Synthesis and characterisation of [OC-6-33][OsCl2(CO)2L2] (L=phosphine). Crystal structure of [OC-6-33][OsCl2(CO)2(PEt3)2]

Article abstract of DOI:10.1016/S0277-5387(98)00417-3

A series of [OC-6-33][OsCl₂(CO)₂L₂] (L=phosphine) complexes have been prepared by cleavage of [OsCl(μ-Cl)(CO)₃]₂ with a variety of phosphines for a comparison of spectroscopic data with those for the related [OC-6-13][OsF₂(CO)₂L₂] (L=phosphine). The X-ray structural characterisation of [OC-6-33][OsCl₂(CO)₂(PEt₃)₂] represents the first structural characterisation for this class of complex.

Full text of DOI:10.1016/S0277-5387(98)00417-3

Polyhedron 18 (1999) 1207–1210
Synthesis and characterisation of [OC-6-33][OsCl2(CO)2L2]
(L5phosphine). Crystal structure of [OC-6-33][OsCl2(CO)2(PEt3)2]
*
Howard C.S. Clark, Karl S. Coleman, John Fawcett, John H. Holloway, Eric G. Hope ,
Jane Redding, David R. Russell
Department of Chemistry, University of Leicester, Leicester, LE1 7RH, UK
Received 21 September 1998; accepted 16 November 1998
Abstract
A series of [OC-6-33][OsCl2(CO)2L2] (L5phosphine) complexes have been prepared by cleavage of [OsCl(m-Cl)(CO)3]2 with a
variety of phosphines for a comparison of spectroscopic data with those for the related [OC-6-13][OsF2(CO)2L2] (L5phosphine). The
X-ray structural characterisation of [OC-6-33][OsCl2(CO)2(PEt3)2] represents the first structural characterisation for this class of
complex.
1999 Elsevier Science Ltd. All rights reserved.
Keywords: Osmium(II) complexes; Carbonyl; Phosphine; Crystal structure
1. Introduction
ing
the
structural
characterisation
of
[OC-6-
33][OsCl2(CO)2(PEt3)2], and compare results from this
study with those from the related study of the difluoride
complexes.
We have recently described the preparation of a range of
[OC-6-13][OsF2(CO)2L2] (L5phosphine) complexes [1]
and were surprised to find that, even though the first
example of one of the structurally related chloride com-
plexes, [OC-6-33][OsCl2(CO)2(PPh3)2], was first reported
in 1966 [2,3], there was little 31P NMR data with which to
compare those for our fluoride complexes, and that there
had been no single crystal X-ray structural characterisa-
tions. Although a wide variety of synthetic routes to
examples of the osmium dichloride complexes, particularly
when L5PPh3, have been described in the literature [4],
there is no single, general route to prepare these deriva-
tives. Since our route [1] to the fluoride complexes, namely
cleavage of the fluoride-bridged, tetrameric [OsF2(CO)3]4,
represents a widely applicable synthetic procedure and
since a clean, high-yield route to a similar, chloride-
bridged, starting material, h[OsCl(m-Cl)(CO)3]2j, had re-
cently been reported [5], we have re-investigated the
cleavage of this dimer with a range of phosphine ligands.
Early applications of this synthetic route include the
preparation of [OC-6-33][OsCl2(CO)2(PPh3)2] [2,6] and
[OC-6-33][OsCl2(CO)2(PhC6H11j3)2] [2]. Here, we report
the synthesis and characterisation of a series of established
and novel [OC-6-33][OsCl2(CO)2L2] complexes, includ-
2. Experimental
1H and 31P NMR spectroscopic studies were carried out
on a Bruker ARX 250 spectrometer at 250.13 and 101.26
MHz or a Bruker DRX 400 spectrometer at 400.13 and
161.98 MHz, respectively. All chemical shifts are quoted
1
in ppm using the high-frequency positive convention; H
NMR spectra were referenced internally to tetra-
methylsilane and 31P NMR spectra were referenced exter-
nally to 85% H3PO4. IR spectra were recorded on a
Digilab FTS40 Fourier transform spectrometer for Nujol
mulls held between KBr plates at 4 cm21 resolution.
Elemental analyses were performed by Butterworth Lab-
oratories and fast atom bombardment (FAB) mass spectra
were recorded on a Kratos Concept 1H mass spectrometer.
Dichloromethane was dried by heating to reflux over
CaH2 and was stored over molecular sieves in a closed
ampoule. The phosphines (Aldrich, Fluorochem) were used
without purification and, where appropriate, were handled
under nitrogen. The [OsCl(m-Cl)(CO)3]2 was prepared by
the literature route [5].
*
Corresponding author. Fax: 144-116-2523789.
In a typical experiment, [OsCl(m-Cl)(CO)3]2 (100 mg,
0277-5387/99/$ – see front matter
PII: S0277-5387(98)00417-3
1999 Elsevier Science Ltd. All rights reserved.

1208
H.C.S. Clark et al. / Polyhedron 18 (1999) 1207–1210
0.145 mmol) and the ligand (0.658 mmol) in dichlorome-
thane (40 cm3) were heated to reflux for 4 h under
nitrogen. The solution was allowed to cool, filtered, and
the solvent was removed by rotary evaporation to give the
products as cream solids in 75–80% yields.
rection based on c scans, maximum and minimum trans-
mission factors of 0.464 and 0.1043, respectively, Siemens
P4 diffractometer, v scans, data collection range 5.16,
2u,54.008, 21#h#10, 21#k#25, 216#l#15, no crys-
tal decay was detected from periodically measured check
reflections; 5050 reflections were measured, and 3964 were
unique (Rint50.0347). The data were corrected for Lorentz
and polarisation effects.
Product identification was achieved using IR and NMR
spectroscopic studies (Table 1) and FAB mass spec-
trometry. [OC-6-33][OsCl2(CO)2L2]: L5PEt3, m/z 526
(M1), 491 ([M2Cl]1); L5P(C6H11)3, m/z 878 (M1),
843 ([M2Cl]1); L5PPh3, m/z 807 ([M2Cl]1), 779
([M2Cl2CO]1); L5PMePh2, m/z 718 (M1), 683 ([M2
Cl]1), 655 ([M2Cl2CO]1); L5PEtPh2, m/z 746 (M1),
711 ([M2Cl]1), 683 ([M2Cl2CO]1). Satisfactory
elemental analyses were obtained for representative prod-
ucts: [OsCl2(CO)2hP(C6H11)3j2] (Found: C, 51.86; H,
7.44; P, 7.02. C38H66Cl2O2OsP2 requires C, 52.04; H,
7.58; P, 7.06); [OsCl2(CO)2(PMePh2)2] (Found: C, 46.79;
H, 3.52; P, 8.28. C28H26Cl2O2OsP2 requires C, 46.87; H,
3.65; P, 8.63); [OsCl2(CO)2(PEtPh2)2] (Found: C, 48.32;
H, 4.03; P, 7.23. C30H30Cl2O2OsP2 requires C, 48.33; H,
4.06; P, 8.31).
2.3. Structure solution and refinement
Structure solution by Patterson methods and structure
refinement of F2 employed SHELXTL/PC version 5.0 [7].
Hydrogen atoms were included in calculated positions
˚
(C–H50.96 A) with isotropic displacement parameters set
to 1.2 Ueq(C) for methylene H atoms and 1.5 Ueq(C) for
methyl H atoms. All non H atoms were refined with
anisotropic displacement parameters. Final, R150.0278,
wR250.0678 (0.033 and 0.070, respectively, for all data)
for 190 variables. The final residual Fourier map showed
23
˚
˚
at ,1 A from the
peaks of 11.174 and 21.294 eA
osmium atom.
2.1. Crystal structure determination of [OC-6-
33][OsCl2(CO)2(PEt3 )2 ]
3. Results and discussion
Crystals were grown by slow evaporation from a
solution of the complex in dichloromethane.
As shown previously in the cleavage of the fluoride
bridges in [OsF2(CO)3]4 with phosphines [1], cleavage of
the chloride bridges in [OsCl2(CO)3]2 represents a clean
and widely applicable route to a range of osmium–phos-
phine–carbonyl–halide complexes. Although this meth-
odology had been utilised in the earliest preparations of
complexes of this type, the straightforward new synthetic
route to the chloride-bridged starting material has allowed
a comprehensive series of these complexes to be prepared
(Table 1). The cis-,cis-,trans-geometry for these complex-
es is, and has previously been, implied from the IR
spectroscopic data and our results are in acceptable agree-
ment with that in the literature. This geometry is now
2.2. Crystal data
C14H30Cl2O2OsP2, M5553.42, monoclinic, a5
˚
8.286(1), b520.210(3), c512.717(1) A, b5107.5(1)8,
3
˚
U52031.0(4) A (by least-squares refinement on diffrac-
tometer angles from 39 centred reflections, 5.03 to 12.538),
T5190(2) K, space group P21 /c, graphite-monochromated
˚
Mo–Ka radiation, l50.71073 A, Z54, Dc51.810 g
cm23, F(000)51080, dimensions 0.6030.2130.17 mm,
m(Mo–Ka)56.700 mm21, semiempirical absorption cor-
Table 1
Spectroscopic data for cis-,cis-,trans-[OsX2(CO)2L2] (X5F, Cl; L5phosphine)
n(CO)a /cm21
d(P)b /ppm
L
Fc
Cl
Br
Fc
Cl
Br
PEt3
P(C6H11
PPh3
PEtPh2
PMePh2
2034, 1963
2005, 1925
2017, 1937
2031, 1950
2026, 1941
2029, 1953
2008, 1931
2041, 1970
2043, 1962
2043, 1971
2
11.1
15.5
1.0
4.4
21.8
29.3
2
2
)
2
22.2d
29.9
3
2035, 1970e
2046, 1977g
2045, 1970f,h
216.5d,f
2
26.0d
214.6d
223.6d,f
aRecorded as Nujol mulls unless otherwise stated; 62 cm21
bSpectra recorded in CD2Cl2 unless otherwise stated.
cData taken from ref. [1].
.
dCDCl3 solution.
eKBr pellets, data taken from ref. [3].
fData taken from ref. [8].
gCHCl3 solution, data taken from ref. [9].
hCH2Cl2 solution.

H.C.S. Clark et al. / Polyhedron 18 (1999) 1207–1210
1209
confirmed by a single crystal X-ray crystallographic study
(vide infra). When L5PPh3, PMePh2 and PEtPh2, the data
confirm our earlier contention [1] that n(CO) is lower for
fluoride than chloride¯bromide, which may be accounted
for by p-electron donation by the fluoride ligand [10].
However, this trend is not repeated for the better s-donor
ligands PEt3 and P(C6H11)3. Indeed, when L5PEt3,
n(CO) for fluoride $n(CO) for chloride, indicating that,
here, the electron-withdrawing effects of the fluoride
ligands are only partially offset by Os–F p bonding, which
must arise from the different s-donor/p-acceptor prop-
erties of the axial phosphine ligands. Further work is
necessary in this area to fully understand the nature of the
metal–halide interaction in these low-valent metal com-
plexes.
The 31Ph1Hj NMR data (Table 1) again confirm our
earlier suggestion [1] that d(P) F.Cl.Br is part of a
general trend in line with the nephelauxetic effect. How-
ever, here again, the effect is more pronounced for the
alkyl than the aryl phosphines, mirroring the variations in
n(CO), and suggesting differences in the metal–ligand
interactions between the two groups of complexes.
Slow evaporation from a dichloromethane solution of
[OC-6-33][OsCl2(CO)2(PEt3)2] produces colourless crys-
tals that were studied by X-ray crystallography. The
molecular structure of [OC-6-33][OsCl2(CO)2(PEt3)2] is
shown in Fig. 1 and selected bond lengths and angles are
given in Table 2. All other crystallographic data may be
obtained from the Cambridge Crystallographic Data Cen-
tre, where the CIF file has been deposited (deposition
number 103014). The complex is pseudo-octahedral with
the two phosphine ligands trans to each other and the two
chloride ligands trans to the carbonyl groups, as indicated
by IR spectroscopy. The Os–P bond lengths are similar
and entirely reasonable. However, the Os–Cl and the
Os–C bond lengths, which are consistent, appear unusually
long and short, respectively, in comparison with other
Os(II)–Cl or Os(II)–CO bond lengths [11]. Indeed, the
osmium–chlorine bond lengths are closer to the Os–
Clbridging bond lengths in [OsCl2(CO)3]2 than to the Os–
Clterminal bond length [5]. However, the unusually short
C–O bond lengths and unusually high carbonyl stretching
frequencies for this dimer suggest that it contains a
distorted charge distribution. The carbonyl and chloride
ligands and the osmium atom are essentially co-planar,
with the largest inter-ligand angle occurring between the
two carbonyl ligands. The ethyl substituents on the mutual-
ly trans phosphine ligands adopt a staggered conformation
in contrast to the eclipsed conformation in [OC-6-
13][MF2(CO)2L2] [M5Ru, L5PEtPh2; M5Os, L5
P(C6H11)3] [1]. Although the P(1)–Os(1)–P(2) axis bends
slightly (1788) towards the chloride ligands, there are no
H...Cl interactions that are significantly shorter than the
sum of the van der Waals radii of H and Cl [rvdw (H)5
Fig. 1. Molecular structure of [OC-6-33][OsCl2(CO)2(PEt3)2], showing
the atom labelling scheme with 30% probability ellipsoids. H atoms are
shown as spheres of arbitrary radii.
related difluoride complexes [OC-6-13][MF2(CO)2L2]
[M5Ru, L5PPh3, PEtPh2; M5Os, L5PPh3, P(C6H11)3]
[1,13], do not appear to influence the packing or ligand
arrangement for [OC-6-33][OsCl2(CO)2(PEt3)2] in the
solid state.
Table 2
˚
Selected bond distances (A) and angles (8) for [OC-6-
33][OsCl2(CO)2(PEt3)2]
Os(1)–C(2)
Os(1)–P(2)
Os(1)–Cl(2)
C(1)–O(1)
P(1)–C(5)
P(1)–C(3)
P(1)–C(7)
C(1)–Os(1)–C(2)
Cl(1)–Os(1)–Cl(2)
C(1)–Os(1)–Cl(2)
P(1)–Os(1)–P(2)
O(1)–C(1)–Os(1)
C(5)–P(1)–C(3)
C(7)–P(1)–C(3)
C(5)–P(1)–Os(1)
1.867(4)
2.4048(11) Os(1)–P(1)
Os(1)–C(1)
1.869(5)
2.4054(11)
2.4452(11)
1.134(5)
1.820(5)
1.823(4)
1.831(4)
2.444(1)
1.132(5)
1.818(4)
1.826(5)
1.826(4)
93.5(2)
88.61(4)
89.50(14)
178.05(3)
179.3(4)
105.7(2)
100.5(2)
114.7(2)
Os(1)–Cl(1)
C(2)–O(2)
P(2)–C(9)
P(2)–C(11)
P(2)–C(13)
C(1)–Os(1)–Cl(1) 178.10(14)
Cl(2)–Os(1)–C(2) 176.96(14)
C(2)–Os(1)–Cl(1)
P(1)–Os(1)–Cl(1)
O(2)–C(2)–Os(1)
C(5)–P(1)–C(7)
C(3)–P(1)–Os(1)
C(7)–P(1)–Os(1)
88.36(14)
89.22(4)
178.1(4)
105.9(2)
114.3(2)
114.3(2)
˚
1.20, rvdw (Cl)51.75 A] [12]. Hence, intra- and inter-
molecular interactions, which appear to be important in the

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H.C.S. Clark et al. / Polyhedron 18 (1999) 1207–1210
4. Conclusions
References
Cleavage of halide bridges in [OsX2(CO)3]n complexes
with donor ligands offers high yield route to
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Structural characterisation when X5Cl and L5PEt3 con-
firms the cis-,cis-,trans-ligand arrangement suggested by
the spectroscopic studies.
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Acknowledgements
We would like to thank the EPSRC (H.C.S.C. and
K.S.C.) and the Royal Society (E.G.H.) for financial
support.