans. 2007, 859. (b) Vavasori, A.;
Bellieni, A.; Ronchin, L.; Acqua, F. D.; Toniolo, L.; Cavinato, G. J. Mol.
Catal. A: Chem. 2007, 263, 9. (c) Ng, S. Y.; Leong, W. K. Goh, L. Y.;
Webster, R. D. Eur. J. Inorg. Chem. 2007, 463. (d) Ichikawa, H.; Ohno,
Y.; Usami, Y.; Hrimoto, M. Heterocycles 2006, 68, 2247. (e) Cadierno,
V.; Diez, J.; Garcia-Garrido, S. E.; Gimeno, J.; Nebra, N. AdV. Synth Catal.
2006, 348, 2125. (f) Wang, X. L.; Zheng, X. F.; Wang, L. Reiner, J.; Xie,
W. L.; Chang, J. B. Synthesis 2007, 989. (g) Wu, J.; Zhang, L.; Gao, K.;
Eur. J. Org. Chem. 2006, 5260.
(23) Brandoli, G.; Dolmella, A. Coord. Chem. ReV. 2000, 209, 161.
(24) Gan, K.-S.; Hor, T. S. A. In Ferrocene; Tongi, A., Hayashi T., Eds.;
VCH: New York, 1995; Chapter 1.
(25) Colacot, T. J. Platinum Met. ReV. 2001, 45.
(26) Yan, Y. K.; Chan, H. S. Q.; Hor, T. S. A.; Tan, K.-L.; Liu, L.-K.;
Wen, Y.-S. J. Chem. Soc., Dalton Trans. 1992, 423.
(14) Poe¨, A.; Sekhar, V. C. J. Am. Chem. Soc. 1984, 106, 5034.
(15) Clucas, J. A.; Foster, D. F.; Harding, M. M.; Smith, A. K. J. Chem.
Soc., Chem. Commun. 1984, 949.
(16) Deeming, A. J.; Donovan-Mtunzi, S.; Kabir, S. E. J. Organomet.
Chem. 1984, 276, C65.
(17) Deeming, A. J.; Donovan-Mtunzi, S.; Hardcastle, K. I.; Henrick,
K.; McPartlin, M.; Kabir, S. E. J. Chem. Soc., Dalton Trans. 1988, 579.
(18) Kabir, S. E.; Miah, A.; Nesa, L.; Uddin, K.; Hardcastle, K. I.;
Rosenberg, E.; Deeming, A. J. J. Organomet. Chem. 1995, 492, 41.
(19) Watson, W. H.; Wu, G.; Richmond, M. G. Organometallics 2005,
24, 5431.
(27) Ohs, A. C.; Rheingold, A. L.; Shaw, M. J.; Nataro, C. Organome-
tallics 2004, 23, 4655.
(28) Hor, T. S. A.; Phang, L.-T. J. Organomet. Chem. 1989, 373, 423.
(29) Hor, T. S. A.; Chan, H. S. O.; Tan, K.-L.; Phang, L.-T.; Yan, Y.
K.; Liu, L.-K.; Wen, Y.-S. Polyhedron 1991, 10, 2437.
(30) Lu, X. L.; Ng, S. Y.; Vittal, J. J.; Tan, G. K.; Goh, L. Y.; Hor, T.
S. A. J. Organomet. Chem. 2003, 688, 100.
(31) Kawano, H.; Nishimura, Y.; Onishi, M. Dalton Trans. 2003, 1808.
(20) Watson, W. H.; Wu, G.; Richmond, M. G. Organometallics 2006,
25, 930.

6464 Organometallics, Vol. 26, No. 25, 2007
Begum et al.
Scheme 2
In comparison to the extensive number of trinuclear clusters,
[M3(CO)10(diphosphine)] (M ) Os, Ru), to date there have been
only a few literature reports of trimetallic Group 8 carbonyls
bearing the dppf ligand. Thus, three derivatives of [Ru3(CO)12]
containing dppf have been reported.32,33 In two of these, [Ru3-
(CO)10(µ-dppf)] and [Ru3(CO)8(µ-dppf)2], the dppf(s) bridge
metal-metal bonds, whereas in [{Ru3(CO)11}2(µ-dppf)], it acts
as open bridge, linking together the two triruthenium units. To
our knowledge, the reactivity of dppf with simple triosmium
clusters has not yet been investigated. In this report, we give
details of the synthesis of a number of new triosmium and
triruthenium dppf complexes, showing how the different
coordination modes can be interconverted, and through a number
of crystallographic studies, highlighting the ability of dppf to
bridge a wide range of metal-metal distances.
and dppf at 60 °C in the presence of Me3NO leads to the
complete consumption of the starting cluster in 1 h and furnishes
three triosmium clusters: [Os3(CO)11(κ1-dppf)] (1), [Os3(CO)10-
(κ2-dppf)] (2), and [Os3(CO)10(µ-dppf)] (3) in 10, 20, and 30%
yields, respectively. Treatment of the labile cluster [Os3(CO)10-
(MeCN)2] with dppf at room temperature also affords 1, 2, and
3 in 5, 10, and 35% yields, respectively. Cluster 1 is a precursor
of 2 and 3, and we have shown in separate experiments that
it converts into a mixture of 2 and 3 at room temperature via
the Me3NO initiated decarbonylation. Further, refluxing 2 in
toluene cleanly affords 3, confirming the reaction sequence 1
f 2 f 3.
Since we were not able to obtain single crystals of 1, its
molecular structure was determined from spectroscopic data and
elemental analysis. It is straightforwardly characterized by
comparison with spectroscopic data of other pendant diphos-
phine clusters, [Os3(CO)11(κ1-diphosphine)] (diphosphine )
dppm, dppe, dppp).39 The ν(CO) absorption spectrum is very
similar to that observed for [Os3(CO)11(κ1-dppe)], whereas the
mass spectrum shows a molecular ion at m/z 1434 together with
fragmentation peaks due to the sequential loss of all 11 CO
ligands. In the room temperature 1H NMR spectrum, in addition
to aromatic protons, four equal intensity resonances at δ 4.43,
4.22, 4.12, and 3.90 (each integrating to 2H) are assigned to
the protons of the cyclopentadienyl rings, whereas the 31P{1H}
NMR spectrum displays two equal intensity singlets at δ -16.8
and 9.4, assigned to the free and coordinated diphenylphosphine
groups, respectively.
Results and Discussion
Stepwise Conversion of Pendant to Chelate to Bridge dppf
at the Triosmium Center: Crystal Structures of Bridge and
Chelate Isomers. Heating equimolar amounts of [Os3(CO)12]
(32) Chacon, S. T.; Cullen, W. R.; Bruce, M. I.; Shawkataly. O. B.;
Einstein, F. W. B.; Jones, R. H.; Willis, A. C. Can. J. Chem. 1990, 68,
2001.
(33) O’Connor, A. R.; Nataro, C.; Rheingold, A. L. J. Organomet. Chem.
2003, 679, 72.
(34) Fabrizi de Biani, F.; Caudia, G.; Graiff, C.; Opromolla, G.; Predieri,
G.; Tiripicchio, A.; Zanello, P. J. Organomet. Chem. 2001, 637-639, 586.
(35) Cauzzi, D.; Graiff, C.; Massera, C.; Predieri, G.; Tiripicchio, A.;
Acquotti, D. J. Chem. Soc., Dalton Trans. 1999, 3515.
(36) Cauzzi, D.; Graiff, C.; Lanfranchi, M.; Predieri, G.; Tiripicchio, A.
J. Organomet. Chem. 1997, 536-537, 497.
(37) Kim, T.-J.; Kwon, S.-C.; Kim, Y.-H.; Heo, N. H.; Teeter, M. M.;
Yamano, A. J. Organomet. Chem. 1991, 426, 71.
(38) Onaka, S.; Mizuno, A.; Takagi, S. Chem. Lett. 1989, 2037.
The molecular structures of 2 and 3 can also be unambigu-
ously assigned on the basis of spectroscopic data; for example,
(39) Deeming, A. J.; Donovan-Mtunzi, S.; Kabir, S. E. J. Organomet.
Chem. 1987, 333, 253.

Chelate and Bridge Diphosphine Isomerization
Organometallics, Vol. 26, No. 25, 2007 6465
in their mass spectra, both exhibit a molecular ion peak at m/z
1406 corresponding to the formulation [Os3(CO)10(dppf)] and
fragment ions due to the sequential loss of 10 carbonyls. The
pattern of ν(CO) absorption spectrum for 2 is similar to that of
[Os3(CO)10(κ2-dppe)]16 but quite different from isomeric 3,
indicating that the distribution of the carbonyl ligands differs
between the two, whereas the ν(CO) absorption spectrum of 3
similarly bears a close resemblance to that of [Os3(CO)10(µ-
dppe)].16,17 As usually found, these absorption frequencies are
lower for the bridging isomer than for the corresponding
chelating isomer. Both 31P{1H} NMR spectra show singlets, at
δ -6.7 for 2 and at δ -5.0 for 3, implying that both 2 and 3
contain equivalent phosphorus nuclei. These values should be
compared to those of δ -6.4 and 37.4 for the bridge and chelate
isomers of [Os3(CO)10(dppv)], respectively.19 Although chemical
shifts for the bridge isomers are very similar, the small bite-
angle of the diphosphine in [Os3(CO)10(κ2-dppv)] leads to a
marked downfield shift. The very similar values for 2 and 3
suggest that the phosphorus centers in these isomers have similar
electronic properties. In the room temperature 1H NMR spectra,
2 shows two signals at δ 4.52 and 4.37 and 3 exhibits a sharp
signal at δ 4.57 and a broader one at δ 4.45 assigned to the
cyclopentadienyl protons (In all these complexes, the ring
protons should appear as virtual triplets. Generally, these were
not resolved, and thus, we describe them as singlets or broad
singlets.). Thus, spectroscopic data for 2 point to a structure
with the dppf ligand chelating to a single osmium atom, whereas
in 3 the dppf ligand is coordinated to two adjacent osmium
atoms, and in both cases the phosphines occupy equatorial sites,
i.e., in the plane of the osmium triangle.
To confirm this assertion and to compare the structures with
those of the chelate and bridge isomers of [Os3(CO)10(dppv)]19
and [Os3(CO)10(dmpe)]40 reported by Richmond and Watson,
we undertook X-ray crystallographic studies of both 2 and 3.
The molecular structure of 2 is shown in Figure 1 and, selected
bond distances and angles are listed in the caption. The molecule
consists of an isosceles triangle of osmium atoms with two
longer but almost equal metal-metal bonds [Os(1)-Os(3) )
2.9241(2) Å and Os(1)-Os(2) ) 2.9176(3) Å] and one relatively
short metal-metal bond [Os(2)-Os(3) ) 2.8859(2) Å] with
10 terminal carbonyl ligands, 4 bonded to Os(1) and 3 to each
of Os(2) and Os(3). The average osmium-osmium distance of
2.9092(2) Å is in agreement with those in related triosmium
clusters.19-21,41 A salient feature of 2 is the coordination of the
dppf ligand in a chelating mode to Os(1) and arranged
equatorially so that the steric interaction between the phenyl
rings and adjacent CO ligands is minimized. The Os-P bond
distances [Os(1)-P(1) ) 2.3425(10) Å and Os(2)-P(1) )
2.3284(10) Å] are comparable to those found in [Os3(CO)10-
(κ2-dppv)] [2.299(2) and 2.293(2) Å].19 The two longer Os-
Os bonds are each cis to the dppf-chelated osmium atom, in
agreement with previous observations that tertiary phosphine
ligands tends to lengthen the cis-Os-Os bond in phosphine-
substituted trimetallic clusters.42 The two cyclopentadienyl
ligands are staggered with respect to one another and the P(1)-
Os(1)-P(2) bite angle of 105.89(4)o is consistent with cis-
Figure 1. ORTEP diagram of [Os3(CO)10(κ2-dppf)] (2) showing
50% probability thermal ellipsoids. Selected interatomic distances
(Å) and angles (deg): Os(1)-Os(2) ) 2.9176(3), Os(1)-Os(3) )
2.9241(2), Os(2)-Os(3) ) 2.8859(2), Os(1)-P(1) ) 2.343(1), Os-
(1)-P(2) ) 2.328(1), Fe-C(av) ) 2.0398(4), P(1)...P(2) ) 3.73,
P(2)-Os(1)-P(1) ) 105.89(4), P(1)-Os(1)-Os(2) ) 100.79(2),
P(1)-Os(1)-Os(3) ) 160.00(3), C(11)-Os(1)-Os(2) ) 92.3(1),
P(2)-Os(1)-Os(2) ) 153.32.(3), P(2)-Os(1)-Os(3) ) 94.11.-
(3), C(12)-Os(1)-Os(3) ) 93.4(1), C(12)-Os(1)-Os(2) ) 90.73-
(12), Os(2)-Os(2)-Os(1) ) 60.28(1), Os(2)-Os(1)-Os(3) )
59.210(5), Os(3)-Os(2)-Os(1) ) 60.507(6).
chelating dppf ligand and significantly larger than the analogous
angles in [Os3(CO)10(κ2-dppv)] [84.66(7)o],16 [Os3(CO)10(κ2-
bpcd)] [87.15(6)o],17 and [Os3(CO)10(κ2-bmi)] [87.3(2)o].18
Reactions of [Ru3(CO)12] with dppf yield only the bridging
complex [Ru3(CO)10(µ-dppf)]32 and to our knowledge, the
chelating coordination mode of the dppf ligand on a trinuclear
group 8 metal cluster has only previously been observed once
before.35 Thus, Predieri and co-workers have reported that
reaction of the diselenide of dppf (dppfSe2) with [Ru3(CO)12]
in the presence of Me3NO affords the open triruthenium cluster
[Ru3(CO)7(µ3-Se)2(κ2-dppf)] in which the dppf ligand chelates
to an open ruthenium atom. The bridge isomer is seen in small
amounts and no attempt at converting one into the other was
made. Interestingly, the dppe analogue, [Ru3(CO)7(µ3-Se)2(µ-
dppe)], exists only in the bridging form, highlighting the better
chelating ability of dppf vs dppe.
The molecular structure of 3 is shown in Figure 2 and,
selected bond distances and angles are listed in the caption. The
three osmium atoms define an isosceles triangle with two short
[Os(1)-Os(2) ) 2.8816(3) Å, Os(2)-Os(1A) ) 2.8816(3) Å ]
and one longer [Os(1)-Os(1A) ) 2.9507(4) Å] osmium-
osmium distances and of the 10 carbonyl ligands, 4 are bonded
to Os(2) and 3 to each of Os(1)/Os(1A). The dppf ligand bridges
the Os(1)-Os(1A) edge, occupying adjacent equatorial coor-
dination sites the phosphine moieties lying trans to the non-
bridged osmium-osmium edges [P(1)-Os(1)-Os(2) ) 170.27-
(3)o]. The dppf bridged vector [Os(1)-Os(1A) ) 2.9507(4) Å]
is significantly longer than the nonbridged osmium-osmium
bonds, which is in contrast to the situation in [Os3(CO)10(µ-
dppe)] [2.891(1) vs 2.878(1), 2.871(1) Å]17 and [Os3(CO)10(µ-
dmpe)] [2.8832(6) vs 2.8819(6), 2.8817(6) Å].40 The osmium-
(40) Watson, W. H.; Poola, B.; Richmond, M. G. J. Chem. Crystallogr.
2006, 36, 123.
(41) (a) Hansen, V. K.; Ma, A. K.; Biradha, R. K.; Pomeroy, R. K.;
Zaworotko, Organometallics 1998, 17, 5267. (b) Bruce, M. I.; Liddell, M.
J.; Hughes, C. A.; Patrick, J. M.; Skelton, B. W.; White, A. H. J. Organomet.
Chem. 1988, 347, 157. (c) Kazemifar, N. K. K.; Stchedroff, M. J.; Mottalib,
M. A.; Selva, S.; Monari, M.; Nordlander, E. Eur. J. Inorg. Chem. 2006,
2058.
(42) Dierkes, P.; van Leeuwen, P. W. N. M. J. Chem. Soc., Dalton Trans.
1999, 1519.

6466 Organometallics, Vol. 26, No. 25, 2007
Begum et al.
Figure 3. ORTEP diagram of [Os3(CO)8(µ-dppf)(µ-H)2] (6)
showing 50% probability thermal ellipsoids. Selected interatomic
distances (Å) and angles (deg): Os(1)-Os(2) ) 2.7167(3), Os-
(2)-Os(3) ) 2.8164(2), Os(2)-Os(3) ) 2.8253(2), Os(1)-P(1)
) 2.3327(9), Os(2)-P(2) ) 2.3511(9), Fe-C(av) ) 2.0411(4),
P(1)-Os(1)-Os(2) ) 116.74(2), P(2)-Os(2)-Os(1) ) 117.68-
(3), P(1)-Os(1)-Os(3) ) 172.16(2), P(2)-Os(2)-Os(3) ) 176.84-
(3), C(11)-Os(1)-Os(2) ) 127.1(1), C(12)-Os(1)-Os(2) )
129.7(1), C(21)-Os(2)-Os(1) ) 128.3(1), C(22)-Os(2)-Os(1) )
127.8(1), Os(1)-Os(2)-Os(3) ) 61.050(5), Os(2)-Os(1)-Os(3)
) 61.378(6), Os(1)-Os(3)-Os(2) ) 57.572(6).
Figure 2. ORTEP diagram of [Os3(CO)10(µ-dppf)] (3) showing
50% probability thermal ellipsoids. Selected interatomic distances
(Å) and angles (deg): Os(1)-Os(2) ) 2.8816(3), Os(1)-Os(1A)
) 2.9507(4), Os(1)-P(1) ) 2.349(1), Fe-C(av) ) 2.042(1),
P(1)...P(1A) ) 5.20, P(1)-Os(1)-Os(2) ) 170.27(3), C(11)-Os-
(1)-Os(2) ) 95.3(1), C(11)-Os(1)-Os(1A) ) 80.75(13), P(1)-
Os(1)-Os(1A) ) 117.82.(3), C(13)-Os(1)-Os(1A) ) 147.0(1),
Os(1)-Os(2)-Os(1A) ) 61.594(9), C(12)-Os(1)-Os(2) ) 84.08-
(14), C(12)-Os(1)-Os(1A) ) 92.1(1), Os(2)-Os(2)-Os(1A) )
59.203(4).
phosphorus bond distances [Os(1)-P(1) ) 2.3425(10) Å,
Os(1)-P(2) ) 2.3284(10) Å] are almost the same as those in 2
and [Os3(CO)10(µ-dppe)] [2.328(3) and 2.333(3) Å].17 A major
difference between 2 and 3 is the relative conformations of the
cyclopentadienyl rings. Whereas in 3 they are eclipsed (imposed
by crystal symmetry), in 2 they are staggered. Coordination of
dppf across the Os(1)-Os(1A) edge results in a significant
stretching of the ligand relative to cluster 2. The inter-nuclear
P(1)-P(1A) distance of 5.20 Å found for 3 is some 1.47 Å
longer than the corresponding P(1)-P(2) distance of 3.73 Å
in 2.
Upon heating in refluxing toluene, chelate 2 slowly converts
to the bridge isomer 3, a process which is irreversible. This
observation is in contrast to those reported by Richmond and
co-workers for the chelate-bridge pair [Os3(CO)10(dppv)] in
which isomerization is reversible16 and [Os3(CO)10(bpcd)]17 and
[Os3(CO)10(bmi)]18 in which irreversible bridge to chelate
isomerization occurs. Further, we note that for [Os3(CO)10-
(diphosphine)] (diphosphine ) dppe, dppp), although both
chelate and bridge isomers are accessible, no isomerization is
observed. Our observations with dppe and dppp also parallel a
recent report by Richmond et al.40 on [Os3(CO)10(dmpe)] where
chelate-bridge isomerization is also absent. Hence, it is clear
that the nature of the diphosphine plays a crucial role in chelate-
bridge isomerization.
Synthesis and Crystal Structure of [Os3(CO)8(µ-dppf)(µ-
H)2]. Reactions of the unsaturated triosmium cluster [Os3(CO)10-
(µ-H)2] (4) with a range of diphosphines has been carried out.
Significantly, in all cases, the bridge complexes [Os3(CO)8(µ-
diphosphine)(µ-H)2] are the sole products of dicarbonyl sub-
stitution, with the diphosphine always bridging the short Os(µ-
H)2Os edge.43 Thus, recently we reported the chiral diphosphine
substituted compounds [Os3(CO)8(µ-diphosphine)(µ-H)2] (diphos-
phine ) BINAP, R-tol-BINAP and DIOP) from their thermal
reactions with [Os3(CO)10(µ-H)2].43 We were interested to
see if a chelate complex of dppf could be prepared at this
metal center and also wanted to prepare the bridge complex to
compare its fluxionality with that of 3. Hence, following our
synthetic procedure, the addition of 1 equiv of dppf to a purple
solution of 4 resulted in an immediate color change to yellow.
Comparison of the IR spectrum with those of known adducts,
[HOs3(CO)10(L)(µ-H)],43 indicated formation of [HOs3(CO)10-
(κ1-dppf)(µ-H)] (5). This was not isolated, but heating the
solution at 66 °C for 4 h led to the clean formation of [Os3-
(CO)8(µ-dppf)(µ-H)2] (6) (Scheme 1), isolated after chroma-
tography as green crystals (64% yield). Cluster 6 was also
obtained upon hydrogenation of 3. It has been characterized by
1
a combination of IR, H NMR, and 31P{1H} NMR and single-
crystal X-ray diffraction studies. The ν(CO) spectrum is very
similar to that of [Os3(CO)8(µ-BINAP)(µ-H)2], suggesting that
they are isostructural.43 At room temperature, the hydride region
1
of the H NMR shows a triplet at δ -9.33 (JP-H ) 6.8 Hz)
integrating to 2H, whereas the aliphatic region contains a sharp
singlet at δ 4.39 and a broad singlet δ 3.94 each integrating
for 4H. A singlet at δ -7.2 in the 31P{1H} NMR indicates
equivalent 31P nuclei. On the basis of this data, a bridging
diphosphine was suggested, and to confirm this, an X-ray
structure was undertaken.
The molecular structure of 6 is shown in Figure 3 and selected
bond distances and angles are listed in the caption. The structure
contains an isosceles triangle of osmium atoms, one bearing
four carbonyl groups and the others two. The hydride ligands
were crystallographically located and refined and found to bridge
across the shortest Os(1)-Os(2) edge. The orientation of the
equatorial carbonyl groups [C(11)-Os(1)-Os(2) ) 127.08(13)°,
C(12)-Os(1)-Os(2) ) 129.71(13)°, C(21)-Os(2)-Os(1) )
(43) Stchedroff, M.; Moberg, V.; Rodriguez, E.; Aliev, A. E.; Bottcher,
J.; Steed, J. W.; Nordlander, E.; Monari, M.; Deeming, A. J. Inorg. Chim.
Acta 2006, 359, 926.

Chelate and Bridge Diphosphine Isomerization
Organometallics, Vol. 26, No. 25, 2007 6467
Scheme 3
128.30(14)°, C(22)-Os(2)-Os(1) ) 127.81(14)°], which are
bent away from the this site, also supports this observation. The
dppf ligand also bridges across the hydride-bridged vector,
binding in equatorial sites. The osmium-osmium distance
between bridged metal atoms [Os(1)-Os(2) ) 2.7167(3) Å] is
significantly shorter than the unbridged distances [Os(1)-Os-
(3) ) 2.8164(2) Å, Os(2)-Os(3) ) 2.8253(2) Å], being
attributed to its formal double bond character. Cluster 6 closely
resembles precursor 4, whose structure was determined by both
X-ray44 and neutron diffraction45 studies. The unbridged os-
mium-osmium distance is comparable with the OsdOs double
bond distance of 2.681(1) Å in 4.44 The osmium-phosphorus
bond distances [Os(1)-P(1) ) 2.3327(9) Å, Os(2)-P(2) )
2.3511(9) Å] are comparable to the corresponding distances in
[Os3(CO)8(µ-dppm)(µ-H)2], synthesized from the reaction of 8
with molecular hydrogen.46 The Os-Os-P angles in the flexible
dppf coordinated phosphametallacyclic ring in 6 [Os(1)-Os-
(2)-P(2) ) 117.68(3)°, Os(2)-Os(1)-P(1) ) 116.74(2)°] are
significantly larger than the corresponding angles in [Os3(CO)8-
(µ-dppm)(µ-H)2] [95.3(1), 93.4(1)°],46 implying that the ring
size and strain of the phosphametallacycle exerts some influence
on the geometry at the coordinated osmium centers. The
cyclopentadienyl rings in 6 are eclipsed. Another effect of the
short Os(1)-Os(2) edge is seen in the P...P separation of 4.88
Å, being shorter by 0.48 Å than the corresponding nonbonding
separation in 3. Formation of dihydride 6 from the ring-closure
of 5 is in contrast to that observed for 1, which furnishes both
chelate and bridge isomers. The latter coordination is most
probably favored over the chelate since in the bridging mode
the metallacycle can alleviate the steric strain more efficiently
than in a chelating mode.
is well-established.13 This is highlighted in the structure of [Os3-
(CO)8(µ-dppm)2], formed upon addition of dppm to [Os3(CO)10-
(µ-dppm)] (7) and in which both diphosphines adopt bridging
modes despite this leading to one of them occupying the
unfavorable axial coordination sites.18 The unsaturated cluster
[Os3(CO)8{µ3-Ph2PCH2P(Ph)C6H4}(µ-H)] (8) acts as a source
of dppm, reacting with monodentate phosphines at room
temperature to give bis(adducts) [Os3(CO)8(PR3)2(µ2-dppm)] as
the major products, together with small amounts of the mono-
substituted orthometalated complexes [Os3(CO)8(PR3){µ3-Ph2-
PCH2P(Ph)C6H4}(µ-H)]. This then provides a useful low-
temperature route to mixed phosphine derivatives of [Os3(CO)12].47
Thus, to synthesize dppf derivatives of 7 without resorting to
extended thermolysis (which may result in secondary isomer-
ization reactions), we investigated the reaction of 8 with dppf.
Addition of dppf to 8 at room temperature leads to the formation
of [Os3(CO)9(κ1-dppf)(µ-dppm)] (9) and [Os3(CO)8(κ2-dppf)-
(µ-dppm)] (10) (Scheme 3) in 33 and 44% yields, respectively.
Unfortunately, we were unable to obtain X-ray quality crystals
of either, but unequivocal characterization was made on the basis
of analytical and spectroscopic data.
In 9, the presence of a dangling dppf and a bridging dppm is
easily deduced from the 31P{1H} NMR spectrum, which exhibits
four equal intensity signals; a pair of doublets at δ -24.1 and
-27.9 (JP-P ) 30 Hz) and two singlets at δ -16.5 and -9.1.
The former are readily assigned to a bridging dppm ligand and
1
the latter to the pendant dppf. The H NMR spectrum shows
four singlets in the aliphatic region at δ 4.39, 4.23, 4.15, and
3.83 due to the cyclopentadienyl protons and a triplet at δ 4.96
assigned to the methylene protons of the dppm ligand. As
detailed for 1, the presence of four cyclopentadienyl resonances
is compatible with the pendant coordination of dppf. The FAB
mass spectrum shows a molecular ion peak at m/z 1762 together
with peaks due to the sequential loss of all nine carbonyls.
Cluster 9 is isostructural with [Os3(CO)9(κ1-dppm)(µ-dppm)],
synthesized from the reaction of 7 with dppm and characterized
by X-ray diffraction studies.18 It formally results from simul-
Mixed Diphosphine Complexes. The Interplay Between
Chelate and Bridge Coordination Modes. We were interested
in preparing a triosmium cluster containing both dppm and dppf
ligands to assess their relative propensity to adopt bridge or
chelate coordination modes. The bridging capability of dppm
(44) (a) Allen, V. F.; Mason, R.; Hitchcock, P. B. J. Organomet. Chem.
1977, 140, 297. (b) Churchill, M. R.; Hollander, F. J.; Hutchinson, J. P.
Inorg. Chem. 1977, 16, 2697.
(45) Broach, R. W.; Williams, J. M. Inorg. Chem. 1979, 18, 314.
(46) Clucas, J. A.; Foster, D. F.; Harding, M. M.; Smith, A. K. J. Chem.
Soc., Chem. Commun. 1985, 2080.
(47) (a) Brown, M. P.; Dolby, P. A.; Harding, M. M.; Mathews, A. J.
Smith, A. K.; J. Chem. Soc., Dalton Trans. 1993, 1671. (b) Azam, K. A.;
Hursthouse, M. B.; Islam, Md. R.; Kabir, S. E.; Malik, K. M. A.; Rashid,
M. A.; Sudbrake, C.; Vahrenkamp, H. J. Chem. Soc., Dalton Trans. 1998,
1097.

6468 Organometallics, Vol. 26, No. 25, 2007
Begum et al.
Scheme 4
taneous addition of carbonyl and dppf ligands followed by
reductive-elimination of the orthometalated phenyl group of the
diphosphine.
substituted derivatives.48 Since we were interested in the
possibility of forming a pendant dppf complex and perhaps even
a chelate derivative, we carried out the reaction of [Ru3(CO)12]
and dppf using Me3NO as an activating agent. Somewhat
surprisingly then we found that the reaction of [Ru3(CO)12] with
dppf in the presence of Me3NO gave, in addition to the
previously reported32 clusters 11 and 12, the dihydroxy com-
pound [Ru3(CO)8(µ-dppf)(µ-OH)2] (13) as the major product
(Scheme 4). To investigate the formation of 13 more fully, we
found that addition of a drop of water to the reaction mixture
increased the yield of 13 up to 40%. Thus, we believe that the
origin of the hydroxy ligands in 13 is most probably water.
Cluster 11 was previously reported by Bruce et al.33 to be formed
in 76% yield from the [PPN][acetate] catalyzed reaction of [Ru3-
(CO)12] with dppf and 12 by a thermal reaction at 80 °C. To
see if the dihydroxide 13 was also formed in the ketyl catalyzed
reaction, we investigated the reaction of [Ru3(CO)12] with dppf
in the presence of sodium diphenylketyl and obtained 11 as the
only product (85% yield). This is in contrast to the report of
Bruce and co-workers who obtained a very-low yield of 11 from
the sodium diphenylketyl catalyzed reaction.32
The ν(CO) pattern of 10 is quite different from that of [Os3-
(CO)8(µ-dppm)2], which was synthesized from the reaction of
7 with dppm at 110 °C, indicating that they have different
distribution of carbonyl ligands.18 The 31P{1H} NMR spectrum
is very simple, showing only two equal intensity singlets at δ
-32.5 and -7.5 and suggesting that dppm is bound to two
adjacent metal atoms in an edge-bridging mode and the dppf
chelates to the third metal. Apart from the multiplets in the
1
aromatic of the H NMR spectrum, in the aliphatic region, a
triplet at δ 4.87 is assigned to the equivalent methylene protons
of the dppm and two singlets at δ 4.52 and 4.31 are assigned to
the cyclopentadienyl protons of the dppf. The FAB mass
spectrum exhibits a molecular ion peak at m/z 1734 correspond-
ing to [Os3(CO)8(dppf)(dppm)] and fragmentation peaks due
to the successive loss of eight carbonyls.
Spectroscopic data for 10 clearly point toward a structure in
which the dppf is chelating (in equatorial sites) to one osmium
atom while the dppf bridges the other two metal atoms again
occupying equatorial sites. Alternative structures with both dppm
and dppf ligands in edge-bridging coordination modes can be
ruled out on the basis of 31P NMR data and although a second
conformation in which the dppf is bridging and the dppm
chelating cannot be unequivocally dismissed, the strong bridging
propensity of dppm and its position in this site in the starting
material point clearly to the proposed molecular structure. This
is further supported by the clean conversion of 9 (with a bridging
dppm) to 10 upon heating at 110 °C in toluene. The chelating
mode of the dppf in 10 is probably favored since it can alleviate
the steric strain of the diphosphine more efficiently than if it
bridges to the other metal.
The new cluster 13 was characterized by spectroscopic data
and unequivocally by an X-ray diffraction study. In addition to
1
the phenyl proton resonances in the aromatic region, the H
NMR spectrum shows two multiplets at δ 4.80 and 4.22 assigned
to the cyclopentadienyl protons and a triplet at δ -0.68 (JP-H
) 3.4 Hz) due to the hydroxide bridges. The latter is typical
and compares well with that of other structurally characterized
hydroxyl-bridged trimetallic complexes: [Ru3(CO)8(µ-BINAP)-
(µ-OH)2] [δ -1.48, JP-H ) 4.0 Hz],48 [Os3(CO)8(µ-dppm)(µ-
OH)(µ-H)] [δ -0.44, JP-H ) 4.3 Hz],49 and [Os3(CO)8(PPh3)2-
(µ-OH)2(µ-H)] [δ -0.18, JP-H ) 3.6 Hz].50 The 31P{1H} NMR
spectrum shows a singlet at δ 2.4, indicating the equivalence
of the phosphorus atoms. The ν(CO) region of the IR spectrum
is very similar to that of [Ru3(CO)8(µ-BINAP)(µ-OH)2], sug-
gesting they are isostructural.48
Reactions of Triruthenium Clusters with dppf: Bridging
of Dihydroxy and dppf Across Open Ruthenium-Ruthe-
nium Edge. Reactions between [Ru3(CO)12] and dppf have
previously been explored under a variety of different conditions
leading to the formation of [Ru3(CO)10(µ-dppf)] (11), [Ru3(CO)8-
(µ-dppf)2] (12), and the linked hexanuclear cluster [{Ru3-
(CO)11}2(µ-κ1,κ1-dppf)].32,33 In no instance is a chelate dppf
complex identified. More generally, [Ru3(CO)12] has been shown
to react with diphosphines in the presence of Me3NO to give
(48) Deeming, A. J.; Speel, D. M.; Stchedroff, M. Organometallics 1997,
16, 6004.
(49) Hodge, S. R.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R.; J. Chem.
Soc., Dalton Trans. 1987, 931.
(50) Akter, H.; Deeming, A. J.; Hossain, G. M. G.; Kabir, S. E.; Mondol,
D. N.; Nordlander, E.; Sharmin, A.; Tocher, D. A. J. Organomet. Chem.
2005, 690, 4639.

Chelate and Bridge Diphosphine Isomerization
Organometallics, Vol. 26, No. 25, 2007 6469
Figure 4. ORTEP diagram of [Ru3(CO)8(µ-dppf)(µ-OH)2] (13)
showing 50% probability thermal ellipsoids. Selected interatomic
distances (Å) and angles (deg): Ru(1)-Ru(3) ) 2.8345(5), Ru-
(1)-Ru(3) ) 2.8317(6), Ru(1)...Ru(2) ) 3.0308(6), Ru(1)-O(1)
) 2.111(3), Ru(2)-O(1) ) 2.119(4), Ru(1)-O(2) ) 2.128(3), Ru-
(2)-O(2) ) 2.135(3), Fe-C(av) ) 2.042(6), Ru(1)-P(1) ) 2.391-
(1), Ru(2)-P(2) ) 2.365(1), P(1)...P(2) ) 5.26, O(1)-Ru(1)-Ru(3)
) 83.7(1), O(2)-Ru(1)-Ru(3) ) 85.85(9), P(1)-Ru(1)-Ru(3) )
175.16(3), P(2)-Ru(2)-Ru(3) ) 172.41(3), O(1)-Ru(1)-O(2) )
75.4(1), O(1)-Ru(2)-O(2) ) 75.1(1), O(2)-Ru(2)-Ru(3) ) 85.80-
(9), O(1)-Ru(2)-Ru(3) ) 83.7(1), Ru(2)-Ru(3)-Ru(1) ) 64.67-
(1), Ru(1)-O(1)-Ru(2) ) 91.5(1), Ru(1)-O(2)-Ru(2) ) 90.7(1).
Figure 5. Observed (left) and computed (using gNMR52) (right)
1H NMR spectra for [Os3(CO)10(µ-dppf)] (3) measured in CD2Cl2
at 400 MHz.
To confirm this, the molecular structure of 13 was determined
the results of which are shown in Figure 4 and selected bond
distances and angles are listed in the caption. The molecule
consists of an open cluster of three ruthenium atoms with two
equal metal-metal bonds [Ru(2)-Ru(3) ) 2.8317(6) Å and
Ru(1)-Ru(3) ) 2.8345(5) Å], eight terminal carbonyl groups,
two bridging hydroxyl ligands, and a bridging dppf ligand. The
nonbonded Ru(1)....Ru(2) distance of 3.0308(6) Å is signifi-
cantly longer than the two bonded ruthenium-ruthenium
distances but, interestingly, it is still within the accepted range
of ruthenium-ruthenium bonding distances.51 Nevertheless, the
cluster is electron-precise without the Ru(1)-Ru(2) bond. It is
possible that unusual shortening of the nonbonded vector is due
to the presence of the two hydroxyl-bridges, and in support of
this, we note that a similar shortening is seen in [Ru3(CO)8(µ-
BINAP)(µ-OH)2] [3.023(2) Å].48 Interestingly, the bridging dppf
ligand in [Ru3(CO)7(µ-dppf)(µ3-Se)2] spans the nonbonded
ruthenium-ruthenium edge [Ru...Ru ) 3.83 Å],34 which is
significantly longer than that observed in 13. Therefore, it is
likely this distance in 13 is controlled by hydroxyl-bridges and
not by the dppf itself. Both hydroxide groups are symmetrically
bound, the ruthenium-oxygen distances [Ru(1)-O(1) ) 2.111-
(3) Å, Ru(2)-O(1) ) 2.119(3) Å, Ru(1)-O(2) ) 2.128(3) Å,
Ru(2)-O(2) ) 2.135(3) Å] being comparable to those in [Ru3-
(CO)8(µ-BINAP)(µ-OH)2] [2.118(13)-2.102(13) Å].48 As ex-
pected, the phosphorus atoms of the dppf ligand occupy
equatorial sites and the two ruthenium-phosphorus distances
are unsymmetrical and somewhat longer [Ru(1)-(P(1) )
2.3914(12) Å and Ru(2)-(P(2) ) 2.3614(12) Å ] than the
corresponding distances in [Ru3(CO)10(µ-dppf)] (11) [2.3503-
(8) Å].32 The overall structure of 13 is similar to that of the
BINAP analog [Ru3(CO)8(µ-BINAP)(µ-OH)2].48
Dynamic Behavior of dppf Complexes. As detailed in the
introduction, dppf displays great conformational flexibility,
which results from the tilting motion of the two cyclopentadienyl
ring planes and a torsional rotation around the axis passing
through the two ring centroids. In light of this, many dppf
complexes are fluxional, being attributed to the mutual twisting
of the cyclopentadienyl ligands and bridge-reversal at the
metal.30,35 The fluxionality of the dppf ligand in the trimetallic
clusters [Os3(CO)10(κ2-dppf)] (2), [Os3(CO)10(µ-dppf)] (3), [Os3-
(CO)8(µ-dppf)(µ-H)2] (6), and [Ru3(CO)8(µ-dppf)(µ-OH)2] (13)
1
were investigated in a series of variable-temperature H NMR
studies, monitoring changes to the cyclopentadienyl resonances.
In chelate 2, these appear as two pseudo-triplets at δ 4.52 and
4.37 at room temperature, suggesting that the two cyclopenta-
dienyl ligands are twisting rapidly. Cooling a CD2Cl2 solution
down to -90 °C resulted in little change, and importantly, the
line width of the signals was virtually unchanged, suggesting
that the twisting motion has a low activation energy when the
1
ligand binds in a chelate manner. The room temperature H
NMR spectrum in CD2Cl2 of the bridge isomer 3 shows one
sharp pseudo triplet (δ 4.57) and one broad signal (δ 4.45)
assigned to the cyclopentadienyl protons but this changes
significantly upon lowering the temperature (Figure 5a). Upon
cooling to -30 °C, the latter broadens into the baseline, whereas
the former remains quite sharp. By -70 °C, the upfield signal
is resolved into a pair of singlets at δ 4.59 and 4.22, whereas
the low-field signal now begins to split such that by -90 °C,
four well-defined signals are apparent, those at δ 4.65 and 4.63
being attributed to the initial low-field signal. From these data,
it is easy to measure the coalescence temperature of the upfield
signal (ca. -30 °C) and thus extrapolate a free energy of
activation (∆G#) of 47.4 ( 1.0 kJ mol-1 for the process. To
(51) Adams, R. D.; Captain, B.; Fu, W.; Hall, M. B.; Smith, M. D.;
Webster, C. D. Inorg. Chem. 2004, 43, 3921.

6470 Organometallics, Vol. 26, No. 25, 2007
Begum et al.
process is somewhat similar to the previously observed inversion
of the OsPCCPOs ring in [Os3(CO)10(µ-dppe)].17
Variable-temperature 1H NMR spectra of 6 show very similar
changes to those discussed above for 3. Thus, low-temperature
limiting spectra consist of four well-separated signals (δ 4.77,
4.38, 4.02, 3.33), whereas at room temperature one sharp and
one broad signal are observed. From an analysis of these data,
thermodynamic parameters can be ascertained [∆G#(298 K) 43.6
( 1.0 kJ mol-1; ∆H# 32.0 ( 0.3 kJ mol-1; ∆S# -39 ( 4 J K-1
mol-1]. The free energy of activation is somewhat smaller than
that measured for 3 (∆∆G#(298 K) ca. 5.0 kJ mol-1), perhaps
being a measure of the smaller degree of twisting seen in 6
(42.6°). Variable-temperature 1H NMR spectra of 13 (twist angle
37.6°) follow a similar pattern to those discussed above, the
major difference being the greater chemical shift range of the
low-temperature limiting signals (δ 5.75, 4.39, 4.00, 3.58).
Again, from a simulation of the spectra thermodynamic
parameters could be extrapolated [∆G#(298 K) 44.2 ( 1.0 kJ
mol-1; ∆H# 34.4 ( 0.3 kJ mol-1; ∆S# -33 ( 1 J K-1 mol-1],
the free energy of activation being similar to that measured in
6. The latter is interesting since in the two clusters the dppf
ligand spans quite different length metal-metal vectors [6, Os-
Os ) 2.7167(3) Å; 13, Ru-Ru 3.0308(6) Å].
Conclusions
The present study has demonstrated that three coordination
modes of dppf ligand are possible on trimetallic clusters: the
thermally induced Me3NO initiated reaction of [Os3(CO)12] with
dppf providing sequentially [Os3(CO)11(κ1-dppf)] (1), [Os3-
(CO)10(κ2-dppf)] (2), and [Os3(CO)10(µ-dppf)] (3), although the
bridging mode is the thermodynamic product. This contrasts
with the reaction with [Os3(CO)10(µ-H)2] (4) where the bridged
complex [Os3(CO)8(µ-dppf)(µ-H)2] (6) results and with saturated
[Os3(CO)10(µ-dppm)] (7) or electron-deficient [Os3(CO)8{µ3-
Ph2PCH2P(Ph)C6H4}(µ-H)] (8), which afford chelate [Os3(CO)8-
(µ-dppm)(κ2-dppf)] (10) as the final product, although both
proceed via a pendant intermediate. The observation of chelating
dppf and bridging dppm ligands in the latter suggests that dppf
is the better chelating ligand of the two. Another finding of
this study is the wide range of metal-metal bond distances that
the dppf ligand can bridge across, accommodating these by
varying the twist angle with respect to the trimetal framework.
The fluxionality of a number of these clusters has been studied
by VT NMR establishing the low-energy torsional rotation about
metal-ring centroid vector and once again highlighting the
tremendous flexibility of this ligand when bound to multinuclear
metal centers.
Figure 6. Views of (a) 3 and (b) 2 highlighting the orientation of
the ferrocene unit of the dppf ligand with respect to the triosmium
framework.
probe the thermodynamic parameters in more detail, the spectra
were simulated using gNMR52 (Figure 5b). From this analysis,
values of 39.7 ( 1.0 kJ mol-1 and -30 ( 4 J K mol-1 were
calculated for ∆H# and ∆S#, respectively, giving a ∆G#(298 K)
of 48.6 ( 1.0 kJ mol-1
.
These observed changes are attributed to a torsional rotation
around the axis passing through the two ring centroids which
results in the twisting of the dppf ligand with respect to the
plane of the triosmium triangle. This is illustrated in Figure 6,
which shows views of 2 and 3 looking approximately parallel
to the triosmium plane. For bridge isomer 3, it is clear that this
is greater than for chelate 2, and this can be quantified by
considering the angles between the plane of the three osmium
atoms and that containing the iron atom and centroids of the
cyclopentadienyl rings. Thus, in 2 the twisting is approximately
27.2°, whereas in 3 it is nearly twice as large at 49.6°. This
difference probably accounts for the lower activation barrier
for the process in 2 as compared to 3. A similar torsional rotation
was found in chelate [Ru3(CO)7(µ3-Se)2(κ2-dppf)], although here,
because of the inequivalence of the phosphine coordination sites,
eight signals were observed at the low-temperature, and four at
the high-temperature, limit.35 A free energy of activation of 50.2
kJ mol-1 was measured, being considerably higher than that in
2. This may be a result of the smaller bite-angle of the dppf
ligand in [Ru3(CO)7(µ3-Se)2(κ2-dppf)] [P-Ru-P 100.6(1)°]
versus that of 105.89(4)° in 2. We also note that this fluxional
Experimental Section
General Comments. Unless otherwise stated, all of the reactions
were performed under a nitrogen atmosphere using standard Schlenk
techniques. Solvents were dried and distilled prior to use by standard
methods. [Os3(CO)12] and [Ru3(CO)12] were purchased from Strem
Chemicals and 1,1′-bis(diphenylphosphino)ferrocene (dppf) was
purchased from Aldrich and used as received. The compounds [Os3-
(CO)10(µ-dppm)],15 [Os3(CO)8{µ3-Ph2PCH2P(Ph)C6H4}(µ-H)],15 and
[Os3(CO)10(µ-H)2]53 were prepared according to published proce-
dures. Infrared spectra were recorded on a Shimadzu FTIR 8101
1
spectrophotometer. H and 31P{1H} NMR spectra were recorded
on Varian Unity Plus 500 and Bruker DPX 400 instruments. All
chemical shifts are reported in δ units with reference to
(52) gNMR, Ver. 4.1; Charwell Scientific Ltd.: Oxford, UK, 1995.
(53) Kaesz, H. D. Inorg. Synth. 1989, 28, 238.

Chelate and Bridge Diphosphine Isomerization
Organometallics, Vol. 26, No. 25, 2007 6471
Table 1. Crystallographic Data and Structure Refinementa for 2, 3, 6, and 13
2
3‚2CH2Cl2
6‚1/2C6H14
13
Formula
Mw
C44H28FeO10Os3P2
1405.05
C46H32Cl4FeO10Os3P2
1574.91
C45H37FeO8Os3P2
1394.14
C42H30FeO10P2Ru3
1115.66
cryst syst
space group
a (Å)
b (Å)
c (Å)
orthorhombic
P21/c
12.9196 (7)
15.5471 (9)
19.998 (1)
90
orthorhombic
Pbcn
16.3658 (9)
16.2298 (9)
18.042 (1)
90
monoclinic
P21/n
19.671(1)
11.8123(7)
21.007(1)
90
05.971(1)
90
4692.7(5)
4
1.973
8.516
2620
0.45 × 0.24 × 0.05
1.67 to 28.29
-26 e h e 26
-15 e k e 15
-27 e l e 28
39840
monoclinic,
P21/n
19.920(1)
11.6063(8)
21.438(2)
90
108.091(1)
90
4711.2(6)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
90
90
90
90
4017.0 (4)
4
2.323
9.954
2624
0.49 × 0.30 × 0.21
1.66 to 28.29
-17 e h e 16
-20 e k e 20
-26 e l e 25
35449
4792.3 (5)
4
2.183
8.572
2960
0.44 × 0.36 × 0.26
1.77 to 28.30
-21 e h e 21
-21 e k e 21
-23 e l e 23
40419
4
F (g cm-3
)
1.573
1.363
2200
0.28 × 0.16 × 0.12
1.68 to 28.31
-26 e h e 26
-15 e k e 15
-26 e l e 27
40988
µ (mm-1
F(000)
)
size (mm3)
θ
max (deg)
index ranges
reflns collected
independent reflns
reflections with F2 > 2σ
Tmax, Tmin
weighting parameters a, b
data/restraints/parameters
GOF on F2
9661 [R(int) ) 0.0317]
5852 [R(int) ) 0.0405]
11178 (Rint ) 0.0412)
11256 (Rint ) 0.0351)
9525
5479
10032
9867
0.0847 and 0.2290
0.0044, 0.1138
9661/0/541
1.082
0.1165 and 0.2140
0.0279, 27.1726
5852/0/299
1.013
0.6754 and 0.1142
0.0336, 7.4150
11178/0/567
1.013
0.8535 and 0.7014
0.0806, 13.3192
11256/0/519
1.113
Final R indices [I > 2σ(I)]
R1 ) 0.0194
wR2 ) 0.0424
R1 ) 0.0199
wR2 ) 0.0426
1.538 and -0.773
R1 ) 0.0296
wR2 ) 0.0666
R1 ) 0.0327
wR2 ) 0.0683
1.245 and -1.043
R1 ) 0.0278
wR2 ) 0.0704
R1 ) 0.0323
wR2 ) 0.0725
1.854 and -0.929
R1 ) 0.0546
wR2 ) 0.1503
R1 ) 0.0632
wR2 ) 0.1558
2.066 and -0.909
R indices (all data)
largest diff peak and hole,
e.Å-3
a Details in common: X-radiation, Mo KR (λ ) 0.71073 Å), temperature (K) 150(2), refinement method: full-matrix least-squares on F2.
the residual protons of the deuterated solvents for proton and to
external 85% H3PO4 for 31P chemical shifts. Elemental analyses
were performed by the Microanalytical Laboratories, University
College London. Fast atom bombardment mass spectra were
obtained on a JEOL SX-102 spectrometer using 3-nitrobenzyl
alcohol as matrix and CsI as calibrant.
(m, 10H), 4.57 (s, br, 4H), 4.45 (s, br, 4H). 31P-{1H} NMR (CD2-
Cl2): δ -5.0 (s). FAB MS: m/z 1406 (M+).
Conversion of 1 to 2 and 3. To a dichloromethane solution (15
mL) of 1 (25 mg, 0.017 mmol) was added Me3NO (2 mg, 0.027
mmol) and it allowed to stir for 1 h under a slow purge of N2. The
solvent was removed under reduced pressure, and the residue was
taken up in CH2Cl2 and applied to silica ge TLC plates. Elution
with hexane/CH2Cl2 (4:1, v/v) developed two bands. The faster-
moving band afforded compound 2 (10 mg, 40%) and the slower-
moving band gave 3 (8 mg, 32%).
Conversion of 2 to 3. A toluene solution (15 mL) of 2 (25 mg,
0.018 mmol) was refluxed for 3 h under a slow purge of N2, during
which time the color changed from orange to red. A similar
chromatographic separation to that above afforded compound 3 (13
mg, 52%).
Reaction of [Os3(CO)12] with dppf. A benzene (50 mL)
suspension of [Os3(CO)12] (250 mg, 0.260 mmol) and dppf (152
mg, 0.274 mmol) was warmed to 60 °C for 1 h, and a solution of
freshly sublimed Me3NO (42 mg, 0.559 mmol) in MeOH (7 mL)
was added dropwise from a pressure-equalizing dropping funnel
(30 min), during which time the color changed from yellow to red.
The solvent was removed under reduced pressure, and the residue
was chromatographed by TLC on silica gel. Elution with hexane/
CH2Cl2 (8:2, v/v) gave three bands. The faster-moving band
afforded [Os3(CO)11(κ1-dppf)] (1) (39 mg, 10%) as orange crystals
after recrystallization from hexane/CH2Cl2 at -4 °C. Anal. calcd
for C45H28FeO11Os3P2: C, 37.71; H, 1.97. Found: C, 37.97; H,
2.15%. IR (ν(CO), CH2Cl2): 2107 s, 2054 vs, 2033 m, 2018 s,
1987 m, 1910 w cm-1. 1H NMR (CD2Cl2): δ 7.52 (m, 10H), 7.27
(m, 10H), 4.43 (s, 2H), 4.22 (s, 2H), 4.12 (s, 2H), 3.90 (s, 2H).
31P-{1H} NMR (CD2Cl2): δ -9.4 (s, 1P), -16.8 (s, 1P). FAB
MS: m/z 1434 (M+). The second band yielded [Os3(CO)10(κ2-dppf)]
(2) (68 mg, 20%) as orange crystals from hexane/CH2Cl2 at -4
°C. Anal. calcd for C44H28FeO10Os3P2: C, 37.61; H, 2.01. Found:
C, 37.8 4; H, 2.16%. IR (ν(CO), CH2Cl2): 2093 s, 2043 vs, 2006
vs, 1989 w, 1962 m, 1910 m cm-1. 1H NMR (CDCl3): δ 7.63 (m,
10H), 7.33 (m, 10H), 4.52 (s, br, 4H), 4.37 (s, br, 4H). 31P-{1H}
NMR (CDCl3): δ -6.7 (s). FAB MS: m/z 1406 (M+). The third
band afforded [Os3(CO)10(µ-dppf)] (3) (102 mg, 30%) as red
crystals after recrystallization from hexane/CH2Cl2 at -4 °C. Anal.
calcd for C44H28FeO10Os3P2: C, 37.61; H, 2.01. Found: C, 37.78;
H, 2.15%. IR (ν(CO), CH2Cl2): 2087 s, 2054 w, 2022 m, 2002 vs,
1968 w, 1952 w cm-1. 1H NMR (CD2Cl2): δ 7.58 (m, 10H), 7.43
Reaction of 3 with Molecular Hydrogen. Hydrogen gas was
bubbled through a refluxing toluene solution (20 mL) of 3 (30 mg,
0.021 mmol) for 2 h. The solvent was removed under reduced
pressure, and the residue was chromatographed by TLC on silica
gel. Elution with hexane/CH2Cl2 (7:3, v/v) gave [Os3 (CO)8(µ-dppf)-
(µ-H)2] (6) (17 mg, 55%) as orange crystals from hexane/CH2Cl2
at -4 °C. Anal. calcd for C44H30FeO10Os3P2: C, 37.56; H, 2.15.
Found: C, 37.67; H, 2.24%. IR (ν(CO), CH2Cl2): 2064 vs, 2011
1
vs, 1983 vs, 1951 m cm-1. H NMR (CD2Cl2): δ 7.46 (m, 20H),
4.39 (s, 4H), 3.94 (s, br, 4H), -9.33 (t, JP-H ) 6.8 Hz; 2H). 31P-
{1H} NMR (CD2Cl2): δ -7.2 (s, 2P). FAB MS: m/z 1408 (M+).
Reaction of [Os3 (CO)10(µ-H)2] (4) with dppf. A mixture of 4
(100 mg, 0.105 mmol) and 1,1′-bis(diphenylphosphino)-ferrocene
(dppf) (65 mg, 0.117 mmol) in THF (30 mL) was heated to reflux
under nitrogen for 4 h. A similar workup and chromatographic
separation as above afforded 6 (106 mg, 64%).
Reaction of [Os3(µ-H)(CO)8{µ-Ph2PCH2PPh(C6H4)}] (8) with
dppf. A CH2Cl2 solution (30 mL) of compound 8 (100 mg, 0.085
mmol) and dppf (50 mg, 0.09 mmol) was stirred for 16 h at room

6472 Organometallics, Vol. 26, No. 25, 2007
Begum et al.
temperature during which time the color changed from green to
orange. The solvent was evaporated to dryness, and the residue
was chromatographed by TLC on silica gel. Elution with hexane/
CH2Cl2 (7:3, v/v) gave two bands. The faster-moving band [Os3-
(CO)9(µ-dppm)(κ1-dppf) (9) (49 mg, 33%) as yellow crystals after
recrystallization from hexane/CH2Cl2 at -4 °C. Anal. calcd for
C68H50FeO9Os3P4: C, 46.36; H, 2.86. Found: C, 46.59; H, 2.98.
IR (νCO, CH2Cl2): 2062 vs, 2017 vs, 1992 s, 1975 s, 1960 s, 1932
m, 1911 w cm-1. 1H NMR (CDCl3): δ 7.36 (m, 40H), 4.96 (s, br,
2H), 4.39 (s, 2H), 4.23 (s, 2H), 4.15 (s, 2H), 3.83 (s, 2H). 31P{1H}
NMR (CDCl3): δ -9.1 (s, 1P), -16.5 (s, 1P), -24.1 (d, J ) 30
Hz, 1P), -27.9 (d, J ) 30 Hz, 1P). MS (FAB): m/z 1762 (M+).
The slower-moving band yielded [Os3(CO)8(µ-dppm)(κ2-dppf)] (10)
(65 mg, 44%) as orange crystals after recrystallization from hexane/
CH2Cl2 at -4 °C. Anal. calcd for C67H50FeO8Os3P4: C, 46.42; H,
2.91. Found: C, 46.69; H, 3.19. IR (νCO, CH2Cl2): 1987 s, 1956
vs, 1920 s cm-1. 1H NMR (CDCl3): δ 7.41 (m, 40H), 4.87 (s, br,
2H), 4.52 (s, br, 4H), 4.31 (s, br, 4H). 31P-{1H} NMR (CDCl3): δ
-7.5 (s, 2P), -32.5 (s, 2P). MS (FAB): m/z 1734 (M+).
Reaction of [Os3(CO)10(µ-dppm)] (7) with dppf. Compound
7 (150 mg, 0.121 mmol), dppf (100 mg, 0.180 mmol), and toluene
(35 mL) were combined in a flame-dried 100 mL two-neck round-
bottom flask. The reaction mixture was heated to reflux for 5 h.
After removal of the solvent under reduced pressure, the residue
was dissolved in a minimum volume of dichloromethane and
chromatographed by TLC on silica gel. Elution with cyclohexane/
CH2Cl2 (7:3, v/v) developed two bands. The faster-moving band
yielded 9 (72 mg, 34%), whereas the slower-moving band gave 10
(61 mg, 29%).
Conversion of 9 to 10. A toluene solution (15 mL) of 9 (25
mg, 0.014 mmol) was refluxed for 5 h during which time the color
changed from orange to red. The solvent was removed under
reduced pressure and residue was taken up in CH2Cl2 and applied
to thin-layer silica plates. Elution with hexane/CH2Cl2 (4:1, v/v)
yielded compound 10 (20 mg, 81%).
Reaction of [Ru3(CO)12] with dppf. A dichloromethane solution
(50 mL) of [Ru3(CO)12] (200 mg, 0.312 mmol) and dppf (260 mg,
0.468 mmol) was warmed to 40 °C for 1 h, and a solution of Me3-
NO (50 mg, 0.667 mmol) in MeOH (4 mL) was added dropwise
over a period of 15 min during which time the color changed from
yellow to red. After passing through a short silica column to remove
any excess Me3NO, the solvent was removed in vacuo and the
residue was dissolved in CH2Cl2 and applied on silica gel TLC
plates. Elution with hexane/dichloromethane (7:3, v/v) developed
three bands. The first two bands afforded the previously reported
compounds [Ru3(CO)10(µ-dppf)] (11) (16 mg, 10%) and [Ru3(CO)8-
(µ-dppf)2] (12) (8 mg, 5%), respectively. The third band gave [Ru3
(CO)8(µ-OH)2(µ-dppf)] (13) (32 mg, 20%) as orange crystals after
recrystallization from CH2Cl2/hexane at -4 °C. Anal. calcd for
C42H30FeO10P2Ru3: C, 45.21; H, 2.71. Found: C, 45.39; H, 2.94%.
1
IR (ν(CO), CH2Cl2): 2056 vs, 2008 s, 1964 vs, 1937 w cm-1. H
NMR (CD2Cl2): δ 7.43 (m, 20H), 4.80 (s, br, 4H), 4.22 (s, br,
4H), -0.68 (t, JP-H ) 3.4 Hz, 2H). 31P NMR (CD2Cl2): δ 2.4 (s,
2P). MS (FAB): m/z 1117 (M+).
X-Ray Structure Determination of Compounds 2, 3, 6, and
13. Single crystals of 2, 3, 6, and 13 suitable for X-ray diffraction
were grown by slow diffusion of hexane into a dichloromethane
solution at -4 °C. All geometric and crystallographic data for 2,
3, 6, and 13 were collected at 150 K on a Bruker SMART APEX
CCD diffractometer using Mo KR radiation (λ ) 0.71073 Å). Data
reduction and integration were carried out with SAINT+, and
absorption corrections were applied using the program SADABS.54
Structures were solved by direct methods and developed using
alternating cycles of least-squares refinement and difference Fourier
synthesis. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms, except those bonded to Os, were placed in the
calculated positions, and their thermal parameters were linked to
those of the atoms to which they were attached (riding model).
Hydrogen atoms bridging Os atoms were located and their positions
refined for compound 6 using fixed isotropic thermal parameters.
The SHELXTL PLUS V6.10 program package was used for
structure solution and refinement.55 Final difference maps did not
show any residual electron density of stereochemical significance.
The details of the data collection and structure refinement are given
in Table 1.
Acknowledgment. Part of this work was carried out by
S.E.K. at University College London. He gratefully acknowl-
edges the Royal Society (London) for a fellowship to spend
time at UCL. We thank Dr. Dalia Rokhsana and Dr. Viktor
Moberg for recording VT NMR spectra and Professor A. J.
Deeming for simulation of these.
Supporting Information Available: Crystallographic data for
the structural analyses have been deposited with the Cambridge
Crystallographic Data Centre, CCDC Nos. 237815 for 2, 237816
for 3, 651078 for 6, and 237817 for 13. 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 on the Web at http://www.c-
cdc.ac.uk). This material is available free of charge via the Internet
at http://pubs.acs.org.
OM700759Z
(54) SMART and SAINT+ software for CCDC diffractometers, version
6.1; Bruker AXS Inc.: Madison, WI, 2000.
(55) Sheldrick, G. M. SHELXTL PLUS, version 6; Bruker AXS:
Madison, WI, 2000.