Quantitative solvent extraction from neutral aqueous nitrate media of silver(I) against lead(II) with a new calix[4]arene-based bipyridine podand

Article abstract of DOI:10.1016/S0040-4039(01)00262-3

A new calix[4]arene-based podand incorporating two 2,2′-bipyridine and two benzyl units in alternate positions at the lower rim was shown to quantitatively extract silver(I) from neutral aqueous solutions containing a mixture of lead and silver nitrates. The corresponding AgPF₆ complex was synthesised and characterised.

Full text of DOI:10.1016/S0040-4039(01)00262-3

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 2681–2684
Quantitative solvent extraction from neutral aqueous nitrate
media of silver(I) against lead(II) with a new calix[4]arene-based
bipyridine podand
Jean-Bernard Regnouf-de-Vains,a,* Jean-Olivier Dalbavie,b Roger Lamartineb and B. Fenetc
aGEVSM, UMR 7565 CNRS-UHP, Faculte´ de Pharmacie, 5 rue Albert Lebrun, F-54001 Nancy Cedex, France
bROMB, ESA 5078 du CNRS, La Doua, F-69622 Villeurbanne Cedex, France
cCentre Commun de RMN, UCBL, La Doua, F-69622 Villeurbanne Cedex, France
Received 15 February 2001
Abstract—A new calix[4]arene-based podand incorporating two 2,2%-bipyridine and two benzyl units in alternate positions at the
lower rim was shown to quantitatively extract silver(I) from neutral aqueous solutions containing a mixture of lead and silver
nitrates. The corresponding AgPF6 complex was synthesised and characterised. © 2001 Elsevier Science Ltd. All rights reserved.
The recovery of silver from ores and wastes is of
interest only if the process is economically viable.1
Therefore, it may be interesting to design ligands capa-
ble of selective binding and extraction of the Ag+
cation. However, a further step is needed, allowing by a
decomplexation process, to regenerate the ligand on
one hand, and to isolate the metal on the other hand.
This may be achieved using chemical, hydrometallurgi-
cal or electrolytical processes.
or their thio analogues, ketones, alkenes, ammoniums,
amino acids, thiols, phosphine groups or heterocycles.
Furthermore, the binding as well as the extraction
ability of some of these ligands towards rare2b or toxic3
metals have also been reported.
The liquid extraction of Ag+ by some of the above-
mentioned calixarene derivatives4 has been studied in
the presence of alkaline ions and, in some rare cases, in
the presence of transition metal cations.4b,4c However,
to the best of our knowledge, the extraction ability of
calixarenes bearing bis-heterocycles has not yet been
Calixarenes have been widely used as spatial organisers
for various chelating units,2 e.g. ethers, esters, amides
OH
O
O
CH2Cl
HO O
O O
O O
N
AgX
O
O
O
NaH, DMF,
71%
N
N
N
N
N
N
N
N
Ag(I)
X
N
N
N
-
1
A
2-PF6 : X = PF6
-
2-NO3 : X = NO3
Scheme 1.
* Corresponding author. Fax: (33) 3 83 17 90 57; e-mail: jean-bernard.regnouf@pharma.u-nancy.fr
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00262-3

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J.-B. Regnouf-de-Vains et al. / Tetrahedron Letters 42 (2001) 2681–2684
2
2
2
Figure 1. 1H NMR spectra of 1 (a), 2-PF6 (b); CDCl3, 500 MHz, rt.
investigated. Calix[4]arene podands incorporating at
the lower rim two opposed 2,2%-bipyridine units give
stable and hydrophobic mononuclear Cu+ complexes,5
which, based on an X-ray crystal structure analysis,5c
display a pro-helicoidal tetrahedral geometry. Since
Ag+ adopts a pseudo-tetrahedral geometry with 2,2%-
bipyridine and analogues,6 we assumed that this geome-
try could also be obtained with such podands, allowing
thus selective complexation of Ag+ with respect to other
cations. Owing to the stability and lipophilicity of such
complexes, one may expect an interesting extraction
ability for these podands. Following these ideas, the
ligand 1 described here with its silver complex 2-PF6,
was investigated for its extraction properties in the
presence of Ag+ and Pb2+ cations.
276.7 ppm (N correlated to Me) and 269.9 ppm (N
correlated to O-CH2-), versus internal 15N Bruker refer-
ence. With respect to the free ligand, the strong upfield
shifts of ca. 40 and 42 ppm, similar to those obtained
with parent copper(I) complexes, indicate that the
bipyridines were indeed chelating the silver cation.
Upon reaction of 1 with Pb(NO3)2, no isolable complex
could be obtained, suggesting the absence of competi-
tion between Pb2+ and Ag+ cations during the extrac-
tion process. The extraction experiments were carried
out in solution; AgNO3 and Pb(NO3)2 were dissolved in
various ratios in water, and treated with a solution of 1
in CHCl3 or CH2Cl2.
For the first series of experiments, the Ag/Pb molar
ratio varied from 1 to 1:10000, and the extraction was
performed with a default of 1 versus Ag+. The mixture
was stirred at rt during 2 h, then the organic phase was
separated and evaporated to dryness. The residue was
dissolved in CH2Cl2 and treated with an excess of
KPF6. The resulting complex 2-PF6 was isolated by
chromatography over alumina and checked by 1H
NMR. The results given in Table 1 show that the
extraction of Ag+ was quantitative, with an average
yield of 95%. The concentration of 1 in CHCl3 as well
as the concentrations of Ag+ and Pb2+ cations in the
aqueous phase did not affect the extraction results.
Ligand 1 was prepared in 71% yield by alkylation of
the bis-bipyridyl podand A5b with benzyl chloride in the
presence of NaH in dry DMF (Scheme 1). The pure
air-stable white–silver complex 2-PF6 was obtained in
92% yield after chromatography (Al2O3, CH2Cl2) upon
mixing stoichiometric amounts of ligand 1 with AgPF6
in CH2Cl2. Complex 2-PF6 was also prepared by extrac-
tion of silver nitrate from water using 1, followed by
anion metathesis with KPF6 and chromatography. The
ML stoichiometry was confirmed by elemental analysis
and by mass spectrometry (ES), which revealed a base
peak at 1301.6 amu ([1+Ag]+). 13C NMR showed that 1
and 2-PF6 were both in the cone conformation7 (Ar-
CH2-Ar signals at 31.40 ppm and 31.46, 32.42 ppm,
1
respectively). Upon complexation, the H NMR spec-
3
2
trum of 1 was strongly modified (Fig. 1). Using COSY
NMR experiment, it was observed that the OCH2–
bipyridine and the OCH2–C6H5 signals which respec-
tively appear as singlets at 5.20 and 4.77 ppm for 1,
became two AB systems at 5.20, 6.08 ppm (JAB=12.9
Hz) and 3.92, 4.14 ppm (JAB=11.8 Hz) for 2-PF6. This
observation results from the chiral pro-helicoidal
arrangement of the two bipyridine units around the
metallic centre.
The natural abundance 1H-15N HMBC experiment5d
adapted to 2-PF6 (Fig. 2) showed two 15N signals at
Figure 2. Natural abundance H-15N HMBC spectrum of 1.
1

J.-B. Regnouf-de-Vains et al. / Tetrahedron Letters 42 (2001) 2681–2684
Table 1. Extraction operating data—first series of experiments
2683
Ag/Pb Pb(NO3)2 mg (mol)
AgNO3 mg H2O (ml) [Pb]; [Ag] 1 mg
CHCl3 (ml) [1] (10−3 M) Ag/1 2-PF6 (mg) Yield (%)
(10−5 mol)
(10−3 M) (10−5 mol)
(10−5 mol)
1
28.90 (8.7×10−5
28.70 (8.66×10−5
)
)
15.00 (8.8)
10
8.7; 8.8
8.7; 1.06 10 (0.84) 10
168; 1.85
835; 0.88
838; 0.10
50 (4.2)
25
1.70
0.84
2.80
4.20
0.84
2.1
1.3
1.1
1.0
1.3
56 (3.9)
11.2 (0.78) 93
115 (8.0)
114 (7.9)
12 (0.83)
93
1/10
1/100
1.80 (1.06) 10
15.70 (9.24) 50
14.90 (8.77) 100
1.80 (1.06) 100
2790 (8.4×10−3
)
)
)
100 (8.4)
100 (8.4)
10 (0.84) 10
30
20
95
94
98
1/1000 27750 (8.35×10−2
1/10000 27750 (8.35×10−2
A second set of experiments8 was carried out in order
to develop a continuous extraction process. It was
performed in a decantation funnel containing an
aqueous solution of Pb(NO3)2 at 600 g.l−1, at the limit
of saturation at rt, charged before extraction with
AgNO3. The initial Ag+/Pb2+ molar ratio of ca. 1:30000
was maintained at each addition of AgNO3, assuming
that the extraction was complete. The organic phase
(CH2Cl2) was charged with 15 equivalents of 1 versus
silver, in order to perform 15 successive extractions;
thus, the ligand was in excess during all experiments,
except for the last one. The mixture was shaken for 30
seconds, then allowed to equilibrate for 15 minutes.
TLC monitoring (Al2O3, CH2Cl2) showed a regular loss
of 1 to the benefit of the AgNO3 complex. All the
ligand was complexed with the last aliquot of metal.
The aqueous phase was washed with CH2Cl2, and the
combined organic phases were concentrated, treated
with KPF6 then purified by chromatography to give
2-PF6 in ca. 90% yield. The ligand was quantitatively
recycled in CH2Cl2 by treatment with NH4OH.
2. (a) Wieser, C.; Dieleman, D. B.; Matt, D. Coord. Chem.
Rev. 1997, 165, 93; (b) Yordanov, A. T.; Roundhill, D.
M. Coord. Chem. Rev. 1998, 170, 93–124.
3. Rao, P.; Enger, O.; Graf, E.; Hosseini, M. W.; De Cian,
A.; Fischer, J. Eur. J. Inorg. Chem. 2000, 7, 1503–1508.
4. For example: (a) Roundhill, D. M. In Prog. Inorg.
Chem.; K. D. Karlin, Ed.; John Wiley and Sons, 1995;
43, 533–592; (b) Yordanov, A. T.; Falana, O. M.; Koch,
A. F.; Roundhill, D. M. Inorg. Chem. 1997, 36, 6468–
6471; (c) Yordanov, A. T.; Whittlesey, B. R.; Roundhill,
D. M. Inorg. Chem. 1998, 37, 3526–3531.
5. For example: (a) Beer, P. D.; Martin, J. P.; Drew, M. G.
B. Tetrahedron, 1992, 48, 9917–9928; (b) Regnouf-de-
Vains, J.-B.; Lamartine, R. Helv. Chim. Acta 1994, 77,
1817–1825; (c) Regnouf-de-Vains, J.-B.; Lamartine, R.;
Fenet, B.; Bavoux, C.; Thozet, A.; Perrin, M. Helv. Chim.
Acta 1995, 78, 1607–1619; (d) Pellet-Rostaing, S.; Reg-
nouf-de-Vains, J.-B.; Lamartine, R.; Fenet, B. Inorg.
Chem. Commun. 1999, 2, 4–7.
6. Ward, M. D.; Couchman, S. M.; Jeffrey, J. C. Acta
Crystallogr., Sect. C. 1998, 54, 1820–1823.
7. Jaime, C.; de Mendoza, J.; Prados, P.; Nieto, P. M.;
Sanchez, C. J. Org. Chem. 1991, 56, 3372–3376.
Conclusion
8. Aqueous phase: 100 ml H2O; Pb(NO3)2: 60 g (1.8 mol
l−1); AgNO3: 1.0 mg (5.9×10−5 mol l−1); [Ag]/[Pb]: 1/
30500; organic phase: 20 ml of CH2Cl2; initial mass of 1:
105 mg (8.8×10−5 mol)
The binding ability of the new podand 19 towards Ag+
was studied, affording the stable mononuclear complex
2-PF6.10 We suggested that the tetrahedral mode of
binding could be a driving force in the selective extrac-
tion of Ag+ in the presence of Pb2+. The experimental
results showed that the extraction was selective, quanti-
tative and rapid, authorising a continuous process; this
last point, the improvement of silver and ligand recov-
ering processes, as well as competitive extractions of
Ag+ in the presence of other metal cations are currently
under investigation.
9. Compound 1: White powder. Mp: 157°C. IR: 1570 cm−1
(CꢀN), 2960 (CꢀH). UV–vis (CH2Cl2): 290 (31300). 1H
NMR (300 MHz, CDCl3): 1.00 (s, 18H, Me3C); 1.18 (s,
18H, Me3C); 2.63 (s, 6 H, Mebpy); 2.93,4.28 (‘q’, AB,
J
AB=12.9, 8H, Ar-CH2-Ar); 4.77 (s, 4H, -OCH2C6H5);
5.20 (s, 4 H, -OCH2bpy); 6.67 (s, 4H, ArH); 6.88 (s, 4H,
2+
ArH); 7.06–7.29 (m, 12H, C6H5 H of bpy); 7.44 (t,
J=7.7, 2H, bpy); 7.57 (t, J=7.7, 2H, bpy); 7.65 (d,
J=6.5, 2H, bpy); 8.00 (d, J=8.1, 2H, bpy); 8.26 (d,
J=7.7, 2H, bpy). 13C NMR (75 MHz, CDCl3): 24.66
(Mebpy); 31.35, 31.57 (Me3C); 31.40 (Ar-CH2-Ar); 33.76,
33.89 (Me3C); 77.05, 77.49 (OCH2C6H5, OCH2bpy);
118.33, 119.48, 122.99, 123.47, 124.92, 125.24, 127.51,
127.95, 129.26, 136.91, 137.04 (C(1), C(2), C(3), C(4),
C(5) of C6H5; Cm of Ar; C(3), C(4), C(5), C(3%), C(4%),
C(5%) of bpy); 133.34, 134.30, 138.06, 144.47, 144.58,
152.37, 153.37, 155.21, 155.90, 157.62, 157.88 (C(6) of
C6H5, Co,p,ipso of Ar, C(2), C(2%), C(6), C(6%) of bpy).
ES-MS (pos. mode): 1193.7 ([1+H]+), 1215.7 ([1+Na]+),
597.7 ([1+2 H]2+/2). Anal. calcd for C82H88N4O4
(1193.64): C, 82.51; H, 7.43; N, 4.69; O, 5.36. Found: C,
82.47; H, 7.24; N, 4.77; O, 5.68.
Acknowledgements
We are grateful to the MRES for financial support,
especially J.-O.D. for a Ph.D. fellowship; to SAFAS
(Monaco) and Bruker S.A. for UV spectroscopy and
WinNMR facilities, respectively.
References
1. Guerlet, J.-P.; Pianelli, F., Traite´ de Me´tallurgie, M 2388,
10. Compound 2-PF6: White powder. Mp: 275°C; IR: 1576
Techniques de l’Inge´nieur Ed., Paris, 1992.
.
(C-N), 2955 (CH), 843 (PF6−). UV–vis (CH2Cl2): 291

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J.-B. Regnouf-de-Vains et al. / Tetrahedron Letters 42 (2001) 2681–2684
(36100). 1H NMR (300 MHz, CDCl3): 0.78 (s, 18H,
t-Bu); 1.35 (s, 18H, t-Bu); 2.22 (s, 6H, CH3bpy); 2.74,
3.90 (‘q’, AB, JAB=13.2, 4H, Ar-CH2-Ar); 2.80, 3.52 (‘q’,
AB, JAB=12.5, 4H, Ar-CH2-Ar); 3.94, 4.15 (‘q’, AB,
(Mebpy); 31.08, 31.73 (Me3C); 31.46, 32.42 (Ar-CH2-Ar);
33.60, 34.21 (Me3C); 77.49 (OCH2C6H5); 81.21
(OCH2bpy); 120.37, 122.56, 122.60, 124.21, 124.87,
125.62, 125.98, 126.01, 126.93, 127.77, 127.93, 128.91,
139.64, 139.79 (C(1), C(2), C(3), C(4), C(5) of C6H5; Cm
of Ar; C(3), C(4), C(5), C(3%), C(4%), C(5%) of bpy); 131.20,
131.49, 134.58, 136.14, 137.13, 144.56, 146.02, 151.41,
151.45, 151.56, 151.59, 152.01, 153.43, 158.27, 158.28,
158.30 (C(6) of C6H5, Co,p,ipso of Ar, C(2), C(2%), C(6),
C(6%) of bpy). ES-MS (pos. mode): 1301.6 ([1+Ag(I)]+).
Anal. calcd for C82H88AgF6N4O4P (1446.46): C, 68.09;
H, 6.13; N, 3.87; found: C 68.26, H, 6.15; N 4.27.
JAB=11.8, 4H, OCH2C6H5); 5.22, 6.10 (‘q’, AB, JAB=
12.9, 4H, OCH2bpy); 6.32 (s, 2H, ArH); 6.39 (s, 2H,
ArH); 6.67 (d, J=8.0, 4H, C6H5); 6.97 (t, J=8.0, 4H,
C6H5); 7.03 (t, J=8.0, 2H, C6H5); 7.10 (d, J=3.0, 4H,
ArH); 7.26 (d, J=7.7, 2H, HpyCH2); 7.44 (d, J=7.7, 2H,
HpyMe); 7.97 (t, J=7.7, 2H, HpyMe); 8.12 (t, J=7.7, 2H,
HpyCH2); 8.19 (d, J=8.1, 2H, HpyMe); 8.40 (d, J=8.1,
2H, HpyCH2). 13C NMR (75 MHz, CDCl3): 25.56
.
.