A new route of the reaction of EtAlCl2 with α-olefins catalyzed by Ti complexes

Article abstract of DOI:10.1023/A:1009542721007

A new method for the synthesis of dialkyl(ethyl)alanes by the reaction of EtAlCl₂ with α-olefins in the presence of Mg and a catalytic amount of Cp₂TiCl₂ (Ti(OPrⁱ)₄, Ti(OBuⁿ)₄) in THF was developed.

Full text of DOI:10.1023/A:1009542721007

292
Russian Chemical Bulletin, International Edition, Vol. 50, No. 2, pp. 292—296, February, 2001
Organometallic Chemistry
A new route of the reaction of EtAlCl2 with α-olefins
catalyzed by Ti complexes
A. G. Ibragimov, L. O. Khafizova, I. V. Zagrebel´naya, L. V. Parfenova,
R. M. Sultanov, L. M. Khalilov, and U. M. Dzhemilev«
Institute of Petrochemistry and Catalysis,
Bashkortostan Republic Academy of Sciences and Ufa Research Center of the Russian Academy of Sciences,
141 prosp. Oktyabrya, 450075 Ufa, Russian Federation.
Fax: +7 (347 2) 31 2750. E-mail: ink@anrb.ru
A new method for the synthesis of dialkyl(ethyl)alanes by the reaction of EtAlCl2 with
α-olefins in the presence of Mg and a catalytic amount of Cp2TiCl2 (Ti(OPri)4, Ti(OBun)4) in
THF was developed.
Key words: organoaluminum compounds, catalysis, hydrometallation, dehydrogenation, Ti
complexes, olefins.
Recently1, we have proposed an approach to the
However, dialkyl(ethyl)alanes 2a—d were formed in-
synthesis of a new series of organoaluminum compounds
(OAC), viz., substituted aluminacyclopropanes (1), by
cyclometallation of arylethenes with EtAlCl2 in the pres-
ence of metallic Mg in THF and a catalytic amount of
Cp2TiCl2.
stead of the corresponding aluminacyclopropanes.
Mg, [Ti]
EtAlCl2
+
R
–MgCl2
(60—85%)
Ar
D2O
D
I
R
R
R
Mg, [Cp2TiCl2]
EtAlCl2
+
Al
Et
1
Ar
(1)
3b,c
4b
I2
R
(2)
EtAl
2
To extend the area of application of this method, to
obtain new types of small metallacycles, and to deter-
mine the possibility of cyclometallation of aliphatic
α-olefins, we studied the interaction of α-olefins con-
taining H atoms at the allylic C atom (aliphatic Ñ6—Ñ11
α-olefins, allylbenzene, and allylnaphthalene) with
EtAlCl2 under the conditions described previously1
(5 mol.% Cp2TiCl2, THF, ∼20 °C).
2a—d
O2
HO
H3O+
5a—d
R = Prn (a), n-C5H11 (b), n-C7H15 (c), n-C8H17 (d)
The OAC obtained were transformed into the corre-
sponding partially deuterated alkanes 3b,c, 1-iodoalkane
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 280—284, February, 2001.
1066-5285/00/5002-292 $25.00 © 2001 Plenum Publishing Corporation

Reaction of EtAlCl2 with α-olefins
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 2, February, 2001
293
4b, and alcohols 5a—d. These results allowed us to
suggest the formulae 2à—d for the OAC synthesized.
The presence of the broadened high-field signals in the
13C NMR spectra of 2à,b at δ 0.29 and 9.77 assigned to
the α-C atoms of the ethyl and alkyl groups, respec-
tively, confirmed their structures.2
In this reaction, acyclic OAC 2 can be obtained only
by catalytic hydrometallation via intermediate titanium
hydride complexes (Ti—H). The idea on the key role of
the Ti—H complexes in the reaction under discussion is
confirmed by the results of the study reported previ-
ously3, which have demonstrated that the low-valent Ti
complexes obtained by the reduction of TiCl4 with
metallic Mg split tetrahydrofuran yielding Ti hydrides
and a mixture of gaseous products.
Based on the results obtained, we suggested a scheme
of the reaction of α-olefins with EtAlCl2. Its first stage
includes reduction of Cp2TiCl2 with Mg to "Cp2Ti",
which coordinates α-olefin and tetrahydrofuran molecules
resulting in the formation of complex 6. Dehydrogena-
tion3 of the tetrahydrofuran molecule by low-valent Ti
complexes 6 affords titanium hydrides7, which hydrometal-
late olefin molecules to give Ti alkyl derivatives 8. Trans-
metallation of alkyl complexes 8 by the starting EtAlCl2
resulting in the formation of OAC 2 and regeneration of
the catalyst Cp2TiCl2 (see Scheme 1) is the terminal stage.
Depending on duration of the reaction and the ratio
of the starting reagents and the catalyst, the reaction
mixture contains 15—30% of disubstituted (Z/E)-olefins
9a—d, which are likely generated by isomerisation of the
starting α-olefins upon treatment with Ti complexes.11
Unlike aliphatic α-olefins, arylethenes give aryl-sub-
stituted aluminacyclopropanes 1 under the same condi-
tions.1
R
R
R
(3)
The known4—7 schemes of hydrometallation of
α-olefins with "hydride-free" reagents, e.g., Bui3Al,4
Bui2AlCl,5,6 or Et3Al, involving Ti and Zr complexes do
not explain the mechanism of the transformations ob-
served and do not answer the question why EtAlCl2
reacts with arylethenes according to the cyclometallation
route and with aliphatic α-olefins according to the
hydrometallation route under the same conditions.
Experimental and literature data8,9 allow us to as-
sume that arylethenes behave like conjugated dienes and
form stable titanacyclopropane intermediates with "Cp2Ti"
(analogously to phenyl-substituted titanacyclopropenes10),
which are inert with respect to tetrahydrofuran. Aliphatic
α-olefins or allylarenes probably give labile low-valent
titanium complexes 6, which split tetrahydrofuran yield-
ing Ti hydrides,3 which reduce α-olefins.
[Ti]—H
H
H
[Ti]
[Ti]
9a—d
The reactions performed in Et2O result in a decrease
in the yield of OAC 2 to 25—40% and at the same time
increase the content of (Z/E)-olefins 9a—d. The reac-
tion does not proceed in aliphatic solvents. When using
benzene as a solvent, the reported12 reaction of
cyclometallation of α-olefins yielding regioisomeric alkyl-
substituted aluminacyclopentanes is observed. The yield
of alkylalanes 2 is 45—50% in the presence of 3—5 mol.%
of titanium alkoxides (Ti(OPri)4, Ti(OBun)4).
Using 13C NMR spectra, we have established that
the reaction mixture contains alkyl(chloro)ethylalanes
10a,b along with dialkyl(ethyl)alanes, e.g., 2a,b. The
Scheme 1
R
EtAl
2
Mg
2
MgCl2
Cp2TiCl2
EtAlCl2
«Cp2Ti»
Cp2Ti
R
2
8
R
R
O
Cp2Ti
O
R
Cp2Ti
H
R
H
7
6
Ñ1, Ñ2-hydrocarbons,
Al—O—
,
O

294
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 2, February, 2001
Ibragimov et al.
former compounds can be generated13 by the exchange
reaction of OAC 2 with the starting EtAlCl2.
The results obtained attest that we have found a new
direction of the reaction of EtAlCl2 with α-olefins con-
taining H atoms at the allylic C atom in the presence of
the catalysts based on Ti complexes, which permits one
to obtain acyclic OAC in the ether-type solvents.
EtAlCl2
+
R
EtAl
2
2a,b
Experimental
(4)
R
2 EtAl
Cl
The reactions with organometallic compounds were carried
out in the atmosphere of dry argon. Solvents were distilled from
LiAlH4 immediately before use. GLC analysis of the products of
hydrolysis, deuterolysis, or iodinolysis was performed on a
Chrom-5 instrument with He as the carrier gas, using a
1200½3-mm column with 5% SE-30 or 15% PEG-6000 on
Chromaton N-AW. IR spectra were recorded on a UR-20
spectrometer (film). Mass spectra were measured on an
10a,b
Allylbenzene and allylnaphthalene were found to
react with EtAlCl2 in the presence of Cp2TiCl2 as the
catalyst resulting in the corresponding higher OAC 11a,b
(Scheme 2) in the same way as alkyl-substituted α-olefins.
1
MKh-1306 spectrometer (70 eV, 200 °C). H and 13C NMR
spectra were registered in CDCl3 on JEOL. FX-90 Q (90 and
22.5 MHz) and Bruker AM-300 (300 and 75 MHz) spectrom-
eters, respectively, with Me4Si as the internal standard. The
13C NMR spectra of OAC were taken on a JEOL. FX-90Q
spectrometer (22.5 MHz) in complete and partial proton
decoupling modes. Dilute solutions of OAC in THF were used
with the addition of C6D12 for the internal field stabilization.
The OAC solutions were placed in sealed ampoules under dry
argon. The yields of OAC were determined by GLC analysis of
the hydrolysis products. Alcohols 5a—d were identified by
comparison with the authentic samples.14
Reactions of α-olefins with EtAlCl2—Mg—[Ti] (general
procedure). An α-olefin (10 mmol), Cp2TiCl2 (Ti(OBun)4,
Ti(OPri)4) (0.5 mmol), Mg powder (10 mg-at.), THF (10 mL),
and EtAlCl2 (12 mmol) were placed into a glass reactor at
–5 °C under dry argon. The solution was heated to 21—22 °C
and stirred for 8 h. The reaction mixture was oxidized with
atmospheric oxygen at ∼50 °C or treated with 15% DCl in D2O
or with I2. The products were extracted with ether and isolated
by distillation. Below is shown the numbering of the atoms of
the resulting OAC and the products of their hydrolysis,
deuterolysis, oxidation, and iodinolysis:
Scheme 2
EtAlCl2
Mg, [Ti]
–MgCl2
–MgCl2
EtAl
Mg, [Ti]
(55%)
(60%)
EtAl
2
11a
2
11b
D3O+
D3O+
D
D
12a
12b
1
1
l
A
l
A
2
2
4
6
8
4
6
8
10
1
3
5
7
D
3
5
7
3
1
5
3
7
9
7
2
2
4
6
6
8
8
2
2
2a
2b
3b
1
3
5
7
9
5
1
3
5
7
D
I
HO
2
4
6
8
10
2
2
4
6
6
8
8
4
3c
4b
5b
2
2
4
6
2
4
6
8
4
10
2
2
4
6
8
10
1
1
3
5
1
3
5
7
1
1
3
5
7
9
1
1
3
5
7
9
11
E 9a
-
E 9b
-
E 9c
-
E 9d
-
3
5
2
3
5
7
2
3
5
7
9
3
5
7
9
11
4
6
1
4
6
8
4
6
8
10
4
6
8
10
Z 9a
-
Z 9b
-
Z 9c
-
Z 9d
-
1
2
3
5
7
l
A
5
6
5
6
4
6
8
l
C
4
2
2
10a
7
7
D
D
1
3
4
1
3
13
12
8
12a
9
1
2
3
5
7
9
Al
4
6
8
10
Cl
11
10
10b
12b

Reaction of EtAlCl2 with α-olefins
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 2, February, 2001
295
Di(n-hexyl)ethylalane (2a). 13C NMR (C6D12, δ): 0.29
(br.t, C(2)); 8.15 (q, C(1)); 9.77 (br.t, C(3)); 14.07 (q, C(8));
23.04 (t, C(7)); 27.79 (t, C(4)); 32.08 (t, C(6)); 35.46 (t, C(5)).
Di(n-octyl)ethylalane (2b). 13C NMR (C6D12, δ): 0.29
(br.t, C(2)); 8.15 (q, C(1)); 9.77 (br.t, C(3)); 13.94 (q, C(10));
22.91 (t, C(9)); 27.79 (t, C(4)); 28.64 (t, C(6)); 29.61 (t, C(7));
32.21 (t, C(8)); 35.85 (t, C(5)).
Found (%): C, 85.60; H, 14.19. C11H22. Calculated (%):
C, 85.71; H, 14.29.
trans-Hex-2-ene (E-9a). 13C NMR (CDCl3), δ: 14.11
(q, C(6)); 17.95 (q, C(1)); 22.80 (t, C(5)); 32.80 (t, C(4));
125.02 (d, C(2)); 132.22 (d, C(3)).
cis-Hex-2-ene (Z-9a). 13C NMR (CDCl3), δ: 12.92
(q, C(1)); 14.11 (q, C(6)); 22.80 (t, C(5)); 27.00 (t, C(4));
123.62 (d, C(2)); 130.94 (d, C(3)).
20
1-Deuteriohexane (3a), b.p. 68—69 °C, nD 1.3756. IR,
1
ν/cm–1: 3000, 2160 (C—D), 1460, 1380, 950, 700. H NMR,
trans-Oct-2-ene (E-9b). 13C NMR (CDCl3), δ: 14.09
(q, C(8)); 17.92 (q, C(1)); 22.79 (t, C(7)); 29.50 (t, C(5)); 32.75
(t, C(4)); 32.10 (t, C(6)); 124.57 (d, C(2)); 131.79 (d, C(3)).
cis-Oct-2-ene (Z-9b). 13C NMR (CDCl3), δ: 12.72
(q, C(1)); 14.09 (q, C(8)); 22.79 (t, C(7)); 26.96 (t, C(4)); 28.98
(t, C(5)); 32.10 (t, C(6)); 123.60 (d, C(2)); 130.94 (d, C(3)).
trans-Dec-2-ene (E-9c). 13C NMR (CDCl3), δ: 14.15
(q, C(10)); 17.92 (q, C(1)); 22.80 (t, C(9)); 29.50 (t, C(7));
29.76 (t, C(5), C(6)); 32.04 (t, C(8)); 32.69 (t, C(4)); 124.57
(d, C(2)); 131.73 (d, C(3)).
cis-Dec-2-ene (Z-9c). 13C NMR (CDCl3), δ: 12.72
(q, C(1)); 14.15 (q, C(10)); 22.80 (t, C(9)); 26.96 (t, C(4));
29.50 (t, C(7)); 29.76 (t, C(5), C(6)); 32.04 (t, C(8)); 123.60
(d, C(2)); 130.95 (d, C(3)).
trans-Undec-2-ene (E-9d). 13C NMR (CDCl3), δ: 14.18
(q, C(11)); 17.97 (q, C(1)); 22.82 (t, C(10)); 29.50 (t, C(7));
29.68 (t, C(5), C(6)); 29.82 (t, C(8)); 32.06 (t, C(9)); 32.71
(t, C(4)); 124.75 (d, C(2)); 131.90 (d, C(3)).
cis-Undec-2-ene (Z-9d). 13C NMR (CDCl3), δ: 12.74
(q, C(1)); 14.18 (q, C(11)); 22.82 (t, C(10)); 26.98 (t, C(4));
29.50 (t, C(7)); 29.68 (t, C(5), C(6)); 29.82 (t, C(8)); 32.06
(t, C(9)); 123.62 (d, C(2)); 130.96 (d, C(3)).
δ: 0.79—0.90 (m, 5 H, CH2D, CH3); 1.10—1.25 (m, 8 H,
CH2). MS, m/z: 87 [M]+. Found (%): C, 82.68; H, 17.15.
C6H13D. Calculated (%): C, 82.76; H, 14.94; D, 2.30.
20
1-Deuteriooctane (3b), b.p. 124—125 °C, nD 1.3973. IR,
ν/cm–1: 3000, 2165 (C—D), 1455, 1390, 1075, 960, 700.
1H NMR, δ: 0.80—0.94 (m, 5 H, CH2D, CH3); 1.20—1.42
(m, 12 H, CH2). 13C NMR (CDCl3, δ): 13.83 (t, C(1),
1JCD = 19.1 Hz); 14.09 (q, C(8)); 22.80 (t, C(2), C(7)); 29.56
(t, C(4), C(5)); 31.64 (t, C(3), C(6)). MS, m/z: 115 [M]+.
Found (%): C, 83.39; H, 16.43. C8H17D. Calculated (%):
C, 83.48; H, 14.78; D, 1.74.
1-Deuteriodecane (3c), b.p. 57—58 °C (10 Torr),
nD20 1.4112. IR, ν/cm–1: 2160 (C—D). 1H NMR, δ: 0.81—0.93
(m, 5 H, CH2D, CH3); 1.12—1.40 (m, 16 H, CH2). 13C NMR
(CDCl3, δ): 13.83 (t, C(1), 1JCD = 19.1 Hz); 14.15 (q, C(10));
22.80 (t, C(2), C(9)); 29.50 (t, C(4), C(7)); 29.76 (t, C(5),
C(6)); 32.04 (t, C(3), C(8)). MS, m/z: 143 [M]+. Found (%):
C, 83.82; H, 15.99. C10H21D. Calculated (%): C, 83.91;
H, 14.69; D, 1.40.
1-Deuterioundecane (3d), b.p. 75—76 °C (10 Torr),
nD 1.4168. IR, ν/cm–1: 2160 (C—D).1H NMR δ: 0.81—0.94
20
(m, 5 H, CH2D, CH3); 1.13—1.39 (m, 16 H, CH2). MS, m/z:
157 [M]+. Found (%): C, 83.99; H, 15.84. C11H23D. Calcu-
lated (%): C, 84.08; H, 14.65; D, 1.27.
Ethyl(n-hexyl)aluminum chloride (10a). 13C NMR (C6D12),
δ: 0.29 (br.t, C(2)); 8.67 (q, C(1)); 9.56 (br.t, C(3)); 13.94
(q, C(8)); 22.91 (t, C(7)); 27.07 (t, C(4)); 31.82 (t, C(6));
34.86 (t, C(5)).
Ethyl(n-octyl)aluminum chloride (10b). 13C NMR (C6D12),
δ: 0.29 (br.t, C(2)); 8.73 (q, C(1)); 9.77 (br.t, C(3)); 14.20
(q, C(10)); 22.91 (t, C(9)); 27.07 (t, C(4)); 28.12 (t, C(6));
29.61 (t, C(7)); 32.21 (t, C(8)); 35.27 (t, C(5)).
20
1-Iodoctane (4b), b.p. 100 °C (10 Torr), nD 1.4875. IR,
ν/cm–1: 510, 585, 720, 1160, 1465, 2860, 2965. 1H NMR,
δ: 0.78—0.94 (m, 3 H, CH3); 1.25 (m, 10 H, CH2); 1.69—1.86
(m, 2 H, CH2CH2I); 3.02—3.22 (m, 2 H, CH2I). 13C NMR
(CDCl3, δ): 6.93 (t, C(1)); 14.09 (q, C(8)); 22.67 (t, C(7));
28.12 (t, C(5)); 29.11 (t, C(4)); 30.54 (t, C(3)); 31.77 (t, C(6));
33.60 (t, C(2)). MS, m/z: 240 [M]+. Found (%): C, 40.25;
H, 7.05. C8H17I. Calculated (%): C, 40.00; H, 7.08; I, 52.92.
Hex-2-ene (9a) (Z : E ≈ 1 : 9), b.p. 68—69 °C, nD20 1.3966.
1H NMR, δ: 0.88 (t, 3 H, CH3, J = 7.1 Hz); 1.20—1.35 (m,
2 H, CH2CH3); 1.97—2.05 (m, 2 H, CH2CH2CH3); 1.59—1.70
(m, 3 H, CH3CH); 5.36—5.42 (m, 2 H, CH=CH). MS, m/z:
84 [M]+. Found (%): C, 85.62; H, 14.19. C6H12. Calcu-
(3-Deuteriopropyl)benzene (12a), b.p. 65 °C (30 Torr),
nD20 1.4921. IR, ν/cm–1: 3020, 3010, 2960, 2850, 2160 (C—D),
1500, 1450, 1020, 730, 690. 1H NMR, δ: 0.90 (t, 2 H, CH2D,
J = 7.1 Hz); 1.35—1.70 (m, 2 H, CH2); 2.58 (t, 2 H, CH2—Ph,
J = 7.1 Hz); 7.10—7.35 (m, 5 H, Ph). 13C NMR (CDCl3), δ:
13.66 (t, C(1), 1JCD = 19.1 Hz); 22.30 (t, C(2)); 35.27 (t, C(3));
142.54 (s, C(4)); 126.83 (d, C(5)); 126.42 (d, C(6)); 125.57
(d, C(7)). MS, m/z: 121 [M]+. Found (%): C, 89.14; H, 10.66.
C9H11D. Calculated (%): C, 89.26; H, 9.09; D, 1.65.
1-(3-Deuteriopropyl)naphthalene (12b), b.p. 116 °C (1 Torr),
nD20 1.5307. IR, ν/cm–1: 3000, 2160 (C—D), 1940, 1800, 1600,
lated (%): C, 85.71; H, 14.29.
20
Oct-2-ene (9b), b.p. 123 °C, nD
1.4129. 1H NMR,
δ: 0.90 (t, 3 H, CH3, J = 7.1 Hz); 1.20—1.31 (m, 6 H,
CH2); 1.86—2.12 (m, 2 H, CH2CH); 1.58—1.67 (m, 3 H,
CH3CH); 5.33—5.45 (m, 2 H, CH=CH). MS, m/z: 112 [M]+.
Found (%): C, 85.63; H, 14.19. C8H16. Calculated (%): C, 85.71;
H, 14.29.
Dec-2-ene (9c), b.p. 78—80 °C (30 Torr). 1H NMR,
δ: 0.88 (t, 3 H, CH3, J = 7.0 Hz); 1.12—1.40 (m, 10 H,
CH2); 1.93—2.05 (m, 2 H, CH2CH); 1.61—1.65 (m, 3 H,
CH3CH); 5.33—5.45 (m, 2 H, CH=CH). MS, m/z: 140 [M]+.
Found (%): C, 85.62; H, 14.20. C10H20. Calculated (%):
C, 85.71; H, 14.29.
1
1500, 1450, 980, 730, 690. H NMR, δ: 1.10 (t, 2 H, CH2D,
J = 7.0 Hz); 1.80—1.90 (m, 2 H, CH2); 2.98 (t, 2 H, CH2—Ph,
J = 7.0 Hz); 7.25—8.02 (m, 7 H, H arom.). 13C NMR
1
(CDCl3), δ: 13.96 (t, C(1), JCD = 19.1 Hz); 23.78 (t, C(2));
35.09 (t, C(3)); 123.53 (d, C(6), C(12)); 125.68 (d, C(10));
127.24 (d, C(11)); 128.34 (d, C(7)); 128.47 (d, C(5)); 128.80
(d, C(9)); 131.20 (s, C(13)); 132.12 (s, C(8)); 138.62 (s, C(4)).
MS, m/z: 171 [M]+. Found (%): C, 91.14; H, 8.68. C13H13D.
Calculated (%): C, 91.23; H, 7.60; D, 1.17.
Undec-2-ene (9d), b.p. 70—72 °C (10 Torr). 1H NMR,
δ: 0.88 (t, 3 H, CH3, J = 7.1 Hz); 1.26—1.40 (m, 12 H,
CH2); 1.85—2.05 (m, 2 H, CH2CH); 1.57—1.67 (m, 3 H,
CH3CH); 5.34—5.45 (m, 2 H, CH=CH). MS, m/z: 154 [M]+.
This work was carried out with the financial support
of the Russian Foundation for Basic Research (Project
Nos. 98-03-32913 and 98-03-32912).

296
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 2, February, 2001
Ibragimov et al.
Khim., 1998, 712 [Russ. Chem. Bull., 1998, 47, 691 (Engl.
Transl.)].
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Received March 24, 2000;
in revised form October 19, 2000