Reactions of the μ-alkyne-dicobalt complexes [Co2(CO)6(μ-CF3-CC-R)] (R=CF3, H) with [Co2Cp2(μ-SMe)2]: Substitution and insertion leading to novel thiolato-alkyne tetra- and trico

Article abstract of DOI:10.1016/S0022-328X(01)00994-9

The bis(μ-thiolato)dicobalt complex [Co₂Cp₂(μ-SMe)₂] (1) reacts with alkyne-cobalt complexes [Co₂(CO)₆(μ-F₃CCCR)] (2) to give tri- and tetranuclear cobalt cluster compounds. When R=CF₃

Full text of DOI:10.1016/S0022-328X(01)00994-9

Journal of Organometallic Chemistry 635 (2001) 110–118
www.elsevier.com/locate/jorganchem
Reactions of the m-alkyne-dicobalt complexes
[Co2(CO)6(m-CF3–CꢀC–R)] (R=CF3, H) with [Co2Cp2(m-SMe)2]:
substitution and insertion leading to novel thiolato-alkyne tetra-
and tricobalt clusters
Kenneth W. Muir a,*, Rene´ Rumin b, Franc¸ois Y. Pe´tillon b,*
a Department of Chemistry, Uni6ersity of Glasgow, Glasgow G12 8QQ, Scotland, UK
b UMR CNRS 6521, Laboratoire de Chimie, Electrochimie Mole´culaires et Chimie Analytique, Faculte´ des Sciences,
Uni6ersite´ de Bretagne Occidentale, B.P. 809, 29285 Brest Cedex, France
Received 3 April 2001; accepted 10 May 2001
Abstract
The bis(m-thiolato)dicobalt complex [Co2Cp2(m-SMe)2] (1) reacts with alkyne-cobalt complexes [Co2(CO)6(m-F3CCꢀCR)] (2) to
give tri- and tetranuclear cobalt cluster compounds. When R=CF3 the main product is [Co2(CO)4(m-CF3C2CF3){m-Co2Cp2(m-
SMe)2}] (3) but the trinuclear cluster [Co3Cp(CO)4(m-SMe)2(m-CF3C2CF3)] (4) is also obtained in low yield. When R=H the
products are the isomeric clusters [Co3Cp(CO)4(m-SMe)2(m-CF3C2H)] (5 and 6), [Co3Cp2(CO)3(m-SMe)(m-CF3C2CH)] (7) and
[CpCo(CO)2]. The solid state structures of 3, 4, 5 and 7 have been established by X-ray analysis. The 50 electron triangular cluster
,
4 has weak Co–Co bonds [2.573(1), 2.800(1), 2.838(1) A]. The alkyne ligand bridges the shortest of these bonds in perpendicular
,
fashion. 5 and 7 contain open chain tricobalt units [Co–Co 2.39–2.57 A] more typical of 50 electron M3 species. In these
complexes the alkyne is p-bonded to the central metal atom and s-bonded to both terminal cobalt atoms. Variable temperature
NMR indicates that 5, 6 and 7 each exist in solution as interconverting isomers which differ in the configuration at one sulphur
atom. For 5 the activation parameters [DH‡=64 kJ mol−1 and DS‡= −85 J K−1 mol−1] were obtained spectroscopically. In
,
the solid, molecules of 7 contain an asymmetrically bridging carbonyl [Co–C 1.833(4) and 2.050(3) A] which is not detectable in
the solution spectra. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Cobalt; Triangular clusters; Bridging alkynes; X-ray structures
electronegativity and retro-dative properties, is often
important in determining the architecture of the final
product cluster [2,3]. This work also represents an
extension from molybdenum [4] and iron [5] to cobalt
of our studies of sulphur-rich metal clusters as models
for important biological and catalytic processes. A re-
cent review by Went on reactions of polynuclear cobalt-
alkyne complexes emphasises how easily [Co2(CO)6-
(m-F3CCꢀCCF3)] can undergo decarbonylation under
thermal conditions; this reaction has been exploited
mainly to replace carbonyl by phosphine, phosphite or
arsine, and other ligands have received little attention
[6]. Went also gives a helpful summary of the structural
features of [Co2(CO)6(m-RCꢀCR%)] species. Current
knowledge of Cp-stabilised cluster complexes of Group
9 metals has also been summarised [7]. Finally, we
1. Introduction
We describe here the synthesis and characterisation
of some new cobalt cluster complexes obtained by
reacting the m-thiolato-dicobalt complex [Co2Cp2(m-
SMe)2] (1) with alkyne-cobalt complexes [Co2(CO)6(m-
F3CCꢀCR)] (2a R=CF3; 2b R=H). We have
previously shown that alkyne-dicobalt hexacarbonyl
complexes are useful synthons for the fabrication of tri-
and tetranuclear clusters [1]: they can readily be pre-
pared using a wide variety of mono- and di-substituted
acetylenes and the choice of acetylene, in particular its
* Corresponding authors. Tel.: +44-141-3300-5345; fax: +44-141-
330-4888.
E-mail address: ken@chem.gla.ac.uk (K.W. Muir).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00994-9

K.W. Muir et al. / Journal of Organometallic Chemistry 635 (2001) 110–118
111
Scheme 1. Syntheses and proposed structures of complexes 3–7.
note that the complexes we now describe are stable,
even though they contain highly electronegative alkynes
apparently behaving as four-electron donor ligands.
The explanation of this apparent paradox in terms of
retro-dative bonding was given in response to a ques-
tion at a conference devoted to the Walden inversion
half a century ago [8].
which broaden on heating, finally collapsing at 296 K.
The activation barrier of the observed dynamic process
was estimated from the chemical shift difference (Dw=
49 Hz) and the coalescence temperature (296 K) [9].
The value of the energy barrier associated with site
exchange is low (DG‡=60.6 (91.0) kJ mol−1). Since
no line-change involving the Me resonances was no-
ticed over the temperature range 250–303 K, the flux-
ionality observed for the cyclopentadienyl ligands
evidently does not affect the methyl groups under the
same conditions. The exchange process most probably
reflects the onset of a movement of the alkyne about
the Co–Co bond which replaces the transannular inter-
action between the CpCo(2) and C(3)CF3 groups with
an an equivalent CpCo(3)···C(2)CF3 interaction. At the
same time the C(5) and C(6) carbonyl ligands exchange
position at the cobalt centres.
2. Results and discussion
2.1. Reaction of [Co2Cp2(v-SMe)2] (1) with
[Co2(CO)6(v-CF3C2CF3)] (2a): synthesis and
spectroscopic characterization of complexes 3 and 4
The reaction of the bis-thiolato-compound [Co2Cp2-
(m-SMe)2] (1) with
1 equivalent of [Co2(CO)6(m-
CF3C2CF3)] (2a) was carried out under reflux in te-
trahydrofuran for 2 h. It afforded the tetranuclear
metal complex [Co2(CO)4(m-CF3C2CF3){m-Co2Cp2(m-
SMe)2}] (3) as the major product (87%) (Scheme 1).
Careful separation by column chromatography yielded
one additional by-product, the trinuclear cluster
[Co3Cp(CO)4(m-SMe)2(m-CF3C2CF3)] (4) (6%).
The black product 3 was characterised by a combina-
tion of spectroscopic and X-ray diffraction techniques
(see respectively Sections 3 and 2.3). 3 (Fig. 1) contains
the Co2(CO)4(m-CF3C2CF3) unit found as a building
block in many dinuclear cobalt carbonyl complexes [6]
and is derived by replacing two of the carbonyl ligands
of the starting hexacarbonyl compound 2a by the two
thiolato sulphur atoms of the unsaturated bis(m-thio-
lato) species 1 which displays here its ability to act as a
1
four-electron donor ligand. The H-NMR spectrum of
3 at room temperature contains a singlet methyl reso-
nance at l 2.70 and a broad signal at l 4.91 in the
cyclopentadienyl region. At low temperature (253 K)
the cyclopentadienyl resonance splits into two peaks
Fig. 1. A view of the structure of 3 showing 10% probability
ellipsoids.

112
K.W. Muir et al. / Journal of Organometallic Chemistry 635 (2001) 110–118
low-temperature (233 K) 13C-NMR spectrum revealed
four singlets between 198.7 and 195.9 ppm (intensity
ratio 1:1:1:1) in the region typical for two Co(CO)2
1
groups. The H- and 13C-NMR spectra show the pres-
ence of only one cyclopentadienyl ligand in 4. Reso-
nances for two inequivalent SMe groups are present in
the 1H-NMR spectrum: one Me group is shifted
highfield (l 0.50 ppm) indicating that it is subject to a
strong shielding cone effect. Mass spectroscopy confi-
rmed the proposed trinuclear structure of the complex
4: the upper part of the spectrum consists of the
molecular ion [M]+ and of the ions of the sequence
[M−nCO]+ (n=1–4).
2.2. Reaction of [Co2Cp2(v-SMe)2] (1) with
[Co2(CO)6(v-CF3C2H] (2b): synthesis, spectroscopic
characterisation of complexes 5–7 and kinetic
considerations
Fig. 2. A view of the structure of 4 showing 10% probability
ellipsoids.
Treatment of 1 with 1 equivalent of 2b in refluxing
tetrahydrofuran for 2 h gave a mixture containing the
trinuclear complexes 5 (22%), 6 (23%) and 7 (18%), and
the degradation product [CpCo(CO)2] (19%). The four
compounds were cleanly separated by chromatography.
An unbalanced reaction for the synthesis is shown in
Scheme 1. Complexes 5 and 7 were obtained as crys-
talline solids and have been characterised both by spec-
troscopy and by X-ray diffraction studies (see Figs. 3
and 4), whereas 6 was isolated as a solid paste which
did not yield diffraction-quality crystals. In a formal
sense, insertion of a (Cp)CoSMe unit into either the
Co–C(H) or the Co–C(CF3) bond of 2b gives respec-
tively 5 or 6 after a further transfer of a SMe group to
the Co2(CO)4 framework. In contrast, 7 has a structure
resulting from the insertion of a Co(CO)3(HCꢀCCF3)
fragment into the Co–Co bond of 1.
Fig. 3. A view of one of the two independent molecules of 5 showing
10% probability ellipsoids. The hydrogen atom attached to C9a was
not located.
There is strong evidence that formation of the tri-
cobalt complex 4 from 3 involves loss of CpCo in a
stoichiometrically
clean
fragmentation
reaction
(Scheme 1). Indeed, in dichloromethane solution 3 gave
4 as the only metal carbonyl derivative. On standing at
−20°C in CDCl3, almost 15% of 3 transformed into 4
in 24 h.
The cluster 4 was fully characterised by microanaly-
1
sis, IR, and H-, 19F- and 13C-NMR spectroscopy (see
Section 3), and its molecular structure was also confi-
rmed by an X-ray diffraction study (see Fig. 2 and
Section 2.3). The presence of the m-alkyne carbon
atoms in 4 is clearly indicated by the appearance in the
13C-NMR spectrum of two quartets (2JC–F=45–48
Hz) at l 73.8 and 69.8 ppm. The CO region of the
Fig. 4. A view of the structure of 7 showing 10% probability
ellipsoids.

K.W. Muir et al. / Journal of Organometallic Chemistry 635 (2001) 110–118
113
Table 1
Comparison of selected NMR chemical shift data (l) a for trinuclear-trifluoropropyne-cobalt complexes (5–7%)
Compound 19F
CF3
1H
13C{1H}
ꢁCH
C5H5
SCH3
SCH3
C5H5
CF3
C–CF3
ꢁCH
b
5a
5b
6a
6b
7%a
7%b
−53.25(s) 11.10(s) 5.06(s) 2.19(s) 27.7(s)
85.5(s)
127.4 (q, 1JCF=276.0) b 150.3 (q, 2JCF=40.0) b 162.9(s) b
2.01(s) 23.85(s)
−53.63(s) 11.23(s) 5.06(s) 1.29(s) 24.5(s) b 85.5(s)
127.7 (q, 1JCF=276.0) b 158.0(q) b
171.25(s) b
151.6(s)
2.00(s) 23.85(s)
7.53(s) 5.05(s) 2.31(s) 25.45(s)
1.95(s) 28.45(s)
−54.54(s)
−55.55(s)
82.8(s)
82.8(s)
128.0 (q, 1JCF=278.0)
127.1 (q, 1JCF=278.0)
156.2 (q, 2JCF=34.0)
164.6 (q, 2JCF=35.0)
7.69(s) 5.04(s) 1.28(s) 25.25(s)
1.95(s) 28.45(s)
159.25(s)
163.9(s) b
168.8(s) b
−54.59(s) 11.49(s) 4.77(s) 2.40(s) 29.3(s) b 88.35(s) b 127.85 (q, 1JCF=275.0) b 150.15(q) b
4.67(s)
−53.86(s) 11.62(s) 4.75(s) 1.23(s) 23.2(s) b 88.85(s) b 127.95 (q, 1JCF=275.0) b 157.0(q) b
4.63(s) 83.05(s)
83.10(s)
a Measured in CDCl3 solution at 293 K unless stated by footnote b. J in Hz.
b In (CD3)2 CO at 293 K.
NMR (1H,19F,13C) spectrometry indicated that com-
plex 5 exists in solution as two interconverting isomers.
Since the NMR patterns of these isomers are very
similar, except for the methyl regions (see Table 1), it is
probable that only the methyl groups are responsible
5b interconversion is thought to be slow, since no
fluxional phenomena could be detected on the NMR
1
(19F, H) time scale over the temperature range 193–
293 K in CD2Cl2. First-order rate constants for the
5a“5b interconversion reaction at four different tem-
peratures in the range 218–234 K were therefore
derived from the changes in the 19F-NMR spectra with
time (see Section 3.4). The activation parameters were
calculated from the Eyring plot shown in Fig. 5:
DH‡=64 (91) kJ mol−1, DS‡= −85(91) u.e. The
value of the energy barrier (DG‡298K=89 kJ mol−1) is
high compared to those reported for inversion at bridg-
ing sulphur in many dinuclear complexes (DG‡ꢀ45–62
kJ mol−1) [5,10], but it is of the order of that deter-
mined (DG‡ꢀ74 kJ mol−1) for [W2(h5-C5H4Pri)2Cl4(m-
H)(m-SMe)] [11].
1
for the isomerisation process. Moreover, the H-NMR
spectrum clearly showed that only one of the two SMe
groups is involved in the stereoisomerism, since only
one methyl resonance was shifted to high field when 5a
was transformed into 5b (Table 1), indicating that the
two diastereoisomers differ only in the orientation of
one SMe group, which can be either in or out of the
shielding cone of the cyclopentadienyl group. As shown
in Chart 1, the isomerism probably depends upon the
relative dispositions of the cyclopentadienyl ligand and
the methyl group attached to the S atom which bridges
(Cp)Co and Co(CO)2 groups (i.e. S2a in Fig. 3). The
choice of S2a, rather than S1a, as the source of the
isomerism is based on the observation that very similar
Complex 6 was unequivocally characterised in solu-
1
tion by IR and H-, 19F- and 13C-NMR spectroscopy
and by comparison with complex 5. Indeed, the close
similarity between 6 and 5 in chemical behaviour (solu-
tions of both complexes contain two interconverting
isomers) and in their NMR spectra (see Table 1)
strongly suggest that both compounds contain a similar
1
changes in the H-NMR patterns of 5 and 7 (see Table
1) occur when the isomers interconvert and that 7
contains only one SMe group, which bridges a dicobalt
unit in a manner corresponding to S2a in 5. The 5a:5b
ratios were found to depend on the solvent polarity: the
more polar solvent favoured the anti-isomer (e.g.
5a:5b=1:1.04 in CDCl3, 1:0.92 in (CD3)2CO and 1:0.66
in CD3CN). The syn-isomer was the only product
obtained in the solid state. CD2Cl2 solutions of 5b at
1
193 K displayed a single H-NMR pattern in accor-
dance with the structure found for this complex by
X-ray analysis (see below). Under these conditions, 5a
isomerised over several hours to give an equilibrium
mixture of 5a and 5b in the ratio 1:1.04. The conversion
of 5a to 5b can be regarded as the result of inversion at
sulphur. The exchange process responsible for the 5a“
Chart 1.

114
K.W. Muir et al. / Journal of Organometallic Chemistry 635 (2001) 110–118
Fig. 5. Eyring plot for the reaction in which 5a isomerises to give 5b.
Chart 2.
CoC(H)C(CF3)CoS(Me) cyclodicobaltathiapentene ring
p-bonded to a Co(CO)2 group. It is likely that 6 differs
from 5 by an interchange of the positions of the alkyne
CH and CCF3 groups. This view is supported by the
significant shift to high field of the CH resonance
are very similar, with significant differences only in the
methyl regions, suggesting that 7%a and 7%b correspond
respectively to anti- and syn-isomers (Chart 2). In the
1
room-temperature H-NMR spectrum the distinct iso-
mers 7%a and 7%b give rise to methyl singlets at l 2.40
and 1.23, respectively. In the 13C{1H}-NMR spectrum a
set of two singlets at l 163.9 and 168.8 and two
quartets at l 150.15 and 157.0 belong to the bridging
C2 group and have chemical shifts close to those of the
corresponding atoms in 5a and 5b. Like 5 and 6, the
7%a:7%b ratios depend on the solvent polarity: the more
polar solvent again favours the anti-isomer (e.g.
7%a:7%b=1:0.96 in CDCl3, 1:0.92 in (CD3)2CO and
1:0.75 in CD3CN). Since CD2Cl2 solutions of crystals of
1
(lꢀ7.6 ppm) in the H-NMR spectrum of 6, where the
CH bridges two Co(CO)2 groups, relative to that (lꢀ
11.2 ppm) in the spectrum of 5, where the CH links
Co(Cp) and Co(CO)2 units. As stated above, the room-
temperature 1H-, 19F- and 13C-NMR spectra of 6
(Table 1) are consistent with the presence of two inter-
converting isomers, which will be referred to as 6a and
6b. The very close similarities between the 1H-NMR
spectra of 6 and 5 in the methyl regions (Table 1)
suggest strongly that the conversion of 6a to 6b again
involves inversion of the sulphur atom of the (Cp)Co(m-
SMe)Co(CO)2 unit, the anti-position of the methyl and
the cyclopentadienyl groups in 6a being replaced by a a
syn arrangement in 6b.
The IR spectra of 7 in the w(CO) region (see Section
3) show that the structure in the solid differs slightly
from that obtained in solution. To aid clarity the
structure in solution will be referred to as 7%. A bridging
carbonyl [w(CO)=1845 cm−1] was found in the single-
crystal X-ray study (see below), whereas no peak at-
tributable to bridging CO was observed in solution
(Chart 2). Otherwise, spectroscopic data for 7% are
consistent with the structure of 7 obtained by X-ray
analysis. Like 5 and 6, 7% exists in solution as intercon-
verting isomers 7%a and 7%b. NMR spectra of 7%a and 7%b
1
7 at low-temperature (193 K) displayed a double H-
NMR pattern similar to that detailed in Table 1, rates
for 7%a“7%b interconversion could not be determined,
but it is not unreasonable to suggest that DG‡ for this
process is of the same order as that obtained for the
inversion at sulphur in 5.
2.3. Molecular structures of 3 and 4
Complex 3 is formed when two of the carbonyl
ligands in 2a are replaced by the lone pairs of the two
sulphur atoms of 1 (Fig. 1, Table 2). No new metal–
metal bonds are thereby formed, and the stereo-
chemistries and cluster valence electron counts (CVE)
of the metal atoms in the starting complexes are
conserved.

K.W. Muir et al. / Journal of Organometallic Chemistry 635 (2001) 110–118
115
,
and the mean for all 70 alkyne complexes [1.339 A].
Compared with database-derived mean Co–
C(alkyne) distance of 1.969 A [6], the values in 2a are
Molecules of 3 lie across a crystallographic mirror
plane which contains Co2, Co3 and the four alkyne
carbon atoms. In consequence, the alkyne plane is
exactly perpendicular to the Co1–Co1i bond and the
sawhorse skeleton typical of [Co2(CO)6(m-CF3C2CF3)]
a
,
,
short [mean 1.930(5) A], reflecting the high electronega-
tivity of the CF3 group [12] and the consequent impor-
tance of retro-dative bonding in 2a [8]; the Co1–C2 and
Co1–C3 distances in 3 [1.916(4) and 1.924(4) A] also
show this shortening. The correlation noted between
Co–C(alkyne) distances and alkyne CꢀC–C angles [6]
is complicated in 3 by a steric effect: while the C1–C2–
C3 angle [138.8(5)°] agrees with the values in 2b
[137.4(4)–139.5(4)°] (cf. the mean of 142.6° for all 70
analogues] the C2–C3–C4 angle narrows to 133.7(5)°
to relieve intramolecular Cp···CF3 contacts.
(2a) [12] and its analogues [6] is retained. The Co1–
i
,
,
Co1 distance [2.454(1) A] is comparable with the values
,
in 2a [2.464(4) and 2.472(2) A] and with a database-
derived average of 2.467 A for 70 [Co2(CO)6(m-RC2R)]
complexes [6]. Similarly, the C2–C3 distance [1.346(7)
,
,
,
A] agrees with values for 2a [1.355(7) and 1.360(7) A]
Table 2
,
Bond lengths (A) for 3
Although the structure of 1 itself has not been deter-
mined, the portion of 3 derived from 1 is geometrically
extremely similar to the corresponding parts of
[Co2Cp2(m-SMe)(m3-SMe)CoCp{(CCF3)4}] [13], a com-
plex which also illustrates the Lewis base capabilities of
the sulphur atoms of 1. In 3 S1 is equidistant from Co2
Co(1)ꢂC(6)
Co(1)ꢂC(5)
Co(1)ꢂC(2)
Co(1)ꢂC(3)
Co(1)ꢂS(1)
Co(1)ꢂCo(1)i
Co(2)ꢂC(12)
Co(2)ꢂC(11)
Co(2)ꢂC(13)
Co(2)ꢂS(1)
Co(2)ꢂCo(3)
Co(3)ꢂC(10)
Co(3)ꢂC(8)
Co(3)ꢂC(9)
Co(3)ꢂS(1)
C(1)ꢂC(2)
1.773(4)
1.809(4)
1.916(4)
1.924(4)
2.283(2)
2.454(1)
2.019(7)
2.046(12)
2.055(6)
2.178(1)
2.436(1)
2.043(6)
2.049(6)
2.065(8)
2.181(1)
1.477(7)
1.346(7)
1.463(8)
,
,
and Co3 [2.178(1) and 2.181(1) A] and 0.1 A further
,
from Co1 [2.283(2) A]. The m3-bridging role of the SMe
group in 3 appears to preclude low-energy inversion of
the sulphur atom, consistent with the interpretation of
the NMR spectrum (see Section 2.1).
Removal of Co2 and its associated Cp group from 3
to give 4 is achieved with remarkably little alteration in
stereochemistry, as may be seen by comparing Fig. 1
with Fig. 2. Indeed, careful comparison of the struc-
tures (Tables 2 and 3) reveals only four changes of any
significance. (i) The methyl groups on S1 and S2 are
respectively syn and anti to the Co3 Cp ring in 4
whereas in 3 they are both syn; this difference is
consistent with the NMR spectra of 4 discussed above.
C(2)ꢂC(3)
C(3)ꢂC(4)
Symmetry transformations used to generate equivalent atoms: (i)
−x+2, y, z.
Table 3
Bond lengths (A) for 4
,
,
(ii) The Co1–Co2 bond length in 4 is 2.573(1) A, 0.12
,
A longer than the corresponding bond in 3. (iii) The
Co(1)ꢂC(7)
Co(1)ꢂC(8)
Co(1)ꢂC(2)
Co(1)ꢂC(3)
Co(1)ꢂS(1)
Co(1)ꢂCo(2)
Co(1)ꢂCo(3)
Co(2)ꢂC(9)
Co(2)ꢂC(10)
Co(2)ꢂC(3)
Co(2)ꢂC(2)
Co(2)ꢂS(2)
Co(2)ꢂCo(3)
Co(3)ꢂC(13)
Co(3)ꢂC(12)
Co(3)ꢂC(14)
Co(3)ꢂC(11)
Co(3)ꢂC(15)
Co(3)ꢂS(1)
Co(3)ꢂS(2)
C(1)ꢂC(2)
1.775(5)
1.794(5)
1.937(4)
1.941(4)
2.234(1)
2.573(1)
2.800(1)
1.769(5)
1.795(5)
1.937(4)
1.933(4)
2.233(1)
2.838(1)
2.030(5)
2.044(5)
2.057(6)
2.075(5)
2.102(6)
2.171(1)
2.194(1)
1.472(7)
1.366(6)
1.463(6)
,
Co3 atom is respectively 2.800(1) and 2.838(1) A from
Co1 and Co2; although these distances are very long
,
for Co–Co bonds, they are still more than 1 A shorter
than the corresponding distances in 3 which are clearly
non-bonding. (iv) The Co1–S1 and Co2–S2 distances
,
,
in 4 of 2.234(1) and 2.233(1) A are 0.05 A shorter than
the comparable distances in 4.
Since the dicobalt-hexafluorobut-2-yne portions of 3
and 4 are nearly identical it is logical to regard the
alkyne as a four-electron donor in both molecules. All
four metal atoms in 3 then have 18-electron configura-
tions but 4 must then be regarded as rare example of a
50 CVE tricobalt cluster which has one weak and two
very weak Co–Co bonds. According to Went, three
metal atoms can form either a 50 CVE open chain with
two strong metal–metal bonds or, more commonly, a
triangular 48 CVE framework [6]. Presumably, the un-
usual pattern of M–M distances in 4 is a consequence
of the anti-bonding nature of the HOMO.
C(2)ꢂC(3)
C(3)ꢂC(4)

116
K.W. Muir et al. / Journal of Organometallic Chemistry 635 (2001) 110–118
Table 4
,
Bond lengths (A) for 5
Molecule A
Molecule B
Molecule A
Molecule B
Co(1)ꢂC(3)
Co(1)ꢂC(4)
Co(1)ꢂC(8)
Co(1)ꢂS(1)
Co(1)ꢂS(2)
Co(1)ꢂCo(2)
Co(2)ꢂC(6)
Co(2)ꢂC(5)
Co(2)ꢂC(8)
Co(2)ꢂC(9)
1.76(2)
1.78(2)
2.00(2)
2.257(6)
2.280(6)
2.398(3)
1.71(2)
1.74(2)
2.00(2)
2.04(2)
1.77(2)
1.71(2)
1.95(2)
2.247(6)
2.277(6)
2.386(3)
1.73(2)
1.78(3)
2.02(2)
2.09(2)
Co(2)ꢂS(1)
Co(2)ꢂCo(3)
Co(3)ꢂC(9)
Co(3)ꢂS(2)
Co(3)···C(6)
S(1)ꢂC(1)
S(2)ꢂC(2)
C(7)ꢂC(8)
C(8)ꢂC(9)
2.202(6)
2.514(4)
1.90(2)
2.208(5)
2.50(2)
1.81(2)
1.81(2)
1.47(3)
1.40(3)
2.210(6)
2.507(4)
1.87(2)
2.206(5)
2.57(2)
1.82(2)
1.84(2)
1.43(3)
1.45(2)
2.4. Molecular structures of 5 and 7
vents were deoxygenated and dried by standard meth-
ods. Column chromatography was carried out with
silica gel purchased from SDS and deoxygenated before
use. Alkynes we purchased from Fluorochem Limited.
Literature methods were used for the preparation of
[Co2Cp2(m-SMe)2] [12] and [{Co(CO)3}2(m-CF3CꢀCR)]
(R=CF3, H) [14]. All other reagents were commercial
grade and were used as obtained. Yields are either with
respect to the starting complex 2 for the preparation of
3–6 or with respect to compound 1 for the synthesis of
7 and [CpCo(CO)2].
Infrared spectra were obtained with a Perkin–Elmer
1430 either in hexane–CH2Cl2 solutions or in KBr
pellets in the w(CO) region. The mass spectra were
measured on a GC/MS Hewlett–Packard spectrometer
at the Laboratoire de Biochimie, Faculte´ de Me´decine
(Brest). Chemical analyses were performed either by the
‘Oce´anographie Chimique’ Laboratory or by the ‘Spec-
troscopie Atomique’ Laboratory at the University of
Brest. The NMR spectra (1H, 13C, 19F), in CDCl3 or
(CD3)2CO solutions, were recorded on either a Bruker
AC300 or DRX400 spectrometer and were referenced
to SiMe4 (1H, 13C) or CFCl3 (13F). Part of the NMR
data for 5–7 are compared in Table 1. The remaining
The structures of the 50 CVE clusters 5 and 7 are
based on a more conventional molecular framework
and share several common features (see Figs. 3 and 4,
Tables 4 and 5). Thus, both clusters have an open chain
Co3 unit, with one intramolecular non-bonding Co···Co
,
distance of 3.3–3.4 A which is bridged by a methylthio-
late ligand whose S–Me bond is syn to the Cp–Co
bond in 5 (see Chart 1) and to both Co–Cp bonds in 7
(see Chart 2). The terminal atoms of the tricobalt chain
are also bridged in parallel fashion via s-bonds by the
CF3CꢀCH ligand which additionally is retro-datively
bonded to the central metal atom. The s-Co–C dis-
tances in 7 are comparable to the Co–C(alkyne) dis-
tances in 3 and 4, while the Co1–C6 and Co1–C7
,
p-bond lengths [2.079(3) and 2.003(3) A] are longer and
slightly irregular. The Co–Co distances [2.570(1) and
,
2.483(1) A] differ slightly, the shorter bond being asym-
metrically bridged by the C4 carbonyl group [ÚCo1–
C4–O3 and ÚCo3–C4–O3, respectively, 149.7(3) and
131.9(3)°]. The two independent molecules present in
crystals of 5 are structurally indistinguishable. The
analysis of 5 is less accuracy than that of 7 (see Section
3) and a detailed discussion of its bond lengths is not
warranted. However, the shortening of the thiolato-
Table 5
,
bridged Co1–Co2 bond [2.398(3) and 2.386(3) A] rela-
tive to the unbridged Co2–Co3 bond [2.514(3) and
,
Bond lengths (A) for 7
,
2.507(3) A] accords with a similar effect in 7. Co–S
Co(1)ꢂC(2)
Co(1)ꢂC(3)
Co(1)ꢂC(4)
Co(1)ꢂC(7)
Co(1)ꢂC(6)
Co(1)ꢂCo(3)
Co(1)ꢂCo(2)
Co(2)ꢂC(6)
Co(2)ꢂS(1)
Co(3)ꢂC(7)
Co(3)ꢂC(4)
Co(3)ꢂS(1)
S(1)ꢂC(1)
1.756(4)
1.786(4)
1.833(4)
2.003(3)
2.079(3)
2.4829(7)
2.5704(7)
1.908(3)
2.203(1)
1.930(4)
2.050(3)
2.208(1)
1.818(4)
1.484(5)
1.375(5)
,
bonds in 5 and 7 are in the range 2.202–2.210 A, except
for the Co1–S distances in 5 which are longer
[2.247(6)–2.280(6) A], reflecting the strong p-acidity of
the CO ligands bonded to Co1.
,
3. Experimental
3.1. General procedures
C(5)ꢂC(6)
C(6)ꢂC(7)
All reactions were performed under either argon or
nitrogen using standard Schlenk techniques, and sol-

K.W. Muir et al. / Journal of Organometallic Chemistry 635 (2001) 110–118
117
spectral data of these complexes are reported in this
section.
4 (black solid). Anal. Found: C, 29.8; H, 1,9; Co,
28.8. Calc. for C15H11Co3F6O4S2 (610.15): C, 29.53; H,
1.82; Co, 28.98%. IR (CH2Cl2): w (CO) 2058 m, 2037 s,
1
3.2. Preparation of [Co2(CO)4(v-CF3C2CF3)-
{v-Co2Cp2(v-SMe)2}] (3) and [Co3Cp(CO)4(v-SMe)2-
(v-CF3C2CF3)] (4)
2005 s cm1. H-NMR (CDCl3, RT): l 5.15 (s, C5H5),
3.24 (s, SCH3), 0.50 (s, SCH3). 19F-NMR (CDCl3, RT):
5
5
l −52.47 (q, JF–F=2.5 Hz, CF3), −48.9 (q, JF–F
=
2.5 Hz, CF3). 13C{1H}-NMR (CDCl3, −40 °C): l
198.7, 197.6, 196.5, 195.9 (s, CO), 129.2 (q, JC–F
281.0 Hz, CF3), 125.6 (q, JC–F=284.0 Hz, CF3), 85.1
1
To a THF solution (30 ml) of [{Co(CO)3}2(m-
CF3C2CF3)] (2a) (896 mg, 2.0 mmol) was added 1
equivalent of [Co2Cp2(m-SMe)2] (1) (684 mg), and the
mixture was heated under reflux for ca. 2 h. The
solution was then dissolved in CH2Cl2, and subjected to
silica gel chromatography. Elution with hexane–
CH2Cl2 (4:1) gave two main dark-brown bands yielding
4 (70 mg, 6%) and 3 (1280 mg, 87%), respectively.
3 (black solid). Anal. Found: C, 32.4; H, 2.1; Co,
31.8. Calc. for C20H16Co4F6O4S2 (734.17): C, 32.72; H,
2.19; Co, 32.11%. IR (CH2Cl2): w(CO) 2057 m, 2037 s,
=
1
2
(s, C5H5), 73.8 (q, JC–F=48.0 Hz, C–CF3), 69.8 (q,
2JCF=45.0 Hz, C–CF3), 26.8 (s, SCH3), 17.3 (s,
SCH3). Mass spectrum: m/z 610 [M]+, 582, 554, 526,
498 [M+−nCO] (n=1–4).
3.3. Preparation of [Co3(CO)4Cp(v-SMe)2(v-CF3C2H)]
(5 and 6) and [Co3(CO)3Cp2(v-CF3C2H)] (7)
A 100 ml Schlenk flask was charged with 1140 mg (3
mmol) of [{Co(CO)3}2(m-CF3C2H)] (2b), 1026 mg (3
mmol) of [Co2Cp2(m-SMe)2] (1) and 30 ml of THF. This
solution was heated under reflux for 2 h with constant
stirring. The progress of the reaction was followed by
19F-NMR until complex 2b totally disappeared. The
solvent was removed in vacuo. The solid residue was
dissolved in 10 ml of CH2Cl2–pentane and chro-
matographed over a silica gel column. Using pentane as
1
2012 s cm−1. H-NMR (CDCl3, −20 °C): l 5.00 (s,
C5H5), 4.83 (s, C5H5), 2.70 (s, 2 SCH3). 19F-NMR
5
(CDCl3, −20 °C): l −56.04 (q, JF–F=2.5 Hz, CF3),
−48.9 (q, 5JF–F=2.5 Hz, CF3). 13C({1H}-NMR
(CDCl3, −20 °C): l 202.8 (s, CO), 196.6 (s br, 3CO),
1
128.5 (q, 1JC–F=271.0 Hz, CF3), 125.5 (q, JC–F
=
268.0 Hz, CF3), 93.1 (m, 2 C–CF3), 85.1 (s, 2C5H5),
32.1 (s, 2SCH3).
Table 6
Crystal data and details of refinements
Compound
3
4
5
7
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
C20H16Co4F6O4S2
734.17
Orthorhombic
Cmc21
C15H11Co3F6O4S2
610.15
Monoclinic
P21/n
C14H12Co3F3O4S2
542.15
Triclinic
C
532.13
Triclinic
P1
17H14Co3F3O3S
(
(
P1
,
a (A)
10.4188(7)
13.7862(8)
17.9176(9)
10.0976(9)
16.2642(9)
13.149(1)
9.8127(9)
13.646(2)
14.306(3)
76.87(2)
85.16(1)
82.85(1)
4
8.7571(7)
10.051(1)
12.097(1)
84.00(1)
71.42(1)
66.68(1)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
99.10(1)
Z
4
4
2
v (mm−1
)
2.764
2.572
2.932
2.810
Crystal size (mm)
Habit and colour
q maximum (°)
0.58×0.48×0.13
Black plate
35.0
0.48×0.20×0.04
Red plate
28.5
0.15×0.10×0.05
Red block
23.3
0.20×0.20×0.02
Red plate
30.0
Reflections collected
Unique reflections [Rint
3981
3290 [0.015]
2159
6651
5189 [0.029]
3092
Analytical
0.904 and 0.372
5189/272
0.041, 0.091
0.102, 0.111
6433
5343 [0.115]
2519
8159
5379 [0.012]
3369
]
Reflections with I\2|(I)
Absorption correction
Max. and min. transmission
Data/parameters
„-scan
None
„-scan
0.664 and 0.441
3290/180
0.035, 0.089
0.065, 0.098
0.05(4)
0.656 and 0.495
5378 /249
0.046, 0.105
0.092, 0.116
5343/259
0.089, 0.224
0.225, 0.296
R1 and wR2 [I\2|(I)] a
R1 and wR2 (all data)
Flack parameter
−3
,
Dz (e A
)
0.76 to −0.31
0.57 to −0.35
1.21 to −1.13
0.73 to −0.57
1/2
a Refinements were on F2. R1=ꢀ ꢁꢁFobsꢁ−ꢁFcalcꢁꢁ/ꢀ ꢁFobsꢁ. wR2={ꢀw(Fo2bs−F2calc)2/ꢀwFo4bs
} .

118
K.W. Muir et al. / Journal of Organometallic Chemistry 635 (2001) 110–118
eluent gave [CoCp(CO)2] as the first fraction which was
evaporated to dryness under vacuum (yield 200 mg of
black–red crystals, 18.5%). Elution with pentane–
CH2Cl2 (9:1) gave a red–brown band containing 6
(yield 370 mg of red–brown pasty solid, 23%) and a
dark-violet band containing 5 (yield 360 mg of brown–
violet crystals, 22%). Further elution with pentane–
CH2Cl2 (4:1) produced a violet band of 7 (290 mg,
18%). Recrystallisation of 5 from cooled dichloro-
methane–pentane resulted in pure crystals of 5a.
S atoms were allowed anisotropic displacement tensors
because of the small number of observed intensities.
4. Supplementary material
Crystallographic information files (CIF files) for each
structure have been deposited with the Cambridge
Structural Database, deposition numbers CCDC
160747–160750 for 3, 4, 5 and 7, respectively. 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: de-
posit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
5 (brown–violet solid). Anal. Found: C, 31.3; H, 2.4;
Co, 32.8. Calc. for Co3C14H12F3O4S (542.14): C, 31.02;
H, 2.23; Co, 32.61%. IR (hexane): w(CO) 2064 m, 2024
s, 1944 m cm−1 13C{1H}-NMR (CDCl3, r.t.): l (CO),
.
206.3 (s), 199.0 (s), 198.3 (s), 196.6 (s).
6 (red–brown pasty solid). Elemental analyses were
tried under nitrogen on independently prepared samples
with identical NMR data, but unreliable data were
obtained probably because the pasty nature of 6. IR
Acknowledgements
(hexane): w(CO) 2060 m, 2020 s, 1956 s cm−1 13C{1H}-
.
We thank the CRNS (France), EPSRC (UK), and
the Universities of Brest and Glasgow.
NMR (CDCl3, −10 °C): l 205.0 (s br, CO), 199.5 (s,
CO), 198.0 (s,2 CO).
7 (dark-violet solid). Anal. Found: C, 38.7; H, 2.8;
Co, 32.9. Calc. for Co3C17H14F3O3S (532.13): C, 38.37;
H, 2.65; Co, 32.22%. IR (hexane): w(CO) 2034 s, 1998 s
cm−1. IR (in KBr pellets): w(CO) 2040 m, 2006 s, 1995
References
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.
212–200 (m, 3CO). Mass spectrum: m/z 532 [M]+.
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3.4. Kinetic measurements: 5a–5b isomerisation reactions
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(282.39 MHz). A 0.2 M solution of isomer 5a was
prepared by placing 0.050 g of the complex in cooled
(195 K) CD2Cl2. The tube was then inserted into the
magnet and taken to the desired temperature. The
progress of the reaction was followed by monitoring the
decreasing intensity of the 19F-NMR resonance of 5a
and the increasing intensity of the signal of 5b. Plots of
ln{(xe/(xe−x)}against time (where x and xe are the
percentages of 5b before and at the point when thermo-
dynamic equilibrium was reached) were linear. The
slope of this line gave the first-order rate constant.
(b) I.B. Benson, S.A.R. Knox, P.J. Naish, A.J. Welsh, J. Chem.
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[12] F. Baert, A. Guelzim, P. Coppens, Acta Crystallogr. Sect. B 40
(1984) 590.
3.5. Crystal structure analysis of 3, 4, 5 and 7
[13] F.Y. Pe´tillon, J.L. Le Que´re´, F. Le Floc’h-Pe´rennou, J.E. Guer-
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[16] Programs used: G.M. Sheldrick, SHELX-97. Programs for Crystal
Structure Analysis (Release 97-2), Institu¨t fu¨r Anorganische
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Measurements were made on a Nonius CAD4 dif-
,
fractometer with Mo–Ka radiation, u=0.71073 A, us-
ing standard procedures [15]. In general, non-hydrogen
atoms were refined with anisotropic displacement ten-
sors. H-atom positions were determined from stereo-
chemical considerations or difference maps and
subsequently rode on parent C atoms [16]. Further
details are given in Table 6. For 5 the crystals were of
poor quality and less than optimum size; only Co and