884
J. Am. Chem. Soc. 1999, 121, 884-885
phoryl azide nitrene insertion chemistry may be due to the inherent
moisture sensitivity of many phosphoryl azides or because of
difficulties in the preparation of phosphoryl compounds with
multiple azide groups.
Synthesis and Reactivity of Alkoxy, Aryloxy, and
Dialkylamino Phosphazene Azides
Michael B. McIntosh, Thomas J. Hartle, and
Harry R. Allcock*
Cyclic phosphazene trimers (N3P3R6) offer a possible solution.
The presence of three phosphorus atoms in these species allows
easy access to compounds with two or three azido groups per
molecule. Also, the properties of phosphazenes can be controlled
by the organic groups connected to the phosphazene ring. The
incorporation of appropriate cosubstituent groups should provide
azido compounds with acceptable stability.26 Despite these
potential advantages, only a few phosphazene azide compounds
have been prepared. These include the shock-sensitive hexa-azido
cyclic trimer [NP(N3)2]3, a triazido-trichloro trimer (N3P3Cl3(N3)3),
a pentafluoroazido trimer (N3P3F5(N3)), a pentaphenylazido trimer
(N3P3(C6H5)5(N3)), a hexaphenyldiazido tetramer (N4P4(C6H5)6-
(N3)2), and several ethylenediaminotetrazido trimers.27-32 Little
investigation of the nitrene chemistry of phosphazene azides has
been conducted, and no evidence of insertion chemistry has been
reported.
The primary goal of this research was to prepare new
phosphazene azido cyclic trimers which also contain aryloxy,
alkoxy, or dialkylamino cosubstituent groups and to examine the
reactivity of the phosphazene azides toward phosphorus(III)
compounds. Numerous organic azides are known to react with
phosphorus(III) species to form imine (NdP) bonds.4,18,33 An
objective of this work was to determine how organic substituents
in both the cyclophosphazene azide and the phosphorus(III)
species affect the formation of the imine bonds. In addition, it
was of interest to determine if the azido derivatives are capable
of undergoing nitrene chemistry. It is known that aryloxy or
alkoxy groups are necessary before phosphoryl compounds will
undergo these reactions.17-19 By contrast, compounds with direct
carbon-phosphorus or amine-phosphorus linkages normally
rearrange in preference to nitrene formation.
In this investigation, phenoxy groups were utilized in mono-
(N3P3(OPh)5(N3)), di- (N3P3(OPh)4(N3)2), and triazido phenoxy
trimers (N3P3(OPh)3(N3)3). 2,2,2-Trifluoroethoxy groups were
employed in the alkoxy derivative (N3P3(OCH2CF3)5(N3)). The
dimethylamino group was used in N3P3(NMe2)4(N3)2, and the
diethylamino group was incorporated in a triaminotriazido phos-
phazene (N3P3(NEt2)3(N3)3).
The synthesis of the azido trimers, with the exception of
N3P3(OCH2CF3)5(N3), was accomplished through treatment of the
corresponding chloro-organocyclophosphazene with sodium azide
in the presence of a catalytic amount of tetrabutylammonium
bromide.34 The reactions were complete within 18 h in refluxing
2-butanone, toluene, or THF. A typical synthesis is illustrated in
Department of Chemistry, The PennsylVania State UniVersity
152 DaVey Laboratory, UniVersity Park, PennsylVania 16802
ReceiVed September 28, 1998
The synthesis of cyclic trimeric phosphazene azides with
aryloxy, alkoxy, or dialkylamino cosubstituents is described. The
azide functional trimers were shown to react with various
phosphorus(III) species to form phosphazene phosphinimines. The
aryloxy azido trimers also undergo insertion chemistry typical of
acyl nitrenes during thermal decomposition at temperatures above
250 °C.
During the past fifty years, organic azides have developed into
important synthetic reagents. Numerous alkyl, acyl, aryl, and vinyl
azides have been utilized to prepare iminophosphoranes (R-Nd
PR′3) which have been employed as building blocks in the
construction of nitrogen-containing heterocycles via aza-Wittig
chemistry.1-3 Other organic azides have been developed for
applications in photoresists, vulcanization, polymer coupling and
cross-linking, and for the surface modification of polymers and
metals.4-13 Aryl azides (PhN3), sulfonyl azides (RSO2N3), and
azidoformates (ROC(dO)N3) have been the principal compounds
analyzed due to their ability to form reactive nitrene intermediates
that are capable of insertion into chemical bonds including
unreactive examples such as C-H. Phosphoryl azides ((RO)2P-
(dO)N3) also form nitrene compounds which undergo insertion
reactions, but relatively little nitrene insertion chemistry appears
to have been conducted with these materials.14-19 Most of the
recent work utilized phosphoryl azide-promoted coupling or
polymerization of organic monomers to produce polypeptides,
polyamides, polyureas, or polyurethanes.20-25 The lack of phos-
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(26) Allcock, H. R. Phosphorus-Nitrogen Compounds. Cyclic, Linear, and
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(34) Isolation of pure N3P3(OCH2CF3)5(N3) has so far been unsuccessful
due to the difficulty of removal of N3P3(OCH2CF3)6. However, its synthesis
has been confirmed by 31P NMR spectrometry and the isolation of its
phosphorus(III) imines: N3P3(OCH2CF3)5(NdPPh3) and N3P3(OCH2CF3)5(Nd
P(OPh)3).
(20) Jin, S.; Mungara, P. M.; Gonslaves, K. E. J. Polym. Sci., Part A:
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10.1021/ja983424q CCC: $18.00 © 1999 American Chemical Society
Published on Web 01/14/1999