Kinetics of Zr-Catalyzed Cycloalumination of Alkenes and Alkynes in the Dzhemilev Reaction

Article abstract of DOI:10.1134/S0023158420010085

Abstract: The kinetics and chemoselectivity of cycloalumination of 1-octene and 4-octyne with Et₃Al in the presence of a catalytic amount of Cp₂ZrCl₂ in hexane at various temperatures and ratios between reactants was studied. It was found that chemoselectivity for the formation of aluminacyclopentanes and aluminacyclopentenes was improved and the reaction time was significantly shortened when the cycloalumination reaction was carried out at an elevated temperature (40°C) and an equimolar ratio between an unsaturated compound (4-octyne or 1-octene) and Et₃Al. Quantitative characteristics of the reactivity of a number of alkenes and alkynes, including functionally substituted ones, were obtained.

Full text of DOI:10.1134/S0023158420010085

ISSN 0023-1584, Kinetics and Catalysis, 2020, Vol. 61, No. 1, pp. 106–111. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Kinetika i Kataliz, 2020, Vol. 61, No. 1, pp. 100–105.
Kinetics of Zr-Catalyzed Cycloalumination of Alkenes and Alkynes
in the Dzhemilev Reaction
I. R. Ramazanova, * and R. N. Kadikovaa
aInstitute of Petrochemistry and Catalysis, Russian Academy of Sciences, Ufa, 450075 Russia
*е-mail: ilfir.ramazanov@gmail.com
Received February 11, 2019; revised July 27, 2019; accepted September 18, 2019
Abstract—The kinetics and chemoselectivity of cycloalumination of 1-octene and 4-octyne with Et3Al in the
presence of a catalytic amount of Cp2ZrCl2 in hexane at various temperatures and ratios between reactants
was studied. It was found that chemoselectivity for the formation of aluminacyclopentanes and aluminacy-
clopentenes was improved and the reaction time was significantly shortened when the cycloalumination reac-
tion was carried out at an elevated temperature (40°C) and an equimolar ratio between an unsaturated com-
pound (4-octyne or 1-octene) and Et3Al. Quantitative characteristics of the reactivity of a number of alkenes
and alkynes, including functionally substituted ones, were obtained.
Keywords: aluminacyclopentanes, aluminacyclopentenes, induction period, temperature effect, cycloalumi-
nation, cyclic carboalumination
DOI: 10.1134/S0023158420010085
INTRODUCTION
Et3Al (1 −3 equiv)
Cp2ZrCl2 (5 mol % )
AlEt
The Zr-catalyzed interaction of alkenes and trieth-
ylaluminum known as the Dzhemilev reaction of ole-
fin cycloalumination [1, 2] was first discovered in
1989, and it has been widely used to obtain cyclic orga-
noaluminum intermediates from various olefins, acet-
ylenes, and allenes, including functionally substituted
ones. The high reactivity of aluminacyclopentanes and
aluminacyclopentenes made it possible to develop
efficient single-reactor syntheses of five-membered
sulfur-, selenium- [3, 4], and phosphorus-containing
[5, 6] heterocycles and spiro compounds [7, 8]. In the
course of studying the cycloalumination reaction of
functionally substituted acetylenes, we established a
significant role of the temperature effect. Thus, the
reaction with propargyl alcohols occurred only at 40–
50°C [9]. In this context, a question arose on the role
of the above effect in the cycloalumination of olefins
and acetylenes and its action on the chemoselectivity
of the reaction. In this work, we studied the kinetics of
conversion of 1-octene and 4-octyne under the Dzhe-
milev reaction conditions at various temperatures and
ratios between reagents (Scheme 1) and reactivity of a
number of olefins and acetylenes, including function-
ally substituted compounds.
Bu
Bu
Bu
hexane, 20−50°C
Bu
AlEt
Et3Al (1 −3 equiv)
Cp2ZrCl2 (5 mol %)
Hex
Hex
hexane,0−50°C
Scheme 1. Cycloalumination of 4-octyne and 1-octene.
EXPERIMENTAL
Starting Substances and Materials
In this work, 98% Et3Al was used (OAO Redkinskii
Opytnyi Zavod). To create an inert atmosphere, pure
grade argon (GOST [State Standard] 10157-73) was
used. The starting reagents 1-octene and 4-octyne are
commercially available.
Methods of Analysis and Physicochemical
Characterization
The reaction products were analyzed by gas–liquid
chromatography (GLC) on an HRGC 5300 Mega
Series chromatograph (Carlo Erba, Italy) with an
Ultra-1 glass capillary column (25 × 0.2 mm) (Hewl-
ett Packard, the United States) and a flame-ionization
detector; the operating temperature was 50–170°C,
and helium was a carrier gas.
The 1Н and 13С NMR spectra were recorded on an
Avance-400 spectrometer (Bruker, Germany) with an
Abbreviations: δ, chemical shifts.
106

KINETICS OF Zr-CATALYZED CYCLOALUMINATION
107
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1.0
0.9
Temperature, °С
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
20
25
30
40
50
Temperature, °С
0
18
25
30
40
50
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Time, h
Time, h
Fig. 1. The time dependence of the concentration of
Fig. 2. The time dependence of the concentration of
4-octyne at various temperatures under cycloalumination
1-octene at various temperatures under cycloalumination
reaction conditions. Hexane, [4-octyne]
[Et Al] = 1.2 M, and [Cp ZrCl ] = 0.02 M.
=
0.4 M,
reaction conditions. Hexane, [1-octene] = 0.4 M,
[Et Al] = 1.2 M, and [Cp ZrCl ] = 0.02 M.
3 2 2
3
2
2
operating frequency of 100.62 MHz for 13С or
400.13 MHz for 1Н. In the measurement of the 1H and
13C NMR spectra, SiMe4 and CDCl3 were used as
internal standards, respectively. Chemical shifts (δ)
are given in ppm. The elemental composition of the
compounds was determined using a Carlo Erba-1106
instrument (Carlo Erba, Italy). The yields of products
were found by the GLC of the hydrolysis products of
corresponding organoaluminum compounds using an
internal standard.
layer was extracted with diethyl ether; the extract was
combined with the organic layer, kept over anhydrous
CaCl2, and concentrated in a vacuum. Individual
products were separated on a silica gel column using
an ethyl acetate–hexane eluant (1 : 10 → 1 : 5).
RESULTS AND DISCUSSION
The kinetics of 1-octene and 4-octyne conversion
was initially studied under the following cycloalumi-
nation reaction conditions: [4-octyne or 1-octene] =
0.4 M, [Et3Al] = 1.2 M, [Cp2ZrCl2] = 0.02 M, hexane,
and a temperature of 25°C (Figs. 1 and 2). Under these
conditions, the kinetic curve of changes in the con-
centration of a starting unsaturated compound
(1-octene or 4-octyne) has an induction period of 2–
3 h. At least 5 h was required to achieve a 95% conver-
sion of 4-octyne and 1-octene. At a temperature of
0°С, the initial concentration of 4-octyne remained
almost unchanged even 24 h after the onset of the
reaction. To complete the reaction at 20°C in the case
of 4-octyne, at least a day was required.
Kinetic Study of the Cycloalumination Reaction
An olefin or acetylene (2 mmol), Cp2ZrCl2
(0.1 mmol, 0.028 g), hexane (5 mL), and Et3Al
(6 mmol) were successively charged in a 50-mL glass
reactor placed in a water bath at a temperature of 40°C
with a magnetic stirrer in an argon atmosphere, and
the contents were stirred at the specified temperature.
The GC analysis of hydrolysis products was performed
after 5, 10, 15, 30, 60, 90, 120, 180, 240, and 480 min
after loading the reagents.
The duration of an induction period of a catalytic
reaction is related to the time taken to establish a
steady-state concentration of intermediates involved
in a catalytic cycle. An increase in the reaction tem-
perature can accelerate this process and shorten the
induction period. Indeed, at a temperature of 40°C and
the above ratio between reactants, the reaction was sig-
nificantly accelerated (Figs. 1 and 2). It should be noted
that changes in the shapes of kinetic curves in the reac-
tions with 4-octyne and 1-octene occurred in tempera-
ture ranges of 30–40 and 25–30°C, respectively.
Study of the Reaction Chemoselectivity of 1-Octene
and 4-Octyne Cycloalumination
1-Octene or 4-octyne (2 mmol), Cp2ZrCl2
(0.1 mmol, 0.028 g), hexane (5 mL), and a specified
amount of Et3Al (2, 4, or 6 mmol) were successively
charged in a 50-mL glass reactor placed in a water bath
at a temperature of 40°C with a magnetic stirrer in an
argon atmosphere, and the contents were stirred at a
specified temperature (20, 25, or 40°C). Hexane
(5 mL) was added to the reaction mass; 3 mL of D2O
The use of a fivefold excess of Et3Al with respect to
was added dropwise upon cooling the reactor in an ice 4-octyne at room temperature (22°C) did not lead to a
bath, and the precipitate was filtered off. The aqueous noticeable decrease in the induction period of the
KINETICS AND CATALYSIS Vol. 61 No. 1 2020

108
RAMAZANOV, KADIKOVA
detail in the publications of Dzhemilev and Negishi
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
with coauthors [11, 12]. However, the effect of tem-
perature on the rate of reaction has not yet been stud-
ied and discussed. According to a recent theoretical
study of the cycloalumination reaction of 1-propene
[12], the stages of Cp2ZrEt2 and zirconacyclopropane
formation are the rate-limiting stages of the overall
process. An earlier experimental work by Balaev et al.
[13] also confirmed the conclusion that the rate of for-
mation of a zirconacyclopropane intermediate con-
trols the rate of a cyclometalation reaction. Thus,
when Cp2ZrCl2 and Et3Al were mixed in a molar ratio
of 1 : 2 in an NMR ampoule, the maximum concen-
tration of a zirconacyclopropane intermediate was
detected approximately 20 min after the onset of the
reaction at a temperature of 20–25°C. Under the cat-
alytic conditions described above, the rate of genera-
tion of zirconocene intermediates should be lower.
Thus, it is reasonable to relate the duration of an
induction period in the test catalytic reaction with the
rate of formation of the zirconacyclopropane interme-
diate and the duration of the establishment of its
steady-state concentration in the reaction system.
[4-Octyne] : [Et3Al]
1 : 1
1 : 2
1 : 3
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Time, h
Fig. 3. The time dependence of the concentration of
4-octyne at various molar ratios between octyne-4 and
Et Al. A reaction temperature of 40°C, [4-octyne] =
3
0.4 M, [Cp ZrCl ] = 0.04 M, and [Et Al] = (1) 0.4,
2
2
3
(2) 0.8, and (3) 1.2 M.
Because the cycloalumination reaction is accom-
panied by the formation of by-products, the effects of
temperature and a ratio between the reagents on the
chemoselectivity of the conversion was studied. It is
well known that the products of carboalumination,
hydroalumination, and cyclic dimerization were also
obtained along with aluminacylopent-2-enes in the
reaction. At the same time, at an elevated temperature
(40°C) and a rationally justified equimolar ratio
between 4-octyne and Et3Al, the reaction took 1 h to
achieve an acetylene conversion of >95% (Fig. 3).
Note that the mechanism of cycloalumination of course of the catalytic cycloalumination of disubsti-
olefins and acetylenes was previously considered in tuted acetylenes (Scheme 2) [10, 11].
Bu
Bu
Bu
Et3Al (3 equiv)
Cp2ZrCl2 (5 mol %)
AlEt2
AlEt
+
+
AlEt2
+
Bu
Bu
Bu
Bu
+
hexane, 20 or 40°C
Bu
Al
Et
Bu
Bu
Bu
Bu
D2O
Bu
Bu
D
D
D
D
D
Bu
D
+
+
Bu
Bu
Bu
Bu
Bu
Bu
Bu
1
2
3
4
Scheme 2. Catalytic cycloalumination of 4-octyne.
With the use of equimolar amounts of 5-decyne amount of carboalumination products estimated from
the 13C NMR spectra did not exceed 5%. A similar
study was conducted for 1-octene. According to Tyu-
mkina et al. [12], the interaction of α-olefins with
Et3Al catalyzed by Cp2ZrCl2 proceeds with the pre-
dominant formation of aluminacyclopentanes; how-
ever, carboalumination and hydroalumination prod-
ucts and methylene alkanes were also detected in the
reaction mass (Scheme 3) [13].
and Et3Al at 40°C, the reaction selectivity for alumina-
cyclopent-2-ene noticeably increased and the fraction
of by-products decreased (Table 1). An increase in the
5-decyne hydroalumination product content with the
use of 3 equiv of Et3Al can be related to the presence of
an impurity of aluminum hydride Et2AlH in Et3Al in
an amount of ~5% (evaluated from the 1H NMR spec-
trum of a commercial Et3Al sample). In all cases, the
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KINETICS OF Zr-CATALYZED CYCLOALUMINATION
109
Table 1. Effects of the reaction temperature and the [4-octyne] : [Et3Al] molar ratio on the composition of the deuterolysis
products of the reaction mixture
[4-octyne] : [Et3Al] ratio
Temperature, °С
Time, h
Yield of 1, %
Yield of 3, %
Yield of 4, %
20
40
40
40
18
2
1 : 3
1 : 1
1 : 2
1 : 3
65
74
59
54
26
12
19
21
9
14
22
25
2
2
Table 2. Effects of the reaction temperature and the [1-octene] : [Et3Al] molar ratio on the composition of the reaction
mixture
[1-octene] : [Et3Al] ratio
Temperature,°С
Time, h
Yield of 5, %
Yield of 8, %
20
40
40
40
8
2
2
2
1 : 3
1 : 1
1 : 2
1 : 3
73
78
72
71
27
22
28
29
Et3Al (3 equiv)
Cp2ZrCl2 (5 mol % )
AlEt2
AlEt
+
+
+
+
AlEt2
Hex
Hex
hexane, 25 or 40°C
Hex
Hex
Hex
D2O
D
D
D
+
+
Hex
D
Hex
Hex
Hex
5
6
7
8
Scheme 3. Catalytic cycloalumination of 1-octene.
It was found that, in the reaction performed at acetylene under the conditions of a cycloalumination
40°C and an equimolar ratio between 1-octene and reaction, we studied the kinetics of conversion of a
Et3Al, the chemoselectivity of aluminacyclopentane number of unsaturated compounds under analogous
conditions at a constant temperature (40°C) (Table 3).
The GC analysis of the hydrolysis products was car-
ried out 10, 20, 30, 60, 90, 120, and 180 min after load-
ing the reagents. The relative reactivity was deter-
mined based on a ratio between the half-times of
1-octene or 1-octyne and an olefin or acetylene sub-
strate. An analysis of the kinetic curves of conversion
of a number of unsaturated compounds showed that
the reactivity of olefins under the conditions of a
cycloalumination reaction decreased in the order
1-octene > α-allylnaphthalene > styrene > allylben-
zene > norbornene > trimethylvinylsilane, and the reac-
tivity of acetylenes decreased in the order 1-octyne >
phenylacetylene > 4-octyne > butyl(trimethylsi-
conversion slightly increased, as compared with that
under standard reaction conditions ([1-octene] :
[Et3Al] = 1 : 3, 23°C). In addition, the reaction time
significantly shortened (Table 2). The fraction of car-
boalumination products and methylene alkanes,
13
which was estimated from C NMR spectra, did not
exceed 5% in all cases. Thus, in the cycloalumination
reaction performed at an elevated temperature (40°C)
and an equimolar ratio between the unsaturated com-
pound (4-octyne or 1-octene) and Et3Al, the chemo-
selectivity of the formation of aluminacyclopentanes
and aluminacyclopentenes was improved and the
reaction time was significantly shortened.
To quantify the effect of the nature of a substituent lyl)acetylene > octyl(trimethylsilyl)acetylene. The rel-
at the multiple bond on the reactivity of an olefin or ative reaction activity of functionally substituted acet-
KINETICS AND CATALYSIS Vol. 61 No. 1 2020

110
Table 3. Relative reactivity of a number of olefins and acetylenes under cycloalumination reaction conditions *
krel Krel
RAMAZANOV, KADIKOVA
Olefin
Acetylene
1-Octene
1
1-Octyne
1
α-Allylnaphthalene
Styrene
0.22
0.18
0.15
0.05
0.01
Phenylacetylene
0.53
0.17
0.09
0.06
4-Octyne
Allylbenzene
Butyl(trimethylsilyl)acetylene
Octyl(trimethylsilyl)acetylene
Norbornene
Trimethylvinylsilane
* Reaction conditions: 40°C, hexane, [alkene or alkyne] = 0.4 M, [Et Al] = 1.2 M, and [Cp ZrCl ] = 0.02 M.
3
2
2
ylenes in the test reaction was evaluated in the same way. teristics of the reactivity of a number of olefins and
At a constant temperature (40°C), we studied the kinetics acetylenes, including functionally substituted com-
ofconversionof1-hexyne,5-decyne,2-heptynol,3-octy- pounds.
nol, and 2-heptinyl(dimethyl)amine in a reaction with
Et3Al (3 molar equivalents) in the presence of Cp2ZrCl2
(20 mol % on an acetylene basis) in a solution of hex-
FUNDING
ane ([acetylene] = 0.2 M, [Et3Al] = 0.6 M, and
[Cp2ZrCl2] = 0.04 M). We found that the reactivity of
acetylene compounds decreased in the order 1-hexyne
(2.7) > 5-decyne (1.0) > heptinyl(dimethyl)amine
(0.5) > 3-octynol (0.2) > 2-heptynol (0.1). An alkyl-
substituted propargyl alcohol exhibited the lowest
activity in the test reaction. Note that the above assess-
ment of the reactivity of functionally substituted acet-
ylenes should not be taken as a characteristic of triple
bond activity in the above compounds with respect to
a cycloalumination reaction because a portion of Et3Al
was consumed in a reaction with hydroxyl groups and
complexation with a nitrogen or oxygen atom. More-
over, side reactions of the hydroalumination and
isomerization of intermediate zirconacyclopentenes
(in the case of alkyl-substituted propargyl alcohols)
occurred along with the process of cycloalumination.
A similar study conducted with respect to functionally
substituted olefins under identical conditions (40°C,
[olefin] = 0.2 M, [Et3Al] = 0.2 M, and [Cp2ZrCl2] =
0.02 M) showed that, in general, the introduction of a
nitrogen, sulfur, or oxygen atom into an unsaturated
compound decreased its relative reactivity in the order
1-octene (1.0) > 3-(heptylsulfanyl)-1-propene (0.21) >
tert-octylallylamine (0.18) ≈ 1-decen-4-ol (0.17).
This work was supported by the Russian Foundation for
Basic Research (grant no. 18-03-00817) and the Institute of
Petrochemistry and Catalysis, Russian Academy of Sci-
ences (state contract nos. AAAA-A19-119022290007-9 and
AAAA-A19-119022290008-6, 2019–2021).
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Translated by V. Makhlyarchuk
KINETICS AND CATALYSIS Vol. 61 No. 1 2020