The effect of thiophene ring substitution position on the properties and electrochemical behaviour of alkyne-dicobaltcarbonylthiophene complexes

Article abstract of DOI:10.1016/j.jorganchem.2008.08.005

A large number of Co₂ (CO)_6^- and Co₂(CO)₄(L-L)-substituted alkyne complexes (L-L = dppa and dmpm) have been prepared, characterized and studied by cyclic and square-wave voltammetry. In this paper we

Full text of DOI:10.1016/j.jorganchem.2008.08.005

Journal of Organometallic Chemistry 693 (2008) 3457–3470
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
The effect of thiophene ring substitution position on the properties and
electrochemical behaviour of alkyne–dicobaltcarbonylthiophene complexes
a
Avelina Arnanz a, María-Luisa Marcos b, Salomé Delgado a, Jaime González-Velasco b, , Consuelo Moreno
*
a Departamento de Química Inorgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
b Departamento de Química, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2008
Received in revised form 31 July 2008
Accepted 1 August 2008
Available online 12 August 2008
A large number of Co2ðCOÞ6ꢀ and Co2(CO)4(L-L)-substituted alkyne complexes (L-L = dppa and dmpm)
have been prepared, characterized and studied by cyclic and square-wave voltammetry. In this paper
we report a comparative electrochemical study of 2,5-, 2,4-, 3,4- and 2,3-bis(trimethylsilylethynyl)thio-
phene dicobalt substituted alkyne complexes, in order to evaluate the extent of the electronic interaction
between the ‘‘Co2C2” redox centres depending on the position of the alkynyl substituent on the thiophene
ring.
Keywords:
Thiophene
Ó 2008 Elsevier B.V. All rights reserved.
Carbonylcobalt complexes
Electrochemistry
1. Introduction
attention [12]. Compounds in the present work contain substitu-
ents on adjacent positions of the thiophene ring, thus in addition
Molecules containing redox-active centres linked by a bridging
ligand capable of transmitting electronic effects have become an
area of significant research during the last two decades [1]. The
interest in these kinds of complexes is due to their possible appli-
cations in materials science as non-linear optical systems [2], qua-
si-one-dimensional conductors [3], electroluminescent devices [4],
‘‘molecular” wires [5,6] or as electrochromic devices and electro-
chemical sensors [7]. Electronic communication through such mol-
ecules is often evaluated by the redox response of electroactive
groups placed at their termini. The properties of such materials
can be modified by changing the metal fragments and/or the bridg-
ing ligands [5b,5d,8].
As alkynyl or polyynediyl bridging ligands have been shown to
be efficient in allowing the passage of electronic effects between
redox-active centres [8e,f,9,10], and therefore the electronic prop-
erties and the use of a thiophene-based diethynyl ligand should
lower the energy barriers and facilitate electron transfer, we have
recently reported the reactivity and the electrochemical behaviour
of 2,5- [10b] and 2,4-bis(trimethylsilylethynyl)thiophene [11]
derivatives, comparing the effects of the substitution position of
the –C„C–SiMe3 groups on the thiophene ring. These results
encouraged us to study the analogous 2,3- and 3,4-bis(trimethyl-
silylethynyl)thiophene ligands that in contrast with the well-stud-
ied 2,5-bis(trimethylsilylethynyl)thiophene have received little
to electronic effects, steric effects are also to be expected.
2. Experimental
2.1. Reagents and general techniques
All manipulations were carried out by using standard Schlenk
vacuum-line and syringe techniques under an atmosphere of
oxygen-free argon. All solvents for synthetic use were dried
and distilled, under an argon atmosphere, by standard proce-
dures [13].
Column chromatography was performed by using silica gel 100
(Fluka) and preparative TLC glass plates coated with silica gel (SDS
60–17 lm, 0.25 mm thick). 3,4- and 2,3-dibromothiophene (Lan-
caster Synthesis Inc.); Me3SiC„CH (TMSA), Co2(CO)8, KOH (Fluka);
CuI, a solution 1.0 M of tetrabutylammonium fluoride (TBAF) in
THF (Aldrich); 1,2-bis(dimethylphosphino)methane (dmpm)
(Streem); NaHCO3, MgSO4 (Panreac) and a solution of HCl (35%)
(Prolabo) were used as received. Trimethylamine N-oxide (Aldrich)
was sublimed prior to use and stored under argon. Compounds
Pd(PPh3)4 [14] and 1,2-bis(diphenylphosphino)amine (dppa) [15]
were prepared according to the literature. The 1H, 1H{31P},
13C{1H}, 31P{1H} NMR spectra and HMQC and HMBC data were re-
corded with Bruker AMX-300 and 500 instruments. Chemical shifts
were measured relative to residual protons of the solvents. Infrared
spectra were measured with a Perkin–Elmer 1650 infrared spec-
trometer. Elemental analyses were performed with a Perkin–Elmer
240 B microanalyser. Electronic spectra were recorded with a
* Corresponding author. Tel.: +34 91 4974830; fax: +34 91 4975238.
E-mail address: jaime.gonzalez@uam.es (J. González-Velasco).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.08.005

3458
A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
Unicam UV 4 UV–Vis spectrophotometer. Mass spectra were mea-
sured with a VG-Autospec mass spectrometer for FAB and EI and
with a Reflex III Bruker mass spectrometer for MALDI-TOF. Spec-
troscopy data are available as Supplementary material. Electro-
chemical measurements were carried out with a computer driven
Par Mo. 273 electrochemistry system in a three-electrode cell un-
der nitrogen atmosphere in anhydrous deoxygenated CH2Cl2 con-
2.5. Synthesis of X-[Co2(CO)4(l-dppa){l2-g
2-(SiMe3C2)}]-Y-
(Me3SiC„C)C4H2S (X = 3, Y = 4 (A2); X = 2, Y = 3 (C3) and X = 3, Y = 2
(C4))
To a solution of A1 (0.90 g, 1.60 mmol) or a solution containing
C1 and C2 (0.75 g, 1.33 mmol in 1.8:1 ratio) in hexane (100 mL)
was added 1 equiv. of dppa and 2 equiv. of trimethylamine
N-oxide, in each case. The reaction mixture, monitored by FT-IR
spectroscopy until the mC„O bands of the parent complex had dis-
appeared, was stirred at 45 °C for 5 days. Finally, the solvent was
removed under vacuum. From A1, the residue was purified by
chromatography on a hexane-packed silica column using hexane/
CH2Cl2 (2:1) to afford A2 (0.90 g, 63% yield) as a stable dark red so-
lid in addition to A (22.1 mg, 5% yield). From C1 and C2, the residue
was purified by thin-layer chromatography (TLC) using hexane/
CH2Cl2 (3:1) to afford C3 (0.27 g, 23% yield) and C4 (0.12 g, 10%
yield) as stable dark red solids in addition to C (0.15 g, 41%
yield).
taining
0.15 M
tetrabutylammonium
hexafluorophosphate
(TBAPF6) as Supporting electrolyte. Cyclic and square-wave vol-
tammetry (CV and SWV, respectively) studies were carried out in
a three-electrode system. Polycrystalline Pt (0.05 cm2) or glassy
carbon were used as working electrodes; the counter electrode
was a Pt gauze and the reference electrode was a silver wire qua-
si-reference electrode. Decamethylferrocene (Fc*) was used as
internal standard, and all potentials in this work are referred to
+
the Fc* /Fc* couple. Under the actual experimental conditions,
+
E1/2 of the ferrocene couple (Fc+/Fc) was +0.55 V versus Fc* /Fc* in
CH2Cl2 solution. Controlled potential electrolysis of A3 was per-
formed at 0.8 V and one mole of electrons per mole of A3 was
found to be consumed in the oxidation process. The number of
electrons involved in the remaining processes were determined
by comparison of peak heights in CV.
2.6. Synthesis of X-[Co2(CO)4(l-dppa){l2-g
2-(SiMe3C2)}]-Y-(Br)-
C4H2S (X = 3, Y = 4 (B2) and X = 2, Y = 3 (D2))
The same procedure as describe above was applied in the
preparation of these compounds from B1 or D1 (0.27 g,
0.50 mmol), dppa (0.19 g, 0.50 mmol) and Me3NO (0.11 g,
1.00 mmol). After the solvent had been removed under vacuum,
2.2. Synthesis of 3,4- and 2,3-bis(trimethylsilylethynyl)thiophene (A
and C) and X-(trimethylsilylethynyl)-Y-bromothiophene (X = 3, Y = 4
(B) and X = 2, Y = 3 (D))
the product was purified by chromatography on
a hexane-
To
a
solution of 3,4- or 2,3-dibromothiophene (3.0 g,
packed silica column using hexane/CH2Cl2 (3:1). From B1, B2
(0.30 g, 70% yield) was obtained as a stable dark red solid in
addition to B (5.1 mg, 4% yield). From D1, D2 (0.20 g, 47% yield)
was obtained as a stable dark red solid in addition to D (40 mg,
31% yield).
12.4 mmol) in Et3N (100 mL) was added at 0 °C, Pd(PPh3)4
(0.70 g, 0.62 mmol), CuI (0.23 g, 1.24 mmol) and excess of tri-
methylsilylacetylene (TMSA) (12.1 g, 17.5 mL, 124 mmol). The
resulting mixture was stirred first at r.t. for 1/2 h and finally at
75 °C for 20 days. The solvent was removed under reduced pres-
sure and the residue dissolved in Et2O (100 mL) and washed
with (i) a solution of HCl 10%, (ii) a saturated solution of NaH-
CO3 and dried (MgSO4). The solvent was evaporated and the res-
idue purified by column chromatography with hexane. From 3,4-
dibromothiophene, A (1.03 g, 30% yield) and B (1.12 g, 35% yield)
were obtained as stable yellow oils. From 2,3-dibromothiophene,
C (0.96 g, 28% yield) and D (1.32 g, 41% yield) were obtained as
stable yellow oils.
2.7. Synthesis of 3-[Co2(CO)4(l-dmpm){l2-g
2-(SiMe3C2)}]-4-
(Me3SiC„C)C4H2S (A3)
By a similar procedure as described above, from A1 (0.75 g,
1.33 mmol), dmpm (0.18 g, 0.21 mL, 1.33 mmol) and Me3NO
(0.30 g, 2.66 mmol). The reaction mixture, monitored by FT-IR
spectroscopy until the mC„O bands of the parent complex had
disappeared, was stirred at r.t. for 24 h and then at 45 °C for
one more day. After the solvent was removed under vacuum,
2.3. Synthesis of X-[Co2(CO)6{l2
-g
2-(SiMe3C2)}]-Y-(Me3SiC„C)C4H2S
the product was purified by chromatography on
a hexane-
(X = 3, Y = 4 (A1); X = 2, Y = 3 (C1) and X = 3, Y = 2 (C2))
packed silica column using hexane/CH2Cl2 (2:1) to afford A3
(0.36 g, 42% yield) as
(77.4 mg, 21% yield).
a stable red solid in addition to A
To a solution of A (0.90 g, 3.26 mmol) or C (0.45 g, 1.63 mmol)
in hexane (100 mL) was added 2 equiv. of Co2(CO)8. The reaction
was monitored by FT-IR and 1H NMR spectroscopy until the sig-
nals of the parent compounds A or C and Co2(CO)8 had disap-
peared. After the mixture had been stirred at r.t. for 1 h, the
solvent was removed under vacuum and the residue purified by
column chromatography with hexane. From A, A1 (1.68 g, 92%
yield) was obtained as an unstable red solid. From C, C1 (0.55 g,
60% yield) together with C2 (0.30 g, 33% yield) were obtained as
unstable solids.
2.8. Synthesis of X-[Co2(CO)4(l-L-L){l2-g
2-(SiMe3C2)}]-Y-
(C„CH)C4H2S (X = 3, Y = 4, L-L = dppa (A4) or dmpm (A5) and X = 2,
Y = 3, L-L = dppa (C5))
A solution of A2 (0.35 g, 0.39 mmol), A3 (0.34 g, 0.53 mmol) or
C3 (0.25 g, 0.28 mmol) in MeOH saturated with KOH was stirred
at r.t. for 24 h. Then, the solvent was removed under vacuum and
the residue extracted with several portions of Et2O and purified
by chromatography on a hexane-packed silica column using hex-
ane/CH2Cl2 (1:1) or by thin-layer chromatography (TLC) using hex-
ane/CH2Cl2 (1.5:1). From C3, C5 (87.3 mg, 38% yield) was obtained
as an unstable reddish solid. From A2 and A3, A4 (0.15 g, 48% yield)
and A5 (0.14 g, 46% yield) were obtained, respectively, as unstable
red solids. A4 was also obtained in 39% yield when TBAF (0.44 mL,
1.0 M in THF, 0.44 mmol) was added to a solution of A2 (0.20 g,
0.22 mmol) in THF/MeOH (10:1), the mixture was stirred at r.t.
for 24 h and subsequent chromatography with hexane/CH2Cl2
(1:1) on a silica column was performed.
2.4. Synthesis of X-[Co2(CO)6{l2
Y = 4 (B1) and X = 2, Y = 3 (D1))
-g
2-(SiMe3C2)}]-Y-(Br)-C4H2S (X = 3,
By a similar procedure as described above, from B or D (0.75 g,
2.89 mmol) and 1 equiv. of Co2(CO)8. After the solvent had been re-
moved under vacuum, the product was eluted with hexane on a
silica column. From B, B1 (1.42 g, 90% yield) was obtained as an
unstable red solid. From D, D1 (1.45 g, 92% yield) was obtained
as an unstable red solid.

A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
3459
2.9. Synthesis of 3-[Co2(CO)4(
(A6)
l
-dppa){l2
-
g
2-(HC2)}]-4-(C„CH)C4H2S
graphic data for this paper. Final positional parameters, anisotropic
thermal parameters, hydrogen atom parameters and structure
amplitudes for A2, B2 and D2 are available as Supplementary
material. Crystallographic details are collected in Table 5, while
important bond lengths and angles are summarized in Table 6
(for A2), Table 7 (for B2) and Table 8 (for D2). ORTEP plots indicat-
ing the atom-labelling schemes are given in Fig. 2 (A2), Fig. 3 (B2)
and Fig. 4 (D2).
To a solution of A2 (0.35 g, 0.39 mmol) in wet THF (100 mL) was
added TBAF (1.95 mL, 1.0 M in THF, 1.95 mmol) and the mixture
stirred at r.t. for 24 h. After the solvent had been removed under
vacuum, the residue was purified by chromatography on a hex-
ane-packed silica column using hexane/CH2Cl2 (1:1) and then by
thin-layer chromatography (TLC) using hexane/CH2Cl2 (4:3), to af-
ford A6 (0.16 g, 55% yield) as an unstable purple solid. This com-
pound has also been obtained from A4, under the same
conditions, in a similar yield.
3. Results and discussion
3.1. Synthesis and spectroscopic characterization
2.10. Synthesis of 3-[Co2(CO)4(
[Co2(CO)6{l2
2-(HC2)}]C4H2S (A7)
l-dppa){l2-g
2-(HC2)}]-4-
A [12a] and C [12b] have been synthesized from coupling reac-
tions of 3,4- and 2,3-dibromothiophene, respectively, with excess
of TMSA in the presence of Pd(PPh3)4, CuI and triethylamine. In
the PdꢀCu catalyzed cross-coupling reactions it is known that
the oxidative addition of the organic electrophile to the active
Pd(0) catalyst is the critical step for the catalytic process [18]. In
agreement with this, the thiophene positions more suitable to an
oxidative addition are 2 and 5. Thus, from the less reactive starting
materials 3,4- and 2,3-dibromothiophene, we have obtained the
desired dialkynyl organic ligands in addition to the respective bro-
moderivatives, B [19] and D. Also, the reaction from 2,6-dibromo-
pyridine [20], under Sonogashira coupling conditions, gave
reasonable yields of both, the partially and fully substituted com-
pounds containing the TMSA group.
A–D have been completely characterized by spectroscopic data,
details of which are given as Supplementary material. IR spectra
show weak absorption bands, typically mC„C stretches of the alky-
nyl units, in the characteristic range of diynyl complexes (two mC„C
stretches at ca. 2060ꢀ2200 cmꢀ1) and monoynyl complexes (one
mC„C stretch at ca. 2090ꢀ2150 cmꢀ1). The 1H NMR spectra exhibit
one singlet signal for A and two doublet signals for B, C and D due
to the thiophene ring protons, with coupling constants that are
consistent with their chemical formulae. In the 13C NMR spectra
the signals belonging to the thiophene ring (C2, C3, C4 and C5)
and the alkynyl units (C6, C7, C8 and C9) can be observed, and the
assignments were made on the basis of the d values and NMR
two-dimensional experiments (HMBC and HMQC). See Schemes
A–D for atomic labelling and Tables 1–4 for NMR data.
-g
To a solution of A6 (0.15 g, 0.20 mmol) in hexane (50 mL) was
added 1 equiv. of Co2(CO)8. The reaction was monitored by FT-IR
spectroscopy and the mixture was stirred at r.t. for 1 h. After the
solvent had been removed under vacuum, the product was purified
by chromatography on a hexane-packed silica column using hex-
ane/CH2Cl2 (2:1) to afford A7 (0.18 g, 87% yield) as an unstable
dark red-purple solid.
2.11. X-ray data collection, structure determination and refinement
Dark red crystals of A2, B2 and D2 were grown by slow evapo-
ration of their respective solutions in n-hexaneꢀCH2Cl2 at r.t. Suit-
able crystals were mounted on a glass fibre and transferred to a
Bruker SMART 6K CCD area-detector three-circle diffractometer
with a MAC Science Co., Ltd. rotating anode (Cu K
a radiation,
k = 1.54178 Å) generator equipped with Goebel mirrors at settings
of 50 kV and 110 mA [16]. The structures were solved and refined
using the SHELXTL/PC V 6.10 package [17]. The structures were solved
by direct methods, refinement was by full-matrix least-squares on
F2 using all data (negative intensities included). The H atom param-
eters were calculated and atoms were constrained as riding atoms
with U isotropic 20% larger than those of the corresponding C-
atoms for the phenyl H-atoms and the NꢀH atom, and 50% larger
for the methyl H-atoms. CCDC-653921 (A2), CCDC-653925 (B2)
and CCDC-682712 (D2) contain the supplementary crystallo-
The C3ꢀC4 bond in a thiophene ring is known to have less dou-
ble bond character than the C2ꢀC3 bond [21]. As a consequence,
the overall conjugation of 3,4-bis(trimethylsilylethynyl)thiophene
is expected to be lower than in 2,5-, 2,3- and 2,4-bis(trimethylsil-
ylethynyl)thiophene. These arguments are supported by the elec-
tronic absorption spectra for the ligands (Fig. 1). It can be
observed that these molecules have kmax at 331 [22], 311 and
277 nm [11], respectively. However, kmax for 3,4-bis(trimethylsily-
lethynyl)thiophene (258 nm) is significantly blue-shifted, thus
indicating a lesser overall conjugation in this molecule. A similar
behaviour takes place in the case of the three diacetylenic dehy-
drothieno[18]annulenes studied by Sakar and Haley [23], where
the electronic spectra of two of them (those in which the thiophene
moieties are fused at the 2- and 3-positions to the [18]annulene
core) exhibit kmax values at around 428 nm, whereas this value
for the third annulene (where two of the thiophene rings are fused
to the macrocycle through the 3-and 4-positions) is significantly
blue-shifted (401 nm), indicating a lesser overall conjugation as
discussed above.
Co2(CO)6-substituted alkyne complexes were obtained by direct
reaction between Co2(CO)8 and the corresponding organic ligand.
When 2 equiv. of Co2(CO)8 were added to A and C, only the mono-
substituted-cobalt–alkyne compounds could be obtained (Schemes
A and C). However, when Co2(CO)8 was added to A6, complex A7
Fig. 1. UV–Vis spectra (CH2Cl2, nm) for the organic ligands 2,5- (a), 2,4- (b), 3,4- (c)
and 2,3-bis(trimethylsilylethynyl)thiophene (d).

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A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
Fig. 2. ORTEP diagram of A2, with 50% ellipsoids.
Fig. 3. ORTEP diagram of B2, with 50% ellipsoids. Hydrogen atoms have been removed for clarity.
was obtained in 87% yield under the same conditions (Scheme A). It
can be explained from the steric hindrance of the –SiMe3 groups.
Thus, the selective synthesis of A1, C1 and C2 indicates that the
addition of ‘‘Co2(CO)6” units to alkynes can be controlled. Clearly
one of the factors that influences the degree and position of the
metallisation is the bulk of the substituents on the alkyne [24].
By a similar manner, it can be observed [10a] that Co2(CO)8 reacts
with the –C„C– free triple-bond in Co2(CO)4(dppm){l2-g
2-(Me3-

A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
3461
Fig. 4. ORTEP diagram of D2, with 50% ellipsoids. Hydrogen atoms have been removed for clarity.
SiMe3
PR2
SiMe3
R2P
SiMe3
SiMe3
9
Co(CO)3
Co(CO)2
(OC)3Co
Me3Si
(OC)2Co
9
7
8
7
6
6
8
Me3Si
4
3
P-P
Co2(CO)8
2
5
S
S
S
A2
A3
P-P= dppa
P-P= dmpm
A1
A
a)
PR2
X
R2P
PR2
Co(CO)2 (OC)3Co
R2P
Co(CO)2
(OC)2Co
X'
(OC)2Co
Co(CO)3
7
6
8
9
H
H
Co2(CO)8
S
S
P-P= dppa;X =H ;X '= SiMe3;a )K OH/M eOH
P-P= dmpm;X =H ;X '= SiMe3;a )K OH/M eOH
P-P= dppa;X =H ;X '= H; a)TBFA,T HF wet
A4
P-P= dppa
A7
A5
A6
Scheme A.
SiC2)}C„CX when X = H; however, when X = SiMe3 the reaction
On the basis of the isolated yield for C1 (60%) and C2 (33%), it
does not take place.
can be observed that the preference of the Co2(CO)6 units for coor-

3462
A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
H
N
PPh2
SiMe3
Ph2P
Co(CO)2
Co(CO)3
(OC)2Co
7
(OC)3Co
Me3Si
Br
Br
Br
7
6
6
Me3Si
4
3
2
5
dppa
Co2(CO)8
S
S
S
B2
B
B1
Scheme B.
SiMe3
SiMe3
9
(OC)3Co
Co(CO)3
SiMe3
8
8
9
4
3
Co2(CO)8
SiMe3
5
7
6
2
S
S
S
6
Co(CO)3
(OC)3Co
SiMe3
7
SiMe3
C2
C
C1
dppa
H
N
Ph2P
PPh2
SiMe3
H
(OC)2Co
Co(CO)2
SiMe3
a)
SiMe3
SiMe3
S
S
S
Co(CO)2
PPh2
(OC)2Co
Ph2P
Co(CO)2
PPh2
(OC)2Co
Ph2P
SiMe3
C4
N
H
N
H
C3
C5
a) KOH/ MeOH
Scheme C.
Br
Br
Br
4
3
dppa
SiMe3
Co2(CO)8
SiMe3
5
2
S
S
S
6
Co(CO)2
PPh2
Co(CO)3
(OC)2Co
Ph2P
(OC)3Co
7
SiMe3
D2
D
D1
N
H
Scheme D.

A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
3463
Table 1
1H NMR (300 MHz, CDCl3, 25 °C, ppm) data for A, B, A1–A7 and B1–B2
H5 H2
@H5
–C„CH
–C6ꢀC7H
–C8ꢀC9H
–
–C„CSiMe3
–CꢀCSiMe3
–
A
B
7.39 (s)
7.44 (s)a
7.67 (s)b
7.47 (d)
–
–
0.25 (s)
0.27 (s)a
0.25 (s)b
0.27 (s)
7.21 (d)
JHH = 3.4 Hz
7.27 (d)a
JHH = 3.4 Hz
7.58 (d)b
–
–
–
–
JHH = 3.4 Hz
7.51 (d)a
JHH = 3.4 Hz
7.78 (d)b
0.26 (s)a
0.24 (s)b
JHH = 3.3 Hz
7.29 (d)
JHH = 3.3 Hz
7.44 (d)
JHH = 3.2 Hz
6.01 (d)
JHH = 3.5 Hz
6.94 (d)
JHH = 3.6 Hz
6.80 (d)
JHH = 3.4 Hz
6.05 (d)
JHH = 3.4 Hz
6.82 (d)
JHH = 3.4 Hz
7.50ꢀ7.35
JHH = 3.3 Hz
7.57 (d)
JHH = 3.3 Hz
7.33 (d)
JHH = 3.0 Hz
7.17 (d)
JHH = 3.5 Hz
6.21 (d)
JHH = 3.6 Hz
7.53 (d)
JHH = 3.4 Hz
7.19 (d)
JHH = 3.3 Hz
7.53 (d)
JHH = 3.4 Hz
7.50ꢀ7.35
A1
B1
A2
B2
A3
A4
A5
A6
A7
–
–
–
–
–
–
–
–
–
0.21 (s)
0.41 (s)
0.42 (s)
0.37 (s)
0.40 (s)
0.30 (s)
0.37 (s)
0.29 (s)
–
–
–
–
–
–
0.15 (s)
–
–
–
–
–
0.17 (s)
3.03 (s)
3.12 (s)
3.14 (s)
–
–
–
–
–
–
–
5.73 (t)
JPH = 9.3 Hz
5.31 (t)
–
7.60ꢀ7.39
7.60ꢀ7.39
5.75 (s)
–
JPH = 10.5 Hz
a
CD2Cl2.
Acetone-d6.
b
dination at the alkyne in 2-position of the thiophene ring is almost
two times greater than that for the 3-position. This preference is
also observed in the synthesis of the analogous complexes 2-[Co2
The IR spectra of Co2(CO)6-substituted alkyne complexes exhi-
bit three strong absorptions in the carbonyl stretching region
(2090ꢀ2022 cmꢀ1); in phosphine–substituted alkyne complexes
these absorptions lie at lower frequencies and the spectral patterns
are similar to those observed for previously reported cobalt–alkyne
and cobalt–substituted-alkyne complexes [8e–f,10,11,20,25–27].
For the dimetallated compound A7, the IR carbonyl region results
from the overlap of the IR carbonyl stretching bands corresponding
to each core. Thus, A7 exhibits five strong absorptions. The three at
lower frequencies (2026, 1995 and 1970 cmꢀ1) belong to the
‘‘Co2(CO)4(dppa)” unit and the two at higher frequencies (2090
and 2054 cmꢀ1) are due to the ‘Co2(CO)6’ unit. A1, A2 and A3 con-
tain an uncomplexed C„C triple-bond, which gives a mC„C weak
absorption between 2154 and 2150 cmꢀ1. For A4, A5 and A6 this
value is not observed, but m„C–H appears at ca. 3302 cmꢀ1. Simi-
larly, C1, C2, C3 and C4 show a mC„C weak absorption at ca.
(CO)6{l2
4-[Co2(CO)6{l2
-g
2-(SiMe3C2)}]-4-(Me3SiC„C)C4H2S and 2-(Me3SiC„C)-
-g
2-(SiMe3C2)}]C4H2S [11]. This result can be
explained by electronic factors, as judged by the 13C NMR shifts
for the alkyne C-atoms in C (Table 4).
In order to enhance the stability of the dicobalt units by bridg-
ing effect between the two metal atoms, we have synthesized com-
plexes containing two different phosphine ligands, dppa and
dmpm. Co2(CO)4(L-L)–substituted alkyne complexes were pre-
pared by substitution reaction of two carbonyl ligands in the pres-
ence of Me3NO at the Co2(CO)6 units of the parent complexes
(Schemes A–D).
By taking advantage of the preferential desilylation of a non-
coordinated alkyne group, A2, A3 and C3 were accomplished by
treatment with saturated solutions of KOH in degassed methanol
at room temperature to give the terminal diyne compounds A4,
A5 and C5, respectively. When A2 was prepared using 2 equiv. of
Bu4NF in THF/MeOH, compound A4 was isolated too, but in less
yield (39%) (see Section 2). Complex A6 was obtained from A2 or
A4 when stronger desilylation conditions were used (5 equiv. of
Bu4NF in wet THF). The analogous diprotonated dmpm-compound
was synthesized by similar conditions from A5 and could be ob-
served by IR and 1H NMR spectroscopies (IR (THF, cmꢀ1): m„CH
3303.3 (m), mCO 2016.5 (s), 1987.2 (vs), 1958.3 (s), 1941.2 (sh). 1H
NMR (300 MHz, CDCl3, 25 °C): d = 7.46 (d, JHH = 3.2 Hz, H2), 7.42
(d, JHH = 3.3 Hz, H5), 5.81 (t, JPH = 7.6 Hz, –C7H), 3.18 (s, „CH),
2.15 (m, 1H, ABXY, –CH2–), 2.00 (m, 1H, ABXY, –CH2–), 1.54 (m,
6H, 2 –PMe), 1.46 (m, 6H, 2 –PMe) ppm). Finally, after being puri-
fied by thin-layer chromatography (TLC) using hexane/CH2Cl2 (4:3)
as eluent, this compound decomposed and it could not be isolated.
All these compounds have been characterized by spectroscopic
data (IR, UV–Vis, 1H, 1H{31P}, 13C{1H}, 31P{1H} NMR and MS) and
elemental analysis, details of which were given as Supplementary
material.
Table 2
1H NMR (300 MHz, CDCl3, 25 °C, ppm) data for C, D, C1–C5 and D1–D2
H5
H4
–C„CH
–C„CSiMe3
–CꢀCSiMe3
C
7.09 (d)
6.96 (d)
–
0.27 (s), 0.28 (s)
–
JHH = 5.3 Hz
7.16 (d)
JHH = 5.4 Hz
7.11 (d)
JHH = 5.4 Hz
7.25 (d)
JHH = 5.3 Hz
7.14 (d)
JHH = 5.3 Hz
6.69 (d)
JHH = 5.4 Hz
6.55 (d)
JHH = 5.3 Hz
6.50 (d)
JHH = 5.3 Hz
6.58 (d)
JHH = 5.3 Hz
6.93 (d)
JHH = 5.4 Hz
7.03 (d)
JHH = 5.4 Hz
6.98 (d)
JHH = 5.3 Hz
6.95 (d)
JHH = 5.3 Hz
6.60 (d)
JHH = 5.4 Hz
6.68 (d)
JHH = 5.3 Hz
5.95 (d)
JHH = 5.3 Hz
6.69 (d)
D
–
0.28 (s)
0.22 (s)
–
–
C1
D1
C2
D2
C3
C4
C5
–
0.41 (s)
0.43 (s)
0.39 (s)
0.39 (s)
0.37 (s)
0.37 (s)
0.36 (s)
–
–
0.23 (s)
–
–
–
0.14 (s)
0.15 (s)
–
–
3.10 (s)
JHH = 5.3 Hz
JHH = 5.3 Hz

3464
A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
Table 3
13C NMR (500 MHz, CDCl3, 25 °C, ppm) data for A, B, A1–A7 and B1–B2
C2
C3
@C4
C4
C5
C6
C7
C8
C9
A
@C5
125.1 (s)
125.4 (s)a
125.7 (s)b
138.7 (s)
142.3 (t)
JCP = 3.5 Hz
145.0 (t)
JCP = 4.1 Hz
143.5 (t)
JCP = 3.5 Hz
146.0 (t)
JCP = 3.7 Hz
144.8 (t)
JCP = 2.1 Hz
141.1 (t)
128.8 (s)
129.5 (s)a
130.6 (s)b
124.8 (s)
124.2 (s)
98.2 (s)
96.6 (s)
= C6
= C7
98.4 (s)a
99.2 (s)b
95.7 (s br)
95.7 (t)
97.1 (s)a
96.8 (s)b
81.1 (s br)
91.2 (t)
A1
A2
133.6 (s)
132.2 (s)
123.6 (s)
122.6 (s)
100.1 (s)
100.8 (s)
99.6 (s)
98.1 (s)
98.9 (s)
82.1 (s)
82.5 (s)
80.5 (s)
74.7 (s)
–
JCP = 8.6 Hz
97.3 (t)
JCP = 7.8 Hz
95.2 (t)
JCP = 8.6 Hz
96.7 (m)
JCP = 11.2 Hz
86.8 (t)
JCP = 10.1 Hz
91.4 (t)
JCP = 11.1 Hz
86.7 (m)
A3
A4
A5
A6
A7
B
133.1 (s)
131.2 (s)
132.0 (s)
130.2 (s)
129.6 (s)
123.0 (s)
121.3 (s)
121.7 (s)
121.8 (s)
124.3 (s)
121.8 (s)
125.0 (t)
100.1 (s)
79.5 (s)
79.1 (s)
79.2 (s)
81.8 (s)
–
121.4 (t)
JCP = 3.1 Hz
135.5 (t)
86.2 (t)
JCP = 17.6 Hz
86.0 (t)
JCP = 17.9 Hz
97.8 (s)
74.0 (t)
JCP = 9.4 Hz
75.1 (t)
JCP = 10.1 Hz
97.7 (s)
JCP = 5.6 Hz
129.0 (t)
JCP = 3.2 Hz
113.8 (s)
JCP = 2.7 Hz
124.6 (s)
JCP = 5.9 Hz
129.6 (s)
130.3 (s)a
131.6 (s)b
124.6 (s)
122.9 (s)
122.7 (s)
123.5 (s)a
124.8 (s)b
126.5 (s)
125.3 (s)
113.9 (s)a
113.7 (s)b
112.6 (s)
124.9 (s)a
125.1 (s)b
137.7 (s)
98.1 (s)a
98.0 (s)a
98.8 (s)b
97.9 (s)b
B1
B2
95.4 (s br)
95.1 (t)
82.1 (s br)
91.4 (t)
–
–
–
–
111.7 (s)
140.9 (t)
JCP = 3.7 Hz
JCP = 8.9 Hz
JCP = 11.2 Hz
a
CD2Cl2.
Acetone-d6.
b
Table 4
13C NMR (500 MHz, CDCl3, 25 °C, ppm) data for C, D, C1–C4 and D1–D2
C2
C3
C4
C5
C6
C7
C8
C9
C
127.1 (s)
143.7 (s)
121.5 (s)
151.5 (m)
127.5 (s)
123.1 (s)
140.6 (s)
118.2 (s)
129.3 (s)
133.7 (s)
130.0 (s)
133.9 (s)
125.7 (s)
124.2 (s)
126.4 (s)
121.8 (s)
98.6 (s)
It is not observed
97.4 (s)
103.5 (s)
82.3 (m)
107.4 (s)
96.2 (s)
100.0 (s)
95.4 (m)
101.8 (s)
98.8 (s)
102.7 (s)
80.9 (m)
100.0 (s)
C1
C2
C3
92.97 (m)
92.90 (m)
C4
D
D1
D2
117.0 (s)
120.8 (s)
136.2 (s)
142.5 (t)
145.6 (s)
116.6 (s)
113.7 (s)
107.5 (s)
134.2 (s)
129.9 (s)
132.2 (s)
131.3 (s)
124.3 (s)
126.9 (s)
126.0 (s)
123.1 (s)
99.0 (s)
95.5 (s)
91.5 (m)
91.2 (t)
105.4 (s)
103.4 (s)
83.2 (m)
95.5 (m)
93.0 (m)
–
–
–
–
–
–
92.6 (t)
JCP = 3.5 Hz
JCP = 8.2 Hz
JCP = 10.5 Hz
2143 cmꢀ1. As expected, for C5 this
m
C„C value (2088 cmꢀ1) is lower.
1.35 ppm) and the diasterotopic protons of the methylene (at ca.
d = 2.20 and 1.96 ppm) of the dmpm ligand, which are coupled
with the P-atoms, and they appear as double triplets with JHH at
ca. 13.4 Hz and JPH at ca. 10.3 Hz. For dppa-complexes the proton
of –NH group is coupled with the two chemically equivalent P-
atoms and it appears as triplet with 1Hꢀ31P coupling constant of
J ꢁ 6.1 Hz.
In addition, C5 exhibits a m„C–H absorption at ca. 3300 cmꢀ1
.
All NMR data are consistent with overall geometry established
in the solid state for A2, B2 and D2 (Figs. 2–4) and with the pro-
posed structures (Schemes A–D) and comparable to those of the
known cobalt-substituted 2,5- [10b] and 2,4-bis(trimethylsilyle-
thynyl)thiophene [11] complexes. The 1H and 13C{1H} NMR data
of all the complexes are summarized in Tables 1–4.
The 13C NMR chemical shifts of the carbonyl groups in all the
complexes appear as one, two or three signals at around d = 200,
204 and 207 ppm, suggesting that they are rapidly interchanging
on the NMR scale. The unambiguous assignments of all carbon
atoms has been carried out by using homonuclear and hetereonu-
clear two-dimensional correlation spectroscopy experiments
(HMQC and HMBC) and by comparison of their spectral data with
those of the known cobalt-substituted 2,5- [10b] and 2,4-bis(trim-
ethylsilylethynyl)thiophene [11] complexes. The carbon reso-
nances of the free and coordinated acetylene carbon atoms were
easily observed and their JCP coupling constants values and chem-
ical shifts show in the range of analogous compounds
In 1H NMR spectra, the chemical shifts for the SiMe3 and C„CH
protons are found to be very sensitive to cobalt complexation on
the adjacent alkyne bond, and they show a significant downfield
shift with respect to the free ligands in accordance with the reduc-
tion in the C„C triple-bond character [28]. Thus, the acetylenic
proton of complexes A4, A5 and A6 (one ‘‘Co2C2” unit) appears as
a singlet signal at ca. 3.10 ppm, while in A7 (two ‘‘Co2C2” units)
the coordination of Co2(CO)6 to the alkyne is evident from the
downfield shift of the terminal proton in the 1H NMR spectrum
(at 5.75 ppm). In A6 the –(CꢀC)coordꢀH signal is coupled with the
two chemically equivalent P-atoms and it appears as a triplet with
1Hꢀ31P coupling constant of J = 9.3 Hz like in other similar com-
pounds [10b,11,29]. This resonance can also be observed in A7 as
a triplet signal at a similar value. The 1H NMR spectra of A3 and
A5 show two doublet signal resonances of the thiophene protons
together with those due to the methyl (at ca. d = 1.45 and
(d = 74ꢀ101 ppm) (Tables
3 and 4) [8e–f,10,11,26b,30]. For
A2ꢀA4 and B2, the C4, C6, and C7 atoms display similar triplets
with 13Cꢀ31P coupling constants of JCP ꢁ 10.9, 8.5 and 3.7 Hz,
respectively. A similar behaviour is observed for the C3, C4, C5, C6
and C7 atoms in A6 and A7 (Table 3).

A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
3465
Table 5
Crystal data and structure refinement for the compounds A2, B2 and D2
A2
B2
D2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C42H41Co2NO4P2SSi2
891.80
100(2)
1.54178
Orthorhombic
Pbca
C37H32BrCo2NO4P2SSi
874.50
293(2)
1.54178
Monoclinic
P2(1)/c
C37H32BrCo2NO4P2SSi
874.50
100(2)
1.54178
Monoclinic
P2(1)/n
Unit cell dimensions
a (Å)
21.5580(3)
90
13.1423(3)
90
15.9429(2)
90
a
(°)
b (Å)
b (°)
c (Å)
13.3336(2)
90
29.3262(3)
90
22.6036(5)
99.164(2)
13.1801(2)
90
12.24850(10)
99.0490(10)
19.1976(2)
90
c
(°)
Volume (Å3)
Z
8429.69(19)
8
3865.35(14)
4
3702.18(7)
4
Dcalc (mg/m3)
1.405
8.224
3680
0.09 ꢂ 0.07 ꢂ 0.03
3.01–70.70°
ꢀ21 6 h 6 24,
ꢀ14 6 k 6 14,
ꢀ35 6 l 6 32
36724
1.503
9.835
1768
0.10 ꢂ 0.05 ꢂ 0.02
3.41–70.60°
ꢀ12 6 h 6 16,
ꢀ26 6 k 6 27,
ꢀ15 6 l 6 16
34480
1.569
10.268
1768
0.30 ꢂ 0.21 ꢂ 0.10
2.81–70.44°.
ꢀ18 6 h 6 19,
ꢀ13 6 k 6 14,
ꢀ23 6 l 6 22
22812
Absorption coefficient (mmꢀ1
F(000)
)
Crystal size (mm3)
Theta range for data collection
Index ranges
Reflections collected
Independent reflections [R(int)
Completeness to theta = 70.70°
]
7616 [0.0679]
94.0%
7128 [0.0427]
96.2%
6639 [0.0550]
93.9%
Absorption correction
Semi-empirical from equivalents
Semi-empirical from equivalents
Semi-empirical from equivalents
(
SADABS v. 2.03)
(
SADABS v. 2.03)
(SADABS v. 2.03)
Refinement method
Data/restraints/parameters
Full-matrix least-squares on F2
7616/0/651
Full-matrix least-squares on F2
7128/0/537
Full-matrix least-squares on F2
6639/0/559
Goodness-of-fit on F2 (GOF)
1.027
1.009
1.062
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.0401,
wR2 = 0.0929
R1 = 0.0594,
R1 = 0.0370,
wR2 = 0.0943
R1 = 0.0512,
R1 = 0.0458,
wR2 = 0.1111
R1 = 0.0540,
wR2 = 0.1028
0.632 and ꢀ0.303
wR2 = 0.1024
0.418 and ꢀ0.571
wR2 = 0.1154
3.069 and ꢀ0.619
Largest difference peak and hole (e Åꢀ3
)
Table 6
Selected bond lengths (Å) and angles (°) for A2
C(1)ꢀO(1)
1.152(4)
1.762(3)
1.141(4)
1.805(3)
1.147(4)
1.783(3)
1.139(4)
1.786(3)
C(5)ꢀC(6)
C(5)ꢀSi(1)
C(5)ꢀCo(2)
C(5)ꢀCo(1)
C(6)ꢀC(7)
C(6)ꢀCo(1)
C(6)ꢀCo(2)
C(10)ꢀC(11)
151.1(2)
1.352(4)
1.851(3)
1.976(3)
1.991(3)
1.459(4)
1.972(3)
1.988(3)
1.483(4)
C(5)ꢀC(6)ꢀC(7)
C(7)ꢀC(10)ꢀC(11)
C(11)ꢀC(12)ꢀSi(2)
C(1)ꢀCo(1)ꢀC(6)
C(1)ꢀCo(1)ꢀC(5)
C(6)ꢀCo(1)ꢀC(5)
C(2)ꢀCo(1)ꢀP(2)
C(5)ꢀCo(1)ꢀP(2)
C(2)ꢀCo(1)ꢀCo(2)
C(5)ꢀCo(1)ꢀCo(2)
C(3)ꢀCo(2)ꢀC(4)
C(4)ꢀCo(2)ꢀC(5)
C(4)ꢀCo(2)ꢀC(6)
C(3)ꢀCo(2)ꢀP(1)
C(5)ꢀCo(2)ꢀP(1)
C(3)ꢀCo(2)ꢀCo(1)
C(5)ꢀCo(2)ꢀCo(1)
P(1)ꢀCo(2)ꢀCo(1)
C(11)ꢀC(12)
1.145(4)
1.864(4)
2.2123(9)
2.1917(9)
1.703(3)
1.706(3)
2.4592(7)
C(1)ꢀCo(1)
C(12)ꢀSi(2)
Co(1)ꢀP(2)
Co(2)ꢀP(1)
N(1)ꢀP(2)
N(1)ꢀP(1)
Co(1)ꢀCo(2)
C(2)ꢀO(2)
C(2)ꢀCo(1)
C(3)ꢀO(3)
C(3)ꢀCo(2)
C(4)ꢀO(4)
C(4)ꢀCo(2)
C(6)ꢀC(5)ꢀSi(1)
C(9)ꢀC(10)ꢀC(11)
C(12)ꢀC(11)ꢀC(10)
C(1)ꢀCo(1)ꢀC(2)
C(2)ꢀCo(1)ꢀC(6)
C(2)ꢀCo(1)ꢀC(5)
C(1)ꢀCo(1)ꢀP(2)
C(6)ꢀCo(1)ꢀP(2)
C(1)ꢀCo(1)ꢀCo(2)
C(6)ꢀCo(1)ꢀCo(2)
P(2)ꢀCo(1)ꢀCo(2)
C(3)ꢀCo(2)ꢀC(5)
C(3)ꢀCo(2)ꢀC(6)
C(5)ꢀCo(2)ꢀC(6)
C(4)ꢀCo(2)ꢀP(1)
C(6)ꢀCo(2)ꢀP(1)
C(4)ꢀCo(2)ꢀCo(1)
C(6)ꢀCo(2)ꢀCo(1)
P(2)ꢀN(1)ꢀP(1)
143.3(3)
127.1(3)
171.0(3)
121.0(3)
177.9(3)
99.54(14)
143.59(13)
104.47(14)
108.21(10)
104.68(9)
145.68(10)
51.90(8)
94.84(13)
98.87(13)
39.91(12)
102.26(11)
137.80(9)
104.21(10)
51.42(9)
99.04(15)
99.85(13)
109.31(13)
106.83(10)
133.38(9)
91.29(10)
51.95(8)
90.64(3)
109.38(13)
140.30(14)
39.90(12)
102.43(11)
93.84(9)
151.79(10)
51.33(9)
120.20(15)
99.51(3)
The 31P{1H} NMR spectra for all of the phosphine-substituted
compounds, show one broad single resonance that is shifted to
higher frequencies (ca. 13 and 93 ppm for dmpm and dppa-com-
plexes, respectively) with respect to that of the free ligand because
of the coordination. The UV–Vis spectra of all complexes exhibit
broad low-intensity absorption bands with k between 531 and
566 nm attributed to the d–d transitions. These spectra, for
dppa-complexes, are dominated by the characteristic UV band at

3466
A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
ca. 330 nm associated with
p
–
p* transitions within the phenyl
Compound A2 consists of a disubstituted thiophene ring with a
groups of the bisphosphine ligand. In addition, strong absorptions
trimethylsilylethyne at the 3- and 4-positions and one bimetallic
Co unit. The bimetallic Co moiety has two terminal CO ligands on
the Co atoms, bridging dppa ligand and one of the trimethylsilyle-
thynyl ligands. The X-ray structure of A2 shows that the ‘‘Co2C2”
core adopts the usual pseudo-tetrahedral geometry with the al-
kyne vector lying essentially perpendicular to the CoꢀCo vector.
This geometry has been observed in other carbonylcobalt bimetal-
lic complexes possessing a bridging acetylene ligand [31]. The
CoꢀCo bond length (2.459(7) Å) found in A2 is in the region ex-
pected for other dicobalt systems that are bridged by perpendicu-
lar alkyne ligands, indicating the presence of a metalꢀmetal bond
are observed around 231, 255 and 280 nm attributed to
p–p
* tran-
sition associated with the thiophene ring. All compounds gave sat-
isfactory mass spectrometric data.
3.2. Crystal and molecular structures of A2, B2 and D2
Single-crystal X-ray diffraction studies were performed on com-
plexes A2, B2 and D2. These structural studies serve the obvious
purpose of confirming the structures presented in Schemes A–D.
The thermal ellipsoid plots shown in Figs. 2–4 depict the structures
determined in this work. Crystal data and structure refinements
are given in Table 5, and selected bond lengths and angles in Tables
6–8 for A2, B2 and D2, respectively.
[27b,32] and is similar to CoꢀCo lengths found in the related
l-al-
kyne complexes [Co2(CO)4(l-dppm){l2-g
2-(SiMe3C2)}]2(SiMe3C„ C)
(1,3,5-C6H3) [8e], 2,5-[Co2(CO)4(
l
-dppm){l2
-g
2-(SiMe3C2)}]2C4H2S
Table 7
Selected bond lengths (Å) and angles (°) for B2
C(1)ꢀC(2)
1.345(4)
1.994(3)
1.979(3)
1.844(3)
1.451(4)
1.981(3)
1.982(3)
C(6)ꢀBr(1)
C(7)ꢀO(1)
C(7)ꢀCo(1)
C(8)ꢀO(2)
C(8)ꢀCo(1)
C(9)ꢀO(3)
C(9)ꢀCo(2)
98.86(16)
141.86(14)
103.17(15)
99.73(12)
105.15(9)
149.47(11)
51.71(8)
1.885(4)
1.138(4)
1.769(3)
1.136(4)
1.802(4)
1.136(4)
1.785(4)
C(7)–Co(1)–C(2)
C(7)–Co(1)–C(1)
C(2)–Co(1)–C(1)
C(8)–Co(1)–P(1)
C(1)–Co(1)–P(1)
C(8)–Co(1)–Co(2)
C(1)–Co(1)–Co(2)
C(9)–Co(2)–C(10)
C(10)–Co(2)–C(1)
C(10)–Co(2)–C(2)
C(9)–Co(2)–P(2)
C(1)–Co(2)–P(2)
C(9)–Co(2)–Co(1)
C(1)–Co(2)–Co(1)
P(2)–Co(2)–Co(1)
C(3)–C(6)–Br(1)
C(1)–C(2)–C(3)
C(10)ꢀCo(2)
C(10)ꢀO(4)
Co(1)ꢀP(1)
Co(2)ꢀP(2)
N(1)ꢀP(2)
1.787(3)
1.128(4)
2.2084(8)
2.1901(8)
1.687(2)
C(1)ꢀCo(1)
C(1)ꢀCo(2)
C(1)ꢀSi(1)
C(2)ꢀC(3)
C(2)ꢀCo(1)
N(1)ꢀP(1)
1.692(2)
C(2)ꢀCo(2)
Co(1)ꢀCo(2)
2.4568(6)
98.31(14)
103.00(14)
39.54(12)
105.14(12)
140.14(9)
103.17(11)
51.52(8)
97.41(15)
103.10(14)
109.14(13)
101.45(11)
135.83(9)
94.88(11)
52.08(8)
C(7)–Co(1)–C(8)
C(8)–Co(1)–C(2)
C(8)–Co(1)–C(1)
C(7)–Co(1)–P(1)
C(2)–Co(1)–P(1)
C(7)–Co(1)–Co(2)
C(2)–Co(1)–Co(2)
P(1)–Co(1)–Co(2)
C(9)–Co(2)–C(1)
C(9)–Co(2)–C(2)
C(1)–Co(2)–C(2)
C(10)–Co(2)–P(2)
C(2)–Co(2)–P(2)
C(10)–Co(2)–Co(1)
C(2)–Co(2)–Co(1)
C(5)–C(6)–Br(1)
Si(1)–C(1)–Co(2)
P(2)–N(1)–P(1)
94.67(2)
111.19(15)
143.63(14)
39.69(12)
101.24(11)
97.33(9)
155.06(11)
51.68(8)
121.5(3)
97.45(2)
123.8(3)
141.9(3)
136.86(17)
122.08(16)
Table 8
Selected bond lengths (Å) and angles (°) for D2
C(1)ꢀC(2)
1.350(6)
1.849(4)
1.982(4)
1.976(4)
1.454(5)
1.983(4)
1.952(4)
C(4)ꢀBr(1)
C(10)ꢀO(4)
C(10)ꢀCo(1)
C(11)ꢀO(3)
C(11)ꢀCo(1)
C(12)ꢀO(2)
C(12)ꢀCo(2)
145.4(3)
1.891(4)
1.141(5)
1.772(4)
1.140(5)
1.800(4)
1.142(5)
1.797(4)
C(1)–C(2)–C(3)
C(5)–C(4)–Br(1)
C(10)–Co(1)–C(11)
C(10)–Co(1)–C(2)
C(10)–Co(1)–C(1)
C(11)–Co(1)–P(1)
C(2)–Co(1)–P(1)
C(2)–Co(1)–Co(2)
C(11)–Co(1)–Co(2)
C(13)–Co(2)–C(1)
C(13)–Co(2)–C(2)
C(2)–Co(2)–C(1)
C(12)–Co(2)–P(2)
C(2)–Co(2)–P(2)
C(12)–Co(2)–Co(1)
C(2)–Co(2)–Co(1)
P(2)–Co(2)–Co(1)
C(13)ꢀO(1)
C(13)ꢀCo(2)
N(1)ꢀP(1)
1.134(5)
1.786(4)
1.690(4)
1.698(3)
2.1981(11)
2.2151(11)
2.4478(8)
139.4(4)
C(1)ꢀSi(1)
C(1)ꢀCo(2)
C(1)ꢀCo(1)
N(1)ꢀP(2)
C(2)ꢀC(3)
Co(1)ꢀP(1)
Co(2)ꢀP(2)
Co(1)ꢀCo(2)
C(2)ꢀCo(1)
C(2)ꢀCo(2)
C(2)–C(1)–Si(1)
C(3)–C(4)–Br(1)
C(11)–Co(1)–C(2)
C(11)–Co(1)–C(1)
C(1)–Co(1)–C(2)
C(10)–Co(1)–P(1)
C(1)–Co(1)–P(1)
C(1)–Co(1)–Co(2)
C(10)–Co(1)–Co(2)
C(13)–Co(2)–C(12)
C(12)–Co(2)–C(1)
C(12)–Co(2)–C(2)
C(13)–Co(2)–P(2)
C(1)–Co(2)–P(2)
C(13)–Co(2)–Co(1)
C(1)–Co(2)–Co(1)
P(1)–Co(1)–Co(2)
P(1)–N(1)–P(2)
123.2(3)
121.0(3)
142.98(17)
108.25(17)
39.88(17)
101.95(13)
138.26(12)
51.92(11)
150.99(12)
101.65(18)
103.49(17)
141.64(17)
103.16(13)
141.04(12)
147.61(13)
51.67(11)
97.27(4)
99.89(18)
103.84(16)
100.10(17)
102.29(13)
100.11(12)
50.96(11)
96.98(13)
99.15(17)
97.26(17)
40.13(17)
102.76(13)
104.99(12)
99.26(12)
52.11(11)
95.95(3)
122.4(2)

A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
3467
[10b] and 2-[Co2(CO)4(
[11]. However, such a distance is shorter than that in the parent
carbonyl, [Co2(CO)8], (average 2.52 Å) [33].
l
-dppm){l2
-
g
2-(SiMe3C2)}]-4-(Br)-C4H2S
123.2(3)° and 121.0(3)°, respectively. The thiophene ring in B2
and in D2 is also essentially planar with a root mean square devi-
ation of 0.0019 Å and 0.0018 Å, respectively. The remaining inter-
atomic distances and angles in the molecules are normal and
compare well with the values reported above.
The C(5)ꢀC(6) bond length of the bridging ethynyl ligand,
1.352(4) Å, is much longer than the C(11)ꢀC(12) triple-bond value,
1.145(4) Å, and this reflects the loss of triple-bond character as a
result of coordination of the acetylenic moiety to the Co2 fragment.
This distance lies in the range 1.33ꢀ1.36 Å reported for the alky-
lenic CꢀC bond in related dicobalt complexes [27b]. The change
in hybridization at C(5) and C(6) is also reflected in the
C(5)ꢀC(6)ꢀC(7) angle of 143.3(3)° and C(6)ꢀC(5)ꢀSi(1) angle of
151.1(2)°.
The bond lengths of the apex carbonyl groups to the Co atoms,
C(2)ꢀCo(1) and C(3)ꢀCo(2), are 1.805(3) and 1.783(3) Å, respec-
tively. These bond lengths are statistically not different from those
of the base carbonyl groups to the Co atoms, which are 1.762(3)
and 1.786(3) Å, for C(1)ꢀCo(1) and C(4)ꢀCo(2), respectively. The
dihedral angle Co(1)ꢀC(6)ꢀC(5)ꢀCo(2) was determined to be
ꢀ82.6(9)°, whereas the dihedral angle C(6)ꢀCo(1)ꢀCo(2)ꢀC(5)
was determined to be ꢀ51.6(15)°. The average PꢀN distance of
the bridging (Ph2P)2NH ligand, 1.704(3) Å, is normal; the PꢀN bond
lengths are statistically equivalent. The PꢀNꢀP angle is 122.2(15)°.
This value is comparable with the average found for bridging
(Ph2P)2NR ligands of 119.3° [9b,34]. All other bond lengths and
angles are comparable to those reported for similar structures
[8e–f,10,11,35]. The average carbonyl C„O bond length was deter-
mined to be 1.145(4) Å, where all the bond lengths are sufficiently
similar. The thiophene ring is essentially planar with a root mean
square deviation of 0.0042 Å. There does not appear to be any
intramolecular hydrogen bonding within the molecule.
Compounds B2 and D2 consist of a monosubstituted X-trimeth-
ylsilylethynyl-Y-bromothiophene ligand (X = 3, Y = 4 (B2) and
X = 2, Y = 3 (D2) with a bimetallic Co unit at the 3- and 2-position,
respectively. It can be observed that B2 is derived from A2 by sub-
stitution of the –C„CSiMe3 group by a Br atom. In general, the
structural parameters of the common fragments are the same,
within experimental error. The basic structural skeleton of B2
and D2 resembles that of A2 and the cobalt–alkyne complex with
the ‘‘Co2C2” unit linked to a 2-trimethylsilylethynyl-4-bromothio-
phene ligand [11].
The bond length between Co(1) and Co(2) (2.457(6) Å in B2 and
2.4478(8) Å in D2) is similar to that of A2 and the bond length be-
tween C(1) and C(2) (1.345(4) Å in B2 and 1.350(6) Å in D2) also
lies within the expected range for alkyne groups bound to Co2(CO)6
units. In addition, the BrꢀC(6) bond length in B2 is 1.886(4) Å and
the BrꢀC(4) bond length in D2 is 1.891(4) Å. C(3)ꢀC(6)ꢀBr and
C(5)ꢀC(6)ꢀBr angles in B2 are 123.8(3)° and 121.5(3)°, respec-
tively. C(3)ꢀC(4)ꢀBr and C(5)ꢀC(4)ꢀBr angles in D2 are
3.3. Electrochemical studies
The electrochemical behaviour of A1–A7, B1, B2, C1+C2, C5 and
D2 in CH2Cl2 solution was studied by means of the cyclic voltam-
metry (CV) and square-wave voltammetry (SWV) techniques.
Table 9 presents data of E1/2 (E1/2 = (Epa + Epc)/2) for the electro-
chemical reduction and oxidation of these compounds. All E values
+
are given versus E1/2 of Fc* /Fc* (Fc* = decamethyl- ferrocene).
3.3.1. Electrochemistry of compounds containing one Co2(CO)6-alkyne
redox centre (A1, B1 and C1 + C2)
It should be noted that C1 and C2 could not be isolated, and that
a solution containing C1 together with C2 in 1.8:1 ratio, respec-
tively, was used for the electrochemical measurements. A single
oxidation and a single reduction peak were obtained for that mix-
ture, indicating that both compounds are oxidized and reduced at
almost the same potential value.
A1 and B1 show irreversible voltammetric oxidation and reduc-
tion peaks at room temperature and moderate sweep rates
(v ꢁ 0.1 V/s), but partially chemical reversibility is attained in the
oxidation process at room temperature and v = 1 V/s. The mixture
C1 + C2 shows a partially chemically reversible voltammetric
oxidation peak at room temperature and moderate sweep rates
(ipc/ipa = 0.7 at v = 0.1 V/s). The reduction of C1 + C2 is chemically
irreversible at room temperature. This indicates that A1+, B1+,
C1+ + C2+, A1ꢀ, B1ꢀ and C1ꢀ + C2ꢀ undergo decomposition pro-
cesses [8e–f,9d,10,11,36] in solution which are somewhat slower
for cations. Sweeping potential beyond ca. 1.2 V involves a serious
contamination of the electrode surface by an adsorbed cobalt-
containing product, which can be reduced at ca. ꢀ0.65 V.
It is noteworthy that ions formed from A1, B1 and C1 + C2 show
a greater overall chemical stability than those from closely related
species derived from 2,5- and 2,4-bis(trimethylsilylethynyl)thio-
phene, probably due to steric reasons [10b,11]. When temperature
is ꢀ30 °C, the oxidation and reduction processes of A1, B1 and
C1 + C2 appear as chemically partially reversible (Fig. 5), and
coupled peaks allow the determination of E1/2 as listed in Table
9. Potential values are in the range expected for C2Co2(CO)6 con-
100
Table 9
Electrochemical data for A1–A7, B1–B2, C1 + C2, D2 and C5a
0
E1/2 for reduction
E1/2 for oxidation
A1
C1 + C2
B1
A2
B2
D2
A3
A4
A5
C5
ꢀ1.05b
+1.18b
+1.18b
+1.19b
+0.57
+0.60
+0.62
+0.50
+0.57
+0.51
+0.60
ꢀ1.07b
ꢀ1.02b
ꢀ1.59b
ꢀ1.53b
ꢀ1.53b
ꢀ1.74b
ꢀ1.57b
ꢀ1.73b
ꢀ1.49b
ꢀ1.57b
ꢀ1.08b; ꢀ1.71b
-100
-1.5
-1.0
-0.5
0.0
0.5
1.0
1. 5
A6
A7
+0.62
Potential (V vs Fc*+/Fc*)
+0.64, +1.26b
Data in V vs. Fc*+/Fc* in CH2Cl2 solution. Data are taken from CV and SWV at
a
Fig. 5. Cyclic voltammograms for the oxidation and reduction of A1 in CH2Cl2
containing 0.2 M TBAPF6 at ꢀ30 °C on a glassy carbon working electrode. (—)
v = 0.1 V/s; (--) v = 0.5 V/s.
25 °C unless otherwise stated.
b
Data from CV and SWV at ꢀ30 °C.

3468
A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
taining compounds [8e–f,10b,11,36d,36f]. A comparison of E1/2 val-
ues with those of related species 2-[Co2(CO)6{l2
2-SiMe3C2}]-5-
(Me3SiC„C)C4H2S (E1/2(ox) = 1.23 V; E1/2(red) = ꢀ1.01 V) [10b]
and 2-[Co2(CO)6{l2
2-(SiMe3C2)}]-4-(Me3SiC„C)C4H2S (E1/2(ox) =
1.24 V; E1/2(red) = ꢀ0.99 V) [11] shows that A1 and C1 + C2 are sig-
nificantly easier to oxidize and more difficult to reduce. This fact is
related to the proximity of the electron-donating substituent
–C2SiMe3 and will also be evident for phosphine-containing
compounds.
100
50
-
g
Fc* added as
-g
internal reference
0
-50
3.3.2. Electrochemistry of compounds containing one
Co2(CO)4(phosphine)-alkyne redox centre (A2–A6, B2, C5 and D2)
All C2Co2(CO)4dppa or C2Co2(CO)4dmpm containing compounds
A2ꢀA6, B2, C5 and D2 show chemically completely reversible (in
the 0.01–10 V/s range of sweep rates) monoelectronic oxidation
processes at room temperature (Fig. 6), with E1/2 in the 0.50–
0.62 V range (Table 9), characteristic of this kind of compounds
in which the chelating phoshine stabilizes cations (and anions)
against decomposition, and makes the redox centre much more
electron-rich and easier to be oxidized, as compared with related
C2Co2(CO)6 compounds. ip increases linearly with v1/2 as corre-
sponds to diffusion-controlled processes. Reductions are partially
chemically reversible at room temperature, but ipa equals ipc at
ꢀ30 °C (Fig. 7). E1/2(red) are in the ꢀ1.53 to ꢀ1.74 V range of po-
tential (Table 9). The higher basicity and electron-donating capac-
ity of dmpm as compared to dppa [37] is reflected in the very
significantly less positive E1/2(ox) and more negative E1/2(red) of
A3 and A5 than values for A2, A4, A6, B2, C5, and D2. Compounds
A2 and A4 have less positive oxidation and more negative reduc-
tion potentials than closely related species derived from 2,5-
bis(trimethylsilylethynyl)thiophene, as already observed for A1.
-100
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
Potential (V vs Fc* +/Fc*)
Fig. 7. Cyclic voltammogram for the reduction and oxidation of A2 in CH2Cl2
containing 0.2 M TBAPF6 at ꢀ30 °C and v = 0.1 V/s on a glassy carbon working
electrode.
C2SiMe3 containing compounds easier to oxidize and more difficult
to reduce. This is particularly evident for A6, which contains two –
H capping atoms, one of them directly bonded to the C2Co2
(CO)4dppa redox centre.
3.3.3. Electrochemistry of A7
One of our goals for this work was to evaluate the electronic
communication through 3,4- and 2,3-bis(trimethylsilylethynyl)thi-
ophene, comparing it with those found for 2,4- and 2,5-analogous
ligands. Thus, we intended to prepare complexes containing two
equal redox centres. Unfortunately, our efforts proved vain and
only A7, which contains two unequal redox centres (HC2Co2(CO)6
and HC2Co2(CO)4dppa), could be prepared and isolated.
In order to evaluate the electronic communication in A7, we
cannot only measure the difference in E1/2 for the oxidation or
Thus, for 2-[Co2(CO)4(
l
-dppa){l2
2-SiMe3C2}]-5-(Me3SiC„C)-
-dppa){l2-g
2-SiMe3C2}]-5-(C„CH)C4H2S,
-g
C4H2S and 2-[Co2(CO)4(
l
E1/2(ox) are 0.61 V and 0.63 V and E1/2(red) are ꢀ1.51 V and
ꢀ1.50 V, respectively [10b].
Table 9 shows the effect of the higher electron-donating proper-
ties of the capping group –SiMe3 as compared to –H, which makes
the reduction waves (DE1/2), as is usually made for compounds
containing two equivalent redox centres [36f,38], but we also have
to take into account the intrinsic difference in E1/2 values of the
C2Co2(CO)6 and the C2Co2(CO)4dppa units, independent of the pos-
sible existence of interaction, and which is manifested in the very
different E1/2 values of A1 and A2, A4 or A6.
30
Reduction of A7 in CH2Cl2 solution and ꢀ30 °C shows a first
wave, which is chemically irreversible, at ꢀ1.08 V (SWV). This peak
can be assigned to the C2Co2(CO)6 redox centre and is followed by a
chemically quasi-reversible wave at E1/2 = ꢀ1.71 V, which is in the
range of potential values characteristic in C2Co2(CO)4(phosphine)
containing compounds. The complete chemical irreversibility of
the first reduction peak means that A7ꢀ undergoes a fast homoge-
neous reaction, and the wave at ꢀ1.71 V is due to the reduction of a
C2Co2(CO)4(phosphine) containing product of it. Thus, evaluation
of the electronic interaction from the reduction behaviour of A7
is not feasible. However, oxidation of A7 in CH2Cl2 solution at room
temperature shows a first monoelectronic completely reversible
wave at E1/2 = +0.64 V, which is attributable to the C2Co2(CO)4dppa
redox centre. A second peak, irreversible even at ꢀ30 °C, is ob-
served at 1.26 V (SWV), which is a potential value characteristic
of C2Co2(CO)6 containing compounds. The chemical reversibility
of the first oxidation process indicates that the species, which is
oxidized in the second wave is A7+. Thus, a study based on the
comparison of the oxidation data of A7 with those of A1 and A6
could tentatively afford a very preliminary estimation of the de-
gree of electronic interaction between both redox centres in A7.
In order to achieve a more precise comparison, A1 should be
0
-30
0.2
0.4
0.6
0.8
+
1.0
1.2
Potential (V vs Fc* /Fc*)
Fig. 6. Cyclic voltammograms for the oxidation of C5 in CH2Cl2 containing 0.2 M
TBAPF6 at 25 °C on a Pt working electrode at different sweep rates: v = 0.02ꢀ10 V/s
(0.02, 0.05, 0.1, 0.2, 0.5, 2, 5 and 10 V/s).

A. Arnanz et al. / Journal of Organometallic Chemistry 693 (2008) 3457–3470
3469
(e) P. Li, B. Ahrens, N. Feeder, P.R. Raithby, S.J. Teat, M.S. Khan, J. Chem. Soc.,
Dalton Trans. (2005) 874–883;
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[5] (a) P.I. Dosa, C. Erben, V.S. Iyer, K.P.C. Vollhardt, I.M. Wasser, J. Am. Chem. Soc.
121 (1999) 10430–10431;
replaced by the related compound in which the capping group
were –H instead of –SiMe3 (we will name this species A1*). Such
compound could not be obtained but, taking into account the influ-
ence of the capping group (H or SiMe3) on E1/2(ox) values (see Table
9, compounds A2 and A6) it can be expected that A1* were oxi-
dized at a potential value slightly more positive than that of A1.
Therefore, if the difference in E1/2(ox) for A2 and A6 (50 mV) is
extrapolated to A1 and A1*, E1/2(ox) for A1* would be ca. 1.23 V
and therefore E1/2(A1*) ꢀ E1/2(A6) ffi 0.61 V. Even if we take into ac-
count the considerable error margin of these calculations and com-
(b) D.T. McQuade, A.E. Pullen, T.M. Swager, Chem. Rev. 100 (2000) 2537–2574;
(c) N. Robertson, C.A. McGowan, Chem. Soc. Rev. 32 (2003) 96–103;
(d) C.J. Elsevier, J. Reedijk, P.H. Walton, M.D. Ward, J. Chem. Soc., Dalton Trans.
(2003) 1869–1880;
(e) J. Stahl, J. Bohling, C. James, E.B. Bauer, B. Eike, T.B. Peters, W. Mohr, J.M.
Martin-Alvarez, F. Hampel, J.A. Gladysz, A. John, Angew. Chem., Int. Ed. 41
(2002) 1871–1876;
(f) L. De Quadras, E.B. Bauer, W. Mohr, J.C. Bohling, T.B. Peters, J.M. Martin-
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Chemistry Series 240, American Chemical Society, 1994;
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Academic, New York, 1992;
parisons, it can be observed that E1/2(A1*) ꢀ E1/2(A6) ffi
DE1/2 (A7).
Thus, no electronic interaction is observed between the two ‘‘Co2”
redox centres in A7. If such interaction exists, it must be very scarce.
This result contrasts with those found for 2,5- [10b] and 2,4-
bis(trimethylsilylethynyl)thiophene [11] derivatives with two
‘‘Co2” redox centres (which belong to class II in the Hush-Robin-
Day classification of mixed valence compounds) and agrees with
the fact that the C3ꢀC4 bond in the thiophene ring possesses less
multiple character than C2ꢀC3 [21]. Thus, less overall conjugation
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Appendix A. Supplementary material
CCDC 653921, 653925 and 682712 contains the supplementary
crystallographic data for A2, B2 and D2. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.08.005.
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