Synthesis and Properties of New Dimeric η2-Diyne Complexes of Cobalt Linked through an Azobenzene Ligand

Article abstract of DOI:10.1021/acs.organomet.5b00257

The reaction between 4,4′-diiodoazobenzene (0) with excess trimethylsilylacetylene or dec-1-yne in the presence of catalytic amounts of PdCl₂(PPh₃)₂ and CuI, Sonogashira coupling conditions, gave rise to the formation of 4,4′-bis(trimethylsilylethynyl)azobenzene (1) and 4,4′-bis(dec-1-ynyl)azobenzene (2), in good yield, in addition to icosa-9,11-diyne (3) as byproduct in the last case. The analogous reactions from 0 and the alkynyl-cobalt complexes Co₂(CO)₄(μ-L-L)(μ₂-η²-SiMe₃C₂)](C≡CH) (L-L = dppm, dmpm) afforded 12-14. Complexes 4-7 and 15 have been obtained by direct reaction between Co₂(CO)₈ and the organic ligands 1-3. In order to increase the stabilization of Co-Co bonds, diphenylphosphinomethane-substituted alkyne-carbonyl complexes 8-11 were prepared by substitution reaction of carbonyl ligands in the presence of Me₃NO at the Co₂(CO)₆ units from 4-7. All products were characterized by analytical and spectroscopic data (IR, ¹H, ¹³C, and ³¹P NMR, and MS). Crystals of 9 suitable for single-crystal X-ray diffraction were grown, and the molecular structure of this compound is discussed. In this paper we report a comparative electrochemical study of these complexes by means of cyclic and square-wave voltammetry techniques, the trans-cis photoisomerization study of azobenzene compounds, and the thermotropic liquid-crystalline behavior. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.organomet.5b00257

Article
pubs.acs.org/Organometallics
Synthesis and Properties of New Dimeric η2‑Diyne Complexes of
Cobalt Linked through an Azobenzene Ligand
Consuelo Moreno,*,† Avelina Arnanz,† Rosa-María Medina,† María-Jose Macazaga,† Mario Pascual,†
́
Eva M. García-Frutos,§ Esther Martínez-Gimeno,† and María-Luisa Marcos*,‡
‡
†Departamento de Química Inorgan
́
ica and Departamento de Química, Universidad Auton
́
oma de Madrid, 28049 Madrid, Spain
§Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Ines
́
de la Cruz 3, 28049 Madrid, Spain
S
* Supporting Information
ABSTRACT: The reaction between 4,4′-diiodoazobenzene (0) with excess trimethylsilylace-
tylene or dec-1-yne in the presence of catalytic amounts of PdCl2(PPh3)2 and CuI, Sonogashira
coupling conditions, gave rise to the formation of 4,4′-bis(trimethylsilylethynyl)azobenzene (1)
and 4,4′-bis(dec-1-ynyl)azobenzene (2), in good yield, in addition to icosa-9,11-diyne (3) as
byproduct in the last case. The analogous reactions from 0 and the alkynyl-cobalt complexes
Co2(CO)4(μ-L-L)(μ2-η2-SiMe3C2)](CCH) (L-L = dppm, dmpm) afforded 12−14.
Complexes 4−7 and 15 have been obtained by direct reaction between Co2(CO)8 and the
organic ligands 1−3. In order to increase the stabilization of Co−Co bonds, diphenylphosphino-
methane-substituted alkyne-carbonyl complexes 8−11 were prepared by substitution reaction of
carbonyl ligands in the presence of Me3NO at the Co2(CO)6 units from 4−7. All products were
characterized by analytical and spectroscopic data (IR, 1H, 13C, and 31P NMR, and MS). Crystals
of 9 suitable for single-crystal X-ray diffraction were grown, and the molecular structure of this
compound is discussed. In this paper we report a comparative electrochemical study of these
complexes by means of cyclic and square-wave voltammetry techniques, the trans−cis
photoisomerization study of azobenzene compounds, and the thermotropic liquid-crystalline behavior.
sion, and inversion-assisted rotation. The actual mechanism
INTRODUCTION
■
depends on the exact surroundings of the azo group.3,6
Since the two isomers exhibit well-separated absorption
bands in the UV−visible region and different physical
properties, such as dielectric constant and refractive index,
and azo polymers are also found to have liquid-crystalline (LC)
properties due to the rod-like nature of the azobenzene moiety,
azobenzene and its derivatives are good candidates for many
applications such as light-triggered switches,7 constituents of
erasable holographic data, image storage devices and materials
with photomodulable properties,3−8 and a possible basis for a
light-powered molecular machine.9
Azobenzene and its derivatives constitute a family of dye
molecules known since the middle of the last century.1 These
chromophores are very versatile molecules that have received
much attention in both fundamental and applied research
areas.2 Basically, they are characterized by intense color, high
thermal stability (up to 350 °C), and a trans to cis reversible
isomerization of the NN double bond upon UV light
irradiation, whereas the reverse isomerization can take place by
visible light irradiation or by heating, the trans-form being
generally more stable than the cis-form.3 Photoinduced
isomerization involves dramatic structural rearrangements: the
distance between the para carbon atoms in the molecule
decreases from about 9.0 Å in the trans-form to 5.5 Å in the cis-
form. Furthermore, the change in the configuration leads to a
significant increase in the dipole moment. The trans-form has
no dipole moment, while the dipole moment of the nonplanar
cis compound is 3.0 D.4
Azobenzene and nearly all its monosubstituted derivatives
show a strong band in the UV region attributed to the π−π*
transition at ca. 290 nm in the cis-form (depending on the
solvent) and at ca. 320 nm in the trans-form and a much weaker
band in the visible region (around 450 nm), due to the n−π*
transition.5 On conversion to the cis-isomer, the π−π* band
shifts to shorter wavelengths, and the intensity of the n−π*
absorption increases. Usually, four mechanisms for the trans−cis
reaction are considered: rotation, inversion, concerted inver-
The combination of these remarkable photoswitching
properties of azobenzene with the electrochemical, magnetic,
catalytic, or biological properties of the metal complexes could
give rise to multifunctional molecules.10 In many of these metal
species, the ligand is chelated to the metal through one of the
nitrogen atoms and either a second nitrogen donor substituent
or a carbon atom, so that the photoisomerization of the azo
group is not possible.11 Only a few organometallic compounds
are known in which the azo group is free to undergo
isomerization.12
The chemistry of cobalt with any azo ligand is limited up to
the present to a few coordination cobalt complexes;13 for this
reason we wished to explore the chemistry of organometallic
Received: April 8, 2015
© XXXX American Chemical Society
A
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Table 1. 1H NMR Data in CDCl3 Solution of 4, 5, 8, and 9 (Obtained from 1), 6, 7, 10, and 11 (Obtained from 2), and 12−14
a
(in Comparison with 1 and 4,4′-Diiodoazobenzene (0))
H2,2
H3,3
H6,6
H7,7
H2,2
H3,3
H6,6
H7,7
H2,2
H3,3
H6,6
H7,7
1
4
5
8
9
7.86
7.86
7.60
7.60
2
7.83
7.86
7.51
7.53
1
7.86
7.70
7.68
7.60
7.84
7.88
7.89
7.90
7.73
7.69
7.64
7.65
7.25
7.21
6
7.89
7.91
7.75
7.76
7.62
7.63
7.33
7.32
0
7
12
13
14
7.90
7.99
7.91
7.46
7.54
7.54
7.89
7.63
10
11
7.86
7.53
7.69
7.91
a
All the signals appear as doublets with JHH ≈ 8.5 Hz.
Table 2. 13C NMR Data in CDCl3 Solution of 4, 5, 8, and 9 (Obtained from 1), 6, 7, 10, and 11 (Obtained from 2), and 12 and
13 (Obtained from 0)
C1
C2,2′
C3,3′
C4
C5
C6,6′
C7,7′
C8
C9C10
C11−C12
1
4
5
8
9
152.4
151.8
122.6
122.8
132.6
132.9
124.9
125.9
105.8; 94.2
104.7; 97.3
152.1
152.0
150.6
150.9
C5
123.6
123.6
123.1
122.9
C6,6′
130.6
130.7
130.4
130.5
C7,7′
142.1
142.0
148.9
147.9
C8
103.7; 80.3
103.8; 80.3
104.7; 90.1
104.8; 89.8
C11−C12
152.3
122.7
132.9
125.4
104.8; 97.0
C1
C2,2′
C3,3′
C4
C9C10
2
151.3
151.5
122.8
122.8
132.3
132.4
127.0
127.1
93.5; 80.5
93.6; 80.5
6
151.7
151.8
150.4
150.8
C5
123.5
123.4
123.0
122.9
C6,6′
129.9
129.9
129.5
129.8
C7,7′
142.0
142.1
148.5
147.7
C8
100.7; 89.7
100.8; 89.7
105.5; 92.5
105.9; 92.7
C11−C12
7
10
11
151.7
122.6
132.3
126.5
93.2; 80.6
C1
C2,2′
C3,3′
C4
C9C10
0
151.7
152.1
124.6
124.5
138.2
138.5
97.4
97.8
12
13
150.9
151.3
123.2
123.1
131.8
131.8
96.9
96.8
82.4; 94.7
82.9; 94.8
90.5; 76.7
90.7; 76.6
Scheme 1
B
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Scheme 2
redox cobalt centers linked through the azobenzene fragment in
order to evaluate the effect of the organometallic group in the
azobenzene properties as trans−cis isomerization or redox
behavior. Thus, in this paper we report the synthesis,
characterization, redox properties, a detailed trans−cis−trans
isomerization study that aims at clarifying the role played by
trans substituents, and the mesomorphic behavior of several
para-alkynyl azobenzene derivatives (R-Azo-R) and their
organometallic cobalt complexes linked to the azobenzene
unit by a π-conjugated carbon bridge.
satisfactory mass spectrometric data. Co2(CO)6-substituted
alkyne complexes 4−7 were synthesized by direct reaction
between Co2(CO)8 and the organic ligand 1 or 2 after
separation and purification by TLC silica plates using hexane/
CH2Cl2 (2:1 or 3:1) as eluent (see Scheme 1). In order to
enhance the stability of the dicobalt units in 4−7 by a bridging
effect between the two metal atoms, we have also prepared
complexes containing L-L = dppm. These new Co2(CO)4(L-
L)-substituted alkyne compounds, 8−11, have been obtained
by substitution reaction of carbonyl ligands, in the presence of
Me3NO, at the Co2(CO)6 units of 4−7 (see Scheme 1). The
FT-IR spectral changes of these reactions were monitored until
the νCO bands of the parent complex had disappeared. In a
similar manner, we have proceeded to obtain the very unstable
green solid disubstituted-cobalt-alkyne compound 15 from
icosa-9,11-diyne (3)14 (see Scheme 2). On the other hand, the
related complexes 12−14 were isolated, together with the well-
known [Co2(CO)4(μ-L-L){μ2-η2-Me3SiC2}]2(CC)2 (L-L =
dppm15 or dmpm16), from a Pd-catalyzed coupling reaction
between [Co2(CO)4(μ-L-L){μ2-η2-SiMe3C2)](CCH) (L-L =
dppm,15 dmpm16) and 4,4′- diiodoazobenzene, in 2:1 ratio.
The mixture of products, in these reactions, was separated by
TLC silica plates using hexane/CH2Cl2 (4:3) as eluent (see
Scheme 2). All these compounds have been fully characterized
RESULTS AND DISCUSSION
■
Synthesis and Characterization. 1 and 2 have been
synthesized from coupling reactions of 4,4′-diiodoazobenzene
(0) with excess trimethylsilylacetylene (TMSA) and 1-decyne,
respectively, under Sonogashira coupling conditions. From 0
and 1-decyne we have obtained the desired dialkynyl organic
ligand 2, in addition to icosa-9,11-diyne (3)14 as a secondary
product, caused by a side reaction of the terminal acetylene
with itself. Moreover the nonanoic acid has also been obtained
as byproduct in this reaction, probably because terminal alkynes
can undergo oxidative CC cleavage to afford the
corresponding carboxylic acid and CO2. 1 and 2, which have
been completely characterized by analytical and spectroscopic
data (details of which are given in the Experimental Section),
1
by spectroscopic data (IR, UV−vis, H, 13C{1H}, and 31P{1H}
1
NMR, and MS) and elemental analysis, details of which are
given in the Experimental Section.
show in the H NMR spectra two doublet signals due to the
azobenzene ring protons, with coupling constants that are
consistent with their chemical formulations, and in the 13C
NMR spectra six singlet signals belonging to the azobenzene
rings (C1, C2,2′, C3,3′, and C4) and the alkynyl units (C9 and
C10), in addition to the corresponding signals due to the carbon
chain in 2 (Tables 1 and 2). The assignments were made on the
basis of the δ values and two-dimensional NMR experiments
(HMBC and HMQC). The FT-IR spectrum of 1 in CH2Cl2
displays a weak absorption band, typically CC stretches of
the alkynyl unit, in the characteristic range of monoynyl
complexes (one νCC stretch at ca. 2090−2160 cm−1) that
could not be observed in 2. Both organic ligands gave
The IR spectra of Co2(CO)6-substituted alkyne complexes
(C2v symmetry) exhibit four medium to strong absorptions in
the carbonyl stretching region (at ca. 2089, 2054, 2030, and
2025 cm−1). As expected, in phosphine-substituted alkyne
complexes these absorptions lie at lower frequencies (2024−
1969 cm−1 for 8−13 with L-L= dppm and 2014−1953 cm−1 for
14 with L-L= dmpm) because of the donor character of the
ligands, and the spectral patterns are similar to those observed
for previously reported cobalt-alkyne and cobalt-substituted-
alkyne complexes.15−22 Complexes 4, 8, and 12−14 contain
uncomplexed CC triple bonds, which display a νCC weak
C
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Figure 1. ORTEP diagram of 9.
absorption between 2160 and 2145 cm−1 that could not be
observed in 6 or 10.
the diasterotopic protons of the P−CH2−P group are coupled
with the two P atoms, giving two double triplet signals with JHH
and JPH around 13.2 and 10.4 Hz, respectively. These
resonances can also be observed in 14 (L-L = dmpm) with
similar coupling constant values for JHH and JPH. The 13C{1H}
NMR chemical shifts of the carbonyl ligands bonded to the Co2
units, in all complexes, appear as one or two signals at around δ
199 ppm or δ 202 and 207 ppm, which indicates a fast
interchange on the NMR scale. The resonances of the free and
coordinated acetylene units were easily observed, and the
chemical shifts of their carbon atoms are in the range of
analogous complexes (δ 80−105 ppm).15,16,18,22,24 Azobenzene
carbon resonances appear between δ 120 and 155 ppm. The
chemical shift for the C4 atom in 4, 6, 8, and 10 is found to be
very sensitive to cobalt complexation on the adjacent alkyne
and shows a significant downfield shift (from 126 to 142 or 149
ppm) when they become 5, 7, 9, and 11 (Table 2). For
disubstituted-cobalt-azobenzene-decyne complexes, 7 and 11,
the carbon resonances due to the carbon chains, −(CH2)7−
CH3, confirm the chemical equivalence in these molecules,
whereas in the analogous monosubstituted-cobalt-azobenzene-
decyne complexes, 6 and 10, different carbon resonances for
both chains are observed for each of them (see the
Experimental Section). The 13C{1H} NMR spectrum of 15
shows the resonances due to the coordinated carbon atoms in
addition to those of the carbon chains, and, in the same manner
as 7 and 11, the chemical equivalence of the molecule is
demonstrated. The unambiguous assignments of all carbon
All NMR data are consistent with the overall geometry
established in the solid state for 9 (Figure 1) and with the
proposed structures (Schemes 1 and 2). 1H and 13C{1H} NMR
1
data are summarized in Tables 1 and 2. The H NMR spectra
of 1 and 2 prior to irradiation consist of two doublets of
intensity 4 at ca. 7.85 ppm, corresponding to the 2 and 2′
protons, and at ca. 7.55 ppm for the 3 and 3′ protons. The 1H
NMR spectrum of the cis-form is expected to contain a set of
signals similar in pattern to that of the trans-form, but with
different chemical shifts. Under laser irradiation two new
doublets are observed, and both 1H resonances move
significantly upfield (ca. 7.3 and 6.7 ppm), which suggests
that the planar cis configuration leads to increased π-electron
density in the rings. The 1H NMR spectra of 4, 5, 8, 9, and 12−
14 show, as expected, that the −SiMe3 is greatly affected by the
coordination of “Co2(CO)6” or “Co2(CO)4(L-L)” units to an
adjacent −CC− group. In fact, the SiMe3 resonance is
shifted from 0.27 ppm, in the free ligand, to about 0.40 ppm,
owing to the loss of CC triple-bond character.23 In 4−14, the
azobenzene proton signals are consistent with the incorpo-
ration of one or two Co2(CO)6 or Co2(CO)4(L-L) units and
appear as apparent doublets (AA′XX′ system) in the aromatic
compound range (7.0−8.0 ppm). They are easily identified
because of their symmetry (they are mirror images) (Table 1).
The phosphine phenyl rings protons are also observed in this
range. It can be observed that in the 1H NMR spectra of 10−13
D
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Table 3. Selected Bond Distances (Å) and Angles (deg) for 9
N(1)−N(1)#1
C(4)−N(1)
Co(1)−Co(2)
C(11)−C(12)
C(12)−Si(1)
C(1)−C(11)
Co(1)−C(11)
Co(2)−C(11)
N(1)#1−N(1)−C(4)
C(3)−C(4)−N(1)
C(2)−C(3)−C(4)
C(3)−C(2)−C(1)
C(2)−C(1)−C(11)
C(12)−C(11)−C(1)
C(5)−C(4)−N(1)
C(6)−C(5)−C(4)
C(5)−C(6)−C(1)
C(6)−C(1)−C(11)
C(11)−C(12)−Si(1)
C(6)−C(1)−C(11)−C(12)
C(2)−C(1)−C(11)−C(12)
1.263(6)
1.418(5)
2.4631(7)
1.338(5)
1.837(4)
1.456(5)
1.955(4)
1.975(3)
114.4(4)
123.8(3)
119.8(4)
121.2(3)
120.6(3)
139.9(3)
116.4(3)
120.8(4)
120.2(4)
121.2(3)
146.3(3)
62.8(6)
Co(1)−C(12)
Co(2)−C(12)
C(16)−P(1)
C(16)−P(2)
C(17)−P(1)
C(23)−P(1)
C(29)−P(2)
C(35)−P(2)
1.978(4)
1.963(4)
1.831(4)
1.831(4)
1.827(4)
1.827(4)
1.825(4)
1.820(4)
−117.7(5)
atoms have been carried out by using homonuclear and
heteronuclear two-dimensional correlation spectroscopy experi-
ments and by comparison with analogous com-
pounds.15,16,18,22,24 The room-temperature 31P{1H} NMR
spectra in CDCl3 present a broad singlet that is shifted to
higher frequencies (ca. 36 and 13 ppm for dppm and dmpm
complexes, respectively) with respect to that of the free
phosphine ligand because of the coordination. The positive
FAB mass spectra of the substituted-cobalt alkyne complexes
show the respective molecular ion or M+ − CO, as well as
peaks corresponding to the loss of CO ligands.
dicobalt complexes.16,27,29,30 This C−C distance shows a
lengthening of ca. 0.15 Å from the value of 1.192(4) Å found
in (CH3)3Si CCC6H4NNC6H4CCSi(CH3)3,26 and this
reflects the loss of triple-bond character as a result of
coordination of the acetylenic moieties to the Co2 units. The
change in hybridization at C(11)−C(12) is also reflected in the
angles C(12)−C(11)−C(1), 139.9(3)°, and C(11)−C(12)−
Si(1), 146.3(3)°. The bridging ethynyl ligands are twisted out
of the plane of the aryl group. The relevant torsion angles are
C(6)−C(1)−C(11)−C(12), 62.8(6)°, and C(2)−C(1)−
C(11)-C(12), −117.7(5)°.
Description of the Crystal and Molecular Structure of
9. A single-crystal X-ray diffraction study was performed on
complex 9. This study serves the obvious purpose of confirming
the structure presented in Scheme 1. Figure 1 presents a
molecular diagram of 9, and the selected geometric parameters
for this compound have been summarized in Table 3.
Compound 9 crystallizes with three CH2Cl2 molecules in the
monoclinic crystal system, space group P2(1)/c (Table S1). Its
crystal structure consists of discrete monomeric molecules of
[{SiMe3(Co2(CO)4dppm)C2}2{(1,4-C6H4)N}2] in trans-form.
The acetylenic moieties are coordinated to Co2(CO)4dppm
fragments in each case. The “Co2C2” core adopts a
pseudotetrahedral geometry, and each of the cobalt atoms is
also coordinated to two terminal carbonyl ligands and to the
phosphorus atom from the dppm ligand.
The Co−C distances in the “Co2C2” core of 9 range from
1.955(4) to 1.978(4) Å, and these distances do not show an
asymmetry pattern as observed in [{Co2(CO)6(H C
C)}2(C6H4)]29 and in [Co2(CO)4(μ-dppm)]2(μ-η2-HC2(C
C)2C2H).16
The average P−C distance of the bridging dppm ligands,
1.826(4) Å, is normal.31
The bond angle of N(1)#1−N(1)−C(4) is 114.4(4)° and
indicates that the two nitrogen atoms exist at almost sp2
hybridization. The angles C(3)−C(4)−N(1) and C(5)−
C(4)−N(1) are 123.8(3)° and 116.4(3)°, respectively.
Electrochemical Study. Table 4 assembles potential values
for the reduction and oxidation of compounds 1, 2, and 4−13
in CH2Cl2 solution. All values are referred to the Fc*+/Fc*
system.
The electrochemical reductions of 1 and 2 render two
distinct waves in both cases (Figure 2). The first (less negative)
ones at E1/2 = −1.03 and −1.13 V are chemically and
electrochemically reversible either at room temperature or at
−30 °C. The more negative waves at E1/2 = −1.52 and −1.70 V
are chemically quasi-reversible. Reduction potentials are more
negative for 2, as a consequence of the higher electron-donating
nature of the decynyl tails. Positive scans until the limit allowed
by the solvent system (ca. +1.6 V) did not show any
voltammetric oxidation peaks.
The bond length N−N#1 found in 9 is 1.263(6) Å, similar to
those reported in C6H5CCC6H4NNC6H4CCC6H5
(1.264(5) Å),25 (C6H5)4C6HC6H4NNC6H4HC6(C6H5)4
(1.263(3) Å),25 (CH3)3SiCCC6H4NNC6H4CCSi-
(CH3)3 (1.230(5) Å),26 {[Co2(CO)6(μ-HCC)]C6H4N}2
(1.240(5) Å),27 HCCC6H4NNC6H4CCH (1.247(2)
Å),27 and H3CC6H4NNC6H4CH3 (1.251(2) Å).28
The interatomic distance of Co(1)−Co(2), at 2.4631(7) Å,
falls within the normal range for a Co−Co single bond27 and is
similar to Co−Co lengths observed for other dicobalt systems
that are bridged by alkyne ligands.16,27,29,30
Compounds 4−7, containing one (4 and 6) or two (5 and 7)
C2Co2(CO)6 redox centers, lead to quite similar voltammetric
responses. Positive oxidation sweeps show, in all cases, only one
The C(11)−C(12) length, 1.338(5) Å, lies in the range
1.33−1.36 Å reported for the alkylenic C−C bond in related
E
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a
between both peaks (better observed in SWV, Figure 3)
indicates that the less negative process is C2Co2(CO)6-centered
and the more negative one is azobenzene-centered.
Table 4. E1/2 Values for Compounds 1, 2, and 4−13
reduction
oxidation
E1/2
C2Co2(CO)6
E1/2
azob 1
E1/2
E1/2
E1/2
C2Co2
azob 2 C2Co2(CO)6dppm
1
−1.03
−1.13
−1.07
−1.08
−1.12
−1.14
−1.08
−1.15
−1.17
−1.19
−1.04
−1.02
−1.52
−1.70
−1.66
−1.64
−1.71
−1.76
2
4
−0.95
−0.95
−1.01
−0.98
1.23
1.23
1.19
1.18
0.73
0.73
0.66
0.65
0.76
0.76
5
6
7
8
−1.50
−1.63
−1.61
−1.72
−1.74
−1.58
−1.57
b
9
n.d.
−1.60
−1.55
n.d.
10
11
12
13
n.d.
a
All data in V vs Fc*+/Fc* taken from CV and SWV experiments.
n.d. = cannot be determined due to peaks overlapping.
b
Figure 3. Square wave voltammograms for the reduction and oxidation
of solutions of 4 and 5 in CH2Cl2 containing 0.15 M TBAPF6 at −30
°C on a glassy carbon working electrode. Scan increment = 2 mV, SW
amplitude = 25 mV, frequency = 30 Hz.
The voltammetric oxidation sweep of compounds 5 and 7,
with a single bielectronic wave (and not two consecutive
monoelectronic ones), indicates that no electronic communi-
cation between the two equivalent C2Co2(CO)6 units through
the azobenzene bridge can be appreciated by electrochemical
means.
Compounds 8−13 contain C2Co2(CO)4(dppm) redox
centers. Substitution of two CO ligands by electron-donating
dppm makes the redox centers much easier to oxidize and more
difficult to reduce than in 4−7. Also, bidentate dppm stabilizes
cations and anions that are now much more resistant to
chemical decomposition in solution in the time scale of the
electrochemical cyclic and square wave voltammetry (CV and
SWV, respectively) experiments.33
Figure 2. Cyclic and square wave voltammograms for the reduction of
a solution of 1 in CH2Cl2 containing 0.15 M TBAPF6 at 25 °C on a Pt
working electrode. CV: v = 0.1 V s−1; SWV: scan increment = 2 mV,
SW amplitude = 25 mV, frequency = 30 Hz.
Electrochemical oxidation of 8−13 leads to a completely
chemically reversible wave (even at room temperature)
appearing at E1/2 in the 0.65 to 0.76 V range (see Table 4
and Figures 4 and 5) and corresponding to the loss of electrons
from the C2Co2(CO)4(dppm) clusters. The wave is mono-
peak, which is irreversible at 25 °C but turns chemically
reversible at −30 °C (E1/2 around 1.20 V). Thus, the losses of
one (4 and 6) or two (5 and 7) electrons produce cations that
decompose in solution, but these homogeneous reactions are
slow enough so that CV reversible waves can be observed at
−30 °C.
In the reduction sweeps of 4−7, two very close and
irreversible (at 25 °C) peaks are obtained at ca. −1 V. When
the temperature is decreased to −30 °C, the corresponding
anodic peaks can be observed for both processes, but complete
chemical reversibility is not attained. The potential values for
these peaks (see Table 4) indicate that one of them should be
assigned to an azobenzene-group-centered reduction, while the
other should involve reductions centered in the Co2(CO)6
units (which always appear at potentials near −1 V, with small
differences due to the environment of the cluster).18,24b,c,32
Both processes are so close in potential that it is quite difficult
to ensure which of the redox centers corresponds to each of the
reductions in 4−7. However, if we take into account that the
C2Co2(CO)6-cluster-centered reduction corresponds to the
gain of one and two electrons per molecule for 4, 6 and 5, 7,
respectively (analogous to the oxidation processes), while the
reduction centered in the azobenzene ligand involves just one
electron per molecule in all compounds, the intensity difference
Figure 4. Cyclic voltammograms for the reduction and oxidation of a
solution of 8 in CH2Cl2 containing 0.15 M TBAPF6 at −30 °C on a
glassy carbon working electrode at v = 0.1 V s−1.
F
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Article
and 10, but is most evident with 9 and 11, containing two such
donating clusters. However, with compounds 12 and 13, the
intermediate −CC− groups somewhat shield the cluster effect.
When the sweep is extended to even more negative potentials,
some of the compounds show a wave at around −1.55 V, which
is chemically quasi-reversible and can be assigned to a second
reduction centered in the azobenzene ligand. This wave is
clearly distinguished for 8, 10, and 11 (Figure 4), but is partly
masked in the remaining compounds by a further reduction
process, between −1.57 and −1.74 V, which is completely
chemically reversible at low temperature and whose peak
current is equivalent to that of the oxidation process described
above (Figure 5). This process corresponds to
C2Co2(CO)4(dppm)-centered reductions.18,24b,c,33
Compound 15 is closely related to those studied by Duffy et
al.32 At room temperature, reduction renders a single
completely irreversible peak at 1.07 V, as the anion readily
decomposes in solution. However, at −30 °C, the homoge-
neous decomposition is slow enough so that two waves, the
first one chemically reversible and the second one quasi-
Figure 5. Cyclic voltammograms for the reduction and oxidation of a
solution of 9 in CH2Cl2 containing 0.15 M TBAPF6 at −30 °C on a
glassy carbon working electrode at v = 0.1 V s−1.
electronic for 8, 10, and 12 and bielectronic for 9, 11, and 13.
The appearance of a single bielectronic wave for the oxidation
of 9, 11, and 13 (containing two equivalent redox centers)
indicates that no significant electronic communication between
both centers through the azobenzene ligand can be appreciated.
The easier oxidation observed for 10 and 11 agrees with the
more electron donating nature of the organic chain, as also
observed above for the free ligand 2.
When sweeping to negative potentials, a monoelectronic and
completely reversible wave, between −1.02 and −1.19 V,
appears for 8−13 (Table 4, Figures 4 and 5). The
characteristics and potential of this peak allow to assign it
unambiguously to an azobenzene-centered reduction. The
electron-donating C2Co2(CO)4(dppm) group shifts the reduc-
tion of the azobenzene group toward potentials more negative
than for the free ligands 1 and 2. This fact is observed with 8
reversible, are observed at E1/2 = −0.99 and −1.26 V (ΔE1/2
=
270 mV). Correspondingly, two quasi-reversible waves are
observed in the oxidation of 15 at rt (+1.24 and +1.53 V), the
first one chemically reversible at −30 °C. ΔE1/2 = 290 mV
agrees well with the reduction result and with related
compounds32 and shows that significant electronic communi-
cation takes place between both redox centers through the
carbon bridge,33 as expected.
Electronic Absorption Spectra. The UV−vis spectra of
trans-azobenzene derivatives 1, 2, and 9−13 (Table 5) show
three well-separated absorption bands:3,34 the lowest energy
and much weaker one corresponds to the parity-forbidden n →
π* transition at ca. 445 nm (ε = 90 M−1 cm−1) for the organic
ligands and at ca. 472 nm for compounds containing a
Table 5. Electronic Spectral Data and Transition Assignments of Azobenzene Derivative Compounds in DCM
π→π* (nm) ε
n→π* (nm)
Φ→Φ* (nm)
σ→σ* (nm)
MLCT (nm)
(M−1 cm−1
)
ε(M−1 cm−1
)
ε(M−1 cm−1
)
ε(M−1 cm−1
)
ε(M−1 cm−1
)
trans-Cpd
1
368
442
80
249
1600
369
980
2
446
160
457
230
468
660
246
3090
350
1320
258
a
L-12
2300
371
4300
258
a
L-13
2100
382
4190
9
471
238
17 618
334 sh
17 800
472
51 680
236
11
12
13
271 sh
24 860
378
87 140
235
342 sh
2060
474
5300
237
376
2230
2120
6156
cis-Cpd
1
268
447
100
450
210
253
1030
267
1000
255
2
1390
1346
a
L-12 1-[(CC)C2SiMe3]-1′-(I)[(1,4-C6H4)N]2 and L-13 1,1′-[(CC)C2SiMe3]2[(1,4-C6H4)N]2.
G
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Article
1
Figure 6. H NMR spectra of 1 (a) before UV light irradiation and (b) after UV light irradiation.
C2Co2(CO)4(dppm) unit; the strong UV band at ca. 370 nm (ε
= 1600 M−1 cm−1) arises from the symmetry-allowed π → π*
transition; the highest energy band at ca. 240 nm (ε = 700 M−1
cm−1) is due to a Φ → Φ* transition. This may be considered
as localized in the rings, because of the close association of the
Φ orbitals with the benzene rings. In addition, the electronic
spectra of compounds 9−13 present the σ → σ* transition of
the Co−Co bond at ca. 474 nm and the intense MLCT band at
ca. 335 nm. In the cis-azobenzene compounds 1 and 2 while the
n → π* transition is slightly more intense and appears at similar
wavelengths, the π → π* transition is weaker and appears at
higher energy, ca. 235 nm (ε = 750 M−1 cm−1). The marked
difference between the trans- and cis-isomers is due to the
nonplanar configuration of the cis-form.
Photochemical trans-to-cis and Thermal cis-to-trans
Isomerizations. Isomerization kinetics of 1 and 2 were
investigated in dichloromethane (DCM). Excitation in the π →
π* transition leads to an overall trans-to-cis isomerization, while
reverse cis-to-trans isomerization can be induced either
thermally or photochemically by excitation in the n → π*
transition. The rate constants, of both process, were determined
by monitoring the decreasing or increasing absorbance of the
trans-π → π* or cis-π → π* transition (Table S2).
A reverse cis-to-trans reaction is induced thermally, and the
rate constants for the thermal isomerization of 1 and 2 are
summarized in Table S2.
Both processes follow a first-order reaction according to the
kinetic equation
ln[(A0 − A∞)/(At − A∞)] = kt
where A0, At, and A∞ are the initial absorbance, absorbance at
time t, and absorbance at the photostationary state; k is the
isomerization rate constant.
The presence of clear isosbestic points during the course of
the reactions confirms that a transition between only the cis and
the trans species is taking place.
Isomerization is further evidenced by 1H NMR spectra of the
solutions, which clearly show that changes in UV−vis spectra
can be correlated to NMR peaks attributed to the trans- and cis-
forms of compounds 1 and 2 (Figure 6).
The isomerization rate constants of 2 are much lower than
that of 1 (Figure S80), and the half-life time is about twice
higher (Table S2). Photo- and thermal isomerization become
more difficult due to the steric hindrance effect of the decyne
groups.
The experimental rate constants of cobalt complex isomer-
ization processes could not be calculated, because of the
decomposition of the organometallic complex under UV
irradiation to give rise to a free organic ligand.
Undertaking a comparative study with other azobenzene
derivatives12c,35 has not been possible because of the different
experimental conditions.
Mesomorphic Properties of 2. Compounds 8, 9, 10, and
11 do not exhibit mesomorphic behavior. However, compound
2 shows a monotropic liquid-crystalline phase with a nematic
Figure S79 shows typical absorbance changes during trans-to-
cis isomerization of 1 as a function of 365 nm light irradiation
time. Under irradiation the intensity of the absorption peak at
368 nm gradually decreases until an equilibrium state is
reached. At the same time, a new peak at 268 nm gradually
increases and the weaker peak at 447 nm becomes a little more
pronounced. Similar behavior was also observed for compound
2.
H
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mesophase. This mesophase is investigated by polarized optical
microscopy studies (POM), thermogravimetric analysis (TGA),
and differential scanning calorimetry (DSC) (see the SI).
The nematic phase is monotropic, which means that the
mesophase is thermodynamically unstable, and, therefore, it
only appears in the cooling process, due to hysteresis in the
crystallization. Mesophase identification was achieved by
polarized microscopy, with a magnification of 20×. The
polarizing optical microscopy images show a typical nematic
Schlieren texture36,37 when compound 2 is cooling down from
the isotropic liquid at 10 °C/min. The nematic droplets began
to form a nematic texture (Figure 7), but finally, when the
structure of azobenzene and, thus, for 2 are much lower
because of the higher steric effects.
EXPERIMENTAL SECTION
■
General Considerations. All reactions and manipulations were
routinely carried out by using standard Schlenk vacuum-line and
syringe techniques under an atmosphere of oxygen-free Ar. All
solvents for synthetic use were dried and distilled under argon by
standard procedures38 and bubbled with Ar for 1 h after distillation
and before use. The reactions were monitored by IR spectroscopy, 1H
NMR, and TLC, and the products were characterized by IR, 1H,
31P{1H}, and 13C{1H} NMR, DEPT, COSY, HMBC, HMQC, UV−
vis, elemental analyses, and mass spectrometry. Column chromatog-
raphy was performed by using silica gel (60 mesh, 40−63 Å) (Fluka)
and preparative TLC on 20 × 20 cm glass plates coated with silica gel
(SDS 60−17 μm, 0.25 mm thick). Trimethylsililacetylene,
PdCl2(PPh3)2, Co2(CO)8, and PPh3 (Fluka) and 1,2-bis-
(diphenylphosphino)methane (dppm), CuI, 4,4′-diiodoazobenzene,
hexafluorophosphate of tetrabutylamonium, and 1-decyne (Aldrich)
were used as received. Trimethylamine N-oxide (Aldrich) was
sublimed prior to use and stored under Ar. Compounds
[(SiMe3CC)(1,4-C6H4)N]2 (1)39 and [Co2(CO)4(μ-L-L)(μ2-η2-
SiMe3C2)](CCH) (L-L = dppm15 or dmpm16) were prepared
according to the literature. The 1H, 13C{1H}, and 31P{1H} NMR
spectra and HMQC (heteronuclear multiple quantum correlation) and
HMBC (heteronuclear multiple bond correlation) experiments were
recorded on Bruker AMX-300 and Bruker DRX-500 instruments.
Chemical shifts were measured relative to either an internal reference
of tetramethylsilane or residual protons of the solvents. Infrared
spectra were measured on a Nicolet 380 FT-IR spectrometer.
Elemental analyses were performed by the Microanalytical Laboratory
́
of the University Autonoma of Madrid on a PerkinElmer 240 B
microanalyzer. Electronic spectra were recorded on a Unicam UV 2
UV−visible spectrophotometer, 10 mm quartz cells with a capacity of
3.5 cm3 were utilized for measurements, and initial concentrations of
compounds were ca. 10−4 M. Mass spectra were measured on a VG-
Autospec mass spectrometer for FAB and EI by the Mass Laboratory
Figure 7. Polarizing optical photomicrograph (20×) of 2 obtained at
37 °C on cooling from the isotropic liquid.
temperature was reduced to 35.3 °C, a crystalline texture is
formed. On the other hand, the thermogravimetric analysis
showed that the mesogen begins to decompose at 260 °C. The
DSC traces of 2 do not exhibit a nematic phase on heating, but
they reveal a narrow nematic phase on cooling. On the first
heating, compound 2 melts to a isotropic liquid at 52.5 °C (ΔH
= 176 kJ mol−1), and on the first cooling, it enters a nematic
phase at 38.2 °C (ΔH = 13 kJ mol−1) and a crystalline phase at
32.0 °C (ΔH = 151 kJ mol−1), with a short mesophase range of
ΔT = 6.18 °C. The difference in these transition enthalpies is
due to the fact that a larger energy is considered necessary to
interrupt both the positional and the orientational order of the
crystalline phase, while less energy is required to interrupt the
orientational order of the nematic phase.
́
of the University Autonoma of Madrid. Electrochemical measurements
were carried out with an AUTOLAB 30 potentiostat/galvanostat.
Cyclic and square wave voltammetry experiments were performed with
a three-electrode cell under a N2 (>99.9995%) atmosphere. A Pt-mesh
counter electrode and an Ag-wire quasi-reference electrode were used.
The working electrodes were either Pt or glassy carbon disks.
Compounds were dissolved in dry CH2Cl2 containing 0.15 M
tetrabutylammonium hexafluorophosphate (TBAPF6) as supporting
electrolyte. All potential values in this work are referred to the Fc*+/
Fc* (Fc* = decamethylferrocene) system, which was added as internal
reference after each short series of measurements. E1/2 = (Epa + Epc)/2
of the ferrocene/ferricinium couple (Fc+/Fc) was also measured as
+0.55 V vs Fc*+/Fc* in the CH2Cl2 solution. Experiments were
carried out at 25 °C and at −30 °C. For studying the liquid crystalline
behavior, the optical textures of the mesophases were studied with a
Nikon Eclipse LV 100 POL polarizing microscope equipped with a
Linkam hot-stage and Linkam THMS 600 central processor. The
transition temperatures and enthalpies were measured by differential
scanning calorimetry with a TA Instruments Q20 instrument operated
at a scanning rate of 10 °C min−1 on both heating and cooling. The
apparatus was calibrated with indium (156.6 °C; 28.71 J g−1) as the
standard. TGA was carried out in a TGA-Q5000 apparatus at a heating
rate of 10°/min under nitrogen up to 600 °C and under air from 600
to 750 °C.
CONCLUSION
■
Organic ligands have been synthesized from coupling reactions
of 4,4′-diiodoazobenzene with TMSA or 1-decyne, under
Sonogashira coupling conditions. para-Alkynyl azobenzene
derivatives (R-Azo-R) and their organometallic cobalt com-
plexes linked to the azobenzene unit by a π-conjugated carbon
bridge have been synthesized in satisfactory yields by direct
reaction between Co2(CO)8 and the organic ligands.
Complexes containing Co2(CO)4(L-L) have been obtained
by substitution reaction of carbonyl ligands, in the presence of
Me3NO.
[(SiMe3CC)(1,4-C6H4)N]2 (1). To a solution of 4,4′-diiodoazo-
benzene (0.50 g, 1.15 mmol) in Et3N (30 mL) was added, at room
temperature (rt), 1.6 mL (1.10 g, 11.3 mmol) of TMSA in the
presence of the PdCl2(PPh3)2 catalyst (80.7 mg, 0.115 mmol), CuI
(21.9 mg, 0.115 mmol), and PPh3 (60.3 mg, 0.23 mmol). The
resulting mixture was stirred at rt for 36 h. The reaction was monitored
by thin-layer chromatography (TLC). The solvent was evaporated
under reduced pressure, and the residue purified by chromatography
Photochemical and thermal trans-to-cis and cis-to-trans
isomerization processes have been studied for organic ligands.
The rate constants show obvious dependence on the molecular
I
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on a hexane-packed silica column (200 g) using hexane/CH2Cl2 (2:1)
product in high yield (89%) from 2 and Co2(CO)8, in a ratio of 1:2,
and subsequent chromatography with hexane/CH2Cl2 (3:1) on a silica
column.
as eluent, to afford 1 (0.41 g, 95% yield) as a stable orange-red solid.
1
1: IR (CH2Cl2, cm−1): 2155 vw (CC). H NMR (300 MHz,
CDCl3, ppm): δ 7.86 (d, JHH = 8.7 Hz, 2H2,2′); 7.60 (d, JHH = 8.7 Hz,
2H3,3′); 0.27 (s, 18H, 2 −SiMe3). 13C NMR (125 MHz, CDCl3, ppm):
δ 151.9 (s, 2C1); 132.8 (s, 2C3,3′); 126.1 (s, 2C4); 122.9 (s, 2C2,2′);
104.6 (s, 2C9); 97.2 (s, 2C10); −0.1 (s, 2 −SiMe3). MS (EI+, m/z):
374.2 [M+]. Anal. Calcd for C22H26N2Si2 (374.6): C, 70.53; H, 7.00;
N, 7.48. Found: C, 70.68; H, 7.23; N, 7.15.
6: IR (CH2Cl2, cm−1): 2089 m (CO), 2053 vs (CO), 2028 vs (CO),
2022 s (CO). 1H NMR (300 MHz, CDCl3, ppm): δ 7.89 (d, JHH = 8.5
Hz, H6,6′); 7.86 (d, JHH = 8.6 Hz, H2,2′); 7.62 (d, JHH = 8.5 Hz, H7,7′);
7.53 (d, JHH = 8.5 Hz, H3,3′); 3.08 (t, JHH = 8.0 Hz, 4H, 2 −CH2−);
2.45 (t, JHH = 7.0 Hz, 4H, 2 −CH2−); 1.77 (q, JHH = 7.6 Hz, 4H, 2
−CH2−); 1.64 (q, JHH = 7.2 Hz, 4H, 2 −CH2−); 1.49 (q, JHH = 7.3
Hz, 4H, 2 −CH2−); 1.30 (m, 8H, 2 −(CH2)2−); 0.90 (t, JHH = 7.0 Hz,
3H, −CH3); 0.89 (t, JHH = 6.6 Hz, 3H, −CH3). 13C NMR (125 MHz,
CDCl3, ppm): δ 199.6 (s, CO); 151.7 (s, C5); 151.5 (s, C1); 142.0 (s,
C8); 132.4 (s, C3,3′); 129.9 (s, C7,7′); 127.1 (s, C4); 123.5 (s, C6,6′);
122.8 (s, C2,2′); 100.7 (s, C11); 93.6 (s, C9); 89.7 (s, C12); 80.5 (s,
C10); 34.3 (s, C), 32.0 (s, C), 31.9 (s, C), 31.8 (s, C), 29.7 (s, C), 29.4
(s, C), 29.2 (s, 2C), 29.1 (s, C), 29.0 (s, C), 28.7 (s, C), 22.7 (s, C),
22.6 (s, C), and 19.6 (s, C) (14C, 2 −(CH2)7−); 14.2 (s, −CH3); 14.1
(s, −CH3). MS (FAB+, m/z): 741.0 [M+]; 712.0 [M+ − CO]; 656.0
[M+ − 3CO]; 628.0 [M+ − 4CO]; 600.0 [M+ − 5CO]; 573.0 [M+ −
6CO].
{[CH3-(CH2)7-CC][(1,4-C6H4)N]}2 (2) and Icosa-9,11-diyne (3).
To a solution of 4,4′-diiodoazobenzene (0.21 g, 0.48 mmol) in Et3N
(35 mL) and THF (10 mL) was added, at room temperature, 0.87 mL
(0.667 g, 4.83 mmol) of 1-decyne in the presence of PdCl2(PPh3)2
catalyst (33.7 mg, 0.048 mmol), CuI (9.14 mg, 0.048 mmol), and PPh3
(25.18 mg, 0.096 mmol). The resulting mixture was stirred at rt for 60
h. The reaction was monitored by TLC. The solvent was evaporated
under reduced pressure, and the residue purified by chromatography
on a hexane-packed silica column (200 g) using hexane as eluent, to
afford 2 (185 mg, 84% yield) as a stable orange solid in addition to the
well-known icosa-9,11-diyne (3)14 and nonanoic acid, as byproducts.
7: IR (CH2Cl2, cm−1): 2089 m (CO), 2053 vs (CO), 2029 vs (CO),
2023 s (CO). 1H NMR (300 MHz, CDCl3, ppm): δ 7.91 (d, JHH = 8.4
Hz, 2H6,6′); 7.63 (d, JHH = 8.4 Hz, 2H7,7′); 3.00 (t, JHH = 8.0 Hz, 4H, 2
−CH2−); 1.69 (q, JHH = 7.6 Hz, 4H, 2 −CH2−); 1.45 (q, JHH = 7.4
Hz, 4H, 2 −CH2−); 1.32 (m, 4H, 2 −CH2−); 1.22 (m, 12H, 2
−(CH2)3−); 0.82 (t, JHH = 6.8 Hz, 6H, 2 −CH3). 13C NMR (125
MHz, CDCl3, ppm): δ 199.5 (s, CO); 151.8 (s, 2C5); 142.1 (s, 2C8);
129.9 (s, 2C7,7′); 123.4 (s, 2C6,6′); 100.8 (s, 2C11); 89.7 (s, 2C12); 34.3
(s, 2C), 32.0 (s, 2C), 31.8 (s, 2C), 29.7 (s, 2C), 29.4 (s, 2C), 29.2 (s,
2C) and 22.7 (s, 2C) (14C, 2 −(CH2)7−); 14.1 (s, 2C, 2 −CH3). MS
(FAB+, m/z): 1026.5 [M+]; 914.5 [M+ − 4CO]; 802.5 [M+ − 8CO];
746.5 [M+ − 10CO].
1
2: H NMR (300 MHz, CDCl3, ppm): δ 7.83 (d, JHH = 8.6 Hz,
2H2,2′); 7.51 (d, JHH = 8.6 Hz, 2H3,3′); 2.44 (t, JHH = 7.0 Hz, 4H, 2
−CH2−); 1.63 (q, JHH = 7.1 Hz, 4H, 2 −CH2−); 1.47 (m, 4H, 2
−CH2−); 1.31 (m, 16H, 2 −(CH2)4−); 0.89 (t, JHH = 6.7 Hz, 6H, 2
−CH3). 13C NMR (125 MHz, CDCl3, ppm): δ 151.3 (s, 2C1); 132.3
(s, 2C3,3′); 127.0 (s, 2C4); 122.8 (s, 2C2,2′); 93.5 (s, 2C9); 80.5 (s,
2C10); 31.8 (s), 29.2 (s), 29.1 (s), 28.9 (s), 28.6 (s), 22.6 (s), and 19.6
(s) (14C, 2 −(CH2)7−); 14.1 (s, 2C, 2 −CH3). MS (FAB+, m/z):
455.3 [M+]. Anal. Calcd for C32H42N2 (454.7): C, 84.53; H, 9.31; N,
6.16. Found: C, 84.70; H, 9.40; N, 6.00.
1-[Co2(CO)6{μ2-η2-C2SiMe3}]-1′-(CCSiMe3)[(1,4-C6H4)N]2 (4) and
1,1′-[Co2(CO)6){μ2-η2-C2SiMe3}]2[(1,4-C6H4)N]2 (5). To a solution of 1
(0.40 g, 1.07 mmol) in CH2Cl2 (50 mL) was added 0.5 equiv of
1-[Co2(CO)4(μ-dppm){μ2-η2-C2SiMe3}]-1′-(CCSiMe3)[(1,4-
C6H4)N]2 (8). A solution of 4 (41 mg, 0.062 mmol) and 0.062 mmol of
dppm in CH2Cl2 (50 mL) was prepared. Trimethylamine N-oxide
(13.8 mg, 0.124 mmol) was added, and the reaction mixture,
monitored by FT-IR, was stirred at 40 °C for 24 h. The reaction
was stopped when all the starting material had been consumed. After
removal of solvent under vacuum, the residue was purified by TLC
using hexane/CH2Cl2 (2:1) as eluent, to afford 8 (56.4 mg, 92% yield)
as a stable reddish-brown solid.
1
Co2(CO)8. The reaction mixture was monitored by FT-IR, H NMR
spectroscopy, and TLC until the signals of the parent compounds, 1
and Co2(CO)8, had disappeared. After stirring the mixture at room
temperature for 26 h, the solvent was removed under vacuum and the
residue was purified by TLC using hexane/CH2Cl2 (2:1) as eluent, to
afford 4 (226 mg, 32% yield) and 5 (202 mg, 20% yield) as unstable
reddish-brown solids. 5 has also been obtained as the only product in
high yield (97%) from 1 and Co2(CO)8, in a ratio of 1:2, and
subsequent chromatography with hexane/CH2Cl2 (2:1) on a silica
column.
8: IR (CH2Cl2, cm−1): 2155 vw (CC), 2019 s (CO), 1994 vs
1
(CO), 1966 s (CO). H NMR (300 MHz, CDCl3, ppm): δ 7.89 (d,
4: IR (CH2Cl2, cm−1): 2159 vw (CC), 2088 m (CO), 2054 s
JHH = 8.6 Hz, H2,2′); 7.73 (d, JHH = 8.5 Hz, H6,6′); 7.63 (d, JHH = 8.6
Hz, H3,3′); 7.25 (d, JHH = 8.5 Hz, H7,7′); 7.30−7.08 (m, 12H), (8H, m-
Ph), (4H, p-Ph); 6.99 (t, JHH = 7.4 Hz, 8H, o-Ph); 3.36−3.27 (m, 2H,
P-CH2-P); 0.37 (s, 9H, −CSiMe3); 0.29 (s, 9H, CSiMe3). 31P NMR
(121 MHz, CDCl3, ppm): δ 34.8 (s br, 2P, P-CH2-P). 13C NMR (125
MHz, CDCl3, ppm): δ 207.3 (m, CO); 202.8 (m, CO); 152.3 (s, C1);
150.6 (s, C5); 148.9 (s, C8); 138.7 (t, JCP = 24.4 Hz, i-Ph); 134.5 (t, JCP
= 16.6 Hz, i-Ph); 132.9 (s, C3,3′); 132.7 (t, JCP = 6.5 Hz, o-Ph); 130.4
(s, C7,7′); 130.3 (t, JCP = 5.9 Hz, o-Ph); 129.7 (s, p-Ph); 129.2 (s, p-
Ph); 128.5 (t, JCP = 4.7 Hz, m-Ph); 127.9 (t, JCP = 4.7 Hz, m-Ph);
125.4 (s, C4); 123.1 (s, C6,6′); 122.7 (s, C2,2′); 104.8 (s, C9); 104.7 (t,
JCP = 7.5 Hz, C11); 97.0 (s, C10); 90.1 (t, JCP = 10.0 Hz, C12); 35.7 (t,
JCP = 20.6 Hz, P-CH2-P); 0.89 (s, −CSiMe3); −0.03 (s, CSiMe3).
MS (FAB+, m/z): 989.2 [M+]; 961.2 [M+ − CO]; 933.2 [M+ −
2CO]; 905.2 [M+ − 3CO]; 877.2 [M+ − 4CO].
1
(CO), 2027 vs (CO). H NMR (300 MHz, CDCl3, ppm): δ 7.89 (d,
JHH = 8.7 Hz, H6,6′); 7.86 (d, JHH = 8.5 Hz, H2,2′); 7.64 (d, JHH = 8.7
Hz, H7,7′); 7.60 (d, JHH = 8.5 Hz, H3,3′); 0.43 (s, 9H, −CSiMe3); 0.28
(s, 9H, CSiMe3). 13C NMR (125 MHz, CDCl3, ppm): δ 199.7 (s,
CO); 152.1 (s, C5); 151.8 (s, C1); 142.1 (s, C8); 132.9 (s, C3,3′); 130.6
(s, C7,7′); 125.9 (s, C4); 123.6 (s, C6,6′); 122.8 (s, C2,2′); 104.7 (s, C9);
103.7 (s, C11); 97.3 (s, C10); 80.3 (s, C12); 0.91 (s, −CSiMe3); −0.07
(s, CSiMe3). MS (FAB+, m/z): 632.1 [M+ − CO]; 576.1 [M+ −
3CO]; 548.1 [M+ − 4CO]; 520.1 [M+ − 5CO]; 492.1 [M+ − 6CO].
5: IR (CH2Cl2, cm−1): 2088 m (CO), 2053 s (CO), 2023 vs (CO).
1H NMR (300 MHz, CDCl3, ppm): δ 7.90 (d, JHH = 8.5 Hz, 2H6,6′);
7.65 (d, JHH = 8.5 Hz, 2H7,7′); 0.43 (s, 18H, 2 −CSiMe3). 13C NMR
(125 MHz, CDCl3, ppm): δ 199.8 (s, CO); 152.0 (s, 2C5); 142.0 (s,
2C8); 130.7 (s, 2C7,7′); 123.6 (s, 2C6,6′); 103.8 (s, 2C11); 80.3 (s,
2C12); 0.92 (s, 2 −SiMe3). MS (FAB+, m/z): 918.1 [M+ − CO]; 862.1
[M+ − 3CO]; 806.1 [M+ − 5CO].
1,1′-[Co2(CO)4(μ-dppm){μ2-η2-C2SiMe3}]2[(1,4-C6H4)N]2 (9). The
procedure described above was used, but with 5 (115 mg, 0.12
mmol), dppm (0.24 mmol), and trimethylamine N-oxide (0.48 mmol)
as reactants. A stable reddish-brown solid was obtained (185 mg, 95%
yield).
1-[Co2(CO)6{μ2-η2-C2-(CH2)7-CH3}]-1′-[CH3-(CH2)7-CC][(1,4-
C6H4)N]2 (6) and 1,1′-[Co2(CO)6{μ2-η2-C2-(CH2)7-CH3}]2[(1,4-C6H4)N]2
(7). To a solution of 2 (150 mg, 0.33 mmol) in CH2Cl2 (40 mL) was
added 0.5 equiv of Co2(CO)8. The reaction mixture was monitored by
FT-IR, 1H NMR spectroscopy, and TLC until the signals of the parent
compounds, 2 and Co2(CO)8, disappeared. After stirring the mixture
at room temperature for 72 h, the solvent was removed under vacuum
and the residue was purified by TLC using hexane/CH2Cl2 (3:1) as
eluent, to afford 6 (85.5 mg, 35% yield) and 7 (77.9 mg, 23% yield) as
unstable reddish-brown solids. 7 has also been obtained as an only
9: IR (CH2Cl2, cm−1): 2017 s (CO), 1991 vs (CO), 1966 s (CO).
1H NMR (300 MHz, CDCl3, ppm): δ 7.69 (d, JHH = 8.1 Hz, 2H6,6′);
7.21 (d, JHH = 8.3 Hz, 2H7,7′); 7.24−7.03 (m, 24H) (16H, m-Ph), (8H,
p-Ph); 6.93 (t, JHH = 7.5 Hz, 16H, o-Ph); 3.30 (m, 2H, 2 P-CH2-P);
3.25 (m, 2H, 2 P-CH2-P); 0.38 (s, 18H, 2 −CSiMe3). 31P NMR (121
MHz, CDCl3, ppm): δ 34.9 (s br, 4P, 2 P-CH2-P). 13C NMR (125
MHz, CDCl3, ppm): δ 207.3 (m, CO); 202.8 (m, CO); 150.9 (s,
J
DOI: 10.1021/acs.organomet.5b00257
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
2C5); 147.9 (s, 2C8); 138.8 (t, JCP = 24.3 Hz, i-Ph); 134.6 (t, JCP
=
0 °C, PdCl2(PPh3)2 (13.3 mg, 0.019 mmol), CuI (3.6 mg, 0.019
mmol), PPh3 (10.0 mg, 0.038 mmol), and [Co2(CO)4(μ-dppm)(μ2-
η2-SiMe3C2)](CCH)15 (0.28 g, 0.38 mmol). After 30 min, the
reaction mixture was progressively warmed to room temperature and
stirred for 72 h. After the solvent was removed under vacuum, the
residue was extracted with CH2Cl2 and purified by TLC using hexane/
CH2Cl2 (4:3) as eluent, to afford 12 (band 1) (79.2 mg, 40% yield)
and 13 (band 3) (62.7 mg, 20% yield) as stable reddish-brown solids
in addition to [Co2(CO)4(μ-dppm){μ2-η2-SiMe3C2}]2(CC)2 (band
2), whose spectroscopy data are already reported in and are consistent
with the compound described above.15
16.5 Hz, i-Ph); 132.7 (t, JCP = 6.4 Hz, o-Ph); 130.5 (s, 2C7,7′); 130.4 (t,
JCP = 5.9 Hz, o-Ph); 129.7 (s, p-Ph); 129.2 (s, p-Ph); 128.5 (t, JCP = 4.7
Hz, m-Ph); 127.9 (t, JCP = 4.7 Hz, m-Ph); 122.9 (s, 2C6,6′); 104.8 (t,
JCP = 7.4 Hz, 2C11); 89.8 (t, JCP = 10.0 Hz, 2C12); 35.7 (t, JCP = 20.6
Hz, 2 P-CH2-P); 0.94 (s, 2 −CSiMe3). MS (FAB+, m/z): 1603.1 [M+];
1575.1 [M+ − CO]; 1547.1 [M+ − 2CO]; 1519.1 [M+ − 3CO];
1463.1 [M+ − 5CO]; 1435.1 [M+ − 6CO]; 1407.1 [M+ − 7CO];
1379.1 [M+ − 8CO].
1-[Co2(CO)4(μ-dppm){μ2-η2-C2-(CH2)7-CH3}]-1′-[CH3-(CH2)7-CC]-
[(1,4-C6H4)N]2 (10). A solution of 6 (50.0 mg, 0.0675 mmol) and
0.0675 mmol of dppm in CH2Cl2 (50 mL) was prepared.
Trimethylamine N-oxide (15.0 mg, 0.135 mmol) was added, and the
reaction mixture, monitored by FT-IR, was stirred at 45 °C for 48 h.
The reaction was stopped when all the starting material had been
consumed. After removal of the solvent under vacuum, the residue was
purified by TLC using hexane/CH2Cl2 (3:2) as eluent, to afford 10
(64.2 mg, 89% yield) as a stable dark red solid.
12: IR (CH2Cl2, cm−1): 2155 vw (CC), 2020 s (CO), 1993 vs
1
(CO), 1965 s (CO). H NMR (300 MHz, CDCl3, ppm): δ 7.90 (d,
JHH = 8.5 Hz, H6,6′); 7.88 (d, JHH = 8.6 Hz, H3,3′); 7.68 (d, JHH = 8.6
Hz, H2,2′); 7.46 (d, JHH = 8.5 Hz, H7,7′); 7.31−7.19 (m, 12H), (8H, m-
Ph), (4H, p-Ph); 7.14−7.09 (m, 8H, o-Ph); 3.96 (dt, JHH = 13.3 Hz,
JPH = 10.9 Hz, 1H, ABXY, P-CH2-P); 3.32 (dt, JHH = 13.0 Hz, JPH
=
10.1 Hz, 1H, ABXY, P-CH2-P); 0.41 (s, 9H, −CSiMe3). 31P NMR
(121 MHz, CDCl3, ppm): δ 37.3 (s br, 2P, P-CH2-P). 13C NMR (125
MHz, CDCl3, ppm): δ 207.0 (m, CO); 201.6 (m, CO); 152.1 (s, C1);
150.9 (s, C5); 138.5 (s, C3,3′); 137.8 (m, i-Ph); 137.7 (m, i-Ph); 134.5
(m, i-Ph); 134.4 (m, i-Ph); 132.7 (t, JCP = 6.5 Hz, o-Ph); 132.6 (t, JCP
= 6.4 Hz, o-Ph); 131.8 (s, C7,7′); 131.1 (t, JCP = 6.0 Hz, o-Ph); 131.0 (t,
JCP = 6.0 Hz, o-Ph); 129.9 (s, p-Ph); 129.8 (s, p-Ph); 129.4 (s, p-Ph);
129.3 (s, p-Ph); 128.4 (t, JCP = 4.8 Hz, m-Ph); 128.3 (t, JCP = 3.7 Hz,
m-Ph); 128.2 (t, JCP = 4.9 Hz, m-Ph); 128.1 (t, JCP = 4.8 Hz, m-Ph);
124.5 (s, C2,2′); 123.2 (s, C6,6′); 97.8 (s, C4); 96.9 (s, C8); 94.7 (s,
C10); 90.5 (m, C11); 82.4 (s, C9); 76.7 (m, C12); 37.8 (t, JCP = 20.2 Hz;
P-CH2-P); 0.59 (s, −CSiMe3). MS (FAB+, m/z): 1013.7 [M+ − CO];
957.7 [M+ − 3CO]; 929.7 [M+ − 4CO].
10: IR (CH2Cl2, cm−1): 2024 s (CO), 1998 vs (CO), 1974 s (CO).
1H NMR (300 MHz, CDCl3, ppm): δ 7.86 (d, JHH = 8.5 Hz, H2,2′);
7.75 (d, JHH = 8.5 Hz, H6,6′); 7.53 (d, JHH = 8.5 Hz, H3,3′); 7.33 (d, JHH
= 8.5 Hz, H7,7′); 7.30−7.20 (m, 12H), (8H, m-Ph), (4H, p-Ph); 7.17
(t, JHH = 7.0 Hz, 4H, o-Ph); 7.08 (t, JHH = 7.3 Hz, 4H, o-Ph); 3.28 (dt,
JHH = 13.1 Hz, JPH = 10.3 Hz, 1H, ABXY, P-CH2-P); 3.16 (dt, JHH
=
13.0 Hz, JPH = 10.5 Hz, 1H, ABXY, P-CH2-P); 3.05−2.96 (m, 2H,
−CH2−); 2.45 (t, JHH = 7.0 Hz, 2H, −CH2−); 1.73−1.60 (m, 4H, 2
−CH2−); 1.52−1.45 (m, 2H, −CH2−); 1.32−1.23 (m, 18H, 9
−CH2−); 0.90 (t, JHH = 6.7 Hz, 3H, −CH3); 0.86 (t, JHH = 6.7 Hz, 3H,
−CH3). 31P NMR (121 MHz, CDCl3, ppm): δ 37.7 (s br, 2P, P-CH2-
P). 13C NMR (125 MHz, CDCl3, ppm): δ 206.1 (m, CO); 202.2 (m,
CO); 151.7 (s, C1); 150.4 (s, C5); 148.5 (s, C8); 138.0 (t, JCP = 22.2
13: IR (CH2Cl2, cm−1): 2145 vw (CC), 2023 s (CO), 1998 vs
1
(CO), 1975 s (CO). H NMR (300 MHz, CDCl3, ppm): δ 7.99 (d,
Hz, i-Ph); 135.5 (t, JCP = 17.5 Hz, i-Ph); 132.3 (s, C3,3′); 132.2 (t, JCP
6.5 Hz, o-Ph); 130.8 (t, JCP = 6.1 Hz, o-Ph); 129.7 (s, p-Ph); 129.5 (s,
7,7′); 129.2 (s, p-Ph); 128.3 (t, JCP = 4.6 Hz, m-Ph); 128.0 (t, JCP
=
JHH = 8.4 Hz, 2H6,6′); 7.54 (d, JHH = 8.4 Hz, 2H7,7′); 7.50−7.26 (m,
24H), (16H, m-Ph), (8H, p-Ph); 7.24−7.15 (m, 16H, o-Ph); 4.02 (dt,
C
=
JHH = 13.4 Hz, JPH = 10.7 Hz, 2H, ABXY, 2 P-CH2-P); 3.38 (dt, JHH
=
4.7 Hz, m-Ph); 126.5 (s, C4); 123.0 (s, C6,6′); 122.6 (s, C2,2′); 105.5
(m, C11); 93.2 (s, C9); 92.5 (t, JCP = 8.2 Hz, C12); 80.6 (s, C10); 35.7
(s, C); 35.6 (m, P-CH2-P); 31.86 (s, C), 31.85 (s, C), 31.6 (t, JCP = 2.5
Hz, C), 29.9 (s, C), 29.4 (s, C), 29.3 (s, C), 29.2 (s, C), 29.1 (s, C),
29.0 (s, C), 28.7 (s, C), 22.68 (s, C), 22.66 (s, C), and 19.6 (s, C)
(14C, 2 −(CH2)7−); 14.12 (s, −CH3); 14.09 (s, −CH3). MS (FAB+,
m/z): 1041.0 [M+ − CO]; 957.0 [M+ − 4CO].
13.4 Hz, JPH = 10.1 Hz, 2H, ABXY, 2 P-CH2-P); 0.47 (s, 18H, 2
−CSiMe3). 31P NMR (121 MHz, CDCl3, ppm): δ 37.3 (s br, 4P, 2 P-
CH2-P). 13C NMR (125 MHz, CDCl3, ppm): δ 207.1 (m, CO); 201.7
(m, CO); 151.3 (s, 2C5); 137.8 (t, JCP = 23.2 Hz, i- Ph); 134.5 (t, JCP
=
17.7 Hz, i-Ph); 132.6 (t, JCP = 6.4 Hz, o-Ph); 131.8 (s, 2C7,7′); 131.1 (t,
JCP = 6.1 Hz, o-Ph); 129.9 (s, p-Ph); 129.4 (s, p-Ph); 128.4 (t, JCP = 4.7
Hz, m-Ph); 128.2 (t, JCP = 4.8 Hz, m-Ph); 123.1 (s, 2C6,6′); 96.8 (s,
2C8); 94.8 (s, 2C10); 90.7 (m, 2C11); 82.9 (s, 2C9); 76.6 (m, 2C12);
37.8 (t, JCP = 20.1, 2 P-CH2-P); 0.60 (s, 2 −CSiMe3). MS (FAB+, m/
z): 1651.9 [M+]; 1623.9 [M+ − CO]; 1567.9 [M+ − 3CO]; 1539.9
[M+ − 4CO]; 1511.9 [M+ − 5CO]; 1483.9 [M+ − 6CO]; 1455.9 [M+
− 7CO]; 1427.9 [M+ − 8CO].
1,1′-[Co2(CO)4(μ-dppm){μ2-η2-C2-(CH2)7-CH3}]2[(1,4-C6H4)N]2 (11).
The procedure described above was used, but with 7 (50.3 mg, 0.049
mmol), dppm (0.098 mmol), and trimethylamine N-oxide (0.196
mmol) as reactants. A stable reddish-brown solid was obtained (70.9
mg, 86% yield).
11: IR (CH2Cl2, cm−1): 2022 s (CO), 1997 vs (CO), 1973 s (CO).
1H NMR (300 MHz, CDCl3, ppm): δ 7.76 (d, JHH = 8.4 Hz, 2H6,6′);
7.32 (d, JHH = 8.4 Hz, 2H7,7′); 7.28−7.18 (m, 28H), (16H, o-Ph), (8H,
m-Ph), (4H, p-Ph); 7.15 (t, JHH = 7.4 Hz, 4H, p-Ph); 7.06 (t, JHH = 7.4
Hz, 8H, m-Ph); 3.27 (dt, JHH = 13.0 Hz, JPH = 10.3 Hz, 2H, ABXY, 2
P-CH2-P); 3.17 (dt, JHH = 13.0 Hz, JPH = 10.4 Hz, 2H, ABXY, 2 P-
CH2-P); 3.02−2.97 (m, 4H, 2 −CH2−); 1.69−1.66 (m, 4H, 2
−CH2−); 1.37−1.33 (m, 4H, 2 −CH2−); 1.26−1.22 (m, 16H, 8
−CH2−); 0.85 (t, JHH = 7.0 Hz, 6H, 2 −CH3). 31P NMR (121 MHz,
CDCl3, ppm): δ 37.7 (s br, 4P, 2 P-CH2-P). 13C NMR (125 MHz,
CDCl3, ppm): δ 206.2 (m, CO); 204.1 (m, CO); 150.8 (s, 2C5); 147.7
(s, 2C8); 138.0 (t, JCP = 22.2 Hz, i-Ph); 135.6 (t, JCP = 17.5 Hz, i-Ph);
132.3 (t, JCP = 6.4 Hz, o-Ph); 130.9 (t, JCP = 6.1 Hz, o-Ph); 129.8 (s,
2C7,7′); 129.6 (s, p-Ph); 129.3 (s, p-Ph); 128.4 (t, JCP = 4.6 Hz, m-Ph);
128.1 (t, JCP = 4.7 Hz, m-Ph); 122.9 (s, 2C6,6′); 105.9 (m, 2C11); 92.7
(m, 2C12); 35.8 (s, 2C); 35.7 (m, 2 P-CH2-P); 31.9 (s, 2C), 31.7 (s,
2C), 30.0 (s, 2C), 29.5 (s, 2C), 29.3 (s, 2C), and 22.7 (s, 2C) (14C, 2
−(CH2)7−); 14.1 (s, 2C, 2 −CH3). MS (FAB+, m/z): 1655.4 [M+ −
1-[Co2(CO)4(μ-dmpm){μ2-η2-(CC)C2SiMe3}]-1′-(I)[(1,4-C6H4)N]2
(14). The procedure described above was used from 4,4′-
diiodoazobenzene (18.0 mg, 0.041 mmol), PdCl2(PPh3)2 (10%
mmol), CuI (10% mmol), and PPh3 (20% mmol), but with
[Co2(CO)4(μ-dmpm)(μ2-η2-SiMe3C2)](CCH)16 (40.5 mg, 0.082
mmol) as terminal alkyne. 14 was obtained as a stable reddish-brown
solid in 25% yield in addition to [Co2(CO)4(μ-dmpm){μ2-η2-
SiMe3C2}]2(CC)2, whose spectroscopy data are already reported
in and are consistent with the compound described above.16
14: IR (CH2Cl2, cm−1): 2152 vw (CC), 2014 s (CO), 1985 vs
1
(CO), 1953 s (CO). H NMR (300 MHz, CDCl3, ppm): δ 7.91 (d,
JHH = 8.5 Hz, 4H, H6,6′, H3,3′); 7.69 (d, JHH = 8.6 Hz, H2,2′); 7.54 (d,
JHH = 8.5 Hz, H7,7′); 2.78 (dt, JHH = 13.5 Hz, JPH = 10.0 Hz, 1H,
ABXY, P-CH2-P); 2.17 (dt, JHH = 13.6 Hz, JPH = 10.1 Hz, 1H, ABXY,
P-CH2-P); 1.58 (m, 12H, Me2P-CH2-PMe2); 0.36 (s, 9H, −CSiMe3).
31P NMR (121 MHz, CDCl3, ppm): δ 13.7 (s br, 2P, P-CH2-P). MS
(FAB+, m/z): 793.8 [M+]; 765.8 [M+ − CO]; 737.8 [M+ − 2CO];
709.8 [M+ − 3CO]; 681.8 [M+ − 4CO].
CO]; 1627.4 [M+ − 2CO]; 1571.4 [M+ − 4CO]; 1543.4 [M+
5CO]; 1515.4 [M+ − 6CO]; 1459.4 [M+ − 8CO].
−
[Co2(CO)6{μ2-η2-C2-(CH2)7-CH3}]2 (15). To a solution of icosa-9,11-
diyne (3) (111.0 mg, 0.406 mmol) in hexane (50 mL) was added
Co2(CO)8 (277.9 mg, 0.812 mmol), and the reaction mixture was
stirred at room temperature for 24 h. The reaction was monitored by
FT-IR and 1H NMR spectroscopy until the signals of the parent
1-[Co2(CO)4(μ-dppm){μ2-η2-(CC)C2SiMe3}]-1′-(I)[(1,4-C6H4)N]2
(12) and 1,1′-[Co2(CO)4(μ-dppm){μ2-η2-(CC)C2SiMe3}]2[(1,4-
C6H4)N]2 (13). To a solution of 4,4′-diiodoazobenzene (82.0 mg,
0.19 mmol) in Et3N (30 mL) were added, under stirring and cooling at
K
DOI: 10.1021/acs.organomet.5b00257
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
compounds had disappeared. After the solvent was removed under
vacuum, the residue was extracted with hexane/CH2Cl2 (5:1) and
purified by TLC using hexane/CH2Cl2 (3:1) as eluent, to afford 15
(337.0 mg, 98% yield) as a unstable dark red solid.
AUTHOR INFORMATION
Corresponding Authors
*E-mail (C. Moreno): mconsuelo.moreno@uam.es.
*E-mail (M. L. Marcos): mluisa.marcos@uam.es.
Notes
■
15: IR (CH2Cl2, cm−1): 2060 s (CO), 2006 vs (CO), 1960 sh
(CO). 1H NMR (300 MHz, CDCl3, ppm): δ 2.88 (m, 4H, 2 −CH2−);
1.79 (q, JHH = 7.7 Hz, 4H, 2 −CH2−); 1.57 (q, JHH = 7.2 Hz, 4H, 2
−CH2−); 1.35 (m, 4H, 2 −CH2−); 1.31 (m, 12H, 2 −(CH2)3−); 0.94
(m, 6H, 2 −CH3). 13C NMR (125 MHz, CDCl3, ppm): δ 199.4 (s,
CO); 106.8 (s, 2C) and 91.8 (s, 2C) (4Ccoord); 33.5 (s, 2C), 31.9 (s,
2C), 31.8 (s, 2C), 29.6 (s, 2C), 29.4 (s, 2C), 29.2 (s, 2C), and 22.6 (s,
2C) (14C, 2 −(CH2)7−); 14.1 (s, 2C, 2 −CH3).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Support for this work is acknowledged from the Comunidad de
Madrid (FOTOCARBON-CM S2013/MIT-2841), Spain.
■
[Co2(CO)4(μ-dmpm){μ2-η2-C2-(CH2)7-CH3}]2 (16). A solution of 15
(100 mg, 0.114 mmol) and 0.011 mmol of dmpm in CH2Cl2 (50 mL)
was prepared. Trimethylamine N-oxide (34.3 mg, 0.456 mmol) was
added, and the reaction mixture, monitored by FTIR, was stirred at
room temperature for 10 days. The reaction was stopped when all the
starting material had been consumed. After removal of the solvent
under vacuum, the residue was extracted with CH2Cl2 and purified by
TLC using hexane/CH2Cl2 (2:1) as eluent, to afford 16 (25 mg, 21%
yield) as a very unstable green-red solid.
́
́
Thanks to Joaquın Barbera Gracia (Universidad de Zaragoza,
Spain) for technical and scientific support.
REFERENCES
■
(1) (a) Ichimura, K. In Organic Photochromic and Thermochromic
Compounds; Crano, J. C.; Guglielmetti, R. J., Eds.; Kluwer Academic
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Supporting Information. CCDC-1047086 (9) contains the supple-
mentary crystallographic data for this paper. These data can be
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