Oxidative fluorination of some organoantimony and organotellurium compounds by 2-hydroperfluoropropyl azide

Article abstract of DOI:10.1016/S0022-1139(98)00335-2

Triphenylantimony and diphenyltellurium are readily oxidatively fluorinated by 2-hydroperfluoropropyl azide, CF₃CHFCF₂N₃, to form appropriate difluorides from moderate to high yields.

Full text of DOI:10.1016/S0022-1139(98)00335-2

Journal of Fluorine Chemistry 94 (1999) 43±45
Oxidative ¯uorination of some organoantimony and organotellurium
compounds by 2-hydroper¯uoropropyl azide
Sergei A. Lermontov*, Sergei V. Shkavrov, Anatoly S. Lermontov,
Vladimir O. Zavelsky, Nikolai S. Ze®rov
Institute of Physiologically Active Substances, Russian Academy of Sciences, Chernogolovka Moscow 142432, Russia
Received 23 March 1998; accepted 29 October 1998
Abstract
Triphenylantimony and diphenyltellurium are readily oxidatively ¯uorinated by 2-hydroper¯uoropropyl azide, CF3CHFCF2N3, to form
appropriate di¯uorides from moderate to high yields. # 1999 Elsevier Science S.A. All rights reserved.
Keywords: 2-Hydroper¯uoropropyl azide; Oxidative ¯uorination; Triphenylantimony di¯uoride; Diphenyltellurium di¯uoride
1. Introduction
To determine the scope and limitations of the ¯uorinating
ability of the azide 1 we studied its reactions with some low-
valent compounds of main groups V and VI elements,
namely with Ph3Sb, Ph3Bi, Ph2Te and Ph2Te2.
Fluorinated compounds are of considerable interest in
inorganic, organic, polymer, industrial and medicinal chem-
istry [1±6]. Particularly valuable are mild and selective
¯uorinating agents, and methods for the ready ¯uorination
of organic and organoelement compounds [5±7]. The great
majority of ¯uorinating agents are of nucleophilic character.
The reagents which are capable of electrophilic ¯uorination
include F2 itself [8±10], XeF2 [11±13], PhIF2 [14±16], acetyl
hypo¯uorite, MeCOOF [17±20] and N- ¯uoroamines and
amides [21±24]. Unfortunately, these reagents have various
drawbacks and limitations such as hazardous handling (F2,
RCOOF), high cost and lack of selectivity (XeF2, N-F
compounds) or weak ¯uorinating ability (PhIF2), and ®nally,
they are all usually prepared from F2. Therefore, new
electrophilic ¯uorinating agents that allow the ready intro-
duction of ¯uorine under mild conditions into electron rich
substrates are highly desirable and useful.
1.1. Group V compounds
We have found that the reaction of the azide 1 with Ph3Sb
in methylene chloride leads to a high yield of Ph3SbF2 (2)
over a wide temperature range (reaction (1)):
85 160ꢀC; 3
Ph3Sb‡ CF3CHFCF2N3
!
6 h Ph3SbF2
1
2
‡ CF3CHFCN ‡ N2 "
(1)
This reaction needs higher temperatures than the analo-
gous reactions with organophosphorus compounds (see
Table 1). Some decrease in the di¯uoride 2 yield at
1608C is probably due to the thermal instability of the
product.
We have recently shown [25] that stable 2-hydroper¯uor-
opropyl azide, CF3CHFCF2N3 (1), readily ¯uorinates var-
ious organophosphorus (III) compounds, affording
di¯uorophosphoranes in high yields and serving, hence,
as an oxidative ¯uorinating agent.
The reaction of 1 with Ph3Bi does not take place even on
heating, probably due to a high oxidation potential of Bi(V)
compounds [26] (reaction (2)):
1
Ph3Bi
!
no reaction
(2)
150ꢀC; 3 h
1.2. Group VI compounds
The reaction of Ph2Te with the azide 1 proceeds at higher
temperatures and also gives the desired product of oxidative
*Corresponding author. Tel.: +95-524-50-62; fax: +95-939-02-90.
0022-1139/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved.
P I I : S 0 0 2 2 - 1 1 3 9 ( 9 8 ) 0 0 3 3 5 - 2

44
S.A. Lermontov et al. / Journal of Fluorine Chemistry 94 (1999) 43±45
Table 1
Fluorination of organoelement compounds by the azide 1
Substrate
Ph3Sb
Temperature (8C)
Solvent
Reaction time (h)
Product
Yield (%)
85
120
160
85
CH2Cl2
CH2Cl2
CH2Cl2
CH3CN
5
5
3
6
2
2
2
2
60
100
83
59
Ph2Te
120
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
5
5
3
3
3
3
3
3
6
14
32
60
120a
170
170a
Ph2Te2
160
140
CH2Cl2
CH3CN
4
3
3
5b
11b
7.5
aHMPTA added.
bDiphenyltellurium difluoride.
¯uorination ± di¯uoride Ph2TeF2 (3) in a moderate yield
(reaction (3)). It was found useful to charge the reaction
vessel (stainless steel bomb) with inert CO2 at high pressure
(45±50 atm) prior to heating in order to retain highly volatile
azide 1 and CH2Cl2 in a liquid state at elevated tempera-
tures. In contrast to Ph3Sb, the reaction appeared to be
sensitive to the presence of a dipolar aprotic solvent, e.g.
hexamethylphosphortriamide (HMPTA). The addition of
0.4 ml of HMPTA to a reaction mixture increased the yield
of 3 signi®cantly (see Table 1). However, the addition of
HMPTA to Ph3Sb did not affect the yield of the product 2.
Thus, 2-hydroper¯uoropropyl azide, 1, can be regarded,
to some extent, as a synth of the following mixture:
CF3CHFCF2N3 ) ‰F2Š ‡ N2 ‡ CF3CHFCN
2. Experimental
19 F NMR spectra were recorded on a Bruker CXP-200
spectrometer. Chemical shifts are reported in ꢀ-units down-
®eld from external CF3COOH. Melting points are uncor-
rected. Ph3Sb, Ph2Te2 and Ph3Bi were commercial reagents,
Ph2Te [27] and 2-hydroper¯uoropropyl azide, 1, [25] were
synthesized according to literature procedures. Ph3SbF2 and
Ph2TeF2 for 19 F NMR spectra were synthesized from XeF2
and Ph3Sb [28] and Ph2Te, respectively. When products
were not isolated, their yields were determined by 19 F NMR
(an exact amount of m-¯uorotoluene was added to a reaction
mixture and the signals were integrated).
12 170ꢀC; 3 5 h
Ph2Te ‡ CF3CHFCF2N3
!
Ph2TeF2
3
(3)
pꢁCO† ˆ45 50 atm
1
2
The reaction of Ph2Te2 with 1 does not produce the
expected PhTeF3, 4, but gives di¯uoride 3, probably as a
result of the thermal decomposition of the starting ditellur-
ide (reaction (4)):
2.1. Triphenylantimony difluoride, 2
(4)
350 mg (1 mmol) of Ph3Sb, 580 mg (3 mmol) of azide 1
and 3 ml of dry methylene chloride were mixed in a Te¯on
vessel, sealed in a 100 ml stainless steel bomb and the bomb
was heated at 1208C for 5 h. The bomb was cooled, the
reaction mixture was evaporated. Three hundred and ninty
mg (1 mmol, 100%) of Ph3SbF2 (2) was obtained, mp 118±
1198C. After recrystallization from CH2Cl2: hexane mp
1218C. 19 F NMR (ꢀ, ppm): 74.8 s. Lit. data: mp 121±
1228C [28].
The mechanism of the ¯uorination reaction is undoubt-
edly similar to that described for P(III) compounds [25]
(Scheme 1), and includes a Staudinger-like reaction ± steps
(a) and (b), and sigmatropic ¯uorine transfer with the
formation of a stable nitrile and strong Element-F bonds (c).
2.2. Diphenyltellurium difluoride, 3
280 mg (1 mmol) of Ph2Te, 580 mg (3 mmol) of the azide
1, 3 ml of dry methylene chloride and 0.4 ml of HMPTA
were mixed in a Te¯on vessel and sealed in a 100 ml
stainless steel bomb. The bomb was charged with CO2
(45±50 atm), closed and then was heated at 1708C for
Scheme 1.

S.A. Lermontov et al. / Journal of Fluorine Chemistry 94 (1999) 43±45
45
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according to the integral intensity of the signals. 19 F NMR
(ꢀ, ppm): 49.5, J(Te±F)ˆ568 Hz. After recrystallization
from methylene chloride/hexane, mp 1528C. Lit. data: mp
1538C [29].
The authentic sample of 3 was also prepared by the
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Acknowledgements
This work was supported by the Russian Foundation of
Basic Research (grant no. 98-03-32997).
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