Different fluoride anion sources and (trifluoromethyl)trimethylsilane: Molecular structure of tris(dimethylamino)sulfonium bis(trifluoromethyl)trimethylsiliconate, the first isolated pentacoordinate silicon species with five Si-C bonds

Article abstract of DOI:10.1039/a901953g

(Trifluoromethyl)trimethylsilane, CF₃SiMe₃ reacts with [(Me₂N)₃S]⁺[Me₃SiF₂]^-, Q⁺F^- and Q⁺[HF₂]^-(Q⁺ = Me₄N⁺, [(Me₂N)₃C]⁺, [(Me₂N)₄P]⁺) at -70 to 50°C to afford the first hypervalent silicon species, [(CF₃)₂SiMe₃]^- with five Si-C bonds (stable in monoglyme up to -10°C) as the main reactive species whose molecular structure was determined by X-ray crystallography.

Full text of DOI:10.1039/a901953g

Different fluoride anion sources and (trifluoromethyl)trimethylsilane:
molecular structure of tris(dimethylamino)sulfonium
bis(trifluoromethyl)trimethylsiliconate, the first isolated pentacoordinate silicon
species with five Si–C bonds
a
b
b
a
a
c
Alexander Kolomeitsev,* German Bissky, Enno Lork, Valery Movchun, Eduard Rusanov, Peer Kirsch
and Gerd-Volker R o¨ schenthaler*b
a
Institute of Organic Chemistry, Ukrainian National Academy of Sciences, Murmanskaya 6, 253660 Kiev-94,
Ukraine
b
Institut f u¨ r Anorganische und Physikalische Chemie, Universit a¨ t Bremen, Leobener Strasse, D-28334 Bremen,
Germany. E-mail: j18j@zfn.uni-bremen.de
MERCK KGaA, Liquid Crystals Division, Frankfurter Strasse 250, Darmstadt 64293, Germany
c
Received (in Cambridge, UK) 11th March 1999, Accepted 20th April 1999
(
[
[
Trifluoromethyl)trimethylsilane, CF
3
SiMe
2
3
reacts with
interaction with fluoride ions is very important for designing
selective high-yield trifluoromethylation procedures of synthet-
ical and possible practical use.
+
2
+
2
+
2
+
+
(Me
(Me
2
N)
N)
3
S] [Me
3
SiF
2
N)
4
] , Q F and Q [HF
] (Q = Me
4
N ,
+
+
2
3
C] , [(Me
2
P] ) at 270 to 50 °C to afford the first
2
hypervalent silicon species, [(CF
3
)
2
SiMe
3
]
with five Si–C
3 3
Studying the Lewis acidic properties of P(CF ) we observed
+
2
bonds (stable in monoglyme up to 210 °C) as the main
reactive species whose molecular structure was determined
by X-ray crystallography.
that a 1:2:1 mixture of [(Me
2
N)
3 3 2 3 3
S] [Me SiF ] –CF SiMe –
P(CF
[P(CF
3
)
3
in THF yielded the stable acyclic phosphoranide,
2
2
3
)
4
]
3 3
at 255 °C together with 5–10% [P(CF ) F]
9
impurity. However, if Me
4
NF–CF SiMe (1:2–2.5), forming a
3
3
One of the most useful reagents for anionic trifluoromethylation
of different organic and organometallic electrophiles is (tri-
fluoromethyl)trimethylsilane.1 The instability of the corre-
clear solution at 260 °C in glyme was used and P(CF was
3 3
)
2
3 4
) ] was obtained.
10
added at 260 °C, analytically pure [P(CF
,2
A trifluoromethylating species has been pre-generated, which
sponding lithium and magnesium counterparts (CF
CF MgX decompose even at 2100 °C) and the reduced
nucleophilicity of trifluoromethyl derivatives of zinc, cadmium
3
Li and
we tried to elucidate by reacting CF
fluoride ion sources.
3
SiMe
3
with a range of
3
Here we report results obtained for CF
3
SiMe
3
1 reactions
3,4
+
2
11,12
+
+
2
+
2
and copper makes CF
For the generation of ‘CF
stoichiometric5 quantity of fluoride anion an intermediary
3
SiMe
3
indispensable in many cases.
with Q [Me
3
SiF
3
2
] 2a,
Q F , 3b–d and Q HF
2
, 4b–d [a:
2
4
+
+
+ 13
+
+ 14
3
’ in the presence of a catalytic or
Q = (Me
2
N)
S , b: Q = Me
4
N , c: Q = [(Me
2
N)
3
C] ,
+
+15
2 4
d: Q = [(Me N) P] ).† When 1 was added to a suspension of
4
,6a
hypervalent silicon species has not so far been found.
This
2a or 3b–d (2:1 ratio) in monoglyme at 250 °C or in THF at
4
2
3
’
led to the conclusion that the highly basic nature of the ‘CF
anion together with the high propensity to eliminate a-fluoride
renders the pentavalent CF intermediate elusive. Investigation
278 °C, the solids were immediately dissolved to form a stable
+
2
3
] , 6a–d
colourless solution of the siliconates, Q [(CF
in 95% yield (Scheme 1) with d
F
3
)
2
SiMe
in the range 263.6 to 263.8,
approximately 3.2–3.6 ppm downfield of the CF SiMe reso-
nance.ठAfter recrystallization of 6a monitored by F NMR
spectroscopy only one species with d 263.7 was present,
6a the first isolated penta-
3
+
2
of the Me
and CF D as the only reaction products. Furthermore, if
Me SiCF
Si(CH CN)(F)] was found, but no CF
3 3
SiCF –Me
4
N F system in CD
3
CN revealed Me
3
SiF
3
3
4
19
3
+
2
3
3
–Me
4
2
N F is reacted in MeCN the anion [Me
3
-
F
+
2
3
2
3
containing the
2 3 3 2
namely (Me N) S [(CF ) SiMe ]
6b
hypervalent silicon derivative was found. It is noteworthy that
the generation, structures and spectral properties and reactivities
coordinate silicon species having five Si–C binds, proven by
single-crystal X-ray structural determination (Fig. 1).¶ The new
compound is stable in the solid state upto 0 °C but decomposes
exothermally at 0–5 °C with the formation of 2a. The same
reaction has been observed in monoglyme solution of 6b at
2
22
n
of fluorosiliconates [R SiF52n
]
and [R
n
SiF62n
]
(n = 1–3)
7
have been extensively studied. Despite the fact that fluorine
directly bonded to hypervalent silicon has a stabilizing effect,
no reports have appeared, to the best of our knowledge,
describing their isolation and reliable characterization of
+
2
230 °C with the quantitative formation of Me N [F SiMe ]
4 2 3
2b proven by 19F NMR and single-crystal X-ray diffraction.∑
The corresponding 6d decomposes at 210–0 °C to give 2d.
Obviously, the size of the counter ion plays an important role in
2
2
8a
[
(CF
pentaphenylsiliconate was observed in solution at 280 °C.
Investigation of species formed in the course of Me SiCF
3
)
2
SiF
3
]
and [CF
3 4
SiF ]
in the solid state. Lithium
8b
2
8b
3
3
the thermal stability of [(CF ) SiMe ] . Expected reaction
3 2 3
Scheme 1
Chem. Commun., 1999, 1107–1108
1017

‡
2
General procedure for 6b–d: to a solution of the corresponding fluoride
a–d (0.2 mmol) in monoglyme or THF (5 ml) has added 0.06 g (0.42
mmol) of 1. The use of corresponding bifluorides gave the same products
but the molar ratio of bifluoride to silane was 1:3 in this case. Selected data
for 6b–d: d
F
263.67 (6b), 263.94 (6c), 263.82 (6d), 264.83 (2b), 264.75
(2d).
§
Synthesis of 6a: to a solution of 0.41 g (1.49 mmol) 2a in 5 ml monoglyme
was condensed 0.45 g (3.13 mmol) 1 and the mixture stirred for 3 h at
2
55 °C, d
Crystal data for 6a: C11
/m, a = 769.8(2), b = 1132.1(2), c = 1135.6(2) Å, b 105.26(1)°,
F
264.04. Yield: 95%.
¶
27 6 3
H F N SSi, M = 375.51, monoclinic, space
group P2
V = 0.9548(3) nm , Z = 2, D
Siemens P4 m/v diffractometer, q-2q-scan type, 2.59 @ q @ 24.99°, 173 K;
512 reflections collected, 1775 independent reflections (Rint = 0.0672),
1
3
23
c
= 1.306 g cm , l(Mo-Ka) = 0.71073 Å.
6
2
2
full-matrix least-squares on F , goodness-of-fit (F ) = 1.064, final R values
I > 2s(I)]: R1 = 0.0476, wR2 = 0.1002, R values (all data): R1 = 0.0774,
wR2 0·1157, extinction coefficient 0.0103(18), difference electron
[
=
3
density: 0.264 and 20.244 e Å . CCDC 182/1232. See http://www.rsc.org/
suppdata/cc/1999/1017/ for crystallographic files in .cif format.
∑
Selected data for 2b: d
0.18 (s, Me Si), 3.10 (s, Me
and angles for the anion [Me SiF
within the standard deviation.
† Selected data for 7: bp 166–170 °C (decomp.). d
F
(CD
3
CN, 230 °C) 260.10; d
4
2
2
] in 2b are almost identical with those for
H
(CD
3
CN, 230 °C)
+
2
3
N ). The geometry parameters, bond lengths
3
12
2
†
d
a
Fig. 1 Crystal structure of 6a with thermal ellipsoids. Selected bond lengths
pm) and angles (°): Si(1)–C(1) 205.6(4), Si(1)–C(2) 206.2(4), Si(1)–C(3)
88.2(5), Si(1)–C(4) 188.6(3); C(3)–Si(1)–C(4) 120.85(12), C(3)–Si(1)–
2.33 (5JFH 1.23 Hz);
], 2JCF 23.7
, JCF 305.6 Hz), 94.24 [C(NMe
3
, JCF 2.3 Hz).
H
(
1
1
F
262.48; d
C
127.35 (CF
3
2 3
)
4
Hz), 39.36 (CH
C(1) 91.0(2), C(3)–Si(1)–C(2) 89.6(2), C(1)–Si(1)–C(2) 179.40(19).
1
2
G. K. S. Prakash, R. Krishnamurti and G. A. Olah, J. Am. Chem. Soc.,
1989, 111, 393.
I. Ruppert, K. K. Schlich and W. Volbach, Tetrahedron Lett., 1984, 25,
products16 of difluorocarbene with monoglyme or THF were
not detected. Addition of 1 to 3c in THF at 280 °C afforded 6c
2
195.
F
(d 263.7) as the sole product, which upon warming to 250 °C
3
4
D. J. Burton and Z. Y. Yang, Tetrahedron, 1992, 48, 189.
G. K. S. Prakash and A. K. Yudin, Chem. Rev., 1997, 97, 757.
gave slowly (Me
formation of 7 proceeds much faster and was complete in 1 h
along with gaseous Me SiF and CF H impurity.†† In the case of
2 3 3
N) CCF 7 and 1 (Scheme 1), at 230 °C the
5 (a) A. A. Kolomeitsev, V. N. Movchun and Yu. L. Yagupolskii,
Synthesis, 1990, 1151; (b) A. A. Kolomeitsev, V. N. Movchun and
Yu. L. Yagupolskii, W. Porwisiak and W. Dmowskii, Tetrahedron Lett.,
3
3
hydrogen difluorides and compound 1, a 1:3 ratio has to be
applied to convert 4b–d at 280 °C into the fluorides 3b–d
1
992, 41, 6191.
(a) C. R. J. P. Corriu, C. Reye and J. C. Young, Chem. Rev., 1993, 93,
371; (c) R. Damrauer and J. A. Hankin, Chem. Rev., 1995, 95, 1145; (b)
6
3 3
under formation of CF H and Me SiF (Scheme 1) and
1
subsequently 6b–d are formed.
Probably the siliconates
(CF )Si(F)Me anion were produced initially as inter-
3 3
mediates releasing [CF SiMe yielding
D. J. Adams, J. H. Clark, L. B. Hansen, V. C. Sanders and S. J. Tavener,
J. Fluorine Chem., 1998, 92, 123.
(a) H. J. Frohn and V. V. Bardin, J. Organomet. Chem., 1995, 501, 155
and references cited therein; (b) A. S. Pilcher and P. DeShong, J. Org.
Chem., 1996, 61, 6901.
5a–d
containing
the
2
3
]
[
3
7
2
3
]
to attack CF
2
3 2 3
) SiMe ] . So far, there is no direct spectroscopical
[
(CF
2
observation of [(CF
3
)Si(F)Me
3
] , whereas the isoelectronic
8 (a) H. Beckers, H. B u¨ rger and R. Eujen, Z. Anorg. Allg. Chem., 1988,
563, 39; (b) A. H. J. F. de Keijzer, F. J. J. de Kanter, M. Schakel, R. F.
Schmitz and G. W. Klumpp, Angew. Chem., 1996, 108, 1183 and
references therein.
phosphorane, (CF
3
)P(F)Me could be isolated and fully char-
3
acterized.17
The single crystal X-ray structure determination of 6a
showed almost ideal trigonal-bipyramidal geometry at silicon
3 3
)
F]2 even
9
Because of the high phosphorus affinity to fluorine, [P(CF
being treated with excess of Me SiCF cannot be transformed
] , cf. A. A. Kolomeitsev and G.-V.
3
3
[
C(1)–Si(1)–C(2) 179.40(19), C(3)–Si–C(1) 91.0(2) and C(3)–
2
3 4
quantitatively into [P(CF )
4
Si–C(4) 120.85(12)°] with a rather long apical Si–C(1)F
3
bond
R o¨ schenthaler, 12th ACS Winter Fluorine Conference, St. Petersburg
Beach, FL, USA, January 22–27, 1995, abstract 48.
[
205.6(4)] and a considerably shorter equatorial Si–C(1)H
3
12
bond [188.2(5) pm] (cf. 187.4 pm in 2a ). For the isoelectronic
CF PMe the same structure was found with shorter P–C
distances [P–CF 197.4(4) and P–CH 181.3(2) pm]. The
10 A. A. Kolomeitsev, N. V. Pavlenko, A. B. Rozhenko, U. Dieckbreder,
M. G o¨ rg and G.-V. R o¨ schenthaler, 15th International Symposium on
Fluorine Chemistry, Vancouver, Canada, August 2–7, 1997, Abstract In
(2) C-6.
(
3
)
2
3
18
3
3
+
2 3
geometry parameters of the cation (Me N) S are similar to
those investigated earlier.12
11 W. J. Middleton, US Pat. N3, 940, 402, 1976.
1
1
1
2 D. A. Dixon, W. B. Farnham, W. Heilemann, R. Mews and M.
Noltemeyer, Heteroat. Chem., 1993, 4, 287 and references therein.
3 A. A. Kolomeitsev, F. U. Seifert and G.-V. R o¨ schenthaler, J. Fluorine
Chem., 1995, 71, 47.
4 S. M. Igumnov, N. I. Delyagina and I. L. Knunyants, Izv. Akad. Nauk
SSSR, Ser. Khim., 1986, 1193 and references therein.
The use of the hypervalent trifluoromethylating silicon
compounds for new carbon–carbon bond forming reactions and
synthesis of trifluoromethylated phosphorus(v) derivatives is
underway in our laboratories. The results of the study for
CF
anion sources including (Et
Me N) CCF will be published in due course.
A. A. K. is grateful to the Deutsche Forschungsgemeinschaft
for financial support. The generous gift of CF SiMe by Bayer
3
SiF
3
and CF
3
SiPh
3
interaction with the different fluoride
2
N) PF and Ph CF and reactions of
3
2
3
15 A. A. Kolomeitsev, N. V. Kirij, W. K. Appel, S. V. Pazenok, G.-V.
R o¨ schenthaler, 14th ACS Winter Fluorine Conference, St. Petersburg
Beach, January 17–22, 1999, abstract 37.
(
2
3
3
1
6 (a) R. M o¨ ckel, W. Tyrra and D. Naumann, J. Fluorine Chem., 1995, 73,
29 and references therein; (b) C.-M. Hu, F.-L. Qing and C.-X. Shen,
3
3
2
AG, Leverkusen (Germany) is gratefully acknowledged.
J. Chem. Soc., Perkin Trans. 1, 1993, 335.
1
7 A. A. Kolomeitsev, Yu. L. Yagupolskij, A. Gentzsch, E. Lork and G.-V.
R o¨ schenthaler, Phosphorus, Sulfur Silicon, 1994, 92, 179.
8 A. A. Kolomeitsev, U. Dieckbreder, M. G o¨ rg and G.-V. R o¨ schenthaler,
Phosphorus Sulfur Silicon, 1996, 109–110, 597.
Notes and references
1
†
All reactions were performed under nitrogen in carefully dried solvents.
Compound 7 gave satisfactory elemental analysis. NMR spectra at 200.13
1
19
13
(
H, TMS), 188.31 ( F, CClF
3
), 50.32 MHz ( C, TMS) were recorded.
Communication 9/01953G
1018
Chem. Commun., 1999, 1107–1108