Syntheses of lipophilic tetraarylborate ions substituted with many perfluoroalkyl groups and their stability under acid conditions

Article abstract of DOI:10.1016/S0022-1139(99)00291-2

Syntheses are investigated on several new kinds of perfluoroalkyl-substituted tetraarylborate ions such as tetrakis(3,5-bis(nonafluorobutyl)phenyl)borate, tetrakis(3,5-bis(heptafluoro-2-propyl)phenyl)borate (PFPB), tetrakis(3-(heptafluoro-2-propyl)-1-(tri

Full text of DOI:10.1016/S0022-1139(99)00291-2

Journal of Fluorine Chemistry 102 (2000) 293±300
Syntheses of lipophilic tetraarylborate ions substituted with many
per¯uoroalkyl groups and their stability under acid conditions
Kanji Fujikia, Junji Ichikawab,1, Hiroshi Kobayashib,2, Akinari Sonodaa,3,
Takaaki Sonodab,*
aGraduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816, Japan
bInstitute of Advanced Material Study, Kyushu University Kasuga, Fukuoka 816, Japan
Received 19 July 1999; received in revised form 10 September 1999; accepted 2 October 1999
This paper is dedicated to Professor Paul Tarrant on the occasion of his 85th birthday
Abstract
Syntheses are investigated on several new kinds of per¯uoroalkyl-substituted tetraarylborate ions such as tetrakis(3,5-bis(nona¯uoro-
butyl)phenyl)borate, tetrakis(3,5-bis(hepta¯uoro-2-propyl)phenyl)borate (PFPB), tetrakis(3-(hepta¯uoro-2-propyl)-1-(tri¯uoromethyl)phe-
nyl)borate, and tetrakis(3-(hepta¯uoro-2-propyl)phenyl)borate. Solubilities of tetramethylammonium tetraarylborates in some hydrophobic
halocarbon solvents and rate constants of acid-catalyzed decomposition of the tetraarylborate ions in methanolic sulfuric acid solutions and
in dichloromethane/aqueous sulfuric acid two-phase system are determined. Tri¯uoromethyl- and per¯uoroalkyl-substituent effects on
the lipophilicity and chemical stability of the tetraarylborate ions are discussed in comparisons with a range of those described previously.
# 2000 Elsevier Science S.A. All rights reserved.
Keywords: Weakly coordinating anions; Per¯uoroalkyl-substituted tetraarylborate ions; Syntheses; Lipophilicity; Stability
1. Introduction
borate anions, the primarily extracted cationic species can be
converted to various higher-order electrophilic reagents,
with which novel reaction processes have been developed
[4,5]. TFPB is now widely recognized as an excellent
example of a weakly coordinating anion [6,7] or superweak
anions [8] especially as a useful counter anion of electro-
philic cationic transition metal complexes.
In continuation of our previous work [9], this paper deals
with the syntheses and chemical properties of tetraphenyl-
borates substituted with one or two per¯uoroalkyl groups
on each phenyl group: Tetrakis(3,5-bis(nona¯uorobutyl)-
phenyl)borate (2), tetrakis(3,5-bis(hepta¯uoro-2-propyl)-
phenyl)borate (PFPB) (3), tetrakis(3-(hepta¯uoro-2-
propyl)-1-(tri¯uoromethyl)phenyl)borate (4), and tetrakis-
(3-(hepta¯uoro-2-propyl)phenyl)borate (5) (Fig. 1).
With the purpose of obtaining lipophilic and bulky but
still stable anions, we have ®rst synthesized tetrakis(3,5-
bis(tri¯uoromethyl)phenyl)borate (TFPB) (1) [1] and sev-
eral tetraphenylborate derivatives substituted with many
tri¯uoromethyl groups, which ef®ciently incorporate var-
ious cations into hydrophobic solution phases as ion pairs
and are successfully applied as ion-pair extracting agents
[2,3]. TFPB is a characteristic stable anion, whose anionic
center is tetrahedrally covered by four bulky aryl groups
with many tri¯uoromethyl groups and able to enforce
hydrophilic cations to be incorporated into a less polar
organic solution phase in the form of stable ion pairs. By
taking advantage of such merits of the lipophilic and stable
* Corresponding author. Tel.: ‡81-92-583-7820; fax: ‡81-92-583-7820.
E-mail addresses: fwjf7374@mb.infoweb.ne.jp (H. Kobayashi), sono-
da@cm.kyushu-u.ac.jp (T. Sonoda).
2. Results and discussion
1 Present address. Department of Chemistry, Faculty of Science,
University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan.
2 Co-corresponding author. Tel.: ‡88-92-924-1023; fax: ‡88-92-924-
1983.
3 Present address. Shikoku National Industrial Research Institute,
Hayashi, Takamatsu 761, Japan.
2.1. Preparation of intermediates for the borate syntheses
Per¯uoroalkyl groups such as hepta¯uoro-2-propyl
and nona¯uorobutyl substituents could be introduced to
a benzene ring by coupling reactions of the corresponding
0022-1139/00/$ ± see front matter # 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 9 9 ) 0 0 2 9 1 - 2

294
K. Fujiki et al. / Journal of Fluorine Chemistry 102 (2000) 293±300
(10), 3-(hepta¯uoro-2-propyl)-5-(tri¯uoromethyl)iodoben-
zene (11), 3,5-bis(hepta¯uoro-2-propyl)iodobenzene (12),
and 3,5-bis(nona¯uorobutyl)iodobenzene (13), respectively,
in fair yields.
2.2. Syntheses of perfluoroalkyl-substituted
tetraarylborates
Fig. 1. Perfluoroalkyl-substituted tetraarylborates.
The method and reaction conditions for the syntheses of
per¯uoroalkyl-substituted tetraarylborates (Scheme 2) are
basically the same as previously described [9]. Grignard
reagents were prepared in ether from the per¯uoroalkyl-
substituted iodo- or bromo-benzenes in the presence of 10%
molar amount of butylmagnesium bromide as initiating
catalyst, which was necessary for the preparation of the
per¯uoroalkyl-substituted phenyl Grignard reagents. A 25%
excess amount of the Grignard reagent was added into ether
solution of boron tri¯uoride etherate and the mixture was
re¯uxed for suf®cient time to complete the reaction. The
resulting tetraarylborate derivatives, 2±5, were easily iso-
lated as corresponding tetramethylammonium salts. Tetra-
kis(3-(tri¯uoromethyl)phenyl)borate salt (14) was also
prepared as one of the reference compounds according to
the literature [13] (Table 1).
aryl iodides or bromides with the desired per¯uoroalkyl
iodides in the presence of an excess amount of activated
copper [10,11] to afford per¯uoroalkyl-substituted benzene
derivatives such as (hepta¯uoro-2-propyl)benzene (6),
3-(hepta¯uoro-2-propyl)-1-(tri¯uoromethyl)benzene (7),
1,3-bis(hepta¯uoro-2-propyl)benzene (8), and 1,3-bis(no-
na¯uorobutyl)benzene (9) in satisfactory yields. Dimethyl-
formamide (DMF) was most favorable as solvent for
higher yields of products compared to dimethylsulfoxide
(DMSO).
Per¯uoroalkyl-substituted
iodobenzene
derivatives
(Scheme 1) were synthesized as precursors for Grignard
reagents by direct iodination of the per¯uoroalkyl-substi-
tuted benzene derivatives with iodine in 20% fuming sul-
furic acid [12] to give 3-(hepta¯uoro-2-propyl)iodobenzene
Scheme 1. Syntheses of perfluoroalkyl-substituted iodobenzenes.

K. Fujiki et al. / Journal of Fluorine Chemistry 102 (2000) 293±300
295
groups and at the same time with the bulkiness of the
substitutent as a whole.
An interesting feature is that in a poly¯uorinated solvent,
(CBrF2)2, PFPB (3) is approximately 100-times more solu-
ble than TFPB (1). An increasing number of tri¯uoromethyl
substituents enhances solubility in the poly¯uorinated sol-
vent, but not always so in chloromethane solvents.
A similar correlation can be observed when the solubility
of TFPB (1) is compared with those of the reference
borates, 4, 14, 17, and 18, of which each phenyl group is
unsymmetrically substituted with the combination of tri-
¯uoromethyl and various tri¯uoromethylated groups.
Increase in the solubility of borate 5 containing a per¯uoro-
isopropyl group in the poly¯uorinated solvent is also
remarkable when compared with that of borate 14 contain-
ing a tri¯uoromethyl group.
Scheme 2. Syntheses of tetraarylborates.
Table 1
Preparation of tetramethylammonium perfluoroalkyl-substituted tetra-
arylborates
Borate
Substituenta
R1
Yield (%) m.p. (8C)
R2
2
PFPB (3) CF(CF3)2
(CF2)3CF3 (CF2)3CF3 62
151±152 (decomp.)
260±263 (decomp.)
146±147
CF(CF3)2
CF(CF3)2
CF(CF3)2
CF3
50
64
62
24
The observed correlation seems of interest in connection
with the interaction among the ¯uorine substituents on the
solute and solvent molecules, which might be useful for
designing molecules soluble in less polar poly¯uorinated
solvents.
4
CF3
H
5
14
158±160
H
167±168 [13]
a For R1 and R2, see Fig. 1.
2.3. Properties of tetraarylborate derivatives
2.3.2. Chemical stability against acid
Another effect of tri¯uoromethyl substituent was shown
in the increased chemical stability of TFPB (1), especially
against acid. TPB (15) is known to decompose easily under
acid conditions by rate-determining electrophilic attack of
proton to the phenyl ring at the ipso carbon to give benzene
via a Wheland-type intermediate [14,15]. Beside the poor
lipophilicity of TPB (15), this is another defect with respect
to less versatile applications such as to an ion-pair extractant
under acid conditions and an electrophilic metal ion cata-
lyst. Especially, the lability under acid conditions is a fatal
one as an anionic PTC catalyst; i.e., in the anionic PTC
process to promote the electrophilic reactions of cationic
reagents in an organic phase, oxonium ion or protonated
species is a primary by-product which ion-pairs with the
anionic catalyst in the same phase. TPB (15) ion, when used
as the catalyst, is decomposed autocatalytically [16,17].
Similarly, TPB is not an effective counter anion for a highly
electrophilic metal ion catalyst which autocatalytically
2.3.1. Solubility
Lipophilicity is one of the most important properties of an
ion-pair extracting agent. As a parameter of this property,
the solubilities of tetraarylborates were measured in a range
of hydrophobic organic solvents.
TFPB (1) salt is much more soluble in organic solvents
than its unsubstituted tetraphenylborate (TPB) (15) counter-
part, which is due to the substitution by lipophilic tri¯uor-
omethyl groups on each phenyl ring. Table 2 shows the
solubilities of some borates including those previously
described [9] in polychloromethane and poly¯uorocarbon
solvents. One can readily notice that a branched side chain
causes increasing solubility, while a straight one depresses
solubility in spite of the increasing number of lipophilic
di¯uoromethylene units, which seems indicative that the
solubility of tetraarylborate in a hydrophobic solvent is
closely correlated with the number of tri¯uoromethyl
Table 2
Solubility of polyfluoroalkyl-substituted tetraarylboratesa
3
Borate
Substituent
R1
Solubility in solvent (mol dm
)
R2
CH2Cl2
CHCl3
(CBrF2)2
2
1
1
4
1
1
2
3
2
4
3
4
5
4
4
3
5
4
5
4
3
5
7
4
4
3
4
TFPB (1)
HFPB (16)
CF3
CF3
2.0 Â 10
2.2 Â 10
1.2 Â 10
6.2 Â 10
1.4 Â 10
1.4 Â 10
7.7 Â 10
4.0 Â 10
4.7 Â 10
1.4 Â 10
3.6 Â 10
5.0 Â 10
1.3 Â 10
7.5 Â 10
6.6 Â 10
3.1 Â 10
1.8 Â 10
7.6 Â 10
<1.4 Â 10
4.5 Â 10
1.8 Â 10
5.8 Â 10
<2.2 Â 10
2.0 Â 10
2.2 Â 10
1.4 Â 10
1.3 Â 10
C(CF3)2OCH3
CF(CF3)2
(CF2)3CF3
H
C(CF3)2OCH3
CF(CF3)2
(CF2)3CF3
CF3
PFPB (3)
2
14
4
CF(CF3)2
C(CF3)2OCH3
C(CF3)2OCH2CF3
H
CF3
CF3
17
18
5
CF3
CF(CF3)2
a Dielectric constant at 258C: CH2Cl2 (8.93), CHCl3 (4.81), (CBrF2)2 (4.81).

296
K. Fujiki et al. / Journal of Fluorine Chemistry 102 (2000) 293±300
Table 3
Stability of polyfluoroalkyl-substituted tetraarylborates under acid two-phase conditions
1
Borate
Substituent
R1
Pseudo first-order rate const. k10 /s  104 at 278C
3
Acid concn./mol dm H2SO4 aq
R2
0.5
3.0
5.1
10.3
TFPB(1)
HFPB(16)
17
CF3
CF3
C(CF3)2OCH3
n.d.a
1.45
n.d.a
n.d.a
n.d.a
5.23
1.18
n.d.a
n.d.a
87.1
2.96
0.32
n.d.a
db
C(CF3)2OCH3
C(CF3)2OCH3
C(CF3)2OCH2CF3
CF3
CF3
db
18
2.08
a Not decomposed.
b Immediately decomposed.
decomposes TPB ion by metal-ion promoted protonation or
oxidation. An ef®cient anionic PTC catalyst, therefore,
requires its higher chemical stability under acid conditions
in addition to its high lipophilicity.
On the other hand, the pseudo-®rst-order rate constants of
the acid-catalyzed decomposition of tetraarylborates were
obtained also in homogeneous aqueous methanolic sulfuric
solution by monitoring the decrease in 19F-NMR signal
intensities of the remained tetraarylborates (Table 4).
Even under more sever acid conditions, TFPB (1) remain
completely intact, while PFPB (3) decomposes slowly
under the same acid conditions; i.e. the stabilizing effect
of tri¯uoromethyl group is much greater than that of per-
¯uoroisopropyl group, when each phenyl group of the
borates is symmetrically disubstituted at 3,5-positions.
In a series of singly substituted derivatives the tri¯uoro-
methyl-substituted borate 14 is only three times more
stable in terms of decompostion-rate constant than the
per¯uoroisopropyl-substituted homologue 5 in parallel to
their sm values: 0.43 and 0.37 for tri¯uoromethyl- and
per¯uoroisopropyl substituents, respectively. Thus, one
would need to presume some additional effects to explain
the extreme stability of TFPB (1), which are still under
investigation.
The pseudo-®rst-order rate constants were obtained in the
decomposition of tetraarylborates under dichloromethane/
aqueous sulfuric acid two-phase conditions by monitoring
the formation of arenes by gas-chromatography (Table 3).
Under these two-phase conditions, when the concentration
of aqueous sulfuric acid is increased, then the activity of
oxonium ion incorporated by the borate ion as an ion pair
into the organic phase is increased due to less hydration of
oxonium ion, to promote the decomposition of the counter
borate ion [4].
The results in Table 3 indicate that the durabilities of the
borates under acid conditions decrease in the order of
TFPBꢀ1† > 18 > 17 > 16;
in accordance with the order of electron-withdrawing ability
of the meta-substituents [18],
Comparison of the rate constants of the decomposition of
PFPB (3) and HFPB (16) indicates that the introduction of a
methoxyl group onto the isopropyl chain in place of a
tertiary ¯uorine atom is not favorable as far as the stability
under acid conditions is concerned, which might be readily
understood in terms of the inductive effects (sI values) of
CF3 > CꢀCF3†2OCH2CF3 > CꢀCF3†2OCH3:
Obviously, the Wheland intermediate formed by rate-
limiting protonation to the borate ion is destabilized by the
electron-withdrawing meta-substituents to suppress the
decomposition.
Table 4
Stability of polyfluoroalkyl-substituted tetraarylborates under acid homogeneous solutions.
1
Borate
Substituent
R1
Pseudo first-order rate const. (k10 /min at 258C)
R2
Acid conditions
[I]a
[II]b
TFPB(1)
PFPB(3)
5
CF3
CF3
n.d.c
n.d.c
5
3
CF(CF3)2
H
CF(CF3)2
CF(CF3)2
CF3
n.d.c
8.2 Â 10
3
3
3.7 Â 10
1.4 Â 10
n.d.c
dd
14
HFPB(16)
H
dd
C(CF3)2OCH3
C(CF3)2OCH3
2.8 Â 10
3
a Acid conditions: [I]; 3.1 mol dm H2SO4 in MeOH ‡ 9% water.
b Acid conditions: [II]; 3.6 mol dm H2SO4 in MeOH.
3
c Not decomposed.
d Immediately decomposed.

K. Fujiki et al. / Journal of Fluorine Chemistry 102 (2000) 293±300
297
¯uorine- and methoxyl substituents, whose sI values are
0.50 and 0.27, respectively.
7.4 ppm (br, arom., 4 H). 19F-NMR: d ˆ 86.22 (d, J ˆ
7.3 Hz, CF(CF3)2, 6F) and 20.58 ppm (sep, J ˆ 7.3 Hz,
‡
CF(CF3)2, 1F). MS: m/z (rel. intensity) ˆ 414(M ), 395,
and 345. Obsd. accurate m/z ˆ 414.0089. Calcd. for
C12H4F14 ˆ 414.0089.
3. Experimental
1H-, 13C-, and 19F-NMR and mass spectra were obtained
on the corresponding spectrometers in similar manners as
described previously [9]. Iodobenzene, 1,3-dibromoben-
zene, 3-(tri¯uoromethyl)bromobenzene, hepta¯uoro-2-
iodopropane, and nona¯uoro-1-iodobutane are commer-
cially available reagents. All the starting compounds were
used after puri®cation by appropriate methods.
3.2.3. 1,3-Bis(nonafluorobutyl)benzene (9)
The reaction of 1,3-dibromobenzene (9.75 g, 39.2 mmol)
with hepta¯uoro-2-iodopropane (40.72 g, 118 mmol) in the
presence of activated copper (17.40 g, 274 mmol) in DMF
(60 ml) under an argon atmosphere at 1008C for 44 h
afforded a colorless oil 9 (14.20 g, 70% yield) boiling at
1
708C/4.5 torr. H-NMR: d ˆ 7.9±7.4 ppm (br, arom., 4H).
19F-NMR: d ˆ 80.81 (br-tr, CF3, 6F), 50.52 (br-tr, CF2-1,
3.1. Preparation of activated copper powder
4F), 39.16 (m, CF2-2, 4F), and 36.32 ppm (br-tr, CF2-3,
4F). MS: m/z (rel. intensity) ˆ 514(M ), 495, 346, and
‡
Into an aqueous solution (350 ml) of cupric sulfate pen-
tahydrate (100 g, 0.29 mol) was added portionwise zinc
powder (35 g, 0.54 mol) with vigorous stirring until the
aqueous layer discolored. Aqueous supernatant was dis-
carded and residual zinc metal was removed by treating with
1 mol dm 3 hydrochloric acid. Precipitated copper powder
345.
3.2.4. (Heptafluoro-2-propyl)benzene (6)
The reaction of iodobenzene (14.65 g, 71.8 mmol) with
hepta¯uoro-2-iodopropane (27.62 g, 93.3 mmol) in the pre-
sence of activated copper (11.87 g, 186.8 mmol) in DMF
(50 ml) yielded the corresponding colorless oil 6 (11.61 g,
66% yield) boiling at 1258C (lit. [11], 54% yield, bp 124±
124.58C). 1H-NMR: d ˆ 7.7±7.3 ppm (br, arom., 5H). 19F-
NMR: d ˆ 86.14 (d, J ˆ 7.3 Hz, CF(CF3)2, 6F) and
20.58 ppm (sep, J ˆ 7.3 Hz, CF(CF3)2, 1F). MS: m/z
3
was collected by decantation, washed with 1 mol dm
hydrochloric acid, deionized water, methanol, ethanol, acet-
one, and ether, successively, and dried under reduced pres-
sure. The activated copper powder was stored under a
nitrogen atmosphere [19].
‡
‡
(rel. intensity) ˆ 246(M ), 177, 127, 77(C6H5 ). Obsd.
accurate m/z ˆ 246.0280. Calcd. for C9H5F7 ˆ 246.0279.
3.2. Copper-catalyzed coupling of arylhalide with
perfluoroalkyl iodide
3.3. Direct iodination
3.2.1. Typical procedure 3-(Heptafluoro-2-propyl)-
(trifluoromethyl)benzene (7)
3.3.1. Typical procedure 3,5-Bis(heptafluoro-2-
propyl)iodobenzene (12)
Into a mixture of 3-(tri¯uoromethyl)bromobenzene
(15.00 g, 66.7 mmol) and activated copper powder
(13.88 g, 218 mmol) in DMF (80 ml) was added hepta-
¯uoro-2-iodopropane (27.00 g, 91.2 mmol) at room tem-
perature with vigorous stirring. The resulting mixture was
kept stirred for an additional 15 h at 908C. The reaction
mixture was diluted with water and ®ltered off. Combined
Into a dark solution of iodine (1.04 g, 4.1 mmol) in 20%
fuming sulfuric acid (15 ml) was added dropwise 3,5-
bis(hepta¯uoro-2-propyl)benzene (8) (3.10 g, 7.5 mmol)
over 2 h at room temperature with vigorous stirring. The
resulting mixture was kept stirring for an additional 14 h at
room temperature and subsequently for 10 h at 658C until
the starting substance disappeared in the gas-chromato-
graphic monitoring, and then poured portionwise into
crashed ice (100 g). Separated dark oil was extracted repeat-
edly with ether, and the combined extracts were washed
with 10% aqueous sodium hydrogen sul®te, saturated aqu-
eous sodium hydrogen carbonate, water, and saturated
aqueous sodium chloride, successively. The ether solution
was dried over sodium sulfate and evaporated to give oily
residue, which was fractionated under reduced pressure, to
afford a colorless oil 12 boiling at 56.08C/2.0 torr (2.92 g,
72% yield). 1H-NMR: d ˆ 8.2±8.0 (br, arom., 2H) and 7.9±
7.6 ppm (br, arom., 1H). 19F-NMR: d ˆ 86.34 (d, J ˆ
7.3 Hz, CF(CF3)2, 12F) and 20.34 ppm (sept, J ˆ 7.3 Hz,
ethereal extracts from the ®ltrate were washed with water,
3
2 mol dm
hydrochloric acid, and saturated aqueous
sodium chloride, successively. After usual work-up, the
crude product was fractionated by distillation, to afford a
colorless oil 7 boiling at 568C/30 torr. (13.18 g, 63% yield).
1H-NMR: d ˆ 7.9±7.4 ppm (br, arom., 4H). 19F-NMR:
d ˆ 98.86 (s, CF3, 3F), 86.26 (d, J ˆ 7.3 Hz, CF(CF3)2,
6F), and 20.58 ppm (sep, J ˆ 7.3 Hz, CF(CF3)2, 1F).
3.2.2. 1,3-Bis(heptafluoro-2-propyl)benzene (8)
The reaction of 1,3-dibromobenzene (10.17 g,
43.1 mmol) with hepta¯uoro-2-iodopropane (33.21 g,
112 mmol) in the presence of activated copper (17.62 g,
276 mmol) in DMF (80 ml) at 908C for 44 hr afforded a
colorless oil 8 (11.88 g, 67% yield) boiling at 568C/20 torr
‡
CF(CF3)2, 2F). MS: m/z (rel. intensity) ˆ 540(M ). Obsd.
accurate m/z ˆ 539.9057. Calcd. for C12H3F14I ˆ
1
(lit. [9], 72% yield, bp 146±1488C). H-NMR: d ˆ 7.9±
539.9057.

298
K. Fujiki et al. / Journal of Fluorine Chemistry 102 (2000) 293±300
3.3.2. 3-(Heptafluoro-2-propyl)iodobenzene (10)
The resulting mixture was quenched by the addition of
saturated aqueous sodium hydrogen carbonate (20 ml).
Precipitates were removed by ®ltration and washed with
ether, and an aqueous ®ltrate was extracted with ether
repeatedly. An ethereal ®ltrate, washings, and extracts were
combined and worked up as usual. The brown crude product
was fractionated on an activated alumina column by elution
with dichloromethane and methanol, successively. The frac-
tion eluted with methanol was sonicated after the addition of
methanolic tetramethylammonium chloride, and then eva-
porated off. The solid residue was dispersed in water and the
mixture was extracted with dichloromethane. The extract
was evaporated off, and a residual solid was recrystallized
from a dichloromethane-hexane mixture, to yield colorless
crystals of tetramethylammonium tetrakis(3,5-bis(hepta-
¯uoro-2-propyl)phenyl)borate (3) (1.55 g, 50% yield) melt-
By the iodination of the starting compound 6 (3.0 g,
12.2 mmol) with iodine (1.7 g, 6.7 mmol) in 20% fuming
sulfuric acid (20 ml) was isolated the corresponding product
10 (1.76 g, 39% yield) as a colorless oil boiling at 66/
1
8.0 torr. H-NMR: d ˆ 8.2±7.0 ppm (m, 4H, arom.). 19F-
NMR: d ˆ 86.22 (d, J ˆ 7.3 Hz, CF(CF3)2, 6F) and
20.65 ppm (sept, J ˆ 7.3 Hz, CF(CF3)2, 1F). MS: m/z
‡
(rel. intensity) ˆ 372(M ), 303, 253. Obsd. accurate m/
z ˆ 371.9247. Calcd. for C9H4F7I ˆ 371.9247.
3.3.3. 3-(Heptafluoro-2-propyl)-5-(trifluoromethyl)-
iodobenzene (11)
From the reaction of the starting compound 7 (3.35 g,
10.7 mmol) and iodine (1.62 g, 6.4 mmol) was isolated the
corresponding iodide 11 (2.09 g, 45% yield) as a colorless
oil boiling at 508C/3.0 torr. 1H-NMR: d ˆ 8.2±8.0 (br,
arom., 1H) and 7.9±7.6 ppm (br, arom., 2H). 19F-NMR:
d ˆ 98.66 (s, CF3, 3F), 86.34 (d, J ˆ 7 Hz, CF(CF3)2, 6F),
and 20.34 ppm (m, J ˆ 7 Hz, CF(CF3)2, 1F). MS: m/z (rel.
1
ing at 260±2638C. H-NMR(CD3CN): d ˆ 7.3±7.6 (br-s,
arom., 12H) and 2.14 ppm (s, N(CH3)4, 12H). 19F-
NMR(CD3CN): d ˆ 87.43 (d, J ˆ 6.3 Hz, CF(CF3)2, 48F)
and 18.86 ppm (sept, J ˆ 6.3 Hz, CF(CF3)2, 8F). 13C-
NMR(CD3CN): d ˆ 162.32 (q, J ˆ 49.9 Hz, arom. C-1),
135.32 (d, J ˆ 7.8 Hz, arom. C-2,6), 126.49 (dsept, J ˆ 19.6
and 2.9 Hz, arom. C-3,5), 121.53 (dq, J ˆ 27.4 and
285.6 Hz, CF(CF3)2), 119.02 (d, J ˆ 13.7 Hz, arom. C-4),
92.61 (dsept, J ˆ 201.5 and 33.3 Hz, CF(CF3)2), and
56.25 ppm (t, JN±C ˆ 3.9 Hz, NCH3).
‡
intensity) ˆ 440(M ), 371, 321. Obsd. accurate m/z ˆ
439.9120. Calcd. for C10H3F10I ˆ 439.9121.
3.3.4. 3,5-Bis(nonafluoro-1-butyl)iodobenzene (13)
From the reaction of the starting compound 9 (14.13 g,
27.5 mmol) and iodine (4.98 g, 19.6 mmol) in 20% fuming
sulfuric acid (46 ml) was isolated the corresponding iodide
13 (13.75 g, 78% yield) as a colorless oil boiling at 808C/
2.0 torr, which solidi®ed to sublimable colorless crystals
melting at 50±518C. 1H-NMR: d ˆ 8.2±8.0 (br, arom., 2H)
and 7.8±7.6 ppm (br, arom., 1H). 19F-NMR: d ˆ 80.80 (br-
tr, CF3, 6F), 50.43 (br-tr, CF2-1, 4F), 39.41 (m, CF2-2, 4F),
and 36.29 ppm (br-tr, CF2-3, 4F). MS: m/z (rel.
3.4.2. Tetramethylammonium tetrakis(3,5-bis(nonafluor-
obutyl)phenyl)borate (2)
The Grignard reagent, which was prepared from 3,5-
bis(nona¯uorobutyl)iodobenzene (13) (13.75 g, 21.5 mmol)
and magnesium (0.52 g, 21.4 mmol) in the presence of
butylmagnesium bromide (0.66 mmol), was reacted in situ
with boron tri¯uoride etherate (669 mg, 4.71 mmol). Work-
up as usual yielded colorless crystals of tetramethylammo-
nium tetrakis(3,5-bis(nona¯uoro-1-butyl)phenyl)borate (2)
(6.24 g, 62% yield) melting at 151±1528C (from ethyl
acetate-hexane). 1H-NMR(CD3OD): d ˆ 7.7±7.3 (br,
arom., 12H) and 3.21 ppm (s, N(CH3)4, 12H). 19F-
NMR(CD3OD): d ˆ 82.30 (t-like m, J ˆ 9.8 Hz, CF3,
12F), 52.60 (t-like m, J ˆ 12.2 Hz, CF2-1, 8F), 40.37 (br-
m, CF2-2, 8F), and 38.18 ppm (t-like m, J ˆ 12.2 Hz, CF2-3,
8F).
‡
intensity) ˆ 540(M ).
3.4. Syntheses of tetraarylborates
3.4.1. Typical procedure Tetramethylammonium
tetrakis(3,5-bis(heptafluoro-2-propyl)phenyl)borate
(PFPB) (3)
A mixture of magnesium and butylmagnesium bromide
(initiating catalyst) which was prepared from butyl bromide
(0.030 g, 0.22 mmol) and magnesium turnings (0.22 g,
9.05 mmol) in freshly distilled dry ether (1.5 ml) under
an argon atmosphere, was diluted with an additional
1.5 ml of dry ether and cooled on an ice bath. Into the cold
mixture was slowly added an ethereal solution (15 ml) of
3,5-bis(hepta¯uoro-2-propyl)iodobenzene (12) (4.80 g,
8.89 mmol). The reaction mixture was kept stirred for an
additional 3 h to complete the reaction. The resulting
Grignard reagent was chilled to 408C, and boron tri¯uor-
ide etherate (252 mg, 1.78 mmol) in dry ether (5 ml) was
added dropwise so slowly that the temperature was kept not
higher than 408C. The reaction mixture was kept stirred
without a cold bath, to be warmed by itself up to room
temperature, then heated under re¯ux for an additional 36 h.
3.4.3. Tetramethylammonium tetrakis(3-(heptafluoro-2-
propyl)-5-(trifluoromethyl)-phenyl)borate (4)
The Grignard reagent, which was prepared from 3-(hep-
ta¯uoro-2-propyl)-5-(tri¯uoromethyl)iodobenzene
(11)
(1.99 g, 4.5 mmol) and magnesium (0.13 g, 5.3 mmol) in
the presence of butylmagnesium bromide (0.4 mmol), was
reacted in situ with boron tri¯uoride etherate (137 mg,
1.0 mmol). Work-up as usual yielded colorless crystals of
tetramethylammonium tetrakis(3-(hepta¯uoro-2-propyl)-5-
(tri¯uoromethyl)phenyl)borate (4) (0.83 g, 64% yield)
melting at 146±1478C (from dichloromethane-hexane).
1H-NMR(CD3OD): d ˆ 7.7±7.4 (br, arom., 12H) and

K. Fujiki et al. / Journal of Fluorine Chemistry 102 (2000) 293±300
299
3.20 ppm (s, N(CH3)4, 12H). 19F-NMR(CD3OD): d ˆ
Table 5
Molar extinction coefficients at absorption maximum
18.78 (sept, J ˆ 7 Hz, CF(CF3)2, 4H), 87.75 (d, J ˆ 7 Hz,
CF(CF3)2, 24F) and 100.77 ppm (s, CF3, 12F). 13C-
NMR(CD3OD): d ˆ 162.87 (q, J ˆ 49.9 Hz, arom. C-1),
136.96 (s, arom. C-6), 134.75 (s, arom. C-2), 130.77 (q,
J ˆ 32.3 Hz, arom. C-5), 126.62 (d, J ˆ 19.6 Hz, arom. C-
3), 125.88 (q, J ˆ 271.9 Hz, Ar-CF3), 122.00 (dq, J ˆ 27.4
and 284.6 Hz, CF(CF3)2), 118.86 (d, J ˆ 11.7 Hz, arom. C-
4), 93.04 (dsep, J ˆ 201.5 and 32.3 Hz, CF(CF3)2), and
55.92 ppm (t, JC±N) ˆ 3.9 Hz, NCH3).
Borate
Substituent
R1
e (l max/nm)
R2
2
PFPB(3)
(CF2)3CF3
CF(CF3)2
(CF2)3CF3
CF(CF3)2
CF(CF3)2
CF(CF3)2
CF3
5889 (272)
4942 (270)
4775 (270)
4796 (270)
5214 (270)
4
CF3
H
5
14
H
3.4.4. Tetramethylammonium tetrakis(3-(heptafluoro-2-
propyl)phenyl)borate (5)
57.85; H, 4.23; N, 2.11%. Calcd. for C32H28NBF12: C,
57.76; H, 4.24; N, 2.11%.
The Grignard reagent, which was prepared from 3-hepta-
¯uoroisopropyliodobenzene (10) (4.07 g, 10.9 mmol) and
magnesium (0.32 g, 13.1 mmol) in the presence of butyl-
magnesium bromide (1.1 mmol), was reacted in situ with
boron tri¯uoride etherate (317 mg, 2.2 mmol). The reaction
mixture was heated under re¯ux for 48 h, and then worked
up as above to yield colorless crystals of tetramethylam-
monium tetrakis(3-(hepta¯uoro-2-propyl)phenyl)borate (5)
(1.48 g, 62% yield) melting at 158±1608C (from dichloro-
methane-hexane). 1H-NMR (CD2Cl2): d ˆ 7.6±7.0 (br,
arom., 16H) and 2.51 ppm (s, N(CH3)4, 12H). 19F-NMR
(CD2Cl2): d ˆ 86.57 (d, J ˆ 7 Hz, CF(CF3)2, 24F), and
19.83 ppm (sept, J ˆ 7 Hz, CF(CF3)2, 4F). 13C-NMR-
(CD3OD): d ˆ 163.80 (q, JC±B ˆ 49.9 Hz, arom. C-1),
139.15 (s, arom. C-6), 133.71 (d, J ˆ 8.8 Hz, arom. C-2),
127.02 (d, J ˆ 2.9 Hz, arom. C-5), 124.61 (dsept, J ˆ 2.9
and 16.6 Hz, arom. C-3), 122.13 (dq, J ˆ 29.4 and
285.6 Hz, CF3), 120.52 (d, J ˆ 10.8 Hz, arom. C-4),
93.52 (dsept, J ˆ 32.3 and 198.6 Hz, CF(CF3)2), and
55.76 ppm (t, JC±N ˆ 3.9 Hz, N(CH3)4). Anal. Found: C,
44.86; H, 2.69; N, 1.57%. Calcd. for C40H28NBF28: C,
45.09; H, 2.65; N, 1.31%.
3.5. Measurements of solubilities of tetraarylborates
A relationship between concentration and absorbance at a
keyband was determined with dichloromethane solutions of
a range of known concentrations of each tetraarylborate.
Molar extinction coef®cients in dichloromethane were cal-
culated from the slopes of these linear plots as summarized
in Table 5. Solubilities were determined by the photometric
method in a similar manner as previously described [9].
3.6. Measurements of decomposition rates of
tetraarylborates
3.6.1. Decomposition under dichloromethane/aqueous
sulfuric acid two-phase conditions
Aqueous sulfuric acid (2 ml) of prescribed concentration
was added into a 2 ml portion of the dichloromethane
3
solution of tetraarylborate (3.87 Â 10 3 mol dm borate)
with vigorously stirring by rotating paddles at 1100 rpm on
a water bath thermostatted at 27.08C. Aliquots were taken
from the dichloromethane layer at regular intervals, and
quenched immediately with aqueous sodium carbonate.
Formation of acid-catalyzed decomposition product, i.e.,
poly¯uoroalkyl-substituted benzene, was traced by moni-
toring the increase in a gas-chromatographic peak intensity
relative to that of decane which was added in advance into
the reaction mixture as an internal standard. Pseudo-®rst-
order rate constants, k10 (Table 3), were calculated from the
gradient at the initial stage of rate plots which were linear
with the correlation coef®cients of more than 0.99 in each
reaction system through the decompostion of two-thirds of
the initial charge.
3.4.5. Tetramethylammonium tetrakis(3-(trifluoromethyl)-
phenyl)borate (14)
The Grignard reagent, which was prepared from 3-(tri-
¯uoromethyl)bromobenzene (4.26 g, 17.8 mmol) and mag-
nesium (0.52 g, 21.4 mmol) in the presence of butylmagne-
sium bromide prepared in situ by the addition of butyl
bromide (26 mg, 0.2 mmol), was reacted with boron tri-
¯uoride etherate (537 mg, 3.8 mmol). The reaction mixture
was heated under re¯ux for 21 h, and then worked up as
above to yield colorless crystals of tetramethylammonium
tetrakis(3-(tri¯uoromethyl)phenyl)borate (14) (600 mg,
24% yield) melting at 167±1688C (from dichloro-
methane-hexane). 1H-NMR (CD3CN): d ˆ 7.6±7.0 (br,
arom., 16H) and 3.02 ppm (s, N(CH3)4, 12H). 19F-NMR
(CD3CN): d ˆ 101.87 ppm (s, CF3). 13C-NMR(CD3CN):
d ˆ 163.30 (q, JC±B ˆ 49.9 Hz, arom. C-1), 140.14 (s,
arom. C-6), 131.91 (s, arom. C-2), 128.44 (q, J ˆ 30.0 Hz,
arom. C-3), 127.49 (q, J ˆ 2.9 Hz, arom. C-5), 126.59 (q,
J ˆ 271.4 Hz, CF3), 120.54 (d, J ˆ 4.9 Hz, arom. C-4), and
56.14 ppm (t, JC±N ˆ 3.9 Hz, N(CH3)4). Anal. Found: C,
3.6.2. Decomposition in methanolic sulfuric acid
Into a precisely weighed amount of tetraarylborate salt
(ca. 20 mg) placed in an NMR-sample tube was added
methanolic sulfuric acid up to 25 mm high. The sum total
of 19F-NMR signal intensities and the decrease in the
intensity of CF3 signals due to the tetraarylborate were
traced at 258C at regular intervals. Pseudo-®rst-order rate
constants (Table 4) were calculated from the rate plots
which were linear with the correlation coef®cients of more

300
K. Fujiki et al. / Journal of Fluorine Chemistry 102 (2000) 293±300
[5] H. Iwamoto, H. Kobayashi, P. Murer, T. Sonoda, H. Zollinger, Bull.
Chem. Soc. Jpn. 66 (1993) 2590 and references therein.
[6] S.H. Strauss, Chem. Rev. 93 (1993) 927.
than 0.999 through three half-life periods in each reaction
system except PFPB (3). Decomposition of the last borate
(4) was traced for 4500 min up to 20% decrease, which
followed a pseudo-®rst-order rate plot with the correlation
coef®cient of more than 0.999.
[7] C.A. Reed, Acc. Chem. Res. 31 (1998) 133.
[8] A.J. Lupinetti, S.H. Strauss, Chemtracts-Inorg. Chem. 11 (1998)
565.
[9] K. Fujiki, M. Kashiwagi, H. Miyamoto, A. Sonoda, J. Ichikawa, T.
Sonoda, H. Kobayashi, J. Fluorine Chem. 57 (1992) 307.
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[11] N. Ishikawa, M. Ochiai, J. Chem. Soc. Jpn. (1973) 2351.
[12] J. Sepiol, S. Soulen, J. Fluorine Chem. 24 (1984) 61.
[13] J.Y. Vandeberg, C.E. Moore, F.P. Cassaretto, H. Posvic, Anal. Chim.
Acta 44 (1969) 175.
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