Synthesis, characterisation, crystal structures and electrochemistry of triosmium nitrite carbonyl clusters containing ferrocenyl phosphines

Article abstract of DOI:10.1016/S0022-328X(01)00918-4

The triosmium nitrite carbonyl cluster [Os₃(μ-H)(CO)₁₀(μ-η²-NO₂)] (1) was allowed to react with 1,1′-bis(diphenylphosphino)ferrocene (dppf) and N,N-dimethyl-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethylamine (ppfa) in the presence of Me₃NO in CH₂Cl₂, and clusters [Os₃(μ-H)(CO)₈(μ-η²-NO₂)(μ-dppf)] (2) and [Os₃(μ-H)(CO)₈(μ-η²-NO₂)(μ-ppfa)] (3) were afforded in moderate yields. Clusters 2 and 3 were fully characterised by spectroscopic techniques and X-ray crystallography. The nitrite, hydride and the ferrocenyl phosphine ligands are all bridged across the same Os-Os edge. The amine group of the ppfa ligand shows a preference to coordinate with the Os atom with a σ-bonded nitrite O atom. The redox properties of the nitrite complexes were investigated using cyclic voltammetry.

Full text of DOI:10.1016/S0022-328X(01)00918-4

Journal of Organometallic Chemistry 637–639 (2001) 276–283
www.elsevier.com/locate/jorganchem
Synthesis, characterisation, crystal structures and electrochemistry
of triosmium nitrite carbonyl clusters containing ferrocenyl
phosphines
Emmie Ngai-Man Ho *, Bernard Kwok-Man Hui, Wing-Tak Wong *
Department of Chemistry, The Uni6ersity of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong
Received 2 January 2001; received in revised form 6 March 2001; accepted 10 April 2001
Abstract
The triosmium nitrite carbonyl cluster [Os3(m-H)(CO)10(m-h2-NO2)] (1) was allowed to react with 1,1%-bis(diphenylphos-
phino)ferrocene (dppf) and N,N-dimethyl-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethylamine (ppfa) in the presence of Me3NO in
CH2Cl2, and clusters [Os3(m-H)(CO)8(m-h2-NO2)(m-dppf)] (2) and [Os3(m-H)(CO)8(m-h2-NO2)(m-ppfa)] (3) were afforded in
moderate yields. Clusters 2 and 3 were fully characterised by spectroscopic techniques and X-ray crystallography. The nitrite,
hydride and the ferrocenyl phosphine ligands are all bridged across the same OsꢀOs edge. The amine group of the ppfa ligand
shows a preference to coordinate with the Os atom with a s-bonded nitrite O atom. The redox properties of the nitrite complexes
were investigated using cyclic voltammetry. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Osmium; Cluster; Nitrite; Ferrocene; Electrochemistry
1. Introduction
[10], and further development of new ligands is an
interesting area of research. Among these, ferro-
cenylphosphines, in particular 1,1%-bis(diphenylphos-
phino)ferrocene (dppf) and N,N-dimethyl-1-[(S)-2-
(diphenylphosphino)ferrocenyl]ethylamine (ppfa), have
been extensively employed as chelating agents for tran-
sition-metal complexes, and show interesting properties
and are also widely utilised in metal carbonyl com-
plexes [11–15]. Ferrocenyl-based chiral ligands have
been examined in a number of enantioselective reac-
tions such as hydrogenation, hydrosilylation, cross-cou-
pling reactions, the addition of dialkylzinc to aldehydes,
aldol type condensations, amongst others [16,17]. The
incorporation of this redox active moiety into the clus-
ter framework is a good candidate for the study of the
multiple oxidation states that these compounds exhibit.
It is believed that the reaction of the nitrite cluster with
asymmetric ferrocenyl phosphine will also be useful to
investigate the site selectivity of the substitution of CO
onto the cluster, which may give us some insight into
the chemistry of the nitrite clusters.
The synthesis and reactions of triosmium nitrite car-
bonyl clusters have been a subject of our interest [1–3].
Much of our attention has been focused on the synthe-
sis and properties of nitrite-containing clusters with
functionalised phosphine [2] and amine [3] ligands. It is
believed that the presence of an electron-withdrawing
m-h2-NO2 group on the cluster framework would have
a pronounced effect on the cluster reactivity, which
should be revealed through the ligand addition and
substitution reactions. Metallocenes, in particular fer-
rocene, possess properties that have led to their use as
ferromagnets [4,5], molecular sensors [6–8], and elec-
trochemical agents [9]. During the last few years, bi-
and multi-functional ferrocene derivatives have been
used successfully as ligands for homogeneous catalysts
* Corresponding authors. Fax: +86-852-2547-2933.
E-mail address: wtwong@hkucc.hku.hk (W.-T. Wong).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00918-4

E.N.-M. Ho et al. / Journal of Organometallic Chemistry 637–639 (2001) 276–283
277
In this paper, we report the facile synthesis of
2. Results and discussion
the complexes [Os3(m-H)(CO)8(m-h2-NO2)(m-dppf)]
(2) and [Os3(m-H)(CO)8(m-h2-NO2)(m-ppfa)] (3) by
the oxidative decarbonylation of [Os3(m-H)(CO)10(m-h2-
NO2)] (1) with Me3NO in the presence of the ferro-
cenylphosphines, dppf and ppfa. In order to investi-
gate the redox properties of these nitrite carbonyl
clusters, the electrochemistry of clusters 1–3 and a
related cluster anion [Os3 (CO)10(m-h2-NO2)]− [1] were
studied.
2.1. Synthesis and characterisation
2.1.1. Reaction of [Os3(v-H)(CO)10(v-p2-NO2)] (1)
with dppf
Cluster 1 was treated with dppf and Me3NO in
CH2Cl2 at room temperature (r.t.) to give a red cluster
[Os3(m-H)(CO)8(m-h2-NO2)(m-dppf)] (2) in 46% yield
(Scheme 1). A summary of the spectroscopic data is
Scheme 1.
Table 1
Spectroscopic data for clusters 1–3
Cluster
IR spectra a, w (CO) (cm−1
)
1H-NMR spectra b, (l, J (Hz))
31P-NMR spectra c, (l)
Mass spectra d, (m/z)
2
2080s, 2020vs, 2010vs, 1997s, 1968w
1949w
7.6 (m, 8H, Cp)
2.1
1.3
1396 (1396)
7.4 (m, 20H, phenyl)
−10.0 (s br, 1H, OsꢀH
8.3 (m, 3H, Cp)
3
2083s, 2006vs, 1966w, 1940w, 1923w
17.5
1283 (1283)
7.6 (s, 5H, Cp)
7.4 (m, 10H, phenyl)
3.5 (s br, 6H, NCH3)
1.1 (s, 1H, CH)
0.8 (s, 3H, CH3)
−10.4 (s br, 1H, OsꢀH)
a In CH2Cl2 unless otherwise stated.
b In CD2Cl2.
c In CDCl3, with 1H decoupled.
d Calculated values in parentheses.

278
E.N.-M. Ho et al. / Journal of Organometallic Chemistry 637–639 (2001) 276–283
Fig. 1. The molecular structure of [Os3(m-H)(CO)8(m-h2-NO2)(m-dppf)] (2) with the atom-numbering scheme.
given in Table 1, in which all spectroscopic data are
found to be fully consistent with the solid state struc-
ture of 2. Eight terminal carbonyls are associated with
the metal core. A hydride ligand is bridged across one
of the OsꢀOs edges, with the resonance signal observed
ligand is terminally coordinated to the cluster via P(1)
,
[Os(1)ꢀP(1) 2.381(3) A] and P(2) [Os(2)ꢀP(2) 2.357(3)
,
A] and are arranged equatorially so that steric interac-
tion between the phenyl rings and adjacent CO ligands
1
at l −10.0 in its H-NMR spectrum. Solid-state IR
Table 2
spectroscopy revealed the stretching frequencies of the
coordinated NO2 group at 1478 and 1122 cm−1. This is
comparable to the values observed in the parent cluster
1 [1]. Single crystals were obtained from a saturated
CH2Cl2 solution by slow evaporation. The molecular
structure of 2 was established by X-ray analysis. Two
molecules of CH2Cl2, as solvent of crystallisation, were
revealed in the asymmetric unit. The geometry of clus-
ter 2 is presented in Fig. 1 and the pertinent bond
parameters are summarised in Table 2.
,
Selected bond lengths (A) and bond angles (°) for clusters 2 and 3
2
3
Os(1)–Os(2)
Os(1)ꢀOs(3)
Os(2)ꢀOs(3)
Os(1)ꢀP(1)
Os(1)ꢀO(9)
Os(1)ꢀN(2)
Os(2)ꢀP(1)
Os(2)ꢀP(2)
Os(2)ꢀN(1)
O(9)ꢀN(1)
O(10)ꢀN(1)
2.9314(8)
2.8732(7)
2.8676(7)
2.381(3)
2.158(8)
–
2.908(2)
2.831(2)
2.849(1)
–
2.14(2)
2.34(3)
2.359(7)
–
–
2.357(3)
2.082(9)
1.28(1)
1.23(1)
The metal framework is found to be an irregular
triangle with the Os(1)ꢀOs(2) being the longest edge
2.07(2)
1.31(3)
1.25(5)
,
[2.9314(8) A]. The hydride, the nitrite ligand and the
dppf are all bridged across this long edge. The bridging
nitrite moiety is bonded to the edge via bonds
Os(2)ꢀOs(1)ꢀOs(3)
Os(1)ꢀOs(2)ꢀOs(3)
Os(1)ꢀOs(3)ꢀOs(2)
Os(2)ꢀOs(1)ꢀP(1)
Os(2)ꢀOs(1)ꢀO(9)
Os(2)ꢀOs(1)ꢀN(2)
Os(1)ꢀOs(2)ꢀP(1)
Os(1)ꢀOs(2)ꢀP(2)
Os(1)ꢀOs(2)ꢀN(1)
Os(1)ꢀO(9)ꢀN(1)
Os(2)ꢀN(1)ꢀO(9)
Os(2)ꢀN(1)ꢀO(10)
O(9)ꢀN(1)ꢀO(10)
59.20(2)
59.39(2)
61.41(2)
121.08(8)
67.2(2)
–
59.51(4)
58.90(4)
61.59(4)
–
65.7(7)
111.1(7)
107.1(2)
–
69.5(7)
113(1)
113(1)
141(2)
107(2)
,
[Os(2)ꢀN(1) 2.082(9) and Os(1)ꢀO(9) 2.158(8) A]. The
NꢀO bond distances in the m-h2-NO2 moiety are
,
,
O(9)ꢀN(1) 1.28(1) A and O(10)ꢀN(1) 1.23(1) A. The
dihedral angle defined by the nitrite ligand and the
metal framework is 78.8°, which is significantly smaller
than that in the starting cluster 1 (102.3°) [1]. This may
be attributed to the steric interaction with the bulky
dppf substituent on cluster 2. The organic dppf moiety
is bridged across Os(1) and Os(2) and displays two
separated signals in its 31P-NMR spectrum. The dppf
–
115.45(7)
66.7(3)
109.3(6)
116.5(7)
127.4(7)
116.0(9)

E.N.-M. Ho et al. / Journal of Organometallic Chemistry 637–639 (2001) 276–283
279
Fig. 2. The molecular structure of [Os3(m-H)(CO)8(m-h2-NO2)(m-ppfa)] (3) with the atom numbering scheme.
is minimised. The two cyclopentadienyl rings are ar-
ranged in an eclipsed conformation, as confirmed by
X-ray structural determination. They are almost paral-
lel with each other, have a tilted angle of 4.7°, and
view of 3 is shown in Fig. 2. Selected intramolecular
bond distances and angles are listed in Table 2. The IR
spectrum indicates that only terminal carbonyls are
1
bonded to the metal core. The H-NMR spectrum of 3
,
distances of 1.652 and 1.650 A from their centroids to
the iron centre. The average FeꢀC (cyclopentadienyl)
exhibits a hydride signal at l −10.4, while a signal at
l 3.5 for the methyl protons of the amine group is
observed. The 31P-NMR spectrum exhibits a phospho-
rus signal at l 17.5. The stretching frequencies of the
coordinated NO2 group are found at 1481 and 1129
cm−1. The positive fast atom bombardment (FAB)
mass spectrum shows a molecular ion peak at m/z 1284,
together with daughter ions due to the sequential losses
of eight carbonyls.
distance and CꢀC bond length in the ferrocene moiety
are 2.05 and 1.42 A, respectively, which is comparable
to other compounds containing dppf. There is no sig-
nificant interaction between the Fe atom in the dppf
moiety and the osmium cluster core.
,
2.1.2. Reactions of [Os3(v-H)(CO)10(v-p2-NO2)] (1)
with ppfa
Cluster 3 crystallises in the orthorhombic space
group P212121 with four molecules in the unit cell. The
Os3(NO2) core is similar to that of cluster 2. The three
osmium atoms in cluster 3 define an irregular triangle.
The Os(1)ꢀOs(2) edge is bridged by a hydride, a bridg-
ing nitrite and the ppfa ligands. The OsꢀOs distances
observed in 3 are significantly shorter than the corre-
sponding one in 2. This is believed to be the result of
different electronic effects of the N-donor in 3 and
P-donor in 2. A similar difference has been observed for
The treatment of cluster 1 with ppfa in the presence
of Me3NO in CH2Cl2 at 40 °C resulted in a colour
change from yellow to dark red. The reaction was
monitored by IR and TLC until the complete consump-
tion of 1. The red solution was concentrated under
reduced pressure and the residue separated by TLC to
give one intensive red band. It was characterised as
[Os3(m-H)(CO)8(m-h2-NO2)(m-ppfa)] (3) in 40% yield
(Scheme 1). The spectroscopic data are given in Table
1. Single crystals of 3 suitable for X-ray analysis were
obtained from a CHCl3–n-hexane solution by slow
evaporation. The solid state structure of cluster 3 was
established by X-ray crystallography. A perspective
[Os3(m-H)(CO)10−x(m-h2-NO2)(PPh3)x], x=1,
2
in
which the disubstituted product gives longer OsꢀOs
distances [2]. The nitrite ligand is coordinated to the
osmium atoms through N(1) and O(9) atoms, and is

280
E.N.-M. Ho et al. / Journal of Organometallic Chemistry 637–639 (2001) 276–283
attached to Os(2) through a dative bond from N(1)
2.2. Electrochemistry
,
[Os(2)ꢀN(1) 2.07(2) A] and bonded to Os(1) with a s
,
bond from O(9) [Os(1)ꢀO(9) 2.14(2) A]. The NꢀO bond
Incorporation of the redox-active ferrocenyl groups
in the cluster framework may lead to interesting electro-
chemical properties as these groups are well known to
be excellent electron donors. Electronic and/or electro-
static communications between redox-active centres
have been observed in some ferrocene-containing metal
complexes and cluster compounds [18]. The electro-
chemical behaviour of clusters 1–3 has been examined
in CH2Cl2 using cyclic voltammetry, with n-tetrabutyl-
ammonium hexafluorophosphate (TBAHFP) as a sup-
porting electrolyte. The redox potential values obtained
are summarised in Table 3.
lengths in the nitrite moiety are [O(9)ꢀN(1) 1.31(3) and
O(10)ꢀN(1) 1.25(5) A], and O(9)ꢀN(1)ꢀO(10) is equal to
107(2)°. The dihedral angle between the planes defined
by the triosmium metal core and the nitrite moiety is
78.3°. The ppfa ligand bridges across the Os(1) and
Os(2) edge with N(2) [Os(1)ꢀN(2) 2.34(3) A] and P(1)
[Os(2)ꢀP(1) 2.359(7) A] atoms. The general structural
features of the ferrocene unit of 3 is very similar to that
of 2: the average FeꢀC (cyclopentadienyl) bond length
is 2.00 A, and the average CꢀC bond distance is 1.39 A.
The eclipsed nature of the rings is established by struc-
tural analysis and they are found to have distances of
,
,
,
,
,
Cluster anion [Os3(CO)10(m-h2-NO2)]− displays two
irreversible reductions at −2.23 and −2.73 V at a
scan rate of 100 mV s−1. It is believed that the metal
core of the cluster is reduced to give the 49e− species
[Os3(CO)10(NO2)]2−, and then further reduced to give
the 50e− species [Os3(CO)10(NO2)]3−, both being very
unstable. The first oxidation at 0.08 V corresponds to
the oxidation of the triosmium core to give the 47e−
species [Os3(CO)10(NO2)] and the second one is as-
signed to the further oxidation of these 47e− species to
give the 46e− species [Os3(CO)10(NO2)]+. The proto-
nated derivative of [Os3(CO)10(m-h2-NO2)]−, cluster 1,
exhibits two irreversible reductions at −1.73 and
−2.17 V and these potentials are significantly increased
as compared to the corresponding potentials of
[Os3(CO)10(m-h2-NO2)]− (−2.23 and −2.73 V). These
redox couples are metal-oriented, as there are great
differences between the anionic metal complex and the
neutral metal complex. The Os3(NO2) core of cluster 1
is electron deficient as compared with that of the an-
ionic cluster [Os3(CO)10(m-h2-NO2)]−. As a result, the
reduction process in [Os3(CO)10(m-h2-NO2)]− is less fa-
vourable and the reduction potentials are shifted to a
more negative region. The irreversible oxidation of 1 is
assigned to the oxidation of the triosmium core to form
the 47e− species [Os3(H)(CO)10(NO2)]+. Cluster 2 con-
tains an electroactive dppf ligand and the intramolecu-
lar redox reactivity is useful for investigating the
electrochemical properties of the triosmium nitrite clus-
ter. The cyclic voltammogram of 2 exhibits a quasi-re-
,
1.633 and 1.587 A from their centroids to the iron
atom. The ferrocenyl cyclopentadienyl (Cp) rings are
not parallel with respect to each other (dihedral angle,
12.3°). The asymmetrically bridging nitrite ligand leads
to differences in strength of back p bonding to their
adjacent carbonyl groups, which in turn, affects the
ease of substitution of these CO groups. We have
isolated just one isomer with the phosphine P atom
bonded to Os(2) and the nitrite N(2) atom coordinated,
from the reaction between cluster 1 and ppfa. The site
selectivity observed in this case may be due to the
combined effect of difference in donor capacity between
P and N and the electronic imbalance between two
osmium centres. The more electron-accepting phos-
phine fragment appears to prefer Os(2), which has a
dative bond from N(1) and is more electron rich, whilst
the amine nitrogen substituted the carbonyl on Os(1) to
where O(9) s-bonded. Although these results are con-
sistent with the previous studies with functionalised
phosphine and amine ligands [2,3], we could not rule
out the possibility of formation of the other isomers in
minute quantity.
Table 3
Electrochemical data a for compounds 1–3
Cluster
Oxidation
Reduction
Epa2 (V) b Epa1 (V) b Epc1 (V) b Epc2 (V) b
versible oxidation wave at
E1/2=0.61 V versus
[Os3(CO)10
-
0.96
0.08
−2.23
−2.73
(m-h2-NO2)]−
Ag ꢀ AgNO3 in acetonitrile. It is likely that this anodic
wave is dppf-based in nature, as it occurs at a similar
potential as the free dppf ligand (E1/2=0.55 V). In this
context, it is evident that the ferrocene–ferrocenium
couple in 2 is subjected to minor electronic influence
imposed by the triosmium nitrite cluster unit. In addi-
tion, cluster 2 displays an irreversible reduction at
−2.03 V that is assigned to the reduction of the
triosmium core, to form the 49e− species
[Os3(H)(CO)8(NO2)(dppf)]−, which exhibits a cathodic
shift of 0.30 V. Cluster 3 also contains an electrochem-
1
2
3
–
–
–
0.78
−1.73
−2.03
−2.15
−2.17
–
–
(0.61) c
(0.33) c
a ꢀ10−3 M cluster in 0.1 M TBAHFP in acetonitrile at 298 K, the
working electrode was a glassy carbon electrode, the auxiliary elec-
trode and the reference electrode were
a platinum wire and
Ag ꢀ AgNO3, respectively. Scan rate was 100 mV s−1. The potentials
are referenced to the Ag ꢀ AgNO3 (0 V) under the same conditions,
calibrated with ferrocene.
b Epa and Epc are the anodic and cathodic potentials, respectively.
c Values in parentheses is E1/2, half-wave potential values.

E.N.-M. Ho et al. / Journal of Organometallic Chemistry 637–639 (2001) 276–283
281
ically active ligand, ppfa. The redox property of 3 is
3.2. Reaction of [Os3(v-H)(CO)10(v-p2-NO2)] (1) with
dppf
very similar to that of 2. In cluster 3, the ppfa moiety
gives a ferrocene–ferrocenium quasi-reversible process
at 0.33 V that is similar to that of a free ppfa ligand
(E1/2=0.24 V). Cluster 3 also displays an irreversible
reduction at −2.15 V that is assigned to the reduc-
tion of the metal core to give the one-electron re-
duced species [Os3(H)(CO)8(NO2)(ppfa)]−. Since the
amine group is a better s-donor than the phosphine
fragment, the coordination of such a good s-donor in
1 would raise both the HOMO and the LUMO ener-
gies by an inductive effect; thus reduction would be
more difficult and oxidation becomes easier than in
cluster 2. We therefore assign the one-electron reduc-
tion of 2 and 3 as primarily cluster-based and the
oxidation as primarily dppf- or ppfa-based. These re-
sults show that the cluster and ferrocenyl phosphine
moieties are more difficult to reduce and oxidise, re-
spectively, than in the parent cluster 1 and free dppf
and ppfa. It is suggested that there is a slight interac-
tion between the ferrocene and the cluster cage fron-
tier orbitals. It is likely that the HOMO is solely
ferrocene-based, while the LUMO is primarily cage-
based with a significant ferrocene admixture which
results in its more difficult reduction.
A solution of 1 (50 mg, 0.055 mmol) in 30 cm3
CH2Cl2 was treated with dppf (30.5 mg, 0.055 mmol)
and Me3NO (6 mg, 0.066 mmol) at r.t. for 12 h. The
red solution was concentrated under reduced pressure.
Separation of the residue by TLC, with CH2Cl2–n-
hexane (1:1, v/v) as eluent, yielded one intense red
band (Rf 0.45). It was characterised as cluster [Os3(m-
H)(CO)8(m-h2-NO2)(m-dppf)] (2) and recrystallised
from a CH2Cl2 solution by slow evaporation to give
red, block crystals (36 mg, 46%). (Anal. Found: C,
36.4; H, 2.2; N, 1.1; P, 4.6. Calc. for C42
H29NO10P2FeOs3 2: C, 36.12; H, 2.08; N, 1.00; P,
4.44%).
3.3. Reactions of [Os3(v-H)(CO)10(v-p2-NO2)] 1 with
ppfa
Solid of 1 (50 mg, 0.055 mmol) was reacted with
ppfa (25 mg, 0.056 mmol) and Me3NO (6 mg, 0.066
mmol) in 30 cm3 CH2Cl2 at 40 °C for 4 h. The sol-
vent was removed under reduced pressure, the red
residue was dissolved in a minimum amount of
CH2Cl2 and chromatographed on silica. Elution with
CH2Cl2–n-hexane (4:6, v/v) gave a major orange
band (Rf 0.35). It was characterised as cluster [Os3(m-
H)(CO)8(m-h2-NO2)(m-ppfa)] (3). Cluster 3 was recrys-
tallised from a CHCl3–n-hexane solution to give red
crystals (28 mg, 40%). (Anal. Found: C, 31.6; H, 2.4;
N, 1.2; P, 2.4. Calc. for C34H29N2O10PFeOs3 3: C,
31.82; H, 2.26; N, 1.09; P, 2.42%)
3. Experimental
3.1. General procedures
All reactions and manipulations were carried out
under Ar using standard Schlenk techniques, except
for the chromatographic separations. Solvents were
purified by standard procedures and distilled prior to
use. [Os3(m-H)(CO)10(m-h2-NO2)] (1) was prepared ac-
cording to the reported method [1]. All chemicals,
unless otherwise stated, were purchased commercially
and used as received. Reactions were monitored by
IR spectroscopy and analytical thin-layer chromatog-
raphy (Merck Kieselgel 60 F254) and the products
were separated by thin-layer chromatography on
plates coated with silica (Merck Kieselgel 60 GF254).
Infrared spectra were recorded on a Bio-Rad FTS-7
IR spectrometer, using 0.5 mm CaF2 solution cells.
1H-NMR spectra were recorded on a Bruker DPX300
NMR spectrometer using CD2Cl2 and referenced to
3.4. Electrochemical studies
Electrochemical measurements were carried out by
using EG&G Princeton Applied Research (PAR)
Model 273A potentiostat/galvanostat connected to an
interfaced computer employing PAR 270 electrochem-
ical software. Cyclic voltammograms were obtained
at r.t. with a gas sealed (Ar) two compartment
cell, equipped with a glassy carbon working elec-
trode (Bioanalytical), platinum wire auxiliary
(Aldrich) and Ag ꢀ AgNO3 reference (Bioanalytical)
electrodes. n-Tetrabutylammonium hexafluorophos-
phate (TBAHFP), 0.1 mol dm−3, in anhydrous de-
SiMe4 (l=0), 31P-NMR spectra on
a
Bruker
oxygenated MeCN was used as
a
supporting
DPX500 NMR spectrometer using CDCl3 solvent
with 85% H3PO4 as a reference. Positive ionisation
FAB mass spectra were recorded on a Finnigan MAT
95 mass spectrometer, using m-nitrobenzyl alcohol or
a-thioglycerol as matrix solvents. Microanalyses were
performed on thoroughly dried samples by Butter-
worth Laboratories, UK.
electrolyte. Ferrocene was added at the end of each
experiment as an internal standard [19]. Potential
data (vs. Ag ꢀ AgNO3) were checked against the fer-
rocene (0/+1) couple; under the actual experimental
conditions the ferrocene–ferrocenium couple is lo-
cated at −0.14 V in MeCN.

282
E.N.-M. Ho et al. / Journal of Organometallic Chemistry 637–639 (2001) 276–283
Table 4
the Flack parameter [0.0027(3)]. Calculations were per-
formed on a Silicon-Graphics computer, using the pro-
gram package TEXSAN [24].
Crystal data and data collection parameters for compounds 2, 3
2·2CH2Cl2
3
Empirical formula
C44H33NO10P2-
Cl4FeOs3
C34H29N2O10P-
FeOs3
Formula weight
Crystal system
Space group
1565.95
1283.03
4. Supplementary material
Monoclinic
P21/n (c14)
Orthorhombic
P212121 (c19)
Crystallographic data (excluding structure factors)
for the structural analysis have been deposited with the
Cambridge Crystallographic Data Centre, CCDC nos.
154816 and 154817 for complexes 2 and 3. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Unit cell dimensions
,
a (A)
16.957(2)
11.979(1)
24.687(2)
10.072(1)
15.909(2)
22.742(2)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
103.06(2)
3
,
U (A )
Z
4885.0(9)
4
2.129
84.04
Red, block
0.25×0.26×0.33 0.19×0.23×0.24
6884
4618
3644.1(6)
4
2.338
109.12
Red, block
Dcalc (g cm−3
)
v (Mo–Ka) (cm−1
)
Crystal colour, habit
Crystal size (mm)
Unique reflections
Observed reflections
[F\3|(F)]
Acknowledgements
3544
2578
We gratefully acknowledge financial support from
the Hong Kong Research Grants Council and the
University of Hong Kong. B.K.-M. Hui acknowledges
the receipt of a postgraduate studentship, administered
by the University of Hong Kong.
R
R%
0.036
0.040
1.68
0.052
0.061
1.72
Goodness-of-fit (S)
3.5. Crystallography
References
Crystals suitable for X-ray analyses were glued on
glass fibres with epoxy resin or sealed in 0.3 mm glass
capillaries. Intensity data were collected at ambient
temperatures either on an Enraf–Nonius CAD4 dif-
fractometer (complex 2) or on a MAR research image
plate scanner (complex 3) equipped with graphite-
[1] B.K.-M. Hui, W.-T. Wong, J. Chem. Soc. Dalton Trans. (1996)
2177.
[2] B.K.-M. Hui, W.-T. Wong, J. Chem. Soc. Dalton Trans. (1998)
447.
[3] B.K.-M. Hui, W.-T. Wong, J. Chem. Soc. Dalton Trans. (1998)
3977.
,
monochromated Mo–Ka radiation (u=0.710 73 A)
[4] C. Kollmar, M. Couty, O. Kahn, J. Am. Chem. Soc. 113 (1991)
7994.
using ꢀꢀ2q and ꢀ scan types. Details of the intensity
data collection and crystal data are given in Table 4.
The diffracted intensities were corrected for Lorentz
and polarisation effects. The c scan method was em-
ployed for semi-empirical absorption corrections for 2
[20], however, an approximation to absorption correc-
tion by inter-image scaling was applied for 3. Scattering
factors were taken from Ref. 21a and anomalous dis-
persion effects [21b] were included in Fc. The structures
were solved by direct methods (SIR88 [22] for 2 and
SIR92 [23] for 3) and expanded by Fourier-difference
techniques. Atomic coordinates and thermal parameters
were refined by full-matrix least-squares analysis on F,
with the osmium, iron, phosphorus and chlorine atoms
being refined anisotropically. The metal hydride was
located by Fourier-difference synthesis based on low
angle data and analysis of CO ligands distribution
while those of the organic moieties were generated in
[5] J.S. Millarm, A.J. Epstein, Angew. Chem. Int. Ed. Engl. 33
(1994) 385.
[6] R.W. Wagner, P.A. Brown, T.E. Johnson, J.S. Lindsey, J. Chem.
Soc. Chem. Commun. (1991) 1463.
[7] E.C. Constable, Angew. Chem. Int. Ed. Engl. 30 (1991) 407.
[8] P.D. Beer, Z. Chen, M.G.B. Drew, A.J. Pilgrim, Inorg. Chim.
Acta 225 (1994) 137.
[9] I.R. Butler, Organometallic Chemistry, in: E.W. Abel (Ed.),
Specialist Periodic Reports 21, Royal Society of Chemistry,
Letchworth, UK, 1992, p. 338.
[10] A. Togni, T. Hayashi (Eds.), Ferrocenes, VCH, Weinheim, 1995.
[11] S.T. Chacon, W.R. Cullen, M.I. Bruce, O.B. Shawkataly,
F.W.B. Einstein, R.H. Jones, A.C. Willis, Can. J. Chem. 68
(1990) 2001.
[12] F.G. Torre, F.A. Jalo´n, A. Lo´pez-Agenjo, B.R. Manzano, A.
Rodr´ıguez, Organometallics 17 (1998) 4634.
[13] A.J. Blake, A. Harrison, B.F.G. Johnson, E.J.L. Mclnnes, S.
Parsons, D.S. Shephard, L.J. Yellowlees, Organometallics 14
(1995) 2160.
[14] S. Onaka, T. Moriya, S. Takagi, A. Mizuno, H. Furuta, Bull.
Chem. Soc. Jpn. 65 (1992) 1415.
[15] A. Mernyi, C. Kratky, W. Weissensteiner, M. Widhalm, J.
Organomet. Chem. 508 (1996) 209.
,
their ideal positions (CꢀH 0.95 A). The absolute
configuration of cluster 3 was established by refining

E.N.-M. Ho et al. / Journal of Organometallic Chemistry 637–639 (2001) 276–283
283
[16] H. Brunner, W. Zettlmeier, Handbook of Enantioselective Catal-
ysis with Transition Metal Compounds, VCH, Weinheim, 1993.
[17] M. Sawamura, Y. Ito, Chem. Rev. 92 (1992) 857.
[18] W.-Y. Wong, K.-K. Cheung, W.-T. Wong, J. Chem. Soc. Dalton
Trans. (1995) 1379.
[19] G. Gritzner, J. Kute, Pure Appl. Chem. 56 (1984) 461.
[20] A.C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystallogr.
Sect. A 24 (1968) 351.
(b) D.T. Cromer, J.T. Waber, Table 2.3.1, International Tables
for X-Ray Crystallography, Kynoch Press, Birmingham, vol. 4,
1974.
[22] M.C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, G.
Polidori, R. Spagna, D. Viterbo, J. Appl. Crystallogr. 22 (1989)
389.
[23] A. Altomare, M.C. Burla, M. Camalli, M. Cascarano, C. Giaco-
vazzo, A. Guagliardi, G. Polidori, J. Appl. Crystallogr. 25 (1992)
210.
[21] (a) D.T. Cromer, J.T. Waber, Table 2.2B, International Tables
for X-Ray Crystallography, Kynoch Press, Birmingham, vol. 4,
1974;
[24] TEXSAN, Crystal Structure Analysis Package, Molecular Struc-
ture Corporation, Houston, TX, 1985 and 1992.