Palladium-catalysed borylsilylation and borylstannylative dimerization of 1,2-dienes

Article abstract of DOI:10.1039/a905127i

A borylsilane regioselectively adds to 1,2-dienes in the presence of palladium complexes to afford high yields of alkenylboranes having allylsilane moieties, whereas a borylstannane gives a 1:2 telomer with 3-methylbuta-1,2-diene due to borylstannylative

Full text of DOI:10.1039/a905127i

Palladium-catalysed borylsilylation and borylstannylative dimerization of
1,2-dienes
Shun-ya Onozawa, Yasuo Hatanaka and Masato Tanaka*
National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305-8565, Japan.
E-mail: mtanaka@home.nimc.go.jp
Received (in Cambridge, UK) 25th June 1999, Accepted 16th August 1999
A borylsilane regioselectively adds to 1,2-dienes in the
presence of palladium complexes to afford high yields of
alkenylboranes having allylsilane moieties, whereas a boryl-
stannane gives a 1 : 2 telomer with 3-methylbuta-1,2-diene
due to borylstannylative dimerization.
conditions, another monosubstituted 1,2-diene, 2b, also under-
went the borylsilylation at the internal double bond, affording
3b in 86% yield as the sole product (entry 2). Propa-1,2-diene 2c
and sterically congested 2,4-dimethylpenta-2,3-diene 2d effec-
tively participated in the borylsilylation with high regioselectiv-
ity (entries 3 and 4).
Addition reactions of metal–metal bonds to 1,2-dienes provide
a straightforward route to organometallic compounds having
both vinylic and allylic metal moieties, which are versatile
reagents in organic synthesis.1 Although several studies on the
transition-metal-catalysed reactions of 1,2-dienes with Si–Si,2
Sn–Sn,3 Si–Sn,3 Ge–Sn4 and B–B bonds5 have been reported,
similar reactions of B–Si or B–Sn bonds have received little
attention.6,7 In the course of our investigation on the transition-
metal-catalysed additions of these bonds to unsaturated organic
compounds,8,9 we have found that palladium catalysts effec-
tively promote the reactions with 1,2-dienes, giving the
corresponding adducts with extremely high regioselectivity
(Scheme 1).
The following procedure is representative (Table 1, entry 1).
A mixture of Pd2(dba)3 (2.5 mol%; dba = dibenzylideneace-
tone) and etpo as ligand [10 mol%; etpo = 4-ethyl-2,6,7-trioxa-
1-phosphabicyclo[2,2,2]octane, P(OCH2)3CEt] in THF (1 ml)
was heated at 80 °C for 5 min, while the color of the solution
turned to green from red. To this solution were added
2-dimethylphenylsilyl-4,4,5,5-tetramethyl-2-bora-1,3-dioxacy-
clopentane 1 (0.33 mmol), buta-1,2-diene 2a (1.0 mmol) and
decane (30 ml; as internal standard for GC analysis), and the
reaction mixture was heated at 80 °C. GC-MS analysis of the
mixture indicated the complete consumption of the borylsilane
1 after 9 h and quantitative formation of a borylsilylation
product 3a (98% GC yield). It should be noted that the NMR
analysis of the reaction mixture indicated the lack of formation
of regioisomers like 4a. Thus, the addition of the B–Si bond
smoothly proceeded at the internal double bond of 2a, and the
boryl group was regioselectively introduced to the central
carbon, leading to the exclusive formation of alkenylborane
moiety. Purification of the crude product by TLC (silica gel;
hexane–CH2Cl2 as eluent) gave analytically pure 3a in 88%
yield.†
The regioselectivity of the Pd–etpo-catalysed borylsilylation
of 1,1-disubstituted propa-1,2-dienes was strongly influenced
by the nature of substituents. For example, the reaction of
1,1-diphenylpropa-1,2-diene 2e with 1 selectively proceeded at
the terminal double bond to give 4e in 94% yield (entry 5),
whereas the borylsilylation of 3-methylbuta-1,2-diene 2f took
place at both the internal and terminal double bonds, affording
a regioisomeric mixture of 3f and 4f with a 52+48 ratio (entry 6).
The low regioselectivity of the latter reaction could be
successfully improved by tuning the phosphorus ligands; the
best result (3f+4f = 100+0) was achieved by using Pd2(dba)3
(2.5 mol%)–PPh3 (10 mol%) (entry 7). The use of the Pd2(dba)3
(2.5 mol%)–PMe3 (10 mol%) system was less effective, giving
a mixture containing 3f as major product (3f+4f = 71+29, entry
8).
To our surprise, the regioselectivity of this reaction com-
pletely changed when the reaction was conducted with a
platinum catalyst. Thus, in the presence of a catalytic amount of
(CH2NCH2)Pt(PPh3)2 (5 mol%), the B–Si bond of 1 preferen-
tially added to the terminal double bond of 2f, furnishing 4f as
the sole product (94% GC yield, entry 9). However, application
of this catalyst to the borylsilylation of monosubstituted
Table 1 Borylsilylation of 1,2-dienesab
1,2-Diene
Entry
2
R1
R2
R3
Yield (%)c
3+4d
Representative results of the reactions between 1 and various
1,2-dienes 2a–f are summarized in Table 1. All of the products
listed have exhibited satisfactory spectral data.† Under similar
1
2a
2b
2c
2d
2e
2f
2f
2f
2f
H
H
H
Me
H
H
H
H
H
Me
OMe
H
Me
Ph
Me
Me
Me
Me
H
H
H
Me
Ph
Me
Me
Me
Me
88 (98)
86 (93)
91 (96)
92 (94)
94
84 (85)
(90)
(90)
87 (94)
100+0
100+0
—
2
3e
4
5
6
—
0+100
52+48
100+0
71+29
0+100
7f
8g
9h
a
Reaction conditions: borylsilane 1 (0.33 mmol), 1,2-dienes (1.0 mmol),
catalyst Pd2(dba)3 (2.5 mol%)–etpo (10.0 mol%), THF (1 ml), 80 °C, 9 h
unless otherwise noted. b Si = SiMe2Ph, B = B(OCMe2)2. c Isolated yields
based on the amount of the borylsilane 1. Figures in parentheses are GC
yields. Determined by 1H NMR spectroscopy. A large excess of
1,2-diene was used. f Pd2(dba)3 (2.5 mol%)–PPh3 (10.0 mol%) was used as
d
e
g
catalyst. Pd2(dba)3 (2.5 mol%)–PMe3 (10.0 mol%) was used as catalyst.
h Run in the presence of (CH2NCH2)Pt(PPh3)2 (5 mol%) at 80 °C for 3 h.
Scheme 1
Chem. Commun., 1999, 1863–1864
1863

24.5 (SiCH3), 24.9 and 25.0 (OCCH3), 58.4 (OCH3), 78.7 (CH), 83.3
(OCCH3), 126.7 (NCH2), 127.9, 129.3, 135.0, 137.8 (arom), NCB not
observed; dSi 25.9; dB 30.0. For 3c: dH 0.32 (s, 6H, SiCH3), 1.02 (s, 12H,
OCCH3), 2.11 (s, 2H, SiCH2), 5.49 (s, 1H, NCH2), 6.09 (s, 1H, NCH2),
7.18–7.23 (m, 3H, arom), 7.51–7.54 (m, 2H, arom); dC 23.0 (SiCH3), 24.6
(SiCH2), 24,9 (OCCH3), 83.4 (OCCH3), 128.0 (arom), 128.3 (NCH2), 129.1,
134.3 (arom), 138.9 (br s, NCB), 139.3 (arom); dSi 24.1; dB 30.2. For 3d: dH
0.45 (s, 6H, SiCH3), 1.11 (s, 12H, OCCH3), 1.27 (s, 3H, NCCH3), 1.33 (s,
6H, CCH3), 1.82 (s, 3H, NCCH3), 7.18–7.21 (m, 3H, arom), 7.57–7.61 (m,
2H, arom); dC 23.7 (SiCH3), 23.5 (NCCH3), 25.5 (OCCH3), 27.2 (NCCSi),
27.4 (NCCH3), 27.8 (CCH3), 82.9 (OCCH3), 127.6, 128.9, 135.1 (arom),
136.4 (NCMe2), 139.3 (arom), NCB not observed; dSi 1.7; dBi 31.1. For 3e:
dH 0.39 (s, 6H, SiCH3), 0.94 (s, 12H, OCCH3), 2.36 (s, 2H, SiCH2),
6.96–7.21 (m, 11H, arom), 7.30–7.35 (m, 2H, arom), 7.43–7.48 (m, 2H,
arom); dC 21.5 (SiCH3), 23.1 (SiCH2), 24.9 (OCCH3), 83.2 (OCCH3),
126.7, 126.9, 127.8, 127.9, 128.5, 129.0, 130.0 (two peaks), 134.2, 140.1,
143.4, 145.9 (arom), 149.7 (NCPh2), NCB not observed; dSi 22.6; dB 31.4.
For 3f: dH 0.36 (s, 6H, SiCH3), 1.02 (s, 12H, OCCH3), 1.30 (s, 6H, CCH3),
5.45 (s, 1H, NCH2), 6.19 (s, 1H, NCH2), 7.18–7.23 (m, 3H, arom), 7.53–7.54
(m, 2H, arom); dC 24.8 (SiCH3), 24.8 (CCH3), 24.9 (OCCH3), 29.0
(SiCH2), 83.0 (OCCH3), 127.1 (NCH2), 127.7, 129.0, 135.2, 138.1 (arom),
149.6 (br s, NCB); dSi 1.2; dB 30.6. For 4f: dH 0.36 (s, 6H, SiCH3), 1.05 (s,
12H, OCCH3), 1.52 (s, 3H, NCCH3), 2.15 (s, 2H, SiCH2), 2.21 (s, 3H,
NCCH3), 7.18–7.23 (m, 3H, arom), 7.56–7.59 (m, 2H, arom); dC 22.0
(SiCH3), 21.2 (SiCH2), 22.5 (NCCH3), 24.6 (NCCH3), 25.1 (OCCH3),
82.7(OCCH3), 122.0 (br s, NCB), 127.9, 129.0, 134.2, 140.4 (arom), 145.9
[NC(CH3)2]; dSi 23.6; dB 30.7. For 6: bp 116–118 °C/5.4 3 1023 mmHg;
dH 0.29 (s, JHSn 52.1, 9H, SnCH3), 1.71–1.76 (m, 11H, 3CH3CN and BCH2),
1.83 (s, JHSn 12.5, 3H, NCCH3), 2.57 (s, 6H, NCH3), 2.96 (s, 4H, NCH2),
3.22 [s, JHSn 67.6, 2H, (NC)2CH2]; dC 27.2 (JCSn 324.8, SnCH3), 16.2 (br
s, BCH2), 19.8 (JCSn 54.8, NCCH3), 20.9 (NCCH3), 21.6 (CCH3), 28.3 (JCSn
53.8, NCCH3), 33.5 (NCH3), 38.8 (JCSn 50.7, CH2), 51.8 (NCH2), 122.5 (C),
130.9 (C), 136.8 (JCSn 525.5, C), 141.3 (JCSn 32.1, C); dB 31.7; dSn 249.6;
m/z (EI, 70 eV) 398 ([M]+, 0.9%), 383 ([M 2 Me]+, 5), 233 ([M 2 SnMe3]+,
100).
Scheme 2 Reagents and conditions: i, Pd2(dba)3 (2.5 mol%)–etpo (10
mol%), THF, 50 °C, 3 h.
1,2-dienes such as 2a made the reaction sluggish, resulting in
the formation of a mixture of many products.
The reactivities of borylsilanes in the present reaction were
strongly influenced by the structure of the boryl group. For
instance, PhMe2Si–(BNMeCH2CH2NMe) failed to undergo the
addition reaction with 2f even at elevated temperatures (e.g.
110 °C) in the presence of the Pd2(dba)3–etpo system.
In contrast to the borylsilylation of 1,2-dienes, the B–Sn bond
of borylstannane 5 underwent the palladium-catalysed addition
reaction with 3-methylbuta-1,2-diene 2f, predominantly yield-
ing telomer 6 having both vinyl–Sn and allyl–B moieties (74%
GC yield) along with an isomeric mixture of simple boryl-
stannylation products 7 (18% GC yield) (Scheme 2). The
reaction proceeded smoothly at 50 °C in the presence of the
Pd2(dba)3–etpo system and was complete within 3 h. The
purification of the reaction mixture by bulb-to-bulb distillation
(116–118 °C/5.4 3 1023 mmHg) afforded analytically pure 6 in
63% yield.† The structure of 6 was determined by NMR
spectroscopy; its 119Sn NMR spectrum displayed a signal at d
249.6 assignable to tin attached to an alkenyl group.3,4 In
addition, the 13C NMR spectrum showed a broad signal at d
16.2 indicative of an allylic carbon bonded to boron. Further
studies on the reaction mechanism are in progress.
In conclusion, the transition-metal-catalysed addition reac-
tion of B–Si or B–Sn bonds to 1,2-dienes provides a selective
and facile route to organometallic compounds containing both
vinyl- and allyl-metal moieties. In view of the different
reactivities of these metal moieties in electrophilic substitution,
the products will find considerable synthetic applications for
complex organic molecules.
Partial financial support from the Science and Technology
Corporation (JST) through the CREST (Core Research for
Evolutional Science and Technology) program is gratefully
acknowledged.
1 For the applications of alkenyl- and allyl-metals in organic synthesis, see
Comprehensive Organometallic Chemistry II, ed. E. W. Abel, F. G. A.
Stone, G. Wilkinson and A. McKillop, Pergamon, Oxford, 1995,
vol. 11.
2 H. Watanabe, M. Saito, N. Sutou, K. Kishimoto, J. Inose and Y. Nagai,
J. Organomet. Chem., 1982, 225, 343.
3 T. N. Mitchell and U. Schneider, J. Organomet. Chem., 1991, 407,
319.
4 T. N. Mitchell, U. Schneider and B. Fröhling, J. Organomet. Chem.,
1990, 384, C53.
5 T. Ishiyama, T. Kitano and N. Miyaura, Tetrahedron Lett., 1998, 39,
2357. For the transition-metal-catalysed reactions of organoboranes with
unsaturated organic compounds, see: T. B. Marder and N. C. Norman,
Top. Catal., 1998, 5, 63; G. J. Irvine, M. J. G. Lesley, T. B. Marder, N. C.
Norman, C. R. Rice, E. G. Robins, W. R. Roper, G. R. Whittell and L. J.
Wright, Chem. Rev., 1998, 98, 2685; L.-B. Han and M. Tanaka, Chem.
Commun., 1999, 395.
6 S-y. Onozawa, Y. Hatanaka and M. Tanaka, presented partly at the 25th
Symposium on Heteroatom Chemistry, Abstract P37, Kyoto, December
9–11th, 1998.
7 For similar selective addition of B–Si bonds to 1,2-dienes catalysed by
Pd–isocyanide complexes, see: M. Suginome, Y. Ohmori and Y. Ito,
presented at the 76th Annual Meeting of the Chemical Society of Japan,
Abstract 1B635, Yokohama, March 28–31st, 1999.
8 S-y. Onozawa, Y. Hatanaka and M. Tanaka, Chem. Commun., 1997,
1229.
9 S-y. Onozawa, Y. Hatanaka, T. Sakakura, S. Shimada and M. Tanaka,
Organometallics, 1996, 15, 5450; S-y. Onozawa, Y. Hatanaka, N. Choi
and M. Tanaka, Organometallics, 1997, 16, 5389; S-y. Onozawa, Y.
Hatanaka and M. Tanaka, Tetrahedron Lett., 1998, 39, 9043.
Notes and references
† Selected data for 3a: dH 0.32 and 0.34 (both s, 6H, SiCH3), 1.03 (s, 12H,
OCCH3), 1.20 (d, J 7.6, 3H, CCH3), 2.52 (q, J 7.6, 1H, CH), 5.52 (d, J 2.9,
1H, NCH2), 6.24 (s, J 2.9, 1H, NCH2), 7.18–7.24 (m, 3H, arom), 7.51–7.59
(m, 2H, aromatic); dC 25.3 and 23.5 (SiCH3), 14.8 (CCH3), 25.0
(OCCH3), 26.8 (CH), 83.3 (OCCH3), 126.3 (NCH2), 127.9, 129.1, 134.6,
138.5 (arom), 145.3 (br s, NCB); dSi 21.7; dB 30.4. For 3b: dH 0.41 and 0.45
(both s, 6H, SiCH3), 0.99 and 1.01 (both s, 12H, OCCH3), 3.21 (s, 3H,
OCH3), 4.28 (s, 1H, CH), 5.97 (d, J 4.0, 1H, NCH2), 6.29 (d, J 4.0, 1H,
NCH2), 7.17–7.25 (m, 3H, arom), 7.67–7.72 (m, 2H, arom); dC 25.6 and
Communication 9/05127I
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Chem. Commun., 1999, 1863–1864