Synthesis and characterisation of phosphane-substituted Co3C clusters having a pendant allyl side-chain

Article abstract of DOI:10.1016/j.jorganchem.2004.03.036

Substituted μ₃-carbido-capped tricobalt carbonyl clusters have been synthesised by reaction of [Co₃(μ₃-C(O)OCH₂ CH=CH₂)(CO)₉] with a range of monodentate and chelating phosphane ligands. The products have been characterised by microanalysis, IR and NMR spectroscopy, mass spectrometry and, in the case of [Co₃(μ₃-CR)(CO)₇(dppe)], [Co₃(μ₃-CR)(CO)₇(dppm)], [Co₃(μ₃-CR)(CO)₇(PPh₃) ₂], [Co₃(μ₃-CR)(CO)₇ (PMe₃)₂] and [Co₃(μ₃-CR) (CO)₆(PEt₃)₃] (R=C(O)OCH₂CH=CH₂), single crystal X-ray diffraction.

Full text of DOI:10.1016/j.jorganchem.2004.03.036

Journal of Organometallic Chemistry 689 (2004) 2103–2113
www.elsevier.com/locate/jorganchem
Synthesis and characterisation of phosphane-substituted Co3C
clusters having a pendant allyl side-chain
a
a,
a
b
Steven J. Black , Christopher P. Morley *, Alun E. Owen , Mark R.J. Elsegood
a
Department of Chemistry, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK
b
Chemistry Department, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK
Received 3 November 2003; accepted 11 March 2004
Abstract
Substituted l3-carbido-capped tricobalt carbonyl clusters have been synthesised by reaction of [Co3(l3-C(O)OCH2CH@CH2)-
(CO)9] with a range of monodentate and chelating phosphane ligands. The products have been characterised by microanalysis, IR
and NMR spectroscopy, mass spectrometry and, in the case of [Co3(l3-CR)(CO)7(dppe)], [Co3(l3-CR)(CO)7(dppm)], [Co3(l3-
CR)(CO)7(PPh3)2], [Co3(l3-CR)(CO)7(PMe3)2] and [Co3(l3-CR)(CO)6(PEt3)3] (R ¼ C(O)OCH2CH@CH2), single crystal X-ray
diffraction.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Clusters; Cobalt; Phosphanes; X-ray crystallography
1. Introduction
phanes are also useful in allowing electron density
‘‘tuning’’ within the core of the cluster to further en-
hance and direct reactivity.
Supported metal cluster units, whether as discrete
particles or as organised carbonyl/organometallic as-
semblies, are among the most important classes of cat-
alysts in an industrial sense [1]. The ability of transition
metal carbonyl clusters to catalyse a wide variety of
reactions has been known for many years [2–4]. More
specifically, there are several examples of l3-alkylidyne
tricobalt carbonyl clusters acting as catalysts [5,6], es-
pecially those substituted derivatives with phosphane
ligands present [7,8]. However, there are problems as-
sociated with the use of late transition metal clusters as
catalysts, mainly in the recovery and identification of the
catalytically active cluster species [9,10], since clusters
often have activity arising through decomposition to a
mononuclear species such as [CoH(CO)4] [11,12]. The
problem of decomposition can be overcome by using a
capping ligand on the cluster and chelating phosphanes
to effectively support the metal atoms within the cluster
and thereby prevent core fragmentation. The phos-
To this end we have met with success in developing
systematic syntheses of a range of cobalt clusters with
both monodentate and chelating phosphane ligands.
These compounds all incorporate a capping moiety
terminating in an unsaturated organic functionality
suitable for linking these clusters to a range of solid
supports.
Our starting point has been the work on l3-alkyli-
dyne tricobalt clusters done by Seyferth et al. [13] who,
some decades ago, reported the action of a 2–3 molar
excess of aluminium halide AlX3 (X ¼ Cl, Br, I) on
halomethylidyne tricobalt nonacarbonyl complexes
[Co3(l3-CX)(CO)9] (X ¼ Cl, Br) [14,15]. This reaction
resulted in the formation of the acylium haloaluminate
salt [Co3(l3-CCO)(CO)9]þ[AlX4]ꢀ even when the reac-
tion was carried out under an inert atmosphere. In
contrast with conventional acylium ions, this cation is
indefinitely stable under anhydrous conditions. The
haloaluminate salt can react with a range of nucleo-
philes to produce clusters of the type [Co3(l3-
CC(O)Y)(CO)9] with Y ¼ OR, OAr, NRR0, SR, R, Ar,
H, etc.
* Corresponding author. Tel.: +44-1792-295273; fax: +44-1792-
295747.
E-mail address: c.p.morley@swan.ac.uk (C.P. Morley).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.03.036

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S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
2. Results and discussion
Using a method based on that of Seyferth et al., the
cluster, [Co3(l3-CC(O)OCH2CH@CH2)(CO)9] (1), was
prepared successfully from [Co3(l3-CCl)(CO)9] [16] and
allyl alcohol in high yield (Scheme 1) [14]. Phosphane
derivatives 2–8 were synthesised by stirring a solution of
1 with the required phosphane at room temperature
(Scheme 2).
There seems to be a paucity of examples in the litera-
ture of clusters being produced via ambient temperature
reaction, with electrochemical or thermal methods being
much more commonly utilised [17]. However, no appar-
ent disadvantage was detected using ambient temperature
reaction. All the reactions produced an identical colour
change from purple to dark green. The products were
isolated by column chromatography and further purified
by recrystallisation if appropriate. Greatest yields were
obtained when stirring was continued for between 4 and
18 h, depending on the phosphane in question.
Fig. 1. X-ray crystal structure of [Co3(l3-CC(O)OCH2-CH@CH2)-
(CO)7(dppe)] (2).
In most cases, a single product was isolated, corre-
sponding to replacement of two of the carbonyl ligands
in 1 by the phosphane. Steric factors may be assumed to
play a key role in inhibiting further substitution. It is
therefore intriguing that a trisubstituted cluster was
obtained as the major product of the reaction with tri-
ethylphosphane. At present we have no explanation for
this apparent anomaly.
The molecular structure of 2 (Fig. 1) shows that the
dppe ligand binds in a bridging mode rather than che-
lating to a single cobalt atom and that it adopts an
equatorial configuration in the solid state. There are
several other examples of bidentate phosphane ligands
bridging two metal centres in this manner [17–19]. The
two cobalt atoms bonded to the phosphane ligand.
Downard et al. [17] have described this type of apical
carbon as adopting a ‘‘semicapping orientation’’ with
respect to the three cobalt atoms. The displacement can
be explained in terms of electronic effects. Greater
electron density will be localised on the cluster arising
from substitution of carbon monoxide with phos-
phane ligands, the latter’s ability as a better r-donor and
worse p-acceptor voluminously documented. However,
the equatorially coordinated dppe ligand prevents the
adoption of a carbonyl-bridged structure to dissipate the
increased electron density on the cluster core. In this
case, electron density can be dissipated through the in-
teraction of appropriate p-orbitals of the apical carbon
and orbitals of Co(1) and Co(2) [17]. Thus the observed
‘‘semicapping orientation’’ is assumed.
ꢀ
dppe-bridged Co–Co bond (2.5179(9) A) is somewhat
longer than the other two Co–Co bonds with bond
ꢀ
lengths of 2.4706(9) and 2.4801(10) A (Table 1). This
phenomenon has been observed previously in dppm-
bridged cobalt clusters, with the bond lengthening be-
lieved to be a consequence of the bonding requirements
of the bridging ligand [17]. Cobalt-capping carbon bond
The bond lengths and angles in the capping moiety of 2
are comparable to those in its parent analogue [15], 1,
except for two parameters: the lengthening of the C(1)–
ꢀ
ꢀ
lengths of 1.939(5), 1.893(5) and 1.881(5) A (Table 1)
C(2) bond from 1.479(5) to 1.506(6) A, and the elonga-
ꢀ
ꢀ
clearly show a lengthening of the Co-capping carbon
bond opposite the phosphane ligand. This indicates that
the l3-capping (apical) carbon in 2 ‘‘leans’’ towards the
tion of C(3)–C(4) to 1.504(9) A (cf. 1.471(5) A). Selected
bond lengths and angles of the structure are listed in
Tables 1 and 2.
The spectroscopic information suggests that the
structure of 2 in solution is identical to that in the solid
state. The infrared spectrum of 2 (Table 3) contains five
bands corresponding to terminal carbonyl absorptions,
with no evidence for the existence of an isomer con-
taining bridging carbonyls. Mass spectrometry (Table
3), in addition to confirming the molecular ion, shows
sequential loss of carbonyl ligands. This is a character-
istic feature in the mass spectra of carbonyl clusters and
is observed for all the clusters described herein. The
NMR data (Tables 4–6) are as expected.
Scheme 1. Preparation of [Co3(l3-CC(O)OCH2CH@CH2)(CO)9] (1).

S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
2105
Scheme 2. Products obtained from the reactions of 1 with phosphanes (R ¼ C(O)OCH2CH@CH2).
Table 1
Selected bond lengths (A) for 2, 3, 5, 6 and 7
ꢀ
2
3
5a
50a
6
7
Co(1)–Co(2)
Co(2)–Co(3)
Co(1)–Co(3)
Co(1)–C(1)
Co(2)–C(1)
Co(3)–C(1)
C(1)–C(2)
C(2)–O(1)
C(2)–O(2)
O(2)–C(3)
C(3)–C(4)
C(4)–C(5)
Co(1)–P(1)
Co(2)–P(2)
Co(3)–P(3)
2.5179(9)
2.4801(10)
2.4706(9)
1.893(5)
1.881(5)
1.939(5)
1.506(6)
1.201(6)
1.328(6)
1.452(6)
1.504(9)
1.301(10)
2.2130(14)
2.2037(14)
–
2.5030(4)
2.4814(4)
2.4712(4)
1.8902(18)
1.8936(18)
1.9323(17)
1.478(3)
1.211(2)
1.354(2)
1.454(3)
1.478(4)
1.311(4)
2.2023(5)
2.2198(5)
–
2.4975(12)
2.4854(11)
2.4953(11)
1.942(7)
1.839(7)
1.907(6)
1.472(9)
1.172(9)
1.359(12)
1.514(14)
1.529(19)
1.12(2)
2.4962(10)
2.4953(10)
2.5061(10)
1.892(5)
1.918(5)
1.895(5)
1.486(7)
1.201(6)
1.353(7)
1.453(6)
1.507(12)
1.129(16)
2.2403(16)
2.2456(14)
–
2.4834(3)
2.4782(3)
2.4947(3)
1.8914(17)
1.8904(17)
1.9102(17)
1.472(2)
1.217(2)
1.347(2)
1.451(2)
1.479(3)
1.279(3)
2.2096(5)
2.2208(6)
–
2.418(2)
2.486(2)
2.491(3)
1.904(13)
1.898(14)
1.968(13)
1.463(18)
1.217(17)
1.298(19)
1.437(19)
1.33(3)
1.34(3)
2.2504(16)
2.2381(18)
–
2.198(4)
2.211(4)
2.259(4)
a 5 and 50 refer to the two cobalt clusters in the asymmetric unit.
Table 2
Selected bond angles (o) for 2, 3, 5, 6 and 7
2
3
5a
50a
6
7
Co(1)–Co(2)–Co(3)
Co(2)–Co(1)–Co(3)
Co(2)–Co(3)–Co(1)
Co(1)–C(1)–Co(2)
Co(1)–C(1)–Co(3)
Co(2)–C(1)–Co(3)
Co(1)–C(1)–C(2)
Co(2)–C(1)–C(2)
Co(3)–C(1)–C(2)
C(1)–C(2)–O(1)
O(1)–C(2)–O(2)
C(1)–C(2)–O(2)
C(2)–O(2)–C(3)
O(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(1)–Co(1)–P(1)
C(1)–Co(2)–P(2)
C(1)–Co(3)–P(3)
59.24(3)
59.61(3)
61.14(3)
83.71(18)
80.29(19)
80.94(18)
131.8(4)
135.7(4)
124.4(3)
123.9(5)
123.9(5)
112.3(4)
115.5(4)
107.3(5)
124.5(7)
110.56(15)
106.47(15)
–
59.442(12)
59.844(11)
60.715(10)
82.83(7)
60.10(3)
60.27(3)
60.371(9)
61.05(7)
60.83(7)
58.12(7)
79.0(5)
59.71(3)
60.19(3)
82.6(3)
59.85(3)
59.88(3)
81.87(19)
82.9(2)
59.712(9)
59.917(9)
82.09(6)
80.55(7)
80.86(7)
80.8(2)
83.1(3)
82.02(7)
81.39(7)
80.1(5)
80.0(5)
81.75(19)
134.9(4)
128.8(4)
127.9(4)
126.2(5)
122.2(5)
111.6(4)
116.9(5)
105.6(6)
131.8(15)
126.84(16)
113.14(15)
–
132.01(13)
131.31(13)
130.01(13)
125.16(18)
122.04(17)
112.80(16)
117.19(17)
112.9(2)
129.7(7)
132.9(6)
129.1(6)
129.7(8)
119.6(7)
110.3(7)
114.6(10)
100.1(13)
120(3)
128.95(13)
131.64(12)
131.97(12)
125.41(17)
121.83(17)
112.76(14)
115.00(14)
109.05(16)
127.4(2)
131.5(10)
132.6(11)
132.7(11)
119.9(14)
120.8(13)
119.2(12)
118.6(13)
116(2)
127.2(2)
131(2)
104.10(5)
104.07(5)
–
119.65(18)
119.5(2)
–
105.55(5)
97.92(5)
100.8(4)
102.7(4)
162.8(4)
–
a 5 and 50 refer to the two cobalt clusters in the asymmetric unit.

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S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
Table 3
Infrared and FAB mass spectrometry data
Compound
m(CO)a
Mass spectrometryb
2
3
4
5
6
7
8
2065 (s), 2014 (s), 2010 (vs), 1998 (m), 1978 (w)
2067 (m), 2016(vs, br), 1975(sh)
2029 (m), 1994 (s), 1976 (s), 1944 (sh)
868 [Mþ]
877 [Mþ + Na], 855 [Mþ + H]
1170 [Mþ ) 2CO]
2083 (w), 2055 (vs), 2029 (w), 1999 (w), 1970 (m)
2053 (s), 2000 (vs), 1962 (sh), 1950 (w), 1911 (w)
2050 (m), 1998 (s), 1977 (vs), 1806 (m), 1740 (w), 1700 (vw)
2062 (m), 2012 (vs), 1994 (s), 1981 (w), 1975 (vw)
995 [Mþ + H]
645 [Mþ + Na], 623 [Mþ + H], 622 [Mþ]
796 [Mþ]
729 [Mþ + Na], 707 [Mþ + H]
a Absorption maxima in cmꢀ1. Abbreviations used: vs, very strong; s, strong; m, medium; w, weak; vw, very weak and sh, shoulder.
b m=z values and assignments of molecular ion peaks. All compounds also exhibited fragment ion peaks due to sequential loss of carbonyl ligands.
Table 4
1H NMR dataa
2
3
4
5
6
7
8
CH3
CH2
–
1.94–2.34
–
–
–
–
1.42–1.46e
–
0.8–1.2
1.5–1.9
0.92–1.14
1.61–1.83
3.30–3.45d
4.39–4.54d
3.30–3.45d
4.11–4.26d
3.25–3.65
3.99–4.09
4.85–4.98
5.02–5.07
5.48–5.60
6.93–7.74
b
Hd
Hb
3.98–4.11
4.85–4.95
5.05–5.10
5.53–5.76
7.02–7.69
4.49–4.59
5.03–5.11
5.17–5.26
5.70–5.84
6.95–7.44
4.31–4.48
4.95–5.05
5.15–5.32
5.72–5.96
7.10–7.64
4.57–4.60
5.17–5.21
5.29–5.38
5.87–6.01
–
4.6–4.7
5.0–5.2
5.27–5.41
5.73–5.98
–
4.49–4.62
5.06–5.18
5.23–5.34
5.83–5.97
–
b;c
b;c
Hc
Ha
b;c
Ph
a Chemical shifts (d) in ppm.
b For key to assignments see Fig. 7.
c For all compounds: J(Hb–Ha) ¼ 10.8 Hz; J(Hc–Ha) ¼ 18.3 Hz.
d
2J(1H–31P) ꢁ J(1H–1H) ꢁ 14.6Hz.
e J(1H–31P) ¼ 9.2 Hz.
Table 5
13C NMR dataa
2
3
4
5
6
7
8
PCH3
PCH2
–
–
–
–
–
19.7h
–
8.1
18.8i, 20.9j
66.0
6.8
23.4c
64.5
39.7f
64.6
32.4, 38.1g
64.6
19.5j
64.6
116.5
132.1
–
b
C3
C5
66.0
66.0
118.3
133.3
–
N.O.d
N.O.d
b
116.2
N.O.d;e
127.4–136.6
181.3
205.0
116.1
N.O.d;e
126.9–136.1
182.7
N.O.d
116.1
117.3
117.4
132.3
–
N.O.d
N.O.d
b
C4
Ph
N.O.d;e
126.4–137.1
183.6
N.O.d;e
128.5–135.0
N.O.d
b
C1
CO
181.1
207.8
N.O.d
205.4
a Chemical shifts (d) in ppm.
b For key to assignments see Fig. 7.
c
1J(13C–31P) ¼ 26.0 Hz.
d N.O. ¼ Not observed.
e Signal obscured by phenyl resonances.
f
1J(13C–31P) ¼ 23.1 Hz.
g
1J(13C–31P) ¼ 22.2 Hz.
h
1J(13C–31P) ¼ 27.7 Hz.
i
1J(13C–31P) ¼ 22.1 Hz.
j
1J(13C–31P) ¼ 23.3 Hz.
The structure of 3 (Fig. 2), a dppm-bridged product,
has much in common with the dppe-bridged product
discussed above. Selected bond lengths and angles are
listed in Tables 1 and 2. The Co–Co bond bridged by the
extent than in 2, compared to the other two Co–Co
ꢀ
bonds (ave. 2.4763(4) A). The alkylidyne carbon also
exhibits the expected ‘‘semicapping orientation,’’ leaning
towards the phosphane bridged Co–Co bond despite the
steric congestion. Each phosphorus atom of the dppm
ꢀ
dppm is lengthened (2.5030(4) A), although to a lesser

S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
2107
Table 6
31P NMR data
Compound
2
3
4
5
6
7
8
d (ppm)
47.3
33.3
22.1a
32.9b
37.9
45.4
2.9
33.2
33.7
a
2J(31P–31P) ¼ 31 Hz.
3J(31P–31P) ¼ 43 Hz.
b
which it is bound, are not observed. This is the case with
the 13C NMR spectra recorded for many of the new
compounds reported here. The 31P NMR spectrum
contains a single resonance at 33.3 ppm, indicating that
the two phosphorus atoms of dppm are equivalent.
After the isolation of 3, a further three bands were
eluted from the column, which were either pale brown or
pale green. Evaporation of the solvent under reduced
pressure in each case yielded only traces of material. Fi-
nally, a dark green band was eluted. After solvent re-
moval, again under reduced pressure, a dark green oily
residue was isolated, which had a 31P NMR spectrum
containing six resonances, at 37.9 (br), 32.9 (br), 29.3 (d),
25.0, 22.1 (d) and )28.4 (d) ppm. The doublets at 29.3 and
)28.4 ppm with J(31P–31P) ꢁ 50 Hz may be assigned
to the presence of dppm monoxide, Ph2PCH2P(O)Ph2
[22]. Traces of dppm dioxide, Ph2P(O)CH2P(O)Ph2, are
revealed by the peak at 25.0 ppm [23].
Dissolving the dark green oily solid in dichlorome-
thane and adding hexane precipitated 4, the compound
responsible for the other three resonances in the 31P
NMR spectrum. Attempts to crystallise 4 under a vari-
ety of conditions were unsuccessful, but on the basis of
mass spectrometry, NMR and infrared spectroscopy
(Tables 3–6) it has been characterised as [Co3(l3-
CC(O)OCH2CH@CH2)(CO)6(l2-dppm)(Ph2PCH2P(O)-
Ph2)].
The mass spectrum of 4 supports the postulate that a
higher mass cluster, i.e., more highly substituted than 3,
has been produced. Although it does not contain a peak
corresponding to [Mþ], one corresponding to
[Mþ ) 2CO] is observed. The 31P resonance at 32.9 ppm
may be assigned to a dppm-ligand bridging two cobalt
atoms, by substituting two equatorial carbonyls, as in 3.
All the carbonyl ligands must be terminally bonded, as
they are precluded from adopting a bridging configu-
ration by the bridging phosphane ligand. The absence of
bridging carbonyls was confirmed by the infrared spec-
trum. The 31P NMR signals at 37.9 and 22.1 ppm are in
the range expected for a coordinated phosphane and a
phosphoryl group, Ph2P@O, respectively, implying that
a dppm monoxide ligand is present, acting as a
monodentate ligand via the phosphorus(III) atom. This
supposition is supported by the observation in the in-
frared spectrum of 4 of a very strong absorption at 1270
cmꢀ1 which is in the range reported for the P@O group.
Fig. 2. X-ray crystal structure of [Co3(l3-CC(O)OCH2CH@CH2)-
(CO)7(dppm)] (3).
ligand binds equatorially to a cobalt atom, thus bridging
a Co–Co bond, forming a thermodynamically stable
five-membered ring. The ring takes the form of a boat
conformation, which is not surprising given the fact that
the same conformation has been reported for other
dppm-bridged Co3C clusters [20,21].
The spectroscopic information recorded (Tables 3–6)
is in line with expectation and indicates that 3 adopts the
same structure in the solid and solution states. More
peaks would have been expected in the carbonyl region
of the infrared spectrum. However, the broad peak at
2016 cmꢀ1 may obscure some of the weak peaks. The 1H
NMR spectrum clearly shows the inequivalence of the
methylene protons on the dppm ligand. The apparent
quartets at 3.38 and 4.44 ppm are presumably doublets
of triplets and each corresponds to one of the two hy-
drogen atoms. The observed pattern of lines arises from
the similiarity of the coupling constants, 2J(31P–1H) and
1
2J(1H–1H) (ca. 14.6 Hz). Remaining signals in the H
NMR spectrum show good agreement with those ex-
pected of the capping moiety. Not all of the expected
signals are, however, present in the 13C NMR spectrum.
Those for the apical carbon, and the carbonyl carbon to

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S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
It may be presumed that 4 is formed by oxidation of
an intermediate of the form [Co3(l3-CC(O)OCH2-
CH@CH2)(CO)6(l2-dppm)(dppm)], although spectro-
scopic evidence for the existence of this species remains
elusive. Compound 4 can, however, be prepared by
treatment of 3 with further dppm and subsequent col-
umn chromatography. Other structures have been re-
ported where the pendant or dangling phosphorus
centre has been oxidised [24,25].
Monosubstituted triphenylphosphane derivatives of
Co3C clusters are well known [5,14,26–28] but examples
of disubstituted derivatives are much rarer [26,29,30]. A
disubstituted derivative, 5 (Fig. 3), resulted from reac-
tion at ambient temperature. The crystal structure of 5
has been determined as the hexane/dichloromethane
solvate. The asymmetric unit comprises two cobalt
clusters, plus the incorporation of half each of a mole-
cule of hexane and dichloromethane. Thus a quarter of
dichloromethane and a quarter of hexane are incorpo-
rated per cluster. The two clusters differ mainly in the
conformation of the capping moiety (see Tables 1 and
2). In the cluster labelled Co(1), Co(2), etc. the capping
ligand leans towards the Co(1)–Co(2) bond, as evi-
denced by the bond angles C(2)–C(1)–Co, while in that
containing Co(4), Co(5), Co(6), etc. the capping frag-
ment lies above Co(4).
(a)
Perhaps the most surprising feature of the structure
of 5 is that all the carbonyl ligands are terminally bon-
ded. Analysis of the infrared spectrum (Table 3) also
indicates the absence of bridging carbonyl ligands in
solution. This is rather unexpected since disubstitution
of Co3C clusters by poor p-accepting, bulky phosphane
ligands very often results in carbonyl-bridged structures
with displacement of the axial carbonyl ligands. Bridg-
ing carbonyl ligands would offer steric relief and reduce
the electron density localised on the Co3C core through
more effective dp(Co)–p*(CO) back donation. Indeed,
Robinson et al. reported that for complexes of general
formula [Co3(l3-CY)(CO)7L2], where Y ¼ Me, Ph or F
and L ¼ PPh3, PBu3, PPhEt2 etc., a carbonyl-bridged
structure was exclusively adopted [29].
This structure also shows that the phosphane ligands
have substituted at equatorial positions. As pointed out
previously, this is most likely to arise because of steric
effects. The bulky triphenylphosphane ligands have only
one neighbouring equatorial carbonyl ligand on an ad-
jacent cobalt atom. If coordinated axially the phosphane
ligand would have two axially coordinated carbonyls
nearby. The 31P NMR spectrum (Table 6) contains a
single resonance at d ¼ 45:4 ppm and thus indicates that
the phosphane ligands are equivalent.
(b)
Fig. 3. X-ray crystal structure of [Co3(l3-CC(O)OCH2CH@CH2)-
(CO)7(PPh3)2] (5), showing the two cobalt clusters that comprise the
asymmetric unit.
repulsive non-bonded interaction between the phenyl
rings of the phosphane ligands and the capping moiety.
The derivative produced from the reaction with
trimethylphosphane, 6, is also a disubstituted cluster
and the cluster’s preference for equatorial substitution is
again shown by the replacement of two equatorial car-
bonyl ligands with phosphane ligands (Fig. 4). The bond
lengths and angles in the cluster core and capping
moiety generally conform closely to those in [Co3(l3-
CC(O)OCH2CH@CH2)(CO)9] [15] with few exceptions.
The three Co–Co bond lengths (Table 1) all exhibit a
very small lengthening compared to that observed in the
The C(1)–Co(1)–P(1) and C(1)–Co(2)–P(2) angles
(Table 2) of 119.65(18)° and 119.5(2)° are relatively large
compared to that reported for the monosubstituted de-
rivative (96.0(5)°) [28]. This bending of the Co–P bonds
towards the tricobalt plane reflects the intramolecular

S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
2109
120
115
110
105
100
115
125
135
145
Phosphane Cone Angle
Fig. 5. Graph of phosphane cone angle versus average C(1)–Co–P
bond angle in structures of 2, 3, 5 and 6.
duced. The FAB mass spectrum, however, indicated that
the product was in factthe trisubstituted cluster. An X-ray
diffraction study of 7 proved this to be the case (Fig. 6).
The reason for the production of a trisubstituted cluster
has not yet been established. However, the reaction with
triethylphosphane was more vigorous than those with the
other phosphane ligands (N.B. trimethylphosphane was
added as the silver iodide adduct). The reaction produced
rapid effervescence, assumed to be carbon monoxide,
whichceased aftertwo hours when it was assumed that the
reaction had proceeded to completion.
Fig. 4. X-ray crystal structure of [Co3(l3-CC(O)OCH2CH@CH2)-
(CO)7(PMe3)2] (6).
The high R values, twinning, and disorder in the
crystal structure of 7 (Table 7) mean that discussion of
parent structure, as do all the other structures reported
herein, as anticipated. Also, the C(4)–C(5) bond length
ꢀ
of 1.279(3) A is noted to be considerably shortened (cf.
ꢀ
1.305(6) A) [15].
Trimethylphosphane is the least sterically bulky li-
gand used for ligand substitution in the experiments
reported here. This is reflected in the C(1)–Co–P bond
angles (Table 2). Angles of 105.55(5)° and 97.92(5)° have
been determined for C(1)–Co(1)–P(1) and C(1)–Co(2)–
P(2), respectively. These are considerably less than the
comparable angles determined for the other structures
reported herein. Non-bonded interactions between the
phosphane ligands and the capping moiety are reduced
as a consequence of the relatively small size of the
trimethylphosphane ligand. For comparison, an average
C(1)–Co–P bond angle of 111° was reported by Simpson
and coworkers [31] for the cluster [Co3(l3-
CCH3)(CO)6(P(OMe)3)3].
The average C(1)–Co–P bond angle, determined for
each disubstituted cluster derivative, was plotted against
the cone angle, as reported by Tolman [34], of the
phosphane ligand in question. The data points share an
approximately linear relationship, as shown in Fig. 5.
Thus it is clearly observed that the steric properties of
the phosphane ligand influence the degree to which the
Co–P bond is bent away from or towards the tricobalt
plane.
Fig. 6. X-ray crystal structure of [Co3(l3-CC(O)OCH2CH@CH2)-
(CO)6(PEt3)3] (7).
When green crystals were isolated from the reaction of
1 with 1.61 equivalents of triethylphosphane, it was as-
sumed that a disubstituted cluster had again been pro-
Fig. 7. Key to NMR assignments for capping group.

2110
S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
Table 7
Crystal data and structure refinement for 2, 3, 5, 6 and 7
2
3
5
6
7
Chemical formula
Formula weight
Crystal system
Space group
C38H29Co3O9P2
868.34
Orthorhombic
C40H34Co3O9P2
897.40
Monoclinic
C49:75H39Cl0:5Co3O9P2
1037.26
Triclinic
C18H23Co3O9P2
622.09
Orthorhombic
C29H50Co3O8P3
796.39
Orthorhombic
ꢁ
P212121
P21=n
P1
P212121
P212121
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Unit cell lengths
a ¼ 13:2057ð9Þ A a ¼ 14:8285ð17Þ A
a ¼ 11:3011ð11Þ A
a ¼ 10:2499ð6Þ A
a ¼ 19:5908ð7Þ A
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
b ¼ 14:2109ð9Þ A b ¼ 15:6559ð18Þ A
b ¼ 20:749ð2Þ A
b ¼ 12:7164ð7Þ A
b ¼ 10:7239ð4Þ A
ꢀ
ꢀ
c ¼ 19:7833ð13Þ A c ¼ 16:8160ð19Þ A
c ¼ 21:897ð2Þ A
c ¼ 19:2840ð11Þ A
a ¼ 90°, b ¼ 90°,
c ¼ 90°
c ¼ 17:2704ð6Þ A
Unit cell angles
a ¼ 90°, b ¼ 90°,
c ¼ 90°
a ¼ 90°,
a ¼ 114:365ð2Þ°,
a ¼ 90°, b ¼ 90°,
c ¼ 90°
b ¼ 92:301ð2Þ°, c ¼ 90° b ¼ 91:815ð2Þ°,
c ¼ 101:376ð2Þ°
3
3
3
3
3
ꢀ
3712.6(4) A
ꢀ
3900.7(8) A
ꢀ
4548.6(8) A
ꢀ
2513.5(2) A
ꢀ
3628.3(2) A
Cell volume
Z
4
4
4
4
4
Absorption coefficient l 1.465 mmꢀ1
Crystal colour and size Red,
1.397 mmꢀ1
Dark green,
1.238 mmꢀ1
Brown,
2.127 mmꢀ1
Dark green,
1.531 mmꢀ1
Red,
0.32 ꢂ 0.26 ꢂ 0.22 0.93 ꢂ 0.77 ꢂ 0.45 mm3 0.49 ꢂ 0.39 ꢂ 0.31 mm3 0.20 ꢂ 0.17 ꢂ 0.17 mm3 0.28 ꢂ 0.24 ꢂ 0.15
mm3
29,767
mm3
Reflections collected
Independent reflections 8417
32,510
9231 (Rint ¼ 0:0327)
36,042
19,578 (Rint ¼ 0:0365)
21,907
6043 (Rint ¼ 0:0271)
19,552
6377
(Rint ¼ 0:0437)
7375
(Rint ¼ 0:0224)
6291
Reflections with
F 2 > 2rðF 2Þ
7128
13,067
5652
Final R indices
[F 2 > 2rðF 2Þ]
R1 ¼ 0:0655,
wR2 ¼ 0:1526
R1 ¼ 0:0756,
wR2 ¼ 0:1663
R1 ¼ 0:0289,
wR2 ¼ 0:0673
R1 ¼ 0:0431,
wR2 ¼ 0:0715
R1 ¼ 0:0679,
wR2 ¼ 0:1638
R1 ¼ 0:1062,
wR2 ¼ 0:1904
R1 ¼ 0:0208,
wR2 ¼ 0:0460
R1 ¼ 0:0240,
wR2 ¼ 0:0473
R1 ¼ 0:0954,
wR2 ¼ 0:2363
R1 ¼ 0:0966,
wR2 ¼ 0:2370
R indices (all data)
bond lengths and angles is inappropriate. The connec-
tivity is, however, assured. It is noted that two of the
phosphane ligands are equatorially bound whilst the
other is axially coordinated. The fact that only one
resonance is observed in the 31P NMR spectrum indi-
cates that the phosphorus nuclei are equivalent on the
timescale of the NMR experiment. This could be
achieved via one of two mechanisms: exchange of
bridging and terminal carbonyl ligands similar to that
observed in [Rh4(CO)12] [32], or interconversion of ax-
around the cluster core in 8. The infrared data are
consistent with those of 5 and 6 (Table 3) and thus an
analogous structure, in which triethylphosphane ligands
have substituted two equatorial carbonyl ligands with
all remaining carbonyl ligands in a terminal configura-
tion, is proposed.
3. Conclusion
1
ial/equatorial ligands [33]. It is notable also that the H
A range of tricobalt clusters has been synthesised
and characterised, containing both monodentate and
bidentate phosphane ligands, with an unsaturated allyl
capping moiety. We shall shortly report on the syn-
thesis of a corresponding series of derivatives possess-
ing a longer acryl capping group. The utility of these
derivatives as hydroformylation catalysts will also be
discussed.
and 13C NMR spectra of 7 are generally broad and
weak, as would be characteristic of a fluxional system at
intermediate temperatures.
A second band was obtained from this reaction via
column chromatography, which was an identical colour
to the first. Spectroscopic analysis of the resultant solid
indicated that a disubstituted derivative, 8, had been
produced. Attempts at crystallising this product, from a
variety of solvents and at low temperatures, failed and
thus no X-ray data can be presented.
4. Experimental
1
The H and 13C NMR spectra of 8 are as expected
(Tables 4 and 5). A single resonance is observed in the
31P NMR spectrum (Table 6), with a small difference in
chemical shift between compounds 7 and 8 (33.2 and
33.7 ppm, respectively). Mass spectrum data support the
proposition that the second fraction is indeed the di-
substituted triethylphosphane derivative. This still
leaves the question as to the orientation of the ligands
All reactions were carried out under an argon or di-
nitrogen atmosphere using standard Schlenk method-
ology. All solvents were dried by boiling for at least 5 h
with either Na/K alloy, or, in the case of halogenated
solvents, CaH2, before being distilled under an atmo-
sphere of dinitrogen. Mass spectra were recorded at the
EPSRC Mass Spectrometry Service Centre using Fast

S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
2111
Atom Bombardment (FAB). H and 13C NMR spectra
were obtained at 400.14 and 100.61 MHz, respectively,
on a Bruker AC400 spectrometer using tetramethylsi-
lane as an internal standard. 31P NMR spectra were
obtained at 101.26 MHz using a Bruker WM250 spec-
trometer with 85% phosphoric acid as an external
standard. IR spectra were recorded in solution using a
Mattson Satellite FTIR spectrometer. Melting points
were recorded in sealed capillaries under dinitrogen and
are uncorrected. Elemental analyses were carried out by
the analytical service, University of Wales Cardiff, or at
Butterworth Laboratories Ltd. X-ray crystallography
studies were carried out at Loughborough University.
[Co3(l3-CCl)(CO)9] [16] and [Co3(l3-CC(O)OCH2-
CH@CH2)(CO)9] (1) [14] were prepared according to
the literature methods. Triphenylphosphane was ob-
tained from Aldrich and purified by recrystallisation
from warm ethanol to remove traces of Ph3PO. Dppe
was obtained from Strem and was used without further
purification. The other phosphane ligands utilised,
dppm, trimethylphosphane silver iodide adduct and
triethylphosphane, were obtained from Aldrich. AlCl3
was purified by sublimation at 100 °C and 0.05 mm Hg
pressure.
green. The reaction mixture was concentrated and
chromatographed on silica with a mixture of hexane/
acetone (20:1) as eluent. An initial brown fraction was
collected which gave an unidentified product (<10 mg).
A second, dark green fraction was collected which, after
concentration to approximately 10 mL and slow cooling
to )10 °C overnight, yielded 3. Yield: 0.19 g, 31%. m.p.:
1
1
160–161 °C. H NMR: d ¼ 3:30 - 3.45 (dt, 1H), 4.39–
4.54 (dt, 1H), 4.49–4.59 (m, 2H), 5.03–5.11 (m, 1H),
5.17–5.26 (m, 1H), 5.70–5.84 (m, 1H), 6.95–7.44 (m,
20H). 13C NMR: d ¼ 39:7 (t), 64.6, 116.1, 126.9–136.1,
182.7. 31P NMR: d ¼ 33:3 (br). IR (CH2Cl2):
m(CO) ¼ 2067 (m), 2016 (vs, br), 1975 (sh) cmꢀ1. MS:
m=z 877 [Mþ + Na], 855 [Mþ + H] plus ions corre-
sponding to sequential loss of carbonyl ligands.
Further elution yielded bands which were pale green,
pale brown and dark green. Evaporation of the solvent
under reduced pressure in the last case resulted in the
isolation of 4 as an oily solid, [Co3(l3-CC(O)OCH2-
CH@CH2)(CO)6(dppm)(Ph2PCH2P(O)Ph2)]. This was
purified by dissolution in a small volume of dichlo-
romethane, and re-precipitation by addition of hexane.
1
Yield: 0.05 g, 9%. H NMR: d ¼ 3:30 - 3.55 (m, 3H),
3.99–4.27 (m, 3H), 4.85–4.98 (m, 1H), 5.02–5.07 (m,
1H), 5.48–5.60 (m, 1H), 6.93–7.74 (m, 40H). 13C NMR:
d ¼ 32:4 (m), 38.1 (t), 64.6, 116.1, 126.4–137.1, 183.6.
31P NMR: d ¼ 22:1(d), 32.9 (br, d), 37.9 (br, m). IR
(CH2Cl2): m ¼ 2029 (m), 1994 (s), 1976 (s), 1944 (sh),
1423 (s), 1270 (vs) cmꢀ1. MS: m=z 1170 [Mþ ) 2CO]
plus ions corresponding to sequential loss of carbonyl
ligands.
4.1. Syntheses of phosphane-substituted clusters
4.1.1.[Co3(l3-CC(O)OCH2CH@CH2)(CO)7(dppe)](2)
[Co3(l3-CC(O)OCH2CH@CH2)(CO)9] (1) (0.39 g,
0.74 mmol), dichloromethane (15 mL) and dppe (0.30 g,
0.74 mmol) were stirred for 18 h at room temperature.
The reaction was accompanied by a colour change from
purple to dark green. TLC was used to show only one
species present in solution. The solvent was removed in
vacuo and the residue chromatographed on silica using
a 70:30 hexane/dichloromethane mixture as eluent.
Concentration of the dark green band, followed by
cooling to )10 °C resulted in crystallisation of 2. Yield:
0.14 g, 22%. m.p.: 102–105 °C. C38H29Co3P2O9: calcd. C
52.56, H 3.37; found C 51.20, H 3.75. 1H NMR:
d ¼ 1:94 - 2.34 (m, 4H), 3.98–4.11 (m, 2H), 4.85–4.95
(m, 1H), 5.05–5.10 (m, 1H), 5.53–5.76 (m, 1H), 7.02–
7.69 (m, 20H). 13C NMR: d ¼ 23:4 (d), 64.5, 116.2,
127.4–136.6, 181.3, 205.0. 31P NMR: d ¼ 47:3 (br). IR
(CH2Cl2): m(CO) ¼ 2065 (s), 2014 (s), 2010 (vs), 1998
(m), 1978 (w) cmꢀ1. MS: m=z 868 [Mþ] plus ions cor-
responding to sequential loss of carbonyl ligands.
4.1.3. [Co3(l3-CC(O)OCH2CH@CH2)(CO)7(PPh3)2]
(5)
A solution of 1 (0.22 g, 0.42 mmol), dichloromethane
(15 mL) and PPh3 (0.22 g, 0.84 mmol) was stirred at
ambient temperature overnight, during which time a
colour change from purple to dark green was ob-
served. After the solvent was removed in vacuo the
residue was dissolved in a minimal volume of hexane
and chromatographed on alumina. Elution with hexane
resulted in a purple fraction being collected containing
starting material 1. Further elution using dichlorome-
thane afforded a dark green band. The dichloromethane
was removed by evaporation under reduced pressure
and the residue dissolved in hexane/dichloromethane
(9:1). Cooling overnight yielded the crystalline product.
Yield: 0.07 g, 17%. m.p.: 132 °C dec. C48H35Co3O9P2:
calcd. C 57.97, H 3.55; found C 57.93, H 4.00. 1H NMR:
d ¼ 4:31 - 4.48 (m, 2H), 4.95–5.05 (m, 1H), 5.15–5.32
(m, 1H), 5.72–5.96 (m, 1H), 7.10–7.64 (m, 30H). 13C
NMR: d ¼ 66:0, 117.3, 128.5–135.0, 205.4. 31P NMR:
d ¼ 45.4 (br). IR (CH2Cl2): m(CO) ¼ 2083 (w), 2055 (vs),
2029 (w), 1999 (w), 1970 (m) cmꢀ1. MS: m=z 995
[Mþ + H], plus ions corresponding to sequential loss of
carbonyl ligands.
4.1.2. [Co3(l3-CC(O)OCH2CH@CH2)(CO)7(dppm)]
(3) and [Co3(l3-CC(O)OCH2CH@CH2)(CO)6(dppm)-
(Ph2PCH2P(O)Ph2)] (4)
To a solution of 1 (0.38 g, 0.72 mmol) and dichlo-
romethane (15 mL), one equivalent of dppm (0.28 g,
0.72 mmol) was added. Stirring was continued over-
night, resulting in a colour change from purple to dark

2112
S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
4.1.4. [Co3(l3-CC(O)OCH2CH@CH2)(CO)7(PMe3)2]
(6)
d ¼ 33:7 (br). IR (CH2Cl2): m(CO) ¼ 2062 (m), 2012 (vs),
1994 (s), 1981 (w), 1975 (vw) cmꢀ1. MS: m=z 729
[Mþ + Na], 707 [Mþ + H].
To a toluene solution (20 mL) of 1 (0.22 g, 0.42
mmol), Ag4I4(PMe3)4 (0.52 g, equivalent to 0.42 mmol
of PMe3) was added. The mixture was stirred under
dinitrogen whilst heating with a hot air blower. A vig-
orous reaction was noted with an accompanying colour
change from purple to dark green. Some effervescence
was also seen. Heating was continued until the evolution
of gas ceased, within 1 h. Stirring was continued at room
temperature overnight. The solvent was evaporated in
vacuo and the residue purified by column chromatog-
raphy on alumina. Using a 2:1 hexane/dichloromethane
mixture as eluent a purple band (1) was eluted. Di-
chloromethane as eluent yielded a dark green band. The
solvent was removed under reduced pressure from the
dark green band and the residue dissolved in hexane/
dichloromethane. Cooling at )10°C overnight resulted
in crystallisation. The product was recrystallised from
4.2. X-ray crystallography for 2, 3, 5, 6 and 7
All measurements were made on a Bruker AXS
SMART 1000 CCD area detector diffractometer equip-
ꢀ
ped with Mo Ka radiation (k ¼ 0:71073 A) at 150 K.
Narrow-frame exposures (0.3° in x) were employed. Cell
parameters were refined from all strong reflections in
each data set. Intensities were corrected semi-empirically
for absorption, based on symmetry-equivalent and re-
peated reflections. The structures were solved by direct
methods (Patterson synthesis for 2) and refined by full-
matrix least-squares on F 2 values for all unique data. All
non-hydrogen atoms were refined anisotropically. H at-
oms were included in a riding model with Uiso set to be
1.2 times (1.5 times for methyl-H) Ueq for the carrier
1
ꢀꢀ3
hexane giving 6. Yield: 0.15 g, 58%. m.p.: 66–68 °C. H
atom. In 2, the residual electron density peaks >1 e A
NMR: d ¼ 1:42 - 1.46 (d, 18H), 4.57–4.60 (m, 2H), 5.17–
were close to Co atoms. In 3, the PLATON ‘Squeeze’
procedure [35] was employed to model a half-hexane
molecule which was badly disordered. ‘Squeeze’ recov-
ered 48 electrons which agrees well with 50 electrons in
half a hexane molecule. In the asymmetric unit of 5 there
are two Co3 clusters plus half a molecule each of CH2Cl2
and hexane. Restraints were applied to the anisotropic
displacement parameters of the solvent molecules and to
those of the capping ligand on the Co3 cluster containing
Co(1). The largest residual electron density peaks were
close to the metal atoms. In 7, a number of crystallo-
graphic problems were overcome. The crystals were
twinned racemically and via a 180° rotation about b
giving four twin components, three of them minor with
2%, 7% and 2% contributions. In addition, atom C(4) in
the capping ligand was disordered over two sets of po-
sitions, while two and three ethyl groups on P(2) and
P(3), respectively, were also disordered.
5.21 (m, 1H), 5.29–5.38 (m, 1H), 5.87–6.01 (m, 1H). 13
C
NMR: d ¼ 19:7 (d), 66.0, 118.3, 133.3. 31P NMR:
d ¼ 2:9 (br). IR (CH2Cl2): m(CO) ¼ 2053 (s), 2000 (vs),
1962 (sh), 1950 (w), 1911 (w) cmꢀ1. MS: m=z 645
[Mþ + Na], 623 [Mþ + H], 622 [Mþ].
4.1.5. [Co3(l3-CC(O)OCH2CH@CH2)(CO)6(PEt3)3] (7)
and [Co3(l3-CC(O)OCH2CH@CH2)(CO)7(PEt3)2] (8)
Cluster 1 (0.40 g, 0.76 mmol), dichloromethane (15
mL) and triethylphosphane (0.18 mL, 1.22 mmol) were
stirred at room temperature. A rapid colour change,
purple to dark green, and vigorous effervescence was
noted. Stirring was continued until the evolution of gas
was complete (within 2 h). Solvent evaporation at re-
duced pressure proceeded and the residue was purified
by column chromatography on silica. Using diethyl
ether as eluent, a dark green band was eluted. After
removal of the solvent in vacuo, the residue was dis-
solved in hexane (ꢁ30 mL)/dichloromethane (ꢁ0.5 mL).
Evaporation of approximately a third of the solvent and
cooling overnight yielded a dark green, crystalline solid
7. Yield: 0.14 g, 23%. m.p.: 90°C. 1H NMR: d ¼ 0:8 - 1.2
(s, br), 1.5–1.9 (s, br), 4.6–4.7 (m, 2H), 5.0–5.2 (m, 1H),
5.27–5.41 (m, 1H), 5.73–5.98 (m, 1H). 13C NMR:
d ¼ 8.1, 18.8 (d), 20.9 (d), 66.0, 117.4, 132.3. 31P NMR:
d ¼ 33:2 (br). IR (CH2Cl2): m(CO) ¼ 2050 (m), 1998 (s),
1977 (vs), 1806 (m), 1740 (w), 1700 (vw) cmꢀ1. MS: m=z
796 [Mþ].
5. Supplementary material
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Center, CCDC No.’s 216491–5. Copies of this infor-
mation may be obtained free of charge from The Di-
rector, CCDC, 12 Union Road, Cambridge CB2 1EK
(Fax: +44-1223-336033; deposit@ccdc.cam.ac.uk or
www.ccdc.cam.ac.uk).
Further, a second dark green fraction was obtained
from the column using the same eluent. Evaporation of
the solvent in vacuo resulted in the isolation of 8. Yield:
50 mg, 9%. 1H NMR: d ¼ 0:92 - 1.14 (m, 6H), 1.61–1.83
(m, 4H), 4.49–4.62 (m, 2H), 5.06–5.18 (m, 1H), 5.23–
5.34 (m, 1H), 5.83–5.97 (m, 1H). 13C NMR: d ¼ 6:8,
19.5 (d), 64.6, 116.5, 132.1, 181.1, 207.8. 31P NMR:
Acknowledgements
The provision of a studentship to A.E.O. by the
EPSRC is gratefully acknowledged.

S.J. Black et al. / Journal of Organometallic Chemistry 689 (2004) 2103–2113
2113
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