Synthesis, characterization, structures and comparative electrochemical study of 2,4-bis(trimethylsilylethynyl)thiophene coordinated carbonylcobalt units

Article abstract of DOI:10.1002/ejic.200700453

The reaction between 2,4-dibromothiophene and trimethylsilylacetylene (TMSA) in the presence of Pd(PPh₃)₄, CuI and triethylamine gave rise to the formation of 2,4-bis(trimethylsilylethynyl)thiophene (2,4T) and 4-bromo-2-(trimethylsil

Full text of DOI:10.1002/ejic.200700453

FULL PAPER
DOI: 10.1002/ejic.200700453
Synthesis, Characterization, Structures and Comparative Electrochemical
Study of 2,4-Bis(trimethylsilylethynyl)thiophene Coordinated Carbonylcobalt
Units
Avelina Arnanz,[a] Consuelo Moreno,*[a] María-Luisa Marcos,[b] Jaime González-Velasco,[b]
and Salomé Delgado[a]
Keywords: Thiophene / Carbonylcobalt complexes / Electrochemistry
The reaction between 2,4-dibromothiophene and trimethyl-
silylacetylene (TMSA) in the presence of Pd(PPh3)4, CuI and
triethylamine gave rise to the formation of 2,4-bis(trimethyl-
silylethynyl)thiophene (2,4T) and 4-bromo-2-(trimethylsilyl-
ethynyl)thiophene (2,4TЈ). Complexes 1, 2, 3 or 1Ј were ob-
tained by direct reaction between Co2(CO)8 and 2,4T or
2,4TЈ, respectively. (Diphenylphosphanyl)methane-substi-
kynes in 4, 5 and 6 occurred on treatment with KOH or tetra-
butylammonium fluoride to give 7, 8 and 9. Crystals of 2Ј
suitable for single-crystal X-ray diffraction were grown, and
the molecular structure of this compound is discussed. A
comparative electrochemical study of these complexes in re-
lation to analogous derivatives obtained from the organic li-
gand 2,5-bis(trimethylsilylethynyl)thiophene (2,5T) is re-
tuted alkyne carbonyl complexes 4, 5, 6 and 2Ј were pre- ported.
pared by substitution reaction of carbonyl ligands in the pres-
ence of Me3NO at the Co2(CO)6 units of 1, 2, 3 and 1Ј, respec-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
tively. Desilylation of the non-metallated and metallated al-
Germany, 2007)
Co2(CO)4(dppa) linked by 1,3,5-tris(trimethylsilylethynyl)-
benzene,[7a] 1,4-bis(trimethylsilyl)butadiyne[7b] and 2,5-bis-
(trimethylsilylethynyl)thiophene (2,5T)[7d] ligands, present
electronic communication between the metal centres. In or-
der to study the effect of the position of the alkynyl substit-
uents on the thiophene ring on the electronic communica-
tion between Co2(CO)6 and Co2(CO)4(dppm) moieties, we
report here the synthesis, characterization and the redox
properties of these units linked by the organic ligand 2,4-
bis(trimethylsilylethynyl)thiophene (2,4T).
Introduction
Recently, the search for molecular systems that are able
to transmit electronic effects between two or more remote
sites efficiently has become an area of increasing endeav-
our.[1] The interest in this kind of complexes is due, in part,
to the stabilising influence of the metal atom on reactive
unsaturated carbon chains and polycarbon ligands[1,2] and,
on the other hand, to their potential optoelectronic proper-
ties as non-linear optical and electroluminescent materials[3]
or in the construction of molecular-scale electronic de-
vices.[4,5] Thus, alkynyl or polyynediyl bridging ligands have
been shown to be particularly efficient in allowing the pass-
age of electronic effects between redox-active centres[6,7] and
therefore the electronic properties can be modified by
changing both, metal fragments and/or alkyne li-
gands.[4b,4d,7b,8] This electronic communication through
such potential molecular wires is often evaluated by exam-
ining the redox response of electroactive groups.[5i,5j,8a,9]
In recent studies we have shown that complexes, where
the redox centres are either Co2(CO)6, Co2(CO)4(dppm) or
Results and Discussion
Synthesis and Spectroscopic Characterization
A similar procedure described for 2,5-bis(trimethylsilyl-
ethynyl)thiophene (2,5T)[10] has been used in our laboratory
for the syntheses of the new ligand 2,4-bis(trimethylsilyl-
ethynyl)thiophene (2,4T). By the coupling reaction of 2,4-
dibromothiophene with excess of TMSA [in the presence of
Pd(PPh3)4, CuI and triethylamine] 2,4-bis(trimethylsilyl-
ethynyl)thiophene (2,4T) (33% yield) and 4-bromo-2-(tri-
methylsilylethynyl)thiophene (2,4TЈ) (35% yield) were ob-
tained, both as stable yellow oils. Large amounts of a cata-
lyst [5% mol Pd(PPh3)4 and 10% mol CuI] and higher tem-
perature and reaction time (75 °C for 20 d) were required,
causing a side reaction of the terminal acetylene, TMSA, to
[a] Departamento de Química Inorgánica, Universidad Autónoma
de Madrid,
28049 Madrid, Spain
Fax: +34-91-4974833
E-mail: mconsuelo.moreno@uam.es
[b] Departamento de Química, Universidad Autónoma de Madrid,
28049 Madrid, Spain
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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C. Moreno et al.
FULL PAPER
afford 1,4-bis(trimethylsilyl)-1,3-butadiyne. Such side reac- minal diyne compounds 7 and 8, respectively, isolated as
tions were often observed in reactions with less reactive aryl unstable red solids. Complex 9 was synthesized from 6 when
bromides.[11] This synthesis needed a longer reaction time stronger desilylation conditions were used (8 equiv. of
than that to obtain the analogous ligand 2,5T, because the Bu4NF in wet THF).
thiophene positions more suitable to an oxidative addition
All these compounds have been characterized by spectro-
1
1
are 2 and 5. Also, from 2,6-dibromopyridine,[12] under scopic data (IR, UV/Vis, H, H{31P}, 13C{1H}, 31P{1H}
Sonogashira coupling conditions, reasonable yields of both, NMR, MS) and elemental analysis, details of which are
the partially and fully substituted compounds containing given as Supporting Information, and X-ray crystallogra-
the TMSA group were obtained. Complexes 1, 2, 3 or 1Ј phy (for 2Ј).
were obtained by direct reaction between Co2(CO)8 and
2,4T or 2,4TЈ, respectively.
The IR spectra of the organic ligands 2,4T [2165 (w),
2152 (w) cm–1] and 2,4TЈ [2156 (w) cm–1] show weak ab-
In order to stabilise the dicobalt units, we have employed sorption bands, typically νCϵC stretches of the alkynyl
the dppm ligand (the small bite angle of dppm was expected units, in the characteristic range of diynyl complexes (two
to lead to the formation of bridged dicobalt complexes). νCϵC stretches at ca. 2060–2200 cm–1) and monoynyl com-
1
Thus, dppm-substituted alkyne carbonyl complexes 4, 5, 6 plexes (one νCϵC stretch at ca. 2090–2150 cm–1). The H
and 2Ј could only be prepared by substitution reaction of NMR spectra of both ligands show two doublet signals due
two or four carbonyl ligands in the presence of Me3NO at to the thiophene ring protons with coupling constants that
the Co2(CO)6 units of complexes 1, 2, 3 and 1Ј, respectively are consistent with their chemical formulations. In the 13C
(Scheme 1), because of the poor yields obtained by direct NMR spectra for 2,4T and 2,4TЈ, the signals belonging to
reaction between the alkyne and “Co2(CO)6(phosphane)” the thiophene ring (C3, C4, C5 and C6) and the alkynyl units
under thermal conditions for the analogous complexes from (C1, C2, C7 and C8) can be observed, and the assignments
2,5T.[7d] The FT-IR spectral changes of these reactions were were made on the basis of the δ values and two-dimensional
monitored until the νCϵO bands of the parent complex had NMR experiments (HMBC and HMQC).
disappeared.
The IR spectra of the (alkyne)cobalt complexes exhibit
On the basis of the isolated yield for 4 and 5, it can be three strong absorptions in the carbonyl stretching region
observed that the preference of the Co2(CO)4(dppm) units (2090–2024 cm–1) except for compound 3 (four absorptions)
for coordination at the alkyne in 2-position of the thio- due to the asymmetry of the molecule; in dppm-substituted
phene ring is two times greater than that for the 4-position. alkyne complexes 4–9 and 2Ј these absorptions lie at lower
This preference is also observed for the analogous com- frequencies (2027–1950 cm–1), and the spectral patterns are
plexes 1 and 2 with Co2(CO)6 units (see Exp. Sect.). More- similar to those observed for previously reported (alkyne)
over, compound 5, in CDCl3 solution at room temp. for cobalt and (substituted alkyne)cobalt complexes.[1a,1c,2c,7,14]
48 h, led to 4 (4 was never observed to yield 5), and complex Complexes 1, 2, 4 and 5 contain an uncomplexed CϵC tri-
6 decomposed to afford 4 and 5 in a 7:1 ratio [determined ple bond, which gives a νCϵC weak absorption at ca.
by thin-layer chromatography (TLC) using hexane/CH2Cl2 2157 cm–1. For 7 and 8 this absorption could not be ob-
(5:4) as eluent]. These results can be explained by simple served, but a νϵC–H one at ca. 3301 cm–1 is exhibited. The
steric or electronic effects.
absence of νCϵC in the region of 2150 cm–1 (for 6 and 9)
As both positions have the same substituent on the al- and νϵC–H around 3300 cm–1 (for 9) indicates that the
kyne (SiMe3), it can be expected that the steric demand at alkynyl bond loses its triple-bond character and both
the end-caps are similar. Then, the preference of the alkyne linkages are coordinated to Co2(CO)4(dppm)
Co2(CO)4X [X = (CO)2 or dppm] moieties to coordinate units.
the alkyne in position 2 can be explained by electronic fac-
The NMR spectroscopic data, which have been recorded
tors. In agreement with this, the electron density on the tri- in several solvents, are consistent with the overall geometry
ple bond of the alkyne in position 4 is higher than on the established in the solid state for complex 2Ј (Figure 1) and
alkyne in position 2, as judged by the 13C NMR shifts for with the proposed structures (Scheme 1).
1
the alkyne C atoms; this situation should disfavor the at-
In H NMR spectra, the chemical shifts for the SiMe3
tachment of the Co atoms to the CϵC group in position 4, and CϵCH protons are found to be very sensitive to cobalt
since back-donation from the Co d-orbitals to the π*-MO complexation on the adjacent alkyne bond, and they show
of an electron-poor ligand is the stabilizing factor in the a significant downfield shift with respect to the free ligands
bonding.[13]
in accordance with the reduction of the CϵC triple-bond
However, Diederich et al. obtained in the reaction of character.[15] The signals of all ring protons in the Co2-
Co2(CO)8 with 1,6-bis(triisopropylsilyl)hexa-1,3,5-triyne (CO)6-substituted alkyne complexes are shifted downfield
the exclusive formation of the compound in which the car- slightly from those of the corresponding alkynylated thio-
bonylcobalt fragment is coordinated to the central CϵC phenes, due to the strong electron-withdrawing effect of the
1
triple bond, which was attributed to the presence of the carbonylcobalt moieties. In addition, the values of the H-
bulky triisopropylsilyl end-caps.[2c]
1H coupling constants of JHH ≈ 1.3 Hz for the thiophene
Removal of the TMS protecting group from 4 and 5 was proton signals are in accordance with their non-adjacent
accomplished by treatment with saturated solutions of positions (Table 1). For dppm complexes 4–8 and 2Ј the dia-
KOH in degassed methanol at room temp. to give the ter- stereotopic protons of the –CH2– group are coupled with
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2,4-Bis(trimethylsilylethynyl)thiophene-Coordinated Carbonylcobalt Units
Scheme 1.
1
1
the P atoms; thus, they appear as two double triplets with in the H and H{31P} NMR spectra in CD2Cl2. Also, in
JHH ≈ 13.3 Hz and JPH ≈ 10.5 Hz, except in 6, where the 9, the two moieties Co2(CO)4(dppm) are inequivalent, and
1
inequivalent Co2(CO)4(dppm) moieties display four signals this is reflected in the H NMR spectrum. This spectrum
Eur. J. Inorg. Chem. 2007, 5215–5225
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C. Moreno et al.
FULL PAPER
Figure 1. ORTEP diagram of 2Ј, with 50% ellipsoids.
shows two resonances for the terminal “alkyne” protons, thiophene carbon signals appear between δ = 120 and
–(C–C)coord–H in the region δ = 5.72–5.80 ppm, and they 150 ppm (Table 2).
are coupled with the P atoms like in similar com-
Compound 6 exhibits low solubility in CDCl3 and
pounds.[7d,16] As expected,[15,17] because of the reduction in CD2Cl2, and for that reason the 13C NMR spectrum was
the CϵC triple-bond character, there is a downfield shift in recorded in [D8]THF. The unambiguous assignment of its
the signal positions of these terminal protons with respect carbon atoms has been carried out by comparison with
to those of the free ligand (δ = 3.32 and 2.99 ppm).
published data of analogous compounds[7d] and by using
The 31P NMR spectra for 4, 5, 7 and 8 present a broad the 13C NMR spectra of 4 and 5 in the same solvent in
singlet, while for 6 and 9, which contain two inequivalent addition to HMQC and HMBC spectroscopy (these experi-
Co2(CO)4(dppm) units, two broad singlets appear. All of ments have also been performed for the rest of the com-
them are shifted to higher frequencies (ca. 35 ppm) with plexes) (Figure 2).
respect to that of the free ligand because of the coordina-
tion.
All compounds gave satisfactory mass spectrometric
data; thus, the positive FAB mass spectra show the respec-
The 13C NMR chemical shifts of the carbonyl groups in tive molecular ions or [M+ – CO], as well as peaks corre-
all the complexes appear as one (1, 2, 3 and 1Ј), two (4, 5, 7, sponding to the consecutive loss of the CO ligands. The
8 and 2Ј) or four (6 and 9) signals at δ ≈ 200 and 207 ppm, UV/Vis spectra of all complexes exhibit broad low-intensity
suggesting that they are rapidly interchanging on the NMR absorption bands with λ between 520 and 558 nm attrib-
scale. The carbon resonances of the free and coordinated uted to the d-d transitions. For 3, 6, and 9, the presence of
acetylene carbon atoms can be assigned on the basis of the the second Co2(CO)6 or Co2(CO)4(dppm) unit results in a
magnitude of the JCP coupling constants, chemical shifts redshift of these absorption bands. These spectra, for com-
and in comparison with analogous complexes.[1c,2c,7,18] plexes 4–9 and 2Ј, are dominated by the characteristic UV
Thus, for 4 and 5, in CDCl3 and CD2Cl2, the C1, C2 and bands below 380 nm associated with π-π* transitions within
C3 atoms display similar triplets with 13C-31P coupling con- the phenyl groups of the bis(phosphane) ligand. In ad-
stants of JCP ≈ 10.1, 8.9 and 3.0 Hz, respectively. The re- dition, strong absorptions are observed around 231, 250
placement of the –SiMe3 group by a proton results in a and 276 nm attributed to π-π* transition associated with
significant deshielding of the C1, C2, C7 and C8 atoms. The the thiophene ring.
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2,4-Bis(trimethylsilylethynyl)thiophene-Coordinated Carbonylcobalt Units
1
Table 1. H NMR (300 MHz, CDCl3, 25 °C, ppm) data for the compounds 1–9 and 2,4T.
H4
H5
–CϵCH
–C–CH
–CϵCSiMe3
–C–CSiMe3
2,4T
7.21 (d)
JHH = 1.3 Hz
7.22 (d)
JHH = 1.3 Hz
7.24 (d)
7.32 (d)
JHH = 1.3 Hz
7.42 (d)
JHH = 1.3 Hz
7.26 (s br)
–
–
0.25 (s), 0.24 (s)
–
1
2
–
–
–
–
–
–
–
–
0.25 (s)
0.26 (s)
0.39 (s)
0.38 (s)
JHH = 1.4 Hz
7.27 (d)[a]
7.31 (d)[a]
JHH = 1.5 Hz
7.33 (d)
0.25 (s)[a]
0.39 (s)[a]
JHH = 1.5 Hz
7.31 (d)
3
4
0.40 (s), 0.38 (s)
0.41 (s), 0.39 (s)[a]
0.36 (s)
JHH = 1.4 Hz
JHH = 1.4 Hz
7.34 (d)[a]
7.39 (d)[a]
–
JHH = 1.2 Hz
6.57 (d)
JHH = 1.2 Hz
7.28 (s br)
0.28 (s)
0.28 (s)[a]
JHH = 1.3 Hz
6.58 (d)[a]
7.31 (d)[a]
JHH = 1.4 Hz
7.37 (s br)[b]
6.63 (d)
0.38 (s)[a]
JHH = 1.4 Hz
6.52 (s br)[b]
6.77 (d)
0.24 (s)[b]
0.29 (s)
0.36 (s)[b]
0.33 (s)
5
6
JHH = 1.4 Hz
JHH = 1.4 Hz
6.76 (d)[a]
6.67 (d)[a]
–
–
–
–
0.29 (s)[a]
0.25 (s)[b]
0.34 (s)[a]
JHH = 1.5 Hz
6.74 (s br)[b]
6.68 (d)
JHH = 1.5 Hz
6.71 (s br)[b]
7.27 (d)
0.32 (s)[b]
0.36 (s), 0.35 (s)
JHH = 1.3 Hz
JHH = 1.4 Hz
6.68 (d)[a]
7.26 (d)[a]
–
0.36 (s), 0.35 (s)[a]
JHH = 1.4 Hz
6.75 (s br)[b]
6.67 (d)
JHH = 1.3 Hz
6.87 (d)
JHH = 1.4 Hz
7.43–7.15
JHH = 1.4 Hz
7.35 (s br)[b]
7.31 (d)
JHH = 1.3 Hz
6.64 (d)
JHH = 1.4 Hz
7.43–7.15
0.385 (s), 0.381(s)[b]
0.38 (s)
7
8
9
2.99 (s)
3.32 (s)
–
–
–
–
–
–
0.33 (s)
5.80 (dt)
JHH = 8.2 Hz
JPH = 6.2 Hz
5.72 (t)
–
JPH = 6.7 Hz
[a] CD2Cl2. [b] [D8]THF.
Table 2. 13C NMR (500 MHz, CDCl3, 25 °C, ppm) data for the compounds 1–9 and 2,4T.
C1
C2
C3
C4
C5
C6
C7
C8
2,4T
99.4 (s)
81.0 (s br)
80.0 (s br)[a]
80.7 (s br)
81.3 (s br)[a]
89.7 (t)
99.0 (s)
93.4 (s br)
97.7 (s br)[a]
93.8 (s br)
94.5 (s br)[a]
93.3 (t)
122.2 (s)
141.9 (s)
134.9 (s)
131.0 (s)
134.2 (s)[a]
130.3 (s)
130.8 (s)[a]
128.9 (s)
130.6 (s)
130.4 (s)
125.9 (s)[a]
124.7 (s)
125.2 (s)[a]
128.3 (s)
123.2 (s)
123.2 (s)
124.6 (s)[a]
139.5 (s)
139.9 (s)[a]
122.1 (s)
96.5 (s)
99.2 (s)
94.1 (s)
94.2 (s)
1
2
3
139.0 (s)[a]
143.0 (s)
96.9 (s)[a]
97.1 (s br)
97.7 (s br)[a]
100.4 (s)
100.1(s)[a]
79.4 (s br)
80.0 (s br)[a]
92.9 (s)
143.1 (s)[a]
147.8 (t)
4
JCP = 10.5 Hz
JCP = 9.2 Hz
JCP = 2.7 Hz
148.2 (t)[a]
JCP = 3.1 Hz
147.5 (t)[b]
JCP = 2.7 Hz
143.7 (t)
JCP = 3.2 Hz
144.1 (t)[a]
JCP = 2.9 Hz
143.6 (t)[b]
JCP = 3.2 Hz
149.5 (t)[b]
JCP = 2.7 Hz
148.3 (t)
89.7 (t)[a]
93.8 (t)[a]
129.1 (s)[a]
128.8 (s)[b]
134.8 (s)
128.6 (s)[a]
128.3 (s)[b]
122.1 (s)
122.6 (s)[a]
122.3 (s)[b]
123.2 (s)
100.4 (s)[a]
100.3 (s)[b]
97.6 (s)
92.3 (s)[a]
91.9 (s)[b]
98.6 (s)
JCP = 10.0 Hz
88.5 (m)[b]
JCP = 9.4 Hz
93.5 (m)[b]
5
87.9 (t)
JCP = 9.9 Hz
87.9 (t)[a]
97.9 (t)
JCP = 8.3 Hz
98.4 (t)[a]
135.0 (s)[a]
134.4 (s)[b]
120.6 (s)[b]
122.6 (s)[a]
122.3 (s)[b]
126.0 (s)[b]
123.7 (s)[a]
123.2 (s)[b]
97.7 (s)[a]
97.4 (s)[b]
98.2 (m)[b]
79.2 (s)
99.1 (s)[a]
97.8 (s)[b]
87.2 (m)[b]
76.2 (s)
JCP = 10.0 Hz
JCP = 8.8 Hz
86.8 (m)[b]
98.0 (m)[b]
6
7
8
9
87.9 (m)[b]
89.6 (m)
93.3 (m)[b]
93.2 (m)
145.1 (t)[b]
JCP = 2.7 Hz
121.0 (s)
128.5 (s)
128.6 (s)
135.2 (s)
JCP = 3.2 Hz
143.9 (t)
88.0 (m)
97.9 (m)
122.3 (s)
122.0 (s)
77.2 (s)
81.1 (s)
JCP = 2.7 Hz
74.5 (m)[a]
83.2 (m)[a]
147.3 (m)[a]
121.7 (s)[a]
128.9 (s)[a]
143.9 (m)[a]
89.4 (m)[a]
75.2 (m)[a]
[a] CD2Cl2. [b] [D8]THF.
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C. Moreno et al.
Table 3. Selected bond lengths [Å] and angles [°] for 2Ј.
FULL PAPER
C(1)–C(2)
1.358(4)
1.853(3)
1.969(2)
1.985(2)
1.450(3)
1.943(2)
1.975(2)
1.894(3)
1.138(3)
1.797(3)
1.141(3)
C(11)–Co(1)
C(12)–O(3)
C(12)–Co(2)
C(13)–O(4)
C(13)–Co(2)
C(26)–P(1)
C(26)–P(2)
Co(1)–P(1)
Co(2)–P(2)
Co(1)–Co(2)
1.767(3)
1.142(4)
1.794(3)
1.139(3)
1.781(3)
1.831(2)
1.843(2)
2.2221(7)
2.2256(7)
2.4850(5)
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(5)–Br(1)
C(10)–O(1)
C(10)–Co(1)
C(11)–O(2)
C(2)–C(1)–Si(1)
C(6)–C(5)–Br(1)
C(11)–Co(1)–C(2)
C(11)–Co(1)–C(1)
C(2)–Co(1)–C(1)
C(10)–Co(1)–P(1)
C(1)–Co(1)–P(1)
C(1)–Co(1)–Co(2)
141.71(19) C(1)–C(2)–C(3)
136.0(2)
121.5(2)
123.7(2)
C(4)–C(5)–Br(1)
97.81(11)
C(11)–Co(1)–C(10) 99.79(14)
101.12(11) C(10)–Co(1)–C(2)
143.70(12)
104.70(12)
99.37(9)
101.25(7)
51.20(7)
40.44(10)
106.82(9)
138.51(7)
50.78(7)
C(10)–Co(1)–C(1)
C(11)–Co(1)–P(1)
C(2)–Co(1)–P(1)
C(2)–Co(1)–Co(2)
C(10)–Co(1)–Co(2) 102.62(11) C(11)–Co(1)–Co(2) 147.76(8)
Figure 2. HMBC NMR (500 MHz, CDCl3, 25 °C, ppm) spectra for
complex 2Ј.
C(13)–Co(2)–C(12) 101.48(14) C(13)–Co(2)–C(1)
102.53(11)
102.79(11)
40.28(10)
111.69(9)
100.46(7)
C(12)–Co(2)–C(1)
C(12)–Co(2)–C(2)
C(13)–Co(2)–P(2)
C(1)–Co(2)–P(2)
98.35(11)
135.73(12) C(1)–Co(2)–C(2)
98.79(9)
138.56(8)
C(13)–Co(2)–C(2)
C(12)–Co(2)–P(2)
C(2)–Co(2)–P(2)
Crystal Structure of 2Ј
C(13)–Co(2)–Co(1) 151.05(9)
C(12)–Co(2)–Co(1) 95.39(10)
The single-crystal X-ray structure determination of 2-
{Co2(CO)4(µ-dppm)[µ2-η2-(SiMe3C2)]}-4-(Br)-C4H2S (2Ј)
confirms the structure presented in Scheme 1. Compound
2Ј consists of a monosubstituted 4-bromo-2-(trimethylsilyl-
ethynyl)thiophene ligand with a dimetallic Co unit at the
C(1)–Co(2)–Co(1)
P(1)–Co(1)–Co(2)
P(1)–C(26)–P(2)
51.34(7)
96.00(2)
107.97(12)
C(2)–Co(2)–Co(1)
P(2)–Co(2)–Co(1)
50.06(7)
96.55(2)
2-position. The dimetallic Co moiety has two terminal car- the two ethynyl carbon atoms, and the other Co atom. The
bonyl ligands on the Co atoms, bridging dppm and trimeth- bond lengths of the apex carbonyl groups to the Co atoms,
ylsilylethynyl groups. This geometry has been observed in C(10)–Co(1) and C(12)–Co(2), are 1.797(3) and 1.794(3) Å,
other carbonylcobalt dimetallic complexes possessing a respectively. These bond lengths are statistically not dif-
bridging acetylene ligand.[19] The geometric parameters for ferent from those of the base carbonyl groups to the Co
2Ј are summarized in Table 5. Table 3 contains selected atoms, which are 1.767(3) and 1.781 Å, for C(11)–Co(1) and
bond lengths and angles. An ORTEP plot indicating the C(13)–Co(2), respectively. The dihedral angle Co(1)–C(1)–
atom-labelling scheme is given in Figure 1. Complex 2Ј C(2)–Co(2) was determined to be –84.5(7)°, whereas the di-
crystallizes in the monoclinic space group P21/c, with one hedral angle C(1)–Co(1)–Co(2)–C(2) was determined to be
molecule in the asymmetric unit, but contains no crystallo- –52.8(13)°. The bite angle of the dppm ligand was found to
graphic symmetry.
be 108.0(12)°, which is consistent with analogous bite
A highly distorted tetrahedron is formed by the coordi- angles of dppm in Co–Co complexes.[21]
nation of the dicobalt unit with the ethynyl carbon atoms,
The C(1)–C(2) bond length of the bridging ethynyl li-
with a Co(1)–Co(2) bond length of 2.4850(5) Å, and the gand, 1.358(4) Å, is consistent with reported ethynyldicob-
average Co–C bond length was determined to be alt complexes.[22] This reflects the loss of triple-bond char-
1.968(2) Å. The Co–Co distance is comparable to those re- acter as a result of coordination of the acetylenic moiety to
ported for the compounds 2,5-{Co2(CO)4(µ-dppm)[µ2-η2- the Co2 unit. The change in hybridisation at C(1)–C(2) is
(SiMe3C2)]}2C4H2S[7d] and [Co2(CO)4(µ-dppm){µ2-η2- also reflected in the C(1)–C(2)–C(3) angle of 136.0(2)° and
(SiMe3C2)}]2(SiMe3CϵC)(1,3,5-C6H3)[7a] and may be con- the C(2)–C(1)–Si(1) angle of 141.7(19)°.
sidered typical for this type of clusters.[14d,20]
The bond lengths of the Co atoms to the phosphorus
The coordination geometry of the Co atom is similar to atoms of the dppm ligand are 2.222(7) Å and 2.226(7) Å for
a pyramid with a pentagonal-shaped base, where the Co Co(1)–P(1) and Co(2)–P(2), respectively. The average P–C
atom is in the centre of the pyramid. The distortion of the distances of the bridging dppm ligand, 1.835(2) Å are nor-
pyramid is due to the constrained tetrahedron comprised of mal;[23] the P–C bond lengths are statistically equivalent.
Co(1)–Co(2)–C(1)–C(2), as well as the bridging of the All other bond lengths and angles are comparable to those
dppm ligand. The carbonyl moieties coordinate to the Co reported for similar structures.[7] The average carbonyl
atoms in the sterically least hindered sites, thus making up CϵO bond length was determined to be 1.140(3) Å, where
the pyramid. The apex of the pyramid is one of the car- all of the bond lengths are sufficiently similar. In addition,
bonyl groups, and the base is comprised of the carbonyl the Br–C(5) bond length is 1.894(3) Å and the C(6)–C(5)–
group, one of the phosphorus atoms of the dppm ligand, Br and C(4)–C(5)–Br angles are 123.7(2)° and 121.5(2)°,
5220
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2,4-Bis(trimethylsilylethynyl)thiophene-Coordinated Carbonylcobalt Units
respectively. The thiophene ring is essentially planar with a
Compound 3, with two “almost” equivalent dicobalt re-
root mean square deviation of 0.0045 Å. There does not dox centers, shows two consecutive monoelectronic re-
appear to be any intramolecular hydrogen bonding within ductions and oxidations to achieve 32– and 32+, respectively.
the molecule.
At room temp., reduction of 3 is chemically completely
irreversible; however, at –30 °C the chemical stability of the
reduced species is greatly enhanced, and two distinct and
almost completely reversible reduction waves are observed
in CV (Figure 3). The ratio ipa/ipc approaches 1 as the sweep
rate increases. As regarding oxidation, two quasi-reversible
waves are also observed, ipc/ipa increasing as the tempera-
ture decreases.
Electrochemical Studies
The electrochemical behaviour of 1, 2Ј and 3–9 in
CH2Cl2 solution was studied by means of cyclic voltamme-
try (CV) and square wave voltammetry (SWV) techniques.
A preliminary study of 1 and 3–6 was previously pub-
lished.[24] Table 4 presents data of E1/2 [E1/2 = (Epa + Epc)/
2] for the electrochemical reduction and oxidation of 1, 2Ј
and 3–9. The organic ligands 2,4T and 2,4TЈ do not show
any oxidation or reduction peaks in the potential range be-
tween –1.8 V and +1.5 V vs. Fc*+/Fc* (Fc* = decamethyl-
ferrocene) in CH2Cl2.
Table 4. Electrochemical data for 1, 2Ј and 3–9.[a]
E1/2 for reduction ∆E1/2 (red) E1/2 for oxidation ∆E1/2 (ox)
1
2Ј
3
4
5
6
–0.99[b]
–1.54[b]
1.24[b]
0.70
–1.00[b], –1.08[b]
–1.56[b]
0.08
1.21[b], 1.29[b]
0.69
0.08
–1.60[b]
0.68
0.65, 0.77
0.69
–1.58[b], –1.72[b]
–1.52[b]
0.14
0.12
0.12
0.10
7+8[c]
9
–1.52[b], –1.64[b]
0.63, 0.73
Figure 3. Cyclic (Ϫ) and square wave (- - -) voltammograms for the
reduction of 3 in CH2Cl2 containing 0.15  TBAPF6 at –30 °C on
a glassy carbon working electrode. CV: v = 0.5 Vs–1. SWV: scan
increment = 2 mV, SW amplitude = 25 mV, frequency = 15 Hz.
[a] In V vs. Fc*+/Fc* in CH2Cl2 solution. Data are taken from CV
and SWV at 25 °C, unless otherwise stated. [b] From CV and SWV
at –30 °C. [c] Equimolecular mixture of compounds 7 and 8.
Electrochemistry of 2Ј and 4–9
Electrochemistry of 1 and 3
Compounds 2Ј and 4–9 contain Co2(CO)4(dppm)C2 re-
CV and SWV of the Co2(CO)6C2 derivative 1 at room dox centers. The dppm ligand increases the electronic den-
temp. show chemically irreversible oxidation and reduction sity and makes oxidations easier (less positive E1/2) and re-
waves at moderate sweep rates (EC processes). Thus, when ductions more difficult (more negative E1/2) as observed in
the sweep is reversed after CV reduction, no coupled anodic Table 4.
peak is observed, but a new small one appears at +0.12 V
The E1/2(ox) values are quite similar for all the com-
(irreversible). This behaviour indicates that the decomposi- pounds containing a single Co2(dppm)(CO)4C2 redox cen-
–
tion of 1– yields, among other fragments, Co(CO)4 (oxi- ter, independent of the nature of the other substituent on
dised at 0.12 V).[6d,7,25] The stability of 1– is greatly en- the thiophene ring (–Br in 2Ј, –C2SiMe3 in 4–5 and –C2H
hanced when low temperature decreases the rate of the fol- in 7–8) or the location of the Co2(dppm)(CO)4C2 unit (posi-
lowing chemical reaction, and at –30 °C chemical reversibil- tion 2 or 4). It should be noted that 7 and 8 could not be
ity is almost completely attained.
isolated, and that an equimolecular mixture of both com-
Decreasing temperature to –30 °C and increasing the pounds was used for the electrochemical measurements. A
sweep rate to 2 V/s allowed to observe a very small coupled single oxidation and a single reduction peak were obtained
reduction peak on sweep reversal after 1+ formation. The for that mixture, indicating that both compounds are oxi-
stability of 1+ is lower than that observed for the related dised and reduced at almost the same potential value. In
cation derived from 2-[Co2(CO)6{µ2-η2-(SiMe3C2)}]-5-(Me- the case of E1/2(red), differences are not too strong among
3SiCϵC)C4H2S (ipc/ipa ≈ 0.55 at –30 °C and 0.1 V/s).[7d] 2Ј, 4, 5 and 7+8, but it seems that the presence of a
This result is in agreement with the higher overall π-conju- –C2SiMe3 substituent makes reduction slightly more diffi-
gation[26] in complexes containing 2,5T (λmax = 331 nm)[27] cult (E1/2 more negative), as a result of the higher electron-
as compared to those of 2,4T (λmax = 277 nm). E1/2(ox) and donating properties of the –SiMe3 group as compared to
E1/2(red) for 1 are very similar to those of the corresponding –H. The bidentate ligand dppm greatly increases the chemi-
2,5T derivative, indicating that the position of the –C2SiMe3 cal stability of the cations (oxidations of the compounds
substituent on the thiophene ring does not have a signifi- with one redox center are chemically completely reversible
cant influence on the electrochemical processes.
at 25 °C and 0.1 V/s) and the anions (reductions are quasi-
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5221

C. Moreno et al.
FULL PAPER
reversible at 25 °C and completely reversible a –30 °C) (Fig- gand.[9a] The two redox centers in 3, 6 and 9 are not com-
ure 4). Potential values and stability trends agree with those pletely equivalent, and the observed ∆E1/2 could be due to
of related 2,5T compounds.[7d]
intrinsic differences; however, results obtained with 4–5 and
7–8 (very scarce influence of the position of the redox cen-
ter on the thiophene ring) allow to assume that most
of ∆E1/2 is due to a low-intensity electronic interaction
between the centers. The ∆E1/2 values observed for 3, 6
and 9 can thus be compared to those measured for the
related compounds 2,5-[Co2(CO)6{µ2-η2-(SiMe3C2)}]2C4H2S
[∆E1/2(red) = 0.11 V; ∆E1/2(ox) = 0.24 V], 2,5-[Co2(CO)4(µ-
dppm){µ2-η2-(SiMe3C2)}]2C4H2S [∆E1/2(red)
= 0.13 V;
∆E1/2(ox) = 0.29 V] and 2,5-[Co2(CO)4(µ-dppm){µ2-η2-
(HC2)}]2C4H2S [∆E1/2(red) = 0.13 V; ∆E1/2(ox) = 0.20 V],
respectively.[7d] All ∆E1/2 values (including those of the pres-
ent work) indicate that a moderate electronic interaction is
established through the aromatic ligand backbone, and the
complexes belong to group II in the Hush–Robin–Day clas-
sification of mixed-valence compounds.[29] Data for the
2,4T and 2,5T derivatives show that the ∆E1/2(ox) values
are significantly larger for the latter. This seems to indicate
that the HOMO (depopulated by oxidation) of the 2,5T de-
rivatives shows a greater π-delocalization than the HOMO
of the 2,4T derivatives and than the LUMO (populated by
reduction) in both groups, in agreement[26] with the higher
conjugation observed in 2,5T derivatives, where the λmax
value is less blue-shifted relative to that of 2,4T compounds.
The differences in ∆E1/2 indicate a significant contribution
of through-bond electronic interactions as compared to
through-space ones in these compounds.
Figure 4. Cyclic voltammogram for the reduction and oxidation of
4 at –30 °C in CH2Cl2 containing 0.15  TBAPF6 on a glassy car-
bon working electrode at v = 0.05 Vs–1.
6 and 9 contain two Co2(dppm)(CO)4C2 centers and
show two consecutive monoelectronic oxidations and re-
ductions. Chemical reversibility is greatly approached at
–30 °C (Figure 5), allowing the determination of E1/2. Anal-
ogous compounds, in which the ligand is 2,5T, show a
greater stability of the corresponding anions and cations, in
agreement with the general trends observed in the synthesis
of both sets of compounds (2,4T and 2,5T derivatives) and
the higher overall π-conjugation of 2,5T, as the C3–C4 bond
in a thiophene ring is known to have less double-bond char-
acter than the C2–C3 bond.[28]
Conclusion
The overall π-conjugation of 2,4T derivatives is smaller
than that of the analogous 2,5T derivatives, and this results
in a lower stability of the ions derived from 2,4T and a
weaker electronic communication through the aromatic li-
gand backbone. The derivatives of 2,4T and 2,5T with two
redox centres belong to group II in the Hush–Robin–Day
classification of mixed-valence compounds.
Experimental Section
Reagents and General Techniques: All manipulations were carried
out by using standard Schlenk vacuum-line and syringe techniques
under oxygen-free argon. All solvents for synthetic use were dried
and distilled under argon by standard procedures.[30] Column
chromatography was performed by using silica gel 100 (Fluka) and
preparative TLC glass plates coated with silica gel (SDS 60–17 µm,
0.25 mm thick). 2,4-Dibromothiophene (Lancaster Synthesis Inc.);
Me3SiCϵCH (TMSA), Co2(CO)8, KOH (Fluka); 1,2-bis(diphenyl-
phosphanyl)methane (dppm), CuI, a solution 1.0  of tetra-
butylammonium fluoride (TBAF) in THF (Aldrich); NaHCO3,
MgSO4 (Panreac) and a solution of HCl (35%) (Prolabo) were used
as received. Trimethylamine N-oxide (Aldrich) was sublimed prior
Figure 5. Voltammograms for the reduction and oxidation of 6 in
CH2Cl2 containing 0.15  TBAPF6. (Ϫ) CV at –30 °C on a glassy
carbon working electrode, v = 0.1 Vs–1. (-·-·-) CV at 25 °C on a Pt
working electrode, v = 0.1 Vs–1. (- - -) SWV at –30 °C on a glassy
carbon working electrode, scan increment = 2 mV, SW amplitude
= 25 mV, frequency = 60 Hz.
The difference between E1/2 of consecutive waves in com-
pounds with two equivalent redox centers, ∆E1/2, is usually
regarded as an estimation of the amount of electronic inter-
[31]
to use and stored under argon. Compound Pd(PPh3)4 was pre-
pared according to the literature. The 1H, 1H{31P}, 13C{1H},
31P{1H} NMR spectra and HMQC and HMBC data were recorded
action between those centers through the bridging li- with Bruker AMX-300 and -500 instruments. Chemical shifts were
5222 Eur. J. Inorg. Chem. 2007, 5215–5225
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2,4-Bis(trimethylsilylethynyl)thiophene-Coordinated Carbonylcobalt Units
(0.68 g, 1.78 mmol) and trimethylamine N-oxide (0.40 g,
measured relative to either an internal reference of tetramethyl-
silane or residual protons of the solvents. Infrared spectra were
measured with a Perkin–Elmer 1650 infrared spectrometer. Ele-
mental analyses were performed with a Perkin–Elmer 240 B micro-
analyser. Electronic spectra were recorded with a Unicam UV 4
UV/Vis spectrophotometer. Mass spectra were measured with a
VG-Autospec mass spectrometer for FAB and EI. Spectroscopy
data are available as Supporting Information. Electrochemical
measurements were carried out with a computer-driven Par
Mo. 273 electrochemistry system in a three-electrode cell under ni-
trogen in anhydrous deoxygenated CH2Cl2 containing 0.15  tetra-
butylammonium hexafluorophosphate (TBAPF6) as supporting
electrolyte. Cyclic and square wave voltammetry (CV and SWV,
respectively) studies were carried out in a three-electrode system.
Polycrystalline Pt (0.05 cm2) or glassy carbon were used as working
electrodes; the counter electrode was a Pt gauze and the reference
electrode was a silver wire quasi-reference electrode. Decamethyl-
ferrocene (Fc*) was used as internal standard, and all potentials in
this work are referenced to the Fc*+/Fc* couple. Under the actual
experimental conditions, E1/2 of the ferrocene couple (Fc+/Fc) was
+0.55 V vs. Fc*+/Fc* in CH2Cl2 solution. Coulometry of 4 was
performed at 1.1 V and 1 mol of electrons per mol of 4 was found
to be consumed in the oxidation process. The number of electrons
involved in the remaining processes were determined by compari-
son of peak heights in CV.
3.56 mmol). The reaction mixture, monitored by FT-IR spec-
troscopy until the νCϵO bands of the parent complexes had disap-
peared, was stirred at 45 °C for 4 d. Finally, the solvent was re-
moved under vacuum and the residue purified by thin-layer
chromatography (TLC) using hexane/CH2Cl2 (6:1) to afford 4
(0.56 g, 56% yield) and 5 (0.16 g, 28% yield) as stable dark red
solids.
Synthesis of 2,4-[Co2(CO)4(µ-dppm){µ2-η2-(SiMe3C2)}]2C4H2S (6):
The same procedure as described above was applied in the prepara-
tion of this compound from
3 (0.82 g, 0.97 mmol), dppm
(1.94 mmol) and Me3NO (3.88 mmol). After the solvent had been
removed under vacuum, the residue was purified by the same man-
ner. Complex 6 (0.48 g, 33% yield) was obtained as air-stable dark
green solid.
Synthesis of 2-[Co2(CO)4(µ-dppm){µ2-η2-(SiMe3C2)}]-4-(Br)-C4H2S
(2Ј): A solution of 1Ј (0.27 g, 0.50 mmol) and dppm (0.50 mmol)
in hexane (50 mL) was prepared. Trimethylamine N-oxide (0.11 g,
1.00 mmol) was added and the reaction mixture, monitored by FT-
IR spectroscopy, stirred at 45 °C for 4 d. After the solvent had been
removed under vacuum, the residue was purified by thin-layer
chromatography (TLC) using hexane/CH2Cl2 (3:1) to afford 2Ј
(0.33 g, 77% yield) as stable dark red solid.
Synthesis of 2-[Co2(CO)4(µ-dppm){µ2-η2-(SiMe3C2)}]-4-(CϵCH)-
C4H2S
(7)
and
2-(CϵCH)-4-[Co2(CO)4(µ-dppm){µ2-η2-
Synthesis of 2,4-Bis(trimethylsilylethynyl)thiophene (2,4T) and 4-
Bromo-2-(trimethylsilylethynyl)thiophene (2,4TЈ): To a solution of
2,4-dibromothiophene (3.0 g, 12.4 mmol) in Et3N (100 mL) was
added at 0 °C Pd(PPh3)4 (0.70 g, 0.62 mmol), CuI (0.23 g,
1.24 mmol) and excess of trimethylsilylacetylene (TMSA) (12.1 g,
17.5 mL, 124 mmol). The resulting mixture was stirred first at room
temperature for 0.5 h and finally at 75 °C for 20 d. The solvent was
removed under reduced pressure and the residue dissolved in Et2O
(100 mL) and wash with (i) a solution of HCl (10%), (ii) a saturated
solution of NaHCO3 and dried (MgSO4). The solvent was evapo-
rated and the residue purified by column chromatography with hex-
ane to yield 2,4T (1.13 g, 33% yield) and 2,4TЈ (1.12 g, 35% yield)
as stable yellow oils.
(SiMe3C2)}]C4H2S (8): An equimolecular solution of 4 and 5 in
MeOH saturated with KOH was stirred for 24 h at 25 °C. Then the
solvent was removed under vacuum and the residue extracted with
several portions of Et2O and purified by chromatography on a hex-
ane-packed silica column (200 g) using hexane/CH2Cl2 (1:1) as elu-
ent to afford 7 (48% yield) together with 8 (50% yield) as unstable
solids.
Synthesis of 2,4-[Co2(CO)4(µ-dppm){µ2-η2-(HC2)}]2C4H2S (9): To a
solution of 6 (0.48 g, 0.32 mmol) in wet THF (50 mL) was added
TBAF (2.56 mL, 1.0  in THF, 2.56 mmol) and the mixture stirred
at room temp. for 24 h. After the solvent had been removed under
vacuum, the product was purified by chromatography on a hexane-
packed silica column using hexane/CH2Cl2 (1:1) as eluent to afford
9 (0.27 g, 62% yield) as unstable dark purplish-red solid.
Synthesis of 2-[Co2(CO)6{µ2-η2-(SiMe3C2)}]-4-(Me3SiCϵC)C4H2S
(1), 2-(Me3SiCϵC)-4-[Co2(CO)6{µ2-η2-(SiMe3C2)}]C4H2S (2) and
2,4-[Co2(CO)6{µ2-η2-(SiMe3C2)}]2C4H2S (3): To a solution of 2,4T
(0.90 g, 3.26 mmol) in hexane (100 mL) was added 1.5 equiv. of
Co2(CO)8. The reaction was monitored by FT-IR and 1H NMR
spectroscopy until the signals of the parent compounds 2,4T and
Co2(CO)8 had disappeared. After the mixture had been stirred at
room temp. for 1 h, the solvent was removed under vacuum and
the residue purified by thin-layer chromatography (TLC) using hex-
ane as eluent to afford 1 (0.64 g, 35% yield) and 2 (0.36 g, 20%
yield) together with 3 (1.24 g, 40% yield) as unstable solids. 3 has
also been obtained as the only product in high yield (0.27 g, 89%)
from 2,4T (0.10 g, 0.36 mmol) and 2 equiv. of Co2(CO)8 and subse-
quent chromatography with hexane on a silica column.
X-ray Data Collection, Structure Determination and Refinement of
2Ј: Dark red crystals were obtained by recrystallisation of the com-
plex from CH2Cl2/hexane mixtures. A summary of selected crystal-
lographic data for 2Ј is given in Table 5. A red single crystal of
approximate dimensions 0.25ϫ0.12ϫ0.09 mm with prismatic
shape was mounted on a glass fibre and transferred to a Bruker
SMART 6K CCD area-detector three-circle diffractometer with a
MAC Science Co., Ltd. rotating anode (Cu-Kα radiation, λ =
1.54178 Å) generator equipped with Goebel mirrors at settings of
50 kV and 110 mA.[32] X-ray data were collected at 100 K, with a
combination of several runs at different φ and 2θ angles. The data
were collected using 0.3° wide ω scans, crystal-to-detector distance
of 4.0 cm. The raw intensity data frames were integrated with the
SAINT program,[33] which also applied corrections for Lorentz and
polarization effects. The substantial redundancy in data allowed
empirical absorption corrections[34] to be applied using multiple
measurements of symmetry-equivalent reflections. A total number
of 24250 reflections were collected, and 6989 independent reflec-
tions remained after merging Rint = 0.0358. The unit-cell param-
Synthesis of 2-[Co2(CO)6{µ2-η2-(SiMe3C2)}]-4-(Br)-C4H2S (1Ј): By
a similar procedure as described above, from 2,4TЈ (0.75 g,
2.89 mmol) and 1 equiv. of Co2(CO)8. After the solvent had been
removed under vacuum, the product was eluted with hexane on a
silica column to afford 1Ј (1.43 g, 91% yield) as an unstable red
solid.
Synthesis of 2-[Co2(CO)4(µ-dppm){µ2-η2-(SiMe3C2)}]-4-(Me3- eters were obtained by full-matrix least-squares refinements of the
SiCϵC)C4H2S (4) and 2-(Me3SiCϵC)-4-[Co2(CO)4(µ-dppm){µ2- complete data set. The structure was solved and refined using the
η2-(SiMe3C2)}]C4H2S (5): A solution containing 1 and 2 (1.0 g,
SHELXTL/PC V 6.10 package.[35] The structure was solved by di-
1.78 mmol in a 1.75:1 ratio) in hexane (100 mL) was added dppm rect methods, refinement by full-matrix least squares on F2 using
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all data (negative intensities included). 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 aniso-
tropic displacement parameters. All scattering factors and anoma-
lous dispersions factors are contained in the SHELXTL 6.10 pro-
gram library. The H-atom parameters were calculated and atoms
were constrained as riding atoms with Uiso 20% larger than those
of the corresponding C atoms for the phenyl H atoms and 50%
larger for the methyl H atoms. CCDC-641070 contains the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Table 3 con-
tains selected bond lengths and angles. Figure 1 presents a molecu-
lar diagram of 2Ј.
[2]
[3]
Table 5. Crystal data and structure refinement for compound 2Ј.
Empirical formula
Formula mass
Temperature
C38H33BrCo2O4P2SSi
873.50
100(2) K
Wavelength
1.54178 Å
Crystal system
Space group
monoclinic
P21/n
Unit-cell dimensions
a = 16.5425(2) Å
b = 12.19370(10) Å
c = 19.1305(2) Å
β = 93.2610(10)°
3852.65(7) Å3
4
Volume
Z
Density (calcd.)
Absorption coefficient
F(000)
1.506 Mg/m3
9.859 mm–1
1768
Crystal size
0.25ϫ0.12ϫ0.09 mm
θ range for data collection 3.44–70.52°
Index ranges
–17 Յ h Յ 19, –14 Յ k Յ 13, –21 Յ l Յ 22
Reflections collected
Independent reflections
24250
6989 [R(int) = 0.0358]
Completeness to θ = 70.52° 94.9%
Absorption correction
Refinement method
SADABS v. 2.03
full-matrix least squares on F2
Data/restraints/parameters 6989/0/574
[4]
Goodness-of-fit on F2
Final R indices [IϾ2σ(I)]
R indices (all data)
1.032
R1 = 0.0330, wR2 = 0.0851
R1 = 0.0369, wR2 = 0.0874
1.213/–0.798 eÅ–3
Largest diff. peak/hole
Supporting Information (see footnote on the first page of this arti-
cle): IR, UV/Vis, MS, 1H, 13C, 31P NMR spectra and elemental
analysis of 1–9, 1Ј–2Ј, 2,4T and 2,4TЈ.
Acknowledgments
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Published Online: September 28, 2007
Eur. J. Inorg. Chem. 2007, 5215–5225
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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