Syntheses, structures and comparative electrochemical study of π-acetylene complexes of cobalt

Article abstract of DOI:10.1016/j.jorganchem.2005.07.065

The preparation and characterization of the complexes [Co ₂(CO)₄(μ-dppm)]₂(μ-η²- Me₃SiC₂(CC)₂C₂H) (2), [Co ₂(CO)₄(μ-dppm)]₂(μ-η²- HC₂(CC)₂C₂H) (3), Co₂(CO) ₄(μ-dmpm)(μ-η²-Me₃SiC ₂CCSiMe₃) (4), Co₂(CO)₄(μ-dmpm) (μ-η²-Me₃SiC₂CCH) (5), [Co ₂(CO)₄(μ-dmpm)]₂(μ-η²- Me₃SiC₂(CC)₂C₂SiMe₃) (6) and [Co₂(CO)₄(μ-dmpm)]₂(μ- η²-HC₂(CC)₂C₂H) (7) are described. A comparative electrochemical study of all these complexes and the related [Co₂(CO)₄(μ-dppm)]₂(μ- η²-Me₃SiC₂(CC)₂C ₂SiMe₃) (1), Co₂(CO)₄(μ-dppm) (μ-η²-Me₃SiC₂CCH) and Co ₂(CO)₄(μ-dppm)(μ-η²-HC ₂CCH) is presented by means of the cyclic and square-wave voltammetry techniques. Crystals of 2 and 3 suitable for single-crystal X-ray diffraction were grown and the molecular structures of these compounds are discussed.

Full text of DOI:10.1016/j.jorganchem.2005.07.065

Journal of Organometallic Chemistry 691 (2006) 138–149
www.elsevier.com/locate/jorganchem
Syntheses, structures and comparative electrochemical study
of p-acetylene complexes of cobalt
a
b
a
a
M.J. Macazaga , M.L. Marcos , C. Moreno , F. Benito-Lopez ,
a
b
a,
*
´
´
J. Gomez-Gonzalez , J. Gonzalez-Velasco , R.M. Medina
a
Departamento de Quı´mica Inorga´nica, Facultad de Ciencias, Universidad Auto´noma de Madrid,
Francisco Tomas y Valiente No. 7, 28049 Madrid, Spain
Departamento de Quı´mica, Facultad de Ciencias, Universidad Auto´noma de Madrid, Francisco Tomas y Valiente No. 7, 28049 Madrid, Spain
b
Received 10 June 2005; received in revised form 14 July 2005; accepted 15 July 2005
Available online 29 September 2005
Abstract
The preparation and characterization of the complexes [Co2(CO)4(l-dppm)]2(l-g2-Me3SiC2(CBC)2C2H) (2), [Co2(CO)4(l-
dppm)]2(l-g2-HC2(CBC)2C2H) (3), Co2(CO)4(l-dmpm)(l-g2-Me3SiC2CBCSiMe3) (4), Co2(CO)4(l-dmpm)(l-g2-Me3SiC2CBCH)
(5), [Co2(CO)4(l-dmpm)]2(l-g2-Me3SiC2(CBC)2C2SiMe3) (6) and [Co2(CO)4(l-dmpm)]2(l-g2-HC2(CBC)2C2H) (7) are described.
A comparative electrochemical study of all these complexes and the related [Co2(CO)4(l-dppm)]2(l-g2-Me3SiC2(CBC)2C2SiMe3)
(1), Co2(CO)4(l-dppm)(l-g2-Me3SiC2CBCH) and Co2(CO)4(l-dppm)(l-g2-HC2CBCH) is presented by means of the cyclic and
square-wave voltammetry techniques. Crystals of 2 and 3 suitable for single-crystal X-ray diffraction were grown and the molecular
structures of these compounds are discussed.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: p-Acetylene; Cobalt carbonyl complexes; Electrochemistry
1. Introduction
cation in these systems is a result of efficient mixing be-
tween filled metal fragment and polyyne-based orbitals.
The redox chemistry of Co2-alkyne is well known and
communication between these redox centres has been
demonstrated for several systems [4].
Carbon rich organometallic containing polyynes and
acetylenic arrays continue to garner attention and in-
creased research interest. Polyynediyl bridging ligands
have been shown to be specially efficient in allowing
the passage of electronic effects between redox active cen-
tres [1] and this raises possibilities for the generation of
wire-like polyynyl materials with electronic properties
tuned by both the end-capping and p-bound metal frag-
ments [1c,2]. Interactions between identical mononuclear
or cluster-based redox active groups bridged by ynyl and
polyynyl spacers have been studied extensively [3], and it
has been concluded that the strong electronic communi-
We have previously reported the electrochemical
behaviour of the complex, synthesized by Diederich [5],
[Co2(CO)4(l-dppm)]2(l-g2-Me3SiC2(CBC)2C2SiMe3)
(1), showing the existence of electronic communication
[1h]. Here, in order to evaluate the influence of the car-
bon chain end groups and the influence of a more basic
and less steric demanding phosphine ligand on the cobalt
atoms, we report the electrochemical study of the
complexes [Co2(CO)4(l-L-L)]2(l-g2-RC2(CBC)2C2R0)
(L–L = dppm, R = H, R0 = SiMe3, 2, R, R0 = H, 3; L–
L = dmpm, R, R0 = SiMe3, 6) together with that of the
individual components, [Co2(CO)4(l-dmpm)](l-g2-Me3-
SiC2CBCR) (R = SiMe3, 4, R = H, 5). The results are
*
Corresponding author. Tel.: +34 91 4974838; fax: +34 91 4974833.
E-mail address: rosam.medina@uam.es (R.M. Medina).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.065

M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
139
compared with those obtained, in our laboratory, for
alkynylthiophene and alkynylbenzene analogous com-
plexes [1h,1j,6]. The X-ray structures of 2 and 3 are given.
(22 mL) was added 1.0 M Bu4NF in THF (70 lL,
0.07 mmol). The mixture was stirred for 24 h and
was monitored by TLC (SiO2). The solution was
concentrated and chromatographed by TLC (SiO2)
using hexane/acetone (2:1) as eluent. The TLC
gave a brown band and two violet bands. The brown
band, isolated from the top of the plate, yielded the
starting [Co2(CO)4(l-dppm)]2(l-g2-Me3SiC2(CBC)2C2-
SiMe3) compound. The first violet band gave the
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. Hexane, tetrahydrofuran (THF)
were dried and distilled over sodium in the presence of
benzophenone under an Ar atmosphere. Also under
Ar, CH2Cl2 and acetone were dried and distilled
over CaH2 and CaCl2, respectively. Methanol (Aldrich)
product 2 as a dark-violet solid (0.028 g, 27%
yield). The second violet band was identified as [Co2-
(CO)4(l-dppm)]2(l-g2-HC2(CBC)2C2H) (0.02 g, 20%
yield).
(2) FT-IR (CHCl3, cmꢀ1): mBCꢀH 3306 (w); mCBC 2068
(vw); mCO 2029 (s), 2007 (vs), 1979 (s). 1H NMR
(300 MHz, CDCl3, ppm): d 7.46–7.08 (m, 40H, Ph);
6.14 (s, br, 1H, BC–H); 4.08–3.95 (m, B of ABX2, 1H,
P–CH2–P (SiMe3)); 3.68–3.52 (m, B of ABX2, 1H,
P–CH2–P (BC–H)); 3.48–3.38 (m, A of ABX2, 1H, P–
CH2–P (BC–H)); 3.37–3.23 (m, A of ABX2, 1H, P–
CH2–P (SiMe3)); 0.438 (s, 9H, –SiMe3). 31P NMR
(121 MHz, CDCl3, ppm): d 40.55 (s, 2P, BC–H); 37.12
(s, 2PBC–SiMe3). 13C NMR (125 MHz, CDCl3, ppm):
d 206.3 (m, CO), 203.8 (m, CO), 202.8 (m, CO), 200.9
(m, CO); 136.4 (t, JCP = 23.1 Hz, i-Ph), 135.6 (t,
JCP = 21.4 Hz, i-Ph), 134.8 (t, JCP = 19.3 Hz, i-Ph),
134.3 (t, JCP = 18.1 Hz, i-Ph), 131.9 (t, JCP = 6.2 Hz,
o-Ph), 131.5 (t, JCP = 6.2 Hz, o-Ph), 130.8 (t,
JCP = 6.4 Hz, o-Ph), 130.5 (t, JCP = 6.2 Hz, o-Ph),
129.3 (s, p-Ph), 129.2 (s, p-Ph), 129.1 (s, p-Ph), 128.9
(s, p-Ph), 127.9 (m, m-Ph), 127.7 (t, JCP = 4.8 Hz,
m-Ph), 127.5 (t, JCP = 4.7 Hz, m-Ph); 90.5 (m,
C2), 86.5 (s br, C3), 82.4, 82.1 (s, C4, C5), 80.2 (m,
C8), 65.9 (m, C7); 39.4 (t, JCP = 19.0 Hz, P–CH2–
P), 37.6 (t, JCP = 20.3 Hz, P–CH2–P); 0.44 (s,
–SiMe3). MS (FAB+, m/z): 1342.1 (M+ ꢀ 2CO); 1286.1
(M+ ꢀ 4CO); 1230.1 (M+ ꢀ 6CO); 1202.1 (M+ ꢀ
7CO); 1174.1 (M+ ꢀ 8CO). Anal. Calc. for C69H54O8-
Co4P4Si: C, 59.2; H, 3.9. Found: C, 58.9; H,
4.1.%.
˚
was stored over molecular sieves (4 A) under Ar. All
solvents were bubbled with Ar for 1 h after distillation
and then stored under Ar, or degassed by means of at
least 3 freeze–pump–thaw cycles after distillation and
before use. Column chromatography was performed
by using Alfa neutral alumina at activity II and silica
gel 100 (Fluka). Preparative TLC was carried out
on glass plates (20 · 20 cm) coated with silica gel 60
(Merck). Co2(CO)8, 1,4-bis(trimethylsilyl)butadiyne
(MeSiCBCCBCSiMe3) (Fluka), Cu(OAc)2 (Prolabo),
1,2-bis(dimethylphosphino)methane (Strem) and 1,2-
bis- (diphenylphosphino)methane, pyridine, tetrabutyl-
amonium fluoride (Bu4NF) (Aldrich) were used as
received. Trimethylamine N-oxide (Me3NO) (Aldrich)
was sublimed prior to use and stored under Ar. The
compounds, Co2(CO)6(l-g2-Me3SiC2CBCSiMe3) [7],
Co2(CO)4(l-dppm)(l-g2-Me3SiC2CBCH) [5], [Co2
(CO)4(l-dppm)]2(l-g2-Me3SiC2(CBC)2C2SiMe3) (1) [5],
were prepared according to literature procedures. All re-
agents were used without further purification unless
otherwise noted. The 1H, 31P and 13C NMR spectra
were recorded on a Bruker AMX-300 or 500 instrument.
Chemical shifts were measured relative either to an
internal reference of tetramethylsilane or to residual
protons of the solvents. Infrared spectra were measured
on a Perkin–Elmer 1650 infrared spectrometer. Elemen-
tal analyses was performed by the Microanalytical Lab-
(3) FT-IR (CHCl3, cmꢀ1): mBCꢀH 3303 (w);
mCBC 2100 (w); mCO 2022 (s), 2002 (vs), 1972 (s), 1951
(sh, w). 1H NMR (300 MHz, CDCl3, ppm):
d
7.46–7.12 (m, 40H, Ph); 6.13 (s, br, 2H, BC–H); 3.66–
3.53 (m, B of ABX2, 2H, P–CH2–P); 3.44–3.32
(m, A of ABX2, 2H, P–CH2–P). 31P NMR (121 MHz,
CDCl3, ppm): d 40.34 (s, 2P). 13C (125 MHz, CDCl3,
ppm): d 206 (s, CO); 135.6 (t, i-Ph), 134.2 (t, i-Ph),
131.3 (t, JCP = 6.8 Hz, o-Ph), 130.2 (t, JCP = 6.4 Hz,
o-Ph), 128.8 (s, p-Ph), 128.6 (s, p-Ph), 127.5 (t,
JCP = 4.2 Hz, m-Ph), 127.2 (t, JCP = 4.1 Hz, m-Ph);
86.8 (s, C3, C6), 81.8 (s, C4, C5); 37.5 (t, JCP = 20.1 Hz,
P–CH2–P). MS (Maldy, ditranol) m/z: 1326.9
(M + 1 + H); 1101.9 (M ꢀ 8CO). Anal. Calc. for
C66H46O8Co4P4: C, 59.8; H, 3.5. Found: C, 59.5; H,
3.6%.
´
oratory of the University Autonoma of Madrid on a
Perkin–Elmer 240 B microanalyzer. Mas spectra were
measured on a VG-Autospec mass spectrometer for
FAB or Maldy by the Mass Laboratory of the Univer-
´
sity Autonoma of Madrid.
2.2. Synthesis of [Co2(CO)4(l-dppm)]2-
(l-g2-Me3SiC2(CBC)2C2H) (2) and
[Co2(CO)4(l-dppm)]2(l-g2-HC2(CBC)2C2H) (3)
To [Co2(CO)4(l-dppm)]2(l-g2-Me3SiC2(CBC)2C2-
SiMe3) (0.11 g, 0.07 mmol) in THF/MeOH (10:1)

140
M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
2.3. Synthesis of [Co2(CO)4(l-dppm)]2-
(l-g2-HC2(CBC)2C2H) (3)
1H NMR (300 MHz, CDCl3, ppm): d 3.45 (s, 1 H,
BC–H); 2.70 (dt, JHH = 11.8 Hz, JPH = 11.7 Hz, 1H,
P–CH2–P), 2.05 (dt, JHH = 11.8 Hz, JPH = 10.4 Hz,
1H, P–CH2–P); 1.56 (s br, 6H, –PMe), 1.46 (s br, 6H,
–PMe); 0.27 (s, 9H, Me3SiC–). 31P NMR (121 MHz,
CDCl3, ppm): d 13.6 (s br, 2P). 13C (125 MHz, CD2
Cl2, ppm): d 206.9 (m, CO), 202.7 (m, CO); 86.4 (t,
C3), 84.2 (s br, C1), 81.5 (s, C4), 76.9 (s br, C2); 40.7
(t, JCP = 22.0 Hz, P–CH2–P); 17.6 (t, JCP = 17.1 Hz,
Me), 11.7 (t, JCP = 22.0 Hz, Me); 0.2 (s, Me3SiC–).
MS (FAB+, m/z): 487.8 (M+); 459.8 (M+ ꢀ CO); 431.8
(M+ ꢀ 2CO); 403.8 (M+ ꢀ 3CO); 375.8 (M+ ꢀ 4CO).
Anal. Calc. for C16H24O4Co2P2Si: C, 39.4; H, 4.9.
Found: C, 39.1; H, 5.2%.
To [Co2(CO)4(l-dppm)]2(l-g2-Me3SiC2(CBC)2C2-
SiMe3) (0.21 g, 0.14 mmol) in wet THF (30 mL) was
added 1.0 M Bu4NF in THF (0.29 mL, 0.29 mmol).
The solution was stirred for 24 h and was monitored
by TLC (SiO2). The solvent was evaporated under vac-
uum and the residue was dissolved in CH2Cl2 and puri-
fied by TLC (SiO2) using hexane/CH2Cl2 (1:4) as eluent.
The product 3 was obtained as a violet solid (0.18 g, 97%
yield).
2.4. Synthesis of Co2(CO)4(l-dmpm)-
(l-g2-Me3SiC2CBCSiMe3) (4)
2.6. Synthesis of [Co2(CO)4(l-dmpm)]2-
(l-g2-Me3SiC2(CBC)2C2SiMe3) (6)
A mixture of Co2(CO)6(l-g2-Me3SiC2CBCSiMe3)
(2.00 g, 4.16 mmol) and 1,2 bis(dimethylphosph-
ino)methane (0.57 g, 4.16 mmol) in hexane (100 mL)
was prepared. Immediately Me3NO (0.92 g, 8.32 mmol)
was added and the reaction mixture was stirred and
heated at 40 ꢁC until the reaction was seen to be com-
pleted by IR spectroscopy and no starting material re-
mained (6 h). After removal of the solvent under
vacuum, the residue was dissolved with CH2Cl2 and
purified by column chromatography on SiO2 packed in
hexane. Hexane/CH2Cl2 (1:1) eluted a red band which
yielded 4 as a red solid (2.21 g, 95% yield). FT-IR (hex-
ane, cmꢀ1): mCBC 2108 (vw); mCO 2024 (s), 1998 (vs), 1972
(s), 1956 (m). 1H NMR (300 MHz, CDCl3, ppm): d 2.79
(dt, JHH = 13.5 Hz, JPH = 11.1 Hz, 1H, P–CH2–P), 2.03
(dt, JHH = 13.5 Hz, JPH = 10.1 Hz, 1H, P–CH2–P); 1.54
(t, JPH = 3.3 Hz, 6H, –P–Me), 1.46 (t, JPH = 3.8 Hz, 6H,
–P–Me); 0.27 (s, 9H, Me3SiC–); 0.16 (s, 9H, BCSiMe3).
To Co2(CO)4(l-dmpm)(l-g2-Me3SiC2CBCH) (0.10 g,
0.2 mmol) in dry pyridine (10 mL) anhydrous
Cu(OAc)2 (0.36 g, 2.0 mmol) was added and the mix-
ture reaction stirred at room temperature for 2 h and
monitored by TLC (SiO2). The solvent was evaporated,
the solid extracted with CH2Cl2, and the resulting solu-
tion concentrated and chromatographed by TLC
(SiO2) using hexane/CH2Cl2 (1:1) as eluent. A brown-
reddish band gave the product 6 (0.12 g, 60% yield).
FT-IR (hexane, cmꢀ1): mCBC 2102 (vw); mCO 2014 (s),
1995 (vs), 1963 (s). 1H NMR (500 MHz, CDCl3,
ppm): d 2.72 (dt, JHH = 13.6 Hz, JPH = 10.8 Hz, 1 H,
P–CH2–P), 2.09 (dt, JHH = 13.7 Hz, JPH = 10.2 Hz,
1H, P–CH2–P); 1.56 (t, JPH = 3.3 Hz, 6H, –PMe),
1.48 (t, JPH = 3.8 Hz, 6H, –PMe); 0.28 (s, 18 H, 2 Me3-
SiC–). 31P NMR (121 MHz, CDCl3, ppm): d 13.2 (s br,
4P). 13C (125 MHz, CD Cl3, ppm): d 206.4 (m, CO),
202.4 (m,CO); 87.3 (t, JCP = 5.0 Hz, C3, C6), 86.6
(t, JCP = 11.5 Hz, C1, C8), 81.5 (s, C4, C5), 76.4 (m,
C2, C7); 41.1 (t, JCP = 21.7 Hz, P–CH2–P); 20.8
(t, JCP = 11.6 Hz, Me), 18.1 (t, JCP = 16.9 Hz, Me);
0.6 (s, Me3SiC–). MS (FAB+, m/z): 974.1 (M+);
918.1 (M+ ꢀ 2CO); 890.1 (M+ ꢀ 3CO); 862.1
(M+ ꢀ 4CO); 834.1 (M+ ꢀ 5CO); 806.1 (M+ ꢀ 6CO);
778.1 (M+ ꢀ 7CO); 750.1 (M+ ꢀ 8CO). Anal. Calc.
for C32H46O8Co4P4Si2: C, 39.4; H, 4.7. Found: C,
39.1; H, 4.9%.
31P NMR (121 MHz, CDCl3, ppm): d 13.8 (s br, 2P). 13
C
(125 MHz, CDCl3, ppm): d 206.7 (m, CO), 202.6 (m,
CO); 108.3 (s, C3), 99.9 (s, C4), 84.4 (t, C1); 40.2 (t,
JCP = 21.7 Hz, P–CH2–P); 20.9 (t, JCP = 11.0 Hz,
–Me), 17.7 (t, JCP = 16.8 Hz, –Me); 1.0 (s, Me3SiC–);
0.2 (s, BCSiMe3). MS (FAB+, m/z): 559.8 (M+); 531.8
(M+ ꢀ CO); 503.8 (M+ ꢀ 2CO); 575.8 (M+ ꢀ 3CO);
547.8 (M+ ꢀ 4CO). Anal. Calc. for C19H32O4Co2P2Si2:
C, 40.7; H, 5.7. Found: C, 40.5; H, 6.0%.
2.5. Synthesis of Co2(CO)4(l-dmpm)-
(l-g2-Me3SiC2CBCH) (5)
2.7. Synthesis of [Co2(CO)4(l-dmpm)]2(l-g2-HC2-
(CBC)2C2H) (7)
To Co2(CO)4(l-dmpm) (l-g2-Me3SiC2CBCSiMe3)
(1.01 g, 1.80 mmol) in THF/MeOH (10:1) (100 mL)
was added 1.0 M Bu4NF in THF (3.6 mL, 3.6 mmol).
The mixture was stirred at room temperature for 24 h
and then poured into hexane (160 mL) and saturated
aqueous NaCl solution. The organic phase was dried
over MgSO4 and evaporation afforded 5 as a red solid
(0.79 g, 90% yield). FT-IR (hexane, cmꢀ1): mBCꢀH 3302
(w); mCBC 2068 (vw); mCO 2021 (s), 1993 (vs), 1964 (s).
To [Co2(CO)4(l-dmpm)]2(l-g2-Me3SiC2(CBC)2C2-
SiMe3) (0.032 g, 0.033 mmol) in THF/MeOH (10:1)
(22 mL) was added 1.0 M Bu4NF in THF (0.066 mL,
0.066 mmol). The mixture was stirred for 1.30 h and
was monitored by TLC (SiO2). The solution was con-
centrated and chromatographed by TLC (SiO2) using
hexane/CH2Cl2 (2:1) as eluent. A violet band gave the

M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
141
compound 7 as a violet solid (0.011 g, 40% yield). FT-IR
(CH2Cl2, cmꢀ1): mB CꢀH 3302 (w); mCBC 2100 (vw); mCO
2015 (s), 1996 (vs), 1970 (s). 1H NMR (500 MHz,
CDCl3, ppm): d 5.80 (s br, 2H, BC–H); 2.52 (dt,
JHH = 12.4 Hz, JPH = 10.7 Hz, 1H, P–CH2–P), 2.33
(dt, JHH = 12.3 Hz, JPH = 11.2 Hz, 1H, P–CH2–P);
1.62 (t, JPH = 3.4 Hz, 6H, –PMe), 1.55 (t, JPH = 3.2 Hz,
6H, –PMe). 31P NMR (121 MHz, CDCl3, ppm): d 16.1
(s br, 4P). 13C (125 MHz, CDCl3, ppm): d 206.8 (s,
CO); 88.8 (s, C3, C6), 82.2 (s, C4, C5), 78.3 (s br, C1,
C8 or C2, C7); 40.4 (t, JCP = 21.5 Hz, P–CH2–P); 20.4
(t, JCP = 12.4 Hz, Me), 18.6 (t, JCP = 16.4 Hz, Me).
MS (FAB+, m/z): 828.1 (M+); 772.1 (M+ ꢀ 2CO);
744.1 (M+ ꢀ 3CO); 716.1 (M+ ꢀ 4CO); 688.1
(M+ ꢀ 5CO); 632.1 (M+ ꢀ 7CO); 604.1 (M+ ꢀ 8CO).
Anal. Calc. for C26H30O8Co4P4: C, 37.7; H, 3.6. Found:
C, 37.4; H, 3.8%.
approximate dimensions 0.14 · 0.10 · 0.04 mm for 2
and 0.20 · 0.10 · 0.02 mm for 3 with prismatic shape
was mounted on a glass fiber and transferred to a Bru-
ker SMART 6K CCD area-detector three-circle diffrac-
tometer with a MAC Science Co., Ltd. Rotating Anode
˚
(Cu Ka radiation, k = 1.54178 A) generator equipped
with Goebel mirrors at settings of 50 kV and 110 mA
[8]. X-ray data were collected at 296 K for 2 and
295 K for 3, with a combination of six runs at different
u and 2h angles, 3600 frames. The data were collected
using 0.3ꢁ wide x scans (15 s/frame at 2h = 40ꢁ and
30 s/frame at 2h = 100ꢁ), crystal-to-detector distance of
4.0 cm.
The raw intensity data frames were integrated with
the SAINT program [9], which also applied corrections
for Lorentz and polarization effects.
The substantial redundancy in data allows empirical
absorption corrections (SADABS) [10] to be applied using
multiple measurements of symmetry-equivalent reflec-
tions (ratio of minimum to maximum apparent trans-
mission: 0.590663 for 2 and 0.608741 for 3). A total
number of 21,992 reflections for 2 and 9655 for 3 were
collected and 11,196 independent reflections for 2 and
5006 for 3 remained after merging R(int) = 0.0559,
2.8. X-ray crystallography
Red crystals of 2 and 3 were obtained by recrystalli-
zation of the complexes from CH2Cl2 to hexane mix-
tures. A summary of selected crystallographic data for
2 and 3 is given in Table 1. A red single crystal of
Table 1
Crystal data and structure refinement for 2 and 3
2
3
Empirical formula
Formula weight
Temperature (K)
C
70H56Cl2Co4O8P4Si
C66H46Co4O8P4
1326.63
295(2)
1483.74
296(2)
1.54178
˚
Wavelength (A)
1.54178
Crystal system
Space group
Triclinic
Triclinic
ꢀ
ꢀ
P1
P1
Unit cell dimensions
˚
a (A)
12.7914(4)
15.4032(5)
18.5139(6)
89.254(2)
81.327(2)
83.438(2)
3582.4(2)
2
10.5807(2)
12.9680(2)
13.0490(2)
101.5080(10)
107.5010(10)
110.3340(10)
1505.81(4)
1
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Density (calculated) (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
1.376
9.230
1512
1.463
9.929
674
)
Crystal size
Theta range for data collection (ꢁ)
0.14 · 0.10 · 0.04
2.41–65.14
0.20 · 0.10 · 0.02
3.78–70.45
Index ranges
ꢀ13 < = h < = 15, ꢀ18 < = k < = 17,
ꢀ11 < = h < = 10, ꢀ13 < = k < = 14,
ꢀ14 < = l < = 15
9655
ꢀ21 < = l < = 21
Reflections collected
21,992
Independent reflections
Completeness to theta = 65.14ꢁ
Absorption correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
11,196 [Rint = 0.0559]
91.6%
YES, SADABS v. 2.03
Full-matrix least-squares on F2
11,196/0/805
5006 [Rint = 0.0397]
86.9%
YES, SADABS v. 2.03
Full-matrix least-squares on F2
5006/0/462
0.963
1.030
R1 = 0.0633, wR2 = 0.1413
R1 = 0.1553, wR2 = 0.1790
0.333 and ꢀ0.244
R1 = 0.0354, wR2 = 0.0919
R1 = 0.0417, wR2 = 0.0966
0.434 and ꢀ0.211
ꢀ3
˚
Largest different peak and hole (e A
)

142
M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
Table 2
R(sigma) = 0.1028 for 2 and R(int) = 0.0397, R(sig-
ma) = 0.0508 for 3. The unit cell parameters were ob-
tained by full-matrix least-squares refinements of 2501
and 3931 reflections for 2 and 3, respectively.
˚
Bond lengths (A) and angles (ꢁ) for 2
˚
Bond lengths (A)
C(1)–C(2)
1.349(9)
1.837(7)
1.966(7)
1.985(7)
1.387(9)
1.958(6)
1.966(7)
1.210(9)
1.345(9)
1.207(9)
1.405(9)
1.344(9)
1.954(6)
1.965(7)
1.944(7)
1.952(7)
1.825(6)
1.828(6)
1.817(7)
1.840(7)
1.776(8)
1.763(9)
1.780(9)
1.796(9)
1.796(9)
1.787(10)
1.773(8)
1.797(9)
1.822(7)
1.820(7)
1.814(7)
1.825(7)
1.823(8)
1.822(8)
1.824(8)
1.830(7)
2.232(2)
2.4814(15)
2.238(2)
2.222(2)
2.4885(16)
2.214(2)
C(1)–Si(1)
C(1)–Co(2)
C(1)–Co(1)
C(2)–C(3)
C(2)–Co(1)
C(2)–Co(2)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(7)–Co(3)
C(7)–Co(4)
C(8)–Co(4)
C(8)–Co(3)
C(9)–P(2)
The software package SHELXTL version 6.10 [11] was
used for space group determination, structure solution
and refinement. The structure was solved by direct meth-
ods (SHELXS-97) [12], completed with difference Fourier
syntheses, and refined with full-matrix least-squares
2
using SHELXL-97 [13] minimizing x ðF o2 ꢀ F c2Þ . Weighted
R factors (Rw) and all goodness of fit S are based on F2;
conventional R factors (R) are based on F. All non-
hydrogen atoms were refined with anisotropic displace-
ment parameters. All scattering factors and anomalous
dispersions factors are contained in the SHELXTL 6.10 pro-
gram library. The hydrogen atom positions for the com-
plex 2 were calculated geometrically and were allowed to
ride on their parent carbon atoms with fixed isotropic U.
For the complex 3 the hydrogens atoms were localized by
its electronic densities and isotropically refined.
C(9)–P(1)
C(10)–P(3)
C(10)–P(4)
C(11)–Co(1)
C(12)–Co(1)
C(13)–Co(2)
C(14)–Co(2)
C(15)–Co(3)
C(16)–Co(3)
C(17)–Co(4)
C(18)–Co(4)
C(19)–P(1)
C(25)–P(1)
C(31)–P(2)
C(37)–P(2)
C(43)–P(3)
C(49)–P(3)
C(55)–P(4)
C(61)–P(4)
Co(1)–P(1)
Co(1)–Co(2)
Co(2)–P(2)
Co(3)–P(3)
Co(3)–Co(4)
Co(4)–P(4)
Final positional parameters, anisotropic thermal
parameters, hydrogen atom parameters and structure
amplitudes are available as supplementary material.
Tables 2 and 3 contain selected bond distances and
angles for 2 and 3, respectively. Figs. 1 and 2 present a
molecular diagram of 2 and 3, respectively.
2.9. Electrochemical experiments
Electrochemical measurements were carried out with
a computer driven AUTOLAB PGSTAT30 electro-
chemistry system in a three electrode cell under N2
atmosphere in anhydrous deoxygenated solvents (THF
and CH2Cl2) containing 0.2 M tetrabutylammonium
hexafluorophosphate (TBAPF6) as supporting electro-
lyte. Cyclic and square-wave voltammetry (CV and
SWV, respectively) were made. Polycrystalline Pt
(0.05 cm2) and glassy carbon were used as working elec-
trodes; the counter electrode was a Pt gauze and the ref-
erence electrode was a silver wire quasi-reference
electrode. Decamethylferrocene (Fc*) was used as an
internal standard, and all potential values in this work
are referred to the Fc*+/Fc* couple. Under the actual
experimental conditions, E1/2 of the ferrocene couple
(Fc+/Fc) was +0.44 V vs. Fc*+/Fc* in THF solution
and +0.55 V vs. Fc*+/Fc* in CH2Cl2 solution.
Bond angles (ꢁ)
C(2)–C(1)–Si(1)
C(2)–C(1)–Co(2)
Si(1)–C(1)–Co(2)
C(2)–C(1)–Co(1)
Si(1)–C(1)–Co(1)
Co(2)–C(1)–Co(1)
C(1)–C(2)–C(3)
C(1)–C(2)–Co(1)
C(3)–C(2)–Co(1)
C(1)–C(2)–Co(2)
C(3)–C(2)–Co(2)
Co(1)–C(2)–Co(2)
C(4)–C(3)–C(2)
C(3)–C(4)–C(5)
C(6)–C(5)–C(4)
C(5)–C(6)–C(7)
C(8)–C(7)–C(6)
C(8)–C(7)–Co(3)
C(6)–C(7)–Co(3)
C(8)–C(7)–Co(4)
139.5(5)
69.9(4)
136.4(4)
68.9(4)
135.4(4)
77.8(3)
143.2(7)
71.1(4)
133.8(5)
70.0(4)
132.8(5)
78.5(2)
3. Results and discussion
173.0(8)
178.7(8)
178.4(8)
171.2(8)
145.3(7)
69.8(4)
3.1. Synthesis and spectroscopic characterization
The complexes [Co2(CO)4(l-dppm)]2(l-g2-Me3SiC2-
(CBC)2C2H) (2) and [Co2(CO)4(l-dppm)]2(l-g2-HC2-
(CBC)2C2H) (3) were synthesized from 1, following
one of the standard methods of proteodesilylation.
134.2(5)
69.1(4)

M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
143
Table 2 (continued)
Table 3
˚
Bond lengths (A) and angles (ꢁ) for 3
Bond angles (ꢁ)
C(6)–C(7)–Co(4)
Co(3)–C(7)–Co(4)
C(7)–C(8)–Co(4)
C(7)–C(8)–Co(3)
Co(4)–C(8)–Co(3)
P(2)–C(9)–P(1)
P(3)–C(10)–P(4)
C(2)–Co(1)–C(1)
C(2)–Co(1)–Co(2)
C(1)–Co(1)–Co(2)
P(1)–Co(1)–Co(2)
C(2)–Co(2)–C(1)
C(2)–Co(2)–Co(1)
C(1)–Co(2)–Co(1)
P(2)–Co(2)–Co(1)
C(8)–Co(3)–C(7)
C(8)–Co(3)–Co(4)
C(7)–Co(3)–Co(4)
P(3)–Co(3)–Co(4)
C(8)–Co(4)–C(7)
C(8)–Co(4)–Co(3)
C(7)–Co(4)–Co(3)
P(4)–Co(4)–Co(3)
˚
131.5(5)
78.8(2)
70.7(4)
70.0(4)
79.4(3)
110.9(3)
110.9(3)
40.0(3)
50.9(2)
50.8(2)
96.79(7)
40.1(3)
50.63(19)
51.4(2)
96.72(7)
40.2(3)
50.2(2)
50.76(19)
97.07(7)
40.2(3)
50.4(2)
50.39(19)
96.47(7)
Bond lengths (A)
Co(1)–C(8)
Co(1)–C(7)
Co(1)–C(1)
Co(1)–C(2)
Co(1)–P(1)
Co(1)–Co(2)
Co(2)–C(5)
Co(2)–C(6)
Co(2)–C(1)
Co(2)–C(2)
Co(2)–P(2)
P(1)–C(16)
P(1)–C(10)
P(1)–C(9)
1.784(3)
1.792(3)
1.950(3)
1.975(2)
2.2281(7)
2.4742(6)
1.773(3)
1.786(3)
1.942(3)
1.970(2)
2.2352(7)
1.828(3)
1.832(3)
1.842(3)
1.825(3)
1.835(3)
1.837(3)
1.354(4)
1.380(3)
1.217(4)
1.348(5)
P(2)–C(22)
P(2)–C(28)
P(2)–C(9)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(4)#1
Bond angles (ꢁ)
C(1)–Co(1)–C(2)
C(1)–Co(1)–Co(2)
C(2)–Co(1)–Co(2)
P(1)–Co(1)–Co(2)
C(1)–Co(2)–C(2)
C(1)–Co(2)–Co(1)
C(2)–Co(2)–Co(1)
P(2)–Co(2)–Co(1)
C(2)–C(1)–Co(2)
C(2)–C(1)–Co(1)
Co(2)–C(1)–Co(1)
C(1)–C(2)–C(3)
C(1)–C(2)–Co(2)
C(3)–C(2)–Co(2)
C(1)–C(2)–Co(1)
C(3)–C(2)–Co(1)
Co(2)–C(2)–Co(1)
C(4)–C(3)–C(2)
C(3)–C(4)–C(4)#1
P(2)–C(9)–P(1)
40.37(10)
50.37(8)
51.06(7)
95.16(2)
40.51(10)
50.67(8)
51.24(7)
98.86(2)
70.86(16)
70.80(16)
78.96(10)
146.2(3)
68.63(15)
137.1(2)
68.83(15)
129.05(19)
77.70(9)
170.7(3)
179.2(4)
110.33(13)
The reaction with NBu4F in THF/MeOH (10:1) at room
temperature leads to the monoprotonate and diproto-
nate derivatives, 2 and 3, respectively. When wet THF
is used only the compound 3 is obtained. The IR spectra
of both compounds show two weak bands around 3300
and 2100 cmꢀ1 owing to mBCꢀH and mCBC, respectively.
The mCO of carbonyl ligands appear in the range 2030–
1
1970 cmꢀ1. In the H NMR spectrum of 2 two singlets
at d = 0.44 and 6.14 ppm owing to the trimethylsilyl
group and acetylenic hydrogen respectively are ob-
served. In this complex the two Co2(dppm) units are
inequivalent and the CH2 of the phosphine ligands give
rise to four multiplets, a double number than in 3 where
the two Co2(dppm) units are equivalent. The two
acetylenic hydrogens in 3 give a singlet signal at
d = 6.13 ppm. In the 13C NMR spectrum of 2 six reso-
nances are observed in the 90–66 ppm range, owing to
the carbon chain atoms, and the dppm ligands give four
triplet signals for the ipso, ortho and meta carbon atoms
and four singlets for the carbon atoms in para position.
The CH2 of the phosphine ligands give rise to two trip-
lets at 39.4 and 37.6 ppm, and a singlet at 0.44 ppm is
assigned to SiMe3 group. The higher symmetry of com-
plex 3 is manifested again in the 13C NMR spectrum,
two resonances are observed for the chain carbon atoms
in the 86–82 ppm range and the dppm ligands give two
triplet signals for the ipso, ortho and meta carbon atoms
and two singlets for those in para position. The CH2 is
located at 37.5 ppm as a triplet. In the 31P spectra the
dppm ligands of 3 give rise to a singlet resonance at
d = 40.34 ppm and the unequivalent ligands in 2 give
two singlets at d = 40.55 and 37.12 ppm. In addition,
the molecular structure of both compounds were deter-
mined by single-crystal X-ray diffraction (Figs. 1 and 2).
Ph
CH 2
CH 2
Ph
P
P
Ph
Ph
Ph
Ph
Ph
P
P
Ph
Co (CO)2
Co (CO)2
Co (CO)2
Co(CO)2
R'
R
R = R ' = S iMe3
R = S iMe3; R' = H (2)
R = R' =H
(1)
(3)
In order to study the effect of a more basic and less
bulky phosphine ligand, in the electrochemical response
of this kind of complexes, we prepared the compound 4,

144
M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
Fig. 1. ORTEP diagram of 2.
Fig. 2. ORTEP diagram of 3.
[Co2(CO)4(l-dmpm)](l-g2-Me3SiC2CBCSiMe3)],
by
(5), which by oxidative coupling under Eglington-Glaser
conditions [14] leads to complex [Co2(CO)4(l-
dmpm)]2(l-g2-SiMe3C2(CBC)2C2SiMe3) (6). The desily-
lation of 6 with NBu4F in THF/MeOH (10:1) at room
temperature leads to compound [Co2(CO)4(l-dmpm)]2-
(l-g2-HC2(CBC)2C2H) (7) (see Scheme 1).
substitution reaction of carbonyl ligands on Co2-
(CO)6(l-g2-Me3SiC2CBCSiMe3) by dmpm in presence
of Me3NO. The reaction of 4 with NBu4F in THF/
MeOH (10:1) at room temperature leads to the mono-
protonate [Co2(CO)4(l-dmpm)](l-g2-Me3SiC2CBCH)

M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
145
NBu 4
F
H
Si
Me3
SiMe 3
Me3Si
THF/ MeOH
Me
Me
Me
Me
P
P
(5 )
(4 )
P
CH2
P
CH2
Me
Me
Me
Me
Cu(OAc)2
Py
CH2
CH2
P
Me
Me
Me
Me
Me
Me
P
P
Me
Me
P
Co(CO)2
Co(CO)2
Co(CO)2
Co(CO)2
Me3Si
SiMe3
(6 )
NBu 4
F
THF/ MeOH
CH2
CH2
P
Me
Me
Me
Me
Me
Me
P
P
Me
Me
P
Co(CO)2
Co(CO)2
Co(CO)2
Co(CO)2
H
H
(7 )
Scheme 1.
The four compounds have been characterized by IR,
1H, 13C and 31P NMR and mass spectroscopy. The IR
and NMR spectra for 4 and 5 show the same pattern than
those for the analogous dppm complexes synthesized by
Diederich [5], with the expected signals shifts owing to
thepresenceofthemorebasicdmpmligand(seeSection2).
The IR spectrum of 6 shows three bands, in the 1960–
2015 range, due to the terminal carbonyl ligands which
are shifted to lower frequencies compared with those
owing to the acetylenic protons is shown. The rest of
the spectral data are similar to those for compound 6
(see Section 2).
The electrochemical study of 2, 3, 4, 5 and 6 is de-
scribed below. That of 7 was not completed due to insta-
bility of intermediate species.
3.2. Description of the crystal and molecular structures of
2 and 3
1
for compound 1 [5]. The H NMR spectrum shows a
singlet at 0.28 owing to the SiMe3 groups. The CH2 pro-
tons of the dmpm ligands give rise to two double triplets
at 2.72 and 2.09 ppm and the methyl groups are ob-
served as triplets at 1.56 and 1.48 ppm. In the 13C
NMR spectrum the –C8– chain gives four resonances
in the 87.3–76.4 ppm range which are assigned on basis
of its multiplicity and intensity together with HMQC
and HMBC experiments. The CH2 of the phosphine li-
gands give a triplet signal at 41.4 and the methyl groups
are observed as two triplets at 20.8 and 18.1. The equiv-
alent SiMe3 groups give a singlet at 0.6 ppm.
The compounds 2 and 3 crystallize (2 with one
CH2Cl2 molecule) in the triclinic crystal system, space
ꢀ
group P1. The molecular structures consist of an octa-
tetrayne chain capped by a H atom and a SiMe3 group
(2) or two H toms (3). The outermost acetylenic moieties
are coordinated to Co2(CO)4dppm fragments in each
case, giving rise to two opposite Co2C2 tetrahedrons
with respect to the carbon chain. In the Co2C2 tetrahe-
drons, both Co centres are connected to both carbon
atoms. A phosphorus from the dppm ligand and two
carbonyl ligands complete the coordination geometry
around each Co centre. Treating the plane defined by
the two cobalt atoms and the terminal carbon as the
In the 1H NMR of 7 this singlet, obviously, is not ob-
served but instead a broad singlet signal at 5.80 ppm,

146
M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
base of the Co2C2 tetrahedron, the bidentate dppm li-
gand occupies the two available pseudoequatorial posi-
tions. The geometric parameters for 2 and 3 have been
summarized in Table 1 and Figs. 1 and 2 present a view
of the molecules with the atom-labelling scheme.
substituted Co2C2 redox centres [1h,1i,4a,4d,16b,19].
In 4 and 5, the cluster bound SiMe3 group also contrib-
utes to this reversible chemistry [20]. However, to
achieve complete chemical reversibility of the reduction
processes in CH2Cl2, temperatures of ca.ꢀ30 ꢁC at
v = 0.1 V sꢀ1, or sweep rates as fast as 1 V sꢀ1 at 25 ꢁC
have to be employed (see Fig. 3). This indicates that
both anions 4ꢀ and 5ꢀ are involved in slow decomposi-
tion reactions in CH2Cl2. When the solvent employed is
THF, the reduction process of 4 is chemically reversible
at room temperature and 0.1 V sꢀ1, showing the influ-
ence of the solvent on the stability of the anions formed.
Table 4 gathers E1/2 values for the oxidation and
reduction of 4 and 5 together with those of closely re-
lated compounds measured in our laboratory under
the same experimental conditions [1i]. It can be observed
that both E1/2(ox) and E1/2(red) change with the basicity
of the phosphine employed (dmpm > dppa > dppm).
Thus, for dmpm complexes 4 and 5, the electron-donat-
ing character of the phosphine makes oxidation easier
(less positive E1/2) and reduction more difficult (more
negative E1/2). As observed, there is no significant influ-
ence on the E1/2 values due to the substitution of a ter-
minal SiMe3 group in 4 by –H in 5.
In compound 2 the uncoordinated carbon atoms
fragment is almost linear (angles C(6)–C(5)–C(4) and
C(3)–C(4)–C(5) 178.4(8) and 178.7(8), respectively)
and show the typical short, long, short, long bond length
alternation associated with a diyne moiety. The Co–Co
˚
distance 2.4814(5) and 2.4885(16) A are comparable to
those reported for the compounds [{SiMe3(Co2(CO)4-
(l-dppm))C2}2(l-g2-SiMe3CBC)(1,3,5-C6H3)] [1j], [{Si-
Me3(Co2(CO)4(l-dppm))C2}2(l-g2-HCBC)(1,3,5-C6H3)]
[1h], Co2(CO)4(l-dppa)(l-g2-Me3SiC2CBCSiMe3) [15]
(and references therein) and other similar clusters [16].
The C(1)–C(2) and C(7)–C(8) distances, 1.349(9) and
˚
1.344(9) A, respectively, are much longer than the C(3)–
C(4) and C(5)–C(6) triple bonds, 1.210(9) and
˚
1.207(9) A, respectively. This reflects the loss of triple
bond character as a result of coordination of the acety-
lenic moiety to the Co2 units. The C(2)–C(3) and C(7)–
˚
C(6) distances, 1.387(9) and 1.405(9) A, respectively, are
shorter than C–C single bonds as a result of conjuga-
tion. The change in hybridization at C(1)–C(2) and
C(7)–C(8) is also reflected in the angles C(1)–C(2)–
C(3), 143.2(7)ꢁ, C(2)–C(1)–Si(1), 139.5(5)ꢁ, C(8)–C(7)–
C(6), 145.3(7)ꢁ and C(7)–C(8)–H, 136.2(1)ꢁ. The Co–C
distances in the Co2C2 core of 2 range from 1.944(7)
Complexes 2, 3 and 6, with two equivalent dicobalt
redox centres, are closely related to 1, which was previ-
ously studied by our group under the same experimental
conditions [1h]. Table 5 summarizes the main electro-
chemical data concerning these compounds. When ade-
quate conditions are set, all these complexes show two
distinct oxidation and two distinct reduction processes,
˚
to 1.985(7) A and these distances do not show an asym-
metry pattern as observed in [{Co2(CO)6(l-g2-HC
BC)}2(C6H4)] [17].
instead of single bielectronic ones. The value of DE1/2
,
The average P–C distance of the bridging dppm li-
gands, 1.824(7) A, is normal [18]. All other bond and an-
gles are comparable to those reported for similar
structures [1h,1j,15,16].
the potential separation between the two waves, can be
related to the thermodynamic stability of the mixed-
valence species in each case, and depends on the extend
˚
Fig. 2 shows that complex 3 is derived from 2 by sub-
stitution of the Si(1)Me3 group by a hydrogen atom. In
general the structural parameters of the common frag-
ments are similar, within experimental error. However
in the Co2C2 core the Co–C distances range from
100
50
˚
1.942(3) to 1.975(2) A and these distances show an
asymmetric pattern as observed in [{Co2(CO)6(l-g2-
HCBC)}2(C6H4)] [17]. The Co2C2 tetrahedron is dis-
torted with the longer Co–C(alkyne) interactions being
associated with the alkylenic carbon coordinated to
the C(3) of the carbon chain.
0
–50
–100
3.3. Electrochemical studies
–2.0
–1.5
–1.0
–0.5
0.0
0.5
1.0
Complexes 4 and 5, with only one dicobalt unit, show
monoelectronic oxidation and reduction processes. Oxi-
dations to 4+ and 5+ are chemically and electrochemi-
cally reversible in THF and CH2Cl2 solution, even at
+
Potential (V vs Fc* /Fc*)
Fig. 3. Cyclic voltammograms for the reduction and oxidation of 5 in
CH2Cl2 containing 0.2 M TBAPF6. (—) at 25 ꢁC and 0.1 V/s on Pt.
(- -) at 25 ꢁC and 1 V/s on Pt. (ÆÆÆÆ) at ꢀ30 ꢁC and 0.1 V/s on C working
room temperature and sweep rates as slow as 20 mV sꢀ1
.
ÆÆ
This behaviour is characteristic of bidentate-phosphine
electrode.

M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
147
Table 4
Electrochemical data for 4–5a (and related compounds)
E1/2 (red)
E1/2 (ox)
[Co2(CO)4(l-dmpm)](l-g2-Me3SiC2CBCSiMe3) (4)
ꢀ1.68
0.66b
(0.64)
(ꢀ1.78)
[Co2(CO)4(l-dmpm)](l-g2-Me3SiC2CBCH) (5)
[Co2(CO)4(l-dppa)](l-g2-Me3SiC2CBCSiMe3)
[Co2(CO)4(l-dppm)](l-g2-Me3SiC2CBCSiMe3)
[Co2(CO)4(l-dppm)] (l-g2-Me3SiC2CBCH)
[Co2(CO)4(l-dppm)](l-g2-HC2CBCH)
ꢀ1.70
(ꢀ1.67)
(ꢀ1.70)
(ꢀ1.70)
ꢀ1.55
0.70b
(0.69)
(0.75)
(0.75)
0.81b
(ꢀ1.68)
(0.77b)
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
temperature has to be decreased to ꢀ30 ꢁC and sweep
Table 5
Electrochemical data for 1–3 and 6a(and related compounds)
rate increased to ca. 1 V sꢀ1 to obtain an almost com-
pletely reversible reduction behaviour in 6 (Fig. 4).
The effect is even greater on the oxidated species; com-
plete chemical reversibility of the two waves could not
be achieved for 6 even at ꢀ30 ꢁC and fast sweep rates.
The irreversible reduction of a decomposition product
of the oxidated species can be observed at 0.06 V
(v = 0.5 V sꢀ1) (Fig. 5).
E1/2 for reduction DE1/2 (red) E1/2 for oxidation DE1/2 (ox)
1
ꢀ1.5;ꢀ1.68
(ꢀ1.57;1.78)
0.18
(0.22)
0.71; 0.91b
(0.69; 0.83b)
0.20
(0.14)
2
3
6
ꢀ1.42b;ꢀ1.60b
ꢀ1.40b;ꢀ1.54b
ꢀ1.56b;ꢀ1.69b
0.18
0.14
0.13
0.71b; 0.95b
0.73b; 0.98b
0.62bl 0.77b
0.24
0.25
0.15
a
In V vs. Fc*+/Fc* in CH2Cl2 solution (values in italics are in THF
When the end-groups SiMe3 in 1 are changed for the
much smaller –H, in 2 and 3, the major influence ob-
served is on the chemical stability of the anions and cat-
ions formed (intermediate species included) in the
reduction and oxidation processes. The oxidation of 1
in CH2Cl2 yields a first completely reversible wave and
a second partially chemically reversible one (ipc/
ipa ꢁ 0.8) at 25 ꢁC and 0.1 V/s; the latter is completely
reversible at ꢀ15 ꢁC. Substitution of one end-group by
solution). Data are taken from CV and SWV at 25 ꢁC unless otherwise
stated.
b
From CV and SWV at ꢀ30 ꢁC.
of electronic interactions between the redox centres
through the bridging ligands [21]. As reflected in Table
5, DE1/2 for the whole family of compounds indicates
a moderate degree of electronic interactions; the substi-
tution of dppm for the more basic and less steric
demanding dmpm seems to decrease these interactions,
hindering efficient mixing between filled metal fragment
and polyyne-based orbitals. However, other factors like
coulombic repulsions or molecular rearrangements dur-
ing the oxidation or reduction processes also influence
DE1/2 [1c]. Values of DE1/2 for 1–3 and 6 are smaller
than those observed when a shorter bridging carbon
chain (4 C atoms) is employed [1h,4c], for which
DE1/2 @ 0.4 V, but comparable to values observed with
longer bridging ligands, like in alkynylthiophene [16b]
and alkynylbenzene [1h,1j] complexes.
The effect of the phosphine nature is more evident on
the potential values for reduction and oxidation. As al-
ready observed for complexes with only one dicobalt re-
dox centre, the more basic (i.e. electron-donating)
dmpm makes removal of electrons easier (E1/2 (ox) less
positive) and their addition more difficult (E1/2 (red)
more negative). Another consequence of the change in
phosphine substituent is the poorer stability of the oxi-
dated and reduced species. Thus, the voltammetric
reduction of 1 at room temperature showed two com-
pletely chemically reversible waves, whilst in the case
of 6 both waves are only partially chemically reversible;
5
0
–5
–10
–15
–20
–2.0
–1.5
Potential (V vs Fc* /Fc*)
–1.0
+
Fig. 4. Cyclic (—) and square-wave (- - -) voltammograms for the
reduction of 6 in CH2Cl2 containing 0.2 M TBAPF6 at ꢀ30 ꢁC. CV:
v = 0.5 V/s. SWV: scan increment = 2 mV; SW amplitude = 25 mV;
frequency = 30 Hz. C working electrode.

148
M.J. Macazaga et al. / Journal of Organometallic Chemistry 691 (2006) 138–149
Acknowledgements
15
10
5
´
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 Mono-
crystal Diffraction Laboratory SidI, Facultad de Cien-
´
cias, Universidad Autonoma de Madrid, Spain.
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