Journal of Fluorine Chemistry 92 (1998) 173±176
Triphenylmethyl ¯uoride as a ¯uorinating agent in
phosphorus±halogen chemistry
Volker Plack, Jens R. Goerlich, Reinhard Schmutzler*
È È
Institut fur Anorganische und Analytische Chemie der Technischen Universitat, Postfach 3329, D-38023 Braunschweig, Germany
Received 26 June 1998; accepted 24 August 1998
Abstract
Triphenylmethyl ¯uoride 1 will effect chlorine±¯uorine exchange in certain phosphorus chlorides. Exchange of chlorine for ¯uorine was
observed only in ꢀ3ꢁ3 (P)- and ꢀ5ꢁ5 (P)-compounds, while phosphorus oxychloride as an example of a ꢀ4ꢁ5 (P)-compound was unreactive
towards 1. # 1998 Elsevier Science S.A. All rights reserved.
Keywords: Triphenylmethyl ¯uoride; Phosphorus±¯uorine compounds; Chlorine±¯uorine exchange
1. Introduction
2. Results and discussion
Owing to their often unique properties, ¯uorinated com-
pounds have found broad interest in chemistry, e.g. [1]. A
key step in their synthesis is, in many cases, the exchange of
a suitable leaving group (e.g. ±Hal, ±OTos, ±OSiMe3) for
¯uorine [1].
Owing to the effective electron charge delocalization over
its three phenyl rings, the triphenylmethyl group is known to
form carbocations of unique stability [2], which explains the
enhanced ionic character of many triphenylmethyl-element
compounds. When we tried to use TrtF
1
The reagents employed in effecting such exchange are
frequently beset with disadvantages. Ionic reagents are
poorly soluble in many common organic solvents and
special solvents or additional reagents, e.g. crown ethers
which contaminate the product may be required. On the
other hand many covalent reagents are of high reactivity but
low selectivity. Further problems may arise from toxicity,
sensitivity to moisture, and handling dif®culties. The syn-
thesis of selective reagents of more complex structure is
often dif®cult, and may require special laboratory equip-
ment. The few selective reagents which are commercially
available are expensive throughout, so that their application
is limited to cases in which only small amounts of them are
needed.
(Trttriphenylmethyl, CPh3) as an alkylating agent in phos-
phorus chemistry [3], we observed that in several cases,
exchange of chlorine for ¯uorine rather than alkylation, had
taken place.
Phosphorus trichloride was readily converted to phos-
phorus tri¯uoride 2 upon treatment with three equivalents of
1 at r.t. (Scheme 1). No mixed ¯uorinated species were
observed. The same product, 2 was obtained in the reaction
of di¯uorochlorophosphine and 1.
Triphenylmethyl ¯uoride 1 failed to act as a chlorine±
¯uorine exchange reagent on phosphorus oxychloride. Not
even traces of the desired phosphorus oxy¯uoride P(:O)F3 or
mixed halogenated compounds were observed in the reac-
tion mixture after 18 h at r.t.
For that reason we wish to present our observations
regarding the potential of triphenylmethyl ¯uoride 1 as a
reagent useful for halogen±¯uorine exchange in phosphorus
chemistry. Triphenylmethyl ¯uoride 1 is only slightly sen-
sitive to moisture. A new synthesis of 1, based on cheap
starting materials, and also suitable on a large scale, without
any special equipment, is indicated.
Phosphorus pentachloride, on the other hand, upon treat-
ment with six equivalents of 1, was quantitatively converted
to triphenyl-methylcarbenium hexa¯uorophosphate 3 within
15 min at r.t. In this case the metathesis, which produced the
strong Lewis acid PF5 [4] as a putative intermediate, was
followed by abstraction of ¯uoride ion from 1 by phosphorus
penta¯uoride (Scheme 1).
An attempt to exchange chlorine for ¯uorine in
dichlorophosphines, e.g. tert-BuPCl2 and (Et2N)PCl2, was
unsuccessful. Surprisingly, the reaction between diphenyl-
*Corresponding author. Tel.: +49-531-391-5304; fax: +49-531-391-
5387; e-mail: r.schmutzler@tu-bs.de
0022-1139/98/$ ± see front matter # 1998 Elsevier Science S.A. All rights reserved.
P I I : S 0 0 2 2 - 1 1 3 9 ( 9 8 ) 0 0 2 7 2 - 3