One-step synthesis of trialkylaluminum derivatives and dialkylaluminum hydrides by the reaction of alkaline metal aluminum hydrides with α-olefins and alkylaluminum chlorides

Article abstract of DOI:10.1023/A:1022412818827

A simple method for one-step preparation of the organoaluminum compounds R₃Al, R₂AlH, R₂R′Al, and RR′AlH by the reaction of MAlH₄ (M = Li, Na) with R₂AlHal (Hal = Cl, Br) and α-olefins (3-methylbut-1-ene, hex-1-ene, oct-1-ene, dec-1-ene) was proposed.

Full text of DOI:10.1023/A:1022412818827

168
Russian Chemical Bulletin, International Edition, Vol. 52, No. 1, pp. 168—169, January, 2003
Oneꢀstep synthesis of trialkylaluminum derivatives and dialkylaluminum
hydrides by the reaction of alkaline metal aluminum hydrides with αꢀolefins
and alkylaluminum chlorides
V. V. Gavrilenko
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: bre@ineos.ac.ru
A simple method for oneꢀstep preparation of the organoaluminum compounds
R3Al, R2AlH, R2R´Al, and RR´AlH by the reaction of MAlH4 (M = Li, Na) with R2AlHal
(Hal = Cl, Br) and αꢀolefins (3ꢀmethylbutꢀ1ꢀene, hexꢀ1ꢀene, octꢀ1ꢀene, decꢀ1ꢀene) was
proposed.
Key words: organoaluminum compounds, trialkylaluminum derivatives, dialkylaluminum
hydrides, mixed alkylaluminum hydrides, mechanochemical activation.
Scheme 1
Hydroalumination of olefins discovered by K. Ziegler
and coꢀauthors in 1954 is one of the most important reacꢀ
tions in the synthesis of organoaluminum compounds
(OAC). The industrial production of OAC is based on the
direct synthesis of alkylaluminum derivatives from Al,
H2, and αꢀolefins.1,2 We have previously3,4 shown that
the reaction of nonꢀsolvated aluminum hydride with
αꢀolefins affords pure R3Al in the individual state. Taking
into account that AlH3 is insufficiently accessible, we
continued to synthesize R3Al from more available reꢀ
agents, viz., MAlH4 (M = Li, Na), αꢀolefins, and R2AlX
(X = Cl, Br). The most of them are commercial reagents
or can easily be prepared in ∼100% yield by the classical
reactions1 and used without additional purification. We
showed that all the reactants do not react upon mixing
and heating for 8 h at 60—100 °C. However, the reaction
occurred readily under mechanochemical activation
(highꢀspeed stirrer or ball mill) both without solvent and
in aliphatic or aromatic hydrocarbons to produce OAC
within 1—2 h in ∼100% yield (monitored by the absence
of halide in solution after HNO3 hydrolysis). This reacꢀ
tion seems to be general and occurs with all the αꢀolefins
studied (3ꢀmethylbutꢀ1ꢀene, hexꢀ1ꢀene, octꢀ1ꢀene, decꢀ
1ꢀene) by Scheme 1. Monoalkyl dichlorides RAlCl2 also
react readily with MAlH4 (2 mol) and olefins to form the
same products.
M = Li, Na
R = Bun, nꢀC6H13, Pri
cess, admixtures of complexes of the MAlR4•AlH3 type
and others can be found in the reaction mixture along
with R3Al and R2AlH. These admixtures can easily be
removed by treatment of the solution with AlCl3 in
amounts equivalent to the metal content.
The further study of the reaction showed that it can
occur without mechanical activation. With this purpose,
MAlH4 should be treated (before the reaction) with a
minor amount of the preliminarily prepared R3Al, the
mixture should be heated to 100 °C, and only then R2AlCl
and olefin should be added. In this case, R2AlCl reacts
with the MAlH4•R3Al complex formed at the first step
and soluble in hydrocarbons, i.e., the process occurs unꢀ
der homogeneous conditions. As the binuclear complex is
consumed, the aluminum hydride is gradually dissolved
to react with R3Al, and to drive the reaction to compleꢀ
tion. Such a procedure is 1.5—2 times longer than that
using mechanochemical activation but gives the same
results.
This reaction can be attributed to general methods for
the synthesis of the R2AlH and R3Al OACs.
When R2AlCl and αꢀolefin contain different R radiꢀ
cals, mixed OACs like RR´AlH and R2R´Al form.
The reaction with Bui2AlCl at first affords R2BuiAl,
which is transformed (in an αꢀolefin excess) into R3Al
with the displacement of isobutylene. In an MAlH4 exꢀ
Thus, we developed the new preparative method for
the synthesis of nonꢀsolvated OAC, viz., R3Al, R2AlH,
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 158—159, January, 2003.
1066ꢀ5285/03/5201ꢀ168 $25.00 © 2003 Plenum Publishing Corporation

Oneꢀstep synthesis of R3Al and R2AlH
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 1, January, 2003
169
Et2AlCl (6.0 g) and 3ꢀmethylbutꢀ1ꢀene (15.9 g) (molar ratio
NaAlH4 : Et2AlCl : Me—CH(Me)—CH=CH2 = 1.04 : 1.0 : 4.5)
was added from a dropping funnel. The reaction was performed
for 1.5 h and ceased at 100 °C. The suspension was filtered off,
and toluene was distilled off in vacuo. The product was obtained
in 93% yield (18.4 g). Found (%): Al, 13.04. C12H27Al. Calcuꢀ
lated (%): Al, 13.60.
R2R´Al, and RR´AlH, based on alkaline metal aluminum
hydrides, αꢀolefins, and alkylaluminum chlorides. The
method provides new challenges of using OAC in syntheꢀ
sis and catalysis.
Experimental
Isoamylethylaluminum hydride was prepared similarly to the
previous synthesis from NaAlH4 (2.8 g), Et2AlCl (6.0 g), and
3ꢀmethylbutꢀ1ꢀene (7.0 g) (reactant ratio 1.04 : 1.00 : 1.98). The
product was obtained in 92.2% yield (13.7 g). Found (%):
Al, 22.41; H–, 0.82. C7H17Al. Calculated (%): Al, 22.63;
H–, 0.846.
Purity of lithium and sodium aluminum hydrides after reꢀ
crystallization from ether—toluene and THF—toluene mixtures
was 98.5 and 99.5%, respectively. Commercial αꢀolefins were
additionally dried over MgSO4 and distilled in the presence
of NaAlEt4 (chromatographic purity was 95—98%, endoꢀ
olefins were admixtures). GLC analyses were performed on an
LKhMꢀ8MD instrument (column 2 m × 0.4 mm, 5% SEꢀ30 on
Chromaton NꢀAW washed with acid, particle size 0.2 mm).
Alkylaluminum chlorides R2AlCl and RAlCl2 were prepared
from pure R3Al and freshly sublimed AlCl3.1 All reagents were
stored under argon. The content of aluminum in samples was
determined by trilonometry.5 The content of hydride hydrogen
in R2AlH was determined using gasꢀvolumetry by the decompoꢀ
sition of a weighted sample of the substance in Et2NH 1,2 folꢀ
lowed by freezing out gaseous products in a trap with liquid
nitrogen.
Synthesis of R3Al or R2AlH from MAlH4, αꢀolefins, and
R2AlCl (general procedure). The specified amount of MAlH4
was loaded in a verticalꢀtype6 ball mill with a 100ꢀmL glass
(steel balls 2—4 mm in diameter) under argon or nitrogen, a
solvent (heptane or toluene) was added, and the mixture was
agitated for 15 min at 70—90 °C. A mixture of αꢀolefin with
R2AlCl (4 : 1 or 2 : 1) was gradually introduced into the reactor
from a dropping funnel. The reaction is accompanied by heat
release. The flow rate was controlled in such a way that the
temperature would not exceed 90—100 °C. The reaction comꢀ
pleted for 1—2 h. The reaction mixture was cooled and filtered,
and the solvent was removed in vacuo. The residue was anaꢀ
lyzed for Cl.
Trihexylaluminum was prepared using the general procedure.
The reactor was loaded with LiAlH4 (2.09 g) in heptane (40 mL),
the mixture was agitated for 15 min at 70 °C, and a mixture of
(C6H13)2AlCl (11.6 g) with hexꢀ1ꢀene (18.5 g) (molar ratio
LiAlH4 : (C6H13)2AlCl : hexꢀ1ꢀene = 1.1 : 1.0 : 4.5) was graduꢀ
ally added from a dropping funnel. The resulting mixture was
agitated for 1.5 h at 90 °C. The product was cooled down and
filtered through a glass filter No. 4 under argon. The solvent and
olefin excess were removed in vacuo (10 Torr) at 60—70 °C to a
constant weight of the residue. The yield was 26.8 g (95%) based
on (C6H13)2AlCl. Found (%): Al, 9.15. C18H39Al. Calcuꢀ
lated (%): Al, 9.55.
Trioctylaluminum. A ball mill was loaded with LiAlH4 (1.95 g)
and octꢀ1ꢀene (24 g), and the mixture was heated to 75 °C with
agitation for 20 min. Then (C8H17)2AlCl (14.4 g) was added
from a dropping funnel for 0.5 h, and the mixture was agitated
for 1 h at 95—100 °C (reactant ratio 1 : 4.28 : 1, respectively).
The precipitate was filtered off, and an octene excess was disꢀ
tilled off in vacuo (1 Torr) at 80—90 °C. The product was obꢀ
tained in 98% yield (35.8 g) as a transparent viscous liquid.
Found (%): Al, 7.07. C24H51Al. Calculated (%): Al, 7.36.
Dioctylaluminum hydride was prepared similarly to the previꢀ
ous synthesis from LiAlH4 (1.95 g), octꢀ1ꢀene (11.0 g), and
(C8H17)2AlCl (14.4 g) (molar ratio 1.03 : 1.96 : 1.00, respecꢀ
tively). The product (C8H17)2AlH was obtained in 94% yield
(28.0 g). Found (%): Al, 11.76; H–, 0.41. C16H35Al. Calcuꢀ
lated (%): Al, 11.95; H–, 0.446.
Tridecylaluminum. Sodium aluminum hydride (3.0 g,
0.056 mol) and decꢀ1ꢀene (45 g, 0.32 mol) were agitated for
10 min at 70 °C, and Bui2AlCl (7.4 g, 0.042 mol) was added for
0.5 h to the reaction mixture. The mixture was stored for 1.5 h at
95—100 °C. Isobutylene (∼4 mL) was collected in a trap cooled
with liquid nitrogen. After the precipitate was separated, the
filtrate was heated for 1 h at 80 °C (1 Torr). The product was
obtained in 97% yield (43.2 g) as a transparent viscous liquid.
Found (%): Al, 5.71. C30H63Al. Calculated (%): Al, 5.98. Acꢀ
cording to the GLC data, after hydrolysis the content of decane
was 98%, that of decene was ∼1%, and other admixtures
amounted to ∼1%.
References
1. H. Lehmkuhl and K. Ziegler, Methoden zur Herstellung und
Umwandlung von organischen AluminiumꢀVerbindungen, in
HoubenꢀWeyl, Methoden der organische Chemie. Band XIII/4.
Metallorganische Verbindungen, Georg Thieme Verlag,
Stuttgart, 1970, 314.
2. Justis Liebigs Ann. Chem., B629, 1960.
Dihexylaluminum hydride was synthesized similarly
from LiAlH4 (2.1 g) in heptane (30 mL) and a mixture of
(C6H13)2AlCl (11.6 g) and hexꢀ1ꢀene (8.2 g) (molar ratio
LiAlH4 : (C6H13)2AlCl : hexꢀ1ꢀene = 1.1 : 1.0 : 1.95). The
reaction proceeded to completion for 2.5 h at 70—100 °C. The
transparent product (18.8 g) was obtained. Found (%): Al, 13.04;
H–, 0.486. C12H27Al. Calculated (%): Al, 13.60; H–, 0.501.
Diisoamylethylaluminum. According to the general proceꢀ
dure, NaAlH4 (2.8 g) and toluene (30 mL) were loaded in a
ball mill equipped with a reflux condenser. The mixture was
heated to 70 °C and agitated for 10 min, and a mixture of
3. V. V. Gavrilenko, Abstr. of XIIth Fechem Conf. of Organomet.
Chem. (August 31—September 5, 1997), Prague, 1997, Pos. 97.
4. V. V. Gavrilenko, Izv. Akad. Nauk, Ser. Khim., 1997, 1709
[Russ. Chem. Bull., 1997, 46, 1630 (Engl. Transl.)].
5. G. Schwarzenbach, Die chemische Analyse, Bd. 45 (Die
Komlexometrische Titration), Ferdinand Enke, Stuttgart,
1955, 73.
6. H. Clasen, Angew. Chem., 1961, 73, 322.
Received July 2, 2002