A modular ligand design for cation sensors: phosphorus-supported pyrene-containing ligands as efficient Cu(II) and Mg(II) sensors

Article abstract of DOI:10.1016/j.tet.2009.03.098

A modular ligand design allowed the assembly of four phosphorus-supported pyrene-containing ligands. The number of pyrene arms could be varied from 1 to 6 depending on the phosphorus support. While ligands containing one and three pyrene arms are excellen

Full text of DOI:10.1016/j.tet.2009.03.098

Tetrahedron 65 (2009) 4540–4546
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A modular ligand design for cation sensors: phosphorus-supported
pyrene-containing ligands as efficient Cu(II) and Mg(II) sensors
,
a
a
b
Vadapalli Chandrasekhar a , Mrituanjay D. Pandey , Prasenjit Bag , Siddharth Pandey
*
a Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India
b Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A modular ligand design allowed the assembly of four phosphorus-supported pyrene-containing ligands.
The number of pyrene arms could be varied from 1 to 6 depending on the phosphorus support. While
ligands containing one and three pyrene arms are excellent fluorescence-based sensors of Cu2þ, the
Received 25 December 2008
Received in revised form 28 March 2009
Accepted 30 March 2009
Available online 5 April 2009
ligand containing two pyrene arms shows a high specificity for Mg2þ
.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Phosphorus
Pyrene
Fluorescence
X-ray crystallography
1. Introduction
affected by metalation. Our particular interest was the possibility of
finding an effective fluorescence-based sensor for Cu2þ in view of
the fact that paramagnetic ions quench fluorescence18–21 and only
in some instances a fluorescence enhancement has been ob-
served.22–26 Accordingly, we report herein, the design, assemblyand
structural characterization of a family of phosphorus-supported
pyrene containing ligands Ph2P(O)[N(Me)N]CH(Py)] (1), PhP(O)[N-
(Me)N]CH(Py)]2 (2), (S)P[N(Me)N]CH-Py]3 (3) and N3P3[N(Me)-
N]CH-Py]6 (4) (Py¼1-pyrenyl). While 1 and 3 are excellent sensors
In recent years there has been considerable research interest in
the area of molecular sensors, which can detect cations (or anions)
with a high degree of specificity even at low concentrations.1–5
Detection techniques based on optical spectroscopic methods have
been favoured in view of the simplicity of the technique as well as
rapid nature of detection. In general the design of ligands is carried
out with a view to induce absorption spectral changes or fluores-
cence emission changes upon interaction with cations.6–8 Fluores-
cence-based methods are more sensitive than the corresponding
absorption techniques and hence there has been considerable in-
terest in the design of new ligands that would show significant
changes in their fluorescence output upon interaction with a cation
input.9–15 We have been interested in phosphorus-based ligands for
some time in view of their modular design and also because the
latter allows ready assembly of a wide choice of ligands with varying
properties. For example, using (S)P[N(Me)N]CH–C6H4–2-OH]3 we
were able to assemble neutral trinuclear derivatives (L2M3) whereas
by the use of (S)P[N(Me)N]CHC6H4–2-OH–3-OMe]3 we could
prepare ionic 3d–4f assemblies possessing interesting magnetic
properties including single molecule magnet behaviour.16,17 In view
of this versatility it was of interest to probe if this design allowed the
preparation of ligands whose fluorescence properties could be
of Cu2þ, 2 is specific for Mg2þ
.
* Corresponding author.
E-mail address: vc@iitk.ac.in (V. Chandrasekhar).
Figure 1. Phosphorus-supported pyrene-containing ligands 1–4.
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.03.098

V. Chandrasekhar et al. / Tetrahedron 65 (2009) 4540–4546
4541
Scheme 1. Synthesis of 1.
2. Results and discussion
The synthesis of the ligands 1–4 was carried out by a two-step
protocol and involved the conversion of the chloro precursors into
the corresponding phosphorus hydrazides by a regiospecific re-
action with N-methylhydrazine. Condensation of the hydrazides
with pyrene-1-carboxaldehyde afforded 1–4 in excellent yields
(Fig. 1). A representative synthetic protocol is shown in Scheme 1.
The conversion of the chloro precursors into the products is readily
Figure 3. ORTEP diagrams of 2 (a) and 3 (b) with 50% and 30% thermal ellipsoids,
respectively. Selected bond distances (Å) and angles (ꢀ) are as follows: 2: C(5)–P(1),
1.788(2); N(1)–P(1), 1.6603(19); N(3)–P(1), 1.678(2); P(1)–O(1), 1.4696(16); O(1)–P(1)–
N(1), 112.42(10); O(1)–P(1)–N(3), 108.65(10); N(1)–P(1)–N(3), 107.87(10); O(1)–P(1)–
C(5), 113.77(10); N(1)–P(1)–C(5), 105.96(10); N(3)–P(1)–C(5), 107.92(11). 3: N(1)–P(1),
1.659(4); N(3)–P(1), 1.667(4); N(5)–P(1), 1.672(4); P(1)–S(1), 1.9247(19); N(1)–P(1)–
N(3), 107.9(2); N(1)–P(1)–N(5), 101.7(2); N(3)–P(1)–N(5), 106.3(2); N(1)–P(1)–S(1),
112.54(16); N(3)–P(1)–S(1), 110.37(15); N(5)–P(1)–S(1), 117.32(15).
monitored by 31P{H} NMR [cf.
d (
31P); (S)PCl3 31.7 (s);
(S)P[N(Me)NH2]3, 84.5 (s); 3, 75.1 (s)]. Compounds 1–4 are soluble
in a wide range of organic solvents. The chemical integrity of these
compounds is retained in solution as evidenced by the presence of
strong [MþH]þ peaks in their ESI-MS spectra recorded under
positive ion mode (see Supplementary data). Finally, 1–3 were also
characterized by solid state X-ray crystallography. Compound 2
crystallized in two modifications, one as a methanol solvate and the
other without any solvent of crystallization. The perspective views
Figure 2. ORTEP diagrams of 1 (a) and 2$MeOH (b) with 50% thermal ellipsoids (solvent
molecules are omitted for clarity). Selected bond distances (Å) and angles (ꢀ) are as
follows: 1: C(3)–P(1), 1.803(3); C(9)–P(1), 1.800(2); N(1)–P(1), 1.687(2); P(1)–O(1),
1.4797(19); O(1)–P(1)–N(1), 116.69(11); O(1)–P(1)–C(9), 113.36(11); N(1)–P(1)–C(9),
103.21(11); O(1)–P(1)–C(3), 110.99(11); N(1)–P(1)–C(3), 104.47(11); C(9)–P(1)–C(3),
107.27(11). 2$MeOH: C(5)–P(1), 1.787(3); N(1)–P(1),1.663(3); N(3)–P(1),1.669(2); O(1)–
P(1), 1.472(2); O(1)–P(1)–N(1), 116.56(12); O(1)–P(1)–N(3), 108.88(12); N(1)–P(1)–N(3),
102.65(12); O(1)–P(1)–C(5), 112.49(13); N(1)–P(1)–C(5), 105.63(13); N(3)–P(1)–C(5),
110.12(13).

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V. Chandrasekhar et al. / Tetrahedron 65 (2009) 4540–4546
Table 1
Crystallographic data and structure refinement details for 1, 2, 2$MeOH and 3
1
2
2$MeOH
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C36H29N2OP
536.58
153(2)
0.71073
Triclinic
C42H31N4OP
638.68
100(2)
0.71073
Monoclinic
P21/n
C43H35N4O2P
670.72
100(2)
0.71073
Triclinic
P-1
C54H39N6PS
834.94
273(2)
0.71073
Triclinic
P-1
P-1
Unit cell
a¼8.4772(11)
b¼10.2534(13)
c¼17.442(2)
a¼10.0285(7)
b¼11.8695(9)
c¼26.634(2)
a¼6.792
b¼15.720
c¼16.618
a¼10.385(5)
b¼13.784(7)
c¼15.118(8)
dimensions (Å), (ꢀ)
a
¼77.418(2)
a
¼90
a
¼75.52
¼89.65
a
¼86.293(10)
¼76.600(11)
b
¼88.766(2)
b
¼99.1170(10)
b
b
g
¼65.632(2)
g
¼90
g
¼78.57
g
¼89.766(10)
Volume (Å3)
1343.9(3)
3130.3(4)
1682.1
2100.6(19)
2, 1.320
Z, Dcalcd [Mg/m3]
2, 1.326
0.136
4, 1.355
0.131
2, 1.324
0.127
m
[mmꢁ1
]
0.162
F(000)
Crystal size (mm3)
Range (ꢀ)
564
1336
704
872
0.11ꢂ0.09ꢂ0.06
2.29–27.00
ꢁ10ꢃhꢃ10
ꢁ13ꢃkꢃ13
ꢁ22ꢃlꢃ11
8130
0.08ꢂ0.05ꢂ0.03
2.08–27.00
ꢁ12ꢃhꢃ12
ꢁ15ꢃkꢃ11
ꢁ34ꢃlꢃ33
18 465
0.103ꢂ0.072ꢂ0.047
2.09–26.50
ꢁ8ꢃhꢃ8
0.087ꢂ0.072ꢂ0.057
2.02–25.00
ꢁ9ꢃhꢃ12
q
Index ranges
ꢁ17ꢃkꢃ19
ꢁ19ꢃlꢃ20
9914
ꢁ15ꢃkꢃ16
ꢁ14ꢃlꢃ17
10 791
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
5683 [R(int)¼0.0261]
5683/0/362
1.059
6803 [R(int)¼0.0434]
6803/0/557
1.062
6795 [R(int)¼0.0277]
6795/0/455
1.018
7261 [R(int)¼0.0480]
7261/0/562
0.954
Final R indices [I>2sigma(I)]
R1¼0.064
R1¼0.0544
wR2¼0.1247
R1¼0.0800
wR2¼0.1513
0.379 and ꢁ0.358
R1¼0.0658
wR2¼0.1650
R1¼0.0990
wR2¼0.2143
0.633 and ꢁ0.358
R1¼0.0702
wR2¼0.1557
R1¼0.1719
wR2¼0.2260
0.356 and ꢁ0.329
wR2¼0.1802
R1¼0.0835
wR2¼0.2450
0.803 and ꢁ0.663
R indices (all data)
Largest diff.
peak and hole
(e Åꢁ3
)
of molecular structures are given in Figures 2 and 3. Selected in-
ternuclear distances and bond angles are included in figure cap-
tions. Crystal and cell parameter data for 1, 2, 2$MeOH and 3 are
given in Table 1. 1, 2$MeOH and 3 crystallize in the triclinic space
group P-1 (No. 2) while 2 crystallizes in the monoclinic space group
P21/n (No.14). The molecular structures of all the compounds reveal
a central tetrahedral phosphorus atom, which acts as a support to
hold the multi-site coordination platform built around it. The P–O
1.687(2) Å, 1.678(2) Å and 1.672(4) Å, respectively. This may be
compared with the P–N single bond distance (observed in P(V)
compounds), which is 1.70 Å.27b The crystal packing of 1–3 shows
a rich supramolecular chemistry as a result of intra- and in-
termolecular CH/p and p/p interactions (Fig. 4). Supramolecular
self-assembly in compounds 1, 2$MeOH and 2 appears to be
effected by the molecular association through C–H/O hydrogen
bonds (Fig. 5). Hydrogen bond parameters for these compounds are
given in Table 2.
bond distances observed in
1 and 2 are 1.4797(19) Å and
1.4696(16) Å, respectively, which is consistent with P]O distances
The absorption spectra of 1–4 in toluene/acetonitrile (10:1, v/v)
are characterized by peaks both at high and low energy. It is
found in literature.27a The P–N bond distances in 1, 2 and 3 are
Figure 4. Interplay of intra- and intermolecular CH/p and p/p interactions of 1 (a), 2 (b) and 3 (c) showing supramolecular architecture. Colour code: orange, carbon; blue,
nitrogen; red, oxygen; pink, phosphorus; yellow, sulfur.

V. Chandrasekhar et al. / Tetrahedron 65 (2009) 4540–4546
4543
Figure 5. Formation of chain in 1 (a), 2$MeOH (b) and 2 (c) via intermolecular hydrogen bonding.
metal salts reveals that only Cu2þ effects a significant fluorescence
enhancement as revealed by a fluorescence enhancement factor
(FEF) of 5.7. The latter was measured with respect to the fluores-
cence intensity. It must be mentioned that FEFs calculated w.r.t.
quantum yields33 also show a similar trend as those found with just
fluorescence intensities. The fluorescence enhancement on in-
teraction of 1–3 with metal ions seems to depend on the efficiency
of binding. Thus 1 and 3 bind Cu2þ more effectively (4.7ꢂ104 and
Table 2
Hydrogen bond parameters
Compounds D–H/A
d(D–H) d(H/A) d(D/A) :(DHA) Symmetryi
ꢀ
Å
Å
Å
1
C6–H6/O1i
0.93
2.4388 3.2734 149.398
(17) (33) (181)
2.6178 3.5172 163.079
(17) (33) (172)
2.7111 3.6077 155.635
(20) (36) (181)
2.4037 3.2065 138.454
(246) (31) (2010)
2.3796 3.2994 163.408
(233) (28) (1969)
(x, ꢁ1þy, z)
(x, ꢁ1þy, z)
(2ꢁx, 2ꢁy, ꢁz)
C16–H16/O1i 0.93
C3–H3C/O1i 0.96
3.1ꢂ105 Mꢁ1
)
while
2
binds to Mg2þ very strongly34,35
2$MeOH
(1.97ꢂ105 Mꢁ1) (Table 3). The fluorescence band, however, does not
experience any significant shift. The maximum FEF obtained for
Cu2þ with 1 occurs at an L:M ratio of 1:10. Further addition of Cu2þ
does not change the FEF. Similar to 1, the ligand with three pyrene
arms also is sensitive Cu2þ, only more so. An FEF of 9.5 is observed
2
C8–H8/O1i
0.98
(1.5ꢁx, 1/2þy,
1/2ꢁz)
C12–H12/O1i 0.95
(2.5ꢁx, 1/2þy,
1/2ꢁz)
in this case. Interestingly, addition of other metal salts (100.0
mM)
to a solution containing 1 or 3 (10.0 M) ions
m
M) and Cu2þ (50.0
m
does not affect the fluorescence behaviour indicating that these
ligands can effectively sense Cu2þ even in the presence of other
metal ions similarly to what was reported previously.36 Ligand 2
containing two pyrene arms, in contrast to 1 and 3, is sensitive
specifically to Mg2þ ions with a very high FEF of 15.5 (Fig. 9).
The mechanism of fluorescence enhancement of 1, 2 and 3 upon
interaction with metal ions seems to lie in an inhibition of a pho-
toinduced electron transfer (PET) process37–40 (Scheme 2). Thus,
the engagement of the lone pairs of nitrogen atoms in coordination
prevents their utilization in a PET-type quenching process. Com-
pound 4 containing six pyrene arms is ineffective in binding to
metal ions presumably because of steric effects.
interesting to note that while the lmax values of all the four ligands
are nearly invariant, their absorbance values increase as the num-
ber of pyrene arms is increased [cf. 1, lmax (3); 286 (15 200), 295
(17 700), 365 (30 000), 380 (27 000)] (Fig. 6A). These spectra are
typical for pyrene-containing compounds and the absorptions are
due to pyrene p–
p* transition.27–32
Compounds 1–4 show an emission around 410 nm upon exci-
tation at 363 nm. A few low energy bands are also seen in the
emission spectra. Similar to the absorbance values, the fluorescence
intensity also increases as the number of pyrene units is increased
from one to six (Fig. 6B).
Although interaction of 1–4 with various metal ions (Ca2þ, Cd2þ
,
Cu2þ, Liþ, Mg2þ, Naþ, Ni2þ, Zn2þ) causes slight changes in the ab-
sorption spectra including the appearance of new d–d bands (see
Supplementary data) clear and specific effects that can be used as
unique detection features for individual metal ions are not dis-
cerned (Fig. 7). This situation, however, changes quite dramatically
in the fluorescence spectra (Fig. 8). Interaction of 1 with various
3. Conclusions
In summary we report a modular design of phosphorus-sup-
ported multi-pyrene ligands. Changing the number of pyrene arms
modulates the specificity of metal ion recognition.
Figure 6. (A) UV–vis and (B) fluorescence spectra of 1–4 (10 mM) in toluene/acetonitrile (10:1, v/v).

4544
V. Chandrasekhar et al. / Tetrahedron 65 (2009) 4540–4546
Figure 7. Absorption spectra of pure ligands, 1 (A), 2 (B), 3 (C) and 4 (D) (10.0 mM) and after addition of metal perchlorates (100.0 mM) in acetonitrile/toluene (1:10).
4. Experimental
4.1. General
DELTA2 500 model spectrometer operating at 500 and 202.5 MHz,
respectively. The chemical shifts are referenced with respect toTMS
for 1H and 85% H3PO4 for 31P NMR. ESI-HRMS mass spectra were
recorded on a MICROMASS QUATTRO II triple quadrupole mass
spectrometer. The ESI capillary was set at 3.5 kV and the cone
voltage was 40 V. The crystal data for the compounds 1, 2 and 3
were collected on a Bruker SMART APEX CCD Diffractometer. The
program SMART (version 6.45) was used for collecting frames of
data, indexing reflections and determining lattice parameters.
SAINT was used for integration of the intensity of reflections and
scaling. The program SADABS was used for absorption correction.
All fluorescence and absorption spectra were recorded on
a Varian Luminescence Cary eclipsed and CARY win 100 Bio UV–vis
spectrophotometer with a 10 mm quartz cell at 25ꢄ0.1 ꢀC. Melting
points were measured using a JSGW melting point apparatus and
are uncorrected. 1H NMR spectra were obtained on a JEOL-JNM
LAMBDA 400 model spectrometer operating at 400.0 MHz. 1H and
31P NMR spectra were also obtained in CDCl3 solutions on a JEOL-
Figure 8. Fluorescence spectra of 1 (A), 2 (B), 3 (C) and 4 (D) (10.0 mM) and after addition of 10 equiv of various metal ions in acetonitrile/toluene (1:10). An excitation wavelength of
363 nm was employed.

V. Chandrasekhar et al. / Tetrahedron 65 (2009) 4540–4546
4545
Table 3
Spectroscopic data of 1–4 upon addition of metal ions
Compounds
lmax, nm (
3)
lem, nm
FF
Ka, Mꢁ1
1
286 (1.52ꢂ104), 295 (1.77ꢂ104),
365 (3.0ꢂ104), 380 (2.7ꢂ104)
284 (7.2ꢂ104), 293 (7.5ꢂ104),
364 (8.19ꢂ104), 382 (6.95ꢂ104)
283 (1.12ꢂ105), 295 (1.02ꢂ105),
362 (1.45ꢂ105), 386 (9.24ꢂ104)
284 (2.91ꢂ105), 290 (3.08ꢂ105),
366 (2.01ꢂ105), 388 (1.56ꢂ105)
286, 295, 365, 380, 490
284, 293, 364, 382
283, 295, 362, 386, 490
284, 290, 366, 388, 490
292, 364, 377
291, 363, 382
287, 293, 363, 384
410, 420
0.0035
d
2
3
4
414
0.0047
0.0050
0.0052
d
d
Scheme 2. Proposed interaction mode between ligand and the metal ion.
413
392, 414
acetonitrile keeping a concentration of 2.0ꢂ10ꢁ3 M. The titration
procedure of the ligands with metal ions was as follows. A 2 mL
solution of the ligand was filled in a quartz cell of 1 cm optical path
1þCu(II)
2þCu(II)
3þCu(II)
4þCu(II)
1þMg(II)
2þMg(II)
3þMg(II)
4þMg(II)
402, 418
413
423
391, 414
407, 423
413
0.046
0.005
0.068
0.0053
0.004
0.070
0.006
0.005
4.7ꢂ104
2.4ꢂ104
3.1ꢂ105
1.57ꢂ104
2.6ꢂ104
1.97ꢂ105
2.1ꢂ104
1.79ꢂ104
length. 100.0 mL of the stock solution of the metal ion was added
into the quartz cell gradually by using a micro-pipette, in order to
maintain the total volume of testing solution without obvious
change. All titrations were carried out at room temperature. For the
fluorescence spectra the excitation wavelength was kept at 363 nm.
Fluorescence quantum yields in each case were determined by
comparing the emission intensity of the sample with that of
a fluorescence standard as anthracene (FF¼0.27ꢄ0.03).33
415
392, 416
288, 364, 391
The crystal structures were solved and refined by full matrix least-
squares methods against F2 by using the program SHELXTL-97.41 All
non-hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen positions were fixed at calculated positions
and refined isotropically. The figures are generated by using
Diamond 3.1e programme. Ph2POCl, PhPOCl2, N3P3Cl6, pyrene-1-
carboxaldehyde and metal salts Cu(ClO4)2, LiClO4 and NaClO4, were
purchased from Aldrich. Zn(ClO4)2, Cd(ClO4)2, Ni(ClO4)2, Mg(ClO4)2,
Ca(ClO4)2 were prepared from their carbonate salts by a reaction
with perchloric acid. (S)PCl3 was purchased from Fluka (Switzer-
land). N-Methylhydrazine was obtained as a gift from the Vikram
Sarabhai Space Research Centre, Thiruvananthapuram, India. Sol-
vents were purchased from S.D. Fine Chemicals (India) and they
were purified prior to use.
ꢀ
ꢁ
FU
¼
FRðAU=ARÞ n2U=n2R
where AU and AR are the integrated area under the corrected fluo-
rescence spectra for the sample and reference, nU and nR are the
refractive indexes of the sample and reference, respectively. The
stability constants42 Ka was obtained from the fluorescence titra-
tion data. The linear fit of the fluorescence intensity data at a par-
ticular wavelength for 1:1 complexation was obtained by the use of
following equation
ꢀ
ꢁ
IF0= IF ꢁ IF0 ¼ ½a=ðb ꢁ aÞꢅ½ð1=Ka½MꢅÞꢅ
where I0F and IF are the fluorescence intensity of the metal free li-
gand and the ML complex, respectively; [M] is the concentration of
the metal ions added for complexation. The Ka is obtained as in-
4.2. General titration procedure of the ligands with
metal ions
tercept/slope ratio from the plot of I0F/(IFꢁIF0) against [M]ꢁ1
.
A 1.0ꢂ10ꢁ5 M stock solutions of 1–4 were prepared in acetoni-
4.3. General synthetic procedure
trile/toluene (1:10). Metal ion stock solutions were prepared in
Quantitative amount of pyrene-1-carboxaldehyde (PyCHO) was
dissolved in hot methanol (30 mL) and to it a methanol solution of
corresponding phosphorus hydrazides was added dropwise. The
reaction mixture was stirred at 50 ꢀC for 12 h. A yellow precipitate
was obtained. This was filtered, washed with hot methanol and
then recrystallized from CH2Cl2/n-hexane mixture at 0 ꢀC to get
products.
4.3.1. Compound 1
PyCHO (0.230 g, 1.0 mmol); Ph2PO[N(CH3)NH2] (0.246 g,
1.0 mmol); 1 (0.357 g, 78%). Mp 180 ꢀC. Crystals suitable for single-
crystal X-ray diffraction were obtained after dissolving 1 in hot
benzene and allowing it to remain at room temperature for three
days. FTIR (KBr) (n
/cmꢁ1): 3044 m, 1583 s, 1436 s, 1306 s,1223 s, 947
s, 826 s, 754 s. 1H NMR (500 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼3.45
(d, –NCH3); 3J (1H–31P)¼6.0 Hz, 8.49 (s, 1H, CH]N), 7.49–8.15 (m,
21H, benzene and pyrene H). 13C NMR (500 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼30.17, 123.02, 124.95, 125.19, 125.44, 125.55, 126.06,
127.38, 127.83, 128.13, 128.32, 128.43, 130.63, 131.38, 131.44, 132.08,
132.36, 132.43. 31P NMR (500 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼32.95 (s). Anal. Calcd for C30H23N2OP; ESI-HRMS:
[MþH]þ¼Calculated 459.1629, found 459.1629.
Figure 9. Fluorescence spectra (lext¼363 nm) of 1–3 (graphs A–C) (10.0
temperature upon the addition of increasing amounts of metal ions; colour code:
0 (black), 20.0 (red), 40.0 (green), 60.0 (yellow), 80.0 (blue), 100.0 (pink) and 120.0
(cyan). (D) Representation of fluorescence spectra in Tabular form 1 (blue), 2 (red) and
3 (green) in the presence of other cations. For 1 and 3, M¼Cu, N¼Mg, and for 2, M¼Mg,
N¼Cu.
mM) at room
mm
4.3.2. Compound 2
PyCHO (0.215 g, 0.92 mmol); PhPO[N(CH3)NH2]2 (0.10 mg,
0.46 mmol); 2 (0.242 g, 80%). Mp 185 ꢀC. Single-crystal X-ray

4546
V. Chandrasekhar et al. / Tetrahedron 65 (2009) 4540–4546
diffraction quality crystals of 2 and 2$MeOH were obtained from its
CH2Cl2/n-hexane and CH2Cl2/methanol solutions. FTIR (KBr) (
References and notes
n
/
cmꢁ1): 3037 m, 1593 s, 1463 s, 1307 s, 1240 s, 958 s, 813 s, 749 s. 1H
1. Uchiyama, S.; Kawai, N.; de Silva, A. P.; Iwai, K. J. Am. Chem. Soc. 2004, 126, 3032.
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NMR (400 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼3.51 (d, –NCH3); 3J
(1H–31P)¼7.0 Hz, 8.58 (s, 1H, CH]N), 7.50–8.25 (m, 29H, pyrene H).
13C NMR (500 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼30.99, 122.94,
124.69, 124.93, 124.98, 125.13, 125.37, 125.46, 125.96, 127.38, 127.72,
128.05, 128.16, 128.23, 128.29, 130.61, 131.33, 131.40, 132.22, 133.30,
31
133.37, 136.04, 136.16. P NMR (500 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼26.620 (s). Anal. Calcd for C42H31N4OP; ESI-HRMS:
[MþH]þ¼Calculated 639.2314, found 639.2312.
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4.3.3. Compound 3
PyCHO (0.460 g, 2.04 mmol); P(S)[N(CH3)NH2]3 (0.135 g,
0.68 mmol); 3 (0.408 g, 72%). Mp 248 ꢀC. Crystals suitable for sin-
gle-crystal X-ray diffraction were obtained by dissolving 3 in hot
acetonitrile/toluene and then allowing to slowly crystallizing at
11. Ravikumar, I.; Ahamed, B. N.; Ghosh, P. Tetrahedron 2007, 63, 12940.
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17. Chandrasekhar, V.; Pandian, B. M.; Boomishankar, R.; Steiner, A.; Vittal, J. J.;
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room temperature over a period of a week. FTIR (KBr) (n
/cmꢁ1):
3036 m, 2935 m, 1592 s, 1458 s, 1375 s, 1239 s, 951 s, 844 s, 761 s. 1H
NMR (400 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼3.60 (d, –NCH3); 3J
(1H–31P)¼9.0 Hz, 8.65 (s, 1H, CH]N), 7.52–8.50 (m, 36H, pyrene H).
13C NMR (500 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼32.68, 122.84,
124.68, 124.86, 125.02, 125.06, 125.31, 125.83, 127.34, 127.49, 127.95,
128.33, 128.68, 130.59, 131.26, 136.02. 31P NMR (500 MHz, CDCl3,
25 ꢀC, TMS)
d
(ppm)¼75.05 (s). Anal. Calcd for C54H39N6PS; ESI-
19. DeSantis, G.; Fabbrizzi, L.; Licchelli, M.; Poggi, A.; Taglietti, A. Angew. Chem., Int.
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HRMS: [MþH]þ¼Calculated 835.2773, found 835.2778.
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25. Park, S. M.; Kim, M. H.; Choe, J.-I.; No, K. T.; Chang, S.-K. J. Org. Chem. 2007,
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27. (a) Vilkov, L. V.; Sadova, N. I.; Zilberg, I. Y. Zh. Strukt. Khim. 1967, 8, 528; (b)
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28. Baker, G. A.; Bright, F. V.; Pandey, S. Chem. Educ. 2001, 6, 223.
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30. Mazur, M.; Blanchard, G. J. J. Phys. Chem. B 2005, 109, 4076.
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4.3.4. Compound 4
PyCHO (0.690 g, 3.00 mmol); N3P3[N(CH3)NH2]6 (0.202 g,
0.50 mmol); 4 (0.57 g, 68%). Mp 210 ꢀC. FTIR (KBr) ( /cmꢁ1): 3037
n
m, 1593 s, 1460 s, 1378 s, 1265 s, 963 s, 844 s, 758 s. 1H NMR
(400 MHz, CDCl3, 25 ꢀC, TMS)
(ppm)¼3.76 (d, –NCH3), 9.37 (s, 1H,
CH]N), 6.35–7.78 (m, 72H, pyrene H). 13C NMR (500 MHz, CDCl3,
25 ꢀC, TMS)
d
d
(ppm)¼32.84, 123.03, 124.57, 124.77, 125.00, 125.13,
125.74, 126.58, 126.85, 127.07, 127.20, 127.30, 127.42, 127.70, 128.17,
129.23, 130.64, 130.73, 130.85, 131.07, 131.31, 131.44. 31P NMR
(500 MHz, CDCl3, 25 ꢀC, TMS)
d
(ppm)¼19.406 (s). Anal. Calcd for
C108H78N15P3; ESI-HRMS: [MþH]þ¼Calculated 1678.5856, found
1678.6138.
Acknowledgements
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41. (a) SMART and SAINT Software Reference Manuals, Version 6.45; Bruker Analytical
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We thank the Department of Science and Technology, India for
financial support. V.C. is a Lalit Kapoor Chair Professor of Chemistry.
V.C. is thankful to the Department of Science and Technology, for
a J.C. Bose fellowship. This work is also supported by the Bio-
inorganic Chemistry Initiative, DST, India.
Supplementary data
CCDC 718403–718406 (for compounds 1, 2, 2$MeOH, and 3)
contain the supplementary 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. Synthetic scheme of 1–4 and ESI-HRMS spectra of 1–4
are given. Supplementary data associated with this article can be
found in the online version, at doi:10.1016/j.tet.2009.03.098.
Empirical Absorption Correction; Ver. 2.05; University of Gottingen: Gottingen,
Germany, 2002; (c) SHELXTL Reference Manual, Ver. 6.1; Bruker Analytical X-ray
Systems: Madison, WI, 2000; (d) Sheldrick, G. M. SHELXTL Ver. 6.12; Bruker AXS:
Madison, WI, 2001; (e) Bradenburg, K. Diamond, Ver. 3.1d; Crystal Impact GbR:
Bonn, Germany, 2006.
¨
¨
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