Preliminary results of the reaction of cyclotrimerization of phenylacetylene [2+2+2] catalyzed by [(Cp?)Co(Indene)] complex

Article abstract of DOI:10.4067/s0717-97072018000103898

This work describes the catalytic study of [(Cp?)Co(Ind)] (with Cp?= pentamethylcyclopentadienyl, Ind= Indenyl, (C₉H₇)) complex in cyclotrimerization of phenylacetylene. From the cylcotrimerization reaction was possible to obtain products such as substituted pyridines 2-methyl-3,5-diphenylpyridine (3), 2-methyl- 4,6-diphenylpyridine (4) and the compound 1,2,4-triphenylbenzene (5) using acetonitrile as solvent. On the other hand, using toluene as solvent under the same working conditions, the product of reaction was 1,3,5-triphenylbenzene (1). Furthermore, by varying the working conditions, the reaction is 90% selective towards the formation of pyridines. In addition, has been appreciated the formation of another product 1,4-diphenilbuta-1,3-diyne (2), which was isolated and characterized by means NMR and GC-Mass spectrometry.

Full text of DOI:10.4067/s0717-97072018000103898

J. Chil. Chem. Soc., 63, Nº 1 (2018)
PRELIMINARY RESULTS OF THE REACTION OF CYCLOTRIMERIZATION OF PHENYLACETYLENE
[2+2+2] CATALYZED BY [(Cp*)Co(Indene)] COMPLEX
1
1
2
2
CESAR MORALES-VERDEJO*, MARÍA BELÉN CAMARADA, VERÓNICA MORALES, ÁLVARO CAÑETE,
3
2
2
IVÁN MARTÍNEZ, JUAN MANUEL MANRIQUEZ, IVONNE CHÁVEZ.*
1
Centro de Nanotecnología Aplicada, Facultad de Ciencias, Universidad Mayor, Santiago, Chile
2
Departamento de Química Inorgánica, Facultad de Química Pontificia Universidad Católica de Chile Vicuña Mackenna 4860, Macul, Santiago, Chile.
3
Universidad Bernardo OHiggins, Departamento de Ciencias Químicas y Biológicas, Centro Integrativo de Biología y Química Aplicada, General Gana 1702,
Santiago, Chile.
ABSTRACT
This work describes the catalytic study of [(Cp*)Co(Ind)] (with Cp*= pentamethylcyclopentadienyl, Ind= Indenyl, (C H )) complex in cyclotrimerization of
9
7
phenylacetylene. From the cylcotrimerization reaction was possible to obtain products such as substituted pyridines 2-methyl-3,5-diphenylpyridine (3), 2-methyl-
,6-diphenylpyridine (4) and the compound 1,2,4-triphenylbenzene (5) using acetonitrile as solvent. On the other hand, using toluene as solvent under the same
4
working conditions, the product of reaction was 1,3,5-triphenylbenzene (1). Furthermore, by varying the working conditions, the reaction is 90% selective towards
the formation of pyridines.
In addition, has been appreciated the formation of another product 1,4-diphenilbuta-1,3-diyne (2), which was isolated and characterized by means NMR and
GC-Mass spectrometry.
Keywords: cobalt complex, cyclotrimerization, [2+2+2] cycloadditions.
INTRODUCTION
2. EXPERIMENTAL SECTION
The transition-metal catalyzed [2+2+2] cycloaddition of alkynes is a very
powerful method for the construction of arenes in a single operational step and
during the past four decades this reaction has been extensively investigated
and the topic reviewed thorough [1-10], and this type of reaction has been
extensively studied using several transition metals [11-20].
2.1. General Information of the catalyst.
All manipulations were carried out under a pure dinitrogen atmosphere by
using a vacuum atmosphere dry box equipped with a Model HE 493 Dri-Train
purifier or with the use of a vacuum line by using standard Schlenk techniques.
The solvents were dried and distilled according to standard procedures
[29].
Cobalt complexes of type [(Cp)Co(L) ] (L = CO, PR , alkenes) have
2
3
been used extensively for mediating cyclization of alkynes, often with high
levels of chemo-, regio-, and stereoselectivity. Although the mechanism of
this reaction has been the subject of multiple experimental and computational
studies, it is not as yet fully elucidated. After pioneering semiempirical
The synthesis of the following complex has been reported previously:
[(Cp*)Co(Ind)], with Cp*= pentamethylcyclopentadiene, and Ind= Indene,
1
13
C H [30] H and C NMR spectra were recorded on Bruker AC-400
9
7
Spectrometer. Chemical shifts were reported in ppm relative to residual
solvents by using deuterated acetone and chloroform.
[21,22] and ab initio efforts [23], a more detailed DFT analysis was reported
by Albright and co-workers in 1999 [24]. In that work are presented [(Cp)
Co(PH ) ] as a model precatalyst and ethyne as a model reagent. Initially one
2.2 General conditions of the catalytic tests
3
2
and then two alkyne moieties displace sequentially two phosphines from the
metal to form alkyne complexes. Bisalkyne complex undergoes spontaneous
oxidative coupling to give the corresponding coordinatively unsaturated [(Cp)
Cobaltacyclopentadiene]. Subsequently, the [(Cp)Cobaltacyclopentadiene]
and ethyne transform into the final intermediate [(Cp)Co(η -benzene)] for
release later a benzene molecule.
On the other hand, Bönnemman in 1978 [25] showed a study in which it
is stated that the [(Cp)Co]- unit is responsible for the formation of pyridines
by reacting acetylene with acetonitrile. Since that time it is proposed that the
mechanism of the reaction both to form an arene as a pyridine passes through
an intermediary metallocyclic of 5 members.
A two-necked flask equipped with a magnetic stirring bar was charged
with the catalytic amount of complex [(Cp*)Co(Ind)] and Zn powder.
Phenylacetylene was used as substrate and the solvent varied between toluene
and acetonitrile depending on the case.
The reactor was evacuated and filled with dinitrogen. The reaction flask
was immersed in an 80 ºC thermo-stabilized bath. The progress of the reaction
was monitored by GC-MS MAT-95X Thermofinnigan with ionization energy
of 70eV. The products obtained were isolated using a silica gel column and
eluted with hexane.
4
3. RESULTS AND DISCUSSION
Inallstudiesavailableinliteratureoncyclotrimerizationcatalyzedbycobalt
z
complexes of type [(Cp )Co(L) ] (z = H, CH ; L= CO, PH , PR ) and carried
The simultaneous cyclotrimerization reaction of acetylenes and nitriles
makes it possible to prepare various benzene and pyridine derivatives in one
step. Cobalt catalysts are generally used as catalysts in these reactions [22-29].
The principles of this reaction process, especially in the case of substituted
acetylenes and nitriles, have not been adequately investigated.
2
3
3
3
out in organic solvents is accepted for the formation of the products in this type
of reaction, in which it is observed that the first step is the discoordination of
the ligand of the metal center to generate the catalytically active species [(Cp)
I
Co ]- which is in charge of forming the metallocycle that give rise to the cyclic
compound. However, to the extent of our knowledge, there is little information
on examples of half-metallocene complexes without the discoordination of
one of its ligands, the sole example of [(Cp)Co(-η -cyclooctadiene)] complex
Thus, the reaction of 5 mg (0.01 mmol) of [(Cp*)Co(Ind)] with 5 mL (50
mmol) of phenylacetylene at 80 ºC for a period of 3 h, gave the corresponding
product depending on the solvent used (toluene or acetonitrile).
4
[26,27]. On the other hand, to the best of our knowledge, the sole example
of cobaltocene species described up to now used as catalyst in cycloaddition
reaction copolymerization of 1,11-dodecadiyne with acetonitrile in toluene at
3.1 Solvent effect
The reaction carried out in toluene at 80 ºC, it was observed the product
formation of cyclotrimerization [2+2+2] 1,3,5-triphenylbenzene (1) (scheme
1
50 °C to afford a poly(pyridine) with a molecular weight up to 18000, which
1
+
is the first example of an efficient cycloaddition copolymerization of a terminal
diyne [28].
1) analyzed using H-NMR and GC-MS (M 306 m/e) (figure 1) and with a
reaction time of 12.66 min. Observed 100% selectivity towards the formation
of this product.
This contribution describes the approach for the preliminary results of the
[
(Cp*)Co(Ind)] complex in its catalytic behavior in cyclotrimerization [2+2+2]
In the case of the reaction carried out in toluene it is logical that only
triphenylbenzene is formed as product of a cycloaddition of phenylacetylene,
the noteworthy about this reaction is that only one isomer was formed
1,3,5-triphenylbenzene (1), red color with 100% selectivity, were not observed
in the presence of acetonitrile and phenylacetylene, in order to gain further
knowledge of the working conditions on its selectivity catalytic towards the
formation of pyridines.
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e-mail: cesar.morales@umayor.cl, ichavez@uc.cl

J. Chil. Chem. Soc., 63, Nº 1 (2018)
1
traces by H-NMR spectroscopy of isomer 1,2,4-triphenylbenzene (5) as it was
The products (2) and (5) were isolated and characterized by GC-MS
independently (see figures 2 and 5). The products (3) and (4) were observed
clearly by GC-MS (figure 3 and 4) but despite many efforts failed to date to
separate the two isomers, currently yielding a crystalline solid red intense able
to form films.
observed when carrying out the same reaction under the same conditions but
using acetonitrile as a solvent. Probably, the difference in the formation of
the isomers was primarily due to the nature of the solvent, toluene is a bulkier
molecule solvent than the acetonitrile, which could “guide” by steric hindrance
to the formation of only one product having phenyls 1,3,5 interleaved positions
in respect to benzene.
Scheme 1: Cycloaddition reaction [2+2+2] phenylacetylene catalyzed by
Figure 2: Mass spectrum of 1,4-diphenilbuta-1,3-diyne (2)
[(Cp*)Co(Ind)] in toluene.
Figure 1: Mass spectrum of 1,3,5-triphenylbenzene (1).
On the other hand, when the reaction was carried out in acetonitrile
Figure 3: Mass spectrum of 2-methyl-3,5-diphenylpyridine (3)
(scheme 2), was observed the formation of four different products. The first
of these corresponds to the reaction product of 1,4-diphenylbuta-1,3-diyne (2)
+
(
M 202 m/e) (figure 2), with a reaction time of de 10.46 min.
The second products correspond to the formation of substituted pyridines.
+
Two structural isomers were observed. The molecular ion corresponds to M
2
45 m/e with a reaction time of 10.92 min for 2-methyl-3,5-diphenylpyridine
(3) and reaction time of 11.05 min for 2-methyl-4,6-diphenylpyridine (4)
(figure 3 and 4 respectively).
Thefourthproductcorrespondstothereactionproductofcyclotrimerization
+
1
1
,2,4-triphenylbenzene (5) (M 306 m/e) (figure 5), with a reaction time of
2.61 min.
Figure 4 Mass spectrum of 2-methyl-4,6-diphenylpyridine (4)
.2 Study of effect of amount of catalyst on the product distribution.
3
This study was carried out under the conditions previously described
for 3 h of reaction using acetonitrile as solvent and 1.7 mL (1.6 mmol) of
phenylacetylene. The range of amount of catalyst [(Cp*)Co(Ind)] was used
-3
between 0.003 g (9.7·10 mmol) and 0.500 g (1.6 mmol) maintaining the
amount of phenylacetylene. The results obtained are shown in table 1.
Scheme 2: Reaction of phenylacetylene catalyzed by [(Cp*)Co(Ind)] in
acetonitrile.
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J. Chil. Chem. Soc., 63, Nº 1 (2018)
the formation of pyridines and by increasing the amount of catalyst was not
favored but the relative ratio of the products, being the constant between 8 h
and 24 h reaching 92% selectivity.
Figure 5: Mass spectrum of 1,2,4-triphenylbenzene (5)
Table 1: Distribution of products according to amount of catalyst.
Cat/
phenylacetylene
Catalyst
(mol)
Catalyst
(g)
Relative proportion
(2):(3):(4):(5)
-
3
1
: 1
1.60 e
0.500
0.250
0.124
0.005
0.003
1 : 9 : 66 : 24
3 : 12 : 72 : 13
6 : 11 : 80 : 3
36 : 5 : 39 : 20
13 : 0 : 0 : 87
Figure 6: Relative distribution 0.25:1 in Acetonitrile.
-
4
4
0
.5 : 1
8.0 e
4.0 e
3
.3.2 Test used as solvent toluene (5mL) and phenylacetylene
-
stoichiometric amounts of catalyst in a ratio 1:3; 187 mg (0.61 mmol) of [(Cp*)
Co(Ind)] and 0.2 mL (1.83 mmol) of phenylacetylene in order to observe the
effect on product formation (1) and phenylacetylene consumption. Monitoring
was carried out for 24 h, showing only the formation of 1,3,5-triphenylbenzene
0
0
.25 : 1
.01 : 1
-
5
1.60 e
-6
0
.005 : 1
9.70 e
(
1).
The selectivity shown by the catalyst towards these products was between
0% and 91% depending on the amount of catalyst used. The study of variation
of amount of catalyst was obtained that the optimum ratio to achieve high
selectivity towards the formation of pyridines is 0.25:1 ratio catalyst/substrate
3
.3.3 Test used as solvent toluene (5 mL) and stoichiometric amounts of
6
catalyst, phenylacetylene and acetonitrile in a ratio 1:5:1; 592 mg (1.92 mmol)
of [(Cp*)Co(Ind)] and 1.1 mL (9.59 mmol) of phenylacetylene and 0.1 mL
1.92 mmol) acetonitrile in order to observe the effect on the products (2) (3)
(
(
phenylacetylene), where it is possible see that the sum of (3) and (4) reaches
and (4) and consumption of phenylacetylene . The results are shown in Table 3.
9
1% of products, where the product (4) was mostly favored. By drastically
reducing the amount of catalyst the products (3) and (4) were practically not
formed, being favored the formation the compounds (2) and (5). This suggests
the importance of the catalyst in the formation of pyridines.
The formation of the compound (2), via dimerization of the phenylacetylene
is favored by temperature (80 °C) and the presence of a solvent such as
acetonitrile which could shown no steric hindrance as is observed with toluene.
In the same way, the formation of the product (5) was favored by mentioned
above.
Table 3: Product distribution and catalyst substrates in a 1:5:1
Relative proportion
Entry
Time (h)
(2):(3):(4):(5)
4 : 41 :43 : 12
2 : 32 : 56 : 10
3 : 36 : 53 : 9
2 : 34 : 55 : 9
1
2
3
4
0
1
2
3
3
.3 Study of reaction with substrate and catalyst in stoichiometric
combination.
.3.1 Test used as solvent CH CN (5 mL) and phenylacetylene
3
2 : 33
3
5
4
stoichiometric amounts of catalyst in a ratio 1:5; 113 mg (0.36 mmoles) of
(Cp*)Co(Ind)] and 0.2 mL (1.83 mmol) of phenylacetylene, in order to observe
:55 : 10
[
6
7
8
9
5
6
2 : 35 : 54 : 9
3 : 36 : 53: 8
3 : 36 : 53: 8
3 : 38 : 51: 8
the effect on the formation of the products (2), (3) and (4) and consumption
of phenylacetylene. Monitoring the reaction, it was performed for 24 h. The
results are shown in Table 2.
7
24
Table 2: Distribution of products with catalyst and
This test was performed attempting to drive the reaction towards the
formation of one of the pyridines, but in this case the formation of the four
products was also observed in constant relative ratio over time (table 3). The
same phenomenon was observed when performing a test stoichiometric in all
participating reactants in the formation of products, ie 1 mol of catalyst : 5
mol of phenylacetylene : 1 mol of acetonitrile in toluene as solvent. Although
the relative ratio of the products is constant, in this ratio can be seen that if the
amount of product (3) obtained compared with that observed in the relationship
0.25:1, this is much more favored decreasing the amount of (4) formed (Figure
substrate in proportion 1:5.
Relative proportion
Entry
Time (h)
(2):(3):(4):(5)
1
2
3
0
8
24 : 14 : 45 : 17
1 : 30 : 62 : 7
1 : 29 : 62 : 8
24
7
). In the figure 7 were plotted some important time of this reaction. If the total
Reaction samples taken every hour checking that the relative ratio remains
practically constant during the reaction time, always favoring the concentration
of pyridines, especially the product (4). In the figure 6 were plotted some
important time of this reaction.
selectivity compared toward the formation of both pyridines have this remains
in the ranges previously described (≈90%). This reaction was monitored until
24 h where almost total consumption of phenylacetylene used (1.1 mL, 9.59
mmol) was observed.
In this case it is possible to appreciate that the selectivity was aimed at
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J. Chil. Chem. Soc., 63, Nº 1 (2018)
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1
1
1
4. N. Weding, M. Hapke, Chem. Soc.Rev. 40, 4525 (2011).
5. G. Domꢂniguez, G.Peꢃez-Castells, J. Chem. Soc. Rev. 40, 3430 (2011).
6. M.S.B Wills, R.L. Danheiser. J. Am. Chem. Soc 120, 9378 (1998).
7. Y. Sato, T. Tamura, M. Mori. Angew. Chem. Int. Ed. Engl. 43, 2436
(2004).
1
8. A.G. Ardizzoia, S. Brenna, S. Cenini, G. LaMonica, N. Masciocchi, A.
Maspero, J. Mol. Catal. A. Chemical. 204-205, 333 (2004).
1
2
9. J. Varela, C. Saá. J. Organomet. Chem. 694, 143 (2009).
0. G. Hilt, W. Hess, T. Vogler, C. Hengst, J. Organomet. Chem. 690, 5170
(2005).
2
2
1. A. Stockis, R. Hoffmann, J. Am. Chem. Soc. 102, 2952 (1980).
2. C. Bianchini, K.G. Caulton, C. Chardon, M.-L. Doublet, O. Eisenstein,
S.A. Jackson, T.J. Johnson, A. Meli, M. Peruzzini, W.E. Streib, A. Vacca,
F. Vizza,. Organometallics 13, 2010 (1994).
2
2
3. J.M. O’Connor, K.D. Bunker, A.L. Rheingold, L. Zakharov, J. Am. Chem.
Soc. 127, 4180 (2005). ꢀ
4. J.H. Hardesty, J.B. Koerner, T.A. Albright, G.-Y. Lee, J. Am. Chem. Soc.
1
21, 6055 (1999).
2
2
5. H. Bönnemman. Angew. Chem. Int. Ed. 17, 505 (1978).
6. M.S. Sigman, A.W. Fatland, B.E. Eaton. J. Am. Chem. Soc. 120, 5130
(1998).
Figure 7: Relative distribution of products in relation cat/phenylacetylene/
acetonitrile 1:5:1 in Toluene.
27. A.W. Fatland, B.E. Eaton, Org. Lett., 2, 3131 (2000).
8. T. Tsuda, H. Maehara, Macromolecules 29, 4544 (1996).
2
4
. CONCLUSION
29. C. L. L. C. W.L.F. Armarego, Purification of Laboratory Chemicals, Fifth
ed., (2003).
Preliminary results have demonstrated that [(Cp*)Co(Ind)] complex is an
efficient catalyst in the synthesis of organic compounds via cyclotrimerization
2+2+2], especially efficient in the formation of substituted pyridines (3) and
4) when phenylacetylene cycloaddition reaction performed in the presence of
acetonitrile both as solvent and reagent, presenting in both cases 90% selectivity
toward the formation of these products, which could be useful in many organic
synthesis. The amount of catalyst used in the reaction does not affect the
relative proportion of formation of pyridines in all cases maintaining high
selectivity. By performing the same reaction in toluene as solvent, the [(Cp*)
Co(Ind)] compound, acts as an effective generator 1,3,5-triphenylbenzene (1)
presenting 100% selectivity towards the formation of this product.
30. Morales V. Study of the catalytic behavior of mononuclear organometallic
complexes of Rh, Ni and Co in the dehydrogenative silylation of
olefins (written in Spanish Estudio del comportamiento catalitico de
complejos organometálicos mononucleares de Rh, Ni y Co en Sililaciꢄn
deshidrogenativa de olefinas), Ph.D. thesis. Pontificia Universidad Catꢄlica
de Chile; (2010). https://www.researchgate.net/publication/321587889
[
(
Although the results are promising, it is worth noting that more evidence is
needed such as studies of polarity differences of the solvents and the role that
plays in the reaction, different substrates and the mechanism of this reaction
via discoordination of the ligand, presumably as it is reported in much of the
literature for such reactions, or perhaps, could occur by changes hapticity of the
indenyl ligand. This hypothesis is still under study and a theoretical simulations
of this system also could prove the rate-determing step for the catalytic cycle
where the highest energy step is the release or changes hapticity of an ancilliary
ligand from the cobalt center.
Further studies must be developed to improve the catalytic activity, we
also have the intention of performing the synthesis of new heterobimetallic
systems in order to get insights on the cooperative effects between metals,
catalytic properties and material science applications of these complexes.
ACKNOWLEDGEMENT
We gratefully acknowledge the financial support from FONDECYT
Grants 1161297, 1141138, 1060588, 1020525 and 1180023.
5
. REFERENCES
1
2
3
.
.
.
H. Bönnemman, Angew. Chem. Int. Ed. 24, 248 (1985).
M. Lautens,W. Klute, W. Tam, Chem. Rev. 96, 49 (1996).
V. Gevorgyan, U. Radhakrishnan, A. Takeda, M. Rubina, M. Rubin, Y.
Yamamoto, J. Org. Chem. 66, 2835 (2001).
4
5
6
7
8
.
.
.
.
.
Y. Yamamoto, Curr. Org. Chem. 9, 503 (2005).
S. Kotha, E. Brahmachar, K. Lahiri, Eur. J. Org. Chem. 4741, (2005).
P.R. Chopade, J. Louie, J. Adv. Synth. Catal. 348, 2307 (2006).
V. Gandon, C. Aubert, M. Malacria, Chem. Commun. 2209 (2006).
N. Agenet, V. Gandon, K. P. C. Vollhardt, M. Malacria, C. Aubert, J. Am.
Chem. Soc. 129, 8860 (2007).
9
.
Ph. Rꢀse, C. C. Magraner Garcia, F. Pꢁnner, K. Harms, G. Hilt, J. Org.
Chem., 80, 7311 (2015).
1
1
1
1
0. A. A. More, C. V. Ramana, J. Org. Chem., 81, 3400 (2016).
1. K. P. C. Vollhardt, Angew. Chem., Int. Ed. Engl. 23, 539 (1984).
2. N.E. Schore, Chem. Rev. 88, 1081 (1988).
3. B.M. Trost, Science 254, 1471 (1991).
3
901