A novel hydrogen transfer hydroalumination of alkenes with triisobutylaluminum catalyzed by Pd and other late transition metal complexes

Article abstract of DOI:10.1016/S0040-4039(00)02142-0

Hydrogen transfer hydroalumination of terminal alkenes and dienes can be achieved with 1.1 equiv. of (i-Bu)₃Al and catalytic amounts of Cl₂Pd(PPh₃)₂ and other late transition metal complexes containing Co, Rh, Ni, and Pt at ambient temperature in high yields.

Full text of DOI:10.1016/S0040-4039(00)02142-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 785–787
A novel hydrogen transfer hydroalumination of alkenes with
triisobutylaluminum catalyzed by Pd and other late transition
metal complexes
Sebastien Gagneur,† Hidefumi Makabe‡ and Ei-ichi Negishi*
Department of Chemistry, Purdue University, West Lafayette, IN 47907-1393, USA
Received 27 June 2000; revised 16 November 2000; accepted 19 November 2000
Abstract—Hydrogen transfer hydroalumination of terminal alkenes and dienes can be achieved with 1.1 equiv. of (i-Bu)3Al and
catalytic amounts of Cl2Pd(PPh3)2 and other late transition metal complexes containing Co, Rh, Ni, and Pt at ambient
temperature in high yields. © 2001 Elsevier Science Ltd. All rights reserved.
(76%), and ClRh(PPh3)3 (79%). The cleanest results
were observed with Pd and Pt catalysts. The use of
Pd(OAc)2 (5 mol%) in place of Cl2Pd(PPh3)2 or
Li2PdCl4 led to no reaction with >90% of 1-decene
remaining unreacted. This may be attributable to the
absence of Cl, and it is tempting to speculate that
bimetallic activation8 involving the AlꢀClꢀPd bond is
important. Another finding of significance is that either
the use of preformed Pd(0) complexes, such as
Pd(PPh3)4 (25%) in place of Cl2Pd(PPh3)2 or Li2PdCl4,
or strongly reducing hydride sources, such as (i-
Bu)2AlH (DIBAH) (25%) and LiAlH4 (<5%), that can
readily convert Pd(II) complexes to Pd(0) complexes in
place of TIBA induced the desired hydroalumination
only to a minor extent, the yield being indicated in
parentheses. These results suggest that the desired
hydroalumination is catalyzed by Pd(II) but not Pd(0)
complexes and that reduction of Pd(II) complexes is to
be avoided. They also provide a reasonable explanation
as to why TIBA rather than DIBAH serves as an effec-
tive hydride source and point to a significant advantage of
hydrogen transfer hydroalumination
Herein reported is a novel hydrogen transfer hydroalu-
mination of alkenes with (i-Bu)3Al (TIBA) and cata-
lytic amounts of Pd and other late transition metal
complexes containing Co, Rh, Ni and Pt. Although
uncatalyzed hydroalumination reactions of alkenes with
di- and trialkylalanes, such as (i-Bu)2AlH (DIBAH)
and (i-Bu)3Al (TIBA), at elevated temperatures1 as well
as their Ni-catalyzed versions at room temperature2
have long been known, their scope and limitations as
well as their synthetic utility do not appear to have
been explored extensively. As a consequence, relative to
hydroboration3 and hydrozirconation,4 hydroalumina-
tion of alkenes5 in general has been a generally sluggish
reaction of limited synthetic scope. In addition to the
Ni-catalyzed hydroalumination mentioned above, we
developed earlier a hydrogen transfer hydroalumination
of alkenes with TIBA and a catalytic amount of
Cl2ZrCp2.6
Following a recent promising lead that a wide variety
of Lewis acidic compounds catalyze hydrozirconation
of alkenes with i-BuZrCp2Cl,7 we found that the reac-
tion of 1-decene with 1.1 molar equiv. of TIBA in the
presence of 2.5–5 mol% of the following chlorine-con-
taining late transition metal complexes led to the for-
mation of 1-iododecane after treatment of the product
with I2: Cl2Pd(PPh3)2 (90%), Li2PdCl4 (78–86%),
K2PtCl4 (86%), Cl2Ni(PPh3)2 (65%), ClCo(PPh3)3
Using 1.1 equiv. of TIBA and 2.5 mol% of
Cl2Pd(PPh3)2 as catalyst, the scope of the hydroalumi-
nation reaction was examined. As the results summa-
rized in Table 1 indicate a variety of alkenes, including
those that are functionally substituted, can be satisfac-
torily hydroaluminated. It should be mentioned, how-
ever, that retardation by strongly electron-donating
functional groups in certain positions of alkenes is also
noticeable. Thus, 4-bromo-1-butene, 11-iodo-1-un-
decene, allyl phenyl ether, allyl benzyl ether, and (3E)-
1,3-decadiene did not provide the desired hydro-
* Corresponding author.
†
Purdue Research Foundation Graduate Research Fellow (1999–
2000).
‡
JSPS Postdoctoral Research Associate on funds provided by
Japanese Society for Promotion of Science (1997–1999).
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)02142-0

786
S. Gagneur et al. / Tetrahedron Letters 42 (2001) 785–787
a
Table 1. Hydroalumination of 1-alkenes with TIBA catalyzed by Cl2Pd(PPh3)2
Product yield,b %
R of
Reaction
Unreacted Reduction
RCH=CH2
Times, h RCH2CH2I RCH2CH2OH alkene, %
product, %
0
0
0
0
n-C8H17
0.5
1
90 (85)
--
73
77
--
(70)
(75)
Cyclohexyl
Benzyl
--
0
0
1
--
5
0
Cl(CH2)9
Br(CH2)9
PhS(CH2)3
PhS(CH2)3
0.5
1
88
81
<5
--
10
90
0
0
--e
--
--
12
6c
0
75
0.5
79
--
0
0
Me
--
--
(80)
(75)
--e
4
5
6
86
81
<8
8
(Z)-C6H13
C
CHCH2
SiMe3
(Z)-BuCH CHCH2
Bu
(E)-BuCH CHCH2
(E)-C6H13CH CHCH2
Me2C CH(CH2)6
--
--
--
14
16
0
12
53
49
80
28
35
0
5
12
a Unless otherwise mentioned, the reaction was carried out with 1.1 equiv of TIBA and 2.5 mol% of
Cl2Pd(PPh3)2 at 25°C in CH2Cl2. b By NMR or GLC. The numbers in parentheses are isolated yields.
c 2.3 equiv of TIBA used. d An unidentified byproduct was present. Its GLC signal intensity was ca.
10% of the major product. e Unreacted alkene and reduction product were not distinguishable on the
GLC trace.
alumination products in detectable yields. a,v-Dienes
saturated monoaluminated products (3 and 5) formed
in varying yields, as summarized in Table 2. These
results shed some light on the mechanistic details of the
reaction. They strongly suggest that, once hydroalumi-
nation has occurred at one end of a diene, the course of
the reaction at the other double bond is significantly
affected by the alkylaluminum group possibly through
chelation depicted in 6 in which a PdꢀClꢀAl bond is
thought to be important.8 As the dienes get longer, the
chelation effect shown in 6 is expected to diminish,
(1) containing two terminal vinyl groups have also been
hydroaluminated. 1,5-Hexadiene undergoes a hydro-
metallation–cyclic carbometallation tandem process to
give cyclopentylcarbinylalane which, upon oxidation
with O2, is converted to cyclopentylmethanol in 84%
yield. With longer a,v-dienes, no cyclic carbometalla-
tion has been observed. Instead, the reaction gives the
expected mono- and dihydroaluminated products (2
and 4) as well as double bond-migrated and fully
a
Table 2. Hydroalumination of a,v-dienes with TIBA catalyzed by Cl2Pd(PPh3)2
OH
+
OH
1. TIBA (1.1 equiv)
2.5 mol% Cl2Pd(PPh3)2
+
(H2C)n
(H2C)n
+
(CH2)n
(H2C)n
(H2C)n
2. O2, NaOH
OH
1
2
3
4
5
OH
OH
Entry
n of
Unreacted
diene, %
Product yield, %b
diene
2
3
2+3
4
5
4+5
1
2
3
4
5
3
4
5
6
10
44
43
36
35
26
10
14
14
16
19
22
21
25
27
54
32
35
39
43
73
0
0
0
0
0
32
20
12
11
0
12
23
24
24
26
a The reaction was carried out in CH2Cl2 at 25°C for 12 h. b By NMR and/or GLC.
(CH2)n
Al(i-Bu)2
Cl
Z(Ph3P)2Pd
(Z = Cl or i-Bu)
6

S. Gagneur et al. / Tetrahedron Letters 42 (2001) 785–787
787
CH2Cl2
Cl2Pd(PPh3)2
Al(i-Bu)3
Pd(PPh3)2
R
R
Pd(PPh3)2
Cl
i-Bu)
Al(i-Bu)2
ClAl(
R
2
H
Bu-i
H
H
H
Al
H
R
Bu-i
Pd(PPh3)2
R
Pd(PPh3)2Cl
Bu-i
H
H
Cl Al
Bu-i
Desired non-redox catalytic cycle
Formation of alkanes by a redox process
Scheme 1.
References
which appears to be reflected by the decrease in the
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increase in the combined yield of 4 and 5. In the reaction
of 1,13-tetradecadiene, 2.26 equiv. of i-BuꢀAl bonds are
required to produce 2–5, indicating that more than two
i-BuꢀAl bonds of TIBA must participate in the reaction.
The overall processes may be accommodated by a
combination of two catalytic cycles shown in Scheme 1.
The formation of 5 is not a consequence of incomplete
oxidation, since quenching the reaction mixture with D2O
after oxidation with O2 did not incorporate D to a
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We thank the National Science Foundation (CHE-
0080795), the National Institute of Health (GM36792),
Purdue University, and Purdue Research Foundation.
We also thank Albemarle, Boulder Chemical, and John-
son-Matthey for their assistance in the procurement of
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Al, Zr, and Pd compounds, respectively.