P-bis(trifluoromethyl) ylides: Synthesis and reactions

Article abstract of DOI:10.1002/hc.10061

The methylation of bis(trifluoromethyl)phosphines by MeOSO₂CF₃, yielding the respective phosphonium salts was described. Methylation was done using methyl triflate at 100 °C without a solvent. It was found that deprotonation using MeN = P(NEt₂)₃ led to the phosphorus ylides stable in solution at ambient temperatures, which could be converted into 1,2λ⁵σ⁵-oxphosphetanes by adding hexafluoroacetone.

Full text of DOI:10.1002/hc.10061

Heteroatom Chemistry
Volume 13, Number 7, 2002
P
-Bis(trifluoromethyl) Ylides: Synthesis
and Reactions
1
1
Uwe Dieckbreder, Gerd-Volker R o¨ schenthaler,
2
and Alexander A. Kolomeitsev
1
Institute f u¨ r Anorganische & Physikalische Chemie, Universit a¨ t Bremen, Leobener Strasse,
D-28334 Bremen, Germany
2
Institute of Organic Chemistry, Ukrainian Academy of Sciences, Murmanskaya 5,
0
2094 Kiev, Ukraine
Received 11 January 2002; revised 5 February 2002
bonded to phosphorus [4]. Because the phosphines
RP(CF ) are easily accessible by
(R = Me, NEt
using “Ruppert’s reagent” [5] [CF Br/P(NEt ],
methylation followed by deprotonation should yield
the desired ylides.
ABSTRACT: Bis(trifluoromethyl)phosphines RP-
3
)
2
2
(
CF
CF
RP(CF
MeN P(NEt
CF CH , stable in solution at ambient tempera-
3
)
2
(R = Me, NEt
2
) were methylated by MeOSO -
2
3
)
2 3
3
, yielding the respective phosphonium salts
+
−
[
3
)
2
Me] and CF
3
SO . Deprotonation using
3
)
2 3
led to the phosphorus ylides RP-
(
3
)
2
2
5
5
RESULTS AND DISCUSSION
ture, which could be converted into 1,2ꢀ ꢁ -oxaphos-
phetanes by adding hexafluoroacetone. ꢀC 2002 Wiley
The Ruppert-system CF
3
Br/(Et
2
N) P [5] proved to
3
Periodicals, Inc. Heteroatom Chem 13:650–653, 2002; Pub-
lished online in Wiley InterScience (www.interscience.
wiley.com). DOI 10.1002/hc.10061
be a useful system to synthesize the bis(trifluoro-
methyl)phosphines 2a–c as oxygen-sensitive liquids
(2a being pyrophoric) from the respective dichloro-
phosphines 1a–c (Scheme 1) in good yields. Com-
pounds 2a and 2c have already been obtained by
other methods [6,7].
INTRODUCTION
While 2b and 2c could be obtained in dichlo-
romethane, in the case of 2a (R = Me), triglyme
had to be used as a solvent because of its higher
Phosphorus ylides are versatile reactants in organic
chemistry, e.g. in the synthesis of naturally ocur-
ring compounds [1]. There are only a few ylides
containing fluorine or perfluoroalkyl groups in the
alkylidene moiety [2] and not many P-halogeno
derivatives [3]. Recently, we synthesized the first
◦
boiling point, necessary to isolate 2a (bp 30 C).
Methylation was possible only using methyl tri-
◦
flate at 100 C without a solvent to give the first
bis-trifluoromethyl phosphonium salts 3a and 3c,
moisture sensitive compounds, in good yields. In
the case of 2b, decomposition was observed during
this procedure. Compounds 3a and 3c decomposed
rapidly in diethyl ether and THF. The phospho-
nium triflates 3a and 3c could be deprotonated
using as a neutral base a weak nucleophile N-
methyliminotris(diethylamino) phosphine imide 4
P-trifluoromethyl ylides, having one CF
3
group
Presented in part at the XIII Int Conf on Phosphorus Chemistry,
Jerusalem, Israel, July 16–21, 1995; A. A. Kolomeitsev, M. Goerg,
U. Dieckbreder, E. Lork, G.-V. R o¨ schenthaler, Phosphorus, Sulfur
Silicon Relat Elem 109, 1996, 597–600.
Correspondence to: Gerd-Volker R o¨ schenthaler or Alexander
Kolomeitsev; e-mail: gvr@chemie.uni-bremen.de; alex@chemie.
uni-bremen.de.
[
pK
s
= 28] [8], yielding the desired ylides 5a and 5c
Contract grant sponsor: Deutsche Forschungsgemeinschaft.
Contract grant number: 436 UKR 113/36/0.
ꢀ
c 2002 Wiley Periodicals, Inc.
(Scheme 2) which were stable in solution at room
temperature, whereas CF Me P CH decomposed at
3
2
2
6
50

P-Bis(trifluoromethyl) Ylides: Synthesis and Reactions 651
SCHEME 1
SCHEME 3
◦
temperatures as low as −50 C. It was of advantage
to obtain the nonvolatile amidophosphonium salt,
2
4
(
δ = −62.6,
J
FP = 52.4,
J
FF = 13.9 Hz), a doublet
group (δ =
67.0, JFP = 123.0, JFF = 13.9 Hz) split further by
through-space” coupling (JF···F = 7.0 Hz) between C-
CF (cis) and P-CF (equatorial). The smaller abso-
lute value of JFP = 52.4, compared to JFP = 123.0 H,
is typical of an axially bonded CF moiety [4,9].
In a similar oxaphosphetane, F· · ·F “through-space”
coupling C-CF (equatorial) was found
(cis) · · P-CF
+
−
[(Et
2
N)
3
PNHMe] CF
3
SO , which could easily be
3
of quartets for the equatorial P-CF
3
separated (Scheme 2).
2
4
−
The reaction of the bis(trifluoromethyl) ylides 5a
and 5c with hexafluoroacetone furnished the 2,2,4,4-
“
5
5
3
3
tetrakis(trifluoromethyl)-1,2λ σ -oxaphosphetanes,
a and 6c, as colourless, moisture-sensitive liquids
Scheme 3).
The structure of the compounds 2–6 was con-
2
2
6
(
3
3
3
firmed by their NMR spectra (see Table 1). The ylides
(
J
F···F = 4.7 Hz) [9].
◦
19
5
a and 5c were characterized at −70 C. In the
F
NMR spectra for the P-CF groups at 308 K, broad
3
doublets were observed, while sharp singlets were
recorded for the C-CF groups. Because of Berry-
pseudorotation, which was fast on the NMR time
scale, axial and equatorial CF substituents at phos-
phorus could not be distinguished. Cooling a so-
lution of phosphetane 6c (R = Et N) in toluene-d
slowed down the ligand permutation process, re-
sulting in the magnetic inequivalence of the P-CF
groups and, also of the C-CF groups (cis and trans
with respect to the equatorial P-CF ) below the co-
alescence temperature of 273 K. At 213 K, a dou-
TABLE 1 NMR Data of 2a–c, 3a, 3c, 5a, 5c, 6a, and 6c at
3
3
08 K (J in Hz)
a
a
3
δ
H
(P-CH)
( JHP)
δ
P
2
a
a
2
Compound
δF (P-CF ) δF (C-CF ) ( JFP)
3 3
2
8
2
2
a
0.95
−62.2
−5.0
(75.7)
13.9
(65.2)
41.7
(86.6)
59.8
(108.8)
47.7
(
4.4)
2.47
6.8)
3
bb
−53.1
−59.8
−54.7
−61.9
−67.0
−71.9
−66.9
−64.0
3
(
2cc
3
3
3
5
5
6
6
ad
ce
a f
c f
a
2.95
16.8)
3.08
blet of quartets for the axial P-CF was observed
3
(
(
13.8)
(113.4)
17.8
(79.3)
32.2
(
87.5)
1.25, 3.45g
15.5), (17.1)
3.03
16.0)
−78.5
−77.0
−60.7
(80.5)
−51.5
(88.0)
(
ch,i
g
(
aHigh-field shifts from TMS, CCl
ative signs.
3
3 4
F, and 85% H PO were given neg-
b1
c1
3
3
H: δ = 1.19 (6 H, Me
2
CH, dd, JHH = 6.9, JHP = 16.2).
3
H: δ = 0.88 (6 H, MeCH
HP = 10.7).
2
, t, JHH = 7.1), 2.95 (4 H, CH
3
CH
2
, dq,
, dq,
3
J
d19
e1
−
F: δ = −74.8 (s, F
3
CSO
3
).
3
H: δ = 1.27 (6 H, CH
3
CH
2
, t, JHH = 7.1), 3.48 (4 H, CH
3
CH
2
3
19
−
fJHP = 12.8); F: δ = −74.2 (s, F
3
CSO
3
).
1H: Not observed because of overlapping signals of (Et
2
N)
3
PNMe.
, dq,
g
2
PCH .
h1
, t, 3JHH = 6.9), 3.03 (4 H, CH
H: δ = 0.77 (6 H, CH
3
CH
2
3
CH
2
3
J
HP = 13.9).
i 19
(ax), 2JFP = 52.4, JFF = 13.9), −67.0
4
F at 213 K: −62.6 (P-CF
3
2
(
P-CF
3
(eq),
J
FP = 123.0,
J
F···F = 7.0), −77.6 (C-CF
3
(cis), qq,
(trans), JFF = 7.8).
4
4
SCHEME 2
J
FF = 7.8, JF···F = 7.0), −77.0 (C-CF
3

6
52 Dieckbreder, R o¨ schenthaler, and Kolomeitsev
TABLE 2 Experimental Details for the Synthesis of Compounds 2a–c
(g)a
CF Br (g)a
3
(Et N) P (g)
2 3
a
Solvent (ml)
Yield (g)b
bp ( C)c
◦
1
2
2
2
ad
b
c
1a 11.1 (95)
1b 11.6 (80)
1c 8.7 (50)
34.3 (230)
30.0 (200)
22.4 (150)
46.9 (190)
39.5 (160)
24.7 (100)
Triglyme 150
8.3 (47)
4.2 (25)
7.7 (64)
30 (1013)
85 (1013)
59 (100)
CH Cl 120
2
2
CH Cl 150
2 2
a
Values in parentheses are in millimoles.
Values in parentheses are the percent values.
Values in parentheses are in millibars.
See Ref. [6].
b
c
d
EXPERIMENTAL
Dimethylbis(trifluoromethyl)phosphonium triflate
3a). Anal calcd for C PS (348.12): C, 17.24;
H, 1.74; F, 49.14; P, 8.90. Found: C, 17.72; H, 1.89; F,
(
5
H
6
F
9
O
3
Mass-spectra (EI, 70 eV) were recorded on a
Finnigan MAT 8222 spectrometer. NMR spectra were
obtained on a Bruker AC 80 instrument operating
4
8.90; P, 8.57.
1
9
at 75.39 MHz ( F, internal standard CCl
3
F) and
Diethylaminomethylbis(trifluoromethyl)phospho-
3
1
3
2.44 MHz ( P, external standard 85% H
3
PO ). All
4
nium triflate (3c). Anal calcd for C
8
H
13
F
9
NO PS
3
reactions and manipulations were conducted under
an atmosphere of dry nitrogen.
(405.21): C, 23.70; H, 3.23; F, 42.22, P, 7.65. Found:
C, 24.02; H, 3.38; F, 41.30: P, 7.42.
General Procedure for the Synthesis
of Compounds 5a and 5c
General Procedure for the Synthesis
of Compounds 2a–c
To compounds 3a (0.18 g, 0.52 mmol) and 3c (0.28 g,
.69 mmol) one equivalent of (Et N) PNMe 4 (0.15 g,
0.52 mmol in the case of 3a; 0.20 g, 0.69 mmol in
In the respective solvent, bromotrifluoromethane
0
2
3
and the dichlorophosphine (1a–c) were cooled to
◦
−
60 to −80 C. Hexaethylphosphorus triamide was
the case of 3c) in 3 ml toluolene-d
8
was added at
added, and the reaction mixture was allowed to
warm to ambient temperature. All volatiles were
pumped off in vacuo (10 mbar) and the residue
◦
−80 C. The reaction mixture was allowed to warm,
◦
−3
first to −50 C, then to ambient temperature, and
was NMR-spectroscopically characterized. There
was no change in the NMR parameters for 2 days.
Methyl-bis(trifluoromethyl)methylene phosphorane
(5a) and diethylamino-bis(trifluoromethyl)methylene
phosphorane (5c), according to the NMR evidence,
were quantitatively formed.
distilled. (See Table 2 for data of 2a–c.)
Isopropylbis(trifluoromethyl)phosphine (2b).
Anal calcd for C
5
H
7
6
F P (212.07): C, 28.30; H, 3.33;
F, 53.76; P, 14.61. Found: C, 28.13; H, 3.18; F, 53.10;
P, 14.36.
General Procedure for the Synthesis
of Compounds 6a and 6c
Diethylaminobis(trifluoromethyl)phosphine (2c)
+
+
[
5
(
7]. MS: m/e (%) = 241 (M , 8), 226 (M − CH
3
,
To a solution of 3a (2.61 g, 7.5 mmol) and 3c (3.49 g,
+
+
), 172 (M − CF
3
, 22), 122 (Et
2
NPF , 100), 94
8
.4 mmol) one equivalent of (Et
2
N) PNMe 4 (1.93 g,
3
+
+
+
Et(H)NPF , 7), 69 (CF
3
, 18), 29 (C
2
H
5
, 45), and
other fragments.
TABLE 3 Experimental Details for the Synthesis of Com-
pounds 3a and 3c
General Procedure for the Synthesis
of Compounds 3a–c
(g)a
Yield (g)b
◦
2
mp ( C)
Compounds 2a–c and one equivalent, methyltrifluo-
3
3
a
b
2a 3.68 (20)
2b 4.24 (20)
2c 8.44 (35)
6.9 (99)
100 (12)
12.5 (89)
131
53
romethansulfonate were heated in a glass ampoule
c
◦
at 100 C for 16 h. The remaining solid was re-
3c
◦
crystallized in dichloromethane at −50 C and dried
a
Values in parentheses are in millimoles.
−
3
in vacuo (10 mbar). (See Table 3 for data of
b
c
Values in parentheses are the percent values.
Nonseparable mixture of decomposition products.
3
a–c.)

P-Bis(trifluoromethyl) Ylides: Synthesis and Reactions 653
7
.0 mmol in the case of 3a; 2.21 g, 8.0 mmol in the
ACKNOWLEDGMENTS
◦
case of 3c) in 10 ml THF was added at −80 C and
We thank the Bayer AG, Leverkusen, the former
Hoechst AG, Frankfurt, and H u¨ rth, for generous gifts
of chemicals.
stirred for 1 h. The reaction mixture was cooled to
◦
−
196 C, evacuated and 1.5 equivalents of hexafluo-
roacetone (2.57 g, 15.5 mmol in the case of 3a; 2.94 g,
7.7 mmol in the case of 3c) added. Within 12 h the
1
reaction mixture was allowed to warm to ambient
temperature and the volatiles were pumped off in
vacuo. The residue was extracted with 5 ml of pen-
tane, which was pumped off in vacuo to yield pure
products.
REFERENCES
[1] Kolodiazhnyi, O. I. Phosphorus Ylides: Chemistry
and Application in Organic Synthesis; Wiley-VCH:
Weinheim, 1999.
[
2] (a) Kolodiazhnyi, O. I. Tetrahedron 1996, 52, 1855–
5
5
1929; (b) Kolodiazhnyi, O. I.; Schmutzler, R. Synlett
2
-Methyl-2,2,4,4-tetrakis(trifluoromethyl)-1,2λ σ -
2
001, 1065–1078.
3] Kolodiazhnyi, O. I. Russ Chem Rev Engl Transl 1991,
0, 391–409.
◦
oxaphosphetane (6a). mp −15 C. MS: m/e (%): 345
[
+
+
+
(
1
M − F, 13); 295 (M − CF
3
, 85); 245 (M − CF
3
CF ,
12OP
2
6
00); and other fragments. Anal calcd for C
7
H
5
F
[4] Dieckbreder, U.; Lork, E.; R o¨ schenthaler, G.-V.;
Kolomeitsev, A. A. Heteroat Chem 1996, 7, 281–
(364.07): C, 23.90; H, 1.38; F, 62.62, P, 8.51. Found:
2
84.
5] (a) Ruppert, I.; Volbach, W. Tetrahedron Lett 1983, 24,
509; (b) Ruppert, I.; Schlich, K.; Volbach, W. Tetra-
C, 24.02; H, 1.40; F, 61.80: P, 8.42.
[
5
2
-Diethylamino-2,2,4,4-tetrakis(trifluoromethyl)-
5
hedron Lett 1984, 25, 2195.
6] Haszeldine, R. N.; West, B. O. J Chem Soc 1957, 3880–
5
◦
1
(
,2λ σ -oxaphosphetane (6c). mp −5 C. MS: m/e
+ +
3
[
%): 402 (M − F, 8); 352 (M − CF
, 42); 257
3
883.
+
+
[Et
2
N(CF
3
)
2
PO , 19]; 242 [Et
2
N(CF
3
)
2
PH , 100];
[7] Adler, O.; Kober, F. J Fluorine Chem 1975, 5, 231–238.
+
+
[
8] Zal’tsman, I. S.; Koidan, G. N.; Kudryavtsev, A. A.;
Marchenko, A. P.; Pinchuk, A. M. Russ J Gen Chem
USSR 1989, 59, 1914–1915.
2
4
6
14 [EtHN(CF
1]; 145 [H
9 (CF
3
)
2
PH , 83]; 164 [F
3
CC(CH
2
+
)CF
3
,
+
2
CC(CF
3
)CF
2
, 33]; 95 [H
2
CCCF , 34];
3
+
3
, 36); and other fragments. Anal calcd for
12NOP (421, 16): C, 28.50; H, 2.87; F, 54.15,
[
9] Kolomeitsev, A. A.; Yagupols’kij, Yu. L.; Gentzsch,
A.; Lork, E.; R o¨ schenthaler, G.-V. Phosphorus, Sulfur
Silicon Relat Elem 1994, 92, 179–187.
C
10
H
12
F
P, 7.36. Found: C, 28.84; H, 3.02; F, 54.50: P, 7.39.