A new and efficient method for the preparation of bismuthonium and telluronium salts using aryl- and alkenylboronic acids. First observation of the chirality at bismuth in an asymmetrical bismuthonium salt

Article abstract of DOI:10.1021/om9804531

Treatment of triarylbismuth difluorides with aryl- and alkenylboronic acids in the presence of BF₃· OEt₂ afforded tetraaryl- and alkenyltriarylbismuthonium tetrafluoroborates, respectively, while similar treatment of diphenyltellurinyl difluoride yielded the corresponding telluronium salts. The chirality at bismuth was observed for the first time from the ¹H NMR spectrum of an asymmetrical bismuthonium salt.

Full text of DOI:10.1021/om9804531

4332
Organometallics 1998, 17, 4332-4334
A New a n d Efficien t Meth od for th e P r ep a r a tion of
Bism u th on iu m a n d Tellu r on iu m Sa lts Usin g Ar yl- a n d
Alk en ylbor on ic Acid s. F ir st Obser va tion of th e Ch ir a lity
a t Bism u th in a n Asym m etr ica l Bism u th on iu m Sa lt
Yoshihiro Matano,* Shameem Ara Begum, Takashi Miyamatsu, and
Hitomi Suzuki*
Department of Chemistry, Graduate School of Science, Kyoto University,
Sakyo-ku, Kyoto 606-8502, J apan
Received J une 3, 1998
Sch em e 1
Summary: Treatment of triarylbismuth difluorides with
aryl- and alkenylboronic acids in the presence of BF3‚
OEt2 afforded tetraaryl- and alkenyltriarylbismutho-
nium tetrafluoroborates, respectively, while similar treat-
ment of diphenyltellurinyl difluoride yielded the corres-
ponding telluronium salts. The chirality at bismuth was
1
observed for the first time from the H NMR spectrum
of an asymmetrical bismuthonium salt.
Onium salts derived from heavy main-group elements
have been receiving increasing interest owing to their
unique properties and reactivity.1 Among the reported
methodologies for the synthesis of this class of com-
pounds, the reaction between a hypervalent compound
of the type RnMX2 (M ) Bi, Te, I, etc.; X ) anionic
species) and an organometallic reagent provides the
most reliable preparation of a variety of carbon-
heteroatom bonds leading to onium salts. Recently, we
reported a convenient method for the synthesis of alkyl-
and alkenyltriarylbismuthonium salts based on the
Lewis-acid-promoted reaction of triarylbismuth difluo-
rides with the corresponding organosilanes and/or -stan-
nanes.2 Although a similar reaction using arylstan-
nanes could also lead to unsymmetrical tetraarylbis-
muthonium salts, comparatively severe conditions were
needed for the Bi-Caryl coupling and the aryl ligands
transferable to the bismuth were limited to the electron-
rich ones.3 To overcome these limitations, we have
investigated arylboronic acids,4 which are well-estab-
lished as useful aryl transfer reagents in organic
synthesis.5 Rather unexpectedly, a literature search
showed that these reagents find at present only limited
use in the preparation of onium salts bearing an aryl
ligand.6
We report herein a new and efficient method for the
preparation of aryl- and alkenylbismuthonium salts by
the BF3‚OEt2-promoted reaction of triarylbismuth di-
fluorides with aryl- and alkenylboronic acids. The
method has been successfully applied to the synthesis
of an asymmetrically tetraarylated bismuthonium salt,
and the chirality at tetrahedral bismuth center was
1
studied by means of H NMR spectroscopy.
As is shown in Scheme 1, treatment of triarylbismuth
difluorides 1 with arylboronic acids 2 in the presence
of BF3‚OEt2 in CH2Cl2 at room temperature afforded
the corresponding symmetrical and unsymmetrical tet-
raarylbismuthonium tetrafluoroborates 3 in the yields
listed in Table 1.7 Onium salts 3 were isolated in a high
state of purity by simple recrystallization from CH2Cl2-
Et2O (1:10) after aqueous workup.8
Aryl ligands bearing either an electron-donating or
electron-withdrawing substituent were both transfer-
able with ease (entries 1-6). The vinyl group remained
intact throughout the reaction (entry 7). When an
excess of the Lewis acid and the compound 2h were
used, the 3-nitrophenyl group also could be transferred
(1) Recent reviews: (a) Huang, Y. Z.; Shi, L. L.; Yang, J . H.; Xiao,
W. J .; Li, S. W.; Wang, W. B. In Heteroatom Chemistry; Block, E., Ed.;
VCH: New York, 1990; p 189. (b) Huang, Y.-Z. Acc. Chem. Res. 1992,
25, 182. (c) Matano, Y.; Suzuki, H. Bull. Chem. Soc. J pn. 1996, 69,
2673. (d) Shimizu, T.; Kamigata, N. Yuki Gosei Kagaku Kyokaishi
1997, 55, 35. (e) Moriarty, R. M.; Vaid, R. K. Synthesis 1990, 431. (f)
Stang, P. J . Angew. Chem., Int. Ed. Engl. 1992, 31, 274. (g) Stang, P.
J .; Zhdankin, V. V. Chem. Rev. 1996, 96, 1123. (h) Varvoglis, A.
Tetrahedron 1997, 53, 1179. (i) Stang, P. J .; Olenyuk, B. Acc. Chem.
Res. 1997, 30, 502 and references therein.
(2) (a) Matano, Y.; Azuma, N.; Suzuki, H. Tetrahedron Lett. 1993,
34, 8457. (b) Matano, Y.; Azuma, N.; Suzuki, H. J . Chem. Soc., Perkin
Trans. 1 1994, 1739. (c) Matano, Y.; Azuma, N.; Suzuki, H. J . Chem.
Soc., Perkin Trans. 1 1995, 2543. (d) Matano, Y.; Yoshimune, M.;
Suzuki, H. Tetrahedron Lett. 1995, 36, 7475. (e) Matano, Y.; Yoshimune,
M.; Azuma, N.; Suzuki, H. J . Chem. Soc., Perkin Trans. 1 1996, 1971.
(3) Matano, Y.; Miyamatsu, T.; Suzuki, H. Chem. Lett. 1998, 127.
Electron-deficient and sterically crowded aryl ligands such as 4-chlo-
rophenyl, 1-naphthyl, and mesityl groups were not transferred ef-
ficiently by this method.
(4) For example, see: (a) Matteson, D. S. In The Chemistry of the
Metal-Carbon Bond; Hartley, F., Patai, S., Eds.; Wiley: New York,
1987; Vol. 4, p 307. (b) Pelter, A.; Smith, K.; Brown, H. C. Borane
Reagents; Academic Press: New York, 1988. (c) Vaultier, M.; Carboni,
B. Comprehensive Organometallic Chemistry II; Abel, W. W., Stone,
F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, U.K., 1995;
Vol. 11, Chapter 5, p 192.
(5) (a) Matteson, D. S. Tetrahedron 1989, 45, 1859. (b) Suzuki, A.
Pure Appl. Chem. 1994, 66, 213. (c) Miyaura, N.; Suzuki, A. Chem.
Rev. 1995, 95, 2457 and references therein.
(6) Quite recently, Ochiai et al. reported an efficient method for the
preparation of vinyl- and aryliodonium salts by the BF3‚OEt2-promoted
reaction between PhI(OAc)2 and vinyl- or arylboronic acids: Ochiai,
M.; Toyonari, M.; Nagaoka, T.; Chen, D.-W.; Kida, M. Tetrahedron Lett.
1997, 38, 6709.
S0276-7333(98)00453-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 09/09/1998

Communications
Organometallics, Vol. 17, No. 20, 1998 4333
Ta ble 1. Syn th esis of Tetr a a r ylbism u th on iu m
Sa ltsa
Sch em e 3
entry
no.
yield
(%)
1
2
product (3)
[Ph4Bi+][BF4-] (3a )
1a 2b [Ph3(4-MeC6H4)Bi+][BF4-] (3b)
1a 2c
[Ph3(2-MeC6H4)Bi+][BF4-] (3c)
1
2
3
4
5
1a 2a
95
97
97
96
96
97
95
55
98
93
98
96
98
99
95
1a 2d [Ph3(4-MeOC6H4)Bi+][BF4-] (3d )
Sch em e 4
1a 2e
1a 2f
[Ph3(4-FC6H4)Bi+][BF4-] (3e)
[Ph3(4-ClC6H4)Bi+][BF4-] (3f)
6
7
1a 2g [Ph3(4-CH2dCHC6H4)Bi+][BF4-] (3g)
1a 2h [Ph3(3-NO2C6H4)Bi+][BF4-] (3h )
8b
9
1a 2i
1a 2j
[Ph3(2,4,6-Me3C6H2)Bi+][BF4-] (3i)
[Ph3(1-C10H7)Bi+][BF4-] (3j)
10
11
12
13
14
15
1a 2k [Ph3(2-C4H3S)Bi+][BF4-] (3k )
1a 2l
1b 2a
1c 2a
1d 2a
[Ph3(2-C4H3O)Bi+][BF4-] (3l)
[(4-MeC6H4)3PhBi+][BF4-] (3m )
[(4-MeOC6H4)3PhBi+][BF4-] (3n )
[(4-ClC6H4)3PhBi+][BF4-] (3o)
a
All reagents were used in an equimolar ratio and the reaction
was carried out at room temperature for 2 h unless otherwise
noted. The yield refers to the isolated yield. Reaction was carried
and 2a in the presence of BF3‚OEt2 even after 24 h at
room temperature. This suggests that the high affinity
between the boron and fluorine atoms is an important
factor in promoting the Bi-Caryl coupling.
b
out for 40 h using 4 equiv of BF3‚OEt2 and 2h .
Sch em e 2
The present method is highly efficient as compared
to the previously reported ones for the synthesis of
unsymmetrical tetraarylbismuthonium salts3,9 in that
(1) a variety of arylboronic acids are readily available,
(2) Bi-C bond formation occurs under mild conditions,
and (3) the inorganic products are not toxic. For
instance, in our previous method based on arylstan-
nanes, less mild conditions (reflux in CH2Cl2, 17-42 h)
were needed for the Bi-Caryl coupling and the transfer-
able ligands were limited to tolyl, anisyl, and thioanisyl
groups (vide supra).3
The reaction also was found to proceed satisfactorily
with alkenylboronic acids to give alkenylbismuthonium
salts.2e Treatment of 1a with alkenylboronic acids 4 in
the presence of BF3‚OEt2 afforded the corresponding
alkenyltriphenylbismuthonium tetrafluoroborates 5 in
good yields (Scheme 3). The stereochemistry of the
alkenyl moiety was retained throughout the reaction.
Aryl and alkenylboronic acids could also be employed
successfully for the preparation of unsymmetrical
telluronium salts. As shown in Scheme 4, (4-methoxy-
phenyl)- and (1-hexenyl)diphenyltelluronium tetrafluo-
roborates 7 and 8 were synthesized in excellent yields
by the BF3‚OEt2-promoted reaction of diphenyltellurinyl
difluoride (6) with 2d and 4a , respectively. Although
such telluronium salts have been prepared previously
by other methods,10 the present method affords a simple
and reliable route.
in moderate yield (entry 8). Sterically hindered aryl
groups such as mesityl and 1-naphthyl as well as
heteroaryl groups such as 2-thienyl and 2-furyl were all
smoothly incorporated into the bismuthonium function
(entries 9-12). para-Substituted derivatives 1b-d
were converted to the corresponding bismuthonium
salts 3 with similar efficiency (entries 13-15), while
tris(2-methylphenyl)bismuth difluoride (1e) failed to
give the expected bismuthonium salt.
The Bi-Caryl coupling did not take place in the
absence of BF3‚OEt2, which illustrates the important
role of the Lewis acid in this transformation. A plau-
sible reaction pathway is depicted in Scheme 2. A BF3
molecule coordinates to one of the fluorine atoms in 1
to activate the bismuth center, onto which the aryl
group is transferred from 2 via simultaneous ligand
exchange in the manner illustrated. No reaction took
place between tris(4-methylphenyl)bismuth dichloride
The advantage of the boron-based method over the
tin-based route3 is manifested in the synthesis of an
asymmetrical bismuthonium salt bearing an oxazoline
group ortho to the bismuth atom. Thus, the asymmetri-
cally tetraarylated bismuthonium salt 10 was pre-
(7) A representative procedure is as follows: to a CH2Cl2 solution
(5 mL) containing triphenylbismuth difluoride (1a ; 239 mg, 0.50 mmol)
and (4-methylphenyl)boronic acid (2b; 68 mg, 0.50 mmol) was added
BF3‚OEt2 (65 µL, 0.50 mmol) at 0 °C, and the mixture was stirred at
room temperature for 2 h. An aqueous solution (20 mL) of NaBF4 (500
mg, 4.55 mmol) then was added, and the resulting two-phase mixture
was vigorously stirred for 30 min. The water phase was extracted with
CH2Cl2 (5 mL × 2), and the combined extracts were dried over MgSO4
and passed through a short silica gel column. Evaporation of the
solvent under reduced pressure left an oily residue, which was
crystallized from Et2O-CH2Cl2 (10:1) to yield (4-methylphenyl)-
triphenylbismuthonium tetrafluoroborate (3b; 300 mg, 97%) as a
colorless solid. The NMR monitoring of this reaction using a 0.050
mmol scale of the reagents and 0.5 mL of CD2Cl2 revealed that the
Bi-C coupling was complete within a few minutes at room tempera-
ture.
(9) Hellwinkel and Bach prepared unsymmetrical tetraarylbismu-
thonium salts by the Bi-C bond cleavage of pentaarylbismuth of the
type Ph3BiAr2 with a protonic or a Lewis acid. Hellwinkel, D.; Bach,
M. J ustus Liebigs Ann. Chem. 1968, 720, 198.
(10) For recent syntheses, see: (a) Zhou, Z.-L.; Huang, Y.-Z.; Shi,
L.-L.; Hu, J . J . Org. Chem. 1992, 57, 6598. (b) Xu, C.; Lu, S.; Huang,
X. Synth. Commun. 1993, 23, 2527. (c) Matano, Y.; Suzuki, H.; Azuma,
N. Organometallics 1996, 15, 3760. (d) Shimizu, T.; Urakubo, T.;
Kamigata, N. J . Org. Chem. 1996, 61, 8032.
(11) Compound 9 was prepared from the corresponding triarylbis-
muthane12 and XeF2. See the Supporting Information.
(12) Matano, Y.; Begum, S. A.; Miyamatsu, T.; Suzuki, H. Unpub-
lished results.
(8) Inorganic boron compounds were easily removed by washing with
water.

4334 Organometallics, Vol. 17, No. 20, 1998
Communications
process at the chiral bismuth center.15 VT-NMR moni-
toring of two oxazoline methyl peaks revealed that they
were discrete up to 110 °C in pyridine-d5 and up to 150
°C in 1,2-dichlorobenzene-d4, suggesting that the chiral-
ity of 10 is stable in these temperature ranges. On the
basis of these observations, we may conclude that the
activation energy (∆Gq) of the isomerization at the
bismuth atom in 10 should be above 23 kcal mol-1 in
1,2-dichlorobenzene-d4 and 21 kcal mol-1 in pyridine-
d5, respectively.16
Sch em e 5
The present work provides a new and efficient method
for the synthesis of group 15 and 16 heavy onium salts
based on the combined use of the Lewis acid and boronic
acids. Further investigation on the stereochemical
behavior of various bismuthonium compounds is now
in progress.
pared in 97% yield from BF3‚OEt2, triarylbismuth
difluoride 9,11 and boronic acid 2b as depicted in Scheme
5.13 In contrast, all attempts to obtain the same
compound by the BF3-promoted reaction with tributyl-
(4-methylphenyl)stannane resulted in the formation of
a complex mixture. As expected, the geminal methyl
groups in the oxazoline ring were observed as a pair of
diastereotopic singlet peaks at δ 0.74 and 0.76 in the
1H NMR spectrum (in CDCl3) of 10 at room tempera-
ture, indicating that it has a stable chirality at bismuth
on the NMR time scale.14
Ack n ow led gm en t. This work was supported by
Grants-in-Aid for Scientific Research (No. 09239225 and
09740469) from the Ministry of Education, Science,
Sports, and Culture of J apan.
With bismuthonium salt 10 bearing four different aryl
ligands in hand, we could investigate the isomerization
Su p p or tin g In for m a tion Ava ila ble: Text giving syn-
thetic, spectroscopic, and analytical data for new compounds
(8 pages). Ordering information is given on any current
masthead page.
(13) 1H NMR of 10 (CDCl3): δ 0.74 (s, 3H, oxazoline Me), 0.76 (s,
3H, oxazoline Me), 2.44 (s, 3H), 3.87 (s, 3H), 4.22 (s, 2H), 7.19 (d, 2H,
J ) 8.8 Hz), 7.48 (d, 2H, J ) 8.0 Hz), 7.60 (d, 2H, J ) 8.0 Hz), 7.62-
7.67 (m, 3H), 7.78-7.84 (m, 2H), 7.86 (s, 4H), 8.29 (dd, 1H, J ) 7.0,
1.5 Hz). Other spectral as well as analytical data are reported in the
Supporting Information.
OM9804531
(14) We have previously prepared a bismuthonium salt bearing four
different aryl groups as a d-camphorsulfonate.3 However, we could not
obtain any positive evidence for the diastereomers; no diastereotopic
signals were observed in the 1H NMR spectra, probably due to a weak
interaction between the bismuthonium moiety and the counteranion.
Therefore, compound 10 is the first example whose chirality is clearly
confirmed by a spectroscopic method.
(15) Akiba and co-workers reported the synthesis and VT-NMR
study of an asymmetrical hypervalent organobismuth compound (10-
Bi-5) bearing a Martin ligand: Chen, X.; Ohdoi, K.; Yamamoto, Y.;
Akiba, K. Organometallics 1993, 12, 1857.
(16) These values were calculated by assuming that the isomeriza-
tion occurs at 110 °C in pyridine-d5 and 150 °C in 1,2-dichlorobenzene-
d4.