A new methodology for synthesis of aryl bismuth compounds: Arylation of bismuth(III) carboxylates by sodium tetraarylborate salts

Article abstract of DOI:10.1021/om7009667

Sodium tetraarylborate salts Na[BAr₄] (Ar = C₆H ₃ (Ph), C₆H₄-MeA (tolyl), C₆H ₄-F-4) are found to be efficient arylating species for a range of bismuth(III) aromatic and aliphatic carboxylates including Bi(Hsal*) ₃ (Hsal* = 2-HO-C₆H₄CO₂ ^- (Hsal); 4-Me-2-HO-C₆H₃CO₂ ^- (Hsal^4Me); or 3-MeO-2-HO-C₆H ₃CO₂^- (Hsal^3OMe)) and Bi(O ₂CR)₃ (R = Me, CMe₃, and CF₃) to produce triaryl bismuth compounds. The reactions may be carried out in ethanol, tetrahydrofuran, or acetone. The arylbismuth bis(salicylates) BiPh(Hsal) ₂ and Bi(tolyl)(Hsal)₂ exhibit similar reactivity in refluxing THF and may be used to produce mixed arylbismuthines BiPh _x(tolyl)_3-x. Formation of the known arylbismuth compounds was confirmed by IR spectroscopy, X-ray crystallography, NMR spectroscopy ( ¹H, ¹¹B, ¹³C, and ¹⁹F), and mass spectrometry. This is a facile synthesis of both symmetrical and unsymmetrical triarylbismuthines involving the aryl group transfer from the tetraarylborate ions to bismuth(III) under mild conditions.

Full text of DOI:10.1021/om7009667

6864
Organometallics 2007, 26, 6864–6866
Notes
A New Methodology for Synthesis of Aryl Bismuth Compounds:
Arylation of Bismuth(III) Carboxylates by Sodium
Tetraarylborate Salts
Vitalie Stavila, John H. Thurston, Darío Prieto-Centurión, and Kenton H. Whitmire*
Department of Chemistry, MS 60, Rice UniVersity, 6100 Main Street, Houston, Texas 77005
ReceiVed September 28, 2007
Scheme 1. Synthetic Procedures to Triarylbismuth Com-
pounds by Arylation with Sodium Tetraarylborates
Summary: Sodium tetraarylborate salts Na[BAr4] (Ar ) C6H5
(Ph), C6H4-Me-4 (tolyl), C6H4-F-4) are found to be efficient
arylating species for a range of bismuth(III) aromatic and
aliphatic carboxylates including Bi(Hsal*)3 (Hsal* ) 2-HO-
C6H4CO2- (Hsal); 4-Me-2-HO-C6H3CO2- (Hsal4Me); or 3-MeO-
2-HO-C6H3CO2- (Hsal3OMe)) and Bi(O2CR)3 (R ) Me, CMe3,
and CF3) to produce triaryl bismuth compounds. The reactions
may be carried out in ethanol, tetrahydrofuran, or acetone. The
arylbismuth bis(salicylates) BiPh(Hsal)2 and Bi(tolyl)(Hsal)2
exhibit similar reactiVity in refluxing THF and may be used to
produce mixed arylbismuthines BiPhx(tolyl)3-x. Formation of
the known arylbismuth compounds was confirmed by IR
spectroscopy, X-ray crystallography, NMR spectroscopy (1H,
11B, 13C, and 19F), and mass spectrometry. This is a facile
synthesis of both symmetrical and unsymmetrical triarylbis-
muthines inVolVing the aryl group transfer from the tetraarylbo-
rate ions to bismuth(III) under mild conditions.
with BiAr3 to give mixtures of BiAr3-xClx (x ) 0–3), so the
stoichiometry must be precisely controlled in order to achieve
good yields of pure materials.
The use of tetraarylborate salts as nucleophilic arylating
agents for metal ions has been reported.4 A number of main
group and transition metals undergo arylation upon treatment
with tetraarylborate salts. During our investigations of hetero-
metallic complexes as precursors for mixed-metal oxide materi-
als, we found that salicylate-alkoxide complexes can be
produced from the reaction of bismuth(III) salicylate with early
transition metal alkoxides. In an attempt to introduce alkali metal
cations in the system, some heterometallic Bi-Nb and Bi-Ta
complexes were treated with sodium tetraphenylborate. The
products contained no sodium; however, one or more salicylate
ions on bismuth were replaced by phenyl groups. These results,
which will be detailed elsewhere, prompted us to explore the
general reactivity of tetraarylborate salts toward bismuth(III)
carboxylates.
Introduction
Aryl bismuth compounds have been known since the 1880s,
when Michaelis reported the synthesis of triphenyl bismuth from
Bi-Na alloys and bromobenzene in ethylacetate.1,2 The chem-
istry and uses of arylbismuth compounds have been recently
reviewed.3 They are employed as co-catalysts for various
polymerization processes, as additives in dental and medical
devices as X-ray opaque substances, and as arylating agents
for a range of organic substrates. They serve as starting
compounds to synthesize various classes of bismuth(III) and
bismuth(V) compounds, and even though the coordinating ability
of bismuth(III) is weak, some examples of their use as ligands
for transition metals have been reported. Triarylbismuth(III)
derivatives are usually prepared from BiCl3 using organomag-
nesium or organolithium reagents in donor solvents such as THF
or diethyl ether. This methodology is well-developed, but the
reactions must be run under a rigorously dry atmosphere and
one must carefully control the rate of addition of the reagents
and the temperature. BiCl3, which is hygroscopic and must be
carefully purified prior to use, undergoes redistribution reactions
Results and Discussion
Symmetrical tris(aryl)bismuth compounds are prepared by the
reaction of bismuth(III) salicylates with sodium tetraaryl borates
(Scheme 1). The reactions proceed smoothly in good to excellent
yields in THF, alcohols, or acetone. In a representative
procedure, freshly prepared Bi(Hsal)3 reacts with 3 equiv of
sodium tetraphenylborate in ethanol at room temperature over
a period of 16 h, during which the initial pale orange color of
the reaction mixture gradually changes to pale yellow. Upon
* To whom correspondence should be addressed. E-mail: whitmir@
rice.edu. Phone: 713-348-5650. Fax: 713-348-5155.
(1) Michaelis, A.; Polis, A. Ber. Dtsch. Chem. Ges. 1887, 20, 55–56.
(2) Michaelis, A.; Marquardt, A. Liebigs Ann. Chem. 1889, 251, 323–
335.
(4) Strauss, S. H. Chem. ReV. 1993, 93, 927–942.
(5) (a) Coombs, D. L.; Aldridge, S.; Rossin, A.; Jones, C.; Willock,
D. J. Organometallics 2004, 23, 2911–2926. (b) Sacconi, L.; Dapporto, P.;
Stoppioni, P. Inorg. Chem. 1976, 15, 325–329. (c) Haines, R. J.; Du Preez,
A. L. J. Am. Chem. Soc. 1971, 93, 2820–2821.
(3) (a) Suzuki, H., Matano, Y., Eds. Organobismuth Chemistry; Elsevier:
New York, 2001; 619 pp. (b) Freedman, L. D.; Doak, G. O. Chem. ReV.
1982, 82, 15–57.
10.1021/om7009667 CCC: $37.00
2007 American Chemical Society
Publication on Web 11/29/2007

Notes
Organometallics, Vol. 26, No. 27, 2007 6865
Table 1. Arylation of Bismuth(III) Carboxylates by Na[BAr4] to
the removal of solvent, the product was extracted into hexanes
and subjected to column filtration to produce BiPh3 in 72% yield.
Reaction of Na[B(tolyl)4] and Bi(Hsal)3 proceeded similarly.
The introduction of a methyl or methoxy substituent on the
salicylate moiety did not have a significant effect on the reaction.
Since the method of preparation of the bismuth salicylates may
affect their solubilities (those prepared in refluxing toluene often
exhibit a lower solubility than those prepared from a solventless
reaction),6 the method of preparation of the bismuth salicylate
was also found to have very little effect on the yield of the aryl
bismuth products.
a
Give BiAr3
time yield
entry Bi(III) carboxylate
Ar
solvent temp
(h)
(%)
1
2
3
4
5
6
7
8
Bi(Hsal)3 sol.
Bi(Hsal)3 sol.
Bi(Hsal)3 sol.
Bi(Hsal4Me)3 sol.
Ph
tolyl
Ph
EtOH
EtOH
THF
THF
THF
THF
THF
THF
THF
THF
rt
rt
rt
rt
rt
rt
reflux
reflux
rt
reflux
reflux
16
16
16
16
16
16
16
4
16
16
16
4
16
16
16
16
16
16
4
72
70
71
65
62
75
83
80
73
82
56
58
64
74
69
72
69
81
77
25
54
58
70
84
60
Ph
Bi(Hsal3OMe)3 sol. Ph
Bi(Hsal)3 s/s
Bi(Hsal)3 s/s
Bi(Hsal)3 s/s
Bi(Hsal)3 s/s
Bi(Hsal)3 s/s
Bi(Hsal)3 s/s
Bi(Hsal)3 s/s
Bi(Hsal)3 s/s
Bi(Hsal4Me)3 s/s
Bi(Hsal3OMe)3 s/s
Bi(Hsal4Me)3 s/s
Bi(Hsal3OMe)3 s/s
Bi(O2CCF3)3
Bi(O2CCF3)3
Bi(O2CMe)3
Bi(O2CMe)3
Bi(O2CMe)3
Bi(O2CCMe3)3
Bi(O2CCF3)3
Bi(O2CCF3)3
Ph
Ph
Ph
tolyl
tolyl
C6H4-F-4 THF
Ph
Ph
Ph
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
A drawback to the procedure described above is that BiPh3
was the reagent used to prepare the bismuth carboxylates. To
develop a useful synthetic methodology, we explored using
bismuth(III) carboxylates prepared from inexpensive, com-
mercially available inorganic reagents such as Bi2O3 or
(BiO)2CO3 as alternative starting materials. For this study,
bismuth(III) acetate, pivalate, and trifluoroacetate were prepared
from the reaction of Bi2O3 with the appropriate carboxylic acids
in the presence of their anhydrides, the latter being added to
scavenge the water produced as a byproduct of the reaction.
After the removal of all volatiles, the carboxylates were
suspended in THF without further purification and treated with
the appropriate tetraarylborate salt. The reactions proceeded in
high yield within a short time with Bi(O2CCMe3)3 or
Bi(O2CCF3)3. In the case of Bi(OAc)3 (OAc ) acetate) lower
yields were obtained even at prolonged reaction times, which
we attribute to the lower solubility of this compound. When
employing a 1:1 mixture of Na[BPh4] and Na[B(tolyl)4] with
either Bi(Hsal)3 or Bi(O2CCF3)3, an approximately statistical
mixture of BiPh3-x(tolyl)x (x ) 0–3) resulted. This mixture is
difficult to separate, but a rational approach to asymmetrically
substituted compounds is available starting with ArBi(OC2R)2.
Such unsymmetrical organobismuth compounds were obtained
by treating BiAr(Hsal*)27 with 2 equiv of Na[BAr*4] (Scheme
1) in yields of about 70%.
Me2CO rt
Me2CO rt
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
rt
rt
Ph
tolyl
tolyl
Ph
Ph
Ph
Ph
Ph
Ph
tolyl
reflux
reflux
reflux
reflux
rt
reflux
reflux
reflux
reflux
reflux
4
16
48
16
16
16
C6H4-F-4 THF
a The products were identified by their IR, 1H and 13C NMR, and
mass spectra and, in the case of Bi(tolyl)3, by X-ray crystallography (see
Supporting Information). The MALDI mass spectra of the products of the
reactions in positive mode resulted in a number of ion fragments
including those attributed to the oxo-species [Bi2O(Ar)5]+ (m/z 819.14,
calc for Ar ) Ph 819.15, and m/z 889.23, calc for Ar ) tolyl 889.23;
see Supporting Information). sol. ) prepared in refluxing toluene; s/s )
prepared by a solid-state reaction at 130 °C; rt ) room temperature.
undergo aryl transfer reactions with aryl boronic acids; however
only traces of BiAr3 were detected in our case.
The use of fluorinated sodium tetraarylborates was also
examined, since these reagents are expected to be less nucleo-
philic than the phenyl or tolyl salts. Use of sodium tetrakis(4-
fluorophenyl)borate produced Bi(C6H4-4-F)3, but the product
was slightly less pure than the phenyl and tolyl derivatives,
apparently contaminated with traces of B(C6H4-4-F)3, as evi-
denced by the 1H NMR spectrum. This product, however, still
gave a sharp melting point close to the literature value.
Conclusions
A new arylation reaction of bismuth(III) carboxylates by using
tetraarylborate salts has been developed. Both Na[BPh4] and
Na[B(tolyl)4] are suitable reagents, producing BiPh3 and Bi-
(tolyl)3 from a range of bismuth(III) carboxylates. Particularly
good results were obtained in THF at room temperature or at
reflux. The reaction works best when using soluble bismuth(III)
carboxylates, such as Bi(O2CCF3)3. Under these conditions, the
reactions go to completion in approximately 16 h with yields
on the order of 70–80%. A potentially useful feature of this
methodology is the production of unsymmetrical triarylbismuth-
ines obtained by reacting ArBi(O2CR)2 with sodium tetrarylbo-
rates. These mild reactions are suitable for the preparation of
various arylbismuth compounds and avoid the use of bis-
muth(III) chloride, a hygroscopic compound that undergoes
facile redistribution reactions with triaryl bismuth compounds.
Advantages of this synthetic procedure include (i) bismuth(III)
carboxylates may serve as a source for Bi(III) and are easily
prepared from inexpensive, common reagents such as bis-
muth(III) oxide or hydroxide; (ii) the reaction occurs under mild
conditions in a range of organic solvents, both at room
temperature and at reflux; (iii) the reaction is far less sensitive
to oxygen and moisture than methods employing Grignard or
organolithium reagents, and (iv) the reaction offers a convenient
method of preparing unsymmetrically substituted triaryl bismuth
complexes.
In some of the reported aryl transfer reactions from tet-
raarylborate salts to metal centers,5 BPh3 was detected as a
byproduct. In our case, however, BPh3 was not detected. It is
known that BPh3 can react even with low levels of oxygen and
water to produce a wide range of decomposition products,
including tetraphenyldiboroxane and phenylboronic acids. In the
reaction with Ar ) C6H4-F-4, NMR data indicated the presence
of B(C6H4-F-4)3, so we assume that BAr3 is formed in each
reaction, and this hypothesis is consistent with the observed 3:1
stoichiometry. The use of only one aryl group on the borate
salt is a limitation of the reaction, so we explored the
possibility of using arylboronic acids, ArB(OH)2, in place
of Na[BAr4]. It is known that lead(IV) carboxylates may
(6) (a) Andrews, P. C.; Deacon, G. B.; Jackson, W. R.; Maguire, M.;
Scott, N. M.; Skelton, B. W.; White, A. H. J. Chem. Soc., Dalton Trans.
2002, 4634–4638. (b) Urano, M.; Wada, S.; Suzuki, H. Chem. Commun.
2003, 1202–1203.
(7) Stavila, V.; Fettinger, J. C.; Whitmire, K. H. Organometallics 2007,
26, 3321–3328.

6866 Organometallics, Vol. 26, No. 27, 2007
Notes
1) was added dropwise at room temperature to a stirred solution or
suspension of the bismuth(III) carboxylate (0.25 mmol) in 20 mL
of the same solvent. The resulting mixture was refluxed and stirred
for 16 h to complete the reaction. After the removal of the solvent
under reduced pressure, the crude product was extracted into
hexanes. The solution was filtered and subjected to column
chromatography on silica gel (eluent: pentane/CH2Cl2, 90:10) to
produce the corresponding triarylbismuthine.
Experimental Section
General Information. All of the manipulations were carried out
under a dry dinitrogen or argon atmosphere using standard Schlenk
and glovebox techniques. Acetone was dried over Drierite and
distilled over freshly activated molecular sieves. Ethanol, toluene,
and tetrahydrofuran were distilled under dinitrogen from magnesium
ethoxide, sodium, and sodium benzophenone ketyl, respectively.
All reagents and chemicals, unless otherwise stated, were purchased
from commercial sources. Commercial BiPh3, H2sal, H2sal4Me, and
H2Sal3OMe were dried for 4 h in Vacuo then transferred to a drybox.
General Procedure for Synthesis of Unsymmetrically Sub-
stituted Triaryl-Bismuth Compounds from Arylbismuth Dicar-
boxylates. The sodium tetraarylborate (0.4 mmol) in 10 mL of THF
was added to a stirred solution of ArBi(Hsal)2 (Ar ) Ph, tolyl)
(0.2 mmol) in THF (10 mL) at room temperature. The mixture was
heated gradually and maintained at reflux overnight. After the THF
was removed in Vacuo, hexanes (20 mL) were added to the reaction
mixture, which was then stirred for 30 min. After filtering, the
compound was purified by column filtration on silica gel (eluent:
pentane/CH2Cl2, 90:10) to produce the corresponding unsymmetri-
cally substituted triarylbismuthine. The yields of BiPh(tolyl)2 and
BiPh2(tolyl) were 71% and 68%, respectively.
Bi(Hsal)3, Bi(Hsal4Me)3, and Bi(Hsal3OMe
) were prepared in
3
refluxing toluene8 or using the solid-state reaction of BiPh3 with
the corresponding acids.6a BiPh(Hsal)2 and Bi(tolyl)(Hsal)2 were
prepared as described in the literature.7 Sodium tetra(p-tolyl)borate
was prepared by a slightly modified procedure reported by Wittig.9
Instrumentation. NMR spectra were recorded at room temper-
ature in CDCl3, CD2Cl2, C6D6, and d6-acetone (containing 0.5%
1
TMS) on Bruker Avance 400 and 500 spectrometers, and the H
and 13C chemical shifts are reported relative to the shift of
tetramethylsilane (TMS). 11B and 19F NMR spectra were referenced
to external BF3 · Et2O and CFCl3, respectively. Mass spectra were
acquired using a Reflex IV (BrukerDaltonics Inc., Billerica, MA)
matrix-assisted laser desorption ionization (MALDI) time-of-flight
instrument equipped with pulsed ion extraction and a pulsed
nitrogen laser (337 nm). IR spectra were recorded on a Nicolet
670 FT-IR spectrometer using attenuated total reflectance. Melting
points were obtained in sealed capillaries on an Electrothermal
melting point instrument and are uncorrected. Characterization data
for all products are provided in the Supporting Information.
General Procedure for Synthesis of Triarylbismuthines by
Tetraarylborate Salts. A solution of the appropriate sodium
tetraarylborate (0.75 mmol) in 10 mL of indicated solvent (Table
Acknowledgment. The Robert A. Welch Foundation is
acknowledged for financial support. V.S. is grateful to NSF
and NATO (DGE-0411679) for a postdoctoral fellowship.
Dr. Larry Alemany and Dr. Sandy Yates are gratefully
acknowledged for help with the NMR and mass spectro-
metric investigations, respectively.
Supporting Information Available: Analytical data for all
products and CIF file giving crystallographic data for Bi(tolyl)3.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(8) Thurston, J. H.; Whitmire, K. H. Inorg. Chem. 2002, 41, 4194.
(9) Wittig, G.; Raff, P. Liebigs Ann. Chem. 1951, 573, 195.
OM7009667