Synthesis and spectral characterization of cyclotriphosphazene based 18-membered macrocycles

Article abstract of DOI:10.1016/j.ica.2012.03.016

New 18-membered cyclotriphosphazene-containing macrocycles 7-10 were obtained by 1 + 1 condensation reaction of [dispiro-N₃P ₃(C₁₂H₈O₂)₂((N(Me)NCH) ₂ N₄C₂₀H

Full text of DOI:10.1016/j.ica.2012.03.016

Inorganica Chimica Acta 390 (2012) 163–166
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Note
Synthesis and spectral characterization of cyclotriphosphazene based 18-membered
macrocycles
⇑
Pakkirisamy Thilagar , Pagidi Sudhakar, P. Chinna Ayya Swamy, Sanjoy Mukherjee
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 August 2011
Received in revised form 23 February 2012
Accepted 3 March 2012
Available online 17 March 2012
New 18-membered cyclotriphosphazene-containing macrocycles 7-10 were obtained by 1 + 1 condensa-
tion reaction of [dispiro-N3P3(C12H8O2)2((N(Me)N@CH)2 N4C20H26)] (2) with N,N0-dimethyl-ethylenedia-
mine-1,4-diyldimethylenebis(4-methyl-2-formylphenol)
(3),
N,N0-dimethyl-ethylenediamine-1,4-
diyldimethylenebis(4,5-dimethyl-2-formylphenol) (4), N,N0-dimethyl-ethylenediamine-1,4-diyldimeth-
ylenebis(5-chloro-2-formylphenol) (5) and N,N0-dimethyl-ethylenediamine-1,4-diyldimethylenebis(5-
bromo-2-formylphenol) (6), respectively.
Keywords:
Ó 2012 Elsevier B.V. All rights reserved.
Cyclophosphazenes
Macrocycles
Condensations
Hydrazide
Cyclophosphazenes are an important family of inorganic hetero-
cyclic rings with large variation of ring size [1]. The cyclotriphos-
phazene N3P3Cl6 has been extensively investigated particularly in
terms of (i) nucleophilic substitution reactions at phosphorus
[1–5], (ii) ring-opening polymerization [1–5], and (iii) utility as a
support for building multisite coordination ligands [1–5]. Several
groups have also shown that in addition to the traditional themes
of investigation as outlined above [1–5]. Cyclophosphazenes can
also be utilized for supporting chiral ligands, multi-electroactive,
photoactive molecules and for studying supramolecular interac-
tions [5,6]. Very interesting work was published by Elias et al. and
others in recent years [6c]. On the other hand the utility of the
cyclophosphazene ring as a support for constructing macrocyclic li-
gands is only slowly being realized [7a,8]. An important step in this
direction is the assembly of several new crown ethers supported on
the phosphazene skeleton. It has been observed that the reaction of
N3P3Cl6 with long chain diols such as tetraethylene glycol or
pentaethylene glycol affords a mixture of products where the
substitution of the glycol has occurred at the same phosphorus
(spirocyclic) or at two different phosphorus atoms (ansa) within
the cyclophosphazene ring. A decade ago Majoral and co-workers
have demonstrated that the reaction of acyclic phosphodihydraz-
ides with various dialdehydes led to a great variety of macrocycles
arising from [1 + 1], [2 + 2], [3 + 3], or even [4 + 4] cyclocondensa-
tions [7a,9]. Recently A similar strategy was suggested by Chandra-
sekhar and co-workers [10]. However, the studies carried out on
cyclophosphazene based macrocycles (apart from cyclophospha-
zene appended crown ethers) till now have been sporadic with
limited success. In this letter we report details of the condensation
reactions of dialdehyde and hydrozene-derived cyclotriphospha-
zene and spectral characterization of the new 18-membered cyclo-
phosphazene-containing macrocycles are described.
The parent cyclotriphosphazene (N3P3Cl6) contains six reactive
P–Cl bonds and is not possible for controlled macrocyclic synthesis
[10]. Consequently, compound 1 (N3P3Cl2(O2C12H8)2 was synthe-
sized from N3P3Cl6 by adopting a known synthetic procedure
[8,10]. The reaction of 1 with MeNH–NH2 in chloroform afforded
2 [5a]. This reaction is regiospecific; the N-methyl end of the bi-
functional reagent reacts with 1 leading to product containing
reactive terminal –NH2 groups. In this reaction MeNH–NH2 was
also used to scavenge the liberated hydrogen chloride, obviating
the need for an additional base. Compound 2 possesses two reac-
tive NH2 groups which could be readily elaborated under mild
reaction conditions. Condensation of the hydrazide 2 with stoichi-
ometric amount N,N0-ethylenediamine-1,4-diyldimethylenebis(4-
methyl-2-formylphenol) (Scheme 1) occurs at room temperature
to afford the corresponding hydrazones 7 in quantitative yield.
The notable feature of this reaction is the complete absence of
2+2 condensed product (Scheme 2) and the isolation of the product
7 (1 + 1 condensed) in excellent yield. Additionally, 7 is also struc-
turally interesting because it is a small macrocycle with more
number of strong donors like phenolate oxygen and nitrogens
which can hold the incoming metal atoms very strongly. All the
compounds were examined by multinuclear NMR spectroscopy.
The 31P{1H} NMR spectrum of compound 2 is of the AX2 type.
⇑
Corresponding author. Tel.: +91 80 2293 3353; fax: +91 80 2360 1552.
E-mail address: thilagar@ipc.iisc.ernet.in (P. Thilagar).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.03.016

164
P. Thilagar et al. / Inorganica Chimica Acta 390 (2012) 163–166
R
R'
H
H
Me
NH
Me
Me
R
N
N
OH
OH
O
O
Paraformaldehyde
R'
O
+
H
NH
Ethanol:Aceticacid (7:3)
36 h, reflux
OH
Me
R'
1eq
2eq
R
3
4
5
6
R = CH3 R' = H
R = CH3 R' = CH3
R = Cl
R = Br
R' = H
R' = H
Scheme 1. Synthesis of compounds 3–6.
R
R
R'
R'
H
O
O
Me
N
O
O
P
Me
Me
Me
N
N
OH
OH
O
O
N
P
N
P
N
N
Me
OH
OH
P
N
N
O
O
N
P
N
P
DCM
N
NH2
NH2
O
O
+
Me
N
N
N
N
Me
H
Me
R'
R'
R
R
7
R = CH3 R' = H
8
9
R = CH3 R' = CH3
R = Cl
R' = H
R' = H
10 R = Br
Me
Me
N
R'
N
R'
R
R
HO
OH
Me
O
N
N
N
N
Me
N
N
N
P
P
O
O
P
N
O
P
N
N
O
N
P
N
O
O
P
N
N
Me
O
Me
R
HO
N
OH
R
R'
N
R'
Me
Me
Scheme 2. Synthesis of macrocycles 7–10.
The spirocyclic phosphorus atoms P(O2C12H8) resonate at 26.2 ppm
(doublet) while P(N(Me)–)2 was seen at 29 ppm (triplet). The 31P
NMR spectrum of 7 revealed the presence of two distinct signals:
d 24.4 (d, –P(–O2C12H8)2), 17.7 (t, –P (O4 N4C20H26(CH@)2)), 2J(P–
N–P) = 98.6 Hz). It is of interest to note that the chemical shift of
the latter is upfield with respect to the free hydrazide 2. Compound
7 also is characterized by the presence of a [M+2]+ ion at 943 in its
FAB mass spectrum (Fig. 1). Compounds 8–10 were prepared fol-
lowing a procedure similar to that used for 7. Compounds 8–10
were characterized by multinuclear NMR (1H, 13C and 31P), and ele-
mental analysis. 1H NMR integration, 31P resonance and molecular
ion peak in ESI Mass spectrum confirms the formation of 8–10 and
are comparable with 7.
In conclusion we report a facile procedure for the assembly of
large macrocycles containing cyclophosphazene rings. The phenol
oxygen and imino and amino nitrogen atoms present in the macro-
cyclic cavity can be utilized for coordination to metal ions. This as-
pect is being investigated.
1. Experimental
All preparations were carried out under nitrogen atmosphere by
means of standard Schlenk techniques. Dispiro-N3P3(C12H8O2)2(N-
(Me)NH2)2 (2) was prepared by literature method reported by us
previously [5a]. Solvents and other general reagents used in this

P. Thilagar et al. / Inorganica Chimica Acta 390 (2012) 163–166
165
Fig. 1. Mass spectrum of compound 7.
work were purified according to standard procedures. 2,20-Dihy-
droxy biphenyl (Fluka) was used as obtained. N3P3Cl6 (Aldrich)
was recrystallized from n-hexane before use. N-Methylhydrazine
was obtained as a gift from Prof. V. Chandrasekhar, Department
of Chemistry, IIT-kanpur, India, and used as such. Melting points
were measured using a JSGW melting point apparatus and are
uncorrected. Elemental analyses were carried out by using a Ther-
moquest CE instruments model EA/110 CHNS-O elemental ana-
lyzer. 1H and 31P NMR spectra were recorded in CDCl3 solution
on a JEOL spectrometer operating at 400.0 and 161.7 MHz, respec-
tively. Chemical shifts are reported with respect to internal tetra-
4.46 mmol) and paraformaldehyde (0.30 g) .Yield: 80%; 1H NMR
(CDCl3, 400 MHz, ppm): 2.26 (s, 3H), 2.28 (s, 3H), 2.67 (s, 3H), 2.68
(s, 3H), 3.0 (s, 4H), 3.65 (s, 4H) 7.25 (s, 2H), 10.20 (s, 1H); Anal. Calc.
for. C24H32N2O4 (%): C, 69.86; H, 7.82; N, 6.79. Found: C, 69.20; H,
6.15; N, 6.45.
1.1.4. Synthesis of 5
Compound 5 was prepared by adopting the similar synthetic
procedure used for 3. The quantities involved and the spectral
characterization are given below. 5-Chloro-2-hydroxy-benzalde-
hyde (760 mg, 4.86 mmol), N,N0-dimethyl-ethane-1,2-diamine
(0.35 mL, 3.24 mmol) and paraformaldehyde (0.32 g) .Yield: 82%;
1H NMR (CDCl3, 400 MHz, ppm): 2.3 (s, 3H), 2.32 (s, 3H), 3.20 (s,
4H), 3.70 (s, 4H) 7.32 (s, 4H), 10.35 (s, 1H); Anal. Calc. for.
methylsilane (1H) or external 85% H3PO4
(
31P).
1.1. Synthesis
C
20H22Cl2N2O4 (%): C, 56.48; H, 5.21; N, 6.59. Found: C, 55.92; H,
1.1.1. Synthesis of 2
4.89; N, 5.96.
Compound 2 was prepared by adopting known synthetic proce-
dure [5a]. The quantities involved and the spectral characterization
are given below. N3P3Cl2(O2C12H8)2 (3.00 g, 5.24 mmol) and N-
methylhydrazine (1.20 g, 26 mmol). (125 mL). Yield (3 g, 88.5%).
Mp: 278 °C. 1H NMR: 2.96 (d, 6H, –N(CH3); 3J(1H-31P)) 11.0 Hz),
3.08 (s, 4H, –NH2), 7.24–7.50 (m, 16H, aromatic). 31P NMR: 29.0
(t, P(N(Me)–)2), 26.2 (d, P(O2C12H8)2), 2J(PN–P)) 57.95 Hz. Anal.
Calc. for C26H26N7O4P3: C, 52.62; H, 4.42; N, 16.52. Found: C,
52.29; H, 4.40; N, 16.41.
1.1.5. Synthesis of 6
Compound 6 was prepared by adopting the similar synthetic
procedure used for 3. The quantities involved and the spectral
characterization are given below. 5-Bromo-2-hydroxy-benzalde-
hyde
(1 g,
2.43 mmol),
N,N0-dimethyl-ethane-1,2-diamine
(0.20 mL, 1.8 mmol) and paraformaldehyde (0.28 g). Yield: 80%;
1H NMR (CDCl3, 400 MHz, ppm): 2.25 (s, 3H), 2.29 (s, 3H), 3.21
(s, 4H), 3.72 (s, 4H) 7.31 (s, 4H), 10.32 (s, 1H); Anal. Calc. for.
C
20H22Br2N2O4 (%): C, 46.72; H, 4.31; N, 5.45. Found: C, 45.98; H,
1.1.2. Synthesis of 3
3.96; N, 4.89.
2-Hydroxy-5-methyl-benzaldehyde (1 g, 7.3 mmol), N,N0-
dimethyl-ethane-1,2-diamine (0.50 mL, 4.86 mmol) and parafor-
maldehyde (0.2 g) in ethanol and acetic acid mixture (7:3)
(100 mL) was heated under reflux for 36 h. The reaction mixture
was filtered and evaporated to afford 2 as a pale yellow solid,
which were purified subsequently by recrystallization in chloro-
form. Yield: 85%; 1H NMR (CDCl3, 400 MHz, ppm): 2.26 (s, 3H),
2.28 (s, 3H), 2.67 (s, 3H), 2.68 (s, 3H), 3.0 (s, 4H), 3.65 (s, 4H)
7.22 (s, 2H), 7.38 (s, 2H), 10.21 (s, 1H); Anal. Calc. for.
1.1.6. Synthesis of 7
A solution of {(C6H5)P(O)[N(Me)NH2]2} (2) (0.42 g, 2.0 mmol) in
methanol (100 mL) and 3 (0.77 g, 2.0 mmol) in chloroform (100 mL)
were added simultaneously drop wise (1 h) to a round bottom flask
containing methanol (100 ml) maintained at 0 °C under constant
stirring. The reaction mixture was stirred at 25 °C for about 5 h
and the solvent evaporated in vacuo to afford 5 as a solid product.
This was purified by column chromatography using chloroform/
hexane (1:9) as eluting solvent. Yield: 0.89 g (75%); Mp. 228 °C
decomposes); 31P NMR (CDCl3, 161.7 MHz): d 24.4 (d, –P(–O2C12
H8)2), 17.7 (t, –P (O4 N4C20H26(CH@)2)), 2J(P–N–P) = 98.6 Hz); 1H
NMR (CDCl3, 400 MHz): 2.28 (s, 3H), 2.30 (s, 3H), 2.71 (s, 3H), 2.74
(s, 3H), 3.13 (s, 6H), 3.25 (s, 4H), 3.68 (s, 4H) 7.24 (s, 2H), 7.41–
7.83 (m, 20H); MS(FAB): 943 (M+1)+. Anal. Calc. for. C48H50N9O6P3:
C, 61.21; H, 5.35; N, 13.38. Found: C, 60.92; H, 4.98; N, 12.86.
C22H28N2O4 (%): C, 68.73; H, 7.34; N, 7.29. Found: C, 68.11; H,
6.98; N, 7.15.
1.1.3. Synthesis of 4
Compound
4 was prepared by adopting above synthetic
procedure. The quantities involved and the spectral characteriza-
tion are given below. 2-Hydroxy-4,5-di-methyl-benzaldehyde
(1 g, 6.66 mmol), N,N0-dimethyl-ethane-1,2-diamine (0.5 mL,

166
P. Thilagar et al. / Inorganica Chimica Acta 390 (2012) 163–166
(e) J.E. Mark, H.R. Allcock, R. West, Inorganic Polymers, Prentice Hall,
1.1.7. Synthesis of 8
Englewood Cliffs, NJ, 1992;
Compound 6 was prepared by adopting above synthetic proce-
dure. The quantities involved and the spectral characterization are
given below. {(C6H5)P(O)[N(Me)NH2]2} (2) (0.42 g, 2.0 mmol), 4
(0.77 g, 2.0 mmol). Yield: 0.89 g (75%); Mp. 242 °C decomposes);
31P NMR (CDCl3, 161.7 MHz): d 25.0 (d, –P(–O2C12H8)2), 18.8 (t,
–P (O4 N4C20H26(CH@)2)), 2J(P–N–P) = 99.2 Hz); 1H NMR (CDCl3,
400 MHz): 2.26 (s, 3H), 2.31 (s, 3H), 2.73 (s, 3H), 2.75 (s, 3H),
3.20 (s, 6H), 3.72 (s, 4H) 7.30–7.75 (m, 18H); MS(FAB): 965
(Mꢀ4)+. Anal. Calc. for. C50H54N9O6P3: C, 61.91; H, 5.61; N, 13.0.
Found: C, 61.45; H, 5.25; N, 12.78.
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1.1.8. Synthesis of 9
Compound 6 was prepared by adopting above synthetic proce-
dure. The quantities involved and the spectral characterization are
given below. {(C6H5)P(O)[N(Me)NH2]2} (2) (0.42 g, 2.0 mmol), 5
(0.85 g, 2.0 mmol). Yield: 78%; Mp. 250 °C decomposes); 31P NMR
(CDCl3, 161.7 MHz): d 25.2 (d, –P(–O2C12H8)2), 18.5 (t, –P (O4
N4C20H26(CH@)2)), 2J(P–N–P) = 99 Hz); 1H NMR (CDCl3, 400 MHz):
1H NMR (CDCl3, 400 MHz): 2.25–2.30 (s, 6H), 3.17 (s, 6H), 3.72 (s,
4H), 7.25–7.82 (m, 20H). Anal. Calc. for. C46H44Cl2N9O6P3: C,
56.21; H, 4.51; N, 12.83. Found: C, 55.52; H, 3.95; N, 11.92.
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1.1.9. Synthesis of 10
Compound 10 was prepared by adopting similar synthetic pro-
cedure used for 7. The quantities involved and the spectral charac-
terization are given below. {(C6H5)P(O)[N(Me)NH2]2} (2) (0.42 g,
2.0 mmol), 6 (1 g, 2.0 mmol). Yield: 72%; Mp. 235 °C decomposes);
31P NMR (CDCl3, 161.7 MHz): d 25.3 (d, –P(–O2C12H8)2), 18.4 (t, –P
(O4 N4C20H26(CH@)2)), 2J(P–N–P) = 99 Hz); 1H NMR (CDCl3,
400 MHz): 2.26–2.31 (s, 6H), 3.15 (s, 6H), 3.73 (s, 4H), 7.28–7.89
(m, 20H). Anal. Calc. for. C46H44Br2N9O6P3: C, 51.56; H, 4.14; N,
11.76. Found: C, 50.86; H, 3.83; N, 11.02.
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Acknowledgements
PT thanks Indian Institute of Science Bangalore, and DST, New
Delhi India, for financial support. We also thank Prof. V. Chandra-
sekhar for his valuable suggestions.
(m) P. Kommana, S. Kumaraswamy, K.C. Kumara Swamy, Inorg. Chem.
Commun. 6 (2003) 394;
Appendix A. Supplementary material
(n) N.S. Kumar, K.C. Kumara Swamy, Polyhedron 24 (2004) 979;
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2012.03.016.
(b) S. Sumitra, Tetrahedron Lett. 44 (2003) 7281;
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(d) C.N. Myer, C.W. Allen, Inorg. Chem. 41 (2002) 60;
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Blanchard-Desce, Chem. Commun. (2006) 915.
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