A simple route to hexamethylguanidinium fluoride

Article abstract of DOI:10.1016/S0022-1139(99)00307-3

Tetramethylchloroformamidinium chloride reacts with 2mol equivalents of tetramethylammonium fluoride to give bis(dimethylamino)difluoromethane (1). The treating of 1 with dimethylaminotrimethylsilane in acetonitrile yields quantitatively hexamethylguanidinium fluoride (2). Reaction of 2 with (trifluoromethyl)trimethylsilane provides an easy access to 1,1,1-trifluoro-2,2,2-tris(dimethylamino)ethane (4).

Full text of DOI:10.1016/S0022-1139(99)00307-3

Journal of Fluorine Chemistry 103 (2000) 159±161
A simple route to hexamethylguanidinium ¯uoride
a,*
A.A. Kolomeitsev , G. Bissky , P. Kirsch , G.-V. R oÈ schenthaler
b
c
b
a
Institute of Organic Chemistry, Ukrainian National Academy of Sciences, Murmanskaya 6, 253660 Kiev-94, Ukraine
Institut f uÈ r Anorganische & Physikalische Chemie, Universit aÈ t Bremen, Leobener Strasse, D-28334 Bremen, Germany
b
c
MERCK KGaA, Liquid Crystals Division, Frankfurter Strasse 250, Darmstadt D-64293, Germany
Received 20 September 1999; accepted 16 November 1999
Dedicated to Prof. Manfred Meisel, on the occasion of his 60th birthday
Abstract
Tetramethylchloroformamidinium chloride reacts with 2 mol equivalents of tetramethylammonium ¯uoride to give bis(dimethylami-
no)di¯uoromethane (1). The treating of 1 with dimethylaminotrimethylsilane in acetonitrile yields quantitatively hexamethylguanidinium
¯uoride (2). Reaction of 2 with (tri¯uoromethyl)trimethylsilane provides an easy access to 1,1,1-tri¯uoro-2,2,2-tris(dimethylamino)ethane
(
4). # 2000 Elsevier Science S.A. All rights reserved.
Keywords: `Naked' ¯uoride ion; Hexamethylguanidinium ¯uoride
1
. Introduction
being a source of `naked' ¯uoride as well [6±10]. Among the
uoride ion sources of the last type the most important is
¯
There has been much interest in recent years in the
TASF [6]. The TAS counterion is remarkably stabilizing for
many ¯uorinated anionic species, e.g. per¯uoroalkyl, per-
¯uoroalkyloxy anions [11]. Hexamethylguanidinium
(HMG) 1,1,1,3,3,3-hexa¯uoro-2-(tri¯uoromethyl)-2-propa-
generation of highly nucleophilic sources of soluble ¯uoride
ion for application in organic and inorganic synthesis. One
of the most useful approaches for `naked' ¯uoride has
proved to be anhydrous tetramethylammonium ¯uoride or
‡
�
nide, [C(NMe ) ] [C(CF ) ] , a stable solid, was prepared
2
3
�
3 3
2
‡
�
‡
�
the salt TDAE 2F [TDAE ˆ tetrakis(dimethylamino)-
ethylene], recently synthesized from elemental ¯uorine,
which could be quite easily prepared in hydrogen di¯uoride
free form [1±5]. Due to elimination reactions, the complete
drying of quaternary ammonium ¯uorides has been found to
be possible only for the simplest representative, tetramethy-
lammonium ¯uoride which lacks b-hydrogen atoms. The
main advantages of TMAF are the high thermal and che-
mical stability of the tetramethylammonium cation and the
extreme high nucleophilicity of the `naked' ¯uoride ion.
Anhydrous TMAF [1,2,4] is a very strong base, deprotonat-
from HMG F , HF and per¯uoroisobutene [12]. The
2
chemistry of hexamethylguanidinium ¯uoride (HMGF)
(2) has not been developed, apparently, because of its
dif®cult access [13]. The dif®culties in growing of single
‡
�
crystals of the phosphoranides [14] NMe [P(CF ) F] and
4
3 3
‡
�
NMe4 [P(CF ) ] prompted us to search for counter ions
3 4
‡
‡
other than Me N , e.g. HMG . For this purpose and also for
4
stabilizing per¯uoroalkyl or per¯uoroalkyloxy anions the
‡
lipophilic and robust HMG cation, where the positive
charge is distributed over three nitrogen atoms should be
superior to TMAF. It seems to be very attractive and useful
for application in basic and applied organo¯uorine chem-
istry. Hence, we decided to ®nd a simple preparative
approach for HMGF excluding or minimizing the content
of hydrogen di¯uoride impurities.
ing CH CN at ambient temperature (its basicity can be
3
reduced by application of azeotropically dried TMAF, which
is also a very good nucleophile, where the remaining water
reduces its basicity signi®cantly) [3]. Another approach
includes the synthesis of hypervalent ¯uorosilicon or tin
onium derivatives showing excellent ¯uorinating power and
2
. Results and discussion
*
Corresponding author. Present address: Institut f uÈ r Anorganische &
Physikalische Chemie, Universit aÈ t Bremen, Leobener Strasse, D-28334
Bremen, Germany. Fax: ‡49-421-218-42-67.
The interaction of bis(dimethylamino)di¯uoromethane
with dimethylaminotrimethylsilane in different solvents
surprisingly gave HMGF (2), in contrast to the reaction
E-mail address: alex@chemie.uni-bremen.de (A.A. Kolomeitsev).
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 3 0 7 - 3

1
60
A.A. Kolomeitsev et al. / Journal of Fluorine Chemistry 103 (2000) 159±161
of dimethylaminotrimethylsilane with sulfur tetra¯uoride
6], where a hypervalent trimethyldi¯uorosilicate anion was
found. Probably, the C±F bond in 2 has a partial covalent
[
‡
character and the (Me N) C cation is more electrophilic
3
2
Scheme 2.
than the competing Me SiF. The reaction proceeds very
3
slowly (over 2 or 3 weeks) in pentane, diethyl ether or
monoglyme. A small addition of CH CN accelerated the
3
reaction. In order to optimize the synthesis, a low tempera-
9
1
ture F NMR study has been carried out. A solution of
dimethylaminotrimethylsilane and bis(dimethylamino)di-
¯
uoromethane in CH CN in a sealed NMR tube was inves-
3
Scheme 3.
tigated at � 45 to 08C. The reaction is rather slow at � 458C,
but at 08C the resonance of bis(dimethylamino)di¯uoro-
1
9
methane at d ˆ � 97 disappeared and only one new
F
NMR signal at d ˆ � 63.1 due to ¯uoride 2 was observed
Interestingly, compound 2 and (tri¯uoromethyl)tri-
methylsilane in monoglyme at � 808C gave the stable
within 2.5 h besides the resonances for Me SiF (d ˆ 157).
3
F
‡ �
hypervalent silicate (Me N) C [(CF ) SiMe ] (3) as the
2 3 3 2 3
The deprotonation of CH CN with 2 at 08C is very slow.
3
‡
�
However, to prevent the formation of [C(NMe ) ] HF
2
sole product, stable in monoglyme solution to � 608C. Upon
2
3
the reaction mixture has to be worked up at � 308C (see
warming to � 508C, compound 3 yielded very slowly
1
Section 3, Scheme 1)
The authors of the previous synthesis [13] observed by
(Me N) CCF (4) and Me SiCF [18] . At � 308C the
2
3
3
3
3
reaction became fast and was complete in 1 h. Most con-
veniently 1,1,1-tri¯uoro-2,2,2-tris(dimethylamino)ethane, 4
can be prepared by reacting 2 with 2±3 equivalents of
Me SiCF in diethyl ether at � 508C followed by warming
1
9
F NMR that the solution of 2 in DMF at ambient tem-
�
perature showed a 50% HF2 impurity. Surprisingly, in our
�
case no signi®cant HF2 concentration was detected. A
saturated solution of 2 in CH CN formed only 5.5% mol of
3
3
up the reaction mixture to ambient temperature [19].
The results of the X-ray structural investigations of
compounds 2 and 4, the use of 4 for new carbon±carbon
bond formation reactions and the interaction of dimethyla-
minotrimethylsilane with dimethylamine addition products
to F-alkenes will be published in due course.
3
�
HF2 within 24 h at 208C. We have also tried to prepare 2 in
accordance with the synthesis of anhydrous TMAF [4]. The
‡
�
metathesis of [C(NMe ) ] BF salt with a solution of oven
4
2
3
dried KF in anhydrous methanol (in isopropanol KF is
sparingly soluble) proceeds quantitatively to afford
‡
�
[
C(NMe ) ] F [d (CH OH) ˆ � 147.9 (s), d (H O) ˆ
In summary, the reaction of bis(dimethylamino)di¯uor-
omethane with dimethylaminotrimethylsilane provides a
rapid and facile access to hexamethylguanidinium ¯uoride
2
3
F
3
F
2
�
119 (s). But after removing methanol (20±1308C,
.01 mbar) [C(NMe ) ] HF
‡
�
0
was obtained (d ˆ 2.83
2
3
2
H
(
(
s); d ˆ � 147.7 (d), J ˆ 120.7 Hz). Just recently
soluble in organic solvents (e.g. CH CN, DMSO, DMF,
3
F
HF
‡
2�
HMG ) SiF
2
synthesis was published, but there was
monoglyme, THF) without hydrogen di¯uoride impurity. In
the light of the present availability of (R N) CF and the
6
no indication on the generation and characterization of
HMGF in this paper [15].
The synthesis of (Me N) CF (1), previously obtained by
2
2
2
proposed simple synthetic protocol of the HMGF synthesis,
‡ �
the salts of the general formula (R N) C F have become
2 3
2
2
2
¯
uorination of tetramethylcarbamide using COF or from
2
easily available for investigation in basic organic and
industrial organo¯uorine chemistry.
tetramethylthiocarbamide and SF4 [16], has also been
improved, namely via the straightforward ¯uorination of
‡ �
(Me N) CCl] Cl using anhydrous Me NF. When this
2 2 4
[
paper had been accepted for publication, a patent describing
a simple high yield Halex synthesis of bis(dialkylamino)-
di¯uoromethanes was published [17] (Scheme 2 and
Scheme 3).
3. Experimental
Mass-spectra (FAB) were recorded on a Finnigan
MAT 8222 spectrometer using a glycerol matrix. NMR
spectra were obtained on a Bruker DPX-200 spectrometer
1
13
operating at 200.13 MHz for H, 50.32 MHz for C (inter-
19
nal standard TMS), 188.31 MHz for F (internal standard
CFCl ). CH CN was distilled from phosphorus pentoxide
3
3
and then stored over calcium hydride. All reactions and
manipulations were conducted under an atmosphere of dry
nitrogen.
1
4,10
0-(Trifluoromethyl)-1,4,7-triazatricyclo[5,2,1,0 ]decane has been
1
synthesized.
Scheme 1.

A.A. Kolomeitsev et al. / Journal of Fluorine Chemistry 103 (2000) 159±161
161
3
.1. Bis(dimethylamino)difluoromethane (1)
92.24 (C(NMe ) , 2JCF ˆ 23.7 Hz), 39.36 (CH3,
2
3
4
JCF ˆ 2.3 Hz).
To a stirred solution of 17.1 g (100 mmol) tetramethyl-
chloroformamidinium chloride in CH Cl (50 ml) held at
2
2
0
8C, 23.3 g (250 mmol) tetramethylammonium ¯uoride was
Acknowledgements
added over 5 min. The cold mixture was stirred for an
additional 5 h, the precipitate ®ltered off, and washed twice
with 25 ml pentane. The resulting solution was distilled
using a 30 cm Vigreux column. Yield 13.1 g (95%). Purity
A.A.K. is grateful to the Deutsche Forschungsge-
meinschaft for ®nancial support.
1
19
9
6±97% ( H NMR); bp 99±1008C. F NMR: d ˆ 97.0 (s)
[
16].
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3
.2. Hexamethylguanidinium fluoride (2)
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0
8C. After cooling to � 308C the reaction mixture was
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[
[
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1
9
1
F NMR: d ˆ � 63.1 (s) (CD CN, � 308C); H NMR:
3
(
d ˆ 2.95 (s) [13]. The same reaction proceeded in 81%
[
[
10] M.-R. Brescia, P. DeShong, J. Org. Chem. 63 (1998) 3156.
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3
(
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[
[
[
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3
.3. 1,1,1-Trifluoro-2,2,2-tris(dimethylamino)-ethane (4)
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R oÈ schenthaler, Phosphorus, Sulfur, Silicon 109/110 (1996) 597.
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3
3
[15] X. Zhang, R. Bau, J.A. Sheehy, K.O. Christe, J. Fluorine Chem. 98
(1999) 121.
for 1 h. Then the temperature was slowly raised to 208C and
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[
16] F.S. Fawcett, C.W. Tullock, D.D. Coffman, J. Am. Chem. Soc. 84
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(
1
66±1698C (dec.); FAB positive(glycerol) m/z (%) 198
‡
‡
[17] H. Sonoda, K. Okada, K. Goto, K. Fukumura, J. Naruse, H. Hayashi,
T. Nagata, A. Takanashi, Eur. Pat. Appl. EP 0949226, 1999.
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Kirsch, G.-V. R oÈ schenthaler, J. Chem. Soc. Chem. Commun. (1999)
1017.
(
(
M � Me, 12), 169 (M � NMe , 100), 144
‡ ‡
2 3 3
2
[C(NMe ) ] , 42), 129 (M � Me � CF , 11) and other
�
fragments; FAB negative (glycerol) 69 (CF , 32) and other
3
1
5
19
fragments. H NMR: d ˆ 2.33 ( JHF ˆ 1.23 Hz); F NMR:
1
3
1
d ˆ � 62.5; C NMR d ˆ 127.35 (CF , JCF ˆ 305.6 Hz),
C
3