Effect of gem 2,2′-disubstitution and base in the formation of spiro- and ansa-1,3-propandioxy derivatives of cyclotriphosphazenes

Article abstract of DOI:10.1016/j.ica.2010.07.005

The gem-dialkyl effect has been investigated in the reactions of cyclotriphosphazene, N₃P₃Cl₆ 1, with various 2,2′-derivatives of 1,3-propandiol, CXY(CH₂OH)₂, in either THF or DCM to form spiro (6-mem

Full text of DOI:10.1016/j.ica.2010.07.005

Inorganica Chimica Acta 363 (2010) 3506–3515
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Effect of gem 2,20-disubstitution and base in the formation
of spiro- and ansa-1,3-propandioxy derivatives of cyclotriphosphazenes
b
c
a
b
a
Aylin Uslu a, , Simon J. Coles , David B. Davies , Mükremin Esen , Michael B. Hursthouse , Adem Kılıç
*
a Department of Chemistry, Gebze Institute of Technology, Kocaeli, Turkey
b Department of Chemistry, University of Southampton, Southampton SO17 1BG, UK
c School of Biological and Chemical Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The gem-dialkyl effect has been investigated in the reactions of cyclotriphosphazene, N3P3Cl6 1, with var-
ious 2,20-derivatives of 1,3-propandiol, CXY(CH2OH)2, in either THF or DCM to form spiro (6-membered)
and ansa (8-membered ring) derivatives. The reactions were made with a number of symmetrically-
substituted (X = Y, methyl, ethyl, n-butyl and a malonate ester) and unsymmetrically-substituted
(X – Y, methyl/H, phenyl/H, methyl/n-propyl, ethyl/n-butyl and Br/NO2) 1,3-propandiols. The products
were analysed by 1H and 31P NMR spectroscopy and some of the spiro and ansa derivatives were also
characterized by X-ray crystallography. Reactions of 1 with unsymmetrically-substituted 1,3-propandiols
results in the formation of two structural isomers of ansa-substituted compounds, both isomers (endo
and exo) have been structurally-characterized by X-ray crystallography for the ethyl/n-butyl derivative.
It is found that the regioselectivity of the reaction is changed when the base is changed. The relative pro-
portions of spiro and ansa compounds formed under different reaction conditions were quantified by 31P
NMR measurements of the reaction mixtures. The results were rationalised mainly in terms of the elec-
tronic effect of the substituents, whereas the steric effect has a secondary role in the formation of both
spiro and ansa compounds.
Received 16 February 2010
Accepted 2 July 2010
Available online 7 July 2010
Keywords:
Cyclotriphosphazene
gem-Dialkyl effect
Regioselectivity
Spiro
Ansa
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
derivatives. The reactions of 1 with difunctional reagents such as
diols can give rise to two types of cyclic derivatives: spiro (in which
Cyclization reactions are frequently critical components of nat-
ural product synthesis, where the nature of the target molecule of-
ten requires the formation of thermodynamically-unfavourable
medium-sized rings. To overcome the problem of formation of se-
ven-, eight or nine-membered rings, advantage has been taken of
the accelerated rate of cyclization resulting from a gem-dialkyl
moiety in the acyclic carbon backbone [1]. The gem-dialkyl effect
(originally described as the Thorpe–Ingold effect [2–4]) is defined
by an increase in both rate and equilibrium constants of cyclization
reactions resulting from the introduction of substituents in the
linking chain [1–6]. Whilst the gem-dialkyl effect has been fre-
quently employed in organic chemistry, there are considerably
fewer examples of its application in inorganic or organometallic
systems [7–10].
the two P–O bonds are formed to the same P-atom) and ansa
(in which the two P–O bonds are formed to different P-atoms)
[11–14]. Previous work on the cyclization reactions of 1 with
different diols (Table 1) shows that using pyridine as base (to neu-
tralize the HCl formed in the reaction) spiro derivatives are over-
whelmingly formed in a range of solvents [15–21], whereas
significant amounts of ansa derivatives are also formed using the
strong base NaH in THF [15,22,23]. It is difficult to rationalise all
the results in Table 1 because the reactions have been done with
different bases, different solvents and even at different tempera-
tures. For example, although the reactions of 1 with various 1,3-
propandiol derivatives, which might provide some insight into
the gem-dialkyl effect, have been done with the same base, pyri-
dine, they have been carried out in three different solvents, viz.
Et2O for 1,3-propanediol [15], dioxane for 2,2-dimethylpropane-
1,3-diol [16] and THF for diethyl bis(hydroxymethyl)malonate
[17,18], bromoneopentyl glycol [20] and at different temperatures.
In order to provide some insight into the importance of the gem-
dialkyl effect in reactions of 1 with diols, it is necessary to investi-
gate the reactions in a systematic manner and to use the same
method(s) for quantifying the relative proportions of the products.
It has recently been shown that 31P NMR spectroscopy of reaction
In this work we have investigated the gem-dialkyl effect on the
cyclization reactions of cyclotriphosphazene, N3P3Cl6 1, an inor-
ganic heterocyclic compound, with a series of 1,3-propanediol
* Corresponding author. Address: Department of Chemistry, Gebze Institute of
Technology, P.O. Box 141 41400, Kocaeli, Turkey. Tel.: +90 262 6053129; fax: +90
262 6053101.
E-mail address: aylin@gyte.edu.tr (A. Uslu).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.07.005

A. Uslu et al. / Inorganica Chimica Acta 363 (2010) 3506–3515
3507
Table 1
The results of cyclization reactions of 1 with some diols.
Reaction
Yield %
Sp.a
Solvent
Base
Temp
Ref.
a
An.
1,3-propanediol
41
29
52
17
53
56
4
-
-
-
-
-
Et2O
dioxane
THF
Et2O
THF
pyridine
pyridine
pyridine
4-dimethylaminopyridine
pyridine
Room temperature
Room temperature
reflux
Room temperature
reflux
[15]
[16]
[17,18]
[19]
[20]
[21]
2,2-dimethylpropane-1,3-diol
diethyl bis(hydroxymethyl)malonate
3-hydroxy-2-(hydroxymethyl)-2-methylpropyl)methacrylate
bromoneopentyl glycol
1,3-butanediol
benzene
triethylamine
reflux
a
Sp. = Spiro, An. = Ansa.
mixtures is a reliable way of quantifying the relative proportions of
spiro and ansa derivatives [24] and these results may be compared
with those for isolation of the compounds. In this work, as summa-
rized in Scheme 1, the reactions of cyclotriphosphazene, N3P3Cl6, 1,
with various 1,3-propandiols, CXY(CH2OH)2, will be investigated
quantitatively under different solutions conditions in order to pro-
vide greater understanding of the effects of substituents (X = Y and
X – Y) on the formation of both of spiro and ansa derivatives.
chemicals were obtained from Merck; 1,3-propanediol (>98%),
2,2-dimethylpropandiol (>98%), silica gel 60, tetrahydrofuran
(ꢀ99.0%), dichloromethane (ꢀ99.0%) ethyl acetate (ꢀ99.0%),
n-hexane (>96%), sodium hydride (>60%), and from Aldrich;
diethylbis(hydroxymethyl)malonate (>97%), 2-butyl-2-ethyl-1,3-
propandiol (>99%), 2,2-diethyl-1,3-propandiol (>99%), 2-methyl-
2-propyl-1,3-propandiol (>98%), 2,2-dibutyl-1,3-propandiol (>97%),
2-bromo-2-nitro-1,3-propandiol (>98%), 2-phenyl-1,3-propandiol
(>98%), 2-methyl-1,3-propandiol (>99%). The deuteriated solvent
(CDCl3) for NMR spectroscopy was obtained from Apollo Scientific.
2. Experimental
2.1. Materials
2.2. Methods
Hexachlorocyclotriphosphazene (Shin Nisso Kako Co. Ltd.) was
purified by fractional crystallisation from hexane. The following
Elemental analyses were obtained using a Carlo Erba 1106
Instrument. Mass spectrometric measurements were made on a
X
Y
X
Y
Cl
Cl
O
O
X
Y
O
P
N
O
P
N
N
P
N
P
N
P
N
P
N
P
P
P
Cl
Cl
Cl
Cl
+
Cl
Cl
Cl
Cl
H2C
CH2
Cl
Cl
+
N
N
OH OH
Cl
Cl
(1)
(2a-11a)
(5b, 7b-10b, 7c-10c)
R1, R2
Spiro
Ansa
i) Symmetrical substitution : X = Y
H
2a
3a
4a
5a
6a
2b
3b
4b
5b
a
CH3
C2H5
C4H9
C(O)OC2H5
ii) Unsymmetrical substitution : X ≠ Y
CH3, H
7a
8a
7b, 7c
8b, 8c
9b, 9c
10b, 10c
a
Ph, H
C3H7, CH3
9a
C4H9, C2H5
Br, NO2
10a
11a
a. Ansa isomer not observed
Scheme 1. Formation of spiro and ansa derivatives in the reactions of cyclophosphazene (1) with 2,20-substituted 1,3-propanediols.

3508
A. Uslu et al. / Inorganica Chimica Acta 363 (2010) 3506–3515
Table 2
HP G1800A GC–MS spectrometer using the HP-5 column and a
Bruker MicrOTOF LC–MS spectrometer with electrospray ioniza-
tion (ESI) method; 35Cl values were used for calculated masses.
Analytical Thin Layer Chromatography (TLC) was performed on
Merck Silica gel plates (Merck, Kieselgel 60, 0.25 mm thickness)
with F254 indicator. Column chromatography was performed on sil-
ica gel (Merck, Kieselgel 60, 230–400 mesh; for 3 g crude mixture,
100 g silica gel was used in a column of 3 cm in diameter and
60 cm in length). 1H and 31P NMR spectra were recorded in CDCl3
solutions on a Varian INOVA 500 MHz spectrometer using 85%
H3PO4 as an external reference for 31P and TMS as internal refer-
ence for 1H NMR. In order to assign the 31P NMR signals of some
compounds both proton-coupled and proton-decoupled 31P NMR
spectra were recorded.
a,b
31P NMR parameters of compounds 2a–11a, 2b–10b and 7c, 10c
.
Cpd
>P(OCH2)
1
>PCl2
2
>PCl2
3
>C(X,Y)
X
2J(PP)/Hz
Y
1, 2
1, 3
2, 3
(i) Symmetrically-substituted Spiro compounds: X = Y
2a
3a
4a
5a
6a
3.07
2.83
4.14
4.22
4.24
23.90
24.14
24.53
24.42
24.98
H
H
69.1
68.7
68.6
68.6
70.7
CH3
C2H5
C4H9
CO2Et
CH3
C2H5
C4H9
CO2Et
(ii) Unsymmetrically-substituted Spiro compounds: X – Y
7a
8a
9a
10a
11a
3.31
3.43
3.74
4.19
3.75
23.42
23.10
24.39
24.31
23.86
25.50
26.16
24.65
24.72
27.11
H
H
C3H7
C4H9
Br
CH3
Ph
CH3
C2H5
NO2
61.7
59.5
67.7
67.8
57.7
76.1
79.7
69.4
69.4
85.5
61.5
60.6
61.0
61.3
58.4
2.3. Synthesis
(iii) Symmetrically-substituted Ansa compounds: X = Y
2b
3b
4b
5b
26.63
27.46
28.05
27.82
25.78
26.17
26.61
26.27
H
H
59.2
57.5
56.4
57.2
CH3
C2H5
C4H9
CH3
C2H5
C4H9
2.3.1. General procedure used for reaction of diols with
cyclotriphosphazene (1) in the presence of pyridine in THF solution
1,3-Propanediol (0.4 g, 1.29 mmol) in 5 mL of THF was added
dropwise to a stirred solution of compound 1 (0.5 g, 1.44 mmol)
dissolved in 5 mL of THF under an argon atmosphere and then pyr-
idine (0.204 g, 2.58 mmol) in 5 mL of dry THF was added dropwise.
The reaction mixture was stirred for a further 3 days at room tem-
perature and the reaction was followed by TLC indicating the pres-
ence of a number of products. The precipitated salt (pyridinium
hydrochloride) was then filtered off and solvent was removed un-
der reduced pressure.
(iv) Unsymmetrically-substituted Ansa compounds: X – Y
7b
7c
8b
8c
9b
9c
10b
10c
27.87
27.01
28.15
28.38
28.12
27.66
28.02
27.90
26.99
25.52
26.88
27.39
26.85
26.18
26.57
26.39
H
H
H
H
C3H7
C3H7
C4H9
C4H9
CH3
CH3
Ph
57.3
58.4
57.8
58.2
56.5
58.1
56.8
57.2
Ph
CH3
CH3
C2H5
C2H5
202.38 MHz 31P NMR measurements in CDCl3 solutions at 298 K in this work,
a
chemical shifts referenced to external H3PO4.
b
The 31P NMR spectra of symmetrically-substituted spiro compounds 2a–6a
2.3.2. General procedure used for reaction of diols with
were analysed as A2X spectra, those for unsymmetrically-substituted spiro com-
pounds 7a–11a as ABX spectra and those for ansa compounds 2b–5b, 7b–10b, 7c–
10c were analysed as A2B spectra.
cyclophosphazene (1) in the presence of NaH in THF solution
1,3-Propanediol (0.4 g, 1.29 mmol) in 5 mL of dry THF was
added dropwise to a stirred solution of compound 1 (0.5 g,
1.44 mmol) dissolved in 5 mL of dry THF under an argon atmo-
sphere, then sodium hydride (0.062 g, 2.58 mmol) in 5 mL of dry
THF was added dropwise. The reaction mixture was stirred for a
further 3 days at room temperature and the reaction was followed
by TLC indicating the presence of a number of products. The pre-
cipitated salt (NaCl) was then filtered off and the solvent was re-
moved under reduced pressure.
2.3.5. X-ray crystallography
X-ray structure determination and crystallographic data were
collected by means of combined phi and omega scans on a Bru-
ker-Nonius Kappa CCD area detector situated at the window of a
rotating anode (kMo Ka = 0.71073 Å). The structures were solved
by direct methods, SHELXS-97 and refined using SHELXL-97 [26]. The
data were corrected for absorption effects using SADABS [27], The
X-ray crystallographic data are summarized in Table 3 and full de-
tails of data collection and structure determination have been
deposited with the Cambridge Crystallographic Data Centre and
assigned deposition numbers.
2.3.3. General procedure used for work-up of the products of the
reaction of each diol with 1
The products were isolated from the combined crude reaction
mixture by column chromatography. Crystals of pure spiro and
ansa derivatives were obtained using DCM:n-hexane (5:1) and
analysed by microanalysis and mass spectrometry and the results
are summarized in Table S1. Each product was also characterized
by 1H and 31P NMR spectroscopy and the 31P NMR parameters
are given in Table 2 and the 1H NMR parameters are given in Table
S2 in the Supplementary material. Crystals suitable for X-ray crys-
tallography were found for spiro compounds 4a, 7a, 8a, 11a and for
ansa compounds 3b–5b, 7b, 10b and 10c. Some compounds (5a,
6a, 9a, 10a, 8b, 9b, 7c, 8c and 9c) remained as oily products.
3. Results and discussion
The aim of the present work is to investigate the gem-dialkyl
effect on the formation of spiro and ansa derivatives of cyclotri-
phosphazene, 1, with various 2,20-substituted 1,3-propandiols
using the same solvents (THF or DCM) but under different condi-
tions that are known to favour ansa compounds using the alkoxide
[28] or favour spiro compounds with pyridine as the hydrogen ha-
lide acceptor [29,30]. The results of the reactions using DCM or
THF as solvent are almost the same and so only those in THF have
been described in detail. In the 1,3-propandiols, HO(CH2)CXY
(CH2)OH, the X and Y groups may be the same (X = Y) or different
(X – Y) (Scheme 1); in most of the substituted 1,3-propandiols, X
or Y are alkyl groups thus making the alkoxide CH2–Oꢁ group
slightly more electron-rich whereas, for comparison purposes,
two of the diols [with two COOC2H5 or NO2/Br groups] contain
electron-withdrawing groups making the CH2–Oꢁ group slightly
less electron-rich.
2.3.4. General procedure used to estimate the relative proportions of
products of the reaction of diols with cyclophosphazene (1) by 31P
NMR spectroscopy
A small portion of each filtered and solvent-free crude reaction
mixture was dissolved in CDCl3 and the relative ratios of the start-
ing material 1, spiro and ansa derivatives and any other products
were estimated from the proton-decoupled 31P NMR spectra per-
formed under pulsing conditions (P/3 pulse, overall repetition
time of 3.6 s) that allowed for relaxation times of the 31P nuclei
of up to 6 s in spiro- and ansa-substituted cyclophosphazene deriv-
atives [25].

Table 3
X-ray data and molecular parameters for spiro (4a, 7a, 8a, 11a) and ansa (3b, 4b, 5b, 7b, 10b, 10c) compound.
4a
7aa
8a
11a
3b
4b
5b
7b
10b
10c
(i) X-ray data
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C7H14Cl4N3O2P3
406.92
C4H8Cl4N3O2P3
364.84
Monoclinic
Cc
C9H10Cl4N3O2P3
426.91
Orthorhombic
Pna21
23.2125(7)
9.1684(2)
7.6006(2)
90
C3H4BrCl4N4O4P3 C5H10Cl4N3O2P3
C7H14Cl4N3O2P3
406.92
Monoclinic
P21/c
15.9483(5)
12.1905(3)
16.5233(4)
90
99.189(2)
90
C11H22Cl4N3O2P3
463.03
Monoclinic
P21/c
10.6315(2)
12.0869(2)
15.6257(3)
90
101.5850(10)
90
C4H8Cl4N3O2P3
364.84
Orthorhombic
Pbca
C9H18Cl4N3O2P3
434.97
C9H18Cl4N3O2P3
434.97
Orthorhombic
Pbca
474.72
Orthorhombic
Pbca
378.87
Orthorhombic
Pnnm
Triclinic
Triclinic
ꢀ
ꢀ
P1
P1
8.03340(10)
10.0791(2)
11.1829(3)
97.4510(10)
111.0060(10)
103.9920(10)
796.48(3)
2
14.8296(9)
6.0926(3)
15.4113(12)
90
109.500(3)
90
1312.56(14)
4
1.846
13.0288(4)
12.2797(4)
18.0331(5)
90
11.5390(9)
12.4271(8)
9.9748(5)
90
13.3334(2)
12.3344(4)
15.9953(4)
90
90
90
2630.58(11)
8
1.842
8.20120(10)
9.06650(10)
12.81310(10)
83.3440(10)
84.0130(10
72.5300(10)
900.230(16)
2
11.4593(2)
16.8538(2)
19.0612(2)
90
90
90
3681.34(9)
8
1.570
b (Å)
c (Å)
a
(°)
b (°)
(°)
90
90
90
90
c
90
90
Volume (Å3)
Z
1617.57(7)
4
1.753
2885.11(15)
8
1430.35(16)
4
3171.20(15)
8
1.705
1967.03(6)
4
1.564
Dcalc (mg/m3)
Absorption
coefficient
1.697
1.043
2.186
1.759
1.605
0.929
1.255
1.033
3.934
1.155
1.048
0.855
1.252
0.908
(mmꢁ1
)
F(0 0 0)
412
728
856
1840
760
1648
952
1456
444
1776
Crystal size (mm)
hmax (°)
Reflections
0.38 ꢂ 0.20 ꢂ 0.05 0.40 ꢂ 0.20 ꢂ 0.20 0.24 ꢂ 0.20 ꢂ 0.02 0.50 ꢂ 0.25 ꢂ 0.10 0.60 ꢂ 0.15 ꢂ 0.13 0.35 ꢂ 0.20 ꢂ 0.20 0.60 ꢂ 0.15 ꢂ 0.15 0.50 ꢂ 0.14 ꢂ 0.02 0.18 ꢂ 0.10 ꢂ 0.05 0.12 ꢂ 0.10 ꢂ 0.02
27.49
27.50
2043
27.49
27.50
27.50
27.50
27.50
27.49
2.96–27.50
37334
3.03–27.48
57233
16270
15068
23902
13938
41102
25240
19829
collected
Independent
reflections
Rint
3645
1519
3611
3290
1723
7260
4512
3013
4131
4213
0.0254
0.0445
0.0443
0.0570
0.0267
0.0477
0.0403
0.0447
0.0350
0.0494
Final R indices
F
R1 = 0.0262
wR2 = 0.0648
R1 = 0.0658,
wR2 = 0.1561
R1 = 0.0309,
wR2 = 0.0657
R1 = 0.0384,
wR2 = 0.0902
R1 = 0.0232,
wR2 = 0.0663
R1 = 0.0347,
wR2 = 0.0766
R1 = 0.0284,
wR2 = 0.0667
R1 = 0.0316,
wR2 = 0.0690
R1 = 0.0235,
wR2 = 0.0614
R1 = 0.0310,
wR2 = 0.0779
2 > 2 F2
r
D
q
max/min
(e Åꢁ3
(ii) Cyclophosphazene ring
Maximum 0.084
deviation (Å)
0.287 and ꢁ0.490 0.792 and ꢁ0.866 0.322 and ꢁ0.295 2.351 and ꢁ0.851 0.273 and ꢁ0.435 0.364 and ꢁ0.503 0.361 and ꢁ0.420 0.366 and ꢁ0.538 0.327 and ꢁ0.389 0.363 and ꢁ0.375
)
0.077
2.741
0.051
2.740
0.085
2.744
0.272
2.644
0.263; 0.227
2.638; 2.673
0.273
2.643
0.294
2.635
0.301
2.634
0.290
2.638
Minimum Pꢃ ꢃ ꢃP
2.744
distance (Å)
(iii) Exocyclic ring pucker (Q)
Spiro
Ansa
Mean
0.5521
0.558
0.547 0.549
( 0.006)
0.538
1.1902
1.1974
1.2023 1.201
( 0.013)
1.175
1.2268
1.2131
a
Chiral space group.

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A. Uslu et al. / Inorganica Chimica Acta 363 (2010) 3506–3515
3.1. Characterization of products by 31P NMR spectroscopy
were observed as ABX spin systems, in which the PCl2 groups exhi-
bit anisochronism; the latter phenomenon has been observed and
explained previously in terms of the two PCl2 groups being in non-
equivalent relationships to the other two different geminal groups
[28,31]. The two sets of 2J(PP) between the >P(OCH2) and >PCl2
groups in the unsymmetrically-substituted spiro compounds are
different and depend on the substituents (ranging from 57.7–
67.8 to 69.4–85.5 Hz) though the average 2J(PP) for each compound
is in the same range (68.6–71.6 Hz) as for the symmetrically-
substituted spiro compounds.
The isolated spiro and ansa derivatives were characterized by
mass spectrometry, microanalysis and 1H NMR and 31P NMR
spectroscopy. The chemical shifts and phosphorus–phosphorus
coupling constants are summarized in Table 2 and the other ana-
lytical information is summarized in the Supplementary material.
The proton-decoupled 31P NMR spectra of spiro compounds
resulting from symmetrically-disubstituted 1,3-propandiols (com-
pounds 2a–6a) were observed as simple AX2 spin systems with
very similar spin-coupling constants between the >P(OCH2) and
>PCl2 [2J(PP) 68.6–70.7 Hz], whereas those resulting from unsym-
metrically-disubstituted 1,3-propandiols (compounds 7a–11a)
The proton-decoupled 31P NMR spectra of the ansa compounds
resulting from symmetrically-disubstituted 1,3-propandiols (com-
pounds 2b–5b) are observed as A2B spin systems, in which the
Fig. 1. (a) Proton-decoupled 31P NMR spectrum of the reaction mixture of the reaction of cyclophosphazene, (1), with 2-butyl-2-ethyl-1,3-propandiol (after filtration,
evaporation of solvent and dissolving in CDCl3 solution). (b) Superposition of the proton-decoupled 31P NMR ABX spin system of the spiro compound 10a together with
expansion of the AB part of the spectrum, (c) expansion of the proton-decoupled 31P NMR A2B spectra of the ansa compounds 10b and (d) 10c on the same chemical shift
scales.

A. Uslu et al. / Inorganica Chimica Acta 363 (2010) 3506–3515
3511
2J(PP) between the >P(OCH2) and >PCl2 groups are similar to each
other (56.4–59.2 Hz) but significantly smaller than those observed
in analogous spiro compounds (2a–6a). Similar differences be-
tween 2J(PP) in spiro- and ansa-substituted 1,3-propanedioxy
derivatives have been observed for both spirane-bridged [25] and
spermine-bridged compounds [32], which must reflect the strain
in the cyclotriphosphazene ring of the ansa-compounds compared
to the spiro-substituted derivatives.
tion data of all compounds are given in Table 3. Other isolated
compounds (5a, 6a, 9a, 10a, 8b, 9b, 7c, 8c and 9c) remained as oily
products. The structures of the pair of unsymmetrically-disubsti-
tuted 1,3-propandiol derivatives 10b and 10c are shown in Fig. 4
with the ethyl and butyl groups either endo or exo to the plane
of the cyclophosphazene ring. Following the notation used by Elias
and co-workers [11,37,38] for the pair of ansa-substituted fluoro-
phosphazenes, where the relationship to the plane of the cyclo-
phosphazene ring of the larger substituent in the ansa ring
defines the endo/exo designations, the structure of 10b is desig-
nated exo and 10c is endo. Comparison of the geminal P–P cou-
pling constants for these two compounds indicates that 2J(PP) for
10c (endo) is slightly larger than for 10b (exo), an observation that
might tentatively be used to assign the endo and exo isomers of the
other unsymmetrically-disubstituted 1,3-propandiol derivatives of
compounds 7–9. Unfortunately the hypothesis cannot be tested
using analogous data for the pair of ansa-substituted fluorophosp-
hazenes, because that data was not recorded by Elias and co-work-
ers [33]. However, the hypothesis is shown to be consistent with
the results for compound 7b, whose crystal structure (Fig. 3d)
shows that it is the exo isomer (i.e. H/endo–CH3/exo) and whose
2J(PP) is slightly smaller than that of the other ansa isomer, 7c.
Using the NMR data in Table 2, it is assumed by analogy that com-
pounds 8b, 9b are also the exo isomers and compounds 8c, 9c are
the endo isomers.
The cyclotriphosphazene rings of spiro 1,3-propandioxy deriva-
tives are essentially strain-free and planar, in which the deviation
of individual atoms from the N3P3 plane in all the compounds re-
ported here (4a, 7a, 8a, 11a) is less than 0.1 Å (Table 3), similar
to that observed previously for 2a [34,35] and 3a [36] and a num-
ber of other 1,3-propandioxy-spiro derivatives of both spirane-
bridged [25] and spermine-bridged compounds [32]. On the other
hand, the eight-membered cis-ansa ring of such 1,3-propanedioxy
cyclophosphazene derivatives causes strain in the cyclophospha-
zene ring, which is relieved by being non-planar. It is found for
all the ansa compounds (3b, 4b, 5b, 7b, 10b and 10c) in this work
that the nitrogen atom between the phosphorus atoms carrying
The proton-decoupled 31P NMR spectra of the ansa compounds
resulting from unsymmetrically-disubstituted 1,3-propandiols
(compounds 7–10) are observed as two sets of A2B spin systems
having slightly different chemical shifts and coupling constants.
There are two structural isomers of unsymmetrically-substituted
ansa compounds, in which substituent groups can be described
as endo or exo with respect to a common structural feature, as re-
ported by Elias and co-workers [11,33] for a pair of ansa-substi-
tuted fluorophosphazenes. The two sets of ansa compounds 7–10
were separated by column chromatography and the 31P NMR
parameters are summarized in Table 2, such that the isomer with
the smaller coupling constant is denoted 7b–10b and with the lar-
ger coupling constant as 7c–10c. Examples of the 31P NMR spectra
of spiro and ansa derivatives formed from an unsymmetrically-
disubstituted 1,3-propandiol are shown in Fig. 1a for the reaction
mixture of cyclophosphazene, 1, with 2-butyl-2-ethyl-1,3-propan-
diol together with the superposition of the proton-decoupled 31P
NMR ABX spin system of the isolated spiro compound 10a
(Fig. 1b), and with expansion of the proton-decoupled 31P NMR
A2B spectra of the two isolated ansa compounds 10b (Fig. 1c)
and 10c (Fig. 1d) on the same chemical shift scales.
3.2. Characterization of products by X-ray crystallography
Compounds 2a [34,35], 2b [25] and 3a [36] have been charac-
terized previously by X-ray crystallography, whereas the molecular
structures of spiro (4a, 7a, 8a, 11a) (Fig. 2a–d) and ansa compounds
(3b, 4b, 5b, 7b) (Fig. 3a–d) and the isomeric pair (10b and 10c)
(Fig. 4a and b) were characterized in this work. The X-ray diffrac-
Fig. 2. X-ray crystal structures of the mono-spiro derivatives 4a, 7a, 8a and 11a.

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A. Uslu et al. / Inorganica Chimica Acta 363 (2010) 3506–3515
Fig. 3. X-ray crystal structures of the mono-ansa derivatives 3b, 4b, 5b and 7b.
the ansa moiety is furthest out-of-plane of the other atoms of the
cyclophosphazene ring and that the deviation from the plane is
greater than 0.2 Å (Table 3), similar to that found previously for
analogous 1,3-propanedioxy cyclophosphazene derivatives 2b
[25,32]. Another indication of the non-planar cyclophosphazene
ring is the significant shortening of the non-bonded Pꢃ ꢃ ꢃP distance
(ca. 2.6 Å) between the ansa-carrying atoms (Table 3), compared to
the normal value of ca. 2.77 Å for planar cyclophosphazene rings
[37,38] and ca. 2.74 Å for the approximately planar cyclophospha-
zene rings of the spiro derivatives in this work (Table 3), and a
number of other 1,3-propandioxy-spiro derivatives of cyclophos-
phazene [25].
Puckering analysis [39] is a useful measure of ring conformation
in which calculation of the mean plane and puckering parameters
provides a unique quantitative descriptor, the total puckering
amplitude (Q), for a ring conformation that can be applied to both
spiro and ansa rings. The spiro rings in the six-membered
P(OCH2C(XY)CH2O) spiro-substituted structures (4a, 7a, 8a, 11a)
are all found to have similar chair conformations with a strictly
alternating positive/negative torsion angle sequence around the
ring and each ring component in a gauche conformation with re-
spect to its neighbour. The puckering amplitude, Q, for each spiro
ring (Table 3) is ca. 0.55, similar to that observed for other 1,3-pro-
pandioxy-spiro derivatives of cyclophosphazene [25]. Although the
overall conformations of the eight-membered NP–OCH2C(XY)-
CH2O–P ansa rings of compounds characterized in this work (3b,
4b, 5b, 7b, 10b and 10c) work are similar, it is found (Table 3) that
there is some dependence of the puckering amplitude, Q, on the
size of the substituents X and Y; the value of Q for 7b (1.175) hav-
ing substituents Me/H is similar to the average value of 1.177 for a
number of 1,3-propandioxy-spiro derivatives of cyclophosphazene
(X = Y = H) [25], whereas increasing size of the substituents X/Y re-
sults in a small increase in the value of Q, viz. Me/Me (3b, 1.190),
Et/Et (4b, 1.197), Bu/Bu (5b, 1.202) and for mixed substituents
Et/Bu (10b, 1.227 and 10c, 1.213).
3.3. Quantitation of products by 31P NMR spectroscopy of reaction
mixtures
The same experimental procedure was used to quantify the
products of each reaction by 31P NMR spectra of the reaction mix-
tures; each reaction was stirred for three days at room tempera-
ture, filtered, the solvent removed under reduced pressure and a
portion of each crude sample dissolved in CDCl3 and the proton-
decoupled 31P NMR measured using the same NMR conditions.
The relative ratios of the starting material 1, spiro and ansa deriv-
atives and any other products (open chain, bridged or polymeric
material) were estimated from the integrated spectrum and the
proportions (%) of each component are summarized in Table 4. A
good example is shown in Fig. 1 for the 31P NMR spectrum of the

A. Uslu et al. / Inorganica Chimica Acta 363 (2010) 3506–3515
3513
derivatives of compound 9 (relative proportions 49% and 36%),
where it is likely that the bulkier propyl moiety is preferred exo
(9b) rather than endo (9c) compared to the methyl group. The dif-
ference in relative proportions of endo and exo isomers is even
more marked for compounds 7 and 8 because of the greater differ-
ence in bulk between the X/Y substituents, viz. CH3/H in com-
pounds 7 (ratio 7b:7c ca. 2:1) and Ph/H in compounds 8 (ratio
8b:8c ca. 4:1). It can be seen in Table 4 that reaction of the various
2,20-substituted 1,3-propandiols with cyclotriphosphazene, 1,
using anhydrous pyridine as HCl receptor leads to formation of
the spiro compounds (2a–11a) with only traces of ansa com-
pounds, as found previously for reactions where 2a [34,35] and
3a [36] were synthesized. As expected, it is also found that the
yield of spiro compounds (22–25%) with 2,20-substituted 1,3-pro-
pandiols containing electron-withdrawing groups (compounds 6
and 11) is significantly smaller than all the other derivatives with
alkyl (or aryl) substituents (69–100%). It can also be seen in Table 4
that reaction of cyclophosphazene, 1, with the alkoxide form of the
various 2,20-substituted 1,3-propandiols, i.e. in the presence of
NaH, leads to formation of both spiro and ansa derivatives, except
for 2,20-substituted 1,3-propandiols containing electron-with-
drawing groups (compounds 6 and 11), where no spiro or ansa
derivatives are formed. Compared to the reaction of 1 with 1,3-pro-
pandiols where the overall yield of compound 2 was only 30%,
reaction of 1 with 2,20-substituted 1,3-propandiols containing alkyl
(or aryl) substituents gave significant overall yield of products for
mono-substituted derivatives (84% for 7 and 90% for 8) and even
greater yields for di-substituted alkyl derivatives with bulkier
groups (91% for 3, Me/Me; 97% for 9, 10, mixed substituents; 98%
for 4, Et/Et; and 99% for 5, Bu/Bu).
3.4. Rationalisation of the effect of gem 2,20-disubstitution in the
formation of spiro- and ansa-1,3-propandioxy derivatives of
cyclotriphosphazene, 1
Fig. 4. The crystal structures of compounds 10b (n-butyl exo) and 10c (n-butyl
endo).
Previous work has shown that reaction of cyclophosphazene, 1,
with diols can give spiro and ansa cyclic products and, when pyri-
dine is used as base to neutralise the hydrochloride formed, the
major product is the spiro compound, because of the great thermo-
dynamic stability of the five-, six-, or seven- membered spiro rings
[40–44]. The preference for spiro over ansa 1,3-propanedioxy
derivatives of cyclophosphazene is not surprising given that the
spiro ring is a six-membered thermodynamically stable chair form,
in contrast to the eight-membered strained ansa ring [15]. It has
reaction mixture of cyclotriphosphazene, 1, with 2-butyl-2-ethyl-
1,3-propandiol, which demonstrates the formation of the spiro
(10a) and the two ansa derivatives (10b, 10c) from this reaction.
It should be noted that there is a slight preference for the exo-ansa
compound (10b, 44%) over the endo-ansa compound (10c, 39%),
which is consistent with a preference for the bulkier butyl moiety
being exo in 10b compared to the ethyl moiety being exo (and
butyl endo) in 10c. A similar effect is observed for the two ansa
Table 4
Estimation by 31P NMR spectroscopy of the relative proportions of the spiro and ansa products from the reaction of 1 with various 1,3-propanediols under different solution
conditions.
CXY(CH2OH)2
X, Y
Yield of products (%)a
Pyridine, THF
NaH, THF
Compound
sp
an1
–
an2
–
Trimer
31
Other
2
sp
an1
10
an2
–
Trimer
39
Other
31
H, H
2
67
20
(i) mono-substituted
CH3, H
Ph, H
7
8
69
100
2
–
1
–
4
–
24
–
41
52
28
30
15
8
7
–
9
10
(ii) di-substituted (symmetrical)
CH3, CH3
C2H5, C2H5
C4H9, C4H9
3
4
5
70
94
100
12
–
–
–
–
–
6
2
–
12
4
–
23
11
11
68
87
88
–
–
–
6
1
1
3
1
–
(iii) di-substituted (unsymmetrical)
CH3, C3H7
C2H5, C4H9
9
10
88
98
–
–
–
–
1
2
11
–
12
14
49
44
36
39
3
3
–
–
(iv) electron-withdrawing substituents
CO2Et
Br, NO2
6
11
25
22
–
–
–
–
5
3
70
75
–
–
–
–
–
–
39
100
61
–
a
Key: sp: spiro compound; an1 and an2: exo and endo-ansa compounds; trimer: starting compound 1; other: other product.

3514
A. Uslu et al. / Inorganica Chimica Acta 363 (2010) 3506–3515
been observed that the formation of ansa derivatives is promoted
by using the more reactive sodium alkoxides (rather than the less
reactive neutral propanediol and tertiary base) [24] which has
been rationalised in terms of the co-coordination (cooperative
binding) with the attacking oxy-nucleophile of the sodium coun-
terion already present in an oxy-substituent [40,45]. These obser-
vations were investigated more systematically and quantitatively
in this work in the reaction of 1 with substituted 1,3-propanediols,
in which the central carbon atom in CXY(CH2OH)2 has various sub-
stituents X and Y (Scheme 1) and the relative ratios of spiro and
ansa compounds in the crude reaction mixtures were estimated
by 31P NMR spectroscopy (Table 4).
Using pyridine as the base to neutralise the hydrochloride
formed, the spiro derivative is formed virtually exclusively for all
the diols and the yield depends mainly on the electronic properties
of the substituents X and Y. This is shown clearly in Fig. 5a; the two
diols containing electron-withdrawing groups [with either two
COOC2H5 or NO2/Br groups] make the CH2–Oꢁ group slightly less
electron-rich and only a small amount (ca. 25%) of spiro compound
is formed; the diols containing two bulky alkyl groups, which make
the CH2–Oꢁ group slightly more electron-rich and significant
amounts (>85%) of the spiro compound is formed; and 1,3-pro-
panediol (X = Y = H) and the two diols containing one (X = H,
Y = Me) or two Me groups (X = Y = Me) result in an intermediate
amount of spiro compound (ca. 67–70%) being formed. In each of
these three groups the size of the substituents X and Y has only
a relatively small effect on the formation of spiro compounds
(Fig. 5a), though there is a significant increase in the formation of
spiro compounds from X = Y = Me (ca. 70%) to the other spiro com-
pounds (>88%) with larger alkyl groups and then the expected
small progressive increase in the formation of spiro compounds
for increasing size of the alkyl group(s) as a result of the gem-dial-
kyl effect [6], or with 2-phenyl-1,3-propandiol, possibly due to the
steric and mesomeric effect of the phenyl group under these neu-
tral reaction conditions [46].
In the reaction of 1 with the alkoxide form of the diols, both
spiro and ansa derivatives may be formed (Table 4). Although no
ansa (or spiro) compounds are found for the two diols containing
electron-withdrawing groups [for either two COOC2H5 or NO2/Br
groups], significant amounts (>83%) of the ansa compounds are
formed with the diols containing two bulky alkyl groups, and inter-
mediate amounts of ansa compounds are produced from diols con-
taining none (H/H, 10%), one (Me/H and Ph/H, ca. 40%) or two small
substituents (Me/Me, ca. 70%). As two types of ansa compounds are
formed when the substituents X and Y are different, it is necessary
to compare the sum total of ansa compounds with the relative pro-
portion formed when substituents X and Y are the same. It can be
seen in Fig. 5b that the formation of ansa compounds mainly re-
flects the electronic properties of the substituents; all the diols
with bulkier substituents have very similar relative proportions
of total ansa compound(s) and so there appears to be a negligible
steric effect under these very basic reaction conditions. The results
using 2-phenyl-1,3-propandiol and 2-methyl-1,3-propandiol are
very similar and in line with those that are intermediate between
the extremes of electron-pulling and electron-pushing substitu-
ents, indicating that the very basic reaction conditions dominate
over steric and any mesomeric effects.
4. Conclusions
Although the reactions of bidentate ligands (e.g. diols, diamines
and polyamines) with cyclophosphazene, N3P3Cl6 1, have been
investigated and reviewed over the years, this is the first system-
atic investigation of the effect of substituents in a bidentate ligand
on the formation of products. The reactions of 1 with various 2,20-
derivatives of 1,3-propandiol, CXY(CH2OH)2, give mainly spiro (6-
membered ring) and/or ansa (8-membered ring) di-substituted
derivatives, which have been characterized by NMR spectroscopy
and, in some cases, by X-ray crystallography. Quantitation of the
products in the reaction mixtures by 31P NMR spectroscopy con-
firms that the spiro derivatives are overwhelmingly formed using
pyridine as the base to neutralise the hydrochloride formed, with
ca. 100% selectivity in some cases; it is found that the yield de-
pends mainly on the electronic properties of the substituents X
and Y, whereas the size of X and Y has only a relatively small effect
on the formation of spiro compounds (Fig. 5a). On the other hand,
although both spiro and ansa derivatives may be formed in the
reaction of 1 with the alkoxide form of the diols, there are signifi-
cant proportions of total ansa compounds for diols with alkyl (aryl)
substituents, with ca. 90% selectivity in some cases; the relative
proportions of ansa compounds also mainly reflect the electronic
properties of the substituents X and Y (Fig. 5b) under these very
basic reaction conditions. These results may also be used to aid
the optimization of conditions for the selective formation of spiro
or ansa derivatives of cyclophosphazenes.
100
(b)
80
60
40
20
0
X, Y
110
90
70
50
30
10
(a)
Acknowledgments
We thank the Shin Nisso KakoCo. Ltd. for gifts of cyclophospha-
zene, the EPSRC for the National Crystallographic Service (South-
ampton, UK), Gebze Institute of Technology Research Fund for
partial support (AK, AU) and Prof. Robert A. Shaw for helpful
discussions.
Appendix A. Supplementary data
X, Y
CCDC 737153, 737154, 737155, 737156, 737157, 737158,
737159, 737160, 737161 and 737162 contains the supplementary
Fig. 5. (a) Yield (%) of spiro products for reactions using pyridine in THF; (b) total
yield (%) of ansa products for reactions using NaH in THF.

A. Uslu et al. / Inorganica Chimica Acta 363 (2010) 3506–3515
3515
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(2006) 963.
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2010.07.005.
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