Polyfluoroorganoboron-oxygen compounds. 4 [1] lithium pentafluorophenyltrimethoxyborate, Li[C6F5B(OMe) 3], reactions with selected electrophiles and nucleophiles

Article abstract of DOI:10.1002/zaac.200500083

Li[C₆F₅B(OMe)₃] (1a) reacted with the electrophiles CD₃C(O)CD₃, CH₃OD, CD ₃CN, CH₃CN, HOC₂H₄OH, Br ₂, and I₂ to give C₆F₅X (X = D, H, Br, I). The treatment of 1a with Me₃SiCl or BF₃ in CH ₂Cl₂ and CCl₃F or pentene resulted in C ₆F₅B(OMe)₂ or C₆F₅BF ₂, respectively. The attempted metathesis of 1a with KF or [Bu ₄N]Br in CH₂Cl₂ led to a mixture of M[(C ₆F₅)₂B(OMe)₂] (2b,c, main product) and M[C₆F₅B(OMe)₃] (1b,c, minor product) (M = [Bu₄N], K). Even in the presence of diethyl ether, THF, DME, or TMEDA salt 1a underwent dismutation to the diarylborate salt [Li(L) _n][(C₆F₅)₂B(OMe)₂] (L = Et₂O, THF, DME, TMEDA) and [Li(L)_n][B(OMe)₄]. In subsequent reactions with aqueous K[HF₂] or [Bu ₄N][HF₂] M[(C₆F₅) ₂B(OMe)₂] (M = K, [Bu₄N], [Li(L)_n]) yielded K[(C₆F₅)₂BF₂] (4c) or [Bu₄N][(C₆F₅)₂BF₂] (4b). The molecular structure of [Li·TMEDA][(C₆F₅) ₂B(OMe)₂] from single crystals showed significant cation-oxygen interactions.

Full text of DOI:10.1002/zaac.200500083

Polyfluoroorganoboron-Oxygen Compounds. 4 [1]
Lithium Pentafluorophenyltrimethoxyborate, Li[C6F5B(OMe)3], Reactions with
Selected Electrophiles and Nucleophiles
Nicolay Yu. Adonina, Vadim V. Bardinb, Ulrich Flörkec, and Hermann-Josef Frohn*,a
a Duisburg/Germany, Department of Chemistry, Inorganic Chemistry, University Duisburg-Essen
b Novosibirsk/Russia, N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, SB RAS
c Paderborn/Germany, Department of Chemistry, University Paderborn
Received February 28th, 2005.
Dedicated to Professor Herbert W. Roesky on the Occasion of his 70th Birthday
Abstract. Li[C6F5B(OMe)3] (1a) reacted with the electrophiles
CD3C(O)CD3, CH3OD, CD3CN, CH3CN, HOC2H4OH, Br2, and
I2 to give C6F5X (X ϭ D, H, Br, I). The treatment of 1a with
Me3SiCl or BF3 in CH2Cl2 and CCl3F or pentene resulted in
C6F5B(OMe)2 or C6F5BF2, respectively. The attempted metathesis
of 1a with KF or [Bu4N]Br in CH2Cl2 led to a mixture of
M[(C6F5)2B(OMe)2] (2b,c, main product) and M[C6F5B(OMe)3]
(1b,c, minor product) (M ϭ [Bu4N], K). Even in the presence of
diethyl ether, THF, DME, or TMEDA salt 1a underwent dismuta-
tion to the diarylborate salt [Li(L)n][(C6F5)2B(OMe)2] (L ϭ Et2O,
THF, DME, TMEDA) and [Li(L)n][B(OMe)4]. In subsequent reac-
tions with aqueous K[HF2] or [Bu4N][HF2] M[(C6F5)2B(OMe)2]
(M
ϭ
K, [Bu4N], [Li(L)n]) yielded K[(C6F5)2BF2] (4c) or
(4b). The molecular structure of
[Bu4N][(C6F5)2BF2]
[Li·TMEDA][(C6F5)2B(OMe)2] from single crystals showed signifi-
cant cation-oxygen interactions.
Keywords: Perfluoroarylborates; Perfluoroarylboranes; Methoxy-
borates; NMR spectroscopy; Dismutation
Introduction
(perfluoroorgano)trimethoxyborates Li[RFB(OMe)3] (RF ϭ
C2F5, CF2ϭCF, and C6F5) was reported for the first time
[14]. Subsequently, the preparation and structural charac-
terization of the salt {[BrMg(OEt2)][(C6F5)2B(µ-OEt)2]}2
[15] and a series of less fluorinated lithium aryltrimethoxy-
borates Li[C6H5ϪnFnB(OMe)3] (n Յ 5) [1] was described.
Very recently, Kolomeitsev et al. obtained the salts
M[CnF2nϩ1B(OR)3] (M ϭ K, [Me4N]; n ϭ 1, 2; R ϭ Me,
Et) by the reaction of CnF2nϩ1SiMe3 with MF and
B(OR)3 [16].
The reactivity of (perfluoroorgano)alkoxyborate salts is
still a less investigated area. They were converted into the
corresponding (perfluoroorgano)fluoroborate salts by the
reaction with aqueous K[HF2] (with or without addition of
aqueous HF) [6, 8, 11Ϫ13, 17]. The reaction of Li[CF2ϭ
CFB(OMe)3] with Me3SiCl resulted in the abstraction of
one methoxy group and the formation of trifluorovinyldi-
methoxyborane [8, 9]. A similar approach was used for the
synthesis of perfluoroalkyldialkoxyboranes CnF2nϩ1B(OR)2
(n ϭ 1, 2) from the salts M[CnF2nϩ1B(OR)3] using the
reagents CF3SO2OMe, MeSO2Cl, Me3SiCl, or TosOMe in
DME or hydrocarbons [16].
During the last decade remarkable progress in the synthesis
and reactivity of perfluoroorganoboron halides and
(perfluoroorgano)fluoroborate salts was reported [2]. The
chemistry of perfluoroorganoboron-oxygen compounds, in
particular
of
(perfluoroorgano)hydroxyborate
and
(perfluoroorgano)alkoxyborate salts, is still scarcely investi-
gated. Although three-coordinated boron parent com-
pounds like pentafluorophenylboronic acid [3, 4],
tris(pentafluorophenyl)boroxine [4], bis(pentafluorophenyl)-
borinic acid [3, 5, 6], bis(pentafluorophenyl)alkoxyboranes
[7], and trifluorovinyldialkoxyboranes [8Ϫ10] were isolated
and described, very little is known about the reactivity of
the related (perfluoroorgano)alkoxyborates. In 2000 we
have found that a mixture of (pentafluorophenyl)(alkoxy)-
borate
salts
M[(C6F5)nB(OAlk)4Ϫn
]
and boranes
(C6F5)nB(OAlk)3Ϫn (n ϭ 1, 2; M ϭ Li, MgBr) were formed
when C6F5M was reacted with B(OAlk)3 in diethyl ether
[11]. Later lithium (perfluoroalk-1-enyl)trimethoxyborates
[8, 12, 13], bis(trifluorovinyl)dimethoxyborate and tris(tri-
fluorovinyl)methoxyborate [9] were characterized in solu-
tion by NMR spectroscopy. In 2001 the isolation of lithium
In a previous paper [1] we have reported the palladium-
catalysed cross-coupling reaction of lithium (polyfluoro-
phenyl)trimethoxyborates with 4-fluoroiodobenzene. In the
course of our systematic investigations on polyfluoro-
organoboron-oxygen compounds, actually we studied un-
known reactivities of lithium (pentafluorophenyl)tri-
methoxyborate Li[C6F5B(OMe)3] (1a) towards selected elec-
trophiles and nucleophiles.
* Prof. Dr. H.-J. Frohn
Fachbereich Chemie der Universität
Lotharstr. 1
D-47048 Duisburg
Fax: (ϩ49)2 03-379 22 31
e-mail: frohn@uni-duisburg.de
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DOI: 10.1002/zaac.200500083
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Polyfluoroorganoboron-Oxygen Compounds. 4
Results and Discussion
yield of only 3 % besides trimethoxyborane (56 %) and
pentafluorobenzene (4 %) (Scheme 2).
Preparation of lithium
pentafluorophenyltrimethoxyborate
Organotrimethoxyborate salts, M[RB(OMe)3] [18] were
principally obtained by the reaction of organometallic com-
pounds, RM (M ϭ Li, MgHal), with trimethoxyboranes.
But usually this reaction is accompanied by more or less
amounts of bis- and trisorganomethoxyborates [18]. The
formation of these undesired by-products depends inter alia
on the nature of the metal and the organo group in RM,
on reaction conditions (the order of mixing the reagents),
the nature (coordination properties) of the solvent, and the
methoxy elimination tendency of the organotrimethoxy-
borate [RB(OMe)3]Ϫ anion [18].
Scheme 2
Hydrodeboration and halodeboration of 1a
Salts M[RB(OAlk)3] (R ϭ hydrocarbon group [20]) are
stable towards hydrodeboration (formal displacement of the
B(OAlk)3 group by hydrogen) in protic organic solvents. In
contrast, salt 1a underwent easily replacement of the tri-
methoxyboron group by hydrogen in protic solvents. The
dissolution of 1a in ethylene glycol at 20 °C was ac-
companied by the spontaneous formation of pentafluoro-
benzene. In CH3OD as well as in CD3C(O)CD3 deutero-
We obtained the title compound, lithium pentafluoro-
phenyltrimethoxyborate, by the reaction of pentafluoro-
phenyllithium and trimethoxyborane [1].
pentafluorobenzene was obtained in
a fast reaction
(Scheme 3). The by-products which resulted from the sol-
vent after deuterium abstraction were not investigated. Un-
expectedly, pentafluorobenzene was the only polyfluoroaro-
matic product in the reaction of 1a with both CH3CN and
CD3CN (Scheme 4). The proton of C6F5H in the reaction
of 1a with CD3CN must originate from the methoxy group
of the borate anion of 1a. The formation of C6F5D or
C6F5H in Scheme 3 or 4 seems to result from a radical
reaction as can be concluded from the observation of the
chemically induced dynamic nuclear polarisation effect
(CIDNP) in a low field (75.39 MHz) 19F NMR experiment
with 1a in methanol.
Scheme 1
To avoid the formation of polyorganomethoxyborates
(mainly lithium bis(pentafluorophenyl)dimethoxyborate),
the cold solution of C6F5Li in ether was added to the
cooled solution (Ϫ78 °C) of trimethoxyborane in pentane.
The combination of low temperature and weak polarity of
the solvent allowed to suppress the [MeO]Ϫ elimination un-
der formation of C6F5B(OMe)2, the key intermediate for
the introduction of a second C6F5 group. C6F5B(OMe)2 can
also result from 1a by elimination of Li[OMe] in interac-
tions with B(OMe)3, present in excess. The target product
1a was isolated in 75 % yield.
Scheme 3
Salt 1a is a white moisture sensitive powder, soluble
in CH2Cl2 (ca. 1 mmol/mL). The viscous CH2Cl2 solution
of 1a is stable for some days at room temperature and con-
tains no ether coordinated at Liϩ (1H NMR). 1a did not
Scheme 4
possess
a reversible melting point. At 110 Ϫ 115 °C
Li[C6F5B(OMe)3] 1a was irreversibly transformed into a
glass-like material, which had not been studied in detail.
The treatment of 1a in CH2Cl2 with bromine gave
bromopentafluorobenzene (93 % yield) besides C6F5H
(trace) (Scheme 5). Under similar conditions, the reaction
of 1a with iodine proceeded more slowly (86 % conversion)
and resulted in only 30 % of C6F5I and 56 % of penta-
fluorobenzene. Iodopentafluorobenzene became the major
product when the reaction was performed in toluene but
here it took more than 30 days until 1a was completely con-
sumed.
Thermal decomposition of 1a
In 1986 Brown et al described the preparation of alkyldiiso-
propylboranes and phenyldiisopropylborane by the thermal
decomposition of the corresponding lithium organotriiso-
propoxyborates in the solid state [19]. They have found that
the stability of the lithium organyltriisopropoxyborates de-
pended on both, steric and electronic factors, and that a
phenyl group stabilises the borate salt more than an alkyl
group. In contrast, the thermolysis of 1a at 150 Ϫ 170 °C
in vacuum gave a volatile fraction which consisted of a mix-
ture of pentafluorophenyldimethoxyborane in the very low
Scheme 5
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N. Yu. Adonin, V. V. Bardin, U. Flörke, H.-J. Frohn
Abstraction of one methoxy group from 1a
Unexpected results were obtained in the attempted meta-
thesis of the lithium cation in 1a by potassium or tetra-
butylammonium. Thus, the cation exchange of lithium by
tetrabutylammonium with [Bu4N]Br in CH2Cl2 and the
subsequent reaction with 48 % HF yielded preferentially
tetrabutylammonium bis(pentafluorophenyl)difluoroborate
(4b) (73 %) whereas desired tetrabutylammonium penta-
fluorophenyltrifluoroborate (3b) turned out to be only the
minor product (22 % yield) besides traces of C6F5H
(19F NMR) (Scheme 10).
Lithium pentafluorophenyltrimethoxyborate reacted with
Me3SiCl in dichloromethane analogous to the related salts
Li[CF2ϭCFB(OMe)3] [8] and M[CnF2nϩ1B(OR)3] (M ϭ K,
[Me4N]; n ϭ 1, 2; R ϭ Me, Et) [16] and formed a solution
of pentafluorophenyldimethoxyborane (Scheme 6). The use
of more volatile trichlorofluoromethane instead of CH2Cl2
facilities the isolation of pure borane C6F5B(OMe)2.
Scheme 6
Scheme 10
The reaction of Li[C6F5B(OMe)3] with BF3 in non-polar
pentane combined the [MeO]Ϫ abstraction and the meth-
oxy-fluorine substitution and provided C6F5BF2 as soluble
product in 60 % yield (Scheme 7). The insoluble by-pro-
ducts were not investigated.
Similarly, the heterogeneous reaction of 1a with KF in
CH2Cl2 gave mainly K[(C6F5)2B(OMe)2] (2c) (61 %). The
desired salt K[C6F5B(OMe)3] (1c) was the minor product
(16 %) besides C6F5H (13 %) (Scheme 11).
Scheme 7
Scheme 11
The interaction of solid lithium pentafluorophenyltrime-
thoxyborate with aqueous hydrochloric acid resulted in the
formation of pentafluorophenyldihydroxyborane (penta-
fluorophenylboronic acid) (Scheme 8).
Borates 1c and 2c were not isolated from the mixture.
Their anions were characterised by H, 11B, and 19F NMR
1
spectroscopy and the absence of the Liϩ cation by 7Li
NMR. Finally 1c and 2c were converted into 3b and 4b by
a chemical transformation, the substitution of methoxy by
fluorine, using aqueous [Bu4N][HF2] (Scheme 12).
Scheme 8
It is noteworthy, that the yield of pentafluorophenyl-
boronic acid depended strongly on the reaction conditions
(order of mixing of the components and intensity of stir-
ring). Thus, the addition of aqueous HCl to solid 1a with-
out stirring resulted in a low yield of C6F5B(OH)2 besides
C6F5H as main product. Alternatively, the quick addition
of solid 1a to a vigorously stirred aqueous HCl affords the
target product in 86 % yield.
Scheme 12
It is important to note, that the molar ratio of the pro-
ducts 3b : 4b was equal to the molar ratio 1c : 2c of the start-
ing material (Scheme 12). That means that the acidic meth-
oxy-fluorine conversion (Scheme 12) was not accompanied
by a further dismutation of the anion [C6F5BX3]Ϫ (X ϭ
OMe or F). In contrast, under non-acidic conditions the
interaction (Schemes 11 and 10) of FϪ and BrϪ with Liϩ in
1a as cation of high charge density seems to break intensive
contacts of Liϩ to the basic oxygen sites in 1 (see such
Liϩ···oxygen contacts later in the molecular structure of 2d)
and induces the metathesis of 1a. To prove how far the in-
teraction of an uncharged base with Liϩ also makes the
dismutation of anion 1 possible we investigated the effect
of such basic ligands on 1a and used 19F NMR spec-
troscopy for monitoring the dismutation process. Solutions
of 1a in dichloromethane were treated with n equivalents of
O- and N-ligands (diethylether, THF) inter alia the chelat-
ing ligands (DME, TMEDA). The resulting solutions were
kept at 20 °C (time is given in Tab. 1) before fluorodemeth-
oxylation of the products was performed with [Bu4N][HF2]
Dismutation of the [C6F5B(OMe)3]؊ anion
In an earlier paper [11], we have reported the synthesis of
K[C6F5BF3] by pentafluorophenylation of B(OAlk)3 with
C6F5M (M ϭ Li, MgBr) and subsequent reaction of the
mixture of M[C6F5B(OAlk)3] and C6F5B(OAlk)2 with an
aqueous solution of K[HF2] (in excess). Similarly, salt 1a
was reacted with a solution of K[HF2] or [Bu4N][HF2] in
aqueous HF and yielded the corresponding pentafluoro-
phenyltrifluoroborate salts (Scheme 9).
Scheme 9
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Polyfluoroorganoboron-Oxygen Compounds. 4
(excess) in aqueous HF. Fluorodemethoxylation allowed the
quantitative identification of the monoϪ and bis(pentafluo-
rophenyl)borate anions by 19F NMR spectroscopy
(Scheme 13).
was formed in 63 % yield and K[C6F5BF3] was only the
minor product (Scheme 14).
Scheme 14
While the treatment of solid Li[C6F5B(OMe)3] with aque-
ous HCl resulted in C6F5B(OH)2 (Scheme 8), the reaction
of 1a Ϫ dissolved in DME Ϫ with aqueous HCl gave only
a trace of pentafluorophenylboronic acid. Bis(pentafluoro-
phenyl)borinic acid was the major product (Scheme 15).
Scheme 13
The checking reaction of 1a with [Bu4N][HF2] in the ab-
sence of the coordinating ligand showed only a negligible
amount of 2 % of 4b deriving from [(C6F5)2B(OMe)2]Ϫ ini-
tially present in 1a (Table 1, entry 1). However, salt 4b be-
came the predominant product when 1 equivalent of DME
was added to 1a followed by the treatment with
[Bu4N][HF2] (Table 1, entry 2). The addition of two or three
equivalents of DME affected only slightly the relative molar
ratio 3b : 4b (Table 1, entries 3, 4). Prolongation of the
reaction time with the ligand from 15 to 60 min decreased
the amount of 3b to 7 %, and increased the amount of 4b
to 88 % (Table 1, entries 5, 6). The reaction with THF (3
equivalents) instead of DME affected a lower conversion of
[C6F5B(OMe)3]Ϫ into [(C6F5)2B(OMe)2]Ϫ (Table 1, entry 7).
Significant less dismutation proceeded when 1a was treated
with diethyl ether. The pentafluorophenyltrifluoroborate
anion 3 was the major product after fluorodemethoxylation
(Table 1, entry 8). The fact, that in all cases C6F5H was
only formed in a low yield, allowed to neglect the influence
of hydrodeboration on the molar ratio 3b : 4b.
Scheme 15
An interesting result was obtained in the course of
the titration of 1a with TMEDA in CH2Cl2 at 32 °C
(Table 2). A fast conversion of [C6F5B(OMe)3]Ϫ (1) to
[(C6F5)2B(OMe)2]Ϫ (2) and [B(OMe)4]Ϫ occurred already
when catalytic amounts (0.11 to 0.60 equiv) of the chelating
reagent were added (Table 2, entries 2 Ϫ 6). When larger
amounts (0.72 Ϫ 2.20 equiv) of TMEDA were used
(Table 2, entries 7 Ϫ 13) only traces of anion 1 were de-
tected. Parallel to the dismutation, a remarkable change of
the 19F NMR shift values of both anions 1 and 2 took
place. The resonance of the ortho-fluorine atoms underwent
a significant deshielding effect (∆δ ϭ 7.2 (1) and 7.9
(2) ppm) whereas the resonances of the meta- and para-fluo-
rine atoms moved in opposite direction [∆δ ϭ Ϫ2.3 ppm
(1 and 2, F3,5) and ∆δ ϭ Ϫ3.4 ppm (1, F4) and ∆δ ϭ
Ϫ2.4 ppm (2, F4)]. The latter shifts can be interpreted by
an increase of the negative charge on the pentafluorophenyl
group for both anions 1 and 2 when going from
Li[(C6F5)nB(OMe)4Ϫn] to [Li(TMEDA)m][(C6F5)nB(OMe)4Ϫn
(Table 3). Li-salts with the anions 1 and 2 in CH2Cl2 in
]
Table 1 The reaction of 1a with ethers (DME, THF, diethyl ether,
n equiv) in CH2Cl2 followed by the substitution of methoxy by
fluorine
Table 2 The dismutation of the [C6F5B(OMe)3]Ϫ anion (1) to
[(C6F5)2B(OMe)2]Ϫ (2) and [B(OMe)4]Ϫ monitored by 19F NMR in
the system Li[C6F5B(OMe)3] (1a) / CH2Cl2 / TMEDA
Yield (%)
Entry
ether (equiv)
Time (min)
3b
4b
C6F5H
TMEDA 1
2
Ratio
1
2
3
4
5
6
7
8
4
95
26
22
19
11
7
2
63
72
76
85
88
68
25
3
11
6
5
4
5
4
3
1a)
2a)
3a)
3a)
3a)
3b)
3c)
15
15
15
30
60
60
60
Entry (equiv) δ (F2, 6
)
δ (F4) δ (F3,5
)
δ (F2, 6) δ (F4) δ (F3,5
)
1 : 2
1
2
3
4
5
6
7
8
0
Ϫ143.9 Ϫ158.9 Ϫ163.9 Ϫ144.6 Ϫ159.2 Ϫ163.9 >98 : 2
Ϫ143.5 Ϫ159.2 Ϫ164.1 Ϫ140.8 Ϫ160.6 Ϫ165.3 58 : 42
Ϫ143.1 Ϫ159.5 Ϫ164.3 Ϫ139.5 Ϫ161.6 Ϫ165.7 36 : 64
Ϫ142.2 Ϫ159.9 Ϫ164.7 Ϫ138.1 Ϫ161.4 Ϫ166.0 23 : 77
Ϫ140.4 Ϫ160.8 Ϫ165.4 Ϫ137.2 Ϫ161.7 Ϫ166.2 16 : 84
Ϫ138.5 Ϫ161.7 Ϫ166.2a) Ϫ136.9 Ϫ161.2 Ϫ166.2 11 : 89
Ϫ137.6 Ϫ161.9 Ϫ166.2a) Ϫ136.8 Ϫ161.7 Ϫ166.2 2 : 98
Ϫ137.2 Ϫ162.1 Ϫ166.2a) Ϫ136.8 Ϫ161.7 Ϫ166.2 2 : 98
Ϫ137.0 Ϫ162.2 Ϫ166.2a) Ϫ136.7 Ϫ161.7 Ϫ166.3 2 : 98
Ϫ136.5 Ϫ162.2 Ϫ166.2a) Ϫ136.7 Ϫ161.6 Ϫ166.2 2 : 98
Ϫ136.7a) Ϫ162.3 Ϫ166.2a) Ϫ136.7 Ϫ161.6 Ϫ166.2 2 : 98
Ϫ136.7a) Ϫ162.3 Ϫ166.2a) Ϫ136.7 Ϫ161.6 Ϫ166.2 2 : 98
Ϫ136.7a) Ϫ162.3 Ϫ166.2a) Ϫ136.7 Ϫ161.6 Ϫ166.2 2 : 98
0.11
0.21
0.31
0.48
0.60
0.72
0.84
1.10
1.20
1.35
1.60
2.20
28
72
a) DME, b) THF, c) Diethyl ether.
9
The dismutation of anion 1 was also observed when a
solution of 1a in DME was subsequently treated with
K[HF2] in HFaq. Again the substitution of methoxy by
fluorine in 1a (Scheme 9) was not the main reaction
channel. Potassium bis(pentafluorophenyl)difluoroborate
10
11
12
13
a) The signal of 1 interfered with the corresponding signal of 2.
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N. Yu. Adonin, V. V. Bardin, U. Flörke, H.-J. Frohn
Table 3 The 19F NMR spectra of M[(C6F5)nB(OMe)4Ϫn] and
K[(C6F5)nBF4Ϫn] (n ϭ 1, 2)
with a sum of angles at both oxygen atoms of 359.68 and
359.63°, respectively. The cyclic unit B(1)-O(1)-Li(1)-O(2) is
planar with
a deviation from the best plane of
δ (F) (ppm)
B(1) Ϫ0.029(2), O(1) 0.023(1), Li(1) Ϫ0.018(3), and O(2)
0.024(1).
Compound
Solvent F2,6
F4
F3,5
BF
a)
Li[C6F5B(OMe)3]
K[C6F5B(OMe)3]
CH2Cl2 Ϫ143.9 Ϫ158.8 Ϫ163.8
CH2Cl2 Ϫ143.7 Ϫ159.8 Ϫ164.5
CH2Cl2 Ϫ142.1 Ϫ160.0 Ϫ164.4
CH2Cl2 Ϫ136.5 Ϫ162.2 Ϫ166.2
CD3OD Ϫ134.7 Ϫ160.7 Ϫ165.7 Ϫ134.7
CH2Cl2 Ϫ135.7 Ϫ161.5 Ϫ166.2 Ϫ134.1
CH2Cl2 Ϫ144.6 Ϫ159.2 Ϫ163.9
Table 4 Crystallographic and refinement data for 2d
[Bu4N][C6F5B(OMe)3]
[Li(TMEDA)][C6F5B(OMe)3]
b)
Sum formula
Crystal system
Space group
C20H22BF10LiN2O2
monoclinic
K[C6F5BF3]
[Bu4N][C6F5BF3]
P 21/c
a ϭ 9.8416(7) A
b ϭ 16.250(1) A
c ϭ 15.085(1) A
Li[(C6F5)2B(OMe)2]
K[(C6F5)2B(OMe)2]
[Bu4N][(C6F5)2B(OMe)2]
˚
˚
˚
˚
Lattice param.
CH2Cl2 Ϫ143.1 Ϫ160.2 Ϫ164.7
CH2Cl2 Ϫ138.8 Ϫ161.2 Ϫ165.6
β ϭ 102.040(1)°
[Li(TMEDA)][(C6F5)2B(OMe)2] CH2Cl2 Ϫ136.7 Ϫ161.7 Ϫ166.2
3
V ϭ 2359.5(3) A
K[(C6F5)2BF2]
[Bu4N][(C6F5)2BF2]
MeOH Ϫ135.5 Ϫ160.7 Ϫ165.5 Ϫ145.8
CH2Cl2 Ϫ136.7 Ϫ161.9 Ϫ166.5 Ϫ139.0
T / K
Z
150(2)
4
1.492
0.148
Density (calc.) / g cmϪ3
Absorption coeff. / mmϪ1
F(000)
a) Ref [1], b) Ref [11].
1080
0.20 x 0.20 x 0.15
Bruker AXS SMART APEX
MoKα (λ ϭ 0.71073 A)
the absence of coordinating ligands can be described by the
model of contact ion pairs where the lithium cation is coor-
dinated by the oxygen atoms of the B(OMe)n fragment of
Crystal size / mm3
Diffractometer
Radiation
˚
Theta range for data collection 1.86 to 28.31°
Index ranges
Reflections collected
Independent reflections
Absorption correction
Refinement method
the [(C6F5)nB(OMe)4Ϫn]
Ϫ anions. Thus the 19F NMR spec-
Ϫ13<h<11, Ϫ18<k<20, Ϫ20<l<19
14923
5532 (Rint ϭ 0.039)
semi-empirical from equivalents
full-matrix least-squares on F2;
all but H-atoms anisotropically; H-atoms riding
5532 / 331
tra reflected the actual equilibrium depending on the
amount of TMEDA between the contact ion pairs
Li[(C6F5)nB(OMe)4Ϫn] and the free ions [Li(L)m]ϩ and
Ϫ
[(C6F5)nB(OMe)4Ϫn
] (n ϭ 1, 2).
Data / parameters
The preparative scale reaction of Li[C6F5B(OMe)3] with
TMEDA (1.5 equivalent) in CH2Cl2 provided the salt [Li-
(TMEDA)][(C6F5)2B(OMe)2] (2d) which was isolated
(Scheme 16) and structurally characterised by X-ray single
crystal diffraction (Figure 1).
Final R indices [21]
Min./max. height in ∆F-map
Programs used [21]
R1 (I>2σ(I)) ϭ 0.041, wR2 (all data) ϭ 0.067
Ϫ0.16/0.20 e A
SMART, SAINT, SADABS, SHELXTL
Ϫ3
˚
Scheme 16
The molecular structure of 2d
Single crystals of [Li(TMEDA)][(C6F5)2B(OMe)2] (2d) were
obtained from a CH2Cl2 solution of 1a and 1.3 equiv
TMEDA after diffusion of pentane at Ϫ78 °C over 3 weeks.
2d crystallises in the monoclinic crystal system, space group
P2(1)/c with 4 molecules per unit cell (for crystallographic
and refinement data [21] see Table 4). Both centres of mole-
cule 2d, B and Liϩ, contain a distorted tetrahedral en-
vironment and are connected by two methoxy bridges. In
the borate subunit the O(1)-B(1)-O(2) angle with 99.48(13)°
deviates significantly from the opposite C(11)-B(1)-C(21)
angle, from the four O-B-C angles, and the tetrahedral ang-
le. Even the presence of two electron-withdrawing C6F5
groups in 2d does not hinder that major quantities of the
total charge of the borate anion are located on the oxygen
atoms O(1) and O(2). This location of charge give rise to
the contact with Liϩ. Both atoms O(1) and O(2) are tri-
gonal planar coordinated by one methyl group, B, and Liϩ
˚
Figure 1 The molecular structure of 2d with selected distances/A
and angles/°:
B(1)-O(2) 1.465(2), B(1)-O(1) 1.467(2), B(1)-C(21) 1.664(3), B(1)-C(11)
1.664(2), Li(1)-O(2) 1.897(3), Li(1)-O(1) 1.916(3), Li(1)-N(2) 2.067(3), Li(1)-
N(1) 2.080(3), O(2)-B(1)-O(1) 99.48(13), O(2)-B(1)-C(21) 109.59(14), O(1)-
B(1)-C(21) 113.08(15), O(2)-B(1)-C(11) 113.21(15), O(1)-B(1)-C(11)
108.33(14), C(21)-B(1)-C(11) 112.50(14), O(2)-Li(1)-O(1) 71.88(11), O(2)-
Li(1)-N(2) 124.89(17), O(1)-Li(1)-N(2) 119.89(16), O(2)-Li(1)-N(1)
123.58(17), O(1)-Li(1)-N(1) 134.42(18), N(2)-Li(1)-N(1) 87.75(12)
2642
 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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Z. Anorg. Allg. Chem. 2005, 631, 2638Ϫ2646

Polyfluoroorganoboron-Oxygen Compounds. 4
The coordination of the neutral oxygen and nitrogen
(µ-OMe)B(OMe)2C6F5]Ϫ which allows the migration of
both, the aryl and methoxy group (Scheme 17).
basic centres at Liϩ differ strongly. In contrast to Li···N
˚
distances of average 2.074(3) A the Li···O distances are
˚
shorter with average 1.907(3) A and accompanied by a very
small O(1)-Li-O(2) angle of 71.88(11)°. The combination of
both, the short distances and the embedded angle express
in addition to the above mentioned argument, the strong
electrostatic interaction of Liϩ to both alkoxy groups.
We compared the structural features of 2d with structural
information known from related compounds. In 2002 Klis
et al [15] published the structure of a related magnesium
borate salt, the dimer {[BrMg(OEt2)][(C6F5)2B(µ-OEt)2]}2
with a rhombohedral Mg2Br2 unit. Both boron and mag-
nesium bridging ethoxy groups of the borate anion formed
an O-Mg-O angle of 66.73(12)° and an O-B-O angle of
96.6(4)°. The C-B-C angle in the borate anion was deter-
mined to 114.5(4)°. In 1989 Eaborn et al [22] had reported
the structure of the lithium tetramethoxyborate salt,
(MeOH)2Li(µ-OMe)2B(OMe)2, and had found that the
O-B-O angle formed by the bridging methoxy groups and
the opposite O-B-O angle formed by the terminal methoxy
groups, both with 103.6(8) and 100.8(8)°, respectively, were
smaller than the tetrahedral angle. The bridging methoxy
groups established with Liϩ an O-Li-O angle of 71.1(8)°
Scheme 17
It is important to mention that the anion
[(C6F5)2B(OMe)2]Ϫ did not undergo a further dismutation.
The anion [(C6F5)2B(OMe)2]Ϫ is stabilised towards [MeO]Ϫ
elimination by the higher Lewis acidity of (C6F5)2BOMe
relative to C6F5B(OMe)2.
Previously we have shown that the addition of C6F5MgBr
or C6F5Li to B(OAlk)3 (Alk ϭ Me, Pr, iϪPr) (in excess) in
diethyl ether gave a mixture of (pentafluorophenyl)alkoxy-
borate
salts M[(C6F5)nB(OAlk)4Ϫn
]
and
boranes
(C6F5)nB(OAlk)3Ϫn (n ϭ 1, 2; M ϭ Li, MgBr) [11]. Even
when B(OEt)3 was reacted with a fourϪfold excess of
C6F5MgBr, exclusively the borate [BrMg(OEt2)]-
[(C6F5)2B(m-OEt)2] was formed while tris(pentafluoro-
phenyl)ethoxyborate and tetrakis(pentafluorophenyl)borate
salts were not detected [15]. Attempts of further arylation
of [BrMg(OEt2)][(C6F5)2B(µ-OEt)2] with C6F5MgBr as well
as with C6F5Li or C6H5Li were precluded by the kinetic
stability of the borate anion [(C6F5)2B(OEt)2]Ϫ in combi-
nation with the [BrMg]ϩ cation (no dissociation to electro-
philic borane (C6F5)2BOEt and BrMgOEt in ether at 35 °C)
(11B NMR) [15].
The relative stability of Li[C6F5B(OMe)3] in CH2Cl2 with
respect to dismutation under formation of the anions 2 and
[B(OMe)4]Ϫ can be explained by the coordination of meth-
oxy groups of anion 1 to the electrophilic lithium cation
which hinders the elimination of the methoxy anion.
Ligands with a better coordination property than the
µ-OMe ligand when added to 1a break the Liϩ-anion inter-
action and in a following step the separated anion 1 is able
to eliminate a [OMe]Ϫ anion. Interaction of C6F5B(OMe)2
with anion 1 results in the dinuclear anion mentioned above
which affords dismutation.
˚
with an O···Li distance of 1.96(2) A.
The N(1)-Li(1)-N(2) bite angle of TMEDA in 2d of
87.75(12)° is directly comparable to those found in
[Li(TMEDA)Cl]2 [23] [87.0(2)°], [Li(TMEDA)2][MnMe4]
[24] [87.2(2) and 87.5(2)°], and [Li(THF)2(TMEDA)2]-
[Ph2PTe] [25] [88.8(2)°] whereas the Li···N distances in 2d
˚
[average 2.074(3) A] tend to be shorter than those in
˚
[Li(TMEDA)Cl]2 [average 2.110(6) A] or [Li(THF)2-
˚
˚
(TMEDA)2][Ph2PTe] [average 2.093(6) A]; those in
[Li(TMEDA)2][MnMe4] [average 2.133(6) A] are signifi-
cantly longer.
Both pentafluorophenyl group in the borate anion of
2d show the expected C-B distance of 1.664(3) and a very
small C-C-C angle at the ipso-carbon atoms of 111.92(16)
and 112.40(16)° which is in the same range as in the
[B(C6F5)4]Ϫ anion [26] [average 113.3(10)°] or in
{[BrMg(OEt2)][(C6F5)2B(µ-OEt)2]}2 [15] [average 112.6(5)°].
This small angle is indicative of pentafluorophenyl groups
bearing remarkable negative partial charge.
In contrast to 1a, salts such as lithium pentafluoroethyl-
trimethoxyborate and related perfluoroalkyltrialkoxybor-
ates Li[(EtO)2P(O)CF2B(OMe)3], and M[CnF2nϩ1B(OAlk)3]
(M ϭ Li, K, [Me4N]; n ϭ 1, 2; Alk ϭ Me, Et) [14, 16]
exhibited no dismutation in diethyl ether, THF, acetone,
DME, and MeOH due to the high kinetic stability of their
anions which is caused by the very high acidity of their
conjugated perfluoroalkyldialkoxyboranes.
Conclusions
The initial step of the dismutation of the [C6F5B(OMe)3]Ϫ
anion to [(C6F5)2B(OMe)2]Ϫ and [B(OMe)4]Ϫ can princi-
pally include the elimination of the methoxy or the penta-
fluorophenyl group from [C6F5B(OMe)3]Ϫ. Formally the
borate anion [(C6F5)2B(OMe)2]Ϫ is the addition product of
borane C6F5B(OMe)2 and the carbanion [C6F5]Ϫ. But
the latter cannot be involved in the dismutation as a free
species. Otherwise C6F5H is expected to be the favoured
product. Therefore we propose a dinuclear methoxy-
bridged borate intermediate such as [C6F5B(OMe)2-
Experimental
The NMR spectra were recorded on the Bruker spectrometers
AVANCE 300 (1H at 300.13 MHz, 19F at 282.40 MHz, 7Li at
116.59 MHz, 11B at 96.29 MHz) and WP 80 SY (1H at 80.13 MHz,
19F at 75.39 MHz). The chemical shifts are referenced to TMS
(1H), CCl3F (19F) with C6F6 as a secondary reference, δ ϭ Ϫ162.9,
Z. Anorg. Allg. Chem. 2005, 631, 2638Ϫ2646
zaac.wiley-vch.de
 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
2643

N. Yu. Adonin, V. V. Bardin, U. Flörke, H.-J. Frohn
BF3 · OEt2/CDCl3 15 % v/v (11B), and 1 m LiBr in D2O (7Li). The
composition of the reaction mixtures and the yields of products
were determined by 1H or 19F NMR spectroscopy using the quanti-
tative standard C6H5CF3.
C6H5CF3 (5 µL, 0.041 mmol) was added as quantitative standard.
The 19F NMR spectrum showed 98 % conversion of 1a and the
formation of C6F5I (0.30 mmol, 30 %) and C6F5H (0.56 mmol,
56 %).
Toluene (Aldrich) and B(OMe)3 (Fluka) were distilled over sodium.
Dichloromethane (Baker), pentane (Riedel-de Hae¨n) and aceto-
nitrile (Riedel-de Hae¨n) were distilled over P4O10 and stored over
B. A suspension of iodine (51 mg, 0.20 mmol) in toluene (0.4 mL)
which contained the quantitative standard C6H5CF3 (4.1 µL,
0.034 mmol) was added to solid 1a (28 mg, 0.1 mmol). The suspen-
sion was stirred in a closed FEP trap at 20 °C for 30 days until 1a
was consumed. The 19F NMR spectrum showed the formation of
C6F5I (0.054 mmol, 54 %) and C6F5H (0.034 mmol, 34 %).
˚
molecular sieve (3 A). Trichlorofluoromethane was stored over mo-
˚
lecular sieve (3 A). DME (Aldrich) was distilled over Li[AlH4] and
stored under an atmosphere of dry argon. Acetonitrile-d3 (Ald-
rich), CH3OD (Aldrich) and acetone-d6 (Aldrich) were stored over
˚
molecular sieve (3 A) and the absence of H2O was controlled by
1H NMR. Iodine (Merck) was finely crushed and stored in a
desiccator over Sicapent. Bromine (Riedel-de Hae¨n), TMEDA
(Aldrich), 48 % HF (Fluka), boron trifluoride (Messer Griesheim),
K[HF2] (Riedel-de Hae¨n), 40 % [Bu4N]OH (Sachem Inc.),
[Bu4N]Br (Fluka), anhydrous diethyl ether (Baker) and KF (spray-
dried, Morita) were used as supplied. All manipulations with lith-
ium pentafluorophenyltrimethoxyborate were performed in FEP
(block copolymer of tetrafluoroethylene and hexafluoropropylene)
equipment under an atmosphere of dry argon. The preparation of
salt 1a was described in paper [1]. Boranes C6F5B(OH)2 [4],
(C6F5)2BOH [5], C6F5B(OMe)2 [11], C6F5BF2 [11], and borates
M[C6F5BF3] [11] and M[(C6F5)2BF2] [11] were identified by
19F NMR spectroscopy.
Reaction of 1a with Me3SiCl in CH2Cl2
A suspension of 1a (280 mg, 1 mmol) in CH2Cl2 (3 mL) and Me3Si-
Cl (0.2 mL, 172 mg, 1.6 mmol) was stirred at 25 °C for 1 h. The
suspension was centrifuged, the mother liquor was decanted. The
19F NMR spectrum of the liquid phase showed the presence of
C6F5B(OMe)2 (48 % yield) besides C6F5H (1 % yield).
Reaction of 1a with Me3SiCl in CCl3F
A 50 mL three-necked flask equipped with an inlet tube for dry
argon, a septum inlet, a magnetic stirring bar, and a reflux con-
denser with a bubble counter on top, was charged with 1a (2.80 g,
10 mmol) and anhydrous CCl3F (25 mL) before Me3SiCl (2 mL,
1.72 g, 1.6 mmol) was added by a syringe. The suspension was
stirred at 20 °C. 19F NMR monitoring displayed the formation of
C6F5B(OMe)2 in 11 % yield (after 1 h) and 72 % (after 2 days).
CCl3F was removed at 25 °C under reduced pressure. Pentafluoro-
phenyldimethoxyborane (0.83 g, 35 %; a moisture sensitive colour-
less oil, bp 82 Ϫ 83 °C at 42 mbar) was obtained by distillation
in vacuum.
Thermolysis of Li[C6F5B(OMe)3]
Two 100 mL round bottomed flasks were connected by a glass tube
supplied with an outlet with a stopcock. The first flask with a mag-
netic stirring bar was charged with 2.8 g (10 mmol) of
Li[C6F5B(OMe)3]. The apparatus was evacuated (3·10Ϫ2 hPa) and
closed. The second flask was cooled with liquid nitrogen, and the
first one was heated to 150 Ϫ 170 °C (bath) for 3 h. At 120 °C,
Li[C6F5B(OMe)3] melted and formed a brown oil. Decomposition
began above 150 °C. The colourless distillate (0.700 g) contained
B(OMe)3 (5.6 mmol, 56 % yield), C6F5B(OMe)2 (0.25 mmol, 2.5 %
yield) and C6F5H (0.36 mmol, 3.6 % yield) (19F and 11B NMR).
C6F5B(OMe)2:
19F NMR (CH2Cl2): δ ϭ Ϫ132.8 (F2, 6), Ϫ153.8 (F4), Ϫ162.6 (F3,5).
3
4
3J(F2,F3) 22; J(F4,F3) 20; J(F4,F2) 2 Hz.
11B NMR (CH2Cl2): δ ϭ 26.1 (s, b).
MS: Calc. for C8H6BF5O: Mr 240.03811; Found: Mr 240.03269.
Reaction of 1a with BF3
Reaction of 1a with CH3OD or (CD3)2CO
Boron trifluoride (ca. 5 mmol) was bubbled into the stirred suspen-
sion of 1a (90 mg, 32 mmol) in pentane (2 mL) and C6H5CF3
(quantitative standard, 10 µL, 0.082 mmol) at Ϫ40 °C for 20 min.
Subsequently the reaction mixture was stirred at 10 to 15 °C for
15 min under the protection of dry argon to remove the excess of
BF3. After centrifugation the mother liquor was decanted. It con-
tained C6F5BF2 (60 % yield) (19F NMR).
Li[C6F5B(OMe)3] (30 mg, 0.11 mmol) was dissolved in anhydrous
CH3OD or (CD3)2CO (0.3 mL) After < 5 min the 19F NMR spec-
trum showed the quantitative formation of C6F5D as the only poly-
fluoroaromatic product.
Reaction of 1a with CH3CN, CD3CN and ethylene glycol
In a similar way Li[C6F5B(OMe)3] (30 mg, 0.11 mmol) reacted with
anhydrous CH3CN (0.3 mL) to give C6F5H as the only poly-
fluoroaromatic product (19F NMR). When CD3CN and ethylene
glycol were used instead of CH3CN, the same result was obtained.
C6F5BF2:
19F NMR (pentane, Ϫ30 °C): δ ϭ Ϫ74.0 (BF2); Ϫ129.3 (F2, 6),
Ϫ144.8 (F4), Ϫ162.2 (F3,5).
Reaction of 1a with aqueous HCl
Reaction of 1a with bromine
A. 3 ml of 5 % aqueous HCl were added to solid Li[C6F5B(OMe)3]
(280 mg, 1 mmol) and stirred at 20 °C for 20 min. The quantitative
standard C6H5CF3 (5 µL, 0.041 mmol) was added and the emulsion
was extracted with ether (3 x 10 mL). The 19F NMR analysis
showed the presence of C6F5B(OH)2 (0.12 mmol, 12 % yield) and
C6F5H (0.85 mmol, 85 % yield).
B. Solid Li[C6F5B(OMe)3] (1 g, 3.6 mmol) was quickly added to
stirred 5 % aqueous HCl (10 mL). The white suspension was stirred
at 20 °C for 1 h. C6H5CF3 (10 µL, 0.082 mmol) was added and the
reaction mixture was extracted with ether (3 x 10 mL). The 19F
NMR spectrum of the combined extracts showed the formation of
C6F5B(OH)2 in 87 % yield.
A solution of bromine (192 mg, 1.20 mmol) in CH2Cl2 (0.5 mL)
was added to a suspension of 1a (280 mg, 1 mmol) in CH2Cl2
(0.5 mL). After 2 h of stirring at 20 °C (closed FEP trap) the 19F
NMR spectrum (with C6H5CF3 as a quantitative standard) showed
the total consumption of 1a and the formation of C6F5Br
(0.93 mmol, 93 %) and C6F5H (0.02 mmol, 2 %).
Reaction of 1a with iodine
A. Dichloromethane (1 mL) was added to
Li[C6F5B(OMe)3] (280 mg, 1 mmol) with finely crushed iodine
(305 mg, 1.2 mmol). The mixture was stirred at 20 °C for 2 h.
a mixture of
2644
 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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Z. Anorg. Allg. Chem. 2005, 631, 2638Ϫ2646

Polyfluoroorganoboron-Oxygen Compounds. 4
Reaction of 1a with K[HF2] in aqueous HF
was stirred for 3 min, kept without stirring for 15 min and diluted
with water (1 mL). After additional 15 min, the organic phase on
bottom was separated and analysed by 19F NMR. The reactions of
1a with THF and diethyl ether were performed in a similar manner
(Table 1).
Solid 1a (1 g, 3.6 mmol) was added to a vigorously stirred solution
of K[HF2] (0.93 g, 11.9 mmol) and 48 % HF (1 mL) in water
(6 mL). The mixture was stirred at 20 °C for 4 h and neutralised
with solid K2CO3. The white precipitate was filtered and dried on
air before it was extracted with hot acetonitrile. The extract was
dried with MgSO4 and the solvent was removed under reduced
pressure to yield 0.24 g (24 %) of K[C6F5BF3] (19F and 11B NMR).
Reaction of 1a dissolved in DME with K[HF2] in aqueous HF
A solution of 1a (1 g, 3.6 mmol) in DME (2 mL) was stirred at
20 °C for 15 min and poured into a solution of K[HF2] (0.93 g,
11.9 mmol) and 48 % HF (1 mL) in water (6 mL). The suspension
was stirred at 20 °C for 4 h, diluted with water (40 mL), and filtered
to give the filter cake and filtrate A. The filter cake was washed
with water (10 mL), dried on air and then in a vacuum desiccator
over Sicapent overnight. Finally the dry solid was dissolved in
methanol (1 mL) and filtered. The filtrate was evaporated under
reduced pressure to give 0.44 g of K[(C6F5)2BF2] besides a small
admixture of K[C6F5BF3]. Filtrate A was neutralised with solid
K2CO3. The resulting precipitate was filtered and dried as de-
scribed above to give 130 mg of K[(C6F5)2BF2] and K[C6F5BF3] in
a molar ratio of 27 : 73 (19F NMR, in MeOH). The total yield
of K[(C6F5)2BF2] and K[C6F5BF3] was 0.475 g (63 %) and 0.095 g
(10 %), respectively.
Reaction of 1a with [Bu4N][HF2] in aqueous HF
A suspension of [Bu4N][HF2] (prepared from 40 % aqueous
[Bu4N]OH (1 mL, 1.53 mmol) and 48 % aqueous HF (1 mL,
28 mmol) was quickly added to a solution of salt 1a (280 mg,
1 mmol) in CH2Cl2 (1 mL). The two-phase system was shaken for
3 Ϫ 4 min before the quantitative standard C6H5CF3 (5 µL,
0.042 mmol) was introduced. After additional shaking, the reaction
mixture was allowed to stand for 30 min until the two phases were
separated. The organic phase on bottom contained
[Bu4N][C6F5BF3]
(0.95 mmol,
95 %),
[Bu4N][(C6F5)2BF2]
(0.01 mmol, 2 %), and C6F5H (0.03 mmol, 3 %) (19F NMR).
Reaction of 1a with [Bu4N]Br in CH2Cl2 and subsequent treatment
with aqueous HF
When dichloromethane (1 mL) was added to a mixture of solid
1a (280 mg, 1 mmol) and [Bu4N]Br (323 mg, 1 mmol) a solution
resulted. Within a few min the precipitation of LiBr occurred. The
suspension was stirred for further 7 min and then treated with 48 %
aqueous HF (1 mL). After 20 min of stirring the quantitative
standard C6H5CF3 (5 µL, 0.041 mmol) was added. The organic
phase on bottom was separated. Its 19F NMR spectrum showed the
anions of [Bu4N][(C6F5)2BF2] (0.73 mmol, 73 %), [Bu4N][C6F5BF3]
(0.22 mmol, 22 %) and additionally C6F5H (0.05 mmol, 5 %).
Reaction of 1a dissolved in DME with aqueous HCl
A solution of 1a (1 g, 3.6 mmol) in DME (2 mL) was stirred at
20 °C for 15 min and poured in 10 ml of concentrated aqueous
HCl. The acidic solution was stirred at 20 °C for 12 days in a closed
FEP trap. During this time, a white precipitate was formed. The
precipitate was filtered, and the mother liquor was extracted with
ether. The extract contained (C6F5)2BOH and C6F5B(OH)2 (yields
68 and 1.4 %, respectively) (19F NMR).
Reaction of 1a with TMEDA in CH2Cl2
Reaction of 1a with KF in CH2Cl2
Li[C6F5B(OMe)3] (27 mg, 0.1 mmol), C6H5CF3 (quantitative
standard, 4.1 µL, 0.034 mmol) and CH2Cl2 (0.30 mL) were charged
in a 3.5 mm i.d. FEP inliner and formed a clear solution. The thin
wall NMR tube with the inliner inside was placed in the probe
head of the NMR spectrometer (32 °C). After 10 min the first 19F
NMR spectrum was measured. TMEDA was added in portions
of 2 µL. After each addition a 19F NMR spectrum was measured
(Table 2).
1 ml of CH2Cl2 and 5 µL (0.041 mmol) of C6H5CF3 were added to
a mixture of 280 mg (1 mmol) of Li[C6F5B(OCH3)3] and 180 mg
(3.1 mmol) of KF placed in a 9 mm FEP trap under a dry argon
atmosphere. The suspension was stirred at 20 °C for 24 h. The
absence of Liϩ cations in the mother liquor was proved by 7Li
NMR. The 19F NMR spectra of the mother liquor showed the
presence of K[C6F5B(OCH3)3] (0.16 mmol, 16 % yield),
K[(C6F5)2B(OCH3)2] (0.30 mmol, 61 % yield) and C6F5H
(0.23 mmol, 23 % yield). The NMR probe was returned into the
reaction trap and the suspension was treated with [Bu4N][HF2]
(from 1 ml of 48 % HF and 1 ml of 40 % [Bu4N]OH) for 1 min.
The 1H, 19F and 11B NMR spectra of the dichloromethane solution
showed the presence of C6F5H (24 % yield), [Bu4N][C6F5BF3]
(14 % yield), and [Bu4N][(C6F5)2BF2] (62 % yield).
Crystals of [Li(TMEDA)][(C6F5)2B(OMe)2] (2d) for X-ray
structural analysis
1a (140 mg, 0.5 mmol) was suspended in dichloromethane
(0.5 mL). After addition of TMEDA (0.100 mL, 77 mg, 0.66 mmol)
a transparent solution was formed. In the 8 mm i.d. FEP tube a
phase of pentane (2 mL) was placed above the reaction solution.
The stoppered FEP tube was stored at Ϫ78 °C for 3 weeks. Crystals
of a quality sufficient for X-ray analysis were obtained.
K[C6F5B(OCH3)3] 1H NMR (CH2Cl2): δ ϭ 3.00. 11B NMR
(CH2Cl2): δ ϭ 3.1.
K[(C6F5)2B(OCH3)2] 1H NMR (CH2Cl2): δ ϭ 3.02. 11B NMR
(CH2Cl2): δ ϭ 2.0.
Acknowledgement. We gratefully acknowledge financial support by
the Deutsche Forschungsgemeinschaft, the Russian Foundation for
Basic Research, and the Fonds der Chemischen Industrie.
K[B(OMe)4] 11B NMR (CH2Cl2): δ ϭ 3.1.
Reaction of 1a with ethers (DME, diethyl ether or THF) in CH2Cl2
and subsequent substitution of methoxy by fluorine
Supporting Information. Details of the crystal structure investi-
gation and the crystallographic data for the structure reported in
this paper have been deposited with the Cambridge Crystallo-
graphic Data Centre as supplementary publication no. CCDC-
263131. Copies of the data can be obtained free of charge on appli-
cation to CCDC, 12 Union Road, Cambridge CB21EZ (Fax: (ϩ44)
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
Li[C6F5B(OMe)3] (280 mg, 1 mmol) was dissolved in CH2Cl2
(1 mL) and DME (n mmol) was added in one portion. The solution
was stirred at 20 °C for the time given in Table 1. Finally C6H5CF3
(quantitative standard, 5 µL, 0.041 mmol) and [Bu4N][HF2] (pre-
pared from 48 % HF (1 mL, 28 mmol) and 40 % [Bu4N]OH (1 mL,
1.53 mmol) were added one after the other. The two phase system
Z. Anorg. Allg. Chem. 2005, 631, 2638Ϫ2646
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 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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