Phosphoroamidate compounds of 1,1′-Bi-2-napthol: Synthesis, structural characterization and solvent-free ring-opening polymerization of -caprolactone and l-lactide

Article abstract of DOI:10.1016/j.ica.2011.01.088

New phosphoroamidate compounds with 1,1′-Bi-2-napthol (binol) ligand were synthesized from the corresponding phosphorochloridate intermediates and benzyl amine or benzyl amine derivatives. They were completely characterized using different spectroscopic methods and single crystal X-ray diffraction studies. These compounds effectively catalyze the ring-opening polymerization of -caprolactone (CL) and l-lactide (LA). This methodology of polymer synthesis is green and environmental benign since phosphorus is a natural constituent of human anatomy and these polymers being completely biodegradable.

Full text of DOI:10.1016/j.ica.2011.01.088

Inorganica Chimica Acta 372 (2011) 88–93
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Phosphoroamidate compounds of 1,10-Bi-2-napthol: Synthesis, structural
characterization and solvent-free ring-opening polymerization
of e-caprolactone and L-lactide
⇑
Ravikumar R. Gowda, Debashis Chakraborty , Venkatachalam Ramkumar
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
New phosphoroamidate compounds with 1,10-Bi-2-napthol (binol) ligand were synthesized from the cor-
responding phosphorochloridate intermediates and benzyl amine or benzyl amine derivatives. They were
completely characterized using different spectroscopic methods and single crystal X-ray diffraction stud-
Article history:
Available online 4 February 2011
Dedicated to Prof. S.S. Krishnamurthy on the
occasion of his 70th birthday.
ies. These compounds effectively catalyze the ring-opening polymerization of e-caprolactone (CL) and L-
lactide (LA). This methodology of polymer synthesis is green and environmental benign since phosphorus
is a natural constituent of human anatomy and these polymers being completely biodegradable.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Phosphorochloridate
Benzylphosphoroamidate
Ring-opening polymerization
e-Caprolactone
L-Lactide
1. Introduction
Horner-Woodward-Emmons reaction [32]. In the recent years,
we were interested in the chemistry of phosphorus (V) compounds
Metal-free catalysts are attracting growing interest as more
economical and environmentally friendly alternatives for classical
organic transformations. To this end, enzymes (such as lipases)
as well as organocatalysts (such as amines, phosphines, and N-het-
erocyclic carbenes) have recently been investigated for transesteri-
fication reactions [1–4], including lactide ring-opening
polymerization [5–8]. These metal-free nucleophilic catalysts are
particularly attractive for biomedical applications of the resulting
polymers, since there is no concern of contamination, waste, and
removal of metals. In this metal-free approach to ring-opening
polymerization of cyclic ester and lactide monomers, enzymes,
amines, phosphines, and carbenes all act as nucleophilic transeste-
rification catalysts, requiring the presence of a protic agent (typi-
cally water for lipases and alcohols for organocatalysts) as an
initiator. Although the precise mode of action of these catalysts re-
mains obscure, it would seem likely that the polymerization occurs
through an activated-monomer mechanism [9–15] involving a
transient monomer–catalyst complex. Organophosphorus chemis-
try has been a popular area of research as a result of the application
of such compounds in agriculture [16], pharmaceuticals [17–22],
biology [23,24] and chemical agents [25–31]. Such compounds
are known to be used extensively in chemical synthesis. These in-
clude the well known olefination reactions: Wittig reaction and
[33]. One of our major objectives has been the use of such reagents
for ring-opening polymerization reactions [34]. The work
presented here reports the synthesis and complete characteriza-
tion of new benzylphosphoroamidate compounds and scope of
their utility in ring-opening polymerization reactions.
2. Experimental
2.1. General methods
The reactions concerning the synthesis of phosphoroamidates
were performed under dry argon atmosphere using standard
Schlenk techniques with rigorous exclusion of moisture and air.
Methylene chloride was dried by stirring over calcium hydride
overnight and distilled fresh prior to use. Phosphorous oxychloride,
benzyl amine and its derivatives were purchased from Aldrich and
used without subsequent purification. Hexane, ethyl acetate and
methylene chloride were purchased from Ranchem India. CDCl3
used for NMR spectral measurements was purchased from Aldrich
and used as received.
2.2. Instrumentation
1H and 13C NMR spectra were recorded with a Bruker Avance
400 instrument. Chemical shifts for 1H and 13C NMR spectra were
referenced to residual solvent resonances and are reported as parts
⇑
Corresponding author. Tel.: +91 44 22574223; fax: +91 44 22574202.
E-mail address: dchakraborty@iitm.ac.in (D. Chakraborty).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.088

R.R. Gowda et al. / Inorganica Chimica Acta 372 (2011) 88–93
89
per million relative to SiMe4. 31P NMR spectra were recorded rela-
tive to 85% H3PO4 as an external standard. Mass spectra of the sam-
125.99 (Ar–C), 125.71 (Ar–C), 121.45 (Ar–C), 120.86, 45.99
(CH2Ph). 31P{1H} NMR (161 MHz CDCl3, ppm): d 13.30.
ple were recorded on
a Micro mass QToF instrument, low
resolution Electro-Spray Ionization (ESI) mass spectrometer using
methanol solvent. Infrared spectra were recorded using a Nicolet
6700 FT-IR instrument. Elemental analyses were done with a Per-
kin–Elmer Series 11 analyzer.
2.3.3. P(O)(O2C20H12)(NHCH2-4-OMeC6H4) (3)
Under a nitrogen atmosphere, to a stirred solution of binol
(200 mg, 0.69 mmol) in CH2Cl2 (20 mL) at 0 °C was added triethyl-
amine (2 mL, 13.96 mmol). To the above reaction mixture, POCl3
(0.07 mL, 0.69 mmol) was added dropwise. Reaction mixture stir-
red at 0 °C for 10 min followed by 4 h under ambient temperature.
To the above, 4-methoxybenzyl amine (0.45 mL, 3.49 mmol) was
added at room temperature and the reaction mixture was stirred
for 2.5 h and washed with water (5 mL) and saturated brine
(5 mL). Organic layer was dried over Na2SO4, filtered and
evaporated to dryness to yield the crude product. This was further
purified by column chromatography to yield a colorless solid com-
pound (310 mg, 96%). M.p. = 55 °C. Anal. Calc. for P(O)(O2C20H12)-
(NHCH2-4-OMeC6H4) [Mr 467]: C, 71.94; H, 4.74; N, 3.00. Found:
C, 71.98; H, 4.79; N, 3.08%. ESI-MS, [P(O)(O2C20H12)(NHCH2-4-
OMeC6H4)]+ m/z 467. IR (neat, cmꢁ1): 3208 (N–H), 1216 (P@O),
700 (P–N). 1H NMR (400 MHz, CDCl3, ppm): d 7.95–6.80 (m, 16H,
ortho, meta, para), 4.01 (m, 2H, CH2Ph), 3.73 (s, 3H, ArOMe),
3.04 (br, 1H, NH). 13C NMR (100 MHz CDCl3, ppm): d 157.61 (Ar–
O), 146.54 (Ar–O), 138.91 (Ar–C), 131.55 (Ar–C), 131.50 (Ar–C),
128.97 (Ar–C), 128.86 (Ar–C), 128.75 (Ar–C), 128.01 (Ar–C),
127.40 (Ar–C), 127.23 (Ar–C), 125.88 (Ar–C), 125.74 (Ar–C),
121.47 (Ar–C), 55.71 (Ar–OMe), 45.92 (CH2Ph). 31P{1H} NMR
(161 MHz CDCl3, ppm): d 13.38.
Molecular weights and the polydispersity indices of the poly-
mers were determined by GPC instrument with Waters 510 pump
and Waters 410 Differential Refractometer as the detector. Three
columns namely WATERS STRYGEL-HR5, STRYGEL-HR4 and STRY-
GEL-HR3 each of dimensions (7.8 ꢀ 300 mm) were connected in
series. Measurements were done in THF at 27 °C. Number average
molecular weights (Mn) and polydispersity (Mw/Mn) of polymers
were measured relative to polystyrene standards. Molecular
weights (Mn) were corrected according to Mark–Houwink correc-
tions [35]. CL and LA were purchased from Aldrich; the former
dried over CaH2 overnight and distilled fresh prior to use and the
later sublimed before use.
2.3. Synthesis of benzylphosphoroamidate (1–3)
2.3.1. P(O)(O2C20H12)(NHCH2C6H5) (1)
Under a nitrogen atmosphere, to a stirred solution of binol
(200 mg, 0.69 mmol) in CH2Cl2 (20 mL) at 0 °C was added triethyl-
amine (2 mL, 13.96 mmol). To the above reaction mixture, POCl3
(0.07 mL, 0.69 mmol) was added dropwise. Reaction mixture stir-
red at 0 °C for 10 min followed by 4 h under ambient temperature.
To the above, benzyl amine (0.38 mL, 3.49 mmol) was added at
room temperature and the reaction mixture was stirred for 2.5 h
and washed with water (5 mL) and saturated brine (5 mL). Organic
layer dried over Na2SO4, filtered and evaporated to dryness to yield
the crude product. This was further purified by column chromatog-
2.4. X-ray crystallography
Single crystals of 2 and 3 suitable for structural studies were ob-
tained by crystallization from 1:1 methylene chloride/hexane mix-
ture at ꢁ10 °C over a period of 1 week. X-ray data collection was
performed with a Bruker AXS (Kappa Apex 2) CCD diffractometer
raphy to yield
a colorless solid compound (290 mg, 97%).
M.p. = 49 °C. Anal. Calc. for P(O)(O2C20H12)(NHCH2C6H5) [Mr 437]:
C, 74.14; H, 4.61; N, 3.20. Found: C, 74.18; H, 4.69; N, 3.24%. ESI-
MS, [P(O)(O2C20H12)(NHCH2C6H5)]H+ m/z 438. IR (neat, cmꢁ1):
3210 (N–H), 1218 (P@O), 701 (P–N). 1H NMR (400 MHz, CDCl3,
ppm): d 7.97–7.18 (m, 17H, ortho, meta, para), 4.10 (m, 2H, CH2Ph),
3.11 (br, 1H, NH). 13C NMR (100 MHz CDCl3, ppm): d 146.77 (Ar–O),
139.19 (Ar–C), 131.50 (Ar–C), 131.21 (Ar–C), 128.96 (Ar–C), 128.76
(Ar–C), 128.64 (Ar–C), 127.98 (Ar–C), 127.80 (Ar–C), 127.43 (Ar–C),
126.02 (Ar–C), 125.91 (Ar–C), 121.25 (Ar–C), 120.86 (Ar–C), 46.22
(CH2Ph). 31P{1H} NMR (161 MHz CDCl3, ppm): d 13.37.
equipped with a graphite monochromated Mo K
radiation source. The data were collected with 100% completeness
for h up to 25°. and / scans was employed to collect the data. The
frame width for was set to 0.5° for data collection. The frames
a (k = 0.7107 Å)
x
x
were integrated and data were reduced for Lorentz and polariza-
tion corrections using SAINT-NT. The multi-scan absorption correc-
tion was applied to the data set. All structures were solved using
SIR-92 and refined using SHELXL-97 [36]. The crystal data are sum-
marized in Table 1. The non-hydrogen atoms were refined with
anisotropic displacement parameter. All the hydrogen atoms could
be located in the difference Fourier map. The hydrogen atoms
bonded to carbon atoms were fixed at chemically meaningful posi-
tions and were allowed to ride with the parent atom during
refinement.
2.3.2. P(O)(O2C20H12)(NHCH2-4-ClC6H4) (2)
Under a nitrogen atmosphere, to a stirred solution of binol
(200 mg, 0.69 mmol) in CH2Cl2 (20 mL) at 0 °C was added triethyl-
amine (2 mL, 13.96 mmol). To the above reaction mixture, POCl3
(0.07 mL, 0.69 mmol) was added dropwise. Reaction mixture stir-
red at 0 °C for 10 min followed by 4 h under ambient temperature.
To the above, 4-chlorobenzyl amine (0.42 mL, 3.49 mmol) was
added at room temperature and the reaction mixture was stirred
for 2.5 h and washed with water (5 mL) and saturated brine
(5 mL). Organic layer dried over Na2SO4, filtered and evaporated
to dryness to yield the crude product. This was further purified
by column chromatography to yield a colorless solid compound
(310 mg, 96%). M.p. = 52 °C. Anal. Calc. for P(O)(O2C20H12)-
(NHCH2-4-ClC6H4) [Mr 471]: C, 68.72; H, 4.06; N, 2.97. Found: C,
68.82; H, 4.12; N, 2.99%. ESI-MS, [P(O)(O2C20H12)(NHCH2-4-
ClC6H4)]+ m/z 471. IR (neat, cmꢁ1): 3204 (N–H), 1215 (P@O), 699
(P–N). 1H NMR (400 MHz, CDCl3, ppm): d 7.88–6.91 (m, 16H, ortho,
meta, para), 4.24 (m, 2H, CH2Ph), 4.04 (br, 1H, NH). 13C NMR
(100 MHz CDCl3, ppm): d 146.57 (Ar–O), 138.99 (Ar–C), 132.60
(Ar–C), 131.60 (Ar–C), 131.51 (Ar–C), 128.99 (Ar–C), 128.96 (Ar–
C), 128.76 (Ar–C), 128.08 (Ar–C), 127.60 (Ar–C), 127.13 (Ar–C),
2.5. General procedure for the bulk polymerization of CL and LA in
200:1 monomer catalyst ratio
For CL polymerization, 23.6 lmol of 1–3 were taken in a flask.
The contents were stirred at 80 °C and 0.50 mL CL (0.54 g,
4.71 mmols) was added neat. The mixture was rapidly stirred at
the given temperature. A rise in viscosity was observed and finally
the stirring ceased. For LA polymerization, 17.3 lmol of 1–3 was
used for 0.50 g (3.47 mmols) of monomer and the contents were
heated to 150 °C. The LA melted slowly at this temperature. A rise
in viscosity was observed and finally the stirring ceased. The poly-
merizations were quenched by pouring the contents into cold
methanol. The polymer was isolated by subsequent filtration and
dried till a constant weight was attained. A similar procedure
was used for higher ratios between monomer and catalyst.

90
R.R. Gowda et al. / Inorganica Chimica Acta 372 (2011) 88–93
Table 1
Table 2
The structures 2 and 3.
Selected bond lengths (Å) and bond angles (°) for compounds 2 and 3.
Compound
2
3
2
3
Empirical formula
Formula weight
Crystal system
Space group
T (K)
Wavelength (Å)
a (Å)
b (Å)
C
27H19ClNO3P
C28H22NO4P
467.44
Monoclinic
P21/c
P(1)–O(1)
P(1)–O(2)
P(1)–O(3)
P(1)–N(1)
O(2)–P(1)–O(3)
O(1)–P(1)–O(2)
O(2)–P(1)–N(1)
O(3)–P(1)–N(1)
1.5868(12)
1.6032(13)
1.4581(14)
1.6098(15)
107.66(7)
102.64(6)
110.78(8)
114.27(8)
1.5915(9)
1.6065(9)
1.4643(10)
1.6100(12)
106.79(5)
102.50(5)
111.74(6)
114.90(6)
471.85
Monoclinic
P21/c
298(2)
298(2)
0.71073
13.9635(5)
11.1393(4)
14.9027(5)
90
0.71073
14.1206(2)
11.0865(2)
15.0681(3)
90
c (Å)
a
(°)
b (°)
111.032(2)
90
2163.59(13)
4
1.449
28 058
5019
110.374(10)
90
2211.31(7)
4
1.404
29 466
ane mixture at ꢁ10 °C over a period of 1 week. Both compounds
crystallize in the monoclinic space group P21/c with four molecules
in the unit cell. Selected bond lengths and angles are enumerated
in Table 2 and the molecular structure is depicted in Figs. 1 and
2, respectively. Analysis of the crystal data reveals that phosphorus
centers in 2 and 3 are in a distorted pyramidal environment. The
c
(°)
V (Å3)
Z
Dcalc (g/cm3)
Reflections collected
Number of unique
reflections
5247
Goodness-of-fit (GOF) on
0.999
1.032
F2
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.0413,
wR2 = 0.1316
R1 = 0.0571,
wR2 = 0.1483
R1 = 0.0347,
wR2 = 0.0961
R1 = 0.0419,
wR2 = 0.1056
P
P
P
P
2
R1
=
|F0| ꢁ |Fc|/ |F0|, wR2 = [ (F0 ꢁ Fc2)2/ w(F02)2]1/2
.
3. Results and discussion
3.1. Synthesis and characterization
Reaction of 1,10-Bi-2-napthol (binol) ligand with POCl3 in a 1:1
stoichiometric ratio in the presence of an acid scavenger like Et3N
afforded the corresponding phosphorochloridate compound which
was subsequently quenched with benzyl amine or substituted ben-
zyl amine derivatives, resulting in the formation of the correspond-
ing benzylphosphoroamidate compounds 1–3, respectively
(Scheme 1). These compounds were isolated in high yield after col-
umn chromatography.
Fig. 1. Molecular structure of 2; thermal ellipsoids were drawn at 30% probability
level.
The 1H NMR of 1–3 contains the signals for all moieties in the
required ratio of integration. 13C NMR reveals that the phenyl car-
bon atom directly bonded to oxygen is considerably deshielded
with respect to the other aromatic peaks. These compounds
showed only one signal in their 31P{1H} NMR as expected from
the structure. ESI-MS spectra recorded on these compounds reveal
the molecular ion peaks. The IR spectra of 1–3 show peaks due to
mN–H, mP@O and mP–N with prominent intensities. Finally, purity of
these compounds was assured through the correct elemental anal-
ysis values.
3.2. Single-crystal X-ray diffraction studies
Single crystals of 2 and 3 suitable for X-ray diffraction studies
were obtained by crystallization from 1:1 methylene chloride/hex-
Fig. 2. Molecular structure of 3; thermal ellipsoids were drawn at 30% probability
level.
NH2
R
O
OH
OH
O
O
Et3N
CH2Cl2
P
NH
P
Cl
CH2Cl2
O
R
O
O
R = H 1
= 4-Cl 2
= 4-OMe 3
Scheme 1. Synthesis of benzylphosphoroamidate compounds.

R.R. Gowda et al. / Inorganica Chimica Acta 372 (2011) 88–93
91
P@O bond length is slightly shorter the P–O lengths. The P–N bond
lengths in these compounds are nearly identical. All the bond
lengths and angles are in agreement with literature precedents
[33].
40
30
20
10
0
3.3. Polymerization studies
Compounds 1 – 3 were tested for their catalytic activity towards
the ring-opening polymerization of CL and LA. The results are de-
picted in Tables 3 and 4, respectively.
M
P(O)(O2C20H12)(NHCH2C6H5)
Analyses of these results depicted reveal that these compounds
are powerful initiators for the polymerization of CL and LA. The
number average molecular weight (Mn) and molecular weight dis-
tribution (MWD) data are much superior to those obtained from
conventional metal catalysts [37]. Good degree of control in the
polymerization process was observed. Our polymerization results
deserve special mention since we have been able to obtain good
Mn and MWDs using this simple initiator system.
P(O)(O2C20H12)(NHCH2-4-ClC6H4)
P(O)(O2C20H12)(NHCH2-4-OMeC6H4)
0
200
400
600
800
1000
1200
[CL]O/[Cat]O
The variations of Mn with [CL]o/[Cat]o ratio and [LA]o/[Cat]o
using 1–3 for CL and LA polymerizations were studied. The plots
(Figs. 3 and 4) are linear indicating that there is a continual rise
Fig. 3. Plot of Mn (vs. polystyrene standards) vs. [CL]o/[Cat]o for CL polymerization
at 80 °C using 1–3.
70
65
60
55
50
45
40
35
30
Table 3
Results of CL polymerization with 1–3 at 80 °C.
b
Catalyst
[CL]o/[Cat]o
ta (h)
103 Mn (g/mol)
MWD
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
200:1
400:1
800:1
1000:1
1200:1
200:1
400:1
800:1
1000:1
1200:1
200:1
29
32
38
41
44
33
36
43
47
50
25
27
32
35
37
21.63
22.89
24.66
26.03
27.15
34.64
35.98
38.32
39.69
40.96
35.10
37.81
42.45
45.06
47.57
1.18
1.24
1.55
1.62
1.50
1.41
1.81
1.30
1.71
1.39
1.67
1.33
1.17
1.20
1.45
M
25
P(O)(O2C20H12)(NHCH2C6H5)
20
P(O)(O2C20H12)(NHCH2-4-ClC6H4)
15
P(O)(O2C20H12)(NHCH2-4-OMeC6H4)
10
5
400:1
800:1
1000:1
1200:1
0
0
200
400
600
800
1000
1200
[L-LA]O/[Cat]O
a
Time of polymerization measured by quenching the polymerization reaction
when all monomer was found consumed at 100% conversion.
Measured by GPC at 27 °C in THF relative to polystyrene standards with Mark–
Houwink corrections for Mn.
Fig. 4. Plot of Mn (vs. polystyrene standards) vs. [LA]o/[Cat]o for LA polymerization
at 150 °C using 1–3.
b
Table 4
Results of LA polymerization with 1–3 at 150 °C.
100
b
Catalyst
[CL]o/[Cat]o
ta (h)
103 Mn (g/mol)
MWD
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
200:1
400:1
800:1
1000:1
1200:1
200:1
400:1
800:1
1000:1
1200:1
200:1
32
35
41
44
48
35
38
45
49
52
29
31
36
39
42
26.69
27.59
29.40
30.39
31.29
42.37
48.13
57.57
63.60
67.73
38.99
43.82
53.89
58.24
63.78
1.14
1.19
1.28
1.51
1.15
1.31
1.64
1.41
1.31
1.37
1.55
1.70
1.61
1.54
1.50
80
P(O)(O2C20H12)(NHCH2C6H5)
P(O)(O2C20H12)(NHCH2-4-ClC6H4)
P(O)(O2C20H12)(NHCH2-4-OMeC6H4)
60
40
20
0
400:1
800:1
1000:1
1200:1
a
Time of polymerization measured by quenching the polymerization reaction
0
5
10
15
20
25
30
when all monomer was found consumed at 100% conversion.
Time (h)
b
Measured by GPC at 27 °C in THF relative to polystyrene standards with Mark–
Houwink corrections for Mn.
Fig. 5. CL conversion vs. time plot using 1–3: [CL]o/[Cat]o = 200 at 80 °C.

92
R.R. Gowda et al. / Inorganica Chimica Acta 372 (2011) 88–93
in Mn with an increase in [CL]o/[Cat]o ratio and [LA]o/[Cat]o ratio,
respectively.
6
5
4
3
2
1
0
Y = -0.000309 + 0.1786 X
3.4. Polymerization kinetics
The kinetic studies for the polymerization of CL and LA using 1–
3 in ratio [M]o/[Cat]o = 200 were performed (see Supplementary
material). The results are depicted in Figs. 5 and 6, respectively.
The plots suggest the complete absence of induction period and
there is a first-order dependence of rate of polymerization on
monomer concentration. The ln[CL]o/[CL]t and ln[LA]o/[LA]t versus
time plots (Figs. 7 and 8) exhibit linear variation. From the slope of
the plots, the values of the apparent rate constant (kapp) for CL
polymerizations initiated by 1–3 were found to be 0.1237,
0.1168 and 0.1607 hꢁ1. Similarly, values of the apparent rate con-
stant (kapp) for LA polymerizations initiated by 1–3 were 0.1786,
0.1072 and 0.1990 hꢁ1, respectively. The orders of magnitude of
kapp for CL and LA polymerization indicate that these behave in a
similar manner like metal catalysts [37].
Y = 0.00457 + 0.199 X
L
Y = 0.0128 + 0.1072 X
L
P(O)(O2C20H12)(NHCH2C6H5)
P(O)(O2C20H12)(NHCH2-4-ClC6H4)
P(O)(O2C20H12)(NHCH2-4-OMeC6H4)
0
5
10
15
20
25
30
35
Time (h)
Fig. 8. Semilogarithmic plots of LA conversion in time initiated by 1 – 3: [LA]o/
[Cat]o = 200 at 150 °C.
4. Conclusions
100
80
In summary, 1–3 are potent towards the ring opening polymer-
ization of CL and LA. This polymerization contributes to an eco-
nomical process employing readily synthesized inorganics as
catalysts and does not necessitate solvents. The overall system is
green, eco-friendly and environmentally benign since phosphorus
is a natural human constituent and these polymers being biode-
gradable. The achievement of obtaining good molecular weights
without having to resort to elaborate ligands and metals is a noted
feature for our system.
P(O)(O2C20H12)(NHCH2C6H5)
60
P(O)(O2C20H12)(NHCH2-4-ClC6H4)
P(O)(O2C20H12)(NHCH2-4-OMeC6H4)
40
20
0
Acknowledgments
This work was supported by Department of Science and
Technology, New Delhi. The services from the NMR facility pur-
chased under the FIST program, sponsored by the Department of
Science and Technology, New Delhi is gratefully acknowledged.
0
5
10
15
20
25
30
35
Time (h)
Fig. 6. LA conversion vs. time plot using 1–3: [LA]o/[Cat]o = 200 at 150 °C.
Appendix A. Supplementary material
CCDC 795746 and 795747 contain the supplementary crystallo-
graphic data for 2 and 3. 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.2011.01.088.
4.5
4.0
3.5
Y = 0.00932 + 0.1237 X
3.0
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Y = -0.00315 + 0.1607 X
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