Palladium-catalyzed dimerization disilylation of 1,3-butadiene with chlorosilanes

Article abstract of DOI:10.1021/ol048751j

(Chemical Equation Presented) 1,3-Butadiene reacted with chlorosilanes and Grignard reagents at 20°C in the presence of a catalytic amount of Pd(acac)₂ to give disilylated dimers 2 regioselectively, which have two silyl groups (R₃Si)

Full text of DOI:10.1021/ol048751j

ORGANIC
LETTERS
2004
Vol. 6, No. 19
3341-3344
Palladium-Catalyzed Dimerization
Disilylation of 1,3-Butadiene with
Chlorosilanes
Jun Terao, Akihiro Oda, and Nobuaki Kambe*
Department of Molecular Chemistry & Science and Technology Center for Atoms,
Molecules and Ions Control, Graduate School of Engineering, Osaka UniVersity,
Suita, Osaka 565-0871, Japan
kambe@chem.eng.osaka-u.ac.jp
Received July 1, 2004
ABSTRACT
1,3-Butadiene reacted with chlorosilanes and Grignard reagents at 20 °C in the presence of a catalytic amount of Pd(acac)2 to give disilylated
dimers 2 regioselectively, which have two silyl groups (R Si) at the 3- and 8-positions of a 1,6-octadiene skeleton. When phenyl- or allyl-
3
substituted chlorosilanes were used, coupling product was obtained stereo- as well as regioselectively, giving rise to only (E)-olefins. It is
proposed that Pd-ate complexes play important roles in both C−Si bond-forming processes.
The carbon-silicon bond-forming reaction is of great
importance and widely used for the synthesis of organosi-
lanes. Among a variety of methods having been developed
for such transformations, transition metal-catalyzed silylation
provides useful routes to organosilanes from carbon-carbon
unsaturated compounds. In these reactions various silylating
reagents possessing silicon-hydrogen,1 silicon-silicon,2 or
silicon-heteroatom bonds2b have been employed; however,
chlorosilanes (R3SiCl) have rarely been employed in transi-
tion metal-catalyzed C-Si bond-forming reactions probably
due to the difficulty of the oxidative addition of the Si-Cl
bond to low-valent metal complexes.3 During the course of
our project on the synthetic use of chlorosilanes in transition
metal-catalyzed reactions, we have reported unique silylation
reactions of olefins and dienes with chlorosilanes by the
combined use of Grignard reagents and early transition metal
catalysts such as Cp2ZrCl24 or Cp2TiCl2.5 As the first example
of late transition metal-catalyzed C-Si bond formation using
chlorosilanes, we have recently developed dimerization
carbosilylation of 1,3-butadienes with chlorosilanes and
Grignard reagents in the presence of a Ni catalyst (Scheme
1).6 When we carried out a similar reaction using Pd, we
Scheme 1
(1) (a) Makabe, H.; Negishi, E. In Handbook of Organopalladium
Chemistry for Organic Synthesis; Negishi, E., Ed.; John Wiley & Sons:
New York, 2002; Vol. II, VII.4, pp 2789-2823. (b) Ojima, I.; Li, Z.; Zhu,
J. In The Chemistry of Organic Silicon Compounds; Patai, S., Rappoport,
Z., Eds.; John Wiley & Sons: New York, 1998; Vol. 2, Part 2, pp 1687-
1792. (c) Ojima, I. In The Chemistry of Organic Silicon Compounds; Li,
Z., Zhu, J., Eds.; John Wiley & Sons: 1989; Vol. 1, Part 2, pp 1479-
1526.
(2) (a) Oshima, K. In Handbook of Organopalladium Chemistry for
Organic Synthesis; Negishi, E., Ed.; John Wiley & Sons: 2002; Vol. II,
VII.5, pp 2825-2839. (b) Suginome, M.; Ito, Y. Chem. ReV. 2000, 100,
3221-3256. (c) Horn, K. A. Chem. ReV. 1995, 95, 1317-1350.
(3) Yamashita, H.; Tanaka, M.; Goto, M. Organometallics 1997, 16,
4696-4704 and references therein.
happened to find that dimerization disilylation of 1,3-
butadiene proceeds regioselectively under mild conditions
to give bis(allylsilane)s (2) (Scheme 1).
(4) (a) Terao, J.; Torii, K.; Saito, K.; Kambe, N.; Baba, A.; Sonoda, N.
Angew. Chem., Int. Ed. 1998, 37, 2653-2656. (b) Terao, J.; Jin, Y.; Torii,
K.; Kambe, N. Tetrahedron 2004, 60, 1301-1308.
10.1021/ol048751j CCC: $27.50 © 2004 American Chemical Society
Published on Web 08/25/2004

Scheme 2
Table 1. Pd-Catalyzed Dimerization Disilylation of
1,3-Butadienes
stereoselectively. The corresponding products 7-9 were
obtained in good yields using chlorotrialkylsilanes; however,
stereoisomers were obtained concomitantly (entries 7-9).
When PdCl2 and PdCl2(PPh3)2 were used instead of Pd(acac)2
as catalysts under conditions identical to those of entry 8 in
Table 1, 8 was obtained in 76 and 64% yields, respectively,
whereas no reaction took place with PdCl2(dppe). Under the
same conditions, isoprene gave 10 in only 18% yield. 2,3-
Dimethyl-1,3-butadiene did not react, resulting in the forma-
tion of a substantial amount of PhMe2SiPh by direct reaction
of PhMe2SiCl with PhMgBr.
It is worth noting that when dichlorosilanes (R2SiCl2) were
used, cyclization took place exclusively to give 2,5-divinyl-
silolanes 11a and 11b in 78 and 69% yields, respectively
(Scheme 2).
When n-BuMgCl was employed, a 47% yield of the
desired product 8 was obtained along with hydrosilylation
products 12 and 13 in 3 and 25% yields, respectively (vide
infra) (Scheme 3).
a 1,3-Butadiene and PhMgBr were used unless otherwise stated. b By
NMR and GC. c Reaction was carried out on a 20 mmol scale. d Isopro-
penylmagnesium bromide was employed. e Isoprene was used.
For example, a reaction of 1,3-butadiene (2 mmol) with
Ph3SiCl (2 mmol) in the presence of PhMgBr (1 M in THF,
2.4 mL, 2.4 mmol) and a catalytic amount of Pd(acac)2 (0.05
mmol) at 20 °C for 6 h gave a 1,6-octadiene 3 possessing
two triphenylsilyl groups at the 3- and 8-positions7 with
perfect regio- and stereoselectivity in 98% NMR yield. The
product was obtained in pure form in 93% yield by HPLC
(Table 1, entry 1). In this reaction, 1.05 mmol of biphenyl
was formed as a byproduct; however, NMR, GC, and GC-
MS analyses of the resulting mixture showed no evidence
for the presence of the regioisomers of 3, dimerization carbo-
silylation products (1),6 or any other monosilylated products.8
Results obtained using various chlorosilanes are shown
in Table 1. Entry 2 shows an example of large-scale
preparation (20 mmol of 1,3-butadiene) under the identical
conditions, where 5.2 g (83%) of 3 was synthesized in pure
form by recrystallization from a 1:2 solution of ether and
n-hexane. Isopropenylmagnesium bromide could be em-
ployed instead of PhMgBr to give 3 in 88% isolated yield
(entry 3). Phenyl- or allyl-substituted chlorosilanes also
afforded the corresponding coupling products 4-6 regio- and
Scheme 3
A plausible reaction pathway is depicted in Scheme 4.
First, Pd(acac)2 is reduced by R′MgX to afford Pd(0) 15 via
14 with the concomitant formation of R′-R′. Then, 15 reacts
with 2 equiv of butadiene, giving rise to bis-π-allylpalladium
complex 16,9 which is attacked by R′MgX to form η1,η3-
octadienediylpalladate complex 17.10 The ate complex 17
reacts with a chlorosilane at the allylic γ-carbon11 leading
to π-allylpalladium complex 18, which reacts again with
R′MgX to form another ate complex 19. Then, 19 reacts with
chlorosilane at the γ-allyl carbon giving rise to disilyl coupl-
ing product 2 along with regeneration of 14 to complete the
(5) (a) Terao, J.; Kambe, N.; Sonoda, N. Tetrahedron Lett. 1998, 39,
9697-9698. (b) Nii, S.; Terao, J.; Kambe, N. J. Org. Chem. 2000, 65,
5291-5297. (c) Watabe, H.; Terao, J.; Kambe, N. Org. Lett. 2001, 3, 1733-
1735. (d) Nii, S.; Terao, J.; Kambe, N. Tetrahedron Lett. 2004, 45, 1699-
1702.
(6) Terao, J.; Oda, A.; Ikumi, A.; Nakamura, A.; Kuniyasu, H.; Kambe,
N. Angew. Chem., Int. Ed. 2003, 42, 3412-3414.
(9) Jolly, P. W. Angew. Chem., Int. Ed. Engl. 1985, 24, 283-295.
(10) π-Allylpalladate complex has been reported for Mg; see: Bog-
danovic´, B.; Huckett, S. C.; Wilczok, U.; Rufinˇska, A. Angew. Chem., Int.
Ed. Engl. 1988, 27, 1513-1516.
(7) It has been reported that the reaction of 1,3-butadienes with
hexamethyldisilane gives rise to 1,8-bis(trimethylsilyl)-2,6-octadiene; see:
Sakurai, H.; Eriyama, Y.; Kamiyama, Y.; Nakadaira, Y. J. Organomet.
Chem. 1984, 264, 229-237.
(11) η1,η3-Octadienediylpalladium complex reacts with Me2HSiCl at the
γ-allylic carbon; see: Jolly, P. W.; Mynott, R.; Raspel, B.; Schick, K.-P.
Organometallics 1986, 5, 473-481.
(8) Trace amount of Ph4Si (<2%) was formed by the direct reaction of
Ph3SiCl with PhMgBr.
3342
Org. Lett., Vol. 6, No. 19, 2004

Scheme 4. Plausible Reaction Pathway
catalytic cycle. When n-BuMgCl is used, â-hydrogen elim-
hand, Pd(acac)2 gave allylsilane 22 in 75% yield along with
79% yield of biphenyl. These results can be rationally
understood by assuming a π-allyl(aryl)metal complex 23 as
a common intermediate that is formed by oxidative addition
of allyl ether to zero-valent Ni12 or Pd13 followed by the
reaction with PhMgBr. The π-allyl(aryl)nickel complex (23a,
M ) Ni) readily undergoes reductive elimination to give 21.14
On the other hand, π-allyl(aryl)palladium complex (23b, M
) Pd) reacts with another PhMgBr molecule to form
palladate complex 24. This is in accordance with the evidence
that reductive elimination of π-allyl(aryl)nickel complex
proceeds ca. 26 times faster than that of the corresponding
Pd complex.15 Nucleophilic attack of a chlorosilane at the
terminal γ-allylic carbon of 24 gives 22. Since it is known
ination from 18 (R′ ) n-Bu) might compete with ate complex
formation leading to 19, resulting in the formation of
hydrosilylation products 12 and 13 as shown in Scheme 3.
Under similar conditions, Ni and Pd follow different
reaction courses leading to different products, i.e., Ni affords
dimerization carbosilylation products 1,6 whereas dimeriza-
tion disilylation products 2 are obtained by using Pd catalyst.
To confirm these unique catalytic features of these metals,
we examined the reaction of allyl ether 20 with 2 equiv of
PhMgBr and PhMe2SiCl in the presence of Ni(acac)2 or
Pd(acac)2 as catalysts (Scheme 5). In the case of the Ni-
catalyzed reaction, allylbenzene derivative 21 was formed
in 81% yield without formation of allylsilane 22. On the other
Scheme 5
Org. Lett., Vol. 6, No. 19, 2004
3343

that the reaction of crotyl Grignard reagent with trimethyl-
chlorosilane gives a mixture of regioisomers of allylsilanes
via both SE2 and SE2′ mechanisms,16 it might not be likely
that a free allyl Grignard reagent 25 is generated by
transmetalation17 of 23 with PhMgBr and reacts with
chlorosilanes.
In conclusion, we have developed a new, simple method
for the synthesis of bis(allylsilanes)18 from dienes and
chlorosilanes, where two C-Si bonds and one C-C bond
can be formed regioselectively using Pd catalyst in the
presence of PhMgBr. This reaction also proceeds stereose-
lectively by the use of aryl- or allyl-substituted chlorosilanes.
Two allylpalladate complexes 17 and 19 play important roles
for regioselective C-Si bond-forming steps.
Acknowledgment. This research was financially sup-
ported in part by a grant from the Ministry of Education,
Culture, Sports, Science and Technology of Japan.
Supporting Information Available: Experimental pro-
cedures and full characterization of new compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OL048751J
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(18) Allylsilanes play important roles in organic synthesis as useful
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