Synthesis of 2,2′-Bis(silyl)azobenzenes by Oxidation of 2-(Silyl)anilines

Article abstract of DOI:10.1134/S1070363220010119

A method was developed for the synthesis of 2,2′-bis(trimethylsilyl)- and 2,2′-bis(triethoxysilyl)-azobenzenes based on oxidation of 2-(silyl)anilines with trimethylamine and N-methylmorpholine oxides in the presence of CuX (X = Cl, Br).

Full text of DOI:10.1134/S1070363220010119

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 1, pp. 78–83. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Obshchei Khimii, 2020, Vol. 90, No. 1, pp. 104–110.
Synthesis of 2,2'-Bis(silyl)azobenzenes by Oxidation
of 2-(Silyl)anilines
N. F. Lazarevaa,* and B. A. Gostevskiia
a A.E. Favorskii Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, 664033 Russia
*e-mail: nataly_lazareva@irioch.irk.ru
Received June 20, 2019; revised June 20, 2019; accepted June 25, 2019
Abstract—A method was developed for the synthesis of 2,2'-bis(trimethylsilyl)- and 2,2'-bis(triethoxysilyl)-
azobenzenes based on oxidation of 2-(silyl)anilines with trimethylamine and N-methylmorpholine oxides in the
presence of CuX (X = Cl, Br).
Keywords: 2-(silyl)anilines, oxidation, 2,2'-bis(trimethylsilyl)azobenzene, 2,2'-bis(triethoxysilyl)azobenzene
DOI: 10.1134/S1070363220010119
The molecular design, the development of new
methods for the synthesis and investigation of physico-
chemical properties of aromatic azo-compounds attract
the attention of researchers during several decades (see,
e.g., reviews [1–8]). Such an enhanced interest is due to
their ability to the cis/trans photoisomerization and wide
application in the chemistry of materials, medical and
analytical chemistry, chemical and food industry. In 2001,
the first representatives of 2-silylsubstituted azobenzenes
A (Scheme 1) which are of special interest, have been
synthesized [9–18].
of these compounds in the design of molecular switches,
nonlinear optical devices, information recording and
storage systems, alternative energy sources. Therefore,
development of efficient methods for the synthesis of Si-
containing azobenzenes is a priority task of organosilicon
chemistry. Nowadays, there are several approaches to the
synthesis of 2-silylsubstituted azobenzenes. The principal
well-approved method for their synthesis is the reaction
of chlorosilanes with lithiated azobenzenes (Scheme 2)
[9–15].According to the data of [9], the preferred starting
reagent in these reactions is 2-iodoazobenzene, because
the use of 2-bromoazobenzene substantially decreases
the yield of the target product (the yield of 2-trimethyl-
silylazobenzene is 80 and 25%, respectively).
The ability of the silicon atom to extension of the
coordination number when interacting with nitrogen-
containing ligands (see, e.g., [19, 20]) is manifested
in 2-(fluorosilyl)azobenzenes as the formation of in-
tramolecular coordination bond N=N→Si-F. The most
important result of these studies is the establishing of
correlation between the process of reversible cis/trans-
photoisomerization of 2-(fluorosilyl)substituted azo-
benzenes and variation of the silicon atom coordination
number. This ability gives a potential possibility of the use
Since recently, the methods of direct CH-silylation of
aromatic compounds are intensively studied [21]. 2-(Tri-
ethylsilyl)azobenzene was synthesized by the reaction
of СН-silylation with triethylsilane in the presence of
Ru3(CO)12 in 49% yield [22]. The method of the synthesis
of symmetrical 2,2'-bis(trimethylsilyl)azobenzene in 22%
yield by oxidation of the corresponding 2-(trimethylsilyl)-
Scheme 1.
Scheme 2.
Ar
R3Si
N N
Ar
Ar
R3Si
N N
X
N N
(1) n-BuLi, THF
(2) R3SiCl
A
78

SYNTHESIS OF 2,2'-BIS(SILYL)AZOBENZENES
79
Scheme 3.
Me3Si
N N
SiMe3
Me3Si
NH2
,
KMnO4
CuSO4·5H2O
CHCl3, '
22%
Scheme 4.
N(SiMe3)2
I
NH2
I
NH2
X3Si
(1) n-BuLi
(2) ClSiX3
Et2NSiMe3, MeI
PhMe
3
1, 2
SiX3 = SiMe3 (1), Si(OEt)3 (2).
aniline with potassium permanganate was developed
(Scheme 3) [9].
morpholine oxide (NMМO). 2-(Trimethylsilyl)aniline
1 and 2-(triethoxysilyl)aniline 2 were synthesized from
2-iodoaniline in two steps (Scheme 4).
Unfortunately, this method was not developed further.
Yet, the methods of synthesis of organic azobenzenes
based on the reactions of oxidation of anilines with vari-
ous oxidants are intensively developed in recent years
[23–29]. The presence of organosilicon substituents
in the benzene ring, especially those containing labile,
easily hydrolyzed Si–X bonds (X = Hal, OR or NRR'),
imposes restrictions on the use of this method. However,
it can be assumed that the use of mild oxidants would
allow avoiding or minimizing side reactions at the Si–C
and Si–X bonds. Amine oxides are known to be used
in synthetic organic chemistry as oxidants [30, 31]. In
particular, recently symmetrical organic azobenzenes
have been synthesized in 69–90% yields by oxidation
of anilines with the system CuBr–N-methylmorpholine
oxide [23]. The analysis of the literature data showed that
N-methylmorpholine oxide can be used for oxidation of
2-silylsubstituted anilines: the Si–O–C, Si–C, Si–O–Si
bonds of organosilicon oligodesoxyribonucleotide
turned out to be stable under the conditions of oxidation
of its allyl group with N-methylmorpholine oxide, and
the expected derivative of 1,2-diol was isolated in 90%
yield [32].
Earlier, it was shown that N,N-bis(silyl)anilines are
formed in good yields in the reaction of the correspond-
ing anilines with N-(trimethylsilyl)diethylamine in the
presence of MeI [33]. Under these conditions, 2-iodo-
N,N-bis(trimethylsilyl)aniline 3 was isolated in 81%
yield. Compounds 1 and 2 were obtained by metalation
of aniline 3 with hexane solution of n-BuLi with subse-
quent treatment with the corresponding chlorosilane. The
N-trimethylsilyl protecting group was removed by reflux
with ethanol, the yields after distillation were 69 and 51%
for anilines 1 and 2, respectively.
The reaction of 2-silylsubstituted anilines 1 and 2 with
TMAO and NMМO in acetonitrile solution gives rise to
the formation of symmetrical 2,2'-bis(silyl)azobenzenes
4 and 5 (Scheme 5). The oxidation reaction conditions
were optimized on the example of compound 1 (Table 1).
The reaction was carried out at room temperature,
because at reflux of the reaction mixture the yield of the
target product was sharply decreased and a large amount
of unidentified by-products was formed. As catalysts,
copper(I) salts were used; no oxidation occurred in the
absence of the catalyst (see runs 1 and 11 in Table 1).
The maximum yields of 2,2'-bis(trimethylsilyl)azoben-
zene 4 were obtained by oxidation of compound 1 in the
system NMMO/CuBr and TMAO/CuCl (76 and 78%,
respectively) at room temperature. When using CuI as
The goal of the present work is to develop an effi-
cient method of synthesis of symmetrical 2,2'-bis(silyl)-
azobenzenes based on the reactions of oxidation of
2-(trimethylsilyl)aniline 1 and 2-(triethoxysilyl)aniline
2 with trimethylamine oxide (TMAO) and N-methyl-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 1 2020

80
LAZAREVA, GOSTEVSKII
Table 1. Effect of the conditions of the reaction of oxidation of 2-trimethylsilylaniline on the yield of compound 4
Run no.
Oxidant
NMMO
NMMO
NMMO
NMMO
NMMO
NMMO
NMMO
NMMO
NMMO
NMMO
TMAO
TMAO
TMAO
TMAO
TMAO
Air
Solvent
MeCN
MeCN
MeCN
MeCN
MeCN
MeOH
MeCN
MeOH
MeCN
MeOH
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
Catalyst, (25 mol%)
Time, h
48
Yield, %
–
1
2
–
CuBr
CuBr
CuBr
CuBr
CuBr
CuCl
CuCl
CuI
12
58
76
77
60
51
71
42
67
59
–
3
48
4
72
5
24
6
48
7
48
8
48
9
48
10
11
12
13
14
15
16
CuI
48
–
48
CuBr
CuBr
CuCl
CuI
24
59
72
78
63
12
48
48
48
CuBr
24
a catalyst, the yield of the product is somewhat lower
(other conditions being equal). Optimal reaction time
was 48 h, prolongation of the reaction to 72 h does not
lead to notable change of the yield of the target product.
2,2'-Bis[(triethoxy)silyl)]azobenzene 5 is formed in low
yield by oxidation of aniline 2 both with the system
NMMO/CuBr and TMAO/CuCl (19 and 23%, respec-
tively). Apparently, this is connected with the fact that
water eliminated in the oxidation reaction (Scheme 6)
leads to the hydrolysis of the Si–OEt bonds of reagent 2
and product 5.
5 in a higher yield as compared to other additives (the
isolated yield was 52%). Compound 5 was isolated as a
viscous orange oil. After storage for a month in a sealed
tube, the growth of thin crystals was observed, but we
failed to obtain crystals appropriate for X-ray analysis.
Therefore, it was shown that 2-silylsubstituted anilines
are oxidized by amine oxides in the presence of copper
salts with retention of the Si–C and Si–OC bonds to give
symmetrical 2,2'-bis(silyl)azobenzenes. The developed
methods can be applied in laboratory practice for prepara-
tion of azobenzenes with labile functional groups.
Because of this, we have studied the effect of additives
absorbing or chemically binding water on the yield of
compound 5 (Table 2).As the additives, molecular sieves
and alumina were tested, and as reagents, anhydrous
salts Na2SO4, MgSO4 and dicyclohexylcarbodiimide
(DСС). The use of DСС, reacting with water to give
N,N'-dicyclohexylurea, allowed to prepare compound
EXPERIMENTAL
Commercial 2-iodoaniline, n-BuLi solution, tri-
methylamaine and N-methylmorpholine oxides, tri-
methylchlorosilane, MeI, CuCl, CuBr, CuI were used.
The solvents were dried by standard procedures [34].
Chlorotriethoxysilane was synthesized by the earlier
Scheme 5.
2-Me3SiC6H4N=NC6H4SiMe3-2
2-Me3SiC6H4NH2
4
1
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SYNTHESIS OF 2,2'-BIS(SILYL)AZOBENZENES
Table 2. Effect of water-binding additives on th yield of compound 5
81
Run no.
Sorbent
Molecular sieves 4 Å
Molecular sieves 3 Å
Аl2O3
Amount, gа
Yield, % Run no. Reagent
Amount, mmolа
Yield, %
1
2
3
1.0
1.0
1.5
27
29
19
4
5
6
Na2SO4
MgSO4
DCC
6
6
4
21
35
52
а To 2 mmol of compound 2.
described procedure [35]. All reactions were performed
in dry argon atmosphere.
119.26, 131.23, 137.48, 154.68. 29Si NMR spectrum: δSi
–57.62 ppm. Found, %: C, 56.19; H, 8.03; N, 5.57.
C12H21NO3Si. Calculated, %: C 56.44; H 8.29; N 5.48.
1Н, 13С and 29Si NMR spectra were registered on
Bruker DPX-400 and Bruker AV-400 spectrometers
(400.13, 100.61, and 161.90 MHz, respectively) in
CDCl3 and CD3CN solutions, internal standard HMDS
or cyclohexane.
2-Iodo-N,N-bis(trimethylsilyl)aniline (3). To the
solution of 32 g (0.22 mol) N-(trimethylsilyl)diethylamine
in 100 mL of toluene 31.25 g (0.22 mol) of methyl iodide
was added dropwise at room temperature and the mixture
was stirred for 4 h at 50°С. Then, the solution of 22 g
(0.1 mol) of 2-iodoaniline in 150 mL of toluene was
slowly added dropwise at vigorous stirring. The tem-
perature of the reaction mixture was rised to 75°С and
stirred at this temperature for 18 h. The formed precipitate
was filtered, washed with benzene (2×25 mL). From the
combined filtrate the solvent was removed, the residue
distilled in vacuum. Yield 32.3 g (89%), bp 122–125°С
2-(Trimethylsilyl)aniline (1). To the solution of 11 g
(0.03 mol) of 2-iodo-N,N-bis(trimethylsilyl)aniline 3
in 75 mL of diethyl ether cooled to –78°С, 19.5 mL
(~0.03 mol) of 1.6 M. solution of n-BuLi in hexane was
added dropwise at vigorous stirring. The reaction mixture
was kept at this temperature for 4 h, then 3.33 g (0.03 mol)
of trimethylchlorosilane was slowly added. The reaction
mixture was allowed to stay overnight, then added 5 mL
of methanol and heated at 40–45°С during 8 h, cooled,
the precipitate filtered and washed with ether (2×10 mL).
From the combined filtrate the solvent was removed, the
residue distilled. Yield 3.42 g (69%), colorless oil, bp
81–83°С (1.5 mmHg), nD = 1.5246. 1Н NMR spectrum, δ,
ppm: 0.35 s (9H, SiMe3), 3.85 br.s (2H, NH2), 6.76–7.21
m (4 H,Ar). 13C NMR spectrum, δC, ppm: –0.52, 115.34,
118.25, 119.63, 130.28, 136.13, 151.72. 29Si NMR spec-
trum: δSi –6.25 ppm. Found, %: 65.24; H, 9.03; N, 8.62.
C9H15NSi. Calculated, %: C 65.39; H, 9.15; N, 8.47.
1
(2 mmHg). H NMR spectrum, δ, ppm: 0.14 s (18H,
Me3Si); 6.78–6.90, 7.22, 7.84 m (4H, Ar). 13C NMR
spectrum, δC, ppm: 2.06, 95.36, 122.58, 122.78, 126.75,
140.72, 151.12. 29Si NMR spectrum: δSi 7.1 ppm. Found,
%: C 39.92; H 6.34; N 3.97. C12H22INSi2. Calculated, %:
C 39.66; H 6.10; N 3.85.
2,2'-Bis(trimethylsilyl)azobenzene (4). To the solu-
tion of 0.16 g (1 mmol) of 2-(trimethylsilyl)aniline in
10 mL of dry acetonitrile equimolar amount of the cor-
responding oxidant and 0.25 mmol of the catalyst was
added. The reaction mixture was stirred at room tempera-
ture (time is given in Table 2), then filtered using reverse
filtration. The solvent removed, the residue crystallized
from the mixture chloroform–cyclohexane–pentane
(1 : 1 : 5). Yields are given in Table 1. Fine-crystalline
orange powder, mp 121–124°C. 13H NMR spectrum,
δ, ppm: 0.38 s (18H, Me3Si); 7.64–7.88, 8.26 (8H, Ar).
13C NMR spectrum, δC, ppm: –0.49, 122.98, 127.12,
130.04, 130.36, 134.23, 157.08. 29Si NMR spectrum: δSi
2-(Triethoxysilyl)aniline (2) was prepared similarly
from 18 g (0.05 mol) of 2-iodo-N,N-bis(trimethylsilyl)-
aniline 3 and 10.0 g (~0.05 mol) of chloro(triethoxy)-
silane. Yield 6.5 g (51%), yellowish viscous oil, bp
1
181–183°С (0.6 mmHg). Н NMR δ, ppm: 1.22 t (9H,
CH3CH2, J = 7.0 Hz), 3.91 q (6H, CH3CH2, J = 7.0
Hz), 4.02 br.s (2H, NH2), 7.36–7.78 m (4 H, Ar). 13C
NMR spectrum, δC, ppm: 17.87, 59.08, 116.52, 119.12,
Scheme 6.
NMMO, MeCN,
CuCl
2-(EtO)3SiC6H4NH2
2-(EtO)3SiC6H4N=NC6H4Si(OEt)3-2
5
2
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LAZAREVA, GOSTEVSKII
https://doi.org/10.1039/c1cs15179g
8. Merino, E., Chem. Soc. Rev., 2011, vol. 40, no. 7,
p. 3835.
–6.84 ppm. Found, %: C 66.54; H 8.27; N 8.71.
C18H26N2Si2. Calculated, %: C 66.20; H 8.02; N 8.58.
(2,2'-Bis(triethoxysilyl)azobenzene (5). 0.5 g
(2 mmol) of 2-(triethoxysilyl)aniline was dissolved in
10 mL of dry acetonitrile, added 0.25 g (2 mmol) of
NMMO, 0.5 mmol of CuBr and water-binding reagent
(the amounts are given in Table 2). The reaction mixture
was stirred at room temperature for 48 h, the precipitate
filtered and volatiles removed in vacuum. By crystalliza-
tion from cyclohexane was isolated viscous orange slowly
https://doi.org/10.1039/c0cs00183j
9. Kano, N., Komatsu, F., and Kawashima, T., Chem. Lett.,
2001, no. 4, p. 338.
https://doi.org/10.1246/cl.2001.338
10. Kano, N., Komatsu, F., and Kawashima, T., J. Am. Chem.
Soc., 2001, vol. 123, no. 43, p. 10778.
https://doi.org/10.1021/ja0165739
11. Kano, N., Yamamura, M., Komatsu, F., and Kawashima, T.,
J. Organomet. Chem., 2003, vol. 686, no. 1–2, p. 192.
https://doi.org/10.1016/S0022-328X(03)00447-9
12. Kano, N., Yamamura, M., and Kawashima, T., J. Am. Chem.
Soc., 2004, vol. 126, no. 20, p. 6250.
1
crystallized oil, yields see in Table 2. Н NMR spec-
trum, δ, ppm: 1.17 t (18H, CH3CH2, J = 7.1 Hz), 3.94 q
(12H, CH3CH2, J = 7.1 Hz), 7.68–8.32 m (8H, Ar). 13C
NMR spectrum, δС, ppm: 18.26, 58.56, 124.76, 128.69,
129.18, 130.64, 137.62, 159.84. 29Si NMR spectrum: δSi
–58.02 ppm. Found, %: 57.05; H 7.82; N 5.41.
C24H38N2O6Si2. Calculated, %: C 56.89; H 7.56; N 5.53.
https://doi.org/10.1021/ja037404m
13. Kano, N., Komatsu, F., Yamamura, M., and Kawashima, T.,
J. Am. Chem. Soc., 2006, vol. 128, no. 21, p. 7097.
https://doi.org/10.1021/ja060926s
14. Yamamura, M., Kano, N., and Kawashima, T., J. Organo-
metal. Chem., 2007, vol. 692, nos. 1–3, p. 313.
https://doi.org/10.1016/j.jorganchem.2006.08.045
15. Yamamura, M., Kano, N., Kawashima, T., Matsumoto, T.,
Harada, J., and Ogawa, K., J. Org. Chem., 2008, vol. 73,
no. 21, p. 8244.
FUNDING
This work was performed with financial support of the Rus-
sian Foundation for Basic Research (grant no. 19-03-00143)
using the equipment of the BaikalAnalytical Center for Collec-
tive Use, Siberian Branch of the RussianAcademy of Sciences.
https://doi.org/10.1021/jo801334a
16. Yamamura, M., Kano, N., and Kawashima, T., Z. Anorg.
Allg. Chem., 2009, vol. 635, nos. 9–10, p. 1295.
https://doi.org/10.1002/zaac.200900024
17. Kakiage, K., Yamamura, M., Kyomen, T., Unno, M., and
Hanaya, M., Key Eng. Mat., 2012, vol. 497, p. 61.
https://doi.org/10.4028/www.scientific.net/KEM.497.61
18. Kano, N., Yamamura, M., and Kawashima, T., Dalton
Trans., 2015, vol. 44, no. 37, p. 16256.
https://doi.org/10.1039/C5DT02038G
19. Chuit, C., Corriu, R.J.P., Reye, C., and Young, J.C.,
Chem. Rev., 1993, vol. 93, no. 4, p. 1371.
https://doi.org/10.1021/cr00020a003
20. Kost, D. and Kalikhman, I., Acc. Chem. Res., 2009, vol. 42,
no. 2, p. 303.
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
REFERENCES
1. Gromov, S.P., Dmitrieva, S.N., and Churakova, M.V.,
Russ. Chem. Rev., 2005, vol. 74, no. 5, p. 461.
https://doi.org/10.1070/RC2005v074n05ABEH001163
2. Zatsepin, T.S., Abrosimova L.A, Monakhova, M.V., Hien
Le Thi, Pingoud, A., Kubareva, E.A., and Oretskaya, T.S.,
Russ. Chem. Rev., 2013, vol. 82, no. 10, p. 942.
https://doi.org/10.1070/RC2013v082n10ABEH004355
3. Luo, W., Feng, Y., and Feng., W., Nanoscale, 2012, vol. 4,
no. 20, p. 6118.
https://doi.org/10.1021/ar800151k
21. Xu, Z., Huanga, W.-S., Zhanga, J., and Xu, L.-W.,
Synthesis, 2015, vol. 47, no. 23, p. 3645.
https://doi.org/10.1039/c2nr31505j
4. TylkowskiB.Trojanowska,A., Marturano,V., Nowak, M.,
Marciniak, L., Giamberini, M., Ambrogi, V., and Cerru-
ti, P., Coord. Chem. Rev., 2017, vol. 351, p. 205.
https://doi.org/10.1016/j.ccr.2017.05.009
5. Wei, Y.-bo, Tanga, Q., Gonga, C.-bin, and Hon-Wah
Lamb, M., Anal. Chim. Acta, 2015, vol. 900, p. 10.
https://doi.org/10.1016/j.aca.2015.10.022
https://doi.org/10.1055/s-0035-1560646
22. Kakiuchi, F., Matsumoto, M., Tsuchiya, K., Igi, K., Hay-
amizu, T., Chatani, N., and Murai, S., J. Organometal.
Chem., 2003, vol. 686, no. 1–2, p. 134.
https://doi.org/10.1016/S0022-328X(03)00448-0
23. Singh, S., Chauhan, P., Ravi, M., Taneja, I., Wahajuddin,
and Yadav, P.P., RSC Adv., 2015, vol. 5, no. 76, p. 61876.
https://doi.org/10.1039/c5ra12535a
6. Beharry, A.A. and Woolley, G.A., Chem. Soc. Rev.,
2011, vol. 40, no. 8, p. 4422.
https://doi.org/10.1039/c1cs15023e
24. John, A.A. and Lin, Q., J. Org. Chem., 2017, vol. 82,
no. 18, p. 9873.
7. Dhammika Bandarab, H.M. and Burdette, S.C., Chem.
Soc. Rev., 2012, vol. 41, no. 5, p. 1809.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 1 2020

SYNTHESIS OF 2,2'-BIS(SILYL)AZOBENZENES
83
https://doi.org/10.1021/acs.joc.7b01530
p. 190.
25. Zhang, C. and Jiao, N., Angew. Chem. Int. Ed.,
2010, vol. 49, no. 35, p. 6174.
https://doi.org/10.1002/prac.19963380138
31. Albini, A., Synthesis, 1993, no. 3, p. 263.
https://doi.org/10.1055/s-1993-25843
https://doi.org/10.1002/anie.201001651
26. Wang, J., He, J., Zhi, C., Luo, B., Li, X., Pan, Y., Cao, X.,
and Gu, H., RSC Adv., 2014, vol. 4, no. 32, p. 16607.
https://doi.org/10.1039/c4ra00749b
32. Zatsepin, T.S., Kachalova, A.V., Romanova, E.A., Stet-
senko, D.A., Gait, M.J., and Oretskaya, T.S., Russ. J.
Bioorg. Chem., 2001, vol. 27, no. 1, p. 39.
27. Rajashekhar Reddy, C.B., Rajasekhara Reddy, S., and
Naidu, S., Catal. Comm., 2014, vol. 56, p. 50.
https://doi.org/10.1016/j.catcom.2014.06.025
28. Cai, S., Rong, H., Yu, X., Liu, X., Wang, D., He, W.,
and Li, Y., ACS Catal., 2013, vol. 3, no. 4, p. 478.
https://doi.org/10.1021/cs300707y
https://doi.org/10.1023/A:1009579002330
33. Hamada, Y., Yamamoto, Y., and Shimizu, H., J. Organomet.
Chem., 1996, vol. 510, no. 1–2, p. l.
https://doi.org/10.1016/0022-328X(95)05821-6
34. Armarego, W.L.F., Purification of Laboratory Chemicals,
Burlingto: Elsevier, 2009. 743 p.
29. Hudwekar, A.D., Verma, P.K., Kour, J., Balgotra, S., and
Sawant, S.D., Eur. J. Org. Chem., 2019, no. 6, p. 1242.
https://doi.org/10.1002/ejoc.201801610
35. Kazakova, V.V., Gorbatsevich, O.B., Skvortsova, S.A.,
Demchenko, N.V., and Muzafarov, A.M., Russ. Chem.
Bull., 2005, vol. 54, no. 5, p. 1350.
30. Knolker, H.-J., J. Prakt. Chem., 1996, vol. 338, no. 1,
https://doi.org/10.1007/s11172-005-0409-y
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 1 2020