Polyfluoroorganoboron-oxygen compounds. 5 Feasible routes to perfluoroalkyltrimethoxyborates M[CnF2n+1B(OMe) 3] (n ≥ 3)

Article abstract of DOI:10.1002/zaac.200600357

A well applicable preparative method for lithium perfluoroalkyltrimethoxyborates, Li[C_nF_2n+1B(OMe) ₃] (n = 3, 4, 6), was elaborated which is based on the reaction of B(OMe)₃ with C_nF_2n+1Li generated from C _nF_2n+1H and t-BuLi. Alternative perfluoroalkylation reactions of B(OMe)₃ with perfluoropropyllithium generated from C₃F₇I and RLi, perfluoropropylmagnesium bromide, or perfluoropropyltrimethylsilane and potassium fluoride gave less satisfactory results for M[C₃F₇B(OMe)₃]. The conversion of M[C_nF_2n+1B(OMe)₃] salts (M = Li, BrMg) into K[C_nF_2n+1B(OMe)₃] salts and basic properties of the new salts are reported.

Full text of DOI:10.1002/zaac.200600357

DOI: 10.1002/zaac.200600357
Polyfluoroorganoboron-Oxygen Compounds. 5 [1]
Feasible Routes to Perfluoroalkyltrimethoxyborates M[CnF2n؉1B(OMe)3] (n Ն 3)
Nicolay Yu. Adonina, Vadim V. Bardinb, and Hermann-Josef Frohna,*
a Duisburg/Germany, Department of Chemistry, Inorganic Chemistry, University of Duisburg-Essen
b Novosibirsk/Russia, N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS
Received December 18th, 2006.
Dedicated to Professor Helge Willner on the Occasion of his 60th Birthday
Abstract. A well applicable preparative method for lithium per-
fluoroalkyltrimethoxyborates, Li[CnF2nϩ1B(OMe)3] (n ϭ 3, 4, 6),
was elaborated which is based on the reaction of B(OMe)3 with
CnF2nϩ1Li generated from CnF2nϩ1H and t-BuLi. Alternative
perfluoroalkylation reactions of B(OMe)3 with perfluoropropyllith-
ium generated from C3F7I and RLi, perfluoropropylmagnesium
bromide, or perfluoropropyltrimethylsilane and potassium fluoride
gave less satisfactory results for M[C3F7B(OMe)3]. The conver-
sion of M[CnF2nϩ1B(OMe)3] salts (M Li, BrMg) into
K[CnF2nϩ1B(OMe)3] salts and basic properties of the new salts
are reported.
ϭ
Keywords: Perfluoroalkylborates; Perfluoroalkylation; Perfluoro-
alkyl lithium compounds; NMR spectroscopy
Introduction
CF3SiMe3 or C2F5SiMe3 with B(OAlk)3 (Alk ϭ CH3,
C2H5) in the presence of the fluoride anion [12, 13]. To our
knowledge, no longer-chain (perfluoroalkyl)trialkoxybor-
ates M[CnF2nϩ1B(OAlk)3] (n Ն 3) have been isolated and
characterised up to now.
Organotrialkoxyborates M[RB(OAlk)3] are well known
compounds, which are widely used in organic syntheses [2].
In contrast, the preparation and reactivity of (perfluoroorg-
ano)trialkoxyborates M[RFB(OAlk)3] is still a less investi-
gated field of organoboron chemistry. In general, these salts
are obtained by the nucleophilic addition of perfluoroorg-
anometallic compounds RFM (M ϭ Li, BrMg) to B(OAlk)3
in ethereal solvents (diethyl ether, THF, or their mixture)
and mainly used without isolation for the syntheses of the
corresponding (perfluoroorgano)trifluoroborates [3]. The
intermediates M[C6F5B(OAlk)3] (M ϭ Li, BrMg; Alk ϭ
CH3, CH2CF3, C3H7 etc.) [4], Li[4ϪC5F4NB(OMe)3] [5],
Li[XCFϭCFB(OMe)3] [6, 7], Li[CF2ϭCXB(OMe)3] [8],
Li[RFCϵCB(OMe)3] [9] were proven by multiϪNMR spec-
troscopy. The first isolation of lithium (perfluoroorgano)tri-
methoxyborates, Li[RFB(OMe)3] (RF ϭ C2F5, CF2ϭCF
and C6F5), was reported by us in 2001 [10]. Later the syn-
thesis and isolation of lithium fluorophenyltrimethoxybor-
ates Li[C6H5ϪnFnB(OMe)3] (n Յ 5) and their palladium cat-
alysed cross-coupling reactions were presented [11]. Re-
cently Kolomeitsev et al. reported the synthesis of
M[C2F5B(OMe)3] (M ϭ Li, K) by a related route [12].
Herein we report a convenient and generally applicable
preparative procedure for a representative series of lithium
(perfluoroalkyl)trimethoxyborates,
Li[CnF2nϩ1B(OMe)3]
(n ϭ 3, 4, 6), and study two alternative approaches to long-
chain (perfluoroalkyl)trimethoxyborates based on reactions
of B(OMe)3 with different perfluoroalkylating agents.
Results and Discussion
We have examined three perfluoroalkylating agents for the
nucleophilic addition to B(OMe)3: perfluoroalkyl(trimethyl)-
silane in combination with potassium fluoride, perfluoro-
alkylmagnesium bromide, and perfluoroalkyllithium. The
perfluoropropyl compounds were chosen as a model for this
addition to find optimal conditions.
Perfluoropropylation of B(OMe)3 with C3F7SiMe3
The fluoride-mediated nucleophilic perfluoroalkylation
with perfluoroalkyltrimethylsilanes was employed in reac-
tions with many types of electrophiles [14, 15]. Thus the
reaction of B(OMe)3 with CnF2nϩ1SiMe3 (n ϭ 1, 2) yielded
K[CF3B(OMe)3] and K[C2F5B(OMe)3], respectively [12, 13].
We had successfully reproduced the synthesis of
K[CF3B(OMe)3] before we tried to apply this method to the
preparation of the corresponding perfluoropropyl analogue.
However, under the same conditions, potassium perfluoro-
propyltrimethoxyborate (1a) was obtained only in a low
Alternatively,
the
salts
M[CF3B(OMe)3]
and
M[C2F5B(OMe)3] were prepared by the reaction of
* Prof. Dr. H.-J. Frohn
Fachbereich Chemie der Universität
Lotharstr. 1
D-47048 Duisburg
Fax: (ϩ49)2 03-379 22 31
e-mail: h-j.frohn@uni-due.de
Z. Anorg. Allg. Chem. 2007, 633, 647Ϫ652
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
647

N. Y. Adonin, V. V. Bardin, H.-J. Frohn
yield of 24 % besides C3F7H, FSiMe3, K[B(OMe)4] (pre-
sumably) and unreacted starting compounds (Scheme 1).
trapped with desired electrophiles at low temperatures [18].
In earlier reports the generation of perfluroalkyllithium was
performed by metalation of perfluoroalkyl iodides with lith-
ium [19] or by transmetalation with RLi (R ϭ Me, Bu, Ph)
[20]. However, the iodine-lithium exchange proceeds with a
sufficient rate only in case of C2F5I [21] and RfOCF2CF2I
DME
C3F7SiMe3 ϩ B(OMe)3 ϩ KF
Ǟ K[C3F7B(OMe)3]
2
1a
ϩ C3F7H ϩ K[B(OMe)4] ϩ FSiMe3
[22]. The elongation of the perfluoroalkyl chain of CnF2nϩ1
I
Scheme 1
showed an increased contribution of by-reactions (detailed
discussion see refs. [23Ϫ25]). More satisfactory results were
achieved with in situ generated CnF2nϩ1Li (n > 2), e.g. by
the simultaneous addition of RLi and the electrophile into
the cold solution of perfluoroalkyl iodide [20], or by the
addition of RLi to the solution of perfluoroalkyl iodide and
the electrophile [20, 22, 24]. In both options the main com-
plication arises from the low nucleophilicity of CnF2nϩ1Li
with respect to non-fluorinated RLi. When RLi was still
present after the transmetalation the desired product was
contaminated with the by-product resulting from the highly
nucleophilic RLi reagent and the electrophile.
Taking into mind these aspects, we decided to examine
the nucleophilic addition of perfluoroalkyllithium to tri-
methoxyborane under different conditions. The treatment
of perfluoropropyl iodide with MeLi (in ether) or BuLi (in
etherϪhexane) below Ϫ90 °C and the subsequent addition
of B(OMe)3 resulted in an incomplete conversion of C3F7I
to C3F7Li and at the end of the reaction sequence
no Li[C3F7B(OMe)3] was found among the reaction pro-
ducts. The addition of BuLi to a solution of C3F7I and
B(OMe)3 in ether at Ϫ78 °C gave the desired borate salt
1c only in low yield (17 %) besides by-products
[C3F7(C4H9)B(OMe)2]Ϫ (proposed), C4H9B(OMe)2, and
[B(OMe)4]Ϫ (11B and 19F NMR) (Scheme 4).
Attempts to increase the conversion of silane 2 as well as
to isolate salt 1a from the reaction mixture failed.
Perfluoropropylation of B(OMe)3 with C3F7MgBr
A solution of perfluoropropylmagnesium bromide was pre-
pared by treating heptafluoropropyl iodide with ethylmag-
nesium bromide in diethyl ether at Ϫ78 °C [16] and reacted
with trimethoxyborane (in excess). Warming above Ϫ20 °C
led to the precipitation of [BrMg][B(OCH3)4] which was
proven after conversion to K[BF4] (treatment with aqueous
HF and subsequent neutralisation with K2CO3). The 19F
and 11B NMR spectra of the mother liquor showed the for-
mation of perfluoropropyltrimethoxyborate and perfluoro-
propyldimethoxyborane (3) (Scheme 2). Likely, the driving
force of the formation of borane 3 besides the tetrameth-
oxyborate salt is the insolubility of the latter in ether. The
demethoxylation of the perfluoropropyltrimethoxyborate
anion with B(OMe)3 is not favoured by acid-base properties
because the Lewis acidity of 3 exceeds that of trimethoxy-
borane [17].
B(OMe)3
C3F7MgBr
Ǟ [BrMg][C3F7B(OMe)3] ϩ C3F7B(OMe)2
1b
3
ϩ [BrMg][B(OCH3)4] ȇ
BuLi
C3F7I ϩ B(OMe)3
Ǟ Li[C3F7B(OMe)3] ϩ by-products
Scheme 2
1c
To exclude the decomposition of magnesium bromide per-
fluoropropyltrimethoxyborate (1b), this salt was precipi-
tated by dilution of the cold (Ϫ30 °C) reaction solution
with cold (Ϫ65 °C) pentane. The subsequent metathesis
with KF in methanol ended up with the quantitative con-
version into the corresponding potassium salt 1a (Scheme 3).
Scheme 4
Kolomeitsev et al. had successfully performed the perfluoro-
ethylation of B(OMe)3 with C2F5Li generated from penta-
fluoroethane and BuLi at Ϫ70 °C [12]. Nevertheless, our
attempt to obtain 1c from C3F7H under the same con-
ditions resulted only in traces of perfluoropropyltrimethoxy-
borate. The main fluoroorganic product was hexafluoropro-
pene indicating the fast thermal decomposition of C3F7Li
in ether at Ϫ70 °C. When the metalation of C3F7H with
BuLi and the subsequent reaction with B(OMe)3 was per-
formed at Ϫ90 to Ϫ95 °C, Li[C3F7B(OMe)3] was obtained
in 20 % yield besides C4H9B(OMe)2, Li[B(OMe)4], and un-
known borates (11B and 19F NMR). The use of MeLi in-
stead of BuLi under the same conditions led to the forma-
tion of methylmethoxyborates and C3F7H could be reco-
vered quantitatively. A significant progress was achieved
when C3F7H was metalated with the more basic and the
less nucleophilic reagent t-butyllithium below Ϫ100 °C.
Indeed, the reaction of C3F7Li generated at Ϫ110 °C from
t-BuLi and 1H-heptafluoropropane in ether with trime-
MeOH
[BrMg][C3F7B(OMe)3] ϩ KF
Ǟ K[C3F7B(OMe)3 ȇ
ϪMg(Br,F)2
1b
1a
Scheme 3
Although salt 1a was moderately stable in MeOH at 20 °C
(80Ϫ90 % decomposition over a period of 3 d), the evapor-
ation of MeOH under reduced pressure at 20Ϫ30 °C (bath)
resulted in the complete decomposition of 1a.
Perfluoroalkylation of B(OMe)3 with
perfluoroalkyllithium
Perfluorinated alkyllithium reagents are thermally highly
unstable compounds which are usually generated and
648
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Z. Anorg. Allg. Chem. 2007, 647Ϫ652

Polyfluoroorganoboron-Oxygen Compounds. 5
1
Table 1 The H, 11B, and 19F NMR spectra of M[CnF2nϩ1B(OMe)3]
Compound
Solvent
δ (F)
δ (B)
δ (H)
CF3
CF3CF2
CF2
CF2B
Li[C3F7B(OMe)3]
[Li(TMEDA)2][C3F7B(OMe)3]
Li[C3F7B(OMe)3]
K[C3F7B(OMe)3]
K[C3F7B(OMe)3]
Ether
Ether
CD3CN
Ether
DME
MeOH
D2O
CD3CN
Ether
Ether
CD3CN
Ether
Ether
Ϫ79.8
Ϫ79.4
Ϫ79.6
Ϫ80.5
Ϫ79.8
Ϫ79.4
Ϫ79.0
Ϫ79.0
Ϫ80.6
Ϫ80.4
Ϫ80.3
Ϫ81.1
Ϫ80.5
Ϫ126.7
Ϫ125.4
Ϫ126.4
Ϫ127.5
Ϫ126.2
Ϫ125.4
Ϫ124.1
Ϫ124.6
Ϫ125.3
Ϫ124.8
Ϫ125.0
Ϫ126.0
Ϫ125.3
Ϫ124.4
Ϫ126.1
Ϫ125.3
Ϫ125.3
Ϫ124.1
Ϫ124.9
Ϫ129.6
Ϫ126.5
Ϫ124.0
Ϫ125.6
Ϫ124.9
Ϫ123.4
Ϫ123.8
1.44
1.89
1.06
0.82
0.78
0.60
Ϫ0.33
1.39
1.38
1.84
1.05
0.78
1.44
3.18
K[C3F7B(OMe)3]
[BrMg][C3F7B(OMe)3]
[BrMg][C3F7B(OMe)3]
Li[C4F9B(OMe)3]
[Li(TMEDA)2][C4F9B(OMe)3]
Li[C4F9B(OMe)3]
K[C4F9B(OMe)3]
Li[C6F13B(OMe)3]
3.36
3.26
Ϫ123.0
Ϫ121.9
Ϫ122.8
Ϫ124.1
Ϫ121.0
Ϫ121.8
Ϫ122.1
Ϫ120.7
Ϫ120.9
Ϫ121.7
Ϫ120.9
Ϫ121.8
Ϫ121.9
Ϫ121.8
Ϫ122.4
Ϫ123.0
3.19
[Li(TMEDA)2][C6F13B(OMe)3]
Li[C6F13B(OMe)3]
Ether
Ϫ80.3
Ϫ80.1
Ϫ81.1
Ϫ125.2
Ϫ125.1
Ϫ126.0
Ϫ125.4
Ϫ124.7
Ϫ123.3
1.86
1.00
0.79
CD3CN
Ether
3.11
K[C6F13B(OMe)3]
thoxyborane resulted in a nearly quantitative yield of lith-
ium heptafluoropropyltrimethoxyborate (Scheme 5).
Li[C6F5B(OMe)3] [1]. In the presence of the chelating ligand
TMEDA (2 equivalents), the coordination at Liϩ changed
and the 19F NMR signal of the CF2B group in
Li[CnF2nϩ1B(OMe)3] was shifted to lower frequency (ca.
1 ppm) indicative of an increased negative charge on these
fluorine atoms. (Table 1). It is noteworthy, that the salts
K[CnF2nϩ1B(OMe)3] underwent faster hydrodeboration to
CnF2nϩ1H in ether than the corresponding lithium salts, but
in contrast to K[C6F5B(OMe)3] [1], the salts
K[CnF2nϩ1B(OMe)3] did not undergo an exchange of bo-
ron-bonded ligands. No K[(CnF2nϩ1)2B(OMe)2] was de-
tected under the investigated conditions.
B(OMe)3, Ϫ110 to 20 °C
tϪBuLi, Ϫ110 °C
C3F7H
Ǟ C3F7Li
Ǟ Li[C3F7B(OMe)3]
ϪtϪBuH
1c
Scheme 5
Furthermore, these reaction conditions were also suitable
for the syntheses of long-chain lithium perfluoroalkyltrime-
thoxyborates, as was demonstrated by the preparation of
Li[C4F9B(OMe)3] (4c) and Li[C6F13B(OMe)3] (5c) in
92Ϫ94 % yield from 1H-perfluorobutane and 1H-per-
fluorohexane, respectively.
Experimental Section
Perfluoroalkyltrimethoxyborates 1a, 1b, 1c, 4c, and 5c
are fine white powders which are soluble in water, ether,
and polar organic solvents (CH3CN, CH3OH, DME).
However, the attempted recovery of these salts from the
above-mentioned solutions (except ether) by evaporation in
vacuum was accompanied by a significant decomposition.
Borates 1c, 4c, and 5c are rarely stable in aqueous solutions
and undergo slow hydrodeboration (within hours). The
constitution of the salts 1b, 1c, 4c, and 5c was unambigu-
ously proved by 1H, 11B and 19F NMR spectroscopy
(Table 1). Although the salts Li[CnF2nϩ1B(OMe)3] were iso-
The NMR spectra were recorded on the Bruker spectrometers AV-
ANCE 300 (1H at 300.13 MHz, 11B at 96.29 MHz, 19F at
282.40 MHz) and WP 80 SY (1H at 80.13 MHz, 19F at 75.39 MHz).
The chemical shifts are referenced to TMS (1H), BF3 ·OEt2/CDCl3
15 % v/v (11B), and CCl3F (19F) (C6F6 as a secondary reference,
δ ϭ Ϫ162.9 ppm). Elemental analysis (C, H) was performed with
a HEKAtech EA3000 analyzer. The composition of the reaction
1
mixtures and the yields of products were determined by H or 19F
NMR spectroscopy using the quantitative standard C6H5CF3.
TMEDA (Aldrich), anhydrous diethyl ether (Baker), 1.7 M MeLi
in ether (Fluka), 1.7 M tϪBuLi in pentane (Aldrich), 2.5 M BuLi
in hexanes (Aldrich), 1Ϫiodoperfluoropropane (ABCR),
1HϪpefluorohexane (Clariant) and KF (spray-dried) (Aldrich)
were used as supplied. B(OMe)3 (Fluka) was distilled over sodium.
Dichloromethane (Baker) and acetonitrile (Riedel-de Hae¨n) were
purified by standard procedures [26] and stored over molecular
1
lated from ethereal solution, neither the H NMR spectra
nor the analytical data showed the presence of ether coordi-
nated to the lithium cation. Consequently, we conclude a
strong coordination of the basic oxygen atoms of the meth-
oxy groups bonded to boron to the electrophilic lithium
cation. Coordination of MeO groups at Liϩ was already
observed in case of the recently studied salt
˚
sieve 3 A. Acetonitrile-d3 (Aldrich) was stored over molecular sieve
˚
3 A. 1HϪPerfluoropropane and 1HϪperfluorobutane were ob-
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649

N. Y. Adonin, V. V. Bardin, H.-J. Frohn
tained by decarboxylation of sodium perfluorobutanoate and so-
dium perfluoropentanoate, respectively [27]. Perfluoropropyltri-
methylsilane was prepared by reaction of 1-iodoperfluoropropane
with P(NEt2)3 and ClSiMe3 [17].
in MeOH (1.2 mL). A white suspension was formed immediately.
After a few min, the suspension was centrifuged and the trans-
parent solution of K[C3F7B(OMe)3] was decanted. Attempts to iso-
late 1a by evaporation of MeOH under reduced pressure led to
complete decomposition, although the decomposition of 1a in
methanol at 20 °C proceeded slowly (80Ϫ90 % decomposition over
a period of 3 d).
Moisture sensitive reactions were carried out under an atmosphere
of dry argon. The addition of M[CnF2nϩ1B(OMe)3] (M ϭ Li,
MgBr) to KF was performed in a Braun glove box under an atmos-
phere of dry argon.
Attempt of perfluoropropylation of B(OMe)3 with
C3F7Li generated from C3F7I and BuLi
Perfluoropropylation of B(OMe)3 with C3F7SiMe3
and KF
A 100 mL, three-necked, round-bottomed flask equipped with a
septum, a low temperature thermometer, a Teflon-coated magnetic
stir bar, and a dry ice-acetone condenser which was connected via
a T-piece to a mineral oil bubbler and an argon line was charged
with C3F7I (3.85 g, 13 mmol) and ether (40 mL). The solution was
cooled (Ϫ90 to Ϫ95 °C) before BuLi (2.5 M, 4 mL, 10 mmol) was
added drop-wise via a syringe (0.2 to 0.3 mL/min) at Յ Ϫ90 °C.
The white suspension was stirred at Ϫ90 to Ϫ95 °C for 1 h before
B(OMe)3 (1.11 g, 10.7 mmol) was added using a syringe. The sus-
pension was stirred for an additional 15 min and then allowed to
warm to 20 °C within 1 h to form a solution which contained C3F7I
(7.2 mmol), C3F7H (1 mmol) and CF3CFϭCF2 (4.0 mmol) (19F)
and no boron compound (11B NMR).
KF (0.34 g, 5.9 mmol) was placed in a flask supplied with a mag-
netic stir bar under an atmosphere of dry argon. DME (4 mL),
C3F7SiMe3 (1.7 g, 7.1 mmol), and B(OMe)3 (610 mg, 5.9 mmol)
were added in sequence using a syringe. A slightly exothermic reac-
tion occurred and within 10Ϫ15 min a transparent solution was
formed. Further stirring for 20 min led to a suspension. The 19F
NMR spectrum of the mother liquor showed the presence of
K[C3F7B(OMe)3] (1.3 mmol), C3F7SiMe3 (4.4 mmol), and C3F7H
(1.5 mmol). The 11B NMR spectrum indicated the presence of
B(OMe)3 and K[B(OMe)4] (traces), besides 1a. The suspension was
centrifuged, the mother liquor was separated from white solid
(mainly, K[B(OMe)4] (500 mg) (11B NMR), diluted with pentane
(2 mL) and was left overnight. A suspension was formed and
the precipitate (190 mg) was isolated to give 1a contaminated
with K[B(OMe)4]. The attempted purification of crude
K[C3F7B(OMe)3] by crystallisation from either methanol or
CH3CN led to its decomposition.
Perfluoropropylation of B(OMe)3 with C3F7Li
generated in the presence of the electrophile
A solution of C3F7I (3.85 g, 13 mmol), B(OMe)3 (1.04 g, 1.12 mL,
10 mmol) in ether (40 mL) was cooled to Ϫ78 °C and BuLi (2.5 M,
4 mL, 10 mmol) was added slowly via a syringe within 30 min.
During the addition the temperature was kept below Ϫ68 °C. Fol-
lowing the white suspension was stirred below Ϫ70 °C for 1 h and
then warmed to 7 °C within 1 h. The 19F and 11B NMR spectra of
the mother liquor are in agreement with the formation of
Li[C3F7B(OMe)3] (17 % yield, NMR see Table 1), Li[C3F7(C4H9)-
Preparation of [BrMg][C3F7B(OMe)3] 1b
A 250 mL, three-necked round-bottomed flask equipped with a
septum, a low-temperature thermometer, a Teflon-coated magnetic
stir bar, and a dry ice-acetone condenser which was connected via
a T-piece to a mineral oil bubbler and an argon line was charged
with C3F7I (11.55 g, 39 mmol), ether (120 mL) before being cooled
(Ϫ70 to Ϫ75 °C). Ethylmagnesium bromide (0.94 M in ether,
35 mL, 32.9 mmol) was added drop-wise within 15 min. The solu-
tion transformed to a white suspension which was stirred at Ϫ75 °C
for 1 h. Subsequently B(OMe)3 (3.15 g, 30.4 mmol) was added
drop-wise using a syringe. The reaction mixture was stirred at
Ϫ75 °C for an additional 2 h. The suspension was gradually
warmed to Ϫ30 °C to form a colourless transparent solution.
Warming of a probe (0.5 mL) to 20 °C was accompanied by
precipitation. The mother liquor showed the presence of
[BrMg][C3F7B(OMe)3], C3F7B(OMe)2, and unreacted C3F7I and
B(OMe)3 (19F and 11B NMR). The cold (Ϫ30 °C) main part of the
solution was transferred into a flask which contained cold (Ϫ65 °C)
pentane (300 mL). Immediately a white precipitate was formed.
The suspension was stirred at Ϫ65 °C for 15Ϫ20 min and kept for
15 min without stirring. The mother liquor was decanted, the pre-
cipitated salt 1b was washed with pentane (3 x 30 mL) at 20 °C,
and dried under reduced pressure (yield 6.89 g) and stored over
P4O10 before use.
4
B(OMe)2] (23 % yield, 19F NMR: Ϫ80.7 (t J(F3, F1) ϭ 10 Hz, 3F,
F3), Ϫ125.7 (br, 2F, F1), Ϫ128.0 (s, 2F, F2) ppm; 11B NMR: 4.21),
11B NMR: 31.4 (C4H9B(OMe)2), 18.3 (B(OMe)3), and 3.0 ppm
(Li[B(OMe)4]) besides unknown by-products.
Attempt of perfluoropropylation of B(OMe)3 with
C3F7Li generated from C3F7H and MeLi
C3F7H (1.70 g, 10 mmol) was dissolved in cold (Ϫ90 °C) ether
(40 mL) and MeLi (1.6 M, 5 mL, 8 mmol) was added drop-wise.
The mixture was stirred at Ϫ90 to Ϫ95 °C for 1 h before B(OMe)3
(830 mg, 8 mmol) was added. Stirring of the reaction mixture was
continued for 1 h at Ϫ90 to Ϫ95 °C and 4 h at Յ Ϫ95 °C (tempera-
ture in the reaction mixture!). Subsequently the mixture was
warmed to Ϫ78 °C within 1 h and finally to 20 °C within 1 h. The
19F NMR spectra showed unreacted C3F7H (quantitative recovery)
and the 11B NMR methylmethoxyborates [MenB(OMe)4Ϫn].
Perfluoropropylation of B(OMe)3 with C3F7Li
generated from C3F7H and BuLi
Preparation of K[C3F7B(OMe)3] from
[BrMg][C3F7B(OMe)3]
A 100 mL, three-necked, round-bottomed flask supplied with a
magnetic stir bar and a low temperature thermometer was charged
with ether (40 mL) and cooled below Ϫ90 °C. 1H-Heptafluoropro-
A solution of [BrMg][C3F7B(OMe)3] (80 mg, 0.2 mmol) in MeOH
(0.35 mL) was added to a stirred solution of KF (80 mg, 1.4 mmol)
650
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Z. Anorg. Allg. Chem. 2007, 647Ϫ652

Polyfluoroorganoboron-Oxygen Compounds. 5
pane (2.04 g, 12 mmol) was condensed into the flask and BuLi
(2.5 M, 4 mL, 10 mmol) was added via a syringe. The temperature
was kept below Ϫ90 °C. The mixture was stirred at Ϫ90 to Ϫ95 °C
for 1 h. After addition of B(OMe)3 (1.04 g, 10 mmol) stirring was
continued for an additional 1 h at Ϫ90 to Ϫ95 °C. Finally the reac-
tion mixture was warmed to 20 °C within 2 h. The 19F and 11B
NMR spectra showed the formation of Li[C3F7B(OMe)3] (20 %
yield) besides C4H9B(OMe)2, B(OMe)3, Li[B(OMe)4], and un-
identified borates.
the 19F and 11B NMR spectra were measured. Solutions of 4c
(33 mg, 0.1 mmol) or 5c (43 mg, 0.1 mmol) were prepared in a simi-
lar manner (Table).
Preparation of K[CnF2nϩ1B(OMe)3] in ether
In the glove box a FEP trap supplied with a magnetic stir bar was
charged with KF (1 g, 17 mmol) and 1c (290 mg, 1 mmol). After
addition of ether (2 mL) the suspension was stirred at 20 °C for
24 h, centrifuged and the mother liquor was decanted. The
reactions of 4c (330 mg, 1 mmol) or 5c (430 mg, 1 mmol) were
performed in the same manner. The 19F and 11B NMR spectra
showed the resonances of the anion [CnF2nϩ1B(OMe)3]Ϫ together
with significant amounts of the corresponding 1H-perfluoroalkane.
Preparation of Li[C3F7B(OMe)3] 1c from C3F7H
and t-BuLi
1HϪHeptafluoropropane (8.0 g, 36.4 mmol) was condensed into
ether (50 mL) at Ϫ70 °C and the solution was cooled below
Ϫ110 °C. t-BuLi (13 mL, 22.1 mmol) was added drop-wise using a
syringe and the temperature was kept below Ϫ110 °C. The mixture
was stirred at this temperature for 40 min before B(OMe)3 (1.94 g,
18.7 mmol) was added. After 1 h of stirring, the suspension was
gradually warmed to 20 °C within 2 h. The suspension was filtered
and the filtrate was evaporated to dryness under reduced pressure.
The solid was dried in vacuum (2.6 hPa) at 60 °C for 2 h to yield
5.0 g (98 %) of 1c (white powder).
Acknowledgements. We gratefully acknowledge financial support
by the Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie.
References
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Z. Anorg. Allg. Chem. 2007, 647Ϫ652
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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652
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 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 647Ϫ652