Synthesis and conversions of metallocycles 22. NMR studies of the mechanism of Cp2ZrCl2-catalyzed cycloalumination of olefins with triethylaluminum to form aluminacyclopentanes

Article abstract of DOI:10.1023/A:1009536328369

The mechanism of cycloalumination of olefins under the action of AlEt₃ in the presence of Cp₂ZrCl₂ giving rise to aluminacyclopentanes was investigated by dynamic ¹H and ¹³C NMR spectroscopy. The bimetallic complex Cp₂ZrEtCl-AlEt₃ is formed initially and is converted into the bridged complex Cp₂Zr(Cl)CH₂CH₂AlEt₂ as a result of β-hydride shift and elimination of the ethane molecule. The resulting complex adds a molecule of the initial olefin yielding aluminacyclopentanes. Under the action of Et₂AlCl in the presence of an excess of AlEt₃, zirconacyclopentanes give rise to intermediate bimetallic complexes stable at -70 °C. Under the reaction conditions, the latter compounds are converted into aluminacyclopentanes.

Full text of DOI:10.1023/A:1009536328369

Russian Chemical Bulletin, International Edition, Vol. 49, No. 12, December, 2000
2051
Organometallic Chemistry
Synthesis and conversions of metallocycles
22.* NMR studies of the mechanism of Cp2ZrCl2-catalyzed cycloalumination
of olefins with triethylaluminum to form aluminacyclopentanes
L. M. Khalilov,« L. V. Parfenova, S. V. Rusakov, A. G. Ibragimov, 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
The mechanism of cycloalumination of olefins under the action of AlEt3 in the presence of
Cp2ZrCl2 giving rise to aluminacyclopentanes was investigated by dynamic 1H and 13C NMR
spectroscopy. The bimetallic complex Cp2ZrEtCl—AlEt3 is formed initially and is converted
into the bridged complex Cp2Zr(Cl)ÑH2CH2AlEt2 as a result of β-hydride shift and elimina-
tion of the ethane molecule. The resulting complex adds a molecule of the initial olefin
yielding aluminacyclopentanes. Under the action of Et2AlCl in the presence of an excess of
AlEt3, zirconacyclopentanes give rise to intermediate bimetallic complexes stable at –70 °C.
Under the reaction conditions, the latter compounds are converted into aluminacyclopentanes.
Key words: reaction mechanism, metal-complex catalysis, cyclometallation, alumina-
cyclopentanes, dynamic NMR spectroscopy.
Although hydro- and carboalumination of unsatur-
ated compounds under the action of alkylhaloalanes are
well-known reactions, which are widely used in synthe-
sis, catalytic cyclometallation of alkenes2 and alkynes3
with the use of organoaluminum compounds (OAC) in
the presence of Cp2ÌCl2 (Ì = Ti or Zr) has been
discovered only recently. This reaction was used for the
preparation of new classes of organoaluminum com-
pounds, for example, aluminacyclopentanes,2 alumina-
cyclopentenes,3 aluminacyclopropanes,4 and alumina-
cyclopropenes.5 The formation of aluminacyclopentenes
in the reactions of alkynes with alkylalanes under the
action of Cp2ZrCl2 (1) was later confirmed.6
Data on identification of intermediates formed under
the conditions of the above-mentioned cycloalumination
of alkenes and alkynes with alkylalanes under the action
of Ti and Zr complexes are virtually lacking in the
literature. However, investigation of the structures of
intermediates formed in the above-mentioned reaction
would allow one to establish the mechanism of catalytic
cycloalumination of unsaturated compounds and to de-
termine the sequence of steps of the formation of cyclic
organoaluminum compounds.
Previously,2 the mechanism of synthesis of alumina-
cyclopentanes was postulated according to which direct
* For Part 21, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2086—2093, December, 2000.
1066-5285/00/4912-2051 $25.00 © 2000 Plenum Publishing Corporation

2052
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000
Khalilov et al.
transmetallation of intermediate zirconacyclopentanes
formed under the reaction conditions gives rise to
aluminacyclopentanes2 according to Scheme 1.
the reactions of styrene afforded aluminacyclopentane
containing one (the major product) and two aryl sub-
stituents at different positions of the heterocycle along
with aluminacyclopropane.11 In the present study, we
consider the mechanism of formation of the major reac-
tion products, viz., aluminacyclopentane containing one
substituent in the aluminacycle.
Scheme 1
[Cp2ZrCl2]
1
In the forthcoming paper of this series, we will report
the results of quantum-chemical calculations for the
proposed experimental model of the reaction.
R
+ AlEt3
2
Results and Discussion
Cp2Zr
Al
R
R
With the aim of establishing the structures of the key
intermediates in cycloalumination of olefins, we studied
the reaction of Cp2ZrCl2 (1) with AlEt3 (2) using Í
Indeed, examples of the direct replacement of the
zirconium atom in zirconacycles by a main-group metal
atom with retention of the initial structure of the ring
have been documented.7,8
An attempt6 has been undertaken to explain the
mechanism of cycloalumination of alkynes under the
action of AlEt3 (2) catalyzed by Cp2ZrCl2 (1) to form
aluminacyclopentenes. The proposed scheme involved
five-membered bimetallic complex 3 as the key interme-
diate, which added the alkyne molecule at the Zr—C
bond giving rise to seven-membered bimetallic complex
4. The latter decomposed to yield Cp2ZrEtCl and the
target aluminacyclopentene 5 (Scheme 2).
1
and 13Ñ NMR spectroscopy. In the 13Ñ NMR spectrum
of the initial triethylaluminum 2 recorded at –90 °Ñ, the
assignment of the signals of the bridging (C(1´) and
C(2´)) and terminal (C(1) and C(2)) ethyl groups was
made (Table 1). The 13Ñ NMR spectrum of Cp2ZrCl2
(1) has12 the only signal for the carbon atoms of the Cp
ring at δ 116.02.
According to the published data,13 alkylalanes in
solutions form four-center associates containing bridging
alkyl groups. In this connection, it can be postulated
that triethylaluminum molecules are coordinated to
Cp2ZrCl2 through the bridging chlorine atoms and the
carbon atoms of the methylene fragment of the ethyl
group (transition states 1a and 1b) (Scheme 3). The
13Ñ NMR spectra of the Cp2ZrCl2—AlEt3 system (1 : 1)
at –70 °Ñ have four broadened high-field signals for the
Cα atoms of the bridging and terminal ethyl groups with
the intensity ratios of 2 (δ 1.11) : 1 (δ 0.59) and 1
(δ –0.52) : 1 (δ –0.26), respectively. Pairs of these
signals coalesce as the temperature increases to –45 °Ñ
resulting in two broadened signals at δ 1.04 and –0.32,
which in turn coalesce into one signal (δ –0.19) at
–20 °Ñ. These phenomena of the intra- and intermo-
lecular exchange (Scheme 4) as well as comparison of
the intensities of the signals observed at high field and
the resonance lines of the Ñð rings located at low field
are indicative of the formation of stable complexes 6 and
7 with composition Cp2ZrEtCl—AlEt3 (see Table 1) (a
portion of the initial Cp2ZrCl2 remained unconsumed).
It was found that the reaction of Cp2ZrCl2 with AlEt3
also afforded a stoichiometric amount of Et2AlÑl (8)
with respect to the initial AlEt3.
Scheme 2
2 AlEt3
R
R
2
Cp2ZrCl2
Cp2Zr
AlEt2
Cl
1
3
R
R
+ Cp2ZrEtCl
Al
Cp2Zr
l
A Et
2
R
Cl
R
4
5
The structure of five-membered bimetallic complex 3,
which was formed in the reaction of AlEt3 (2) with
Cp2ZrCl2 (1), has been discussed previously.6,9,10 How-
ever, the structure of complex 4 has only been postu-
lated and has not been supported by experimental data.
The present study was aimed at monitoring the course
of catalytic cycloalumination of olefins with AlEt3 (2) in
the presence of Cp2ZrCl2 (1) by NMR spectroscopy,
performing the experimental simulation of individual
steps of the process, establishing the structures of the
intermediates responsible for the formation of alumina-
cycles, and revealing the reaction mechanism based on
the experimental data. We used hex-1-ene and styrene as
olefins. In the former case, the reaction proceeded
selectively to give 3-butylaluminacyclopentane,2 whereas
In the 13Ñ NMR spectrum of the Cp2ZrEtCl—AlEt3
system, the resonance line of the C atom observed in the
region of δ 51—56 is of considerable interest. The direct
spin-spin coupling constant J13
= 119.9 Hz14 indi-
1
ї Í
cates that this signal belongs to the C atom of the
methylene fragment of the terminal ethyl group bound
to the Zr atom in complex 6. This spectral line is shifted
upfield, on the average, by 5 ppm as the temperature
increases from –70 to 0 °Ñ, which is indicative of the
rapid (within the NMR time scale) exchange between

Mechanism of cycloalumination of olefins
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000 2053
Scheme 3
Cp2ZrCl2
1
Cl
AlEt2
AlEt3
Et2Al
Et Me
CH2
Cl
AlEt3
2
Cp2Zr
8
Cl
AlEt2
CH2
AlEt2
Cl
A Et
l
2
CH2
Me
1a
Cp2Zr
Me
CH2
Me
1b
Cp2Zr
11
C
l
AlEt3
C
l
–AlEt2Cl
H
CH2
Me
CH2
Et
Cp2Zr
Cl
CH2
A Et
Cp2Zr
Et
Cp2Zr
Et
Cl
A Et
l
2
l
Cl
2
6
7
15
–C2H6
EtAl
Cp
Cp
Zr
–C2H6
Cl
Cl
Zr
AlEt2
Et2Al
R
R
CH2
Me
CH2
Me
14
Cp
Cp
Cp2Zr
AlEt2
9
6
Cl
13
Cp2Zr
AlEt2
7
Cl
3
AlEt2
AlEt2
R
–C2H6
12
Cp2Zr
AlEt3
C
l
12, 13, 14: R = Bun (a), Ph (b)
10
the terminal and bridging ethyl groups bound to the Zr
atom under the reaction conditions. The addition of
tetrahydrofuran to the reaction mixture caused destruc-
tion of dimeric structures 6 and 7 to form the solvated
molecule Cp2ZrEtCl•THF (6à).
rings (δÍ 5.77) of complex 9 corresponds to the signal at
δÑ 110.55 in the 13Ñ NMR spectrum. In compound 10,
the hydrogen atoms of the Ñð rings are sterically
nonequivalent9,10 due to the chiral center of the mol-
ecule, which is manifested in the anisochronism of the
Ñð-group signals (δÍ 5.57 and 5.64) although no analo-
gous splitting was observed in the 13Ñ NMR spectra
(δÑ 108.60). The resonance line of the protons of the Ñð
groups of complex 3 at δÍ 5.49 corresponds to the signal
at δÑ 108.21. In addition, the spectra of the system
under study have signals of ethane (at δÍ 0.78 and at
δÑ 7.05) resulting from β-hydride shift in the course of
formation of structures 3, 9, and 10. The observed
processes of β-hydride shift in alkyl groups are typical of
Group IV transition metals.15
The formation of complexes 3 and 6—10 was also
observed in the reactions with the use of triethylaluminum
taken in ratios of 2 : 1, 5 : 1, 10 : 1, or 20 : 1 with respect
to Cp2ZrCl2. Under these conditions, complex 11 was
obtained along with compounds 3 and 6—10. The struc-
ture of 11 was established by 13Ñ NMR spectroscopy.
The assignment of the signal was made taking into
account that the resonance lines of the carbon atoms of
Therefore, contrary to the data on the stability of the
Cp2ZrCl2—AlEt3 system (1 : 1) reported previously,6
this system was unstable under the condition used in the
present study and changed with time (Fig. 2). Initially,
complexes 6 and 7 were formed, which were then con-
verted into compounds 3 and 9, respectively, through
β-hydride shift and elimination of the ethane molecule,
as has been mentioned previously.9 In complex 9, an
additional β-hydride shift occurred from the methyl
fragment of one of the bridging group to the dizirconium
ethyl bridge giving rise to an equilibrium mixture of
complexes 6 and 7 and five-membered bimetallic com-
plex 3. The latter reacted with an additional triethylalumi-
num molecule to give stable five-membered compound
10. The assignment of the signals in the 13Ñ NMR
spectra of the resulting complexes was made based on
1
the Í NMR spectral data (see Ref. 10) and the 2D
CHCORR spectra (Fig. 3). Thus the signal of the Ñð

2054
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000
Khalilov et al.
1
Table 1. Characteristics of the 13Ñ NMR spectra and the values of selected direct spin-spin coupling constants J13
for
1
C— H
compounds 1—3, 6—10, 12à, 14à, 16—18, and 20 (toluene-d8 as the internal standard and the solvent)*
Com- T/K
δ (1J13C— H/Hz)
1
pound
Ñð
Ñ(1)
d—
Ñ(2)
—
Ñ(1´) Ñ(2´)
Ñ(3)
—
Ñ(4) Ñ(5) Ñ(6) Ñ(7) Ñ(8) Ñ(9) Ñ(10)
1
2
3
6
293
183
293
203
116.02
(175.8)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
–0.26
br.t
36.74
br.t
d1.11
br.t
d51.70
d–0.52
br.t
2.86
br.t
13.52
br.t
43.01
br.d
113.86
t
12.94
br.t
45.46
t
9.18
br.t
12.36
br.t
9.30
q
–0.74
0.13
br.t
—
8.06
q
—
—
108.21
dt
3.71
q
55.54
(119.9)
—
9.56
br.t
9.04
q
113.28
(174.4)
112.52
113.28
(174.4)
—
9.50
q
18.66
8.78
q
9.76
q
0.59
br.t
q
t
18.79
—
—
—
—
—
—
q
6à
7
293
293
t
—
——
—
—
—
—
—
—
—
—
—
—
—
—
—
–0.26 9.37
—
br.t
—
q
—
8
293
293
293
293
293
293
293
293
223
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
9
110.55
dt
108.60
dt
0.91
—
—
—
—
q
8.84
0.91
10
12a
14a
16
17
18
20
–8.91
—
—
—
8.84
br.t
q
—
137.28
d
40.83
dt
46.76
d
35.19
dt
38.95
dt
44.03
dt
33.55
31.08 22.24 13.65
q
t
t
t
33.23
t
38.43
t
34.08
q
37.07
q
—
—
5.07 39.79 30.04 22.95 13.98 0.45
br.t
30.50 23.93 14.05
8.51
—
br.t
—
t
—
t
q
q
111.27
d
—
—
—
—
—
—
—
t
t
q
—
t
—
t
28.43 23.22 13.99 0.85
9.10
9.10
9.10
—
br.t
q
—
—
—
t
—
t
29.85 23.48 13.92 0.85
—
br.t
q
10.28
br.t
—
t
—
t
37.52
q
32.58 23.28 14.11 0.85
—
br.t
q
* The atomic numbering scheme is given in Fig. 1.
2´
1
2
1
2
3
4
1
2
1
2
1´
4
Cl
Zr
Zr
Zr
Al
Al
Al
Al
Cl
Al
3
Cl
1´
2´
1´
2´
3
2
7
6
1
2
4
1
3
10
Cl
6
4
2
Al
Al
Al
Zr
1
3
5
9
Cl
8
2
6
6
2
4
1
12a
5
7
3
5
8
14a
16
8
Al
Al
Cl Al
Cl Al
Al
7
6
6
6
2
4
2
4
3
2
4
1
1
3
5
1
5
3
5
8
7
8
7
17
18
20
Fig. 1. Atomic numbering scheme for the C atoms in compounds 2, 3, 6—8, 12à, 14à, 16—18, and 20.

Mechanism of cycloalumination of olefins
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000 2055
Scheme 4
δ
0
8.78
0.59
9.50
–0.26
ClAl(Et)CH2CH3
9.37 ppm
1.11
9.04 ppm
–0.52
1
2
3
4
5
6
7
–70 °C
Zr
Zr
Al
Cl
Al
Cl
AlOCH2CH3
ClAl(Et)CH2CH3
Cp
(10)
6
7
AlOCH2CH3
Cp
(3)
Cp
(11)
8.91
1.04
9.24
–0.32
Cp
(9)
–45 °C
Zr
Zr
Al
Cl
Al
Cl
120 100
80
60
40
20
δ
Fig. 3. 2D CHCORR spectrum of the 1 : 2 Cp2ZrCl2—AlEt3
system (13Ñ, 75.46 MHz; 1Í, 300.13 MHz).
bimetallic structure 10 formed in the Cp2ZrCl2—AlEt3
system. Two-dimensional CHCORR spectroscopy (see
Fig. 3) demonstrated that the resonance line of the
protons of the Ñð group of complex 11 in the 1Í NMR
spectrum is observed at δ 5.28.
9.17
–0.19
9.17
–0.19
+
+
–20 °C
Zr
Zr
Al
Cl
Al
(AlEt3)
Cl
The addition of olefin 12 to the AlEt3—Cp2ZrCl2
system afforded monosubstituted aluminacyclopentanes
14 both in the case of the Cp2ZrCl2-catalyzed process and
in the case of mixing of all components in the stoichio-
metric ratio, but in the latter case the rate was lower and
the yield was substantially smaller (in the case of the
AlEt3 : Cp2ZrCl2 : styrene ratio of 1 : 1 : 1, the yield of
the final aluminacyclopentane was ∼0.5% after 24 h).
With the aim of elucidating the role of the Zr—Al
complexes in the formation of aluminacycloalkanes, we
prepared a solution of an equilibrium mixture of bime-
tallic complexes 3, 9, and 10 in toluene in the absence
of Et2AlCl. A decrease in the intensity of the resonance
line of the Ñð groups in the 13Ñ NMR spectra of five-
membered bimetallic complex 3 simultaneously with the
appearance of the signals for the C atoms of the corre-
sponding aluminacyclopentanes 14 (Fig. 4) and complex
6, which were observed upon the addition of hex-1-ene
to the reaction mixture, indicate that compound 3 acts
apparently as a catalytically active center responsible for
the coordination of olefin, which eventually leads to the
formation of cycloalumination products. Based on com-
parison of the spectral characteristics and the structures
of the compounds prepared from dimethylzirconocene
and alkylalanes,16 it can be assumed that compound 3 is
a σ-complex in which the zirconium and aluminum
atoms are linked to each other not only through two
carbon atoms but also through the bridging chlorine
atom to form the bimetallic five-membered ring.
the Ñð groups of rather unstable diethylzirconocene
obtained from Cp2ZrÍ2 and ethylene are observed in the
region of δ 102, whereas the addition of triethylaluminum
leads to a slight downfield shift of this signal (δÑ 102.62),
which is equal to the chemical shift of the Ñð rings of
6, 7
9
1
3, 10
4
3
2
1
With the aim of revealing the role of zirconacyclo-
pentane intermediates in cycloalumination of olefins, we
studied the reactions of trans-3,4-dibutylbis(η5-cyclo-
pentadienyl)zirconacyclopentane (16) (see Ref. 17) with
alkylhaloalanes using a model reaction as an example. It
120
115
110
δ
Fig. 2. Evolution of the Cp2ZrCl2—AlEt3 system (1 : 1) with
time: t = 15 (1), 95 (2), 225 (3), and 375 (4) min. The chemical
shifts of the signals of the Cp rings in the 13Ñ NMR spectrum
(22.50 MHz) are given.

2056
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000
Khalilov et al.
Cp
(9)
Zirconacyclopentane was rather slowly converted into
Cp2ZrCl2 and chlorine-containing 1,4-dialuminum com-
pound 18 under the action of ethylaluminum dichloride.
Hence, attempts to perform the stage of transmetallation
of zirconacyclopentane with the use of individual trialkyl-
or alklyhaloalanes were unsuccessful (Scheme 5). We
demonstrated for the first time that the combined use of
AlEt3 and Et2AlCl resulted in the desired transmetal-
lation of zirconacyclopentane 16 to yield aluminacyclo-
pentane 20.
a
Al(CH2CH3)3
C(6)
Cp
C(4)
(12a)
(10)
C(1)
(12a)
(12a)
Cp
(3)
Al(CH2CH3)3
C(2)
(12a)
C(3)
C(5)
(12a)
(12a)
Cp
(11)
The model transmetallation reaction was carried out
under the following reaction conditions: the tenfold
excess of AlEt3 (2) and the stoichiometric amount of
Et2AlCl were added to zirconacyclopentane 16. An in-
termediate (δÑ(Cp) 107.56) (Fig. 5) was detected in the
reaction performed at low temperature (–70 °Ñ). Based
on the published data,18 this intermediate was identified
as a seven-membered bimetallic complex (19). Complex
19 was very unstable and was transformed into 3,4-di-
substituted aluminacyclopentane 20 and Cp2ZrEtCl (15).
The latter in turn was converted into complexes 10 and
11 (see Scheme 3). The 13C NMR spectrum of
aluminacyclopentane 20 has characteristic signals for the
carbon atoms of the metallocycle at position 2 (accord-
ing to Fig. 1) at δ 44.03.
b
Cp
(6, 7)
Cp
(13)
C(8)
(14a)
C(10)
(14a)
C(5)
(14a)
C(6)
(14a)
c
C(1)
(14a)
C(7)
(14a)
C(4)
(14a)
C(2)
(14a)
C(3)
(14a)
C(9)
(14a)
140
120 110 100 40
30
20
10
δ
The fact that the signal for the carbon atoms of the
Ñð rings of complex 19 corresponds to the signal at
δ 107.43 observed in the course of the reaction of an
equilibrium mixture of compounds 3, 9, and 10, which
has been prepared in the absence of Et2AlCl, with
hex-1-ene at –40 °Ñ (see Fig. 4, b), suggests that seven-
membered intermediate 13 is involved in cycloalumi-
nation of α-olefins. This assignment is supported by the
fact that the resonance lines of the carbon nuclei of the
Cp groups are shifted upfield by 5 ppm upon the ring
expansion from the four-membered ring (in complex 6)
to the five-membered ring (in complex 3). An analogous
effect (up to 0.8 ppm) is observed when the number of
Fig. 4. Dynamic 13Ñ NMR spectrum (22.50 MHz; toluene-d8
as the internal standard and the solvent) in studies of the
participation of the Zr—Al-complexes in cyclometallation of
olefins with triethylaluminum exemplified in hex-1-ene at the
initial instant t = 0 min at –70 °Ñ (a), at t = 20 min and –40 °Ñ
(b), and after completion of the reaction at 20 °Ñ (c).
should be noted that zirconacyclopentane does not un-
dergo transformations under the action of triethylalumi-
num. The addition of diethylaluminum chloride afforded
compound 1 (δÑ(Ñð) 116.35) along with Cp2ZrEtCl
(δÑ(Ñð) 113.03) and 1,4-dialuminum compound 17.
Scheme 5
R
R
Et
Zr
R
R
Cl
Et
6
Et2AlCl + AlEt3
Zr
Zr
AlEt2
(1 :10)
Cl AlEt2
16
19
Et2AlCl
EtAlCl2
2 AlEt3
–C2H6
AlEt3
–Cp2ZrEtCl
–Cp2ZrCl2
–Cp2ZrCl2
–Et2AlCl
R
R
AlEt
AlEt2
AlEt2
Et
Zr
R
R
R
R
Et
Al
Al
Cl Al
Cl Al
20
Zr
AlEt2
Cl
Et
17
18
10
11
R = Bun

Mechanism of cycloalumination of olefins
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000 2057
Experimental
Cp
a
(16)
All operations with the use of organometallic compounds
were carried out under an atmosphere of argon. The solvents
were distilled from triisobutylaluminum immediately before use.
A 91.8% solution of triethylaluminum in hexane was used;
Cp2ZrCl2 was synthesized from ZrCl4 according to a procedure
reported previously.19 Glass vessels and NMR tubes were dried
at 200 °Ñ and stored in a desiccator under argon.
Spectral studies were carried out on Jeol FX-90Q and Bruker
AM-300 spectrometers using fully or partially proton-decoupled
dynamic 1Í and 13Ñ NMR spectroscopy in the temperature range
from –90 to 25 °Ñ. Toluene-d8 was used as the internal standard
and the solvent. The mass spectra were measured on a Finnigan
4021 GLC-mass spectrometer and analyzed using a data base.20
Reaction of AlEt3 (2) with Cp2ZrCl2 (1). A. Toluene-d8
(0.5 mL) and Cp2ZrCl2 (0.146 g, 0.5 mmol) were placed in an
NMR tube (d = 5 mm) filled with argon. The tube was cooled to
–63 °Ñ. Then AlEt3 (0.07 mL, 0.5 mmol) was added and the tube
was transferred to a unit of the spectrometer for recording the
Cp
(10)
Cp
(19)
b
c
Cp
(6)
Cp
(11)
Cp
(10)
115
110
105
δ
Fig. 5. Dynamic NMR spectrum in studies of the stage of
transmetallation of zirconacyclopentane 16 with diethylalumi-
num chloride in the presence of an excess of AlEt3 (the region
of resonance lines of the Ñð rings is given) (22.50 MHz;
toluene-d8 as the internal standard and the solvent): the initial
sample at T = 293 K (a), the sample after cooling to 203 K (b),
and the sample after subsequent heating to 293 K (c).
spectrum in a specified temperature mode (from –70 to 25 °Ñ).
B. Toluene-d8 (2 mL), Cp2ZrCl2 (0.584 g, 2 mmol), and
AlEt3 (a 91.8% solution in hexane; 0.3 mL, 2 mmol) were
placed in a three-neck flask equipped with a magnetic stirrer
and filled with argon at 20 °Ñ and the reaction mixture was
stirred. Aliquots (0.4 mL) of the mixture were withdrawn with
the use of a syringe, placed in NMR tubes after 15, 95, 225, and
375 min, and the spectra were recorded at –60 °Ñ (see Fig. 1).
Reactions of AlEt3 (2) with olefins in the presence of
catalytic amounts of Cp2ZrCl2 (1). Toluene-d8 (2 mL),
Cp2ZrCl2 (58.4 mg, 0.2 mmol), α-olefin (10 mmol), and AlEt3
(a 91.8% solution in hexane; 1.79 mL, 12 mmol) were placed in
a three-neck flask equipped with a magnetic stirrer and filled
with argon at 20 °Ñ. The mixture was stirred for 8 h and then
treated with a 20% D2SO4 solution in D2O at 0 °Ñ. The
products were extracted with hexane and the organic layer was
dried with MgSO4. The yields of aluminacyclopentanes were
determined based on GLC of the deuterolysis products.
Cyclometallation of hex-1-ene afforded 3-butyl-1-ethyl-
aluminacyclopentane (14à) in 65.8% yield. The NMR spectral
data for aluminacyclopentane 14à and its deuterolysis product
correspond to the published data.2
Cyclometallation of styrene gave rise to 1-ethyl-3-
phenylaluminacyclopentane (62.6%), 1-ethyl-2-phenylalumina-
cyclopentane (15.9%), 1-ethyl-2,4-diphenylaluminacyclopentane
(3.6%), and 1-ethyl-2,5-diphenylaluminacyclopentane (1.2%).
The assignment of the signals in the 1Í and 13Ñ NMR spectra
of the reaction products have been reported previously.11
Preparation of an equilibrium mixture of bimetallic Zr—Al
complexes 3, 9, and 10. Toluene (0.1 mL), Cp2ZrCl2 (0.292 g,
1 mmol), and AlEt3 (a 91.8% solution in hexane; 1 mmol,
0.14 mL) were placed in an NMR tube filled with argon. The
mixture was stirred at 20 °Ñ. Then the tube was immersed in
liquid nitrogen for a few seconds. Ethane was evolved and
1,2-bis((µ,µ-dichloro)diethylaluminio(dicyclopentadienyl)zir-
conio(IV))ethane precipitated as the mixture was heated to
∼20 °Ñ.9 The solution was decanted from the precipitate and the
precipitate was washed twice with toluene. Toluene-d8 (0.1 mL)
and AlEt3 (a 91.8% solution in hexane; 0.14 mL, 1 mmol) were
added to the solid residue. As a result, a transparent orange
solution of 1,2-bis(chloro(dicyclopentadienyl)zirconio(IV))ethane
(9), Al,Zr-µ-chloro-1-(dicyclopentadienylzirconio(IV))-2-
(diethylaluminio)ethane (3), and Al,Zr-µ-chloro-1-(dicyclo-
pentadienylzirconio(IV))-2,2-bis(diethylaluminio)ethane (10) was
obtained. The 1Í NMR spectra of complexes 3, 9, and 10 agree
with the published data.9
atoms is increased from five (in the initial metallocycle 3)
to seven (in the product of insertion of α-olefin at the
Zr—C bond whose composition corresponds to complex
13). The intensities of the signals for the C atoms of the
cyclopentadienyl groups corresponding to this complex
are small because of the instability of the complex under
the reaction conditions in the presence of an excess of
triethylaluminum. The assignment of the resonance line
at δ 107.43 to structure 13 is confirmed by the published
data on the spectral characteristics of the seven-
membered Zr—Al complex, viz., Al,Zr-µ-chloro-
1-(dicyclopentadienylzirconio(IV))-4-(dichloroalumi-
nio)but-2-ene.18
Taking into account the experimental data, the fol-
lowing general scheme of the reaction mechanism of
cyclometallation of olefins can be assumed (see Scheme 3).
In the first stage, molecules of triethylaluminum 2 and
catalyst 1 form complexes 1à and 1b owing to the rapid
interligand exchange. These complexes give intermediates
6 and 7, respectively, under the action of another mol-
ecule of AlEt3. Intramolecular β-hydride shift with the
simultaneous elimination of ethane affords key interme-
diate 3. The expansion of the five-membered ring of 3
through the insertion of the α-olefin molecule at the
Zr—C bond is favorable for the formation of unstable
complex 13, which is transformed under conditions of
cycloalumination to give aluminacyclopentane 14 and
ethylzirconocene chloride 15. Coordination of the latter
to yet another molecule of AlEt3 gives rise to active
complex 6, thus closing the catalytic cycle.
The structures of the resulting aluminacyclopentanes
1
14 and 20 were established by Í and 13Ñ NMR spec-
troscopy and by analysis of their deuterolysis products.

2058
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000
Khalilov et al.
Reaction of Al,Zr-µ-chloro-1-(dicyclopentadienylzirco-
nio(IV))-2-(diethylaluminio)ethane (3) with styrene. Styrene
(0.11 mL, 1 mmol) was added at 20 °Ñ to a solution of
complexes 3, 9, and 10 in toluene prepared in an NMR tube as
described above. Evolution of ethane (δÑ 7.08) and ethylene
(δÑ 122.25) and the formation of the complex with composition
Cp2ZrEtCl—AlEt3 (6 and 7) (δÑ(Ñð) 113.28) and a mixture of
mono- and diphenyl-substituted aluminacyclopentanes were ob-
served. The mixture was stirred for 1 h and then treated with a
20% D2SO4 solution in D2O at 0 °Ñ. The products were
extracted with hexane and the organic layer was dried with
MgSO4 to obtain a mixture of 1-ethyl-2-phenylalumina-
cyclopentane (71.5%), 1-ethyl-3-phenylaluminacyclopentane
(19.9%), 1-ethyl-2,4-diphenylaluminacyclopentane (0.9%), and
1-ethyl-2,5-diphenylaluminacyclopentane (0.8%), which were
identified based on studies of the deuterolysis products by
We thank L. V. Spirikhin and R. R. Muslukhov (the
Laboratory of Spectral Methods, Institute of Organic
Chemistry, Ufa Research Center of the Russian Acad-
emy of Sciences) for assistance in two-dimensional NMR
spectral studies and O. S. Vostrikova (Institute of Or-
ganic Chemistry, Ufa Research Center of the Russian
Academy of Sciences) for helpful discussion.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos. 98-03-
32912a and 98-03-32913a).
References
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1
GLC-mass spectrometry and Í and 13Ñ NMR spectroscopy.
The assignment of the signals in the 1Í and 13Ñ NMR spectra
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Reaction of Al,Zr-µ-chloro-1-(dicyclopentadienylzir-
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3,4-Dibutylbis(η5-cyclopentadienyl)zirconacyclopentane
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methyl)decane.21
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cyclopentane (16) with EtAlCl2. Ethylaluminum dichloride
(0.85 mmol) was added to a solution of zirconacyclopentane 16
(0.85 mmol) in toluene-d8 at –63 °Ñ and threo-2,3-dibutyl-1,4-
bis((chloro)ethylaluminio)butane (18) was obtained (see
Table 1). Then the mixture was treated with a 20% D2SO4
solution in D2O at 0 °Ñ. Deuterolysis afforded threo-5,6-
bis(deuteriomethyl)decane.21
Reaction of 3,4-dibutyl-bis(η5-cyclopentadienyl)zirconacyclo-
pentane (16) with Et2AlCl in the presence of an excess of AlEt3.
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successively added to a solution of zirconacyclopentane 16 (0.85
mmol) in toluene-d8 at –63 °Ñ. The spectral data of the resulting
3,4-dibutyl-1-ethylaluminacyclopentane (20) are given in Table
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0 °Ñ. Deuterolysis afforded threo-5,6-bis(deuteriomethyl)decane.21
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Received July 20, 2000