The mechanism of a phosphazene-phosphazane rearrangement

Article abstract of DOI:10.1039/c5dt02762d

The phosphazene-phosphazane rearrangement of N₃P₃Cl₅O(CH₂)₂OC(O)CMeCH₂ (8) has been examined in detail using one and two dimensional NMR (³¹P, ¹H) spectroscopy and mass spectrometry. The mixed phosphazene-phosphazane [NPCl₂]₂[N((CH₂)₂OC(O)CMeCH₂)P(O)Cl] (14), [NPCl₂]₂[NHP(O)Cl] (13) and a two ring assembly [NPCl₂]₂[NP(O{(NPCl₂)₂(N((CH₂)₂OC(O)CMeCH₂)P(O)}] (15) have all been detected in the product mixture. The rate of the rearrangement has been measured at five temperatures by ³¹P and ¹H NMR. The reaction is first order in 8 (T_1/2 at 111° is 4.65 hours). The activation enthalpy is positive and the activation entropy is negative. A mechanism involving competing intra and inter molecular processes which fits the product distribution and kinetic data has been proposed. Several other methyacrylphosphazenes were examined under the same thermolysis conditions. The rearrangement was observed and the rates obtained in cases where the (CH₂)₂ spacer unit of the methacrylate was replaced by linear and branched propyl units. The rearrangement was not observed when the methacrylate was appended to a spirocyclic unit, the spacer unit was extended to the n-butyl group and when the methacrylate unit was replaced by a methoxy group. These results are all consistent with the proposed mechanism. This investigation resolves conflicting results previous reported for the rearrangement.

Full text of DOI:10.1039/c5dt02762d

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DOI: 10.1039/C5DT02762D
The Mechanism of a Phosphazene-Phosphazane
Rearrangement.
Robert F. Hayesa and Christopher W. Allena
ABSTRACT
The
phosphazene-phosphazane rearrangement of N3P3Cl5O(CH2)2OC(=O)CMe=CH2 (8)has been examined in
detail using one and two dimensional NMR ( 31P, 1H) spectroscopy and mass spectrometry. The mixed
phosphazene-phosphazane [NPCl2]2[N((CH2)2OC(=O)CMe=CH2)P(O)Cl](14), [NPCl2]2[NHP(O)Cl] (13) and a
two ring assembly [NPCl2]2[NP(O{(NPCl2)2(N((CH2)2OC(=O)CMe=CH2)P(O)}]
(15) have all been detected in the product mixture. The rate of the rearrangement has been measured
at five temperatures by 31P and 1H NMR. The reaction is first order in 8 (T1/2 at 1110 is 4.65 hours). The
activation enthalpy is positive and the activation entropy is negative. A mechanism involving competing
intra and inter molecular processes which fits the product distribution and kinetic data has been
proposed. Several other methyacrylphosphazenes were examined under the same thermolysis
conditions. The rearrangement was observed and the rates obtained in cases where the (CH2)2 spacer
unit of the methacrylate was replaced by linear and branched propyl units. The rearrangement was not
observed when the methacrylate was appended to a spirocyclic unit, the spacer unit was extended to
the n-butyl group and when the methacrylate unit was replaced by a methoxy group. These results are
all consistent with the proposed mechanism. This investigation resolves conflicting results previous
reported for the rearrangement.
a Department of Chemistry, University of Vermont, Burlington, VT 05405-0125. E-
mail: christopher.allen@uvm.edu
INTRODUCTION
The phosphazene-phosphazane rearrangement is a process in which the formal double bond in a
phosphazene unit rearranges to a formal phosphorus-nitrogen single bond (phosphazane) accompanied
by the migration of a hydrogen atom or alkyl group from a POR center to the phosphazene nitrogen
atom leaving formal phosphorus–oxygen double bond. 1-6 This process has been known for

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a long time and plays an important role in cyclo- and polyphosphazes3 but a full understanding of the
mechanism by which the process occurs has yet to be presented. The simplest system in the
cyclophosphazenes is in the degradative hydrolysis of hexachlorocyclotriphosphazene,N3P3Cl6
(1)(Scheme 1), where the rearrangement of the hydroxyphosphazene(2) eventually leads to
-Insert Scheme 1-
trimetaphosphinic acid, [NHP(O)OH]3(3).2,7-9 Semi empirical calculations confirm the energetically
favorable nature of the hydrolysis rearrangement and suggest a proton stabilized by both the oxygen
and nitrogen centers in the intermediate.10 The hydrolytic rearrangement has also been studied by solid
state NMR and the results reproduced by ab initio methods.11 The most widely examined system has
been N3P3(OMe)6(4)1-6,11,12 which undergoes the rearrangement in the distillation temperature range to
give the cyclophosphazane (5). The process can be catalyzed by added alkyl halides.3 Substituent
exchange has been observed in the thermolysis of the N3P3(OMe)6/N3P3(OCD3)6 mixture suggesting an
intermolecular process.13 The rearrangement occurs in the larger per methoxy substituted
cyclophosphazenes,[NP(OMe)2]n up to the hexamer.13,14 The rearrangement of mixed substituent
trimers such as 2,2-N3P3R2(OMe)4(6) leads to six membered rings with both phosphazene and
phosphazane bonds(7).14,15 Certain of these have been examined by X-ray crystallography and the
relative orientations of the phosphoryl and methoxy groups was established.3,15,16 The fact that
poly(dimethoxyphosphazene) also undergoes this rearrangement12,17 has significant implications for the
stability of poly(phosphazenes). The replacement of the methyl group with larger alkyl groups leads to
decomposition in the thermolysis of N3P3(OR)6 ( R= Et,Pr).14 Detailed investigations of the alkoxy
phosphazene-phosphazane rearrangement processes in mixed substituent, alkoxy and (p-
methylphenoxy), derivatives have been reported.14,15 An increase in the number of aryloxy groups or
lengthening of the alkoxy chain leads to an increase in the temperature required for the rearrangement
to occur. Evidence for both inter- and intramolecular pathways was obtained as was evidence that the
first rearrangement in a molecule undergoing multiple rearrangements is the slowest step. 15 While
there have been some kinetic studies, they have been on systems with a high impurity level.
Furthermore, the order of the kinetics was not determined.12 We have previously noted that a
phosphazene-phosphazane rearrangement may be occurring in attempts to purify the monomer,
N3P3Cl5O(CH2)2OC(=O)CMe=CH2(8) by distillation.18,19 If this were to be the case, this would be a system
with only one opportunity for the rearrangement and would be an excellent candidate for a detailed
product and kinetic analysis allowing for a detailed understanding of the phosphazene-phosphazane
rearrangement. This study is reported in this paper.
EXPERIMENTAL SECTION
Materials and Methods. Organic compounds were purchased from Aldrich Chemical Company
and used as delivered except where noted. Solvents such as anhydrous diethyl ether, hexanes,
tetrahydrofuran, toluene, benzene and methylene chloride were purchased from J.T. Baker, Inc. THF
and benzene were dried by distillation over potassium metal prior to use. 4-Hydroxybutyl methacrylate,
hydroxypropyl methacrylate, and were purchased from Polysciences, Inc..
Hexachlorocyclotriphosphazene (1) was received from Nippon Soda Co. and was sublimed prior to use.

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Spiro(2,3-dioxypropylmethacryl)tetrachlorocyclotriphosphazene(9) was prepared by a previously
reported procedure.20 Deuterated solvents (CDCl3, C6D8, d8-toluene, d8-THF) were purchased from
Cambridge Isotope Labs, Inc. and used as delivered except where noted.
NMR spectra were acquired on a Bruker ARX-500 spectrometer equipped with an Aspect Station
Computer. Data work-up was done using Bruker UXNMR software running under the UNIX/X11
operating system. Spectrometer operating frequencies were 500.13 MHz(1H), 202.46 MHz(31P), and
125.76 MHz(13C). Tetramethylsilane was used as an internal reference for 1H and 13C spectra and 85%
H3PO4 as an external reference for 31P spectra. Broad band (Waltz16) 1H decoupling was used for 13C
experiments. Gated decoupling experiments utilized standard Bruker parameter sets and pulse
programs as did two dimensional experiments (COSY and HETCOR). Time domain data sizes for COSY
experiments were adjusted as needed for adequate resolution and zero filling in the f1 domain was used
to square the frequency domain data matrix when necessary. NMR spectra were simulated using the
UNEANMR21 and WinDaisey22 programs. Infrared spectra were recorded on a Perkin Elmer System 2000
FT-IR. Mass spectral analysis was done on a Finnigan 4610 spectrometer operating at ionization energy
of 70 eV.
The rate of the rearrangement process was followed by 31P and 1H NMR spectroscopy. A 10.0mL
volumetric flask was charged with 0.30g of (2-oxyethyl methacryl)pentachlorocyclotriphosphazene (8)
and ~ 2mL of d8-toluene and the phosphazene was dissolved. The flask was brought up to volume,
sealed and the contents mixed. NMR tubes were loaded with ~ 1mL of the solution and the head space
purged with dry nitrogen before sealing the cap. The tubes were placed in an immersion finger
containing silicon oil which in turn was inserted into solvent in a three necked round bottom flask,
equipped with a reflux condenser and a stopper in the remaining neck. The kinetic runs were
accomplished by holding the sample at the reflux temperature of the solvent. The solvents employed
were: toluene (111 0C), isopropyl acetate (89 0C), hexane (70 0C), cyclopentane (50 0C) and diethyl ether
(35 0C). Samples were removed at timed intervals, cleaned of oil and analyzed by NMR. For each
measurement, the probe was tuned matched and shimmed. The receiver gain was held constant so that
the absolute value of the difference in integrations would accurately reflect concentration changes. The
signals for the unreacted material were followed as a function of time to a point which was two to three
times that of the reaction half-life. A series of samples were prepared with reduction of trace moisture.
In these cases, ~ 2mL of dry benzene was added to the monomer and removed under vacuum three
times in order to remove water as the benzene –water azeotrope. After the toluene solution was
prepared, a few 3Å molecular sieves were added and the sample was allowed to sit for ~14 hrs. then
~1mL was transferred to a predried, evacuated NMR tube fitted with a septa/stopcock (Wilmad Glass
Co.) and the headspace flushed with dry nitrogen.
Preparation of (2-oxyethyl methacryl)pentachlorocyclotriphosphazene (8). This synthesis is a
modification of a previously reported procude.15 Freshly distilled pyridine (7.0 mL, 0.087 moles) was
added under an inert atmosphere to a solution of hexachlorocyclotriphosphazene (15.00 g, 0.043
moles) and p-methoxyphenol (~5 mg) in anhydrous diethyl ether (100 mL). A solution of hydroxyethyl-
methacrylate (5.4 mL, 0.043 moles) in anhydrous diethyl ether (50 mL) was then added over 0.5 hour
period to the phosphazene-pyridine solution. Stirring was started while adding the alcohol and was

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continued for 48 hours at room temperature as the reaction was allowed to proceed. The reaction
mixture was filtered to remove the pyridine hydrogen chloride and then washed sequentially with 2M
HCl, saturated NaHCO3 solution, and water. The ethereal solution was dried over MgSO4 then filtered
through a plug of Celite. The ether was removed by rotoevaporation to yield 17.80g of a white paste.
Flash chromatography (20% diethyl ether in low boiling petroleum ether)of 2.50 g of the crude solid
yielded 0.79 g of 5 (31%) as a pale yellow oil. Anal. Calcd. For C6H9O3N3P3Cl5: C, 16.33; H, 2.06; N, 9.52;
mol wt 441.34. Found: C, 17.28; H, 2.29; N, 9.19; mol wt 442 (mass spec).
1H NMR (d8-toluene):
δHc6.28 (d of q, 1 H), 2JHcHt=1.6, 4JHcHMe=1.0; δHt 5.40 (d of q, 1 H), 4JHtHMe=1.6; δEt4.00 (m, 4 H); δMe 1.98 (d
of d, 3 H). 13C NMR (CDCL3); δcarbonyl 167.5; δvinyl 136.2; δvinyl 127.2; δ-CH2OP-67.5 (d), 2JCP=6.54; δ-COCH2-62.9
(d), 3JCP=9.31; δMe 18.8. 31P NMR (d8-toluene); δPCl2 24.2 (d), 2JPP=63.9; δPOCl 16.9 (t of t), 3JPH=9.7. IR
(neat); 2959 (m, CH str); 1725 (s, C=O Str); 1638 (m, C=C str); 1452, 1437 (M, CH2 scsr); 1297 (vs, PN str);
1201, 1122 (vs, CO str); 1066, 1041 (vs, PO str); 876 (m, PCl asym); 752 (m, PCl sym).
Preparation of (3-oxypropyl methacryl)pentachlorocyclotriphosphazene (10). Under an inert
atmosphere (N2) freshly distilled pyridine (2.8 mL, 0.035 moles) was added to a diethyl ether (50 mL)
solution of hexachlorocyclotriphosphazene (11.29 g, 0.032 moles) and p-methoxyphenol (~5 mg)
standing over 4Å molecular sieves (~3 g). A solution of 3-hydroxypropyl methacrylate (3.16 g, 0.022
moles) in anhydrous diethyl ether (5 mL) was then added over 10 minute periods to the phosphazene-
pyridine solution. Stirring was started while adding the alcohol and was continued for 72 hours as the
reaction was allowed to proceed at room temperature. The reaction mixture was filtered to remove the
pyridine hydrogen chloride and then washed sequentially with 2M HCl, saturated NaHCO3 solution, and
water. The ethereal solution was dried over MgSO4 then filtered through a plug of Celite. The ether
was removed by rotoevaporation to yield 11.01g of a white paste. Flash chromatography (25% diethyl
ether in low boiling petroleum ether) of 2.67 g of the crude solid yielded 0.90 g of 6 (34%) as a pale
yellow oil. Anal. Calcd. For C7H11O3N3P3Cl5: C, 18.64, H, 2.43; N, 9.23; mol wt 455.37. Found C, 18.42; H,
2.39; N, 9.19; mol wt 556 (mass spec). 1H NMR (C6D6); δHc 6.30 (d of q, 1 H), 2JHcHt=1.6, 4JHcHMe=0.8; δHt
5.43 (d of q, 1 H), 4JHtHMe=1.6; δ-OCH2- 4.12 (t, 2 H), 3JHH=6.0 ; δ-OCH2- 4.04 (d of t, 2H), 3JHH=6.3 ; 3JHP=9.3; δMe
2.04 (d of d, 3 H); δ-CH2- 1.69 (d of d of d, 2 H), 4JHP=1.6. 13C NMR (C6D6); δcarbonyl 167.2; δvinyl137.3; δvinyl
126.1; δ-CH2OP- 67.2 (d), 2JCP=7.6; δ-COCH2- 60.9; δ-CH2- 29.6 (d), 3JCP=9.2; δMe 19.0 31P NMR (CDCL3); δPCL2 23.4
(d), 2JPP=62.9; δPOCl 15.8 (t of t), 3JPH=9.3. IR(neat); 2965 (m, CH str); 1722(s, C=O str); 1639 (m, C=C str);
1470, 1453 (m, CH2 scsr); 1297 (vs, PN str); 1202 (vs, CO str); 1042 (vs, PO str); 878 (m, PCl asym); 743
(m, PCl sym).
Preparation of (4-oxybutyl methacryl)pentachlorocyclotriphosphazene (11). Under an inert
atmosphere (N2) freshly distilled pyridine (1.8 mL, 0.023 moles) was added to a solution of
hexachlorocyclotriphosphazene (7.68 g, 0.022 moles) and p-methoxyphenol (~5 mg) in anhydrous
diethyl ether (50 mL). A solution of 4-hydroxybutyl methacrylate (3.37 g, 0.021 moles) in anhydrous
diethyl ether (50 mL) was then added over 0.5 hour period to the phosphazene-pyridine solution.
Stirring was started while adding the alcohol and continued for 68 hours at room temperature as the
reaction proceeded. The reaction mixture was filtered to remove the pyridine hydrogen chloride and
then washed sequentially with 2M HCl, saturated NaHCO3 solution, and water. The solution was dried
over MgSO4 then filtered through a plug of Celite. The ether was removed by rotoevaporation to yield

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9.63 g of an off white paste. Flash chromatography (25% diethyl ether in low boiling petroleum ether) of
2.53 g of the crude solid yielded 1.18 g of 7 (47%) as a clear viscous liquid. An attempt was made to
vacuum distill the material too but it decomposed in the pot before pure compound could be collected.
Anal. Calcd for C8H13O3N3P3Cl5: C, 20.47; H, 2.79; N, 8.95; mol wt 469.40. Found: C, 21.56; H, 2.81; N,
1
8.69; mol wt 470 (mass spec.). H NMR (C6D6): δHc 6.32 (d of q, 1 H), 2JHcHt=1.8, 4JHcHMe=0.9; δHt 5.45 (d of
q, 1 H),4JHtHMe=1.7; δ-OCH2- 4.07 (t, 2 H), 3JHH=6.1; δ-CH2OP- 3.96 (d of t, 2H), 3JHH=6.0, 3JHP=9.4; δMe2.06 (d of
d, 3 H); δ-CH2- 1.49 (m, 4 H). 13C NMR (C6D6); δcarbonyl 167.4; δvinyl 137.5; δvinyl 125.8; δ-CH2OP- 70.0 (d),
3JCP=9.6; δ-COCH2CH2- 25.4; δMe 19.0. 31P NMR (C6D6); δPCl2 23.4 (d), 2JPP=62.6, δPOCl 15.7 (t of t). IR(neat);
2961 (m, CH str);1720 (s, C=O str); 1639 (m, C=C str); 1471, 1452, 1437 (m, CH2 scsr); 1247 (vs, PN str);
1206 (vs, CO str); 1041 (vs, PO str); 876 (m, PCl asym); 764 (m, PCl sym).
Preparation of (2-(1-oxypropyl) methacryl)pentachlorocyclotriphosphazene (11a) and (1-(2-
oxypropyl) methacryl)pentachlorocyclotriphosphazene (11b). Under an inert atmosphere (N2) freshly
distilled pyridine (5.9 mL, 0.073 moles) was added to a solution of hexachlorocyclotriphosphazene
(10.12 g, 0.029 moles) and p-methoxyphenol (~5 mg) in anhydrous diethyl ether (40mL). A 4.15 g (0.029
mol) solution of hydroxypropyl methacrylate (a mixture of 30% 2-(1-hydroxypropyl)methacrylate and
70% 1-(2-hydroxypropyl)methacrylate) in anhydrous diethyl ether (10mL) was then added over 1.5 hour
period to the phosphazene-pyridine solution. Stirring was started while adding the alcohol and was
continued for 48 hours at room temperature as the reaction was allowed to proceed. The reaction
mixture was filtered to remove the pyridine hydrogen chloride and then washed sequentially with 2M
HCl, saturated NaHCO3 solution, and water. The ethereal solution was dried over MgSO4 then filtered
through a plug of Celite. The ether was removed by rotoevaporation to yield 10.53 g of a white paste.
Flash chromatography (22% diethyl ether in low boiling petroleum ether) of 2.52 g of the crude solid
yielded 0.83 g of a mixture of 4a and 4b (33%) as a clear viscous liquid. Anal. Calcd for C7H11O3N3P3Cl5 :
C, 18.46; H, 2.43; N, 9.23; mol wt 455.37. Found: C, 19.98; H, 2.70; N, 8.99; mol wt 455 (mass spec.).
(2-(1-oxypropyl) methacryl)pentachlorocyclotriphosphazene (11a); 1H NMR (C6D6): δHc 6.35 (d
of q), 1 H), 2JHcHt=1.6, 4JHCHMe= 1.0; δHt 5.42 (d of q, 1 H), 4JHtHMe= 1.6; δCH 5.16 (m, 1 H), 3JHH(-CH2-)=3.4, 5.5,
3JHHMe=6.5; δ-CH2- 4.02 (m, 2 H), 3JHP=9.2; δMe 2.03 (d of d, 3 H); δMe 1.12 (d, 3 H). 13C NMR (CDCl3); δcarbonyl
167.1; δvinyl 137.1; δvinyl 126.6; δ-CH2OP- 71.2 (d), 2JCP=7.6, δ-COCH- 68.9 (d), 3JCP=9.6; δ-CH(CH3)- 16.3; δMe 18.9.
31P NMR(C6D6); δPCl2 23.6 (d), 2JPP=63.8; δPOCl 16.5 (t of t).
(1-(2-oxypropyl) methacryl)pentachlorocyclotriphosphazene (11b); 1H NMR (C6D6); δHc 6.41 (d
of q, 1 H), 2JHcHt=1.6, 4JHcHMe=1.0, δHt 5.46 (d of q, 1 H), 4JHtHMe=1.6; δCH 4.82 (m, 1 H), 3JHH(-CH2-)=6.5,
3JHP=11.7; δ-CH2- 4.08 (m, 2 H0; δMe 2.06 (d of d, 3 H); δMe 1.16 (d, 3 H). 13C NMR (C6D6); δcarbonyl 166.8;
δvinyl 136.8; δvinyl 127.0; δ-CH2OP- 77.4 (d), 2JCP = 8.0; δ-COCH2- 66.9 (d), 3JCP = 7.2; δ-CH(CH3)- 18.0, 3JCP = 7.2; δ-
CH(CH3)- 18.0, 3JCP = 3.2; δMe 18.9. 31P NMR(C6D6); δPCl2 23.3 (d), 2JPP = 63.1; δPOCl 14.8 (t of d of d), 4JPH =3.3.
Mixture of isomers; IR(neat); 2986 (m, CH str); 1724 (s, C+O str); 1639 (m, C=C str); 1452 (m,
CH2 scssr); 1247 (vs, PN str); 1203 (vs, CO str); 1042 (vs, PO str); 873 (m, PCL asym); 764 (m, PCl sym).
Preparation of (2-methoxy-1-oxyethyl)pentachlorocyclotriphosphazene(12). Under an inert
atmosphere (N2) methoxyethanol (5.6mL, 0.71mol) was added slowly to sodium metal in anhydrous

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diethyl ether (50mL) and allowed to react until all of the metal was consumed. The resulting solution
was added slowly to hexachlorocyclotriphosphazene (12.53g, 0.036mol) in anhydrous diethyl ether (125
mL) over 2.0 hours. After stirring for 12 hours at room temperature, the solution was washed
sequentially with 2M HCl, saturated NaHCO3 solution and water. The ethereal phase was dried over
MgSO4 and filtered through a plug of Celite. The ether was removed by rotoevaporation to yield 18.47g
of a creamy white liquid. Flash chromatography (methylene chloride) of 2.52 g of the crude liquid
yielded 1.67 g (66%) of 5 as a white solid ( mp 30.5-31.5 0C) . Anal.calcd for C3H7O2N3P3Cl5: C,9.30;H,1.82;
1
N, 10.85;mol wt 387.29. Found: c, 9.59;H, 1.71;N,10.82; mol wt 388 ( mass spec.). H NMR (CDCl3): δ-
CH2OP- 4.32(m,2H),3JHP= 10.2; δ-COCH2-3.68( m,2H); δMe 3.419 S,3H). 13C NMR (CDCl3: δ-OCH2-71.0(d),3JCP= 9.0 ;
δ
-CH2OP-69.0(d),2JPC 7.7, δMe 59.8. 31P NMR: δPCl2 23.23(d), 2JPP 62.8; δPOCl 16.2 (t of d). IR(neat): 2889(m,CH
str);1451(m,CH2 scsr); 1245(vs,PN str);1201(vs,CO str); 1051( vs,PO str); 891,875( m, PCl asym); 754( m,
PCl sym).
RESULTS AND DISCUSSION
A series of methacrylcyclophosphosphazens (Scheme 2) has been prepared for investigation of the
rearrangement process proposed for 8.18 The identity of each was confirmed by NMR (1H,13C,31P) and IR
-Insert Scheme 2-
spectroscopy and mass spectrometry. Elemental analyses deviated slightly from optimal values which is
most like due to rearrangement and/or residual solvent from the purification procedure. The first step
in understanding the rearrangement process was to identify the products of the thermolysis of 8. The
31P NMR spectra of 8 before and after heating at 111 0C for 10 hours are shown in Figure 1. The initial
spectrum is the expected doublet and triplet arising from a mono substituted cyclophosphazene.
- Insert Figure 1 -
The sample was heated until there was no further change in the relative peak heights in the spectrum.
The resulting spectrum showed evidence for several components. The combination of high hydrolytic
sensitivity and polarity potentially made isolation of the products difficult, however they could be
identified using NMR spectroscopy and mass spectrometry. A 31P COSY spectrum (Figure S1) showed
four components. The spectrum of 8 was easily identified from the starting material and the published
NMR parameters. 15 The simplest spectrum (doublet, triplet) of the remaining products does not show
any coupling from a CH2 site and matches the known7,8 spectrum reported for (NPCl2)2P(O)NH (13). The
spectra for the remaining two products, 14 and 15 are shown in Figures 2 and 3 respectively. Since
precise measurements of the NMR parameters were complicated by signals arising from other
components, the spectra were also simulated and the NMR data are reported in Table S.1.
-Insert Figure 2-
-Insert Figure 3-

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Compound 14 was identified as the diphosphazene, 1-(N-ethylmethacryl)-2-oxo-2,44,4,6,6 –
pentachlorocyclo-3,5-diphosphazene, obtained from the phosphazene-phosphazane rearrangement of
8. The 31P NMR spectrum shows three unique phosphorus centers. The chemical shift of the alkoxy
center in 8 (16.9 ppm) is replaced by the phosphoryl center of 14 at -10.7 ppm. The PCl2 centers are no
longer equivalent (29.2 and 17.6 ppm). Identification of the high frequency center to the 6 position
(adjacent to the substituted nitrogen center) was based on the observation of PH coupling from the
methylene center attached to the nitrogen. Similar coupling is seen for the phosphoryl center. The JPP
values in 14 are noticeable lower than those observed in 8 due to the decreased s character at nitrogen
upon going from a sp2 nitrogen in 8 to a sp3 nitrogen atom in 14. The 13C and 1H NMR data (Table S.1.)
are all consistent with the assignment of the structure of 14. The 31P NMR spectrum of 15 which shows
five unique phosphorus centers suggested a multi ring assembly. The mass spectrum of the mixture
shows a fragment at m/e of 735 and an isotope pattern from nine chlorine atoms. The connectivity of
the phosphorus centers was established by the 31P COSY spectrum. A comparison of Figures 2a and 3a
shows a phosphazane unit in 15 which is equivalent to that in 14. The phosphoryl center (Figure 3e)
shows additional phosphorus coupling relative to that in 14. The JPP values for phosphorus atoms a, c
and e are in the range noted for 14 while those for d and b are typical of phosphazenes. The chemical
shifts for d and b are very similar to the previously reported values for ( N3P3Cl5)20. 7 These data allow for
assignment of 15 to the oxo bridged dimer shown in Figure 3. Examination of the 1H NMR spectrum
shows, in addition to the resonances arising from 8,14and 15, the spectrum of 2-
chloroethylmethacrylate, CH2=C(Me)C(O)O(CH2)2Cl (16) which was confirmed by comparison to an
authentic sample of same and the observation of the parent ion ( m/e 148) in the mixture mass
spectrum. The concentration of 16 undergoes a significant increase in the late stages of the
rearrangement.
The rearrangement process proceeds slowly enough that rates can be reliably measured by NMR
spectroscopy. Changes in the intensities of both 31P and 1H NMR spectra of the same sample of 8 were
recorded. A second set of 31P NMR measurements on a sample of 8 that was not as rigorously dried
were also obtained. The rates were followed at five temperatures (1110, 890, 700, 500 and 350C) and
always found to fit a first-order rate law. The data and the details of the kinetic fit analyses can be
found in Tables S2, S3 and S4 for the 31P “dry” sample, 31P “wet “sample and 1H respectively. The rate
vs. temperature data was used to generate Eyring plots (Figure S2). The plots exhibited some curvature
especially in the low temperature region so the 350C data was not used in the regression analysis. The
curvature may be related to competing reactions (polymerization and/or hydrolysis) or the activation
parameters may be temperature dependant.23 The Eyring plot and calculations are found in Table S5.
Half life and activation parameter data can be found in Table 1. The internal consistency of the 31P and
-Insert Table 1-
1H NMR data for the dry sample confirms the accuracy of the results. The parameter variation on going
to the less rigorously dried sample demonstrates the importance of the solvent properties in the
rearrangement process. The first order rate behavior and the negative entropy of activation indicate a
dissociative process which somewhat counter intuitively goes to a more organized transition state. The
endothermic enthalpy of activation is consistent with bond breaking in the transition state. A

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mechanism which fits all of the kinetic data and the product distribution is shown in Scheme 3. The
proposed first step involves formation of an intimate ion pair through a transition state where the
developing carbocation is stabilized by an electrostatic interaction with the carbonyl oxygen.
-Scheme 3-
The increased structural organization generated by the carbocation stabilization contributes to the
positive entropy of activation. In general formation of ions from a neutral species results in an entropic
increase which is attributed to ordering of solvent around the developing ion.24 This effect is more
pronounced in low dielectric effect solvents such as toluene which is used in this study. The intimate ion
pair intermediate consists of the well-known 7,8 oxyphosphazene anion and a dioxolane( dioxoenium)
cation which is stabilized by allylic resonance of the positive charge. This type of carbocation has been
observed in other systems 25 and is known to exist in acidic media. These carbocations have been
implicated in other degradation processes 26and can be formed by ring closure reactions.27 There are
two potential outcomes of the collapse of the intimate ion pair via reaction of the oxyphosphazene
anion at the 4 position of the dioxolane ( the position which leads to the thermodynamically stable
products). If the attack is by the oxygen end of the ambident anion, the starting material, 8, is
regenerated. If the attack is by the nitrogen end then the phosphazane, 14 is obtained. If the ions
diffuse out of the solvent cage, then the oxyphosphazene anion can attack 15 generating the observed
oxo linked phosphazene-phosphazane 15. Capture of a chloride ion by the dioxolane leads to the
observed 2-chloroethylmethacrylate, 16. Preliminary 31P NMR data suggests the possibility of reaction
of the oxyphosphazene anion with 16 to yield a three ring system. This additional level of reaction has
been proposed in the hydrolysis of hexachlorocyclophosphazene.8 The observation that the relative
concentration of 15 continues to increase relative to that of 14 is consistent with the formation of the
three ring system..
The mechanism proposed in Scheme 3 fits the observed product distribution, the kinetic order of the
reaction and the activation energies. In order to further test this hypothesis, we have explored the
thermolysis of a series of phosphazene derivatives related to 2. These species are shown in Scheme 2.
The spiro(2,3-dioxypropylmethacryl)tetrachlorocyclotriphosphazene(9) contains the basic (2-oxyethyl
methacryl) unit which undergoes the rearrangement in 8 however as a result of being incorporated into
a spirocyclic unit it has two points of attachment to the phosphazene ring. Phosphazenes with five
membered spirocyclic ring substituents have been shown to undergo a spiro to ansa ( 2,2 to 2,4
attachment) rearrangement but only under the influence of alkoxide anions.28 Exposure of 9 to elevated
temperatures for extended periods of time left the molecule unchanged. In order to undergo the
rearrangement process shown in Scheme 3, the developing carbocation in the transition state and the
ion pair would be significantly constrained by the second point of attachment to the phosphazene. This
constraint provides sufficient barrier to prevent the rearrangement. The stability of the methacrylate on
spirocyclic unit allowed for use of certain of these derivatives to be employed as monomers in
polymerization reactions.29 The next set of mechanistic test reactions involved investigation of the
effect of elaboration of the alkyl chain of the methacrylate unit, specifically to propyl ( 2-oxypropyl(10)),
isopropyl ( 1-2-oxypropyl( 11a) and 2-(1-oxypropyl (11b))and butyl groups ( n-butyl,11). Complete
resolution of the 31P NMR signals in 11a and 11b mixture was not possible and the chemical shifts are

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reported as the average of the pair except where clearly resolved. Products analogous to those
obtained from 8 i.e. the rearranged (phosphazane) and dimeric specie as well the chloromethacrylate
were observed. Partial assignments and knowledge of the isomer ratio available in the parent
methacylates allowed for monitoring of the rearrangement of a mixture of 11a and 11b by 31P and 1H
NMR at 1110 under conditions identical to those employed for 8. The structural changes were clearly
reflected in the kinetic data (half lives, Table 1).30 In each case, an increase in rate is observed which
can be ascribed to the electron releasing methyl group stabilizing the developing carbocation. The
effect is stronger in 11b (11b > 11a > 8) where the methyl group is directly attached to the carbon atom
which is the site of the developing carbocation. In 10, the rearrangement does occur and the products
analogous to those observed for 8 were observed by NMR (31P and 1H) and mass spectrometry. The
extension of the carbon chain to an n-propyl unit between the phosphazene and the methacrylate
moiety results in a 20 fold rate reduction (Table1).30 Due to increased conformational possibilities in 10
relative to 8 (and the related 11a and 11b), the formation of the dioxoenium ion requires a larger loss on
configurational entropy and hence a higher energy transition state. Further extension of the length of
the alkyl chain to the n-butyl derivative (11) increases the cost of loss of configurational entropy to a
degree that it is unchanged after heating of 11 for 12 hrs at 1110. This has allowed for the use of
phosphazenes related to 11 to serve as a monomers in radical initiated olefin polymerization.31-33 The
role of the ester carbonyl was examined by investigating the thermolysis of 12 where the methacrylate
group is replaced by a methoxy group. Even under forcing conditions (1110, 48 hrs), no rearrangement
was observed. The multifunctional derivative, N3P3(O(CH2)2OC(=O)CMe=CH2)6 has been reported to
undergo polymerization at multiple olefin sites to yield a highly cross linked (cyclomatrix)phosphazene
polymer. The resulting hard film has been proposed to be of value in coatings. 34 However, we have
examined the thermolysis of N3P3(O(CH2)2OC(=O)CMe=CH2)6 and have observed preliminary evidence for
the phosphazene-phosphazane rearrangement which may contribute to a decrease of the long term
stability of the films by introducing the more reactive phosphazane component . The corresponding
polymerization of N3P3[ O(CH2)4OC(=O)CMe=CH2]6 has been reported to yield a hard film which can be
plasma etched.33
The mechanism described above and in Scheme 3 fits all of the product distribution and kinetic data.
The structure activity studies involving a range of modification of the organic substituents are all
consistent with the proposed mechanism. The observation of pathways both within and outside of the
solvent cage allow for understanding of the evidence for both inter and intramolecular pathway in the
rearrangement of alkoxyphosphazenes.13,15 The importance of solvent cage effects in other
cyclophosphazene systems will be reported in a future publication. The stability of the oxyphosphazene
anion, N3P3Cl5O- is one of the major diving forces for the reaction and is a commonly observed (or
presumed) products of numerous cyclophosphazene decomposition reactions.2,35 This stability
combined with the stabilization of a developing carbocation , the other major factor identified in this
investigation, allows for understanding of the relative instability of tertiary ( and to some degree
secondary) alcohol phosphazene derivatives since the increased number of alkyl groups provide
stabilization for a developing carbocation. Finally, this study allows for the rational design of methacyl
phosphazene monomers suitable for olefin polymerization.
ACKNOWLEDGEMENTS

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The assistance of Dr. John G. Jewett in clarifying aspects of the rearrangement kinetics is gratefully
acknowledged.
REFERENCES
(1) Shaw,R.A. Z.Naturforsch. 1976,31b,641
(2) Allen,C.W. In The Chemistry of Inorganic Homo- and Heterocycles;
Haiduc,I.,Sowerby,D.B.,Eds.;Academic Press:London,1987; Vol 2, Chapter 20,p 501.
(3) Shaw,R.A. J.Organomet.Chem. 1988,341,357.
(4) Allen,C.W. Chem.Rev. 1991,91,119.
(5) H. R. Allcock, Chemistry and Applications of Polyphosphazenes; Wiley-Interscience: New
York, 2003.
(6) V. Chandrasekhar, Inorganic and Organometallic Polymers; Springer-Verlag: Berlin, 2005.
(7) De Ruiter,B.; Winter,H.; Wilting,T.; van de Grampel,J.C.J.Chem.Soc.,Dalton Trans.
1984,1027.
(8) Gabler,D.G.;Haw,J.F. Inorg.Chem. 1990,29,4018.
(9) Murray,M.; Boulajoun Phosphorus Research Bulletin 1996,6,155.
(10)Alekseiko,L.N.;Gorchakov,V.V.;Ivanov,Yu. V.; Murashov,D.A.;Rozanov,I.A.
Russ.J.Inorg.Chem.1989,34,1958.
(11)Thomas,B.;Paasch,S.;Boehme,U. Z.Anorg.Allg.Chem.2005,631,85.
(12)Cheng,T.C.;Mochel,V.D.;Adams,H.E.;Longo,T.F. Macromolecules 1980,13,158.
(13) Ferrar,W.T.;DiStefano,F.V.;Allcock,H.R. Macromolecules 1980,13,1345.
(14) Dhathathreyan,K.S.; Krishnamurthy,S.S.;Vasudeva Murthy, A.R.; Shaw,R.A.;
Woods,M.J.Chem.Soc.,Dalton Trans.1981,1928.
(15) Karthikeyan,S.;Krisnamurthy,S.S.J.Chem.Soc.,Dalton Trans. 1991,299.
(16) Bullen,G.;Williams,S.J.;Paddock,N.;Patmore,D.J. Acta Crystallogr.,Sect.B:
Stuct.Crystallogr.Cryst.Chem.1981,B37,607.
(17) Mochel,V.D.;Cheng.T.C. Macromolecules 1978,11,176.
(18) Brown,D.E.; Allen,C.W. J.Inorg.Organomet.Polym.1991,1,189.
(19) Hayes,R.F.;Allen,C.W.Phosphorus,Sulfur,Silicon 1994,93-94,269.
(20) Hayes,R.F.;Allen,C.W.Heteroatm.Chem.1998,9,669.
(21) The original version of DNM-3 is in the following: (a) Kleier,D. A.;Binsch,G. J. Magn. Reson.
Relat. Phenom., Proc. Congr. Ampere, 16th 1971,3, 146. Local modifications are described
in the following:(b) Bushweller, C.H.; Bhat, G.; Lentendre, L.; Brunelle, J. A.; Bilofsky, H. S.;
Rubin, H.; Templeton, D. H.; Zalkin, A. J. J. Am. Chem. Soc. 1975, 97, 65.
(22) Weber,U.;Thiele,H., NMR Spectroscopy: Modern Spectral Analysis;Wiley-
VCH:Weinheim,Germany,1998.
(23) Conners, K.A., Chemical Kinetics, The Study of Reaction Rates in Solution; VCH Publishers:
New York,1990,251-253.
(24) Issacs, N., Physical Organic Chemistry, 2nd e.; John Wiley and Sons,inc.: New York,1995,113-
16.
(25) (a) Hart,H.; Tomalia,D.A. Tetrahedron Lett.1967,1347. (b) Hart,H.; Tomalia,D.A.Terahedron
Lett.1966,3383. (c)Hart, H.; Tomalia,D.A. Tetrahedron Lett.1966,3389.

Page 11 of 18
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT02762D
(26) Capon, B: Ghosh,A.K. J.Am.Chem.Soc.1981,103,1765.
(27) (a)Wilen,S.H.; Delguzzo,L.; Saferstein,R. Tetrahedron 1987,43, 5089. (b) Pittman,C.U.;
McManus,S.P. Tetrahedron Lett.1969, 339.
(28) (a) Besli,S.; Coles,S.J.; Coles,L.S.; Davies,D.B.; Kilic,A. Polyhedron 2012,43,176.(b) Besli,S.;
Coles,S.J.: Davies,D.B.;Hursthouse,M.B.;Kilic,A.; Shaw,R.A. J.Chem.Soc., Dalton
Trans.2007,26,2792.
(29) Hayes,R.F.;Allen,C.W. J.Inorg.Organomet.Polym.Mater. 2010,20,528.
(30) Kinetic data available on request.
(31) Allen,C.W. Inorg.Chim.Acta 2011,372,32.
(32) Myer, C.N. J.Inorg.Organomet.Polym.Mater.2007, 17,143.
(33) Hagberg, E.C.; Hart, M.W.; Cong, L.; Allen, C.W.; K.R. Carter, J.Inorg. Organomet. Polym.
Mater.2007,17,377.
17, 377( 2007).
(34) Yaguchi, A.; Mori,S.; Kitayama, M.; Onda,T.; Kurahashi, A.; Ando ,H Thin Solid Films ,
1992,216,123.
(35) Nataro,C.; Myer,C.N.; Cleaver, W.M.;Allen,C.W.J. Organomet. Chem.2001,637-639,
284.

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Table 1. Selected Rearrangement Kinetic Data
Compound
Parameter
Half life a
8 “Dry Sample”
8 “Wet” Sample
10
11a
11b
31P
1H
31P
111b
89
4.65
67.1
343
5.06
73.8
376
4.42
20.3
67.0
215
387
62.6
-169
89.5
4.03 3.61
70
50
35
1210
1940
90.1
1230
3620
89.0
-104
ΔH± c
ΔS± d
-100
a hours. b 0C. c KJ/mole. d J/mole

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O
O
Cl
O
Cl
O
O
O
O
O
P
N
P
N
O
P
N
N
N
N
N
N
N
Cl2 P
PCl2
Cl2 P
PCl2
Cl2 P
PCl2
O
11
10
9
O
Cl
O
Cl
O
Cl
N
O
P
N
P
O
N
N
P
N
N
N
N
O
O
Cl2 P
PCl2
Cl2 P
PCl2
Cl2
P
PCl2
N
O
12
11b
11a
Scheme 2. Methacrylcyclophosphazanes

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O
O
Cl
O
P
N
N
P
N
PCl2
Cl2
8
±
O
O
Cl
O
P
N
O
N
P
N
PCl2
Cl2
O
N
Cl
O
P
O
N
Cl
0
P
N
P
PCl2
Cl2
HN
N
P
PCl2
N
Cl2
H+
diffusion from
solvent cage
13
O
Cl
O
Cl
O
+
P
N
P
N
N
N
O
N
N
0
Cl
2P
PCl2
P
PCl2
Cl2
O
Cl-
14
O
Cl
P
N
CH2=C(Me)C(O)O(CH2)2Cl
N
P
N
O
16
PCl2
Cl2
Cl
P
O
+ Cl-
O
O
N
N
P
PCl2
N
P
Cl2
N
N
P
N
P
Cl2
Cl2
15
Sceme 3. Proposed Mechanism for the Rearrangement of 8

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The mechanism showing both inter- and intramolecular pathway of the phosphazene-phosphazane
rearrangement of N3P3Cl5O(CH2)2OC(=O)CMe=CH2 (8) has been determined.