Mechanism of Cp2ZrCl2-catalyzed olefin hydroalumination by alkylalanes

Article abstract of DOI:10.1007/s11172-005-0254-z

The composition of intermediates of the Cp₂ZrCl ₂-catalyzed hydroalumination of α-olefins by isobutylalanes (HAlBuⁱ ₂, AlBuⁱ ₃, ClAlBu ⁱ ₂) was studied by dynamic

Full text of DOI:10.1007/s11172-005-0254-z

316
Russian Chemical Bulletin, International Edition, Vol. 54, No. 2, pp. 316—327, February, 2005
Mechanism of Cр2ZrCl2ꢀcatalyzed olefin hydroalumination by alkylalanes
ꢀ
L. V. Parfenova, S. V. Pechatkina, L. M. Khalilov, and U. M. Dzhemilev
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences,
141 prosp. Oktyabrya, 450075 Ufa, Russian Federation.
Fax: +7 (347 2) 31 2750. Еꢀmail: ink@anrb.ru
The composition of intermediates of the Cp2ZrCl2ꢀcatalyzed hydroalumination of αꢀoleꢀ
1
fins by isobutylalanes (HAlBui2, AlBui3, ClAlBui2) was studied by dynamic H and 13C NMR
spectroscopy. The reaction of Cp2ZrCl2 with isobutylalanes affords the complex
(Cp2ZrHCl•HAlBui2)2 responsible for αꢀolefin hydroalumination.
Key words: reaction mechanism, hydroalumination, dynamic NMR spectroscopy, olefins,
organozirconium compounds, organoaluminum compounds.
The direct hydroalumination of olefins by activated
The hydroalumination of linear and cyclic olefins by
HAlBui2 (2) has previously9,10 been found to occur more
efficiently when (RO)nZrCl4–n (n = 1—4) are used as
catalysts.
aluminum and hydrogen producing mixed trialkylalanes
has first been performed by Ziegler.1 Further, methods for
direct thermal hydroalumination of alkenes by simplest
organoaluminum compounds (OAC) were developed to
synthesize higher representatives of this class.2—4
The first attempts to extend the scope of this reaction
by metal complex catalysts are related, in particular, to
the use of titanium and zirconium compounds in olefin
hydroalumination followed by the oxidation of higher
OAC produced to primary alcohols.5 Among considerꢀ
able achievements in this area is the development of oleꢀ
fin hydroalumination with LiAlH4 in the presence of
ZrCl4;6,7 monoꢀ and β,β´ꢀdisubstituted αꢀolefins do seꢀ
lectively react to form the corresponding lithium tetraꢀ
alkylalanates.
It is found11 that Cp2ZrCl2 (1) catalyzes the hydroꢀ
alumination of linear αꢀolefins by AlBui3 (3). It is also
shown12—14 that ClAlBui2 (4) hydroaluminates monoꢀ and
disubstituted linear and cyclic olefins in the presence of
Cp2ZrCl2. The yields of products of olefin hydroaluminaꢀ
tion are 85—99% and decrease to 50% when Cp2ZrCl2 is
replaced by ZrCl4. This reaction occurs under very mild
conditions (0—20 °C) and can be applied to diꢀ and
triolefins, including cyclic and functionally substituted
olefins,15 in particular, containing electronꢀdonor subꢀ
stituents,16,17 whose hydroalumination with aluminum
hydrides cannot be performed.
The authors of the known work8 postulate that hydroꢀ
alumination proceeds through intermediate zirconium
hydride complexes, which would hydrozirconate the startꢀ
ing olefins to form active alkylzirconium intermediates.
Their subsequent transmetallation results in the regeneraꢀ
tion of the starting hydrides (Scheme 1).
Based on these results, the authors11 proposed the
mechanism of catalytic olefin hydroalumination by triꢀ
alkylalanes, including steps of alkylation (A), elimination
of isobutylene (B), hydrozirconation (C), and transꢀ
metallation (D) (Scheme 2).
Scheme 2
Scheme 1
LiAlH4
LnZrH
LnZrCH2—CH2—R
LnZrH + al—CH2—CH2R
al = LiAl/4; Ln are ligands at Zr atom
According to available data,6 Cp2ZrCl2 (1), VCl4,
Cp2TiCl2, and TiCl4 can be used along with ZrCl4 as
hydroalumination catalysts. However, the use of the zirꢀ
conium catalysts is preferential in the most cases.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 311—322, February, 2005.
1066ꢀ5285/05/5402ꢀ0316 © 2005 Springer Science+Business Media, Inc.

Mechanism of olefin hydroalumination
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
317
Y (%)
The authors of the aboveꢀconsidered works postulate
that zirconium hydrides are formed in these reactions as
intermediates and, as it has been shown,18—20 can hydroꢀ
zirconate olefins. This was not experimentally proved beꢀ
fore the beginning of our studies.
100
3
80
2
In the present work, we studied olefin hydroaluminaꢀ
tion by alkylalanes, viz., HAlBui2 (2), AlBui3 (3), and
ClAlBui2 (4), in the presence of Cр2ZrCl2 (1) as the cataꢀ
lyst and identified intermediate complexes and key interꢀ
mediates of the process.
60
40
1
20
Results and Discussion
0
100
200
300
t/min
Based on the present studies and published11 and our
data obtained previously,12,16,21,22 we determined the conꢀ
ditions (OAC, reagent ratio, solvent, and temperature)
under which olefin hydroalumination occurs almost comꢀ
pletely. When studying the hydroalumination of such alkꢀ
1ꢀenes as hexꢀ1ꢀene (5a), heptꢀ1ꢀene (5b), octꢀ1ꢀene (5c),
nonꢀ1ꢀene (5d), decꢀ1ꢀene (5e), we found that the yield
of products increases with the elongation of the hydrocarꢀ
bon chain (Table 1), although this increase is insignificant.
Benzene turned out to be an optimum solvent. For
instance, when AlBui3 was used as the hydroaluminating
agent, the yields of the products exceed 90%, while in
THF they are lower than 15%. Among the OAC used,
AlBui3 (3) provides the highest rate of hydroalumination
of αꢀolefins (Fig. 1; molar ratio Cp2ZrCl2 : OAC : oleꢀ
fin = 1 : 60 : 50). The reaction of catalyst 1 with ClAlBui2
(4) has a long induction period (up to 3 h). Among the
studied OAC, the lowest hydroalumination activity beꢀ
longs to HAlBui2 (2), although the highest reaction rate
should be expected in this case, taking into account the
aforesaid. An increase in the catalyst concentration inꢀ
creases the reaction rate. For example, for the reaction
with ClAlBui2 (4), a fivefold increase in the catalyst conꢀ
centration substantially shortens the induction period
(Fig. 2). The temperature plot of the yield of the hydroꢀ
alumination product for AlBui3 (3) is shown in Fig. 3. For
all OAC, yields of the hydroalumination products inꢀ
crease with temperature.
Fig. 1. Influence of the OAC type on the yield of product of octꢀ
1ꢀene hydroalumination (Y): HAlBui2 (1), ClAlBui2 (2), and
AlBui3 (3) (molar ratio Cp2ZrCl2 : OAC : olefin = 1 : 60 : 50,
C6H6, 20 °C).
Y (%)
100
1
2
80
3
60
40
20
0
100
200
300
t/min
Fig. 2. Influence of the catalyst concentration on the yield of
the product of octꢀ1ꢀene hydroalumination (Y ) by diisoꢀ
butylaluminum chloride (4) (C6H6, 20 °C): molar ratio
Cp2ZrCl2 : 4 : olefin = 1 : 12 : 10 (1), 0.3 : 12 : 10 (2), and
0.2 : 12 : 10 (3).
Y (%)
3
100
80
2
60
1
We chose dynamic H and 13C NMR spectroscopy as
1
40
the main technique for studying intermediate complexes
20
Table 1. Yields (%) of the hydroalumination products of olefins
5a—e (5 h, 20 °C, C6H6, molar ratio Cp2ZrCl2 : OAC : olefin =
1 : 60 : 50)
0
100
200
300
t/min
Fig. 3. Temperature effect on the yield of the product of octꢀ1ꢀ
ene hydroalumination (Y) by triisobutylaluminum (3): T = 0 (1),
10 (2), and 20 °C (3) (molar ratio Cp2ZrCl2 : 3 : olefin =
1 : 60 : 50, C6H6).
OAC
Olefin
5a
5b
5c
5d
5e
2
3
4
17
91
75
18
93
76
17
94
78
19
95
81
18
96
82
of the reaction involving Cp2ZrCl2 (1). Complexes of the
Cp2ZrRR´ type contain ten equivalent protons and ten
carbon atoms of the Cp fragment, whose chemical shifts

318
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
Parfenova et al.
depend on the ligand environment of the central Zr atom
and can be used as characteristic labels. For instance, the
replacement of one Cl atom in the starting complex 1
(δH 6.02 and δC 116.02) by Et group to form the
Cp2ZrEtCl•AlEt3 complex23 results in the the upfield shift
of the signal of the Cp rings (δH 5.91 and δC 113.28). The
replacement of the Cl atom by the H atom in a hydride
complex, e.g., Cp2ZrH2•HAlBui2•ClAlBui2,8,18,24,25 reꢀ
sults in a stronger upfield shift of the signals of the Cp
rings (δH 5.71 and δC 104.30).
To establish the structure of intermediate complexes
involved in hydroalumination, we studied the systems conꢀ
sisting of Cp2ZrCl2 (1) and three types of OAC (HAlBui2,
AlBui3, and ClAlBui2). Complex 1 was completely disꢀ
solved in benzeneꢀd6 at 20 °C and the ratio 1 : OAC =
1 : 3. The Cp2ZrCl2—HAlBui2 system turned out to be the
simplest for the description of the results of the reaction.
The monitoring of the reaction at –90—–70 °C revealed
the formation of an unstable complex with the lowꢀintenꢀ
sity signal of the Cp rings in the 13C NMR spectra
(δ 108.50). When the temperature increases to –10 °C,
the complex irreversibly transforms into stable structure 7
with the signal of the Cp rings at δ 105.16 (Scheme 3). An
increase in the HAlBui2 concentration to the molar ratio
Cp2ZrCl2 : OAC = 1 : 15 results in the upfield shift of the
signal of the Cp rings of complex 7 to δ 104.53.
Complex 7 was described in literature8,18,24,25 and
identified by us on the basis of the H NMR spectra. It
1
was shown by the 2D HH—COSY spectra that the system
of three hydride atoms is spinꢀbound. The geminal spinꢀ
spin coupling constant (SSCC), being 6.1 Hz, was found
from the 1D 1H NMR spectrum (Table 2).
The formation of complex 7 involves three HAlBui2
molecules via the successive interligand exchange of the
Cl atoms in the starting Cp2ZrCl2 by the H atoms in
molecule 2. This process proceeds, probably, through reꢀ
versible intermediate steps in which the formation of
bridged structures 6a—c can be assumed (see Scheme 3).
The signal observed at low temperature (δC 108.50) can
belong to the carbon atoms of the Cp rings of one of these
complexes.
Complex 7 is known to reduce carbonyl compounds
to alcohols18 and hydrogenate acetylenes.25 However, the
activity of this complex toward olefins was not studied.
All our attempts to involve complex 7 in the reaction with
alkenes were unsuccessful. These results suggest that one
of the intermediate complexes, viz., 6a, 6b, or 6c, is reꢀ
sponsible for alkene hydroalumination.
Monitoring the reaction of Cp2ZrCl2 with AlBui3 (1 : 3)
in benzeneꢀd6 at 20 °C, we found one more resonance
line of the Cp rings in the 13C NMR spectra at δ 113.24.
Along with the latter, the spectrum contains lines characꢀ
teristic of one of the hypothetical complexes 6a, 6b, or 6c
(δCp 108.50) and complex 7 (δCp 105.16). The signal at
δCp 113.24 is always accompanied by that at δ 81.70,
which is a triplet with the SSCC 1JC,H = 117.2 Hz characꢀ
teristic of organozirconium compounds.26 Based on the
chemical shift and SSCC values, we can assign this signal
to the C atom of the isobutyl group bound to the Zr atom
in alkyl complex 8a (Scheme 4).
Scheme 3
By analogy to the Cp2ZrClEt•AlEt3 complex, whose
structure was discussed in detail,23,27,28 a binuclear strucꢀ
ture can be assigned to complex 8a. With an increase in
the AlBui3 concentration to the molar ratio 1 : 3 = 1 : 15,
the content of alkyl complex 8a decreases, and the conꢀ
centration of complex 7 increases simultaneously. In parꢀ
1
allel (according to the H and 13C NMR spectra), isobuꢀ
tylene (9) is formed, most likely, due to the βꢀhydride
transfer in complex 8a. Trihydride complex 7 appears due
to the interligand exchange in complex 8a through hypoꢀ
thetical complexes 8b and 6b (see Scheme 4). This proꢀ
cess directly involves AlBui3 and, therefore, an increase in
the concentration of the latter increases the rate of transiꢀ
tion 8a → 7. When olefin 5 is introduced into this system
to the molar ratio 1 : 3 : 5 = 1 : 3 : 1, two signals at
δCp 113.24 and 108.50 disappear gradually. A new signal
of the Cp rings appears instead them at δCp 113.43, which
is accompanied by a signal at δC 64.92—65.44 as a triplet
1
with the SSCC JC,H = 119.2 Hz. We assigned the latter
signal to the C atom of the alkyl substituent bound to the
Zr atom in complexes 10a—е. In excess AlBui3, these

Mechanism of olefin hydroalumination
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
319
Table 2. 13C NMR spectra with some direct spinꢀspin coupling constants (1JC,H) for compounds 1—4, 5a, 7, 8a, 9, 10a—e, 11a—e,
13a—e, 15, 16, and 17b,c (benzeneꢀd6 as internal standard and solvent)
Comꢀ
pound
δ (1JC,H/Hz)
Ср
С(1)
—
С(2)
—
С(3)
—
С(4)
С(5)
С(6)
С(7)
С(8)
С(9)
С(10) С(11) С(12) С(13)
1
2
3
4
5a
7
8a
116.02
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
23.17 26.62 28.12
25.51 26.29 28.38
28.25 25.97 27.92
113.86 137.28 33.55 31.08 22.24 13.65
105.16 22.72 26.62 28.18
—
—
—
113.24 25.62 26.53 28.35 81.70 35.18 28.85
(174.4)
—
(117.2)
—
—
—
—
—
9
10a
111.03 142.31 24.21
—
113.43
(174.4)
113.49
113.43
113.43
113.49
—
—
—
—
—
—
—
65.18 34.62 29.74 32.54 23.24 14.46
(119.2)
64.79 34.62 25.97 29.42 32.54 23.11 14.46
65.25 34.55 26.03 30.00 29.68 32.54 23.17 14.46
65.44 34.55 25.90 30.20 29.94 29.94 32.41 23.17 14.46
10b
10c
10d
10e
11a
11b
11c
11d
11e
13a
13b
13c
13d
13e
15
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
64.92 34.62 26.03 30.33 29.74 29.74 30.33 32.47 23.24 14.46
25.25 27.92 28.25 11.30 24.99 35.79 32.21 23.17 14.46
25.88 27.83 28.16 11.51 25.23 36.03 29.59 32.39 23.22 14.37
25.56 26.44 28.26 11.76 23.90 35.95 29.66 29.50 32.33 23.05 14.33
25.63 26.37 28.23 11.98 24.26 36.01 29.79 29.96 29.60 32.30 23.05 14.29
25.59 26.34 28.20 11.95 24.26 35.95 29.72 30.02 30.02 29.56 32.27 23.02 14.26
28.16 25.88 27.83 12.81 24.97 33.95 31.41 22.50 14.44
28.16 25.88 27.83 12.55 24.84 35.57 29.59 32.39 23.22 14.37
28.10 25.76 27.74 12.67 24.65 35.49 29.76 29.76 32.40 23.09 14.33
28.10 25.69 27.68 12.76 24.65 35.49 29.83 29.99 29.83 32.33 23.05 14.29
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
28.13 25.85 27.74 12.37
24.7
—
—
—
—
35.56 29.86 30.15 30.15 29.86 32.33 23.12 14.29
101.08 24.08 26.62 27.92
106.10 28.16 26.99 28.48
106.05 2.67
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
16
17b
17c
10.62
—
106.15 26.42 27.73 29.09
Scheme 4
R = Bu (a), C5H11 (b), C6H13 (c), C7H15 (d), C8H17 (e)

320
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
Parfenova et al.
Scheme 5
R = Bu (a), C5H11 (b), C6H13 (c), C7H15 (d), C8H17 (e)
complexes undergo transmetallation to form diisobutylꢀ
alkylalanes 11a—е with signals of the C atoms in the
13C NMR spectra, which are characteristic of these comꢀ
pounds and similar to those described in the literature.29
For the reaction of Cp2ZrCl2 (1) with ClAlBui2 (4)
(1 : 3), as in the case of the OAC studied above, the NMR
spectra contain signals characteristic of complex 7 and
the signal at δCp 108.50. However, under the experimenꢀ
tal conditions, the complex with the signals at δCp 108.50
is rather stable and detectable at room temperature, unꢀ
like the Cp2ZrCl2—HAlBui2 system. This complex is
transformed into compound 7 only with an increase in
the ClAlBui2 concentration to a ratio of 1 : 15. It is most
likely that in this system complex 7 is formed via several
successive steps (Scheme 5) through the intermediate forꢀ
mation of hydride complexes 6a,b and 8b, which can be
responsible for olefin hydroalumination.
When reagents 1, 4, and 5 are mixed in a molar ratio of
1 : 3 : 1, alkyl complexes 10a—е can be detected, which
are transformed into alkylchloroalanes 13a—e upon the
addition of ClAlBui2. During this reaction we observed
the regeneration of the starting Cp2ZrCl2 (1) and, hence,
assumed that the reaction of complexes 10 with OAC 4
first affords alkylalanes 11, which then react with Cl2AlBui
(12) formed in the initial steps of the process. As a result,
olefin hydroalumination products are formed: alkylꢀ
chloroalanes 13a—е.
for olefin hydroalumination: at the reagent ratios apꢀ
proaching that of the catalytic variant, the content of
stable trihydride complex 7 increases, and the latter is not
involved in olefin hydroalumination.
To establish the structure of true intermediate zircoꢀ
nium complexes, we attempted to perform the encounter
synthesis of hypothetical hydride complexes 6a—d and
8b. For this purpose, we specially studied the interaction
of OAC 2—4 with Cp2ZrH2, which was synthesized acꢀ
cording to a described procedure.8
The reaction of Cp2ZrH2 with HAlBui2 (Scheme 6)
affords the known8 dark blue complex 15 with the pentaꢀ
coordinate Al atom instead of complex 6c. The 1H NMR
spectra of this complex exhibit one broadened signal of
the hydride atoms (∆W1/2 ≈ 33 Hz), whose surface area
corresponds to the resonance line of the Cp rings as 3 : 10.
The position of the broadened signal of the hydride atoms
1
in the H NMR spectrum of complex 15 depends on
the HAlBui2 concentration. At the molar ratio
Cp2ZrH2 : HAlBui2 = 1 : 1, the signal of the hydride
atoms of complex 15 lies at δ –1.94. The further addition
of OAC 2 to a ratio of 1 : 3 results in the downfield shift of
the signal to δ –0.62. The shift of this signal can be exꢀ
plained by the existence of an intermolecular exchange
between HAlBui2 and complex 15 (see Scheme 6). With
an increase in the HAlBui2 concentration, the signal of
the Cp rings in the 13C NMR spectra also shifts from
100.00 to 102.20 ppm. The temperature variation from
–90 to +40 °C does not almost change the position of the
Thus, these studies did not allow us to establish the
structure of the Zr,Alꢀcontaining complexes responsible

Mechanism of olefin hydroalumination
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
321
broadened signal of the hydride atoms. Thus, structure 15
is more probable than structure 6c.
It follows from the 2D HH—COSY NMR spectra that the
system of hydride atoms in complex 16 is strongly bound.
The study of the molecular weight of complex 16 by
cryoscopy in benzene confirmed the dimeric structure of
this compound. The experimental value of the molecular
weight was 788 g mol–1, while the theoretical weight
is equal to 800 g mol–1. The signals of the Cp ring in
the 13C NMR spectrum of this complex appear at
δ 106.10—108.50. It should be mentioned that the chemiꢀ
cal shift depends on the ClAlBui2 concentration: an inꢀ
crease in the content of OAC 4 in the system results in the
descreening of the C atoms of the Cp rings.
Scheme 6
There are published assumptions on the existence
of such dimeric complexes with the composition
(Cp2ZrH2•AlR´3)2 (R´ = Me (17a)8, Et (17b)30), which
are formed in the reaction of Cp2ZrH2 with AlR´3. The
1H NMR spectra of complex 17a exhibit triplet signals of
the bridging hydride atoms of the Zr—H—Zr bond at
δ –2.92 and protons of the Zr—H—Al bond at δ –0.92.
By analogy to complexes 17a,b, we assumed the formaꢀ
tion of a bridged bimetallic zirconium complex in the
case of the reaction of Cp2ZrH2 with AlBui3 (Scheme 8).
In our experiments, the reaction of Cp2ZrH2 with
AlBui3 afforded complex 17c instead of the expected 6d.
For complex 17c, the set of signals of the hydride atoms
To prove additionally the structure of complex 15,
we determined its molecular weight by the cryoscopic
method.8 The experimental value of the molecular weight
was 326 g mol–1, which is close to the theoretical value
for structure 15 (366 g mol–1).
1
in the H NMR spectrum is identical to signals in the
spectra of complexes 17a,b.
It should be noted that the appearance of an OAC
molecule in the composition of complexes 17a—c does not
distort the dimeric structure of the starting [Cp2ZrH2]2,
whose structure has previously31 been discussed in detail.
The formation of complexes 17a—c shifts the triplet sigꢀ
nals of the bridging hydride atoms from δ –3.45 in the
starting [Cp2ZrH2]2 to δ –2.92, and the signal of the
terminal proton shifts substantially: from δ 3.85 to δ –0.92.
The study of the temperature dependence of the spectra
of the starting [Cp2ZrH2]2 showed31 that two triplets of
the hydride atoms are transformed into broadened sinꢀ
glets on heating the sample to +60 °C, while at +70 °C
the intensities of signals from the terminal hydride inꢀ
As shown by experiments, complex 15 reacts with oleꢀ
fins to form hydroalumination products 11a—е.
To synthesize complex 6b, we studied the reaction of
Cp2ZrH2 with ClAlBui2 (1 : 1). However, instead of the
expected compound 6b we observed the formation of preꢀ
1
viously undescribed complex 16 (Scheme 7), whose H
NMR spectrum contains broadened signals of the hydride
H atoms at δ –0.65—–1.35 of the Zr—H—Al (Ha) bond
and at δ –2.80—–2.56 of the Zr—H—Zr (Hb) bond with
an intensity ratio of 1 : 1. At the same time, toward the
signals of the H atoms of the Cp rings, this ratio is 1 : 10.
Scheme 7

322
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
Parfenova et al.
Scheme 8
When the temperature of a solution containing comꢀ
plex 16 in tolueneꢀd8 increases from –60 to +40 °C, the
position of the Hb signal remains virtually unchanged,
whereas the resonance line of Ha undergoes a downfield
shift by 0.5 ppm. At temperatures higher than 40 °C comꢀ
plex 16 would decompose with gas evolution and formaꢀ
tion of paramagnetic dark cherryꢀcolored species.
To synthesize complexes 6a and 8b, which also can be
key intermediates in olefin hydroalumination, we studied
the reaction of the Schwartz reagent Cp2ZrHCl (18)32,33
with OAC 2—4 (reagent 18 was synthesized by the reacꢀ
tion of Cp2ZrH2 with CHCl3).
R´ = Me (a), Et (b), Bui (c)
crease relatively. These facts were explained by two proꢀ
cesses: the fast exchange between the bridging and termiꢀ
nal hydrides at low temperatures and the dimer—monoꢀ
mer equilibrium.
The reaction of Cp2ZrHCl with OAC 2 affords the
same complex 16 (Scheme 9) as the reaction of Cp2ZrH2
with OAC 4.
The association of the [Cp2ZrH2]2 complex and OAC
to form complexes 17a—c induces the same effects in the
NMR spectra as the temperature increase in the case of
nonassociated [Cp2ZrH2]2. The geminal SSCC of the hyꢀ
dride atoms decreases from 7.3 to 4.9 Hz compared to the
starting [Cp2ZrH2]2 but the triplet structure of the signals
remains unchanged. The heating of complexes 17a—c to
+40 °C induces their decomposition. Thus, the appearꢀ
ance of OAC both accelerates processes of the intramoꢀ
lecular exchange between the bridging and terminal hyꢀ
drides and shifts the dimer—monomer equilibrium.
In the 1D 1H NMR spectra of complex 16, the signal
of the Hb proton at δ –2.56 is a broadened triplet with the
SSCC 2J = 4.2 Hz and belongs to the bridging H atom of
the Zr—H—Zr bond. The signal of the Ha proton bound
to the Zr and Al atoms (Zr—H—Al bond) is broader than
the signal of the bridging Hb atom and does not split into a
multiplet. The resonance line width of the Ha proton at
the halfꢀheight is ∆W1/2 ≈ 14.2 Hz. The broadened sigꢀ
nals of the hydride atoms in complex 16 can be due to
both an increase in the rate of the aforementioned exꢀ
change between the Ha and Hb protons and the symmetry
loss in the molecule preceding the formation of this comꢀ
plex (see Scheme 7) by the additional coordination of the
Al and Zr atoms through the Cl atom in structure 16. The
temperature plot of the chemical shifts of the Ha and
Hb protons is presented in Fig. 4.
Scheme 9
–40
–20
0
20
40 T/°C
The reaction of Cp2ZrHCl with ClAlBui2 (4) even at
low temperatures (below –90 °C) affords Cp2ZrCl2 and
complexes 16 and 7 instead of complex 6a. It is most
likely that HAlBui2 (2) appears primarily along with
Cp2ZrCl2. In turn, compound 2 reacts with still unꢀ
consumed Cp2ZrHCl to transform into complex 16, which
reacts with the remaining OAC 4 to yield complex 7.
Attempts to detect complex 8b in the reaction of
Cp2ZrHCl with AlBui3 were unsuccessful: the formation
of complex 16 and isobutylene (9) was observed at differꢀ
ent temperatures, including –90 °C.
Ha
–0.8
–1.2
–1.6
–2.0
–2.4
–2.8
Hb
δ
H
Summarizing the aforesaid, we may conclude that
complexes 6a—d and 8b are unstable. Instead of them, we
Fig. 4. Temperature plot of the chemical shifts of hydride atoms
in complex 16.

Mechanism of olefin hydroalumination
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
323
Scheme 10
R = Bu (a), C5H11 (b), C6H13 (c), C7H15 (d), C8H17 (e)
obtained complexes 15, 16, and 17a—c by the encounter
synthesis and showed that all of them react with olefins to
form alkylalanes 11. However, only complex 16 obeys the
logical scheme of the hydroalumination mechanism. First,
as already mentioned, complex 16 reacts with olefins to
form alkylzirconium complexes 10a—е and hydrometalꢀ
lation products 11a—е (Scheme 10). Second, complex 16
reacts with OAC 2—4 to form the known trihydride comꢀ
plex 7 (see Scheme 10). Third, the chemical shift of the
Cp ring in the 13C NMR spectrum of complex 16 at
δ 108.50 is similar to the signal of the Cp rings observed
for the reaction of Cp2ZrCl2 with OAC 2—4. Therefore, it
seems more reasonable to assume that dimeric structure
16 is involved in the first steps of hydroalumination inꢀ
stead of monomeric complex 6b. All these facts favor
complex 16 as the key intermediate responsible for alkene
hydroalumination. It is most likely that the threefold exꢀ
cess of OAC necessary for the complete dissolution of
Cp2ZrCl2 does not allow the direct observation of comꢀ
plex 16 during studies of the Cp2ZrCl2—OAC systems,
because this complex is unstable under the reaction conꢀ
ditions.
reactions of compounds 10a—е with different OAC
(Scheme 11).
Scheme 11
We assumed first that the reaction of complex 16
with olefin should involve the formation of intermediate
complex 19 (see Scheme 10). However, attempts to deꢀ
tect this complex in the reaction of Cp2ZrCl2 with
OAC or prepare it by the encounter synthesis from
Cp2Zr(CH2)2RCl 20 and HAlBui2 failed. The reaction of
complex 16 with olefin affords stable complexes 10 and
alkylalanes 11. The formation of the latter can be exꢀ
plained by the transmetallation of complexes 10.
The reaction of complexes 10 with OAC 2 affords
alkylalanes 11 and complex 16. The latter is formed due
to the fast reaction of Cp2ZrHCl formed in situ with
HAlBui2. The reaction of complexes 10 with OAC 4 afꢀ
fords Cp2ZrCl2 (1) and alkylalanes 11. It should be emꢀ
phasized that compounds 10 do not react with AlBui3.
However, as we already mentioned, the formation of alkyl
complexes 10 was reliably proved during the studying the
To study the transmetallation step, i.e., transition of
the alkyl fragment from the Zr atom in complexes 10a—е
to the Al atom to form complexes 11a—е, we studied the

324
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
Parfenova et al.
Cp2ZrCl2—AlBui3 system. When reacting with excess
AlBui3, complexes 10 are transformed into alkylalanes 11.
Evidently, the action of complex 10 in hydroalumination is
not isolated. The presence of HAlBui2 is basically imporꢀ
tant: in the Cp2ZrCl2—ClAlBui2 and Cp2ZrCl2—AlBui3
systems, HAlBui2 can be formed only in the reaction step
of complex 16 with olefins (see Scheme 10). Thus, the
fast transmetallation process occurs in the in situ formed
reaction pair Cp2Zr(CH2)2RCl—HAlBui2 (complex 19 in
Scheme 10 or the reaction of Cp2Zr(CH2)2RCl with
HAlBui2 in Scheme 11), i.e., migration of the alkyl fragꢀ
ment from Zr to the Al atom resulting in the formation of
alkylalanes 11 and Cp2ZrHCl. The latter interacts, acꢀ
cording to Scheme 9, with any of the OAC studied to
form the key complex 16 and complete the catalytic cycle.
Thus, based on the experimental data obtained,
we propose the generalized mechanism of olefin hydroꢀ
alumination by diisobutylaluminum hydride, diisoꢀ
butylaluminum chloride, and triisobutylaluminum
(Scheme 12). In all systems studied, viz.,
the Cl atom in molecule 1 by the Bui group of the startꢀ
ing OAC 4. This involves the βꢀhydride transfer followed
by isobutylene elimination. In the case of compounds 1
and 3, alkyl complex 8a is primarily formed and transꢀ
formed into the key complex 16 due to the βꢀhydride
transfer.
Intermediate 16 can further transform into trihydride
complex 7, which does not react with olefin. In the case
of OAC 2, this reaction can be reversible, and the low
hydroalumination rate is explained by the low concentraꢀ
tion of complex 16 in the reaction mixture due to the
predomination of the forward reaction of complex 16
with HAlBui2 over the backward reaction. In the case of
OAC 3 and 4, the transition 16 → 7 is irreversible. Molꢀ
ecules 3 and 4 contain no hydride atoms and, therefore,
the formation of complex 16 is impeded by steps of Cl
atom exchange by the Bui group, βꢀhydride transfer, and
isobutylene elimination. Probably, the total rate in these
steps is lower than the reaction rate of complex 16
with olefin, providing fast hydroalumination in the
Cp2ZrCl2—ClAlBui2 and Cp2ZrCl2—AlBui3 systems.
Complex 16 coordinates olefins to form alkyl comꢀ
plexes 10 and HAlBui2 (2), which then participates in
transmetallation. This process generates alkylalanes 11
and Cp2ZrHCl (18). In the case of OAC 4, alkylalanes 11
react with Cl2AlBui (12) formed in the initial reaction
steps to yield products of olefin hydroalumination: alkylꢀ
chloroalanes 13a—е. The Cp2ZrHCl that formed is transꢀ
formed into complex 16 almost instantly and regardless of
the nature of the starting OAC, thus completing the cataꢀ
lytic cycle.
Cp2ZrCl2—ClAlBui2,
Cp2ZrCl2—HAlBui2,
and
Cp2ZrCl2—AlBui3, the mixed Zr,Alꢀcontaining hydride
complexes are primarily formed, and among the latter
only the complex (Cp2ZrH2•ClAlBui2)2 (16) is an active
species of the catalyst, which hydroaluminates olefins.
Depending on the nature of the starting OAC, complex
16 is formed via different routes. The reaction of Cp2ZrCl2
(1) with HAlBui2 (2) through the step of ligand exchange
of the Cl atom in molecule 1 and H atom in molecule 2
produces complex 16 and ClAlBui2 (4). In the reacꢀ
tion 1 + 4, complex 16 is formed due to the exchange of
Scheme 12

Mechanism of olefin hydroalumination
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
325
mixture was transferred to the spectrometer cell to record specꢀ
tra in the temperature interval from –90 to +25 °C.
Experimental
Study of the structure of intermediate complexes in the reacꢀ
tions of OAC 2—4 with olefins 5a—e in the presence of Cр2ZrCl2
(1) by dynamic 1H and 13C NMR spectroscopy. Studies were
carried out directly in the cell of an NMR spectrometer at
~20 °C. An NMR tube filled with argon was loaded with
Cр2ZrCl2 (1) (0.3 mmol, 87.7 mg), benzeneꢀd6 (0.2 mL), OAC
(0.9 mmol, 0.17 mL of 73% solution of HAlBui2 (2), 0.17 mL of
95% solution of ClAlBui2 (4), or 0.19 mL of 91% solution of
AlBui3 (3)), and olefin 5a—e (0.3 mmol, molar ratio OAC : 1 : 5 =
3 : 1 : 1). The olefin concentration was increased until the molar
ratio was OAC : 1 : 5 = 3 : 1 : 3; and the 1H and 13C NMR
spectra were detected in parallel.
Complex Cp2ZrH2. The synthesis was based on a described
procedure.8 A flask equipped with a magnetic stirrer and filled
with argon was loaded with Cp2ZrCl2 (1) (1.2 mmol, 349.5 mg),
benzene (0.3 mL), and HAlBui2 (2) (3.6 mmol, 0.7 mL, 73%
solution in hexane). After the complete dissolution of comꢀ
plex 1, Et3N (3.6 mmol, 0.50 mL) or Et2NH (3.6 mmol, 0.42 mL)
was added dropwise to the mixture. In the case of using Et2NH,
the yield of Cp2ZrH2 was 95%. The Cp2ZrH2 complex formed a
white precipitate, and the solution became dark violet. The vigꢀ
orous gas evolution was observed. The precipitate was centriꢀ
fuged, washed with hexane (4×2 mL), and dried in vacuo. To
check the structure, a small amount of the Cp2ZrH2 sample was
placed in an NMR tube in C6D6 and treated with acetone. The
ratio of signals of the Cp rings and Me groups showed the preꢀ
dominant formation of diisopropoxyzirconocene (>95%).
Reaction of Cp2ZrH2 with OAC 2. An NMR tube filled with
argon was loaded with Cp2ZrH2 (0.6 mmol, 134 mg) and benꢀ
zeneꢀd6 (0.5 mL), and then HAlBui2 (2) (0.6 mmol, 0.17 mL,
50% solution in hexane) was added dropwise until the precipiꢀ
tate dissolved completely. A dark blue solution of complex 15
was obtained. The tube was transferred to the spectrometer cell
to record spectra. The assignment of signals in the 1H and
13C NMR spectra of the synthesized complex are presented in
Tables 2 and 3.
All procedures with organometallic compounds were carried
out under argon. Prior to use benzene and toluene were distilled
above HAlBui2, and THF and ether were distilled above LiAlH4.
A 73% solution of HAlBui2, a 97% solution of ClAlBui2, and a
91% solution of AlBui3 were used. Complex Cр2ZrCl2 was synꢀ
thesized from ZrCl4 according to a previously described proceꢀ
dure.34
Spectroscopic studies were carried out by dynamic 1H and
13C NMR spectroscopy with complete and partial proton
decoupling in the temperature interval from –90 to +25 °C on
Jeol FXꢀ90Q and Bruker AMꢀ300 spectrometers. Benzeneꢀd6
and tolueneꢀd8 were used as internal standards. Tubes with
d = 5 mm were used.
The yield of hydroalumination products was determined from
the yield of hydrolysis products of a reaction mixture, namely,
saturated hydrocarbon relatively to the starting olefin.
GLC analysis of the hydrolysis products was carried out on a
Chromꢀ5 chromatograph (column 1200×3 mm, 5% SEꢀ30 or
15% PEGꢀ6000 on Chromaton NꢀAW, helium as a carrier gas).
Cryoscopic studies were carried out in benzene according to
a standard procedure35 in a glass cell with three necks: for argon,
a stirrer, and a Beckman thermometer (the accuracy of determiꢀ
nation of the melting point was 0.005 °C).
Study of the influence of the OAC type (HAlBui2, ClAlBui2,
and AlBui3), temperature of the reaction, and concentration of the
Cp2ZrCl2 catalyst on the yield of olefin hydroalumination prodꢀ
ucts. A flask with a magnetic stirrer was filled under argon with
Cp2ZrCl2 (1) (0.20 mmol, 52.4 mg), olefins 5a—e (10 mmol),
and OAC (12 mmol, 2.3 mL of 73% solution of HAlBui2 (2),
2.2 mL of 95% solution of ClAlBui2 (4), or 2.9 mL of 82%
solution of AlBui3 (3)). The mixture was diluted with benzene to
5.9 mL. The reaction was carried out with stirring at three difꢀ
ferent temperatures (0, 10, and 20 °C). In the case of OAC 2
and 4, the process was carried out at different concentrations of
Cp2ZrCl2 (0.20, 0.30, 0.50, and 1.0 mmol). After 5, 10, 15, 20,
30, 60, 90, 120, 150, 180, 240, 300, and 360 min, samples
(0.4 mL) were syringed into tubes filled with argon, and the
samples were decomposed with 10% HCl at 0 °C. Products were
extracted with benzene, and the organic layer was dried above
CaCl2. The yield of alkylalanes 11a—е was determined by GLC
(see Table 1). The NMR data for alkylalanes 11a—е are preꢀ
sented in Table 2.
Reaction of Cp2ZrH2 with OAC 4. An NMR tube filled with
argon was loaded with Cp2ZrH2 (0.6 mmol, 134 mg) and benꢀ
zeneꢀd6 (0.5 mL), and then ClAlBui2 (4) (0.6 mmol, 0.11 mL,
95% solution in hexane) was added drowise until the precipitate
dissolved. The formation of complex 16 was observed. The asꢀ
signment of signals in the 1H and 13C NMR spectra of the
reaction products is presented in Tables 2 and 3.
Study of the structure of intermediate complexes in the reacꢀ
tions of OAC 2—4 with Cр2ZrCl2 (1) by dynamic 1H and 13C NMR
spectroscopy. A. Studies were carried out directly in the cell of
an NMR spectrometer at ~20 °C. An NMR tube filled with
argon was loaded with Cр2ZrCl2 (1) (0.3 mmol, 87.7 mg), benꢀ
zeneꢀd6 (0.2 mL), and OAC (0.9 mmol, 0.17 mL of 73% soluꢀ
tion of HAlBui2 (2), 0.17 mL of 95% solution of ClAlBui2 (4), or
0.20 mL of 91% solution AlBui3 (3)) (molar ratio OAC : 1 =
3 : 1). 1H and 13C NMR spectra were recorded. The concenꢀ
tration of OAC was gradually increased to the molar ratio
OAC : 1 = 15 : 1.
B. An NMR tube filled with argon was loaded with Cр2ZrCl2
(0.3 mmol, 87.7 mg) (1) and tolueneꢀd8 (0.2 mL). The tube was
cooled to –90 °C, then OAC (0.3 mmol, 0.06 mL of 73% soluꢀ
tion of HAlBui2 (2), 0.06 mL of 95% solution of ClAlBui2 (4), or
0.06 mL of 91% solution of AlBui3 (3)) was added, and the
Reaction of Cp2ZrH2 with AlBui3 (3) and AlEt3. An NMR
tube filled with argon was loaded with Cp2ZrH2 (0.6 mmol,
134 mg) and benzeneꢀd6 (0.5 mL), and then OAC (0.6 mmol,
0.13 mL of 91% solution of AlBui3 (3) and 0.07 mL of 94%
solution of AlEt3) was added dropwise until the precipitate disꢀ
solved. The formation of complexes 17b and 17c was observed.
The assignment of signals in the 1H and 13C NMR spectra of the
reaction products is presented in Tables 2 and 3.
Complex 16. A flask equipped with a magnetic stirrer and
filled with argon was loaded with Cp2ZrH2 (0.6 mmol, 134 mg)
and benzene (1.5 mL), and ClAlBui2 (4) (0.6 mmol, 0.14 mL,
76% solution in hexane) was added dropwise until the complete
dissolution of Cp2ZrH2. The solvent was evaporated in vacuo.
A viscous Vaselineꢀlike pinkishꢀbrown mixture was obtained.
The assignment of signals in the 1H and 13C NMR of complex
16 is presented in Tables 2 and 3. IR (Nujol), ν/cm–1: 1780

326
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
Parfenova et al.
Table 3. 1H NMR spectra with some spinꢀspin coupling constants (2JH,H) for compounds 7, 14—16, and 17a—c
(benzeneꢀd6 as internal standard and solvent)
Comꢀ
pound
δ (2JH,H/Hz)
Cp
Ha
Hb
СH2
СH
Me
7
5.75
(10 H)
5.50
(20 Н)
5.64
–2.04 (d, 2 H,
2JH,H = 7.5)
3.85 (t, 2 Н,
2JH,H = 7.3)
–0.62—–1.94
(br.s, 3 H,
–0.87 (t, 1 H,
2JH,H = 7.5)
–3.45 (t, 2 H,
2JH,H = 7.3)
—
0.51 (d, 8 H,
2JH,H = 6.8)
—
2.15
(m, 4 H)
—
1.18 (d, 24 H,
2JH,H = 6.4)
—
14 31
15
0.43 (d, 4 H,
2JH,H = 7.3)
2.14
(m, 2 H)
1.21 (d, 12 H,
2JH,H = 6.4)
(10 H)
∆W1/2 = 33)
–0.65—–1.35
(s, 2 H)
16
5.81
(20 H)
–2.56—–2.80
(br.t, 2 H,
0.43 (d, 8 H,
2.2
(m, 4 H)
1.34 (d, 24 H,
2JH,H = 5.4)
2JH,H = 6.3)
2JH,H = 4.2)
–2.92 (t, 2 H)
17a 8
17b
5.50
(20 Н)
5.72
(20 H)
5.79
–0.92 (t, 2 H)
—
—
—
–0.41
(s, 18 H)
1.50 (t, 18 H,
2JH,H = 8.0)
1.35 (d, 36 H,
2JH,H = 6.3)
–1.23 (t, 2 H,
2JH,H = 5.4)
–1.05 (t, 2 H,
2JH,H = 4.9)
–2.78 (t, 2 H,
2JH,H = 5.4)
–2.74 (t, 2 H,
2JH,H = 4.9)
0.32 (q, 12 H,
2JH,H = 8.0)
0.36 (d, 12 H,
2JH,H = 6.8)
17c
2.21
(m, 6 H)
(20 H)
(Zr—H—Al), 1450 (Zr—H—Zr). Molecular weight/g mol–1
found: 788. Calculated: 800.
,
completely. The formation of complex 16 was observed in soꢀ
lution.
Reaction of complex 16 with OAC 2—4. An NMR tube filled
with argon was loaded with Cp2ZrH2 (0.6 mmol, 134 mg) and
benzeneꢀd6 (0.5 mL), and then ClAlBui2 (4) (0.6 mmol, 0.11 mL,
95% solution in hexane) was added dropwise to the complete
dissolution of the precipitate. Complex 16 was obtained, which
was identified by the 1H and 13C NMR spectra. The tube was
cooled to –60 °C, then OAC 2—4 (0.6 mmol, 0.17 mL of 50%
solution of HAlBui2 (2), 0.11 mL of 95% solution of ClAlBui2 (4),
or 0.13 mL of 91% solution of AlBui3 (3)) was added, and the
mixture was transferred to the cell of an NMR spectrometer to
record spectra in the temperature interval from –60 to 0 °C.
When the temperature increased to 0 °C, complex 16 transꢀ
formed into trihydride complex 7.
Reaction of Cp2ZrHCl (18) with OAC 4. An NMR tube filled
with argon was loaded with complex 18, which was prepared
from 0.6 mmoles of Cp2ZrH2, in tolueneꢀd8, and ClAlBui2 (4)
(0.6 mmol, 0.11 mL, 95% solution in hexane) was added
dropwise. The formation of complexes 1, 16, and 7 was observed
in solution. The assignment of signals of the reaction products in
the 1H and 13C NMR spectra is presented in Tables 2 and 3.
Reaction of Cp2ZrHCl (18) with OAC 3. An NMR tube filled
with argon was loaded with complex 18, which was synthesized
from 0.6 mmoles of Cp2ZrH2, in tolueneꢀd8, and AlBui3 (3)
(0.6 mmol, 0.13 mL, 91% solution in hexane) was added
dropwise. The formation of complex 16 and evolution of isobuꢀ
tylene (9) were observed in solution.
Reaction of complex 16 with olefins 5a—e. Complex 16 was
synthesized as described above. Then the tube was cooled to 0 °C,
olefin 5a—e (0.6 mmol) was added, and the mixture was transꢀ
ferred to the cell of an NMR spectrometer to record spectra in
the temperature interval from 0 to 20 °C. The formation of
complexes 10a—е and 11a—е was observed with the temperaꢀ
ture increase.
Complex Cp2ZrHCl (18). A flask equipped with a magnetic
stirrer and filled with argon was loaded with Cp2ZrH2 (0.6 mmol,
134 mg) and benzene (0.5 mL). Chloroform (0.6 mmol, 0.05 mL)
was added to the resulting suspension with stirring. The precipiꢀ
tate of Cp2ZrHCl (18) was centrifuged and washed with benꢀ
zene (2×2 mL). To verify the structure of complex 18, a small
amount of the sample was treated with acetone, dissolved in
C6D6, and placed in an NMR tube. The ratio of surface areas of
signals of the Cp rings and Me groups showed the predominant
formation of monoisopropoxyzirconocene (>95%).
Complexes Cp2Zr(CH2)2RCl 10a—e. A flask equipped with
a magnetic stirrer and filled with argon was loaded with
Cp2ZrHCl (18) (prepared from 0.6 mmoles of Cp2ZrH2), benꢀ
zene (0.5 mL), and olefins 5a—e (0.6 mmol). The mixture was
stirred for 24 h at 20 °C. Yellow solutions of alkylzirconium
chlorides 10a—е in benzene were obtained.
Reactions of compounds 10a—е with OAC 2—4. An NMR
tube filled with argon was loaded with complexes 10a—е (obꢀ
tained from 0.6 mmoles of Cp2ZrH2) in tolueneꢀd8, and
OAC 2—4 (0.11 mL of 73% solution HAlBui2 (2), 0.11 mL of
95% solution of ClAlBui2 (4), or 0.13 mL of 91% solution of
AlBui3 (3)) was added dropwise. In the case of HAlBui2 (2), the
formation of the reaction products, viz., alkylalanes 11a—е and
complex 16, was observed in solution. In the reaction with
ClAlBui2 (4), we observed the formation of alkylalanes 11a—е
and regeneration of the starting Cp2ZrCl2 (1). Compounds
10a—е did not react with AlBui3 (3).
Reaction of Cp2ZrHCl (18) with OAC 2. An NMR tube filled
with argon was loaded with complex 18 synthesized from
Cp2ZrH2 (0.6 mmol) in tolueneꢀd8, and HAlBui2 (2) (0.6 mmol,
0.17 mL, 73% solution in hexane) until the precipitate dissolved
This work was financially supported by the Foundaꢀ
tion of the President of the Russian Federation (Program
for Support of Young Candidates of Science (Grant

Mechanism of olefin hydroalumination
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
327
konf. po metalloorganicheskoi khimii [Proc. II AllꢀUnion Conf.
on Organometallic Chemistry], Gorkii, 1982, 58 (in Russian).
18. L. I. Shoer and J. Schwartz, J. Am. Chem. Soc., 1977,
99, 5831.
MKꢀ2647.2003.03) and Leading Scientific Schools (Grant
NShꢀ2189.2003.3)) and the Russian Foundation for Baꢀ
sic Research (Project No. 00ꢀ03ꢀ40132 (TsKP REGUTs)).
19. J. Schwartz and J. Latinger, Angew. Chem., Int. Ed. Engl.,
1976, 15, 333.
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Received June 15, 2004;
in revised form October 6, 2004