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Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Chlorine/oxygen transfer reactions of [PCl2N]3
using oxygenated Lewis bases as a possible route
to [PON]3
Benjamin S. Thome, Savannah R. Snyder, Joanna M. Beres, Patrick O.
Wagers, Matthew J. Panzner, Brian D. Wright, Wiley J. Youngs & Claire A.
Tessier
To cite this article: Benjamin S. Thome, Savannah R. Snyder, Joanna M. Beres, Patrick O.
Wagers, Matthew J. Panzner, Brian D. Wright, Wiley J. Youngs & Claire A. Tessier (2016) Chlorine/
oxygen transfer reactions of [PCl2N]3 using oxygenated Lewis bases as a possible route
to [PON]3, Phosphorus, Sulfur, and Silicon and the Related Elements, 191:4, 671-674, DOI:
10.1080/10426507.2015.1128934
To link to this article: http://dx.doi.org/10.1080/10426507.2015.1128934
Accepted author version posted online: 14
Jan 2016.
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2. PHOSPHORUS, SULFUR, AND SILICON
, VOL. , NO. , –
http://dx.doi.org/./..
Chlorine/oxygen transfer reactions of [PClN] using oxygenated Lewis bases as a
possible route to [PON]
Benjamin S. Thome, Savannah R. Snyder, Joanna M. Beres, Patrick O. Wagers, Matthew J. Panzner, Brian D. Wright, Wiley
J. Youngs, and Claire A. Tessier
Department of Chemistry, University of Akron, Akron, Ohio, USA
ARTICLE HISTORY
Received  December 
Accepted  December 
KEYWORDS
Phosphazene; Cl/O
exchange; P NMR
ABSTRACT
The reactions of [PCl2N]3 with oxygen containing Lewis bases (O=E) such as hexamethylphosphoramide
(HMPA) and triethylphosphine oxide result in Cl/O exchange. The reactions occur via a two-step process
which involves (1) formation of an intermediate salt [P3N3Cl5O]-
[E-Cl]+
and (2) attack by more O=E to form
P3N3Cl4O-O=E and [E-Cl]+
[Cl]−
. In addition to spectral characterizations, both phosphazene products of the
HMPA reactions have been characterized by X-ray crystallography. As shown by reaction chemistry and the
Gutmann–Beckett Lewis acidity scale, the P=O of the phosphazene ring in P3N3Cl4O-O=E has a strong Lewis
acid character. We also discuss attempts to use other O=E and more vigorous reaction conditions with the
goal of preparing [PON]3 or its base-stabilized adducts. Such molecules could be precursors to novel PNO
materials.
GRAPHICAL ABSTRACT
Introduction
Phosphazenes are one of the largest and most versatile classes
of inorganic polymers with many applications already known.1
Through substitution of chlorophosphazenes hundreds of
unique phosphazene compounds can be synthesized, making
fundamental research of chlorophosphazenes vital to phosp-
hazene chemistry. A new application of phosphazene chem-
istry might be as precursors to phosphorus oxynitride (PON).
PON is of interest because it is isoelectronic and isostructural
to SiO2.
2,3
The small molecule [PON]3, which could serve as
a precursor to PON, has been reported in patent literature,4
in
gas phase calculations,5
and has been proposed to be a byprod-
uct in the synthesis of β-sultams by the reaction of [PCl2N]3
and sulfonic acids in the presence of trimethylamine.6
This lat-
ter reaction involves Cl/O transfers between [PCl2N]3 and sul-
fonyl compounds, appears to involve the precursor compound
P3Cl4N3O (Figure 1) and may be related to the reaction of
DMSO with [PCl2N]3 that led to the formation of various oxy-
genated phosphazene rings, some of which retain the DMSO
base.7,8
CONTACT Claire A. Tessier tessier@uakron.edu Department of Chemistry, University of Akron,  E Buchtel Commons, Akron, Ohio -, USA.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpss.
Herein, we present the first reported Cl/O transfer reactions
between [PCl2N]3 and P=O containing Lewis bases as possi-
ble routes to a [PON]3 small molecule. The Lewis acidity of
the P3N3Cl4O fragment by way of the Gutmann–Beckett Lewis
acidity scale was also examined in an effort to understand the
bonding within the substituted phosphazene fragments. We also
report the investigation of the reaction [PCl2N]3 with methyl
sulfonic acid in the presence of triethylamine under conditions
similar to those reported earlier.6
Results and discussion
Reaction of [PCl2N]3 and HMPA
When reacted with HMPA, [PCl2N]3 was found to undergo
Cl/O transfers on a single phosphorus center of the phosphazene
ring (Scheme 1). In the first step, one chlorine atom on the phos-
phazene ring was replaced with an oxygen from HMPA lead-
ing to the formation of [P3N3Cl5O]−
[Cl-P(NMe2)3]+
. Multinu-
clear NMR spectra and an X-ray crystal structure were obtained
©  Taylor & Francis Group, LLC
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3. 672 B. S. THOME ET AL.
Figure . Structure of PClNO and [PON].
Scheme . Reactions of [PClN] with O=E (O=P(NMe), or O=PEt).
of this material. If allowed to react further with more HMPA,
a second Cl/O transfer occurs on the same phosphorus center
as the first, leading to the formation of a [P3N3Cl4O-HMPA]
complex and a byproduct salt [PCl(NMe2)3]+
[Cl]−
(Scheme 1).
These compounds have been characterized by NMR, ESI-MS,
and X-ray crystallography.
The X-ray crystal structure of [P3N3Cl4O-HMPA] is
depicted in Figure 2. The most interesting structural features of
the P3N3Cl4O-HMPA complex are the three different P-O bond
lengths, two of which are part of a P-O-P fragment. The P-O
bond that is not part of the P-O-P fragment (P(2)-O(2)) is the
shortest and has a bond length consistent with a normal double
Figure . Thermal ellipsoid plot of PNClO-HMPA, drawn at the % probability
level. Hydrogen atoms are omitted for clarity.
bond. The P-O bonds of the P-O-P fragment have different
lengths. The P-O bond from the phosphazene ring (P(2)-O(1))
is significantly longer than a normal single bond suggesting that
the interaction between the P3N3Cl4O fragment and HMPA is
a dative interaction. Therefore, it appears that the phosphorus
center of the P=O fragment of P3N3Cl4O (Figure 1) is Lewis
acidic.
Reaction of [PCl2N]3 and POEt3
The reaction of [PCl2N]3 and POEt3 was found to follow a sim-
ilar pattern as that of HMPA (Scheme 1). When OPEt3 was
reacted with [PCl2N]3 a Cl/O transfer occurs, resulting in the
formation of the species [P3N3Cl5O]−
[PCl(Et)3]+
, upon con-
tinued reaction a second Cl/O transfer yields the Lewis adduct
P3N3Cl4O-PO(Et)3. Though a crystal structure could not be
obtained, P3N3Cl4O-PO(Et)3 was identified in part through
a unique triplet of doublet signal in its 31
P NMR spectrum
(Figure 3, signal A). The phosphorus center of the P=O frag-
ment of P3N3Cl4O couples to the two equivalent phosphorus
atoms in the ring and to the phosphorus atom of the POEt3.
The use of POEt3 as a reagent in Scheme 1 was chosen specif-
ically because this would allow for the determination of the rel-
ative Lewis acidity of P3N3Cl4O by use of the Guttman-Beckett
acceptor number (AN) scale. By measuring the shift in the 31
P
signal from POEt3 fragment that was bound to P3N3Cl4O, an
AN can be derived using the formula in eq. 1, where the num-
ber 41 corresponds to the 31
P NMR shift of unreacted POEt3 in
hexane.8
AN = 2.21 × (δ31
P(LA ·
.
OPE t3) − 41) (1)
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4. PHOSPHORUS, SULFUR, AND SILICON 673
Figure . P NMR spectra of products formed by the reaction of [PClN] and POEt.
The 31
P NMR signal for the POEt3 fragment of P3N3Cl4O-
POEt3 was found at 93 ppm, which corresponds to an AN for
the P3N3Cl4O fragment of 115. This suggests that P3N3Cl4O has
a greater Lewis acidity than many well-known Lewis acids such
as SbCl5, AlCl3, B(C6F5)3 and SnCl4 which had ANs of; 100, 87,
82, and 59, respectively.8
Calculations on [PON]3 indicate there
is a much positive charge on the phosphorus atoms.5
There-
fore, the existence of considerable positive charge for the phos-
phorus atom of the P=O moiety of P3N3Cl4O is not altogether
surprising.
Reaction of [PCl2N]3 and methanesulfonic acid
While researching the above reactions, another possible route
to [PON]3 was suggested by Zarei who proposed that both
P3N3Cl4O and [PON]3 were formed as byproducts from the
reaction of [PCl2N]3, sulfonic acids, triethylamine and imines.6
No characterizational data was provided for either P3N3Cl4O or
[PON]3, which were removed by an aqueous work-up. The pro-
posed mechanism of the formation P3N3Cl4O and [PON]3 did
not involve the imine reagents.6
Therefore we investigated reac-
tions without the imines.
We attempted to isolate [PON]3 or P3N3Cl4O by reacting
[PCl2N]3 with methanesulfonic acid and triethylamine. It was
discovered that order of addition was important for the suc-
cess of the reaction. If the three reactants are added together
at once little to no reaction occurs. The sulfonic acid species
must be added to Et3N first and stirred, allowing the sulfonic
acid to deprotonate and generate the more Lewis basic species
CH3SO3
−
. This anion then goes on to react with [PCl2N]3.
A mixture of products was obtained. Based on multinuclear
NMR spectra, especially 31
P, the major product appears to be
a NEt3 adduct of P3N3Cl4O. Despite using higher stoichiomet-
ric amounts of CH3SO3H and Et3N as well as harsher reaction
conditions, reaction of only one of the PCl2 groups of [PCl2N]3
was observed by multinuclear NMR thus far.
Conclusions
The reactions of [PCl2N]3 with several P=O or S=O reagents
results in Cl/O transfer processes. To date, all our experiments
indicate that only one of the three PCl2 moieties of [PCl2N]3
reacts easily. We observe formation of Lewis base complexes of
P3N3Cl4O but we see no evidence of [PON]3 or its complexes.
Acknowledgments
The authors thank the Goodyear Corporation for donation of an NMR
instrument used in this work.
Funding
The authors thank Israel Chemical Limited and OMNOVA Foundation
for support. The authors also thank the National Science Foundation
and the Ohio Board of Regents for funds used to purchase the NMR
(CHE-9977144), MS (DMR-0821313) and the X-ray diffractometer (CHE-
0116041) instruments used in this work.
References
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University Press: New York, 2005.
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2012, 51, 4707–4709.
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