The chemistry of borylstannanes: Oxidative addition to palladium species and its application to palladium-catalyzed borylstannation of alkynes

Article abstract of DOI:10.1021/om9607199

cis addition of the borylstannanes Me₃SnB-[NMe(CH₂CH₂)NMe] (1) and Me₃SnB(NEt₂)₂ (4) across alkynes was efficiently catalyzed at room temperature or 80°C by Pd(PPh₃)₄,

Full text of DOI:10.1021/om9607199

5
450
Organometallics 1996, 15, 5450-5452
Th e Ch em istr y of Bor ylsta n n a n es: Oxid a tive Ad d ition to
P a lla d iu m Sp ecies a n d Its Ap p lica tion to
P a lla d iu m -Ca ta lyzed Bor ylsta n n a tion of Alk yn es
Shun-ya Onozawa, Yasuo Hatanaka, Toshiyasu Sakakura,
Shigeru Shimada, and Masato Tanaka*
National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305, J apan
Received August 21, 1996X
Summary: cis addition of the borylstannanes Me3SnB-
NMe(CH2CH2)NMe] (1) and Me3SnB(NEt2)2 (4) across
alkynes was efficiently catalyzed at room temperature
or 80 °C by Pd(PPh3)4, Pd(dba)2, Cl2Pd(PPh3)2, or Me2-
Pd[PMe2(CH2CH2)PMe2] to give (â-stannylalkenyl)bo-
ranes in high yields. Treatments of 1 with Me2Pd-
products having two different heteroatom-carbon bonds
[
allow more elaborative synthetic applications, based on
7
the difference in the intrinsic reactivities. With regard
to the combinations of group 13 and 14 elements, a
recent paper disclosed the inertness of borylsilanes in
attempted reactions with alkynes and alkenes in the
[PMe2(CH2CH2)PMe2] and of 4 with cis-Me2Pd(PPh2Me)2
presence of transition-metal-complex catalysts.8 We
gave [{MeN(CH2CH2)MeN}B](Me3Sn)Pd[PMe2(CH2CH2)-
PMe2] (5) and [(Et2N)2B](Me3Sn)Pd(PPh2Me)2 (6), re-
spectively, with the former characterized by X-ray analy-
sis. Complex 5, when treated with 1-octyne, formed the
corresponding (â-stannyl-1-octen-1-yl)borane and could
catalyze the addition reaction of 1 with 1-octyne.
report herein (1) the facile oxidative addition of boryl-
stannanes to palladium complexes to afford cis-boryl-
(stannyl)palladium species and (2) highly stereo- and
regioselective palladium-catalyzed borylstannation of
alkynes (eq 1) that involves oxidative addition in the
9
catalytic cycle.
Transition-metal-catalyzed addition reactions of inter-
1
1j, 2
3
heteroatom bonds such as Si-Si, Sn-Sn,
Si-Sn,
4
and B-B with unsaturated organic compounds have
recently attracted increasing interest, since the result-
ing compounds are extremely useful as synthetic re-
agents and monomers for heteroatom-containing poly-
mers. However, similar reactions of inter-heteroatom
bonds for elements of two different groups are still very
5
6
rare except for “ate” complexes, though the resulting
X
Abstract published in Advance ACS Abstracts, November 15, 1996.
(
1) (a) Sakurai, H.; Kamiyama, Y.; Nakadaira, Y. J . Am. Chem. Soc.
1
975, 97, 931. (b) Watanabe, H.; Kobayashi, M.; Higuchi, K.; Nagai,
Y. J . Organomet. Chem. 1980, 186, 51. (c) Hayashi, T.; Kobayashi, T.;
Kawamoto, A. M.; Yamashita, H.; Tanaka, M. Organometallics 1990,
In a typical catalytic reaction, 1,3-dimethyl-2-(tri-
9
5
1
, 280. (d) Ito, Y.; Suginome, M.; Murakami, M. J . Org. Chem. 1991,
6, 1948. (e) Yamashita, H.; Catellani, M.; Tanaka, M. Chem. Lett.
991, 241. (f) Tsuji, Y.; Lago, R. M.; Tomohiro, S.; Tsuneishi, H.
methylstannyl)-2-bora-1,3-diazacyclopentane (1; 1.1
10
mmol) and 1-octyne (2a ; 1 mmol) were added at 0 °C
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Fujimoto, K.; Nakamura, H.; Andersson, P. G.; Ito, Y. J . Am. Chem.
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Kobayashi, M.; Shinkai, Y. J . Chem. Soc., Perkin Trans. 1 1995, 599.
to a benzene solution (1 mL) of Pd(PPh3)4 (1 mol %) and
octane (50 µL, internal standard for GC) placed in a
Schlenk tube. The mixture was warmed to room tem-
perature and stirred for 1 h. GC and GC-MS (in
conjunction with an NMR study) of the resulting
mixture revealed that the starting materials were
nearly completely consumed and that 1,3-dimethyl-2-
(2) (a) Mitchell, T. N.; Amamria, A.; Killing, H.; Rutschow, D. J .
Organomet. Chem. 1983, 241, C45. (b) Killing, H.; Mitchell, T. N.
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(
3) (a) Chenard, B. L.; Van Zyl, C. M. J . Org. Chem. 1986, 51, 3561.
(
2-(Z)-(trimethylstannyl)-1-octen-1-yl)-2-bora-1,3-diaza-
(
b) Mitchell, T. N.; Wickenkamp, R.; Amamria, A.; Dicke, R.; Schneider,
cyclopentane (3a I) was formed as the sole product in
98% yield. Evaporation of the mixture, addition of
pentane (15 mL) to the residue, filtration, and Kugelrohr
distillation of the filtrate (oven temperature 80 °C/3.4
U. J . Org. Chem. 1987, 52. 4868. (c) Tsuji, Y.; Obora, Y. J . Am. Chem.
Soc. 1991, 113, 9368. (d) Murakami, M.; Amii, H.; Takizawa, N.; Ito,
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M.; Kawamura, T. Organometallics 1993, 12, 4697.
(4) (a) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J . Am.
-3
Chem. Soc. 1993, 115, 11018. (b) Iverson, C. N.; Smith, M. R., III. J .
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M.; Ozawa, F.; Suzuki, A.; Miyaura, N. Organometallics 1996, 15, 713.
× 10 Torr) afforded analytically pure 3a I in 83% yield.
A spectral study of 3a I, inclusive of comparison of the
(
5) B-S: (a) Ishiyama, T.; Nishijima, K.; Miyaura, N.; Suzuki, A.
J . Am. Chem. Soc. 1993, 115, 7219. P-Se: (b) Han, L.-B.; Choi, N.;
Tanaka, M. J . Am. Chem. Soc. 1996, 118, 7000.
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K.; Nozaki, H. J . Am. Chem. Soc. 1983, 105, 4491. (b) Nozaki, K.;
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Meeting on Boron Chemistry, Heidelberg, Germany, J uly 1996;
Abstract CB-16.
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S0276-7333(96)00719-4 CCC: $12.00 © 1996 American Chemical Society

Communications
Ta ble 1. Bor ylsta n n a tion of Alk yn esa
product (3)
Organometallics, Vol. 15, No. 26, 1996 5451
alkyne (2)
yieldb
(%)
entry
no.
ratio
R1
R2
temp (°C)
(I/II)c
1
2
3
n-C6H13
Ph
Ph
H
H
Ph
room temp 98 (83) >99/1
room temp 97 (73) >99/1
d
80
97 (78)
4
5
MeOC(dO) MeOC(dO) 80
Ph Me 80
91 (84)
97 (86) 85/15
a
All reactions were carried out in benzene using 1 (1.1 equiv),
2
(1.0 equiv), and Pd(PPh3)4 (1 mol %) for 1 h. b GC yields based
on 2. Figures in parentheses are isolated yields. Determined by
NMR. For 3 h; isolated by recrystallization from pentane.
c
d
1
H NMR data with those of related vinylstannanes11 and
an NOE experiment,12 confirmed the regio- and stereo-
chemistry.
F igu r e 1. ORTEP drawing of complex 5. Selected bond
distances (Å): Pd-P(1), 2.338(2); Pd-P(2), 2.280(2); Pd-
Sn, 2.577(1); Pd-B, 2.077(6). Selected bond angles (deg):
Sn-Pd-P(1), 102.9(1); P(1)-Pd-P(2), 86.3(1); P(2)-Pd-
B, 91.2(2); B-Pd-Sn, 79.3(2).
Besides Pd(PPh3)4, Pd(dba)2 and Cl2Pd(PPh3)2 also
exhibited catalytic activity under similar conditions (5
mol % catalyst, room temperature, 3 h) to afford 3a I
quantitatively. Me2Pd(dmpe)13 (dmpe ) 1,2-bis(di-
methylphosphino)ethane) was inactive at room temper-
ature, but it did promote the reaction at 80 °C to give
in deterioration of the products, which did not gave
satisfactory analytical data.
3
a I in 93% yield in 8 h. On the other hand, Pt(PPh3)4,
The catalysis is envisioned to be triggered by oxidative
addition of the B-Sn bond. Although we have been
unable to provide any evidence for oxidative addition
between borylstannanes and Pd(PPh3)4, we did find that
heating a benzene-d6 (1 mL) solution of Me2Pd(dmpe)
(2.25 mmol) and 1 (2.6 equiv) at 130 °C over 17 h in a
sealed NMR tube quantitatively formed a cis adduct (5)
along with SnMe4 (84%) and MeB[NMe(CH2CH2)NMe]
4
which was a good catalyst for diboration of alkynes,
was totally ineffective.
The Pd(PPh3)4-catalyzed borylstannation appears to
1
4
be quite general. As summarized in Table 1, ethy-
nylbenzene also reacted at room temperature to give
only 3bI in an excellent yield. Internal alkynes were
less reactive, but the borylstannation proceeded smoothly
at 80 °C to provide corresponding cis-addition products
1
13
31
(91%) (eq 2). Adduct 5 displays satisfactory H, C, P,
1
1
119
(entries 3-5). Unsymmetrical internal alkynes gave a
B, and
Sn NMR spectra and MS and analytical
1
6
mixture of regioisomers, as exemplified by the phenyl-
propene reaction; optimization to achieve higher control
in the regioselectivity has not been carried out yet.
data. Recrystallization from a toluene-pentane (1:4)
1
5
With regard to the borylstannane, Me3SnB(NEt2)2 (4)
also reacted with various alkynes very similarly to 1.
For instance, the Pd(PPh3)4-catalyzed reactions with
ethynylbenzene (1 mol % catalyst) or 1-octyne (5 mol %
catalyst) at room temperature over 3 h quantitatively
gave the corresponding (â-stannylalkenyl)boranes. How-
ever, the resulting adducts were somewhat thermally
unstable and attempted isolation by distillation resulted
(
12) Irradiation at 2.48 ppm (allylic protons) exhibited a 7%
enhancement of the vinylic proton at 6.39 ppm, suggesting that 3a I is
the Z isomer.
(
13) de Graaf, W.; Boersma, J .; Smeets, W. J . J .; Spek, A. L.; van
Koten, G. Organometallics 1989, 8, 2907.
14) All catalytic reactions were carried out in the same way as in
the typical example with some exceptions in the reaction temperature
and/or time, which were indicated in Table 1. The workup procedure
was also the same except for 3c, which was recrystallized from pentane.
solution afforded colorless parallelepipeds (68%),17 the
structure of which was unequivocally verified by X-ray
diffraction (vide infra). Oxidative addition between cis-
Me2Pd(PPhMe2)2 and 4 also proceeded cleanly under
much milder conditions (60 °C, 46 h) to give an adduct
(6) along with SnMe4 and MeB(NEt2)2. The adduct
being an oil prevents X-ray crystallography, but the
(
(
15) N o¨ th, H.; Schwerth o¨ ffer, R. Chem. Ber. 1981, 114, 3056.
1
(16) Boryl(stannyl)palladium complex 5: mp 120 °C; H NMR (C
6
D
6
)
δ 0.59 (s, 9H, J H-Sn ) 34.3 Hz, SnCH
PCH ), 2.83 (s, 6H, NCH ), 3.23-3.41 (m, 4H, NCH
δ -4.5 (dd, J C-P ) 5.5, 11.5 Hz, SnCH ), 14.3 (dd, J C-P ) 3.4, 16.7 Hz,
PCH ), 14.5 (dd, J C-P ) 2.7, 11.0 Hz, PCH ), 29.2 (dd, J C-P ) 20.1,
), 37.3 (NCH ),
) δ -29.2 (J Sn-Ptrans
CD at -40 °C) δ
3
), 0.89-1.06 (m, 16H, PCH and
3
13
2
3
2 6 6
); C NMR (C D )
3
3
3
31
spectral data, P NMR in particular (-19.2 and -16.6
2
5
1
1
2.1 Hz, PCH
3.9 (d, J C-P ) 5.2 Hz, NCH
666 Hz); 11B NMR (C
2
), 30.0 (dd, J C-P ) 19.9, 21.9 Hz, PCH
2
3
)
2
); 119Sn NMR (C
ppm, J PP ) 17 Hz), suggest that it also has a cis
2
6
D
6
31
6
D
6
) δ 46.9; P NMR (C
6
D
5
3
configuration.
4.0 (J Pcis-Sn ) 167 Hz, Pcis to the stannyl ligand; the Sn satellites did
The structure of 5, the first boryl(stannyl)palladium
complex, is planar (Figure 1); the distortion from
planarity is very small since the repulsion between the
four ligands is reduced by the arrangement of the
1
17
119
not display splitting due to Sn and Sn nuclei), 18.4 (J Ptrans-Pcis ) 7
Hz, J Ptrans-Sn ) 1671 Hz, P +t rans to the stannyl ligand); DI-MS (EI) m/z
11
106
120
(relative intensity) 518 (M for 5 having B, Pd, and Sn isotopes,
2
.6; molecular peaks corresponding to other isotopes were also
observed), 507 (32), 506 (28), 505 (67), 504 (47), 503 (92), 502 (86), 501
(
(
100), 500 (69), 499 (63), 498 (40), 497 (22), 393 (24), 391 (34), 390
24), 389 (52), 388 (18), 387 (18), 353 (15), 352 (15), 260 (22), 258 (45),
56 (51), 255 (44), 254 (21), 243 (10), 241 (17), 135 (17), 122 (16), 111
2 2
(17) X-ray data for 5: SnPdP N BC13H35, triclinic, space group P 1h ,
2
colorless prism, a ) 9.656(2) Å, b ) 10.553(1) Å, c ) 12.442(2) Å, R )
3
(37), 97 (61), 96 (26). Anal. Calcd for C13 PdSn: C, 30.18; H,
H
35BN
2
P
2
90.61(1)°, â ) 90.75(1)°, γ ) 116.93(1)°, V ) 1130.1(3) Å , Z ) 2, R )
6
.82; N, 5.42. Found: C, 30.55; H, 6.79; N, 5.30.
w
0.0340, R ) 0.0551, GOF ) 0.206.

5
452 Organometallics, Vol. 15, No. 26, 1996
Communications
Sch em e 1
On the basis of these results, one can safely conclude
that the boryl(stannyl)palladium species is involved in
the catalytic cycle of the borylstannation (Scheme 1).
In summary, we have developed the palladium-
catalyzed borylstannation of alkynes, which is initiated
by the oxidative addition of the B-Sn bond. This paper
offers another useful demonstration to verify the power
of transition-metal catalysis to activate the inter-het-
eroatom bonds. Extensions to other combinations of
heteroatoms as well as synthetic applications of the (â-
stannylalkenyl)boranes will be the subjects of forthcom-
ing papers.
diazaborolane ring, which is nearly perpendicular to the
BSnPdP2 mean plane. The Pd-P(1) bond (2.338(2) Å)
is longer than the Pd-P(2) bond (2.280(2) Å). This
indicates that the boryl ligand is stronger in trans
influence than the stannyl ligand.
The boryl(stannyl)palladium complexes were found to
react with alkynes. For instance, complex 5 (0.05 mmol)
in benzene-d6 (0.4 mL) reacted with an excess (2.8 equiv)
1
8
of 1-octyne at 80 °C to afford 3a I (36%) in 8 h.
In
addition, the borylstannation of 1-octyne with 1 pro-
ceeded at 80 °C over 8 h in the presence of complex 5 (5
mol %) used as catalyst to give 3a I in 90% yield (eq 3).
Ack n ow led gm en t. We are grateful to the J apan
Science and Technology Corporation (J ST) for the
partial financial support through the CREST (Core
Research for Evolutional Science and Technology) pro-
gram.
(18) Ethyl propiolate proved to be much more reactive toward
complex 5 than 1-octyne. When 5 was treated with ethyl propiolate
1
(
6
1.1 equiv) in benzene-d (0.4 mL) at room temperature for 30 min, H
NMR of the reaction mixture displayed signals presumably assignable
to [(Z)-2-(ethoxycarbonyl)-2-stannylethenyl]palladium species. For
instance, the proton trans to the stannyl group exhibited satellites as
two doublets centered at 8.04 ppm with coupling constants of 157 and
Su p p or tin g In for m a tion Ava ila ble: Text giving detailed
experimental procedures and characterization data for the (â-
stannylalkenyl)boranes and the boryl(stannyl)palladium com-
plexes and text and tables giving full details of the crystal
structure analysis of 5 (12 pages). Ordering information is
given on any current masthead page.
1
19
117
1
50 Hz due respectively to Sn and
Sn nuclei, both the chemical
1
9
11
shift and the coupling constants being in good agreement with the
known values. Accordingly, we tentatively conclude that the acetylenic
bond was inserting into the Sn-Pd bond (stannyl palladation), at least
in this particular case.
(19) Rybin, L. V.; Petrovskaya, E. A.; Rubinskaya, M. I.; Kuz’mina,
L. G.; Struchkov, Y. T.; Kaverin, V. V.; Koneva, N. Y. J . Organomet.
Chem. 1985, 288, 119.
OM9607199