Synthesis, structures and comparative electrochemical study of 2,5-bis(trimethylsilylethynyl)thiophene coordinated cobalt carbonyl units

Article abstract of DOI:10.1016/j.jorganchem.2004.07.028

The reaction between 2,5-bis(trimethylsilylethynyl)thiophene and Co₂(CO)₈ or Co₂(CO)₆(X), (X = dppa, dppm), gave rise to the formation of substituted ethynylcobalt complexes containing one or two Co₂(

Full text of DOI:10.1016/j.jorganchem.2004.07.028

Journal of Organometallic Chemistry 689 (2004) 3218–3231
www.elsevier.com/locate/jorganchem
Synthesis, structures and comparative electrochemical study of
2,5-bis(trimethylsilylethynyl)thiophene coordinated
cobalt carbonyl units
a
b,
a
c
Avelina Arnanz , Maria-Luisa Marcos *, Consuelo Moreno , David H. Farrar ,
c
c
a
Allan J. Lough , Joanne O. Yu , Salome Delgado , Jaime Gonzalez-Velasco
b
´
´
a
´ ´ ´
Departamento de Quımica Inorganica de la Universidad Autonoma de Madrid, 28049 Madrid, Spain
b
´ ´
Departamento de Quımica de la Universidad Autonoma de Madrid, Spain
c
Lash Miller Chemical Laboratories, University of Toronto, 80 St. George Street, Toronto, Canada M5S 3H6
Received 10 June 2004; accepted 20 July 2004
Available online 19 August 2004
Abstract
The reaction between 2,5-bis(trimethylsilylethynyl)thiophene and Co2(CO)8 or Co2(CO)6(X), (X = dppa, dppm), gave rise to the
formation of substituted ethynylcobalt complexes containing one or two Co2(CO)6 or Co2(CO)4(X) units, 2-[Co2(CO)4(X){l2-g2-
(SiMe3)C2}]-5-(Me3SiC„C)C4H2S (X = 2CO (1), dppa (3) or dppm (4)) and 2,5-[Co2(CO)4(X){l2-g2-SiMe3C2}]2C4H2S
(X = 2CO (2), dppa (5) or dppm (6)). Desilylation of the non-metallated and metallated alkynes in 3, 4 and 6 occurred on treatment
with KOH and tetrabutylammonium fluoride to give 2-[Co2(CO)4(l-X){l2-g2-SiMe3C2}]-5-(C„CH)C4H2S (X = dppa (7), dppm
(8)) and 2,5-[Co2(CO)4(l-dppm){l2-g2-HC2}]2C4H2S (9), respectively. Crystals of 6 suitable for single-crystal X-ray diffraction were
grown and the molecular structure of this compound is discussed. A comparative electrochemical study of all these complexes is
presented by means of the cyclic and square-wave voltammetry techniques.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Thiophene; Cobalt carbonyl complexes; Electrochemistry
1. Introduction
of electronic effects between redox active centres [6–8]
and therefore the electronic properties can be modified
by changing both, metal fragments and/or alkyne lig-
ands [9]. The electronic communication through such
potential molecular wires is often evaluated by studying
the redox response of electroactive groups [10].
In recent studies we have observed that complexes
where the redox centres are either Co2(CO)6 or Co2
(CO)4dppm linked by 1,3,5-tris(trimethylsilylethy-
nyl)benzene [7] and 1,4-bis(trimethylsilyl)butadiyne [8]
ligands show electronic communication between the me-
tal centres. In order to study the ability of the metals to
participate in p delocalisation we have now investigated
the electronic communication between Co2(CO6), Co2
(CO)4dppm and Co2(CO)4dppa moieties linked by
The chemistry of alkynes coordinated to transition
metals has been extensively studied and is well estab-
lished [1]. The interest in this kind of complexes is due,
in part, to the stabilising influence of the metal on reac-
tive unsaturated carbon chains and polycarbon ligands
[1,2] and, on the other hand, to their potential optoelec-
tronic properties as non-linear optical and electrolumi-
nescent materials [3], or as ‘‘molecular’’ wires [4,5].
Thus alkynyl or polyynediyl bridging ligands have been
shown to be especially efficient in allowing the passage
*
Corresponding author. Tel.: +3491 49 78665; fax: +3491 49 75238.
E-mail address: mluisa.marcos@uam.es (M.-L. Marcos).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.028

A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
3219
2,5-bis(trimethylsilylethynyl)thiophene. We report here
the synthesis, characterization and the redox properties
of these compounds.
wave voltammetry (CV and SWV, respectively) studies
were made in a three-electrode system. Polycrystalline
Pt (0.05 cm2) or glassy carbon were used as working elec-
trodes; the counter electrode was a Pt gauze and the refer-
ence electrode was a silver wire quasi-reference electrode.
Decamethylferrocene (Fc*) was used as internal stand-
ard, and all potentials in this work are referred to the
Fc*+/Fc* couple. Under the actual experimental condi-
tions, E1/2 of the ferrocene couple (Fc+/Fc) was +0.44 V
vs. Fc*+/Fc* in THF solution and +0.55 V vs. Fc*+/Fc*
in CH2Cl2 solution.
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 Ar. All solvents for synthetic
use were reagent grade. Diethyl ether, hexane and tetra-
hydrofurane (THF) were dried and distilled over sodium
in the presence of benzophenoneunder an Ar atmosphere.
Also under Ar, CH2Cl2 was dried and distilled over CaH2.
2.2. Synthesis of 2-[Co2(CO)6{l2-g2-SiMe3C2}]-5-
(Me3SiC„C)C4H2S (1) and 2,5-[Co2(CO)6{l2-g2-
SiMe3C2}]2C4H2S (2)
˚
Methanol was stored over molecular sieves (4 A) under
To a solution of 2,5-bis(trimethylsilylethynyl)thio-
phene (0.60 g, 2.16 mmol) in hexane (100 mL) was added
1.5 equiv. of Co2(CO)8. The reaction was monitored by
Ar. All solvents were bubbled with Ar for 1 h after distil-
lation and then stored under Ar or degassed by means of
at least three freeze–pump–thaw cycles after distillation
and before use. Column chromatography was performed
by using silica gel 100 (Fluka) and preparative TLC on
20 · 20 cm glass plates coated with silica gel (SDS 60–
17 lm, 0.25 mm thick). Me3SiC„CH (TMSA),
2,5-dibromothiophene, Co2(CO)8, KOH (Fluka),
1,2-bis(diphenylphosphino)methane (dppm), CuI and a
solution 1.0 M of tetrabutylammonium fluoride (TBAF)
in THF (Aldrich) were used as received. Trimethylamine
N-oxide (Aldrich) was sublimed prior to use and stored
under Ar. The compounds 1,2-bis(diphenylphosph-
ino)amine (dppa) [11], Co2(CO)6(dppm) [12], Co2
(CO)6(dppa) [13,14], Pd(PPh3)4[15] and 2,5-bis(trimethyl-
silylethynyl)thiophene [16] were prepared according to
the literature and characterized by their IR and NMR
1
FT-IR and H NMR. After the mixture was stirred for
1 h at room temperature, the solvent was removed under
vacuum and the residue was eluted with hexane on a silica
column to afford 1 (52% yield) and 2 (42% yield) as an
unstable dark red and green solid, respectively. 2 has also
been obtained as an only product in high yield (97%) from
2,5-bis(trimethylsilylethynyl)thiophene (0.30 g, 1.08
mmol) and 2 equiv. of Co2(CO)8 and subsequent chroma-
tography with hexane on a silica column.
(1) IR (hexane, cmꢀ1): mC„C 2151.1 (vw); mCO 2088.2
(m), 2054.6 (s), 2028.0 (vs). 1H NMR (300 MHz, CDCl3,
ppm): d 7.11 (d, H4, JHH = 3.9 Hz); 7.09 (d, H5,
JHH = 3.9 Hz); 0.39 (s, 9H, –CSiMe3); 0.24 (s, 9H,
„CSiMe3). 1H NMR (300 MHz, CD2Cl2, ppm): d
7.13 (d, H4, JHH = 3.8 Hz); 7.11 (d, H5, JHH = 3.8 Hz);
0.40 (s, 9H, –CSiMe3); 0.24 (s, 9H, „CSiMe3). 13C
NMR (125 MHz, CDCl3, ppm): d 199.3 (m, CO);
143.5 (s, C3); 133.7 (s, C5); 128.8 (s, C4); 123.6 (s, C6);
100.5 (s, C8); 97.2 (s, C7); 93.3 (s br, C2); 81.1 (s br,
C1); 0.62 (s, –CSiMe3); ꢀ0.28 (s, „CSiMe3). UV–V
(CH2Cl2, nm): kmax 568, 446 (sh) and 230. MS (FAB+,
m/z): 534.0 [M+ ꢀ CO].
spectra. The H, 13C, 31P, proton-decoupled 31P NMR
1
spectra and HMQC (heteronuclear multiple quantum
correlation) and HMBC (heteronuclear multiple bond
correlation) experiments were recorded on a Bruker
AMX-300 and 500 instrument. Chemical shifts were
measured relative either to an internal reference of tetra-
methylsilane or to residual protons of the solvents. The
coupling constant errors are 0.5 Hz. Infrared spectra
were measured on a Perkin–Elmer 1650 infrared spec-
trometer. Elemental analyses were performed by the
(2) IR (hexane, cmꢀ1): mCO 2086.0 (m), 2055.0 (s),
1
2027.8 (vs). H NMR (300 MHz, CDCl3, ppm): d 7.15
(s, H4,4 ); 0.40 (s, 18H, 2 –SiMe3). 13C NMR (125
0
´
Mycroanalytical Laboratory of the University Autono-
0
MHz, CDCl3, ppm): d 199.8 (m, CO); 142.8 (s, C3,3 );
ma of Madrid on a Perkin–Elmer 240 B microanalyser.
Electronic spectra were recorded on a Unicam UV 4
UV–Vis spectrophotometer. Mass spectra were measured
on a VG-Autospec mass spectrometer for FAB by the
0
0
0
130.7 (s, C4,4 ); 94.1 (s br, C2,2 ); 81.5 (s br, C1,1 ); 1.04
(s, 2 –SiMe3). UV–Vis (CH2Cl2, nm): kmax 595, 450
(sh) and 229. MS (FAB+, m/z): 820.0 [M+ ꢀ CO].
´
Mass Laboratory of the University Autonoma of Madrid.
Electrochemical measurements were carried out with a
computer driven Par Mo. 273 electrochemistry system
in a three electrode cell under N2 atmosphere in anhy-
drous deoxygenated solvents (CH2Cl2 and THF) contain-
ing 0.2 M tetrabutylammonium hexafluorophosphate
(TBAPF6) as supporting electrolyte. Cyclic and square-
2.3. Synthesis of 2-[Co2(CO)4(l-X){l2-g2-SiMe3C2}]-
5-(Me3SiC„C)C4H2S. X = dppa (3) and X = dppm (4)
2.3.1. Method A
A solution of 1 (0.50 g, 0.89 mmol) and 0.89 mmol of
dppa or dppm in hexane (100 mL) was prepared.

3220
A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
Trimethylamine N-oxide (0.20 g, 1.78 mmol) was added
and the reaction mixture, monitored by FT-IR, was stir-
red at 40 ꢁC for 3 days. After the solvent was removed
under vacuum, the product was purified by thin-layer
chromatography (TLC) using hexane/CH2Cl2 (3:1) or
by hexane-packed silica column (200 g) using the same
eluent to afford the stable red solids 3 (65% yield) or 4
(70% yield), respectively.
[M+ ꢀ 3CO]; 779.0 [M+ ꢀ 4CO]. Anal. Calc. for
C43H42O4Co2SP2Si2: C, 58.22; H, 4.72. Found: C,
57.97; H, 4.74%.
2.4. Synthesis of 2,5-[Co2(CO)4(l-X){l2-g2-Si-
Me3C2}]2C4H2S. X = dppa (5) and X = dppm (6)
The same procedure as described above was followed
in the preparation of these compounds. For the Method
A from 2 (0.40 g, 0.47 mmol), dppa or dppm (0.94
mmol) and trimethylamine N-oxide (0.21 g, 1.88 mmol).
For the Method B from 2,5-bis(trimethylsilylethy-
nyl)thiophene (0.20 g, 0.72 mmol) and the derivative
Co2(CO)6(dppa) or Co2(CO)6(dppm) (1.44 mmol). After
the solvent was removed under vacuum, the product was
purified by thin-layer chromatography (TLC) using hex-
ane/CH2Cl2 (3:1) or by hexane-packed silica column
(200 g) using the same eluent to afford the stable green
solids 5 (60% and 25% yields for the Methods A and
B, respectively) or 6 (65% and 30% yields for the Meth-
ods A and B, respectively).
2.3.2. Method B
A suspension of Co2(CO)6(dppa) or Co2(CO)6(dppm)
(1.95 mmol) in hexane (50 mL) was added to a solution
of 2,5-bis(trimethylsilylethynyl)thiophene (0.54 g, 1.95
mmol) in the same solvent. The reaction mixture was
stirred at 65 ꢁC for 15 days. Complex 3 or 4 were iso-
lated in 28% and 33% yields, respectively, in the same
manner used in Method A.
(3) IR (CH2Cl2, cmꢀ1): mNH 3321.8 (w); mC„C 2137.2
(w); mCO 2025.5 (s), 1997.9 (vs), 1971.5 (s), 1957.4 (sh).
1H NMR (300 MHz, CDCl3, ppm): d 7.42–7.28 (m,
20H, Ph); 6.60 (d, H5, JHH = 3.8 Hz); 5.87 (d, H4,
JHH = 3.8 Hz); 3.95 (t, –NH, JPH = 6.4 Hz); 0.37 (s,
9H, –CSiMe3); 0.24 (s, 9H, „CSiMe3). 13C NMR (125
MHz, CDCl3, ppm): d 206.3 (m, CO); 203.2 (m, CO);
148.5 (t, JCP = 4.3 Hz, C3); 142.0 (t, JCP = 22.2 Hz, i-
Ph); 139.0 (t, JCP = 23.2 Hz, i-Ph); 133.2 (s, C5); 131.0
(t, JCP = 6.8 Hz, o-Ph); 130.6 (t, JCP = 6.7 Hz, o-Ph);
130.3 (s, p-Ph); 130.1 (s, p-Ph); 128.8 (t, JCP = 4.9 Hz,
m-Ph); 128.7 (t, JCP = 4.9 Hz, m-Ph); 128.5 (s, C4);
120.7 (s, C6); 98.9 (s) and 98.6 (s), (C„C); 92.1 (m,
C2); 91.1 (m, C1); 1.42 (s, –CSiMe3); 0.37 (s, „CSiMe3).
31P NMR (121 MHz, CDCl3, ppm): d 91.7 (s br, 2P,
dppa). UV–Vis (CH2Cl2, nm): kmax 552 and 229. MS
(FAB+, m/z): 863.0 [M+ ꢀ CO]; 807.0 [M+ ꢀ 3CO];
779.0 [M+ ꢀ 4CO]. Anal. Calc. for C42H41O4Co2SP2-
Si2N: C, 56.67; H, 4.59; N, 1.59. Found: C, 56.52; H,
4.63; N, 1.53%.
(5) IR (CH2Cl2, cmꢀ1): mNH 3321.8 (w); mCO 2020.8
1
(s), 1994.0 (vs), 1966.7 (s), 1952.6 (sh). H NMR (300
MHz, CDCl3, ppm): d 7.42–7.14 (m, 40H, Ph); 5.26 (s,
0
H
4,4 ); 3.95 (t, 2 –NH, JPH = 6.5 Hz); 0.37 (s, 18H, 2
–SiMe3). 13C NMR (125 MHz, CDCl3, ppm): d 206.2
0
(m, CO); 203.6 (m, CO); 142.8 (m, C3,3 ); 142.4 (t,
JCP = 22.1 Hz, i-Ph); 139.1 (t, JCP = 22.1 Hz, i-Ph);
131.2 (t, JCP = 6.8 Hz, o-Ph); 130.6 (t, JCP = 6.8 Hz, o-
Ph); 130.1 (s, p-Ph); 129.9 (s, p-Ph); 128.8 (t, JCP = 4.7
0
Hz, m-Ph); 128.7 (s, C4,4 ); 128.5 (t, JCP = 4.8 Hz, m-
0
0
Ph); 92.4 (m, C2,2 ); 89.0 (m, C1,1 ); 1.43 (s, 2 –SiMe3).
31P NMR (121 MHz, CDCl3, ppm): d 92.0 (s br, 4P, 2
dppa). UV–Vis (CH2Cl2, nm): kmax 591, 404 and 230.
MS (FAB+, m/z): 1478.0 [M+ ꢀ CO]; 1450.1
[M+ ꢀ 2CO]; 1310.2 [M+ ꢀ 7CO]; 1282.2 [M+ ꢀ 8CO].
Anal. Calc. for C70H62O8Co4SP4Si2N2: C, 55.69; H,
4.11; N, 1.86. Found: C, 55.82; H, 4.10; N, 1.83%.
(6) IR (CH2Cl2, cmꢀ1): mCO 2017.6 (s), 1994.5 (vs),
1965.0 (s), 1945.0 (sh). 1H NMR (300 MHz, CDCl3,
(4) IR (CH2Cl2, cmꢀ1): mC„C 2137.7 (w); mCO 2021.3
1
(s), 1995.2 (vs), 1967.9 (s), 1948.7 (sh). H NMR (300
MHz, CDCl3, ppm): 7.32–6.98 (m, 20H, Ph); 6.96 (d,
H5, JHH = 3.7 Hz); 6.46 (d, H4, JHH = 3.7 Hz); 3.60 (dt,
JHH = 13.1 Hz, JPH = 10.5 Hz, 1H, ABXY, –CH2–);
3.37 (dt, JHH = 13.2 Hz, JPH = 10.3 Hz, 1H, ABXY,
–CH2–); 0.36 (s, 9H, –CSiMe3); 0.26 (s, 9H, „CSiMe3).
13C NMR (125 MHz, CDCl3, ppm): d 206.9 (m, CO);
202.2 (m, CO); 150.7 (t, JCP = 3.8 Hz, C3); 138.5 (t,
JCP = 24.1 Hz, i-Ph); 134.6 (t, JCP = 17.2 Hz, i-Ph);
133.2 (s, C5); 132.6 (t, JCP = 6.3 Hz, o-Ph); 130.6 (t,
JCP = 5.9 Hz, o-Ph); 129.8 (s, p-Ph); 129.3 (s, p-Ph);
128.5 (t, JCP = 4.6 Hz, m-Ph); 128.0 (t, JCP = 4.7 Hz, m-
Ph); 126.0 (s, C4); 121.0 (s, C6); 98.7 (s) and 98.2 (s),
(C„C); 93.1 (m, C2); 89.9 (m, C1); 36.5 (t, JCP = 20.3
Hz, –CH2–); 0.82 (s, –CSiMe3); 0.00 (s, „CSiMe3). 31P
NMR (121 MHz, CDCl3, ppm): d 35.0 (s br, 2P, dppm).
UV-V (CH2Cl2, nm): kmax 544 and 230. MS (FAB+, m/z):
891.0 [M+]; 863.0 [M+ ꢀ CO]; 835.0 [M+ ꢀ 2CO]; 807.0
0
ppm): d 7.24–6.97 (m, 40H, Ph); 6.56 (s, H4,4 ); 3.60
(dt, JHH = 13.1 Hz, JPH = 10.5 Hz, 2H, ABXY, 2
–CH2–); 3.47 (dt, JHH = 13.2 Hz, JPH = 10.3 Hz, 2H,
ABXY, 2 –CH2–); 0.40 (s, 18H, 2 –SiMe3). 13C NMR
(125 MHz, CDCl3, ppm): d 206.8 (m, CO); 202.5 (m,
0
CO); 145.8 (t, JCP = 2.9 Hz, C3,3 ); 138.5 (t, JCP = 24.1
Hz, i-Ph); 134.7 (t, JCP = 17.1 Hz, i-Ph); 132.6 (t,
JCP = 6.3 Hz, o-Ph); 130.7 (t, JCP = 6.1 Hz, o-Ph);
129.5 (s, p-Ph); 129.2 (s, p-Ph); 128.4 (t, JCP = 4.6 Hz,
0
m-Ph); 127.8 (t, JCP = 4.6 Hz, m-Ph); 127.2 (s, C4,4 );
0
93.5 (t, JCP = 6.5 Hz, C2,2 ); 89.5 (t, JCP = 9.8 Hz,
0
C
1,1 ); 37.9 (t, JCP = 19.6 Hz, 2 –CH2–); 1.09 (s, 2
–SiMe3). 31P NMR (121 MHz, CDCl3, ppm): d 34.8 (s
br, 4P, 2 dppm). UV–Vis (CH2Cl2, nm): kmax 577, 403
and 229. MS (FAB+, m/z): 1475.9 [M+ ꢀ CO]; 1447.8
[M+ ꢀ 2CO]; 1419.8 [M+ ꢀ 3CO]; 1307.9 [M+ ꢀ 7CO];

A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
3221
1279.9 [M+ ꢀ 8CO]. Anal. Calc. for C72H64O8Co4SP4-
128.7 (s, p-Ph); 128.3 (s, p-Ph); 127.4 (t, JCP = 4.6 Hz,
m-Ph); 126.9 (t, JCP = 4.6 Hz, m-Ph); 124.7 (s, C4);
118.6 (s, C6); 93.0 (m, C2); 91.1 (m, C1); 80.1 (s, C8);
76.5 (s, C7); 36.1 (m, –CH2–); 0.00 (s, –SiMe3). 31P
NMR (121 MHz, CDCl3, ppm): d 34.9 (s br, 2P, dppm).
UV–Vis (CH2Cl2, nm): kmax 536 (sh) and 231. MS
(FAB+, m/z): 791.1 [M+ ꢀ CO]; 735.1 [M+ ꢀ 3CO];
707.1 [M+ ꢀ 4CO].
Si2: C, 57.59; H, 4.26. Found: C, 57.45; H, 4.28%.
2.5. Synthesis of 2-[Co2(CO)4(l-X){l2-g2:g2–SiMe3-
C2}]-5-(C„CH)C4H2S X = dppa (7) and X = dppm
(8)
2.5.1. Method A
3 or 4 (0.62 mmol) was dissolved in a MeOH solution
saturated with KOH and the mixture was stirred for
24 h at 25 ꢁC. After that, the solvent was removed under
vacuum and the residue was extracted with several
portions of Et2O and purified by hexane-packed silica
column (200 g) using hexane/CH2Cl2 (1:1) as eluent to
afford the unstable red solids 7 (53% yield) or 8 (58%
yield).
2.6. Synthesis of 2,5-[Co2(CO)4(l-dppm){l2-g2-
HC2}]2C4H2S (9)
The same procedure as described above in Method B
was carried out from compound 6 (0.24 g, 0.16 mmol)
and TBAF (1.33 mL, 1.0 M in THF, 1.33 mmol). After
the solvent was removed under vacuum, the product was
purified in the same manner to afford the unstable green
solid 9 (55% yield).
2.5.2. Method B
(9) IR (CH2Cl2, cm1): mCO 2022.3 (s), 1997.3 (vs),
1
1968.4 (s), 1951.0 (sh). H NMR (300 MHz, CDCl3,
To a solution of 3 or 4 (0.56 mmol) in THF/MeOH
(10:1) was added TBAF (1.15 mL, 1.0 M in THF, 1.15
mmol) and the mixture was stirred for 24 h at room tem-
perature. After the solvent was removed under vacuum,
the product was purified by hexane-packed silica column
using hexane/CH2Cl2 (1:1) as eluent to afford 7 or 8 in
18% and 21% yield, respectively.
0
ppm): d 7.42–7.16 (m, 40H, Ph); 7.14 (s, H4,4 ); 5.78 (t,
2 –CH, JPH = 6.2 Hz); 3.56 (dt, JHH = 13.1 Hz,
JPH = 10.6 Hz, 2H, ABXY, 2 –CH2–); 3.12 (dt,
JHH = 13.2 Hz, JPH = 10.4 Hz, 2H, ABXY, 2 –CH2–).
13C NMR (125 MHz, CDCl3, ppm): d 205.4 (m, CO);
0
202.1 (m, CO); 144.5 (t, JCP = 2.9 Hz, C3,3 ); 136.0 (t,
(7) IR (CH2Cl2, cmꢀ1): mNH 3328.2 (w); m„CH 3305.6
(m); mC„C 2095.9 (vw); mCO 2028.7 (s), 2001.6 (vs),
1974.8 (s), 1957.7 (sh). H NMR (300 MHz, CDCl3,
JCP = 20.0 Hz, i-Ph); 135.2 (t, JCP = 19.6 Hz, i-Ph);
131.0 (t, JCP = 6.1 Hz, o-Ph); 130.5 (t, JCP = 6.0 Hz, o-
0
Ph); 128.5 (s br, p-Ph); 128.2 (s, C4,4 ); 127.3 (t,
JCP = 4.6 Hz, m-Ph); 127.1 (t, JCP = 4.6 Hz, m-Ph);
1
ppm): d 7.46–7.28 (m, 20H, Ph); 6.64 (d, H5, JHH = 3.9
Hz); 5.92 (d, H4, JHH = 3.8 Hz); 3.94 (t, –NH,
JPH = 6.3 Hz); 3.32 (s, 1H, „CH); 0.37 (s, 9H, –SiMe3).
13C NMR (125 MHz, CDCl3, ppm): d 206.3 (m, CO);
203.2 (m, CO); 149.1 (t, JCP = 3.8 Hz, C3); 142.0 (t,
JCP = 21.1 Hz, i-Ph); 139.0 (t, JCP = 23.0 Hz, i-Ph);
133.5 (s, C5); 130.9 (t, JCP = 6.8 Hz, o-Ph); 130.6 (t,
JCP = 6.8 Hz, o-Ph); 130.2 (s, p-Ph); 130.1 (s, p-Ph);
128.8 (t, JCP = 4.8 Hz, m-Ph); 128.7 (t, JCP = 4.8 Hz,
m-Ph); 128.1 (s, C4); 119.5 (s, C6); 91.9 (t, JCP = 11.0
Hz, C2); 91.1 (m, C1); 81.1 (s, C8); 78.2 (s, C7); 1.42 (s,
–SiMe3). 31P NMR (121 MHz, CDCl3, ppm): d 91.7 (s
br, 2P, dppa). UV–Vis (CH2Cl2, nm): kmax 547 (sh)
and 231. MS (FAB+, m/z): 792.1 [M+ ꢀ CO]; 736.1
[M+ ꢀ 3CO]; 708.1 [M+ ꢀ 4CO].
0
0
84.3 (m, C2,2 ); 74.2 (m, C1,1 ); 39.9 (t, JCP = 19.8 Hz, 2
–CH2–). 31P NMR (121 MHz, CDCl3, ppm): d 43.2 (s
br, 4P, 2 dppm). UV–Vis (CH2Cl2, nm): kmax 579, 400
(sh) and 229. MS (FAB+, m/z): 1361.0 [M+]; 1333.1
[M+ ꢀ CO]; 1277.2 [M+ ꢀ 3CO]; 1137.0 [M+ ꢀ 8CO].
2.7. X-ray crystallography
Green crystals of 2,5-[Co2(CO)4(dppm){l2-g2-Si-
Me3C2}]2C4H2S, 6, are obtained by recrystallisation of
the complex from CH2Cl2–hexane mixtures. A summary
of selected crystallographic data for 6 is given in Table 3.
Data were collected on a Nonius Kappa CCD diffrac-
tometer using graphite monochromated Mo Ka radia-
(8) IR (CH2Cl2, cm1): mC„H 3300.4 (m); mC„C 2094.9
(vw); mCO 2021.7 (s), 1996.1 (vs), 1968.3 (s), 1952.6 (sh).
1H NMR (300 MHz, CDCl3, ppm): d 7.32–6.98 (m,
20H, Ph); 7.01 (d, H5, JHH = 3.7 Hz); 6.51 (d, H4,
JHH = 3.7 Hz); 3.60 (dt, JHH = 13.1 Hz, JPH = 10.4 Hz,
1H, ABXY, –CH2–); 3.38 (dt, JHH = 13.2 Hz,
JPH = 10.3 Hz, 1H, ABXY, –CH2–); 3.37 (s, 1H,
„CH); 0.37 (s, 9H, –SiMe3). 13C NMR (125 MHz,
CDCl3, ppm): d 205.9 (m, CO); 201.1 (m, CO); 150.0
(t, JCP = 2.9 Hz, C3); 137.4 (t, JCP = 24.1 Hz, i-Ph);
133.5 (t, JCP = 16.9 Hz, i-Ph); 132.5 (s, C5); 131.6 (t,
JCP = 6.0 Hz, o-Ph); 129.5 (t, JCP = 6.0 Hz, o-Ph);
tion (k = 0.71073 A). A combination of 1ꢁ / and x
˚
(with j offsets) scans was used to collect sufficient data.
The data frames were integrated and scaled using the
DENZO-SMN package [17]. The structure was solved
and refined using the SHELXTL/PC V5.1 package [18].
The structure was solved by direct methods and refine-
ment 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 rid-
ing atoms with U isotropic 20% larger than the
corresponding C-atoms for the phenyl H-atoms and
50% larger for the methyl H-atoms. Anisotropic thermal

3222
A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
parameters, hydrogen atom parameters and structure
amplitudes are available as supplementary material. Ta-
ble 4 contains selected bond distances and angles. Fig. 2
presents a molecular diagram of 6. CCDC Reference
No. 240985 (compound 6).
yield) or with saturated KOH in degassed methanol
(55%) to yield the terminal diyne compounds 7 and 8
as dark red solids. Complex 9 was only obtained when
stronger desilylation conditions were used (Bu4NF in
THF/MeOH).
All these compounds have been characterized by ana-
lytical and spectroscopic data (IR, 1H, 1H{31P}, 13C, 31
P
3. Results and discussion
NMR, MS and X-ray crystallography), details of which
are given in Section 2. The IR spectra of 1 and 2 exhibit
three strong absorptions in the carbonyl stretching re-
gion at 2088–2028 cmꢀ1; in dppm and dppa substituted
complexes 3–9 these absorptions lie at lower frequencies
2029–1945 cmꢀ1 and the spectral patterns are similar to
those observed for previously reported cobalt-alkyne
and cobalt-substituted-alkyne complexes [1c–1f,2c,7,8].
Complexes 1, 3, 4, 7 and 8 contain uncomplexed C„C
triple bonds which give a mC„C weak absorption be-
tween 2151 and 2095 cmꢀ1 (as expected the mC„C values
of 7 and 8 are lower than 1, 3 and 4). In addition, desil-
ylated compounds 7 and 8 exhibit a m„C–H at ca. 3300
3.1. Synthesis and spectroscopic characterization
2,5-Bis(trimethylsilylethynyl)thiophene (L) was ob-
tained in high yield (87%) by coupling reaction of 2,5-
dibromothiophene with TMSA in the presence of
Pd(PPh3)4 and CuI in triethylamine [16].
Complexes 1 and 2 have been obtained, as red and
green unstable solids, by direct reaction between 2,5-
bis(trimethylsilylethynyl)thiophene (L) and Co2(CO)8
in 1:1.5 and 1:2 ratios, respectively (Scheme 1).
In order to stabilise the dicobalt units by bridging ef-
fect between the two metal atoms, we have prepared
complexes containing dppm or dppa ligands. Phos-
phine-substituted alkyne carbonyl complexes, 2-[Co2
(CO)4(l-X){l2-g2-SiMe3C2}]-5-(Me3SiC„C)C4H2S
(X = dppa (3) or dppm (4)) and 2,5-[Co2(CO)4(l-X){l2-
g2-SiMe3C2}]2C4H2S (X = dppa (5) or dppm (6)), can be
prepared by direct reaction between the alkyne and
Co2(CO)6(X) (X = dppa or dppm), under thermal condi-
tions in a moderate yield (ꢁ30%) or by substitution
reaction of carbonyl ligands in the presence of Me3NO
at the Co2(CO)6 units of complexes 1 and 2 (65% yield)
(Scheme 1). This method, used previously in our labora-
tory for the syntheses of organometallic complexes with
P-donor ligands [19], has clear advantages, namely, mild
conditions, short reaction times and higher yields.
The FT-IR spectral changes of these reactions have
been monitored until the mC„O bands of the parent com-
plex had disappeared. These changes suggest initial for-
mation of monosubstituted intermediate products,
which show five terminal stretching modes mCO (2059
(vs), 2024 (vs), 2003 (vs), 1979 (m) and 1959 (m)), in
the characteristic range of analogous compounds where
the ligand occupies an axial site [8,20]. This assumption
is supported by the cleanness of the reactions as evi-
denced by the presence of isosbestic points in the succes-
sive spectra taken during the course of the reactions.
This is followed by loss of CO and formation of the final
product where the two P-atoms are coordinated to the
Co atoms. The 31P NMR data confirm the existence of
these monosubstituted intermediate products; thus the
spectrum presents two signals for both coordinated
modes, monodentate and chelating phosphine (ca.
92.00 ppm (Pcoord), 43.50 ppm (Pfree) for dppa and ca.
35.00 ppm (Pcoord), ꢀ21.81 ppm (Pfree) for dppm).
Desilylation of 3 and 4 could be accomplished by
treatment with Bu4NF in THF/MeOH (10:1) (ꢁ20%
cmꢀ1
.
The NMR spectroscopic data (1H, 31P and 13C) for
complexes 1–9 are consistent with overall geometry
established in the solid state for complex 6 (Fig. 1), with
the IR spectroscopy studies and with the proposed
structures (Scheme 1).
In 1H NMR spectra, the chemical shifts for the SiMe3
and C„CH protons are found to be very sensitive to co-
balt complexation on the adjacent alkyne bond. As ex-
pected, the NMR spectra show a significant downfield
shift for SiMe3 and terminal protons in the Co2-func-
tionalized complexes 1–9 by ca. 0.15 and 2.5 ppm with
respect to the free ligand, respectively, in accordance
with the reduction in the C„C triple-bond character
[21]. In addition, the chemical shifts of the thiophene
proton signals were consistent with the incorporation
of 1 and 2 Co2(CO)6 or Co2(CO)4(X) (X = dppa or
dppm) units (see Section 2, Table 1). For all dppm-com-
plexes the diastereotopic protons of –CH2– group are
coupled with the two P-atoms, thus they appear as dou-
ble triplet (Table 1, Fig. 1). For complex 9, which con-
tains a terminal alkyne proton, the –CH signal is
coupled with the two chemically equivalent P-atoms
1
and it appears as triplet with H–31P coupling constant
of J = 6.2 Hz as in similar compounds [22]. The set of
proton NMR signals, for all complexes, in the range d
5.3–7.5 ppm evidences the presence of aromatic rings
of the ligands (phenyl and thiophene).
The 31P spectra, at room temperature, of all com-
pounds 3–9 always show a broad singlet that is shifted
to higher frequencies (ca. 35 and 92 ppm for dppm
and dppa complex, respectively) with respect to the free
ligands because of the coordination.
The 13C NMR chemical shifts of the carbonyls in all
the complexes appear as one or two signals at around d
199 ppm or d 202 and 206 ppm, respectively, suggesting

A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
3223
4
4'
1.5 eq. Co2(CO)8
3
3'
S
2
2'
hexane,25 ºC, 1h
52 %
42 %
1
1'
SiMe3
Me3Si
L
4
4'
5
4
Co(CO)3
Co (CO)3
(CO)3Co
(CO)3 Co
Co(CO)3
Co (CO)3
6
3'
3
3
S
2 eq. Co2(CO)8
97 %
S
2
2'
2
7
8
1
1'
1
Me3Si
SiMe3
SiMe3
Me3Si
2
1
Method B
Method A
dppa or dppm
Me3NO
Co2(CO)6(dppa)
or
Method A
dppa or dppm
Me3NO
60 - 65 %
25 - 30 %
Co2(CO)6(dppm)
hexane
hexane, 40ºC, 3 days
65 -7 0 %
X
X
hexane, 40ºC, 3 days
65ºC, 15 days
PPh2
Ph2P
PPh2
4
4'
Ph2P
Co(CO)2
(CO)2Co
Co (CO)2
(CO)2 Co
3'
3
S
2'
2
1'
1
X
SiMe3
Me3Si
PPh2
5
4
28-33 %
Ph2P
X= NH (dppa) (5) or X= CH2 (dppm) (6)
Co(CO)2
Co (CO)2
6
3
S
2
7
8
1
Me3Si
SiMe3
X = NH (dppa)(3) or X = CH2 (dppm) (4)
TBAF/THF : MeO(10:1),25ºC,24h
55 %
Method B
Method A
TBAF/ THF(10) : MeOH (1),25ºC,24h
18 -21 %
KOH / MeOH, 25ºC, 24h
53 -58 %
CH2
CH2
PPh2
Ph2P
(CO)2Co
4
4'
PPh2
Ph2P
Co(CO)2
Co (CO)2
3'
(CO)2 Co
3
2
S
2'
X
1'
1
PPh2
H
5
4
H
Ph2P
Co(CO)2
9
Co (CO)2
2
6
3
S
7
8
1
H
SiMe3
X = NH (dppa) (7) or X =CH2(dppm)(8)
Scheme 1.
that they are rapidly interchanging on the NMR scale.
The 13C NMR resonances of the free and coordinated
acetylene units were easily observed, and the chemical
shifts of the carbon atoms are in the range of analogous
complexes (d 74–100 ppm) [1d,2c]. Thiophene carbons
appear between d 118–150 ppm (Table 2). The unambig-
uous assignment (see Section 2) of all carbon atoms has
been carried out by using heteronuclear two-dimen-
sional correlation spectroscopy (HMBC and HMQC).
All compounds gave satisfactory mass spectral data,
thus the positive FAB mass spectra show the respective
molecular ions or M+ ꢀ CO, as well as peaks corre-
sponding to the consecutive loss of the CO ligands.
The UV–Vis spectra of all complexes exhibit low
intensity absorption bands with kmax. between 536 and
595 nm attributed to the d–d transitions. For complexes
2, 5, 6 and 9, the presence of the second Co2(CO)6 or
Co2(CO)4X (X = dppa or dppm) unit resulted in a red
shift in these absorption bands. In addition an intense
absorption is observed at ca. 230 nm attributed to p–
p* transition associated with the aromatic group.
3.2. X-ray crystallography
The single-crystal X-ray structure of complex 6 con-
firms the structure presented in Scheme 1. Complex 6
consists of a disubstituted thiophene ring with two bime-
tallic Co units at the 2 and 5 positions. Each bimetallic Co
moiety has two terminal CO ligands on the Co atoms,
bridging dppm ligands and bridging trimethylsilylethynyl

3224
A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
(a)
J
H-H
(b)
J
P-H
3.80
3.70
3.60
3.50
3.40
3.30
3.20
3.10
ppm
Fig. 1. (a) 1H{31P} NMR (CDCl3) and (b) 1H NMR (CDCl3)spectra for complex 4.
Table 1
Values of d (1H NMR, CDCl3, ppm) to the compounds 1–9 and 2,5-bis(trimethylsilylethynyl)thiophene (L)
0
H4
H5 or H4
–C„CH
–C–CH
–C„CSiMe3
–C–CSiMe3
>NH
>CH2
L
1
7.04 (s)
7.06 (s)a
7.11 (d)
=H4
=H4
0.24 (s)
0.24 (s)a
0.24 (s)
–
–
–
0.39 (s)
–
–
7.09 (d)
JHH = 3.9 Hz
7.13 (d)a
JHH = 3.8 Hz
JHH = 3.9 Hz
7.11 (d)a
JHH = 3.8 Hz
–
–
–
–
0.24 (s)a
0.40 (s)a
2
3
7.15 (s)
=H4
–
–
–
–
–
0.40 (s)
0.37 (s)
–
–
–
5.87 (d)
JHH = 3.8 Hz
6.60 (d)
JHH = 3.8 Hz
0.24 (s)
3.95 (t)
JPH = 6.4 Hz
4
5
6
7
8
9
6.46 (d)
JHH = 3.7 Hz
6.96 (d)
JHH = 3.7 Hz
–
–
–
–
–
–
0.26 (s)
0.36 (s)
0.37 (s)
0.40 (s)
0.37 (s)
0.37 (s)
–
–
3.60 (dt)
3.37 (dt)
5.26 (s)
6.56 (s)
=H4
=H4
–
–
–
–
–
–
3.95 (t)
JPH = 6.5 Hz
–
–
–
3.60 (dt)
3.47 (dt)
5.92 (d)
JHH = 3.8 Hz
6.64 (d)
JHH = 3.9 Hz
3.32 (s)
3.37 (s)
–
3.94 (t)
JPH = 6.3 Hz
–
6.51 (d)
JHH = 3.7 Hz
7.01 (d)
JHH = 3.7 Hz
–
–
3.60 (dt)
3.38 (dt)
7.14 (s)
=H4
5.78 (t)
JPH = 6.2 Hz
3.56 (dt)
3.12 (dt)
a
CD2Cl2.

A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
3225
Table 2
Values of d (13C NMR, CDCl3, ppm) to the compounds 1–9 and 2,5-bis(trimethylsilylethynyl)thiophene (L)
0
0
0
0
C8 or C1
C1
C2
C3
C
C5 or C4
C6 or C3
C7 or C
4
2
L
1
2
3
99.7 (s)
97.0 (s)
124.5 (s)
132.1 (s)
128.8 (s)
130.7 (s)
128.5 (s)
@C4
@C3
@C2
@C1
81.1 (s br)
81.5 (s br)
91.1 (m)
93.3 (s br)
94.1 (s br)
92.1 (m)
143.5 (s)
142.8 (s)
133.7 (s)
@C4
123.6 (s)
@C3
97.2 (s)
100.5 (s)
@C2
@C1
148.5 (t)
JCP = 4.3 Hz
133.2 (s)
120.7 (s)
98.9 (s)
98.6 (s)
4
89.9 (m)
89.0 (m)
93.1 (m)
92.4 (m)
150.7 (t)
JCP = 3.8 Hz
126.0 (s)
133.2 (s)
121.0 (s)
98.7 (s)
98.2 (s)
5
6
142.8 (m)
128.7 (s)
127.2 (s)
@C4
@C4
@C3
@C3
@C2
@C2
@C1
@C1
89.5 (t)
JCP = 9.8 Hz
93.5 (t)
JCP = 6.5 Hz
145.8 (t)
JCP = 2.9 Hz
7
8
9
91.1 (m)
91.1 (m)
74.2 (m)
91.9 (t)
JCP = 11.0 Hz
149.1 (t)
JCP = 3.8 Hz
128.1 (s)
124.7 (s)
128.2 (s)
133.5 (s)
132.5 (s)
@C4
119.5 (s)
118.6 (s)
@C3
78.2 (s)
76.5 (s)
@C2
81.1 (s)
80.1 (s)
@C1
93.0 (m)
84.3 (m)
150.0 (t)
JCP = 2.9 Hz
144.5 (t)
JCP = 2.9 Hz
Table 3
Crystal data and structure refinement for compound 6
ligands. The geometric parameters for 6 have been sum-
marized in Table 3. Table 4 contains selected bond dis-
tances and angles, Fig. 2 presents a view of the
molecule with the atom-labelling scheme and Fig. 3 is
the extended structure of 6.
Empirical formula
Formula weight
C73H65Cl3Co4O8P4SSi2
1624.44
297(2) K
Temperature
Wavelength
˚
0.71073 A
P2(1)/c
Monoclinic
Complex 6 crystallizes in the monoclinic space group
P21/c, with one molecule in the asymmetric unit. The
structure also contains one molecule of chloroform that
is grossly disordered, which could not be modeled satis-
factorily. The contribution from this solvent molecule
was removed from the observed data using SQUEEZE
in the software program PLATON, but the atom count
from the CHCl3 is included in the empirical formula
[23]. Although the complex does not contain any crystal-
lographic symmetry, the molecule is symmetric about a
mirror plane through the thiophene moiety, the bond
lengths are sufficiently comparable such that discussion
will be confined to one half of the molecule. A highly
distorted tetrahedron is formed by the coordination of
the dicobalt units with the ethynyl carbons, with a
Crystal system
Space group
Unit cell dimensions
a
˚
12.1439(2) A
˚
b
12.5980(2) A
˚
52.5016(8) A
c
a
90ꢁ
b
c
91.441(9)ꢁ
90ꢁ
3
˚
V
8029.6(2) A
Z
4
Dcalc.
1.344 Mg/m3
1.096 mmꢀ1
3320
Absorption coefficient
F(000)
Crystal size
0.10 · 0.07 · 0.04 mm3
0.78–25.79ꢁ
h range for data collection
Index ranges
ꢀ14 6 h 6 14, ꢀ15 6 k 6 15,
ꢀ63 6 l 6 62
˚
Co(1)–Co(2) bond length of 2.504(1) A, and the average
Reflections collected
49454
˚
Co–C bond length was determined to be 1.971(1) A.
Independent reflections
Completeness to h = 25.79ꢁ
Max. and min. transmission
Refinement method
14832 [Rint = 0.0728]
96.0%
0.9575 and 0.8983
Full-matrix least-squares on F2
14832/0/826
0.947
Comparable Co–Co distances of 2.4892(4) and
˚
2.4906(4) A are reported for the related compound
{(Co2(CO)4dppm)(l2-g2-SiMe3C2)}2(SiMe3C„C)(1,3,5-
C6H3) [7]. The distance between the two Co2 moieties
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
˚
was found to be 8.26 A, which was calculated by placing
a centroid between Co(1) and Co(2), and similarly
Co(3) and Co(4), and then determining the distance
R1 = 0.0716, wR2 = 0.1797
R1 = 0.1254, wR2 = 0.2009
ꢀ3
˚
Largest diff. peak and hole
0.630 and ꢀ0.581 e A

3226
A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
Table 4
between the two centroids which spans across the
thiophene ring.
˚
Selected bond distances (A) and angles (ꢁ) for 6
Co(1)–Co(2)
Co(1)–C(6)
2.504(1)
1.958(6)
1.993(5)
1.755(9)
1.792(7)
1.949(5)
1.985(6)
1.791(7)
1.778(8)
2.227(2)
2.211(2)
1.857(6)
101.2(3)
101.9(3)
103.3(3)
101.3(3)
140.1(3)
39.7(2)
Co(3)–Co(4)
Co(3)–C(40)
2.493(1)
1.978(6)
2.006(5)
1.765(7)
1.786(8)
1.945(5)
1.973(5)
1.768(8)
1.804(7)
2.222(2)
2.220(2)
1.834(6)
101.3(3)
103.0(3)
99.9(3)
The coordination geometry of each Co is similar to a
pyramid with a pentagonal-shaped base, where the Co is
in the centre of the pyramid. The distortion of the pyr-
amid is due to the constrained tetrahedron comprised
of Co(1)–Co(2)–C(5)–C(6), as well as the bridging of
the dppm ligand. The carbonyl moieties coordinate to
the Co atoms in the least sterically hindered sites, thus
making up the pyramid. The apex of the pyramid is
one of the carbonyl groups, and the base is comprised
of the other carbonyl group, one of the phosphorus
atoms of the dppm ligand, the two ethynyl carbons,
and the other Co atom. The bond lengths of the apex
carbonyls to the Co atoms, C(8)–Co(1) and C(9)–
Co(1)–C(5)
Co(1)–C(7)
Co(3)–C(39)
Co(3)–C(41)
Co(1)–C(8)
Co(2)–C(5)
Co(3)–C(42)
Co(4)–C(39)
Co(2)–C(6)
Co(2)–C(9)
Co(4)–C(40)
Co(4)–C(43)
Co(2)–C(10)
Co(1)–P(1)
Co(4)–C(44)
Co(3)–P(3)
Co(2)–P(2)
Si(1)–C(6)
Co(4)–P(4)
Si(2)–C(40)
C(7)–Co(1)–C(8)
C(7)–Co(1)–C(6)
C(8)–Co(1)–C(6)
C(7)–Co(1)–C(5)
C(8)–Co(1)–C(5)
C(6)–Co(1)–C(5)
C(7)–Co(1)–P(1)
C(8)–Co(1)–P(1)
C(6)–Co(1)–P(1)
C(5)–Co(1)–P(1)
C(7)–Co(1)–Co(2)
C(8)–Co(1)–Co(2)
C(6)–Co(1)–Co(2)
C(5)–Co(1)–Co(2)
P(1)–Co(1)–Co(2)
C(10)–Co(2)–C(9)
C(10)–Co(2)–C(5)
C(9)–Co(2)–C(5)
C(10)–Co(2)–C(6)
C(9)–Co(2)–C(6)
C(5)–Co(2)–C(6)
C(10)–Co(2)–P(2)
C(9)–Co(2)–P(2)
C(5)–Co(2)–P(2)
C(6)–Co(2)–P(2)
C(10)–Co(2)–Co(1)
C(9)–Co(2)–Co(1)
C(5)–Co(2)–Co(1)
C(6)–Co(2)–Co(1)
P(2)–Co(2)–Co(1)
P(1)–C(14)–P(2)
C(41)–Co(3)–C(42)
C(41)–Co(3)–C(40)
C(42)–Co(3)–C(40)
C(41)–Co(3)–C(39)
C(42)–Co(3)–C(39)
C(40)–Co(3)–C(39)
C(41)–Co(3)–P(3)
C(42)–Co(3)–P(3)
C(40)–Co(3)–P(3)
C(39)–Co(3)–P(3)
C(41)–Co(3)–Co(4)
C(42)–Co(3)–Co(4)
C(40)–Co(3)–Co(4)
C(39)–Co(3)–Co(4)
P(3)–Co(3)–Co(4)
C(43)–Co(4)–C(44)
C(43)–Co(4)–C(39)
C(44)–Co(4)–C(39)
C(43)–Co(4)–C(40)
C(44)–Co(4)–C(40)
C(39)–Co(4)–C(40)
C(43)–Co(4)–P(4)
C(44)–Co(4)–P(4)
C(39)–Co(4)–P(4)
C(40)–Co(4)–P(4)
C(43)–Co(4)–Co(3)
C(44)–Co(4)–Co(3)
C(39)–Co(4)–Co(3)
C(40)–Co(4)–Co(3)
P(4)–Co(4)–Co(3)
P(1)–C(14)–P(2)
103.0(3)
137.2(3)
40.4(2)
˚
Co(2), are 1.792(7) and 1.791(7) A, respectively. These
bond lengths are not statistically different from the base
carbonyls to Co atoms, which are 1.755(9) and 1.778(8)
97.5(2)
97.5(2)
105.8(2)
140.8(2)
103.3(2)
149.6(2)
99.0(2)
110.2(2)
139.2(2)
100.9(2)
151.0(2)
96.3(3)
˚
A, for C(7)–Co(1) and C(10)–Co(2), respectively. The
dihedral angle comprised of Co(2)–C(5)–C(6)–Co(1)
was determined to be ꢀ84.9(2)ꢁ, whereas the dihedral
angle comprised of C(5)–Co(2)–Co(1)–C(6) was deter-
mined to be ꢀ52.2(3)ꢁ. The analogous dihedral angle
of P(2)–Co(2)–Co(1)–P(1) was determined to be
ꢀ4.90(6)ꢁ, thus suggesting a greater strain on the dico-
balt units by the coordination of the ethynyl carbons
compared to the bridging of the dppm ligand. The bite
angle of the dppm ligand was found to be 110.0(3)ꢁ,
which is consistent to analogous bite angles of dppm
on Co–Co complexes [24]. The C(5)–C(6) bond length
51.1(2)
49.8(2)
50.8(2)
49.8(1)
98.48(6)
101.1(3)
97.6(3)
97.88(5)
100.1(3)
97.5(3)
140.1(3)
105.0(3)
100.9(3)
39.8(2)
143.8(3)
101.9(3)
104.0(3)
41.1(2)
98.5(2)
99.8(2)
˚
of the bridging ethynyl ligand is 1.341(7) A, which is
107.3(2)
104.4(2)
138.8(2)
148.7(2)
102.3(2)
51.3(2)
106.1(2)
101.7(2)
138.8(2)
148.4(2)
102.3(3)
52.0(2)
consistent with reported dicobalt ethynyl complexes
[25].
The bond lengths of the Co atoms to the phosphorus
˚
˚
atoms of the dppm ligand are 2.227(2) A and 2.211(2) A
for Co(1)–P(1) and Co(2)–P(2), respectively. The Co–P
bond lengths of the same dppm are statistically different;
however, no chemical significance is ascribed to the
50.1(2)
94.14(5)
110.0(3)
51.0(2)
95.15(5)
110.0(3)
Fig. 2. ORTEP diagram of 6, with 35% ellipsoids. Hydrogen atoms have been removed for clarity.

A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
3227
Fig. 3. Extended structure of 6 showing cavities where the contribution from grossly disordered chloroform solvent molecules occupied.
difference. The phenyl rings on the dppm ligand are ori-
ented in a fashion such that the rings twist in the same
direction with respect to each other in order to minimize
steric crowding. The average carbonyl C„O bond
completely irreversible reduction wave at Ep = ꢀ1.05 V
vs. Fc*+/Fc* (SWV) and at Epc = ꢀ1.14 V (CV, at a
sweep rate v = 0.1 V sꢀ1). Upon scan reversal in CV,
no coupled anodic peak is observed, but a new irrevers-
ible peak at +0.12 V appears. This behaviour resembles
other related Co2(CO)6(alkyne) derivatives [6d,7,8,26–
29] and indicates that a monoelectronic reduction proc-
ess is followed by the fast decomposition of the radical
anion 1ꢀ in a variety of fragments (EC mechanism)
including Co(CO)4ꢀ, which is oxidised at 0.12 V. At
ꢀ30 ꢁC, the chemical disintegration of 1ꢀ is much
slower, as the CV shows a quasi-reversible reduction
wave (ipa/ipc ꢂ 0.6 at 0.1 V sꢀ1, E1/2 = ꢀ1.01 V) and
the diminution of the peak at 0.12 V; however, other
new small anodic peaks can be observed at ꢀ0.61 and
ꢀ0.44 V (Fig. 4(a)).
˚
length was determined to be 1.138(2) A, where all of
the bond lengths were sufficiently similar (differences be-
tween the bond lengths were below 1r). The thiophene
ring is essentially planar with a root mean square devia-
˚
tion of 0.0032 A. There does not appear to be any intra-
molecular hydrogen bonding within the molecule.
3.3. Electrochemical studies
Table 5 summarizes data of E1/2 for the electrochem-
ical oxidation and reduction of compounds 1–9. The lig-
and L does not present any oxidation or reduction peaks
in the potential range between ꢀ1.8 V and +1.6 V vs.
Fc*+/Fc* (Fc* = decamethylferrocene) in CH2Cl2 and
THF solution.
The oxidation of 1 in CH2Cl2 is chemically irreversi-
ble at room temperature and at 0.1 V sꢀ1 (Epa = 1.27 V)
but, as the sweep rate increases, a coupled cathodic
peak can be gradually observed, indicative of an EC
process (ipc/ipa ꢂ 0.55 at 2 V sꢀ1). Accordingly, sweeps
at ꢀ30 ꢁC (Fig. 4(b)) show a partially chemically revers-
ible wave (ipc/ipa ꢂ 0.55 at 0.1 V sꢀ1). The chemical reac-
tion following the oxidation to 1+ leads to a strong
3.3.1. Electrochemistry of 1–2
The cyclic and square-wave voltammetry (CV and
SWV, respectively) in CH2Cl2 solution of the Co2
(CO)6C2 derivative 1 at room temperature show a
Table 5
Electrochemical data for 1–9a
E1/2 for reduction
DE1/2 (red)
E1/2 for oxidation
DE1/2 (ox)
1
2
3
4
5
6
7
8
9
ꢀ1.01b
1.23b
ꢀ0.97b; ꢀ1.08b
ꢀ1.51b
0.11b
1.13b ; 1.37b
0.61 (0.61)
0.67 (0.66)
0.47; 0.76 (0.44); (0.72)
0.54, 0.83
0.63
0.24
ꢀ1.58b (ꢀ1.65)
ꢀ1.55b; ꢀ1.67b (ꢀ1.68b); (ꢀ1.84b)
ꢀ1.55b; ꢀ1.68b
ꢀ1.50
0.12b (0.16b)
0.13b
0.29 (0.28)
0.29
ꢀ1.53b
0.69
0.50; 0.70
ꢀ1.53b; ꢀ1.66b
0.13b
0.20
In V vs. Fc*+/Fc* in CH2Cl2 solution (values in italics are in THF solution). Data are taken from CV and SWV at 25 ꢁC unless otherwise stated.
From CV and SWV at ꢀ30 ꢁC.
a
b

3228
A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
formed to a solution of Co2(CO)8 in CH2Cl2, an irre-
versible reduction peak is observed at ꢀ0.52 V and,
upon scan reversal, [Co(CO)4ꢀ] oxidation takes place
at +0.12 V (measurement in our laboratory). Further-
more, Wong et al. performed experiments at ꢀ78 ꢁC,
where the chemical reaction following reduction of their
complex was completely quenched and, correspond-
ingly, found two reversible reduction peaks. In this latter
case, they still found the oxidation peak, now at +0.66 V
vs. Fc+/Fc (1.21 V vs. Fc*+/Fc*). All this data indicate
that the anodic peak corresponds to the oxidation of
the original complex 5,50-[{Co2(CO)6}{l2-g2-Si-
Me3C2}]2-2,20-(C4H2S)2, which takes place at a potential
value quite similar to 2.
0.1
b
0.0
a
-0.1
-1.0
0.0
1.0
Potential (V vs Fc*+/Fc*)
Fig. 4. Cyclic voltammograms for the reduction (a) and oxidation (b)
of a solution of 1 in CH2Cl2 containing 0.2 M TBAPF6 at 0.1 V sꢀ1
and ꢀ30 ꢁC. Glassy carbon working electrode.
Jung et al. [6d] have studied some closely related com-
plexes, 2,5-[Co2(CO)6{l2-g2-RC2}]2(C4H2S) (R = n-bu-
tyl, phenyl), but only at room temperature, where they
found irreversible waves both for reduction and oxida-
tion. The potential values reported are consistent with
our data for 2.
The appearance of two different reduction and oxida-
tion peaks for 2 and not of a single bielectronic wave in
each case indicates the existence of interaction between
the redox centres through the thiophene ligand. The sep-
aration between the different peaks (DE1/2) is a measure
of the magnitude of this effect and, for 2 corresponds to
class II systems in the Hush–Robin–Day classification of
mixed-valence compounds (systems with low-moderate
electronic delocalization) [5d,33].
contamination of the electrode surface (Pt and glassy
carbon) by an adsorbed substance that is reduced in a
subsequent negative cycle at ca. ꢀ0.7 V. The result of
this reduction is a new adsorbed product that is oxidized
at ca. 0.55 V. This behaviour has also been found in this
laboratory with other related derivatives, like x-[Co2
(CO)6{l2-g2-SiMe3C2}]-y-(Me3SiC„C)C4H2S, (x = 2,
3 and y = 4; x = 2 and y = 3) and even the simple Co2
(CO)6{l2-g2-SiMe3C2H} [30]. The product of the reduc-
tion at ca. ꢀ0.7 V must be adsorbed cobalt (0), which is
desorbed by oxidation at ca. +0.55 V, as the same
anodic desorption peak is obtained from a solution of
CoCl2 after its reduction.
3.3.2. Electrochemistry of 3–9
The reduction of 2, which contains two equivalent
C2Co2(CO)6 redox centres, is irreversible at 25 ꢁC
(Epc = ꢀ1.05 V at 0.1 V sꢀ1), but two distinct peaks
are observed in SWV. At ꢀ30 ꢁC, CV shows two peaks
with coupled anodic ones, indicating enhanced chemical
reversibility. Therefore, the stability of the 2ꢀ anion ob-
tained in the first reduction process is much higher than
that observed in other related complexes [29–32], but
equivalent to that found in this laboratory for {(Co2
(CO)6)l2-g2-SiMe3C2}2(SiMe3C„C)(1,3,5-C6H3) [7].
The CV oxidation of 2 in CH2Cl2 leads to two quasi-re-
versible waves at 25 ꢁC which are almost completely
reversible at ꢀ30 ꢁC. Table 5 assembles E1/2 values.
It is noteworthy that very few studies can be found in
the literature on the oxidation of Co2(CO)6(alkyne)
derivatives. Wong et al. [1e] reported the reduction of
the complex 5,50-[{Co2(CO)6}{l2-g2-SiMe3C2}]2-2,20-
(C4H2S)2 in CH2Cl2, which takes place irreversibly at
ꢀ1.58 V vs. the ferrocene (Fc) couple (ꢀ1.03 V vs.
Fc*+/Fc*, see Section 2) at room temperature. They ob-
served an anodic peak at 0.71 V vs. Fc+/Fc (1.26 V vs.
Fc*+/Fc*) which was assigned to the oxidation of
[Co(CO)4ꢀ] resulting from the decomposition of the
electrogenerated monoanion. However, this potential
value is far too positive for [Co(CO)4ꢀ]; when CV is per-
The coordination of dppm or dppa phosphorous lig-
ands to the Co2C2 core increases its electron density and
facilitates oxidation, whereas it is necessary to apply
potentials 0.5 – 0.6 V more negative than in 1–2 to
achieve reduction. The chelating phosphine ligands also
contribute to the stabilization of the Co–Co bond,
increasing the lifetimes of the radical anions and cations.
In the room temperature CV and SWV oxidation of
3, 4, 7 and 8, one chemically reversible wave is obtained
with ipc/ipa = 1 in the 0.02–10 V sꢀ1 range of CV sweep
rates (Fig. 5, Table 5). Thus, 3+, 4+, 7+ and 8+ are chem-
ically stable under the actual conditions of the experi-
ment. E1/2 in CH2Cl2 is ca. 0.62 V and ca. 0.56 V less
positive than for 1 for the dppa- and dppm-substituted
complexes, respectively. This 0.06 V difference between
the derivatives of the two different phosphine ligands
has also been observed for Co2(CO)4L(l2-g2-Me3-
SiC2C„CSiMe3), where L is dppa or dppm [8].
The CV and SWV reduction of 3, 4, 7 and 8 at 25 ꢁC
takes place at a very negative potential, and a single,
partially chemically reversible peak is obtained in
CH2Cl2 (Fig. 6(a)). ipa/ipc increases with v at room tem-
perature, whereas almost complete chemical reversibility
is attained at ꢀ30 ꢁC (for 3, ipa/ipc = 1 even at a sweep
rate as slow as 0.02 V sꢀ1, Fig. 6(b)), indicating that

A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
3229
25 ꢁC even at v = 0.1 V sꢀ1. The shift in E1/2 upon dppm
or dppa coordination (between 0.50 and 0.57 V, see Ta-
ble 5) and the increased lifetime of the radical anions are
consistent with reported data [31,34,35]. It is noteworthy
that the dppa derivatives 3 and 7 which, as above men-
tioned, are easier to oxidize, also have the less negative
reduction potentials. This behaviour was also observed
for related compounds [8].
15
10
5
0
The electrochemical oxidation of 5, 6 and 9 shows
two sequential reversible waves at 25 ꢁC both in CV
(ipa/ipc = 1 in the 0.02–10 V sꢀ1 range) and SWV (Fig.
7). Correspondingly, the CV and SWV reduction of 5
and 6 displays two distinct waves at ꢀ30 ꢁC, which
are completely reversible at this low temperature (Fig.
8). On the other hand, for the reduction of 9 two peaks
are only distinguished in SWV at ꢀ30 ꢁC (an irreversible
complex peak is observed in CV). E1/2 values are assem-
bled in Table 5.
-5
0.5
1.0
Potential (V vs Fc*+/Fc*)
Fig. 5. Cyclic (—) and square wave (–––) voltammograms for the
oxidation of 7 in CH2Cl2 containing 0.2 M TBAPF6 at 25 ꢁC. CV:
v = 0.1 V sꢀ1. SWV: scan increment = 2 mV, SW amplitude = 25 mV;
frequency = 60 Hz. Pt working electrode.
20
0
0.0
-0.1
(a)
0.0
0.5
Potential (V vs Fc* /Fc*)
1.0
0.1
+
Fig. 7. Cyclic (—) and square wave (–––) voltammograms for the
oxidation of 5 in CH2Cl2 containing 0.2 M TBAPF6 at 25 ꢁC. CV:
v = 0.1 V sꢀ1. SWV: scan increment = 2 mV, SW amplitude = 25 mV;
frequency = 30 Hz. Pt working electrode.
0.0
-0.1
(b)
0
-2.0
-1.5
-1.0
Potential (V vs Fc*+/Fc*)
Fig. 6. Cyclic voltammograms for the reduction of 3 in CH2Cl2
containing 0.2 M TBAPF6 at 0.1 V sꢀ1. (a) At room temperature on a
Pt working electrode; 0.2 V sꢀ1 (–––), 0.5 V sꢀ1 (—). (b) At ꢀ30 ꢁC on
a glassy carbon working electrode; 0.02 V sꢀ1 (- - -), 0.05 V sꢀ1 (—),
0.1 V sꢀ1 (-ꢃ-ꢃ-).
-50
-2.0
-1.5
-1.0
the stabilising effect of the chelating dppm and dppa lig-
ands makes the fragmentation of 3ꢀ, 4ꢀ, 7ꢀ and 8ꢀ
much slower than for the parent 1ꢀ. The reduction of
complex 4 was also performed in THF solution; in this
solvent, complete chemical reversibility is observed at
Potential (V vs Fc*+/Fc*)
Fig. 8. Cyclic (—) and square wave (–––) voltammograms for the
reduction of 5 in CH2Cl2 containing 0.2 M TBAPF6 at ꢀ30 ꢁC. CV:
v = 0.1 V sꢀ1. SWV: scan increment = 2 mV, SW amplitude = 25 mV;
frequency = 30 Hz. Glassy carbon working electrode.

3230
A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
(e) H. Werner, O. Gevert, P. Steinert, J. Wolf, Organometallics
14 (1995) 1786;
From the oxidation waves, DE1/2 is 0.29 V in 5 and 6
and 0.20 V in 9, a bigger value than that obtained from
the reduction processes (DE1/2 = 0.12–0.13 V). Differ-
ences in DE1/2 for oxidations and reductions are not
unusual [31,36], as different MOs are involved in each
process and through-bond interactions dominate
through-space ones in these systems with a p-delocalised
spacer [10f]. Both DE1/2 are in the range corresponding
to class II mixed-valence compounds, and it can be con-
cluded that there is low-moderate interaction between
the two equivalent organometallic redox centres in 5, 6
and 9.
(f) J. Lewis, B. Lin, M.S. Khan, M.R.A. Al-Mandhary, P.R.
Raithby, J. Organomet. Chem. 484 (1994) 161.
[3] (a) M.L.H. Green, S.R. Marder, M.E. Thomson, J.A. Bandy, D.
Bloor, P.V. Kolomsky, R.J. Jones, Nature 330 (1987) 360;
(b) A.D. Hunter, Organometallics 8 (1989) 1118;
(c) R. Chukwu, A.D. Hunter, B.D. Santarsiero, Organometallics
11 (1992) 589;
(d) Z. Yuan, N.J. Taylor, Y. Sun, T.B. Marder, I.D. Williams,
J.T. Cheng, J. Organomet. Chem. 449 (1993) 27;
(e) J.S. Miller, A.J. Epstein, Angew. Chem. Int. Ed. Engl. 33
(1994) 385;
(f) M.S. Khan, M.R.A. Al-Mandhary, M.K. Al-Suti, B. Ahrens,
M.F. Mahon, L. Male, P.R. Raithby, C.E. Boothby, A. Ko¨hler,
J. Chem. Soc., Dalton Trans. (2003) 74;
(g) V.W.-W. Yam, K.-L. Cheuhg, E.C.-C. Cheng, N. Zhu, K.-K.
Cheung, J. Chem. Soc., Dalton Trans. (2003) 1830;
(h) S.K. Hurst, M.G. Humphrey, J.P. Morrall, M.P. Cifuentes,
M. Samoc, B.L. Davies, G.A. Heath, A.C. Willis, J. Organomet.
Chem. 670 (1-2) (2003) 56;
Acknowledgements
´
We express our great appreciation to the Direccion
´
´
´
General de Investigacion Cientıfica y Tecnologica
(Grant No. BQU2002-02522), Spain. X-ray diffraction
data were collected at the Monocrystal Diffraction Lab-
´
oratory SidI, Facultad de Ciencias, Universidad Auto-
noma de Madrid, Spain.
(i) I.S. Le, D.M. Shin, Y. Yoon, S.M. Shin, Y.K. Chung, Inorg.
Chim. Acta 343 (2003) 41;
(j) V.W.-W. Yam, K.M.-C. Wong, N. Zhu, Angew. Chem. Int.
Ed. Eng. 42 (2003) 1400.
[4] (a) S. Creager, C.J. Yu, C. Bamdad, S. OÕConnor, T. Maclean,
E. Lam, Y. Chong, G.T. Olsen, J. Luo, M. Gozon, J.F. Hayyem,
J. Am. Chem. Soc. 121 (1999) 1059;
´
(b) P. Stepnicka, R. Gyepes, I. Cısarova, Organometallics 18
(1999) 627;
(c) P.I. Dosa, C. Erben, V.S. Iyer, K.P.C. Vollhardt, I.M. Wasser,
J. Am. Chem. Soc. 121 (1999) 10430;
Appendix A. Supplementary material
Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/
j.jorganchem.2004.07.028.
(d) D.T. McQuade, A.E. Pullen, T.M. Swager, Chem. Rev. 100
(2000) 2537;
(e) N. Robertson, C.A. McGowan, Chem. Soc. Rev. 32 (2003) 96.
[5] (a) Molecular and Biomolecular Electronics, R.R. Birge (Ed.),
Advances in Chemistry Series, 240, American Chemical Society,
1991;
References
(b) W.P. Kirk, M.A. Reed (Eds.), Nanostructures and Mesoscopic
Systems, Academic, New York, 1992;
[1] (a) A. Sappa, A. Tiripicchio, P. Braunstein, Chem. Rev. 83 (1983)
203;
(c) A. Aviram (Ed.), Molecular Electronics: Science and Technol-
ogy, Confer. Proc. No. 262, American Institute of Physics, New
York, 1992;
(b) P.R. Raithby, M.J. Rosales, Adv. Inorg. Chem. Radiochem.
29 (1985) 169;
(d) D. Astruc, Electron Transfer and Radical Processes in
Transition-Metal Chemistry, VCH Publishers, New York, 1995;
(e) M.D. Ward, Chem. Soc. Rev. 24 (1995) 121;
(f) R.P. Andres, J.D. Bielefeld, J.I. Henderson, D.B. Janes, V.R.
Kolagunta, C.P. Kubiak, W.J. Mahoney, R.G. Osifchin, Science
273 (1996) 1690;
(c) R.S. Dickinson, P.J. Fraser, in: F.G.A. Stone, R. West (Eds.),
Advances in Organometallic Chemistry, vol. 12, 1974, p. 323;
(d) B. Happ, T. Bartik, C. Zucchi, M.C. Rossi, F. Ghelfi, G.
´ ´ ´
Palyi, G. Varadi, G. Szalontai, I.T. Horvath, A. Chiesi-Villa, C.
Guastini, Organometallics 14 (1995) 809;
(e) W.-Y. Wong, H.-Y. Lam, S.-M. Lee, J. Organomet. Chem.
595 (2000) 70;
(g) V. Grosshenny, A. Harriman, M. Hissler, R. Ziessel, Plat.
Met. Rev. 40 (1996) 26;
(f) B.H. Danna, B.H. Robinson, J. Simpson, J. Organomet.
Chem. 648 (2002) 251;
(h) V. Grosshenny, A. Harriman, M. Hissler, R. Ziessel, Plat.
Met. Rev. 40 (1996) 72;
(g) N.J. Long, C.K. Williams, Angew. Chem. Int. Ed. Engl. 42
(2003) 2586;
(i) S. Barlow, D. OÕHare, Chem. Rev. 97 (1997) 637;
(j) D. Feldheim, C.D. Keating, Chem. Soc. Rev. 27 (1998) 1;
(k) F. Paul, C. Lapinte, Coord. Chem. Rev. 431 (1998) 178;
(l) C.P. Collier, E.W. Wong, M. Belohradsky, F.M. Raymo, J.F.
Stoddart, P.J. Kuekes, R.S. Williams, J.R. Heath, Science 285
(1999) 391;
(h) P.J. Low, M.I. Bruce, in: F.G.A. Stone, R. West (Eds.),
Advances in Organometallic Chemistry, 48, 2002, p. 71;
(i) F.-E. Hong, Y.-C. Chang, R.-E. Chang, S.-C. Chen, B.-T. Ko,
Organometallics 21 (2002) 961.
[2] (a) F. Diederich, Y. Rubin, Angew. Chem. Int. Ed. Eng. 104
(1992) 1123;
(m) S. Kheradmandan, K. Heinze, H.W. Schmalle, H. Berke,
Angew. Chem. Int. Ed. Eng. 38 (1999) 2270.
(b) Y. Rubin, C.B. Knobler, F. Diederich, J. Am. Chem. Soc. 112
(1990) 4966;
[6] (a) N. Le Narvor, L. Toupet, C. Lapinte, J. Am. Chem. Soc. 117
(1995) 7129;
(c) F. Diederich, Y. Rubin, O.L. Chapman, S.N.S. Goroff, Helv.
Chim. Acta 77 (1994) 1441;
(d) T. Rappert, O. Nurnberg, H. Werner, Organometallics 12
¨
(b) T. Bartik, B. Bartik, R. Dembinski, J.A. Gladysz, Angew.
Chem. Int. Ed. Engl. 35 (1996) 414;
(c) F. Coat, C. Lapinte, Organometallics 15 (1996) 477;
(d) T.S. Jung, J.H. Kim, E.K. Jang, D.H. Kim, Y.-B. Sim, B.
(1993) 1359;

A. Arnanz et al. / Journal of Organometallic Chemistry 689 (2004) 3218–3231
3231
Park, S.C. Shin, J. Organomet. Chem. 599 (2000) 232;
(e) R.D. Adams, B. Qu, Organometallics 19 (2000) 2411;
(f) H.J. Jiao, J.A. Gladysz, New.J. Chem. 25 (2001) 551.
[18] G.M. Sheldrick, SHELXTL/PC V5.1, Bruker Analytical X-ray
Systems, Madison, WI, USA, 1997.
[19] C. Moreno, M.J. Macazaga, R.M. Medina, D.H. Farrar, S.
Delgado, Organometallics 17 (1998) 3733.
´ ´ ´
[20] (a) G. Varadi, A. Bici-Orisz, V. Sandor, G. Palyi, J. Organomet.
´
[7] (a) C. Moreno, M.L. Marcos, G. Domınguez, A. Arnanz, D.H.
´
Farrar, R. Teeple, A. Lough, J. Gonzalez-Velasco, S. Delgado, J.
Organomet. Chem. 631 (2001) 19;
Chem. 108 (1976) 225;
(b) L.S. Chia, W.R. Cullen, M. Franklin, A.R. Manning, Inorg.
Chem. 14 (1975) 2521.
(b) R.M. Medina, C. Moreno, M.L. Marcos, J.A. Castro, F.
Benito, A. Arnanz, S. Delgado, J. Gonza´lez-Velasco, M.J.
Macazaga, Inorg. Chim. Acta 357 (2004) 2069.
[21] R.K. Harris, Nuclear Magnetic Resonance Spectroscpy: A Physi-
ochemical View, Pitman, London, 1983.
[8] M.L. Marcos, M.J. Macazaga, R.M. Medina, C. Moreno, J.A.
´ ´
Castro, J.L. Gomez, S. Delgado, J. Gonzalez-Velasco, Inorg.
[22] (a) T.J. Snaith, P.J. Low, R. Rousseau, H. Pushmann, J.A.K.
Howard, J. Chem. Soc., Dalton Trans. (2001) 292;
(b) E. Champel, S.M. Draper, J. Chem. Soc., Dalton Trans.
(2001) 1440.
Chim. Acta 312 (2001) 249.
[9] (a) J. Roncali, Chem. Rev. 97 (1997) 173;
(b) D.T. McQuade, A.E. Pullen, T.M. Swager, Chem. Rev. 100
(2000) 2537;
[23] A.L. Spek, PLATON, The University of Utrecht, The Netherlands,
2004.
(c) C.J. Elsevier, J. Reedijk, P.H. Walton, M.D. Ward, J. Chem.
Soc., Dalton Trans. (2003) 1869.
[24] Average bite angle of dppm on Co–Co complexes determined to
be 110.04ꢁ from analysis of Cambridge Crystallographic
Database.
[10] (a) G.H. Worth, B.H. Robinson, J. Simpson, Appl. Organomet.
Chem. 4 (1990) 481;
(b) B.H. Robinson, Chemistry and Reactivity of Metal Cluster
Carbonyl Radical Anions in Paramagnetic Organometallic Spe-
cies in Activation, Selectivity and Catalysis, Kluwer, Dordrecht,
1987;
[25] C.E. Housecroft, B.F.G. Johnson, M.S. Khan, J. Lewis, P.R.
Raithby, M.E. Robson, D.A. Wilkinson, J. Chem. Soc., Dalton
Trans. (1992) 3171.
[26] G.J. Bezems, P.H. Rieger, S.J. Visco, J. Chem. Soc. Chem.
Commun. (1981) 265.
(c) A.J. Bard, L.R. Faulkner, Electrochemical Methods, Wiley,
New York, 1980;
[27] M. Arewgoda, P.H. Rieger, B.H. Robinson, J. Simpson, S.J.
Visco, J. Am. Chem. Soc. 104 (1982) 5633.
(d) H. Yao, M. Sabat, R.N. Grimes, P. Zanello, F. Fabrizi de
Biani, Organometallics 22 (2003) 2581;
[28] D. Osella, J. Fiedler, Organometallics 11 (1992) 3875.
[29] N. Duffy, J. McAdam, C. Nervi, D. Osella, M. Ravera, B.H.
Robinson, J. Simpson, Inorg. Chim. Acta 247 (1996) 99.
[30] (a) M.L. Marcos, M.C. Moreno, A. Arnanz, S. Delgado, J.
(e) H. Yao, M. Sabat, R.N. Grimes, F. Fabrizi de Biani, P.
Zanello, Angew. Chem. Int. Ed. Eng. 42 (2003) 1002;
(f) D. Osella, L. Milone, C. Nervi, M. Ravera, Eur. J. Inorg.
Chem. (1998) 1473;
´
Gonzalez Velasco, Port. Electrochim. Acta (in press);
(b) A. Arnanz, M.L. Marcos, C. Moreno, S. Delgado, J.
(g) A. Ceccon, S. Santi, L. Orian, A. Bisello, Coord. Chem. Rev.
248 (2004) 683.
´
Gonzalez-Velasco, unpublished work.
[31] F. Diederich, Nature 369 (1994) 199.
[11] V.H. No¨th, L. Meinel, Z. Anorg. Allg. Chem. 349 (1967)
225.
[32] D. Osella, L. Milone, C. Nervi, M. Ravera, J. Organomet. Chem.
488 (1995) 1.
[12] E.C. Lisic, B.E. Hanson, Inorg. Chem. 25 (1986) 812.
[13] J. Ellermann, N. Geheeb, G. Zoubek, G. Thiele, Z. Naturfosch.
Teil B 32 (1977) 1271.
[33] (a) G.C. Allen, N.S. Hush, Prog. Inorg. Chem. 8 (1967) 357;
(b) M.B. Robin, D. Day, Adv. Inorg. Chem. Radiochem. 10
(1967) 247.
[14] C. Moreno, M.J. Macazaga, S. Delgado, Inorg. Chim. Acta 182
(1991) 55.
[34] R.P. Aggarwal, N.G. Connelly, M.C. Crespo, B.J. Dunne, P.M.
Hopkins, A.G. Orpen, J. Chem. Soc., Dalton Trans. (1992) 655.
[35] C.J. McAdam, N.W. Duffy, B.H. Robinson, J. Simpson, Organ-
ometallics 15 (1996) 3935.
[15] D.R. Coulson, Inorg. Synth. 28 (1990) 107.
[16] Y.T. Park, I.K. Seo, Y.-R. Kim, Bull. Korean Chem. Soc. 17
(1996) 480.
[17] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307.
[36] J.A. McCleverty, M.D. Ward, Acc. Chem. Res. 31 (1998) 842.