Selective extraction and transport of the [PtCl6]2 anion through Outer-Sphere coordination chemistry

Article abstract of DOI:10.1002/chem.200802377

A series of tripodal receptors designed to recognise the outer coordination sphere of the hexachlorometal-late anion [PtCl6]2~, and thus show se-lectivity for ion-pair formation over chloride binding, has been synthesised and characterised. The tripodal l

Full text of DOI:10.1002/chem.200802377

DOI: 10.1002/chem.200802377
Selective Extraction and Transport of the [PtCl6]2ꢀ Anion through Outer-
Sphere Coordination Chemistry
Rebecca J. Warr,[a] Arjan N. Westra,[b] Katherine J. Bell,[a] Jy Chartres,[b] Ross Ellis,[b]
Christine Tong,[b] Timothy G. Simmance,[b] Anastasia Gadzhieva,[a] Alexander J. Blake,[a]
Peter A. Tasker,*[b] and Martin Schrçder*[a]
Abstract: A series of tripodal receptors
designed to recognise the outer coordi-
nation sphere of the hexachlorometal-
late anion [PtCl6]2ꢀ, and thus show se-
lectivity for ion-pair formation over
chloride binding, has been synthesised
and characterised. The tripodal ligands
contain urea, amido or sulfonamido hy-
drogen-bond donors, which are aligned
to bind to the regions of greatest elec-
tron density along the faces and edges
of the octahedral anion. The ligand
structure incorporates a protonatable
bridgehead nitrogen centre that pro-
vides a positive charge to ensure the
uated by using a pH-swing mechanism
to control the loading and stripping of
the metallate anion. The ligands L1–L3,
L5–L9, L11–L13 and L15 showed extreme-
ly high loading (up to 95% in some
cases) and high selectivity for [PtCl6]2ꢀ
over chloride ions (present in a 60-fold
excess) compared with trioctylamine, a
model Alamine reagent, which, under
identical conditions, only extracted
10% of the PtIV anions. Generally, ex-
traction was observed to be greater for
urea-containing ligands than their
amido analogues, and a quantitative re-
covery of platinum from feed solutions
was achieved. The formation of neutral
2A
([LH]+) [PtCl6]2ꢀ packages in organic
media is supported by single-crystal X-
ray structure determinations of
[(L2H)2PtCl6]·2CH3CN, [(L8H)2PtCl6-
(MeOH)2],
[(L12H)2PtCl6]·2CH3CN
CTHUNGTRENNUNG
AHCTUNGTRENNUNG
and [(L14H)2PtCl6], which confirm the
presence of significant hydrogen bond-
ing between the anion and urea or
amido moieties of the protonated
ligand and the anion. The structure of
[(L1H)
ACHTUNGTRNE(UNG H3O)PtCl6]·C6H6·CH3CN shows
hydrogen bonding of a H3O+ cation to
the receptor and confirms that other
stoichiometries are also possible, indi-
cating that speciation in solution may
be more complex.
solubility of
a ACHTUNG-
neutral 2:1 [LH]+/
TRENNUNG
[PtCl6]2ꢀ complex in water-immiscible
Keywords: amides · anions · hydro-
gen bonds · ionophores · platinum
solvents. The extraction of [PtCl6]2ꢀ
from acidic chloride solutions was eval-
Introduction
Selectivity in the transport of platinum-group metal ions by
solvent extraction in industrial processes critically depends
upon control of the metal coordination chemistry through
the formation of either inner-sphere complexes with dialkyl
sulfides or hydroximes,[1] or outer-sphere organic-soluble
salts with hydrophobic trialkylamine and related reagents of
the Alamine type.[1,2] The outer-sphere salts rely upon con-
trol of the partition coefficients and solubilities such that
anion exchange can be used to transfer the chlorometallate
to a water-immiscible solvent in a pH-dependent equilibri-
um [Eq. (1)].[2]
[a] Dr. R. J. Warr, K. J. Bell, A. Gadzhieva, Prof. Dr. A. J. Blake,
Prof. Dr. M. Schrçder
School of Chemistry, University Park
University of Nottingham
Nottingham, NG7 2RD (UK)
Fax : (+44)115-951-3563
E-mail: M.Schroder@nottingham.ac.uk
[b] Dr. A. N. Westra, Dr. J. Chartres, R. Ellis, Dr. C. Tong,
Dr. T. G. Simmance, Prof. Dr. P. A. Tasker
School of Chemistry, University of Edinburgh
West Main Road, Edinburgh, EH9 3JJ (UK)
Fax : (+44)131-650-6453
E-mail: P.Tasker@ed.ac.uk
nR3NðorgÞþnHþþMClx Ð ½ðR3NHÞnMClxꢁðorgÞ
nꢀ
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200802377. The Supporting In-
formation includes additional views of the crystal structures, crystallo-
graphic data, experimental procedures and analysis and extraction
data.
ð1Þ
Although the solvent extraction of base metals such as
copper and zinc usually involves the formation of inner-
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Chem. Eur. J. 2009, 15, 4836 – 4850

FULL PAPER
sphere and coordination complexes,[3] the very slow ligand
exchange for the hexachloroplatinate anion, [PtCl6]2ꢀ,[4]
makes it necessary to address and recognise the outer coor-
dination sphere of this species to form neutral anion–ligand
packages. Selectivity continues to be a challenge in the de-
velopment of supramolecular recognition of anions,[5] and is
a pervasive problem in extractive metallurgy because the
generation of electrolytes of high purity is essential for effi-
cient electrolytic reduction to produce metals.[6] Thus, an un-
derstanding of the nature and disposition of electrostatic
and supramolecular hydrogen-bonding interactions to chlo-
Figure 1. The structure of [PtCl6]2ꢀ (a) and proposed modes of binding to
tripodal, multiple hydrogen-bond ionophores through interactions with
the edges (b) or the faces (c) of the hexachloro octahedron. The proton-
ated amine of the receptor is shown as a blue sphere and the neutral hy-
drogen-bond donors as red spheres.
A
were prepared and characterised (Scheme 1). These C3-sym-
metric ionophores incorporate a variety of hydrogen-bond-
donor moieties including urea, amide and sulfonamide. It is
essential that the ligands and their [PtCl6]2ꢀ complexes are
soluble in water-immiscible organic solvents, so a variety of
solubilising R groups were therefore included in the ligand
structure to aid solubility. Ligand L1 was designed with a
long spacer between the protonatable amine bridgehead and
the neutral hydrogen-bond donors to allow these to address
the faces of the [PtCl6]2ꢀ octahedron (Figure 2). The ligands
L2–L15 were synthesised to access potential tri- and bifurcat-
ing hydrogen-bonding modes to the [PtCl6]2ꢀ ion (Figure 2).
Receptor L1 was synthesised in four steps from commer-
cially available tren. A Schiff base condensation of the
amine tren with three equivalents of benzylaldehyde, fol-
lowed by borohydride reductions of the imines to amines
gave the Schiff base adduct 1, which was subsequently react-
ed with 2-phthalimidoacetyl chloride.[12,13] Treatment of this
product with hydrazine yielded the free amine 3. Treatment
of 3 with tert-butylbenzoyl chloride gave receptor L1 as a
white powder (Scheme 1). The urea-based receptors L2–L9
were readily obtained as white powders by the treatment of
tren with the appropriate isocyanate in dry THF
(Scheme 1).[14,15] Amido and sulfonamido receptors L10–L15
were synthesised by treating tren with the appropriate ben-
zoyl or sulfonyl chloride in the presence of sodium hydrox-
ide to yield white powders (Scheme 1).[16,17] Purification by
column chromatography was required for some receptors.
Single crystals suitable for X-ray crystallographic analysis
were obtained for receptors L4, L5, L6, L12, L13 and L14. The
molecular structures of L4, L12 and L14 are shown in
Figure 3. Crystallographic data for all structures and views
of the structures of L5, L6 and L13 appear in the Supporting
Information.
for these anions. DFT calculations and NMR spectroscopic
studies of the solvation and ion pairing of [PtCl6]2ꢀ suggest
that hydrogen-bonded solvate molecules, such as methanol,
address the triangular faces of the hexachloro octahedron,[7]
whereas formation of trifurcated hydrogen bonds to the
faces, or bifurcated hydrogen bonding to the edges of the
hexachloro octahedron has been predicted on the basis of
the location of maximum electron density in the anion;[8]
such interactions have indeed been observed in solid-state
structures of chlorometallates.[9]
Our target in this work was to design useful solvent ex-
tractants for the recovery of the platinum(IV) anion from
acidic chloride streams, whereby loading and stripping of
the organic phase are controlled by a “pH-swing” mecha-
nism [Eqs. (2) and (3)].
2LðorgÞþ2Hþþ½PtCl6ꢁ Ð ½ðLHÞ2PtCl6ꢁðorgÞ
½ðLHÞ2PtCl6ꢁðorgÞþ2NaOH Ð Na2½PtCl6ꢁþ2Lþ2H2O
Such a protocol could then be implemented for the recov-
ery of platinum metal anions from the highly acidic chloride
streams currently used in industry. Furthermore, selective
extractions of [PtCl6]2ꢀ over Clꢀ, which is present in substan-
tial excess in industrial feed streams, is essential for an effi-
cient process. Significantly, the simple trialkylamine reagents
of the Alamine type [Eq. (1)] are known to exhibit poor se-
lectivity for [PtCl6]2ꢀ over Clꢀ (see below) at high acid con-
centrations.[10]
We report herein a new approach to the selective com-
plexation and extraction of hexachlorometallates in the
presence of chloride ions by using tripodal ionophores incor-
porating multiple hydrogen-bond donors linked to a proto-
natable bridgehead nitrogen centre.[11] Such a design not
only addresses the 3-fold symmetry of the outer coordina-
tion sphere of [PtCl6]2ꢀ by presenting neutral hydrogen-
bond donors to the faces or edges of the hexachloro octahe-
dron (Figure 1), but also provides a positive charge to
Single-crystal X-ray structures of L4, L12 and L14: Single crys-
tals of the receptor L4 were obtained as colourless laths by
vapour diffusion of diethyl ether into a solution of the re-
ceptor in methanol. The receptor crystallises in the mono-
clinic space group P21/c with four molecules in the unit cell
(Table S1 in the Supporting Information). The molecular
structure shows an intramolecular, bifurcated hydrogen-
ensure the solubility of a neutral 2:1 [LH]+/
plex in water-immiscible solvents.
ꢀ
Results and Discussion
bond between the urea moieties on adjacent arms N2
ꢀ
H2A···O2 (H···A=2.12 ꢁ) and N3 H3A···O2 (H···A=
Synthesis and characterisation of ligands L1–L15: A range of
extractants derived from tris(2-aminoethyl)amine (tren)
2.06 ꢁ) (Figure 3a). The extended structure reveals that
there are bifurcated intermolecular hydrogen bonds be-
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4837

M. Schrçder, P. A. Tasker et al.
gen bonds (H···O=2.25 ꢁ)
giving rise to a chain-like struc-
ture. Hydrogen-bonding details
for L12 are given in Table 2.
Single crystals of L14 were
grown by diffusion of n-hexane
into a concentrated solution of
the receptor in methanol. The
receptor crystallised in the or-
thorhombic space group Pbca
with eight molecules in the
unit cell (Table S1 in the Sup-
porting Information). The mo-
lecular structure (Figure 3c)
ꢀ
shows intramolecular N4
H4A···O2 hydrogen bonding
(H···O=2.28 ꢁ), which encour-
ages the three arms to be ori-
entated in a tripodal, rather
than a splayed, geometry, with
regular spacing between each
arm. Disorder in the phenyl
ꢀ
group C19 C24 was modelled
over two half-occupied sites
for each atom, distance re-
straints were applied and the
structure was refined with iso-
tropic displacement parameters
for the disordered region. The
extended structure showed in-
ꢀ
Scheme 1. Synthesis of receptors L1–L15: a) benzaldehyde, MeOH, RT then NaBH4;[12] b) 2-phthalimidoacetyl
chloride, Et3N, CHCl3, 08C then RT; c) NH2NH2·H2O, EtOH, CHCl3, reflux; d) tert-butylbenzoyl chloride,
Et3N, CHCl3, 08C then RT; e) tert-butyl or n-butyl isocyanate, THF, RT;[14] f) phenyl, 4-iPr-phenyl, 4-tBu-
phenyl, 3,4-dimethoxyphenyl, 3,5-dimethoxyphenyl or 3,4,5-trimethoxyphenyl isocyanate, THF, RT;[15] g) ben-
zoyl, 3,4-dimethoxybenzoyl, 3,5-dimethoxybenzoyl, 3,4,5-trimethoxybenzoyl chloride, NaOH, H2O, CH2Cl2 or
Et2O, RT;[16,17] h) phenyl or 3,4-dimethoxyphenyl sulfonyl chloride, Et2O, H2O, NaOH, RT.[16] (PhthCl=2-
phthalimidoacetyl chloride).
termolecular
(H···A=2.60 ꢁ)
N2 H2A···O3
hydrogen
bonds between the sulfona-
mide moieties on adjacent
molecules of L14, and these interactions lead to a chain of al-
ternating molecules linked by hydrogen bonds. Hydrogen-
bond details are given in Table 3.
These structural data confirm that the breaking of intra-
and intermolecular hydrogen bonds in these metal-free re-
ceptors is required for complexation and binding to metal
anion(s).
Figure 2. Possible binding modes of the arms of tren-based urea and
amide receptors that preserve pseudo-threefold symmetry (only one arm
is shown for clarity).
Synthesis of complexes of [PtCl6]2ꢀ: The outer-sphere com-
plexes of [PtCl6]2ꢀ with L1–L15 were prepared by the treat-
ment of two equivalents of the appropriate receptor in
methanol or acetonitrile with one equivalent of hexachloro-
platinic acid, [H2PtCl6], in acetonitrile. When necessary, dis-
solution of the receptor was aided by heating. The acid
[H2PtCl6] served not only as a source of the [PtCl6]2ꢀ anion,
but also to protonate the tertiary nitrogen of the tren-based
receptors to yield the charge-neutral ion-pair [(LH)2PtCl6].
Alternatively, an aqueous hydrochloric acid solution of
K2PtCl6 was used as the source of metalloanion. Elemental
analysis, mass spectrometry and 1H NMR spectroscopy of
the [PtCl6]2ꢀ complexes established the general formation of
tween the urea moieties on adjacent molecules of the recep-
ꢀ
ꢀ
tor between N4 H4A···O3 and N5 H5A···O3, and also be-
ꢀ
ꢀ
tween N6 H6A···O1 and N7 H7A···O1, which leads to a
chain of molecules linked by hydrogen bonds. Details of all
hydrogen bonds in L4 are given in Table 1.
Single crystals of L12 were obtained by slow evaporation
of a concentrated solution of the receptor in methanol. The
receptor crystallises in the triclinic space group P1 with two
¯
receptors in the unit cell (Table S1 in the Supporting Infor-
mation). The structure contains intramolecular hydrogen
bonds between amide moieties on adjacent arms of the
1
ꢀ
tripod N2 H2A···O7 (H···O=2.04 ꢁ) (Figure 3b). The ex-
2:1 ligand-to-anion complexes. The H NMR spectra of all
complexes showed characteristic downfield shifts of the NH
ꢀ
tended structure shows intermolecular N3 H3A···O1 hydro-
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Selective Extraction and Transport of [PtCl6]2ꢀ
FULL PAPER
Table 2. Intra- and intermolecular hydrogen bonds for L12.
ꢀ
ꢀ
D H···A
dACHTUNGTERNGN(UN D H) [ꢁ] dACHUTGTNRENN(GU H···A) [ꢁ] dACHTUNGERTNN(GUN D···A) [ꢁ] ]ACHTUNGTRENNUNG(DHA) [8]
ꢀ
N2 H2A···O7
0.88
0.88
2.04
2.25
2.910
2.913
170
132
[a]
ꢀ
N3 H3A···O1
[a] Symmetry transformation used to generate equivalent atoms: ꢀx,
ꢀy+1, ꢀz+1.
Table 3. Intra- and intermolecular hydrogen bonds for L14.
ꢀ
ꢀ
D H···A
dACHTUNGTERNGN(UN D H) [ꢁ] dACHUTGTNRENN(GU H···A) [ꢁ] dACHTUNGERTNN(GUN D···A) [ꢁ] ]ACHTUNGTRENNUNG(DHA) [8]
ꢀ
N4 H4A···O2
0.88
0.88
2.28
2.60
2.988
3.081
138
116
[a]
ꢀ
N2 H2A···O3
[a] Symmetry transformation used to generate equivalent atoms: ꢀx+1/2,
yꢀ1/2, z.
Figure 4. 1H NMR spectra ([D6]DMSO, 300 MHz) of a) L4 and
b) [(L4H)2PtCl6].
ble for X-ray crystallographic analysis were obtained for
[(L1H)
N
[(L2H)2PtCl6]·2CH3CN,
[(L8H)2PtCl
C
[(L12H)2PtCl6]·2CH3CN
and
[(L14H)2PtCl6].
Figure 3. View of the molecular structures of a) L4, b) L12 and c) L14
showing intramolecular hydrogen bonding. All hydrogen atoms (except
NH) have been omitted for clarity.
X-ray crystal structures of [(L1H)
[(L2H)2PtCl6]·2CH3CN,
ACHTUNGTRENNUNG
CTHUNGTRENNUNG
[(L12 H)2PtCl6] and [(L14 H)2PtCl6]
Table 1. Intra- and intermolecular hydrogen bonds for L4.
ꢀ
ꢀ
D H···A
d
[ꢁ]
(D H)
d
[ꢁ]
N
d
[ꢁ]
A
]ACTHNGUTERNN(UG DHA)
[8]
E
6ACTHNUGTREN(NUNG H3O)]·C6H6·CH3CN: Colourless plates were
ꢀ
N2 H2A···O2
0.88
0.88
0.88
0.88
0.88
0.88
2.12
2.06
1.97
2.22
2.16
2.02
2.901
2.837
2.808
2.999
2.924
2.846
147
147
159
147
145
156
CTHUNGTRENNUNG
ꢀ
N3 H3A···O2
1
¯
[a]
[a]
[b]
[b]
ꢀ
N4 H4A···O3
ꢀ
N5 H5A···O3
AHCTUNGTRENNUNG
ꢀ
N6 H6A···O1
acetonitrile in the asymmetric unit. The receptor is proton-
ated at the bridgehead nitrogen N1 to give (L1H)+. In addi-
tion, a hydroxonium cation is also present in the structure
and combined with the receptor cation to form a charge-
neutral complex with the [PtCl6]2ꢀ anion (Figure 5a). Two of
the three receptor arms participate in hydrogen bonding
with the anion: N3 forms a bifurcated bond with Cl4 and
ꢀ
N7 H7A···O1
[a] Symmetry transformation used to generate equivalent atoms: ꢀx+1,
ꢀy+1, ꢀz+2. [b] ꢀx, ꢀy+1, ꢀz+1.
protons, indicative of the presence of hydrogen-bonding in-
teractions (Figure 4). Also observed was the development of
a broad peak further downfield, which was assigned to pro-
tonation of the tertiary amine position. Single crystals suita-
ꢀ
ꢀ
Cl5 (N3 H3C···Cl4, H···Cl=2.75 ꢁ; N H3C···Cl5, H···Cl=
2.72 ꢁ) and N5 forms a single hydrogen bond to Cl5 (N5
ꢀ
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4839

M. Schrçder, P. A. Tasker et al.
Table 4. Hydrogen bonds for [(L1H)
ACHTUNGTRENNUNG
ꢀ
ꢀ
D H···A
d
[ꢁ]
(D H)
d
[ꢁ]
E
d
[ꢁ]
G
]ACHTUNGTRENNUNG(DHA)
[8]
ꢀ
N3 H3A···Cl4
0.86
0.86
0.80
0.85
0.85
0.85
0.83
0.84
0.82
2.75
2.72
2.53
2.61
1.87
2.55
1.71
1.74
1.65
3.546
3.274
3.299
3.436
2.684
2.950
2.526
2.568
2.460
156
124
166
165
159
110
172
170
167
ꢀ
N3 H3A···Cl5
ꢀ
N5 H5A···Cl5
[a]
[b]
ꢀ
N7 H7A···Cl6
ꢀ
N1 H1A···O3
ꢀ
N1 H1A···N2
ꢀ
O1S H1S···O6
ꢀ
O1S H2S···O2
ꢀ
O1S H3S···O4
[a] Symmetry transformation used to generate equivalent atoms: x, yꢀ1,
z. [b] xꢀ1, y, z.
eties of the receptor (Figure 6a). A bifurcated hydrogen
ꢀ
bond is observed between N2 H2A···Cl1 (H···Cl=2.80 ꢁ)
ꢀ
and N2 H2A···Cl3 (H···Cl=2.80 ꢁ) with further hydrogen-
ꢀ
bond interactions between N3 H3A···Cl3 (H···Cl=2.66 ꢁ)
ꢀ
and N4 H4A···Cl2 (H···Cl=2.79 ꢁ). The extended structure
shows a hydrogen-bond chain arrangement of the type
···{(L2H)+···[PtCl6]2ꢀ···(L2H)+}···{(L2H)+···[PtCl6]2ꢀ···(L2H)+}···
with two arms of each (L2H)+ cation interacting with the
anion; the third arm participates in hydrogen bonding with
an adjacent molecule of (L2H)+ to form an extended
ribbon-like structure (Figure 6b, Table 5).
Figure 5. a) Molecular
and
b) extended
structure
of
[(L1H)-
ACHTUNGTRENNUNG(H3O)PtCl6]·C6H6·CH3CN showing hydrogen bonding between the recep-
tors and [PtCl6]2ꢀ anion. All hydrogen atoms (except NH) have been
omitted for clarity, as have the solvent molecules. Hydrogen-bond
lengths: i) NH···Cl 2.75, ii) NH···Cl 2.72 and iii) NH···O 2.53 ꢁ.
H5C···Cl5, H···Cl=2.53 ꢁ). There is also an intramolecular
ꢀ
hydrogen bond (N1 H1C···O3) and significant hydrogen
bonding between the receptor and hydroxonium cation. The
extended structure reveals that an arm of each tripodal
ligand forms a single hydrogen bond to a different [PtCl6]2ꢀ
ꢀ
unit N7 H7C···Cl6 (H···Cl=2.61 ꢁ) to form a hydrogen-
bonded polymeric lattice (Figure 5b, Table 4).
ACHTUNGTRENNUNG
[(L2H)2PtCl6]·2CH3CN: Yellow tablets were grown by slow
evaporation of a solution of the complex in acetonitrile. The
¯
complex crystallises in the triclinic space group P1 with one
[(L2H)2PtCl6] molecule and two molecules of acetonitrile in
the unit cell. The [PtCl6]2ꢀ anion lies on a centre of inversion
and the two receptor cations are related by the inversion
centre. Both urea receptors are protonated at the tertiary
bridgehead position (N1) to give an (L2H)+ cation resulting
in the complex having a net charge of zero. There is signifi-
cant hydrogen bonding between the anion and the urea moi-
Figure 6. a) Molecular
and
b) extended
structure
of
[(L2H)2PtCl6]·2CH3CN showing hydrogen bonding between the receptors
and the [PtCl6]2ꢀ anion. All hydrogen atoms (except NH) have been
omitted for clarity, as have the solvent molecules. NH···Cl hydrogen-bond
lengths: i) 2.79, ii) 2.80, iii) 2.80 and iv) 2.66 ꢁ.
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Selective Extraction and Transport of [PtCl6]2ꢀ
Table 5. Hydrogen bonds for [(L2H)2PtCl6].
FULL PAPER
ꢀ
and O1S H1S···Cl2). The remaining two urea arms partici-
pate in intra- and intermolecular hydrogen bonding with
other cations, which results in an extensive hydrogen-bond-
ing network (Figure 7b, Table 6).
ꢀ
ꢀ
D H···A
d
[ꢁ]
(D H)
d
[ꢁ]
(H···A)
d
[ꢁ]
(D···A)
]ACTHNGUTERNN(UG DHA)
[8]
ꢀ
N2 H2A···Cl1
0.86
0.86
0.86
0.86
0.86
0.86
2.80
2.80
2.66
2.79
2.10
2.18
3.4390
3.5778
3.4951
3.3629
2.832
132
150
163
125
143
149
ꢀ
N2 H2A···Cl3
ꢀ
N3 H3A···Cl3
ꢀ
N4 H4A···Cl2
Table 6. Hydrogen bonds for [(L8H)2PtCl
CHTUNGTRENNUNG
6A
(H···A) [ꢁ]
[a]
ꢀ
N6 H6A···O1
[a]
ꢀ
ꢀ
0.93
0.88
D H···A
d
(D H) [ꢁ]
d
E
d
N
]ACHTUNGTRENNUNG(DHA) [8]
ꢀ
N7 H7A···O1
2.951
ꢀ
N1 H1C···O1
N4 H4A···O7
N6 H6A···Cl2 0.88
N7 H7A···O1S 0.88
O1S H4S···Cl2 0.84
O1S H4S···Cl1 0.84
N2 H2A···O4
N3 H3A···O4
1.90
2.00
2.57
2.05
2.53
2.93
2.15
2.28
2.762
2.849
3.3742
2.874
3.2178
3.6062
2.965
3.086
153
161
152
156
140
139
153
153
[a] Symmetry transformation used to generate equivalent atoms: ꢀx+1,
ꢀ
ꢀy+1, ꢀz.
ꢀ
ꢀ
ꢀ
ꢀ
ACHTUNGTRENNUNG 6ACHTUNGTRENNUNG(MeOH)2]: The complex crystallises as pale-
[(L8H)2PtCl
yellow tablets from a concentrated solution in methanol and
2m hydrochloric acid. The space group is triclinic P1 with
[a]
ꢀ
0.88
0.88
[a]
ꢀ
¯
one [(L8H)2PtCl6] molecule and two molecules of methanol
in the unit cell. The structure determination reveals one
[PtCl6]2ꢀ anion lying on a centre of inversion and two recep-
tor cations related by that centre (Figure 7a). Both urea re-
ceptors are protonated at the bridgehead nitrogen (N1) to
give an overall charge-neutral complex. One of the three
urea arms of each receptor is involved in hydrogen bonding
with the [PtCl6]2ꢀ anion, and hydrogen bonding is observed
AHCTUNGTRENNUNG
[(L12 H)2PtCl6]·2CH3CN: The complex crystallises as pale-
yellow columns from a concentrated solution in acetonitrile
12
¯
in the triclinic space group P1 with one [(L H)2PtCl6] mole-
cule and two molecules of acetonitrile in the unit cell. The
structure determination reveals one [PtCl6]2ꢀ anion lying on
a centre of inversion and two receptor cations related by the
inversion centre (Figure 8a). Both amide receptors are pro-
tonated at the bridgehead nitrogen (N1) to give an overall
charge-neutral complex. One
ꢀ
between N6 H6A···Cl2 (H···Cl=2.57 ꢁ) as well as through
ꢀ
ꢀ
the methanol molecules (N7 H7A···O1S, O1S H1S···Cl1
of the three amide NH donors
of (L12H)+ forms hydrogen
bonds to [PtCl6]2ꢀ to form a bi-
ꢀ
furcated
H2A···Cl1
ꢀ
interaction:
N2
(H···Cl=2.95 ꢁ)
and N2 H2A···Cl2 (H···Cl=
2.83 ꢁ). The remaining two
amide groups form hydrogen
bonds to another (L12H)+
cation to give a chain arrange-
ment
(L12H)+}···
(L12H)+}··· (Figure 8b). In ad-
···
G
[PtCl6]2ꢀ···
ACHTUNGTRENNUNG
G
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
dition to the NH···Cl hydrogen
bonds, there is an intraligand
ꢀ
hydrogen bond N3 H3A···O1
(H···O=2.13 ꢁ) and an interli-
ꢀ
gand hydrogen bond N4
H4A···O4
(H···O=2.15 ꢁ)
(Table 7). The structure also
contains two molecules of ace-
tonitrile, which are disordered
over two sites with 0.65:0.35
occupancy. The atoms were re-
fined with isotropic displace-
ment parameters.
AHCTUNGTRENNUNG
[(L14H)2PtCl6]: The complex
crystallises as pale-yellow laths
in the monoclinic space group
Figure 7. a) Molecular and b) extended structure of [(L8H)2PtCl
6ACTHNUTRGNE(NUG MeOH)2] showing hydrogen bonding be-
tween the receptors and the [PtCl6]2ꢀ anion. All hydrogen atoms (except NH) have been omitted for clarity.
Hydrogen-bond lengths: i) NH···Cl 2.57, ii) OH···Cl 2.53, iii) OH···Cl 2.93 and iv) NH···O 2.05 ꢁ.
Chem. Eur. J. 2009, 15, 4836 – 4850
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4841

M. Schrçder, P. A. Tasker et al.
In summary, the crystallo-
graphic studies confirm the for-
mation
anion-receptor
of
charge-neutral
complexes
through extensive intra- and
intermolecular hydrogen bond-
ing.
Potentiometry: To determine
the number of protonation
sites in the receptors and the
pH at which they become pro-
tonated, potentiometry experi-
ments were performed (see the
Experimental Section).[18] Pro-
tonation equilibria were deter-
mined for the urea receptor L7
and the amide receptors L11
and L13 (Table 9). Only one
protonation site was observed
for each receptor represented
by the equilibrium L+H+
ÐLH+ and the pKa values ob-
tained were consistent with
protonation of the tertiary
amine bridgehead nitrogen po-
Figure 8. a) Molecular and b) extended structure of [(L12H)2PtCl6]·2CH3CN showing hydrogen bonding be-
tween the receptors and the [PtCl6]2ꢀ anion. All hydrogen atoms (except NH) have been omitted for clarity, as
have the solvent molecules. NH···Cl hydrogen-bond lengths: i) 2.95 and ii) 2.83 ꢁ.
Table 7. Hydrogen bonds for [(L12H)2PtCl6]·2CH3CN.
ꢀ
ꢀ
D H···A
dACHTUNGTRENNUNG(D H) [ꢁ] dACHUTGTNRENN(GU H···A) [ꢁ] dACHTUNGERTNN(GUN D···A) [ꢁ] ]ACHTNUGTRNE(NUGN DHA) [8]
ꢀ
N2 H2A···Cl2 0.86
2.83
2.95
2.13
2.15
3.438
3.618
2.868
2.950
129
136
144
155
ꢀ
N2 H2A···Cl1 0.86
ꢀ
N3 H3A···O1
0.86
0.86
[a]
ꢀ
N4 H4A···O4
[a] Symmetry transformation used to generate equivalent atoms: ꢀx+1,
ꢀy, ꢀz+1.
P21/c. The structure determination shows one [PtCl6]2ꢀ
anion lying on a centre of inversion with both sulfonamide
receptors protonated at their bridgehead nitrogen atom
(N1) to give an overall charge-neutral complex (Figure 9a).
Disorder involving the atoms C3–C8 in one of the terminal
phenyl rings was modelled by allowing two half-occupied
sites for each atom. Distance restraints were applied and the
disordered atoms were refined with isotopic atomic displace-
ment parameters for the disordered region.
Each (L14H)+ cation is involved in three hydrogen bonds
to two separate [PtCl6]2ꢀ anions with a bifurcated interaction
to one [PtCl6]2ꢀ anion and a single hydrogen bond to anoth-
er [PtCl6]2ꢀ anion. Figure 9a shows the bifurcated hydrogen-
ꢀ
bonding interactions N4 H4B···Cl2 (H···Cl=2.89 ꢁ) and
14
+
ꢀ
N4 H4B···Cl3 (H···Cl=2.61 ꢁ) between two (L H) recep-
tors and a central [PtCl6]2ꢀ anion. The extended structure
(Figure 9b) reveals that, in addition to the bifurcated inter-
action, one arm of each tripod interacts with a different
Figure 9. a) Molecular and b) extended structure of [(L14H)2PtCl6] show-
ing hydrogen bonding between the receptors and the [PtCl6]2ꢀ anion. All
hydrogen atoms (except NH) have been omitted for clarity. NH···Cl hy-
drogen-bond lengths: i) 2.61 and ii) 2.89 ꢁ.
[PtCl6]2ꢀ unit, N2 H2C···Cl3 (H···Cl=2.79 ꢁ). Additionally,
the extended structure shows N H···O, N H···N and N
H···S hydrogen bonds (Table 8).
ꢀ
ꢀ
ꢀ
ꢀ
4842
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ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 4836 – 4850

Selective Extraction and Transport of [PtCl6]2ꢀ
Table 8. Hydrogen bonds for [(L14H)2PtCl6].
FULL PAPER
tion of two tripodal ligands with the anion will lead to the
formation of a neutral outer-sphere complex by means of
which the chlorometallate can be transported into the or-
ganic phase in a liquid–liquid extraction process. Quantita-
tive back extraction of [PtCl6]2ꢀ from the organic layer into
an aqueous solution is achieved by contacting the loaded
chloroform layer with an aqueous solution that contains a
two-fold excess of NaOH over ligand. Finally, an electro-re-
fining technique such as electrowinning can be employed to
recover pure metallic platinum from [PtCl6]2ꢀ.[21,22]
ꢀ
ꢀ
D H···A
d
[ꢁ]
(D H)
d
[ꢁ]
(H···A)
d
[ꢁ]
(D···A)
]ACTHNGUTERNN(UG DHA)
[8]
ꢀ
N4 H4B···Cl3
0.88
0.93
0.93
0.93
0.88
0.88
0.88
0.88
0.88
2.61
2.08
2.53
2.79
2.79
2.89
2.49
2.60
2.99
3.460
2.957
2.991
3.584
3.570
3.422
3.190
3.214
3.627
163
156
111
144
148
121
137
128
131
ꢀ
N1 H1C···O3
ꢀ
N1 H1C···N3
ꢀ
N1 H1C···S2
[a]
[b]
ꢀ
N2 H2C···Cl3
ꢀ
N4 H4B···Cl2
[c]
[c]
ꢀ
N3 H3A···O5
ꢀ
N3 H3A···O4
[c]
ꢀ
N3 H3A···S3
[a] Symmetry transformation used to generate equivalent atoms: x, y+1,
z. [b] ꢀx, ꢀy, ꢀz. [c] ꢀx, y+1/2, ꢀz+1/2.
LEACH Pt þ 6HCl þ 4HNO3 Ð H2PtCl6 þ 4NO2 þ 4H2O
ð4Þ
Table 9. Protonation constants determined in MeCN/H2O (50:50 v/v)
(0.1m NMe4Cl, (298.1ꢂ0.1) K).
EXTRACT H2PtCl6 þ 2L Ð ½ðLHÞ2PtCl6ꢁ
STRIP ½ðLHÞ2PtCl6ꢁ þ 2OHꢀ Ð L þ ½PtCl6ꢁ2ꢀþH2O
ð5Þ
ð6Þ
ð7Þ
Receptor
Equilibrium
pKa
L7
L+H+ÐLH+
L+H+ÐLH+
L+H+ÐLH+
6.43(7)
5.94(2)
5.93(5)
L11
L13
ELECTROWIN
½PtCl6ꢁ2ꢀþ4eꢀ Ð Pt þ 6Clꢀ
To determine the extractive ability of the series of the
multiple hydrogen-bond-donor ligands L1–L15 in the pres-
ence of a large excess of chloride ions, various studies of the
solvent extraction of [PtCl6]2ꢀ from aqueous, acidic media
with the extractants were performed. The extractive behav-
iour of these ligands was compared with that of trioctyl-
amine (TOA), a compound that is acknowledged to be an
efficient extractant for octahedral [MCl6]2ꢀ precious-metal
anions.[23]
sition.[19] The pKa values between the urea and amido li-
gands differ by 0.5, indicating that the type of hydrogen-
bond-donor group has relatively little effect on the basicity
of the bridgehead nitrogen. The receptors L11 and L13 both
have amide hydrogen-bond groups, but contain a different
number of methoxy substituents. The pKa values for these
two receptors are very similar (5.94 and 5.93, respectively),
indicating that the number of methoxy substituents on the
terminal phenyl ring does not affect the basicity of the
bridgehead nitrogen.
Method development: A series of experiments to assess
chloride selectivity, and the effect of pH, mixing time, con-
centration and back extraction were conducted to determine
the optimum extraction conditions.
Solvent extraction: The solvent extractants described in this
work will ideally recover platinum(IV) from acidic chloride
streams, whereby loading and stripping of the organic phase
are controlled by a pH-swing mechanism [Eqs. (2) and (3)].
The flowchart (Figure 10) and Equations (4)–(7) represent
Chloride selectivity: The presence of HCl in the processing
of platinum-containing ores is necessary for the production
of [PtCl6]2ꢀ. However, chloride ions may compete for the
hydrogen-bonding sites on the receptor. The selective ex-
traction of [PtCl6]2ꢀ over Clꢀ, which is present in substantial
excess in industrial feed streams, is thus essential for an effi-
cient extraction process. To assess whether our receptors
would extract Clꢀ, extractions that used L8 were performed
in either 0.1 or 0.6m HCl. For both HCl concentrations stud-
ied, the results showed that the amount of Clꢀ extracted in-
creased with increasing receptor concentration. Further-
more, at higher HCl concentrations, more chloride was ex-
tracted; thus, in the presence of 0.1m HCl the maximum
amount of Clꢀ extracted was 88% compared with 100% Clꢀ
extraction from 0.6m HCl (Figure 11). These results confirm
that under certain conditions the receptor L8, and potential-
ly other tripodal receptors discussed in this work, can ex-
tract Clꢀ to form organic-soluble complexes.
Figure 10. pH-swing-controlled transport of [PtCl6]2ꢀ
.
the processes involved in purifying [PtCl6]2ꢀ. The first step is
leaching in which the platinum-containing ore is dissolved in
aqua regia to produce [H2PtCl6] in an acidic, aqueous solu-
tion.[22] Separation of [PtCl6]2ꢀ is achieved by mixing an or-
ganic phase containing two equivalents of a receptor (L)
with an aqueous, acidic solution of [H2PtCl6]. Under acidic
conditions the bridgehead nitrogen is protonated. Interac-
Effect of pH: To accurately represent the conditions used in
the processing of platinum-containing ores, it is necessary to
perform the extractions in an acidic media. The above pre-
liminary extraction experiments confirm that the tren-based
Chem. Eur. J. 2009, 15, 4836 – 4850
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4843

M. Schrçder, P. A. Tasker et al.
shown that mixing periods ranging from several minutes
(e.g., between 1–5 mins for Alamine 304 and N-n-octylani-
line)[24,25] to several hours (e.g., overnight for trioctyla-
mine)[23] may be necessary to achieve equilibrium. To deter-
mine the optimum mixing time, a chloroform phase contain-
ing L8 and an acidic, aqueous phase containing [H2PtCl6]
were contacted at room temperature for varying periods of
time. The platinum content of the organic phase was mea-
sured at regular intervals and after 4 h the maximum level
of extraction was achieved, suggesting that equilibrium to
the outer-sphere complex [(L8H)2PtCl6] had been estab-
lished. Prolonged mixing (>16 h) led to a slight drop in the
content of platinum in the chloroform layer; this observa-
tion was attributed to an inner-sphere substitution processes
to form insoluble complexes.
Concentration studies: A series of extraction experiments
were performed with the receptor L8 and platinum stock sol-
utions of varying concentrations (1.25, 2.5 and 6.5 mm). No
significant variations in the extraction results were observed.
It was concluded that concentration does not play a major
role in the extraction process.
Figure 11. Plot of percentage of chloride extracted from 0.1 (~) or 0.6m
(&) HCl into CHCl3 by L8.
Back-extraction studies: Back extractions were performed to
establish the use of a pH-swing mechanism to control the
uptake and release of the [PtCl6]2ꢀ anion and also to deter-
mine the amount of platinum present in the organic phase
in a mass balance equation. Yoshizawa and co-workers have
reported solvent extraction experiments with TOA and
[PtCl6]2ꢀ in toluene.[23] They investigated the stripping of
receptors can potentially extract chloride ions. The effect of
feed pH on the extraction of [PtCl6]2ꢀ with L8 in chloroform
was studied. The percentage of platinum extracted into
chloroform in the presence of a three molar excess of L8 or
TOA is given in Table 10. Interestingly and significantly,
[PtCl6]2ꢀ
from
an
organic
phase
containing
Table 10. Percentage of platinum extracted as [PtCl6]2<M-> into CHCl3
from aqueous HCl in the presence of a threefold molar excess of L8 or
TOA.
[(TOA+H)2PtCl6] by using an aqueous solution of NaOH,
which proceeded by deprotonation of the tertiary amine in
(TOA+H)+; this removed the electrostatic attraction be-
tween the receptor and the anion. An alternative approach
in which HCl was used was also investigated in this work.
Experiments were performed to assess if [PtCl6]2ꢀ recov-
ery from the organic phase containing [(LH)2PtCl6] was pos-
sible by addition of NaOH and to identify the volume re-
quired for such a process. In the presence of two equivalents
of OHꢀ, quantitative back extraction of [PtCl6]2ꢀ was
HCl concentration [m]
0.0
0.1
0.6
% Pt extracted with L8
% Pt extracted with TOA
63
62
100
57
98
4
TOA is not an effective extractant of platinum at high con-
centrations of HCl. Although uptake of [PtCl6]2ꢀ by a three-
fold excess of TOA from an aqueous solution of [H2PtCl6]
with no added HCl is around 60% of the theoretical value,
it drops to only about 5% when the aqueous feed solution
contains 0.6m HCl, suggesting a strong transfer of Clꢀ in-
stead of [PtCl6]2ꢀ under these conditions (see the Supporting
Information). As a consequence, the transport efficiency of
platinum from acidic feeds in a flow sheet will be low when
using TOA, and chloride concentrations will build up down-
stream. However, in 0.6m HCl, a three-fold excess of L8 can
extract >98% of the platinum. Most importantly, these re-
actions confirm the selectivity of our receptor for [PtCl6]2ꢀ
over Clꢀ under acidic conditions. Therefore, all subsequent
extractions were carried out in 0.6m HCl.
AHCTUNGTREGaNNUN chieved and a mixing time of 30 min was found to be suffi-
cient.
Platinum extraction: The extraction potential of the recep-
tors L1–L15 for [PtCl6]2ꢀ was determined for each receptor
under optimised conditions. Ligands L4, L10 and L14 afforded
metal complex salts that precipitate from solution or do not
extract into the organic phase. A key requirement for the
success of this solvent extraction process is the solubility of
the resultant [PtCl6]2ꢀ complex in the organic phase, there-
fore, these complexes were not studied further. Results for
the extraction of [PtCl6]2ꢀ by the receptors L1–L3, L5–L9,
L11–L13 and L15 are summarised in Figure 12 along with data
for TOA for comparison.
Mixing time studies: Previous studies of the equilibrium
In the presence of 0.6m HCl, all of the tren-based urea
and amide receptors that were studied show increased ex-
time for [PtCl6]2ꢀ extraction by long-chain alkylamines have
4844
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ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 4836 – 4850

Selective Extraction and Transport of [PtCl6]2ꢀ
FULL PAPER
traction of [PtCl6]2ꢀ is a competitive process given by Equa-
2ꢀ
tion (8), in which K
is given by Equation (9):
½PtCl6ꢁ
K
2ꢀ
½PtCl6
ꢁ
2-
PtCl6 þ 2½ðLHÞClꢁ
½ðLHÞ PtCl ꢁðorgÞþ2Clꢀ
ð8Þ
ð9Þ
ðorgÞG
H
2
6
- 2
½ðLHÞ2PtCl6ꢁ½Cl ꢁ
2ꢀ
K
¼
½PtCl6ꢁ
2-
2
½PtCl6 ꢁ½ðLHÞClꢁ
Assuming that no inner-sphere substitution occurs on the
timescale of the extraction, the distribution coefficient for
platinum is given by Equation (10), in which DPt is defined
by Equation (11):
½ðLHÞ2PtCl6ꢁ
ð10Þ
ð11Þ
DPt
¼
2-
½PtCl6
ꢁ
ꢀ
ꢁ
½ðLHÞClꢁ
½Clꢀꢁ
2-
log DPt ¼ log K½PtCl6 ꢁ þ 2 log
Plots of logDPt versus log{[(LH)Cl]/ACTHNUTRGNEUNG
[Clꢀ]} for TOA and
Figure 12. Plot of percentage of the total platinum extracted as [PtCl6]2ꢀ
six of the receptors show slopes close to two (Figure 13), in
from aqueous 0.6m HCl into CHCl3 as a function of the [L]/[Pt] ratio. &:
accordance with the anticipated formation of 2:1 [LH]+/
ACHTUNG-
5
6
7
8
9
11
12
L1, ~: L2, *: L3, : L , &: L , ~: L , *: L , : L , +: L , ꢂ: L , : L13,
^
^
*
ꢀ: L15 and c: TOA.
traction compared with TOA, confirming that the presence
of hydrogen-bond-donor groups leads to a more effective
extraction of [PtCl6]2ꢀ (Figure 12 and Table 11). The maxi-
Table 11. Percentage of platinum extracted as [PtCl6]2<M-> into CHCl3
from aqueous 0.6m HCl in the presence of three-fold molar excess of L.
Ligand
Pt extracted [%]
Ligand
Pt extracted [%]
L1
L2
L3
L5
L6
L7
L8
89
15
67
76
84
98
98
L9
56
85
89
80
76
5
L11
L12
L13
L15
TOA
Figure 13. Plot of logDPt versus log{[(LH)Cl]/ACTHNUTRGNEUNG
[Clꢀ]} for the extraction of
[PtCl6]2ꢀ with a range of tripodal hydrogen-bonding receptors. &: L1 (y=
1.7988x+5.3463, R2 =0.9947), *: L8 (y=1.8106x+5.9276, R2 =0.9854),
9
2
11
: L (y=1.9342x+4.5674, R =0.8776), +: L (y=1.9886x+5.8554, R2 =
mum extraction occurs at [L]/ACHTNUGRTNEUNG
[PtCl6]2ꢀ ratios greater than or
^
0.985), ꢂ: L12 (y=2.1462x+5.8588, R2 =0.9596); : L13 (y=2.1508x+
*
equal to three, indicating that a slight excess of receptor is
required; this may suggest that there is competition from
Clꢀ anions. Loadings of greater than 90%, however, imply
that the triamide/urea ligands show high selectivity for
[PtCl6]2ꢀ over Clꢀ ions because the latter is present in a 60-
fold excess in the aqueous feed solution. Generally, extrac-
tant strengths are observed to be greater for the urea-con-
taining ligands than their amido analogues (Table 11).
5.8797, R2 =0.9885), ꢀ: TOA (y=2.1473x+3.4067, R2 =0.9992).
TERNNUG
[PtCl6]2ꢀ assemblies in chloroform. For the other ligands
used in this work, and for TOA at high ligand concentra-
tions,[23] the Yoshizawa plots show some deviation from line-
arity (see the Supporting Information). This may be due to
the formation of outer-sphere complexes with alternative
ACTHNUTRGNEUNG
stoichiometries such as 3:1:1 [LH]+/[PtCl6]2ꢀ/Clꢀ at high
Yoshizawa plot: A procedure similar to that described by
ligand concentrations, or may involve the incorporation of a
hydroxonium ion into the outer-sphere complex to give a
Yoshizawa and co-workers[23] was used to determine the
stoi
A
ACTHNGUTRENNUG CAHTUNGTRENNUNG
1:1:1 assembly [LH]+/[H3O]+/[PtCl6]2ꢀ, which would be fav-
the water-immiscible phase and to probe further the selec-
tivity of [PtCl6]2ꢀ over Clꢀ. At low pH values, in which it
can be assumed that the ligand is fully protonated, the ex-
oured at low ligand concentrations (see the discussion of the
crystal structure of [(L1H)
(H3O)PtCl6] above). Alternatively,
the possibility that the receptors, their hydrochloride salts
AHCTUNGTRENNUNG
Chem. Eur. J. 2009, 15, 4836 – 4850
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4845

M. Schrçder, P. A. Tasker et al.
and/or their platinum complexes have some solubility in the
aqueous phase cannot be discounted at this stage. These
caveats notwithstanding, the majority of the triamide/urea li-
gands show very high selectivity for [PtCl6]2ꢀ over Clꢀ, the
latter being present in a 60-fold excess.
the pendant arms of the reagents to allow the selectivity of
receptors to be tuned to accomplish the separation of chlo-
AHCTUNGTRENNUNG
Recycling of the receptor: Recycling experiments were con-
Experimental Section
1
ducted on receptor L8. A H NMR spectrum of L8, recorded
after one extraction cycle indicated that the structure of the
receptor was preserved during the extraction process. The
recycled ligand was put through a series of subsequent ex-
traction phases with minimal loss in observed efficiency.
Methods and materials: All solvents and reagents were commercially
1
available from Aldrich or Fisher. H and 13C NMR spectra were obtained
on Bruker ARX 250, DPX 360 or DPX 300 spectrometers. The chemical
shifts (d) are reported in parts per million (ppm) relative to the residual
protio solvent signal in CDCl3 (d=7.26 (1H) and 77.0 ppm (13C)),
[D6]DMSO (d=2.50 (1H) and 39.5 ppm (13C)), CD3OD (d=3.31 (1H)
and 49.0 ppm (13C)) or [D2]C2H2Cl4 (d=5.91 (1H) and 74.2 ppm (13C)).
Fast atom bombardment (FAB) mass spectra were recorded on a Kratos
MS50TC instrument in a 3-nitrobenzyl alcohol (NOBA) matrix. Electro-
spray (ES) mass spectra were recorded on a VG Autospec instrument.
ICP-OES was carried out by using a Perkin–Elmer Optima 5300DV spec-
trometer and ICP-MS was carried out by using a Thermo-Fisher Scientif-
ic X-SeriesII spectrometer. For pH measurements, an AR50 (Fisher Sci-
entific) pH meter was used.
Deviations: Although many of the ligands described extract
in a similar manner, there are certain deviations from
theory that must be accounted for and which emphasise the
complexity of these systems. One deviation already dis-
cussed is the variation away from a gradient of two in the
Yoshizawa plots (Figure 13). One of these ligands, L9, also
shows a reduced ability to select [PtCl6]2ꢀ over chloride, pre-
sumably because the formation of the outer-sphere complex
X-ray crystallography: Crystallographic data and structure refinement pa-
rameters for ligands L4, L5, L6, L12, L13 and L14, and complexes
[(L9H)
2ACHTUNGTRENNUNG(PtCl6)] is disfavoured. This is unexpected because
CHTUNGTRENNUNG
[(L1H)PtCl (H3O)]·C6H6·CH3CN, [(L2H)2PtCl6]·2CH3CN, [(L8H)2PtCl6-
there are only minor structural differences between L9 and
the related urea-based ligands, L4–L8, highlighting the deli-
cate interactions inherent to the systems. Other sources of
deviations from theory include the interesting binding
modes displayed in the crystal structures of complexes L1
and L8. The former clearly displays the inclusion of a H3O+
the Supporting Information. Crystals were mounted on a dual-stage glass
fibre and diffraction measurements were collected at 150(2) K on a
Bruker APEX CCD diffractomer using graphite-monochromated MoKa
radiation (l=0.71073 ꢁ) and w scans. Structures were solved by direct
methods by using the SHELXS-97 programme.[26] CCDC-707579 (L4),
707580 (L5), 707581 (L6), 707582 (L12), 707583 (L13), 707584 (L14), 707585
moiety, giving a 1:1:1 assembly of [LH]+/
which may account for deviations in the Yoshizawa plot at
high values of log{[(LH)Cl]/
[Clꢀ]}. The crystal structure of
[(L8H)PtCl
6A(MeOH)2] (Figure 7) shows methanol molecules
[H3O]+/[PtCl6]2ꢀ,
ACHUTGTNRENNUG CAHTUNGTRENNUGN
([(L1H)
([(L8H)2PtCl (MeOH)2]), 707587 ([(L12H)2PtCl6]·2CH3CN) and 707588
CTHUNGTRENNUNG
ACHTUNGTRENNUNG
([(L14H)2PtCl6]) 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.
AHCTUNGTRENNUNG
CHTUNGTRENNUNG
hydrogen bonded to and interacting with both the metal
anion and protonated receptor. These examples illustrate
the flexibility of these systems in the way they bind and indi-
cate that the speciation of the outer-sphere complexes in so-
lution may not be as simple as originally proposed.
Potentiometry experiments: All pH-metric measurements (pH=
ꢀlog[H+]) employed for the determination of the protonation constants
were carried out in solutions of NMe4Cl (0.10m) in MeCN/H2O (50:50 v/
v) at (298.1ꢂ0.1) K under a nitrogen atmosphere. A Hamilton glass elec-
trode was calibrated as a hydrogen concentration probe by titrating
known amounts of HCl with CO2-free aqueous solutions of NaOH and
determining the equivalence point by Granꢃs method,[27] which allows
one to determine the standard potential EA and the ionic product of H2O
(pKw =14.99(1)). At least three measurements were performed for each
system in the pH range 2.5–11.0. In all experiments, the ligand concentra-
tion was approximately 1ꢂ10ꢀ4 m. The computer program HYPER-
QUAD[28] was used to calculate the equilibrium constants from electro-
motive force (emf) data.
Conclusion
The efficacy of our tripodal urea and amide ligands in a pH-
swing-controlled process to recover platinum from acid chlo-
ride feed solutions has been established. The very high
[PtCl6]2ꢀ loading (>95%) from acidic chloride solutions for
the new receptors, coupled with the quantitative stripping
and release of metallate anions by base, provides the basis
for a very efficient process for the separation and concentra-
tion of platinum with minimal reagent consumption (two
equivalents of NaOH) and generation of two molar equiva-
lents of NaCl as a byproduct. Significantly, our receptors
show selectivity for [PtCl6]2ꢀ over Clꢀ. Receptors containing
urea moieties extracted slightly more [PtCl6]2ꢀ than analo-
gous amide receptors. Solution and solid-state studies sup-
General experimental procedure for extractions: Analytical grade CHCl3
was used to prepare the ligand solutions without further purification.
Water used to prepare the solutions of [H2PtCl6] was purified by using a
commercial filtration system and reported to a resistance of approximate-
ly 18 W. The acid [H2PtCl6]·6H2O, which was purchased from Aldrich,
was dried over P2O5 to obtain a yellow solid. Calibration curves for ICP-
OES and ICP-MS were prepared by dilution of commercially available
standards.
Solutions of the ligand were prepared at varying concentrations between
0.0005 and 0.01m by weighing aliquots of ligand stock solution (0.01m in
CHCl3) into 5 cm3 volumetric flasks and diluting to the mark with CHCl3.
Solutions of [H2PtCl6] were prepared by weighing [H2PtCl6]·6H2O
(0.03 g) into a 50 cm3 volumetric flask and diluting to the mark with
water, 0.1m HCl or 0.6m HCl.
2ACTHNUTRGNEUNG
port the formation of ([LH]+) [PtCl6]2ꢀ packages in organic
Extractions were prepared by charging 100 cm3 Schott flasks, fitted with
media. Future and current work is focused on the variation
in the disposition and nature of hydrogen-bonding groups in
a magnetic stir bar, with solutions of the ligand (5 cm3) and [H2PtCl6]
4846
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 4836 – 4850

Selective Extraction and Transport of [PtCl6]2ꢀ
FULL PAPER
(5 cm3). The extractions were stirred at 258C for 4 h, after which time the
phases were separated. Aqueous samples for ICP-OES analysis were pre-
pared by weighing the aqueous phase (2 cm3) into 5 cm3 volumetric flasks
and diluting to the mark with water; samples for ICP-MS analysis were
diluted by a thousand fold using 0.6m HCl as the diluent. The organic
phases (4.0 cm3) were transferred into glass snap-top vials fitted with
magnetic stir bars by using a volumetric glass pipette. An aliquot of aque-
ous NaOH (0.06m) was added to these vials so that there were two molar
equivalents of OHꢀ relative to the amount of ligand in the sample, as
well as sufficient water to make the final aqueous volume 4 cm3. The two
phases were contacted for 30 min then separated. Samples for ICP-OES
analysis were prepared by weighing the aqueous phase (2 cm3) into 5 cm3
volumetric flasks and diluting to the mark with water. To determine the
concentration of Pt in the stock solution by ICP-OES or ICP-MS analy-
ses, samples were prepared by weighing in the same manner as the above
aqueous extraction samples.
CDCl3): d=160.8, 55.7, 40.4, 39.9, 32.7, 21.4, 13.8 ppm; IR (KBr): n¯ =
3354 (NꢀH), 1652 cmꢀ1 (C=O); MS (ES+): m/z: 444 [M+H]+; elemental
analysis calcd (%) for C21H45N7O3: C 56.86, H 10.22, N 22.10; found: C
56.77, H 10.22, N 21.96.
Compound L4:[15] Compound L4 was prepared by the treatment of tren
with phenyl isocyanate by following procedure A. Yield: 95%; 1H NMR
(270 MHz, CD3OD): d=7.26 (d, 3J
ACHTUNGTRENNUNG
(m, 6H; HAr), 6.95 (t, 3J
ACHTUNGTRENNUNG
CH2), 2.68 ppm (t, 3J
AHCTUNGTRENNUNG
[D6]DMSO): d=156.3, 141.4, 128.9, 121.6, 118.1, 55.5, 37.4 ppm; IR
(KBr): n¯ =3334 (NH), 1650 cmꢀ1 (C=O); MS (ES+): m/z: 504 [M+H]+,
526 [M+Na]+; elemental analysis calcd (%) for C27H33N7O3: C 64.40, H
6.60, N 19.47; found: C 64.29, H 6.78, N 19.11.
Compound L5: Compound L5 was prepared by the treatment of tren with
4-iso-propylphenyl isocyanate by following procedure A. Yield: 69%;
1H NMR (300 MHz, CDCl3): d=7.43 (s, 3H; NH), 6.97 (s, 12H; HAr),
Compound L1:
A solution of tert-butylbenzoyl chloride (2.70 g,
ACTHNUTRGNEUNG
6.10 (t, 3J(H,H)=4.9 Hz, 3H; NH), 3.13 (br, 6H; CH2), 2.80 (septet, 3J-
13.8 mmol) in CHCl3 (100 cm3) was added to a solution of 3 (2.45 g,
4.17 mmol) in CHCl3 (200 cm3) containing Et3N (2.04 cm3, 14.6 mmol) at
08C over a period of 2 h. The reaction mixture was allowed to warm to
room temperature and was then stirred for 16 h. The solvent was re-
moved in vacuo and the residue was purified by column chromatography
by eluting with 2–5% MeOH/CH2Cl2 to give the product L1 as a colour-
less glass (4.4 g, 99%). The 1H NMR spectrum of this material was ex-
tremely complex, showing severe splitting and broadening of the signals
because of the large number and slow rotation of the amide rotamers.
This was clarified by acquiring the 1H NMR spectrum at 808C in
[D6]DMSO, resulting in broad but separate signals for each set of non-
equivalent protons with the correct integration of signals. High-resolution
FAB mass spectrometry of this material was also consistent with the pro-
posed structure. 1H NMR (360 MHz, [D6]DMSO, 808C): d=8.17 (brs,
ACHUTNGRENNUG ACHTUNGTRENNUNG(H,H)=
(H,H)=6.9 Hz, 3H; iPrCH), 2.23 (br, 6H; CH2), 1.19 ppm (d, 3J
6.9 Hz, 18H; iPrCH3); 13C NMR (75 MHz, CDCl3): d=155.9, 141.5,
138.6, 123.8, 118.5, 54.5, 48.6, 44.8, 24.5 ppm; IR (solid): n¯ =3100 (NꢀH),
1640 (C=O), 1601 cmꢀ1 (C=C); MS (ES+): m/z: 630.41 [M+H]+; elemen-
tal analysis calcd (%) for C36H51N7O3: C 68.65, H 8.16, N 15.57; found: C
68.05, H 8.11, N 15.43.
Compound L6: Compound L6 was prepared by the treatment of tren with
4-tert-butylphenyl isocyanate by following procedure A. Yield: 59%;
1H NMR (300 MHz, CDCl3): d=7.56 (br, 3H; NH), 7.14 (d, 3J
ACHTUNGTRENNUNG
8.6 Hz; 6H; HAr), 7.03 (d, 3J
ACHTUNGTRENNUNG
NH), 3.16 (br, 6H; CH2), 2.27 (br, 6H; CH2), 1.25 ppm (s, 27H; CH3);
13C NMR (75 MHz, [D6]DMSO): d=156.3, 144.9, 138.3, 125.9, 117.2,
54.3, 48.4, 34.2, 31.9 ppm; IR (solid): n¯ =2997 (NꢀH), 1640 (C=O),
1590 cmꢀ1 (C=C, Ar); MS (ES+): m/z: 672.46 [M+H]+; elemental analy-
sis calcd (%) for C39H57N7O3: C 69.71, H 8.55, N 14.59; found: C 69.23, H
8.47, N 14.35.
3H; NH), 7.79 (d, 6H, 3J
(d, 3J
(H,H)=11.2 Hz, 6H; HAr ortho to the tBu group), 7.27 (brs, 15H;
ACHTUNGTERN(UNNG H,H)=11.2 Hz; HAr ortho to the amide), 7.45
ACHTUNGTRENNUNG
HAr), 4.58 (brs, 6H; ArCH2), 4.20 (brs, 6H; NCOCH2), 3.35 (brs, 6H;
NCH2CH2NCO), 2.63 (brs, 6H; NCH2CH2NCO), 1.31 ppm (s, 27H;
CH3); 13C NMR (90 MHz, [D6]DMSO, 1108C): d=168.3, 165.8, 153.6,
137.0, 131.2, 127.8, 126.6, 126.4, 124.2, 51.7 (br), 49.2 (br), 44.9, 40.6, 33.9,
Compound L7: Compound L7 was prepared by the treatment of tren with
3,4-dimethoxyphenyl isocyanate by following procedure A. The product
was purified by column chromatography on silica gel by using 5%
MeOH and 95% CH2Cl2. Yield: 86%; 1H NMR (300 MHz, CDCl3): d=
30.3 ppm; IR (solid): n¯ =2956 (C=C), 1633 cmꢀ1
ACTHNUTRGNE(NUG C=O); HRMS (FAB):
7.50 (s, 3H; NH), 6.91 (s, 3H; HAr), 6.57 (d, 3J
6.49 (d, 3J
ACHTUNGTRENNUNG
m/z calcd for C66H81N7O6: 1068.63211; found: 1068.63445; elemental anal-
ysis calcd (%) for C66H81N7O6: C 74.20, H 7.64, N 9.18; found: C 73.60, H
6.97, N 8.87.
General procedure A: Urea synthesis: Tren (0.20 cm3, 1.35 mmol) was
dissolved in dry THF (30 cm3) under N2. A solution of the appropriate
isocyanate (4.20 mmol) dissolved in THF (30 cm3) was added dropwise
with stirring at room temperature. The reaction was stirred at room tem-
perature for 2 h. If a white precipitate formed, it was collected by filtra-
tion and dried in vacuo. Alternatively, the solvent was removed and the
product was purified by column chromatography.
General procedure B: Amide and sulfonamide synthesis: Tren (0.40 cm3,
2.70 mmol) was dissolved in water (20 cm3) containing NaOH (0.33 g,
8.25 mmol). A solution of the appropriate benzoyl chloride (7.66 mmol)
dissolved in diethyl ether (10 cm3) was added slowly and the reaction was
stirred at room temperature for 2 days. The off-white solid that formed
was collected by filtration, washed with a portion of Et2O (10 cm3) and
dried in vacuo.
Compound L2:[14] Compound L2 was prepared by the treatment of tren
with tert-butyl isocyanate by following procedure A. Yield 98%;
1H NMR (300 MHz, CDCl3): d=5.79 (br, 3H; NH), 5.00–4.80 (m, 3H;
NH), 3.13 (br, 6H; CH2), 2.46 (br, 6H; CH2), 1.33 ppm (s, 27H; CH3);
13C NMR (68 MHz, CDCl3): d=160.6, 56.4, 50.7, 29.7 ppm; IR (KBr): n¯ =
3350 (NꢀH), 1650 cmꢀ1 (C=O); MS (ES+): m/z: 444 [M+H]+, 467
[M+Na]+; elemental analysis calcd (%) for C21H45N7O3: C 56.86, H
10.22, N 22.10; found: C 56.50, H 10.24, N 20.58.
AHCTUNGTRENNUNG
OCH3), 3.68 (s, 9H; OCH3), 3.08 (br, 6H; CH2), 2.35 ppm (br, 6H;
CH2); 13C NMR (75 MHz, [D6]DMSO): d=156.3, 149.9, 144.4, 135.2,
112.9, 110.2, 104.7, 56.1, 55.4, 54.5, 37.2 ppm; IR (solid): n¯ =3299 (NꢀH),
2935 (CꢀH), 2834 (CꢀH), 1627 (C=O), 1205 cmꢀ1 (CꢀO); MS (ES+):
m/z: 684.33 [M+H]+; elemental analysis calcd (%) for C33H45N7O9: C
57.97, H 6.63, N 14.34; found: C 58.07, H 6.69, N 14.36.
Compound L8: Compound L8 was prepared by the treatment of tren with
3,5-dimethoxyphenyl isocyanate by following procedure A. The product
was purified by column chromatography on silica gel by using 10%
MeOH and 90% CH2Cl2. Yield: 81%; 1H NMR (300 MHz, CDCl3): d=
7.39 (s, 3H; NH), 6.44 (s, 6H; HAr), 6.10 (brt, 3H; NH), 6.06 (s, 3H;
HAr), 3.64 (s, 18H; OCH3), 3.22 (br, 6H; CH2), 2.38 ppm (br, 6H; CH2);
13C NMR (75 MHz, CDCl3): d=162.0, 156.3, 142.9, 96.0, 93.5, 56.5, 55.4,
48.4 ppm; IR (solid): n¯ =3333 (NꢀH), 2942 (CꢀH), 2836 (CꢀH), 1647
(C=O), 1148 cmꢀ1 (CꢀO); MS (ES+): m/z: 684.34 [M+H]+; elemental
analysis calcd (%) for C33H45N7O9: C 57.97, H 6.63, N 14.34; found: C
57.74, H 6.61, N 14.10.
Compound L9: Compound L9 was prepared by the treatment of tren with
3,4,5-trimethoxyphenyl isocyanate by following procedure A. The prod-
uct was purified by column chromatography on silica gel by using 7%
MeOH and 93% CHCl3. Yield: 74%; 1H NMR (300 MHz, [D6]DMSO):
d=8.50 (s, 3H; NH), 6.72 (s, 6H; HAr), 6.12 (t, 3J
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Compound L3: Compound L3 was prepared by the treatment of tren with
butyl isocyanate by following procedure A. Yield: 96%; 1H NMR
(300 MHz, CDCl3): d=6.00 (brt, 3H; NH), 5.54 (brt, 3H; NH), 3.17–
[D6]DMSO): 156.2, 154.3, 138.2, 132.8, 96.0, 60.8, 56.1, 54.5, 37.4 ppm; IR
(solid): u¯ =3336 (NꢀH), 1650 (C=O), 1603 (C=C, Ar), 1122 cmꢀ1 (CꢀO);
MS (ES+): m/z: 774 [M+H]+.
[16]
3.10 (m, 6H; CH2), 2.53 (br, 6H; CH2), 1.98 (br, 6H; CH2), 1.53–1.30 (m,
Compound L10
:
Compound L10 was prepared by the treatment of tren
3
12H; CH2), 0.92 ppm (t, J
N
with benzoyl chloride by following procedure B. Yield: 74%; 1H NMR
Chem. Eur. J. 2009, 15, 4836 – 4850
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4847

M. Schrçder, P. A. Tasker et al.
(300 MHz, CDCl3): d=7.60 (d, 3J
(H,H)=9.0 Hz; 6H; HAr), 7.18 (br, 3H; NH), 7.07 (t, 3J
6H; HAr), 3.60–3.55 (m, 6H; CH2), 2.76 ppm (t, 3J
N
7.33 (m, 12H; HAr), 7.24–7.09 (m, 30H; HAr), 6.75 (br, 2H; NH+), 4.35
(br, 12H; CH2), 3.91 (br, 12H; CH2), 3.60 (br, 24H; CH2), 1.18 ppm (br,
54H; CH3); 13C NMR (90 MHz, [D2]C2H2Cl4, 808C): d=172.5, 168.0,
155.7, 135.4, 131.1, 129.4, 128.3, 127.5, 127.4, 125.7, 54.4, 51.8, 42.5, 42.0,
35.0, 31.3 ppm; IR (solid): n¯ =3359 (NꢀH), 1632 cmꢀ1 (C=O); elemental
analysis calcd (%) for C132H164Cl6N14O12Pt: C 62.26, H 6.49, N 7.70;
found: C 62.86, H 6.41, N 7.74.
E
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Compound L11:[17] Compound L11 was prepared by the treatment of tren
with 3,4-dimethoxybenzoyl chloride by following procedure B. The prod-
uct was purified by column chromatography on silica gel by using 7%
AHCTUNGTRENNUNG
[(L2H)2PtCl6]: A solution of L2 (0.02 g, 0.04 mmol) in MeCN (2 cm3) was
added to [H2PtCl6] (0.01 g, 0.02 mmol) in MeCN (1 cm3). An orange pre-
cipitate immediately formed, which was collected by filtration and dried
in vacuo (0.013 g,52%). 1H NMR (270 MHz, [D6]DMSO): d=10.05 (br,
2H; NH+), 6.05 (br, 6H; NH), 4.31 (br, 6H; NH), 3.31 (br, 12H; CH2),
3.20 (br, 12H; CH2), 1.25 (s, 54H; CH3); IR (solid): n¯ =3342 (NꢀH),
1632 cmꢀ1 (C=O); elemental analysis calcd (%) for C42H92Cl6N14O6Pt: C
38.89, H 7.15, N 15.12; found: C 38.82, H 7.09, N 15.03.
MeOH and 93% CH2Cl2. Yield: 66%; 1H NMR (300 MHz, CDCl3): d=
3
7.37 (br, 3H; NH), 7.28 (s, 3H, HAr), 7.12 (d, J
N
6.31 (d, 3J
OCH3), 3.69–3.55 (m, 6H; CH2), 2.77 ppm (t, 3J
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
CH2); 13C NMR (75 MHz, CDCl3): d=167.5, 154.9, 153.2, 147.8, 126.6,
120.8, 110.9, 109.3, 56.1, 53.7, 39.7 ppm; IR (solid): n¯ =3291 (NꢀH), 2936
(CꢀH), 2836 (CꢀH), 1628 (C=O), 1264 cmꢀ1 (CꢀO); MS (ES+): m/z:
639.30 [M+H]+; elemental analysis calcd (%) for C33H42N4O9: C 62.06, H
6.63, N 8.77; found: C 61.97, H 6.55, N 8.69.
AHCTUNGTRENNUNG
a
A
ACHTUNGTRENNUNG
Compound L12: Compound L12 was prepared by the treatment of tren
(H,H)=7.0 Hz, 18H; CH3); IR (solid): n¯ =3364 (NꢀH), 1640 cmꢀ1 (C=
with 3,5-dimethoxybenzoyl chloride by following procedure B. Yield:
74%; 1H NMR (300 MHz, CDCl3): d=7.57 (t, 3J
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(75 MHz, CDCl3): d=167.5, 161.7, 105.5, 103.8, 55.8, 53.7, 39.7 ppm; IR
(solid): n¯ =3304 (NꢀH), 2938 (CꢀH), 2837 (CꢀH), 1637 (C=O),
1151 cmꢀ1 (CꢀO); MS (ES+): m/z: 639.30 [M+H]+; elemental analysis
calcd (%) for C33H42N4O9: C 62.06, H 6.63, N 8.77; found: C 61.98, H
6.81, N 8.59.
a
G
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
6H; NH), 3.51–3.45 (m, 12H; CH2), 3.36–3.38 ppm (m, 12H; CH2); IR
(solid): n¯ =3358 (NꢀH), 1650 cmꢀ1 (C=O); elemental analysis calcd (%)
for C54H68Cl6N14O6Pt +1.4 H2O: C 44.97, H 4.95, N 13.60; found: C
44.97, H 4.71, N 13.56.
Compound L13: Compound L13 was prepared by the treatment of tren
with 3,4,5-trimethoxybenzoyl chloride by following procedure B. The
product was purified by column chromatography on silica gel by using
5% MeOH and 95% CH2Cl2. Yield: 73%; 1H NMR (300 MHz, CDCl3):
AHCTUNGTRENNUNG
[(L5H)2PtCl6]: This compound was prepared in a similar manner to that
d=7.77 (t, 3J
ACHTUNGTRENNUNG(H,H)=4.6 Hz, 3H; NH), 7.00 (s, 6H; HAr), 3.78 (s, 3H;
described for [(L2H)2PtCl6] and precipitated as a yellow powder. Yield=
58%; 1H NMR (270 MHz, [D6]DMSO): d=9.71 (br, 2H; NH+), 8.72 (s,
OCH3), 3.63 (s, 6H; OCH3), 3.44 ppm (br, 6H; CH2), 2.61 (br, 6H;
CH2); 13C NMR (75 MHz, CDCl3): d=167.5, 153.2, 141.6, 129.0, 105.6,
60.8, 56.1, 55.7, 39.7 ppm; IR (solid): n¯ =3304 (NꢀH), 2939 (CꢀH), 2836
(CꢀH), 1636 (C=O), 1120 cmꢀ1 (CꢀO); MS (ES+): m/z: 729 [M+H]+;
elemental analysis calcd (%) for C36H48N4O12: C 59.33, H 6.64, N 7.69;
3
3
6H; NH), 7.30 (d, J
N
ACHTUNGTREN(NUNG H,H)=8.6 Hz,
12H; HAr), 6.43 (t, 3J
AHCTUNGTRENNUNG
2.80–2.72 (m, 6H; iPrCH), 1.18 ppm (d, 36H; iPrCH3); IR (solid): n¯ =
3347 (NꢀH), 1660 cmꢀ1 (C=O); elemental analysis calcd (%) for
C72H104Cl6N14O6Pt: C 51.80, H 6.28, N 11.75; found: C 51.80, H 6.17, N
11.71.
found: C 59.21, H 6.58, N 7.71.
[16]
Compound L14
:
Compound L14 was prepared by the treatment of tren
with phenyl sulfonyl chloride by following procedure B. The product was
AHCTUNGTRENNUNG
[(L6H)2PtCl6]: This compound was prepared in a similar manner to that
1
recrystallised from MeOH. Yield: 82%; H NMR (300 MHz, CDCl3): d=
described for [(L2H)2PtCl6] and precipitated as a yellow powder. Yield=
54%; 1H NMR (270 MHz, [D6]DMSO): d=9.74 (br, 2H; NH+), 8.74 (s,
7.95–7.90 (m, 6H; HAr), 7.90–7.51 (m, 9H; HAr), 6.02 (br, 3H; NH), 2.97
(br, 6H; NCH2), 2.66 ppm (br, 6H; NCH2); 13C NMR (68 MHz, CDCl3):
d=140.5, 133.3, 129.0, 54.5, 41.4 ppm; IR (KBr): n¯ =3297 (NH), 1619
(C=C, Ar), 1350 (SO2), 1150 cmꢀ1 (SO2); MS (ES+): m/z: 567 [M+H]+,
590 [M+Na]+; elemental analysis calcd (%) for C24H30N4O6S3: C 50.87,
H 5.34, N 9.89; found: C 50.85, H 5.34, N 9.73.
3
3
6H; NH), 7.30 (d, J
12H; HAr), 6.44 (t, J
(H,H)=8.8 Hz, 12H; HAr), 7.19 (d, J
N
3
G
(br, 12H; CH2), 1.24 ppm (s, 54H; CH3); IR (solid): n¯ =3333 (NꢀH),
1651 cmꢀ1 (C=O); elemental analysis calcd (%) for C78H116Cl6N14O6Pt: C
53.42, H 6.67, N 11.18; found: C 53.32, H 6.53, N 11.08.
[(L7H)2PtCl6]: This compound was prepared in a similar manner to that
AHCTUNGTRENNUNG
Compound L15: Compound L15 was prepared by the treatment of tren
with 3,4-dimethoxyphenyl sulfonyl chloride in THF for 48 h by following
procedure B. The product was purified by column chromatography on
silica with 5% MeOH and 95% CH2Cl2. Yield: 24%; 1H NMR
described for [(L2H)2PtCl6], but no precipitate formed so the reaction
was repeated in [D3]MeCN to study complexation in solution. 1H NMR
(270 MHz, [D3]MeCN): d=9.65 (br, 2H; NH+), 7.73 (s, 6H; NH), 6.93
(s, 6H; HAr), 6.83 (br, 6H; HAr), 6.59 (br, 6H; HAr), 6.19 (br, 6H; NH),
3.65 (s, 36H; OCH3), 3.56 (br, 12H; CH2), 3.40 ppm (br, 12H; CH2);
195Pt NMR (500 MHz, [D3]MeCN): d=247 ppm.
(270 MHz, CDCl3): d=7.54 (dd, 3J
G
ACHTUNGTRENNUNG
HAr), 7.42 (d, 4J
A
ACHTUNGTRENNUNG
3
HAr), 6.01 (t, J
A
6H; NHCH2), 2.51 (brs, 6H; NCH2); 13C (68 MHz, CDCl3): d=152.5,
149.2, 131.4, 121.0, 110.8, 109.7, 60.4, 54.1, 41.0 ppm; MS (ES+): m/z: 769
[M+Na]+, 747 [M+H]+; IR (CHCl3, ): n¯ =3286 (NꢀH), 2841 (CꢀH),
1590 (C=C), 1509 (C=C), 1326 (S=O), 1263 (CꢀO), 1184 (S=O),
1140 cmꢀ1 (CꢀO); elemental analysis calcd (%) for C30H42N4O12S3: C
47.91, H 5.67, N 7.50; found: C 47.94, H 5.66, N 7.23.
AHCTUNGTRENNUNG
[(L8H)2PtCl6]: This compound was prepared in a similar manner to that
described for [(L2H)2PtCl6], but no precipitate formed so the reaction
was repeated in [D3]MeCN to study complexation in solution. 1H NMR
(270 MHz, [D3]MeCN): d=9.12 (br, 2H; NH+), 6.56 (br, 12H; HAr), 6.15
(br, 6H; HAr), 3.67 (br, 36H; OCH3), 3.55 ppm (br, 6H; CH2) (CH2 peak
obscured by broad H2O signal); MS (ES+): m/z: 981 [(L8-ꢀ2H)PtCl3]ꢀ,
ACHTUNGTRENNUNG
[(L1H)2PtCl6]: A solution of L1 (0.53 g, 0.50 mmol) in MeOH (1 cm3) was
ACTHNUTRGNEUNG
1089 [(L8H)PtCl6]ꢀ, 1772 [L8(L8H)PtCl6]ꢀ.
added to a solution of [H2PtCl6] (0.013 g, 0.025 mmol) in MeOH (1 cm3).
MeOH (1 cm3) and concentrated HCl (6 drops) were added. The pale-
orange solid that resulted after 3 days was filtered off, washed with cold
AHCTUNGTRENNUNG
[(L9H)2PtCl6]: This compound was prepared in a similar manner to that
described for [(L2H)2PtCl6] and precipitated as a yellow powder. Yield=
57%; 1H NMR (300 MHz, [D6]DMSO): d=9.87 (br, 2H; NH+), 8.81 (t,
1
MeOH and dried under high vacuum (0.047 g,74%). H NMR (360 MHz,
[D2]C2H2Cl4): d=7.82–7.80 (m, 12H; HAr), 7.67 (br, 6H; CONH), 7.36–
ACTHUNGTRENUNG ACTHNUGTRNEN(UNG H,H)=7.10 Hz, 12H; HAr), 7.54
3J(H,H)=5.2 Hz, 6H; NH), 7.81 (d, 3J
4848
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ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 4836 – 4850

Selective Extraction and Transport of [PtCl6]2ꢀ
FULL PAPER
(t, 3J
3.72 ppm (d, 3J
ACHTUNGTRENNUNG
G
E
ceipt of a Royal Society Wolfson Merit Award and of a Royal Society
Leverhulme Trust Senior Research Fellowship.
H2O signal); elemental analysis calcd (%) for C54H62Cl6N8O6Pt: C 48.88,
H 4.71, N 8.44; found: C 49.15, H 4.63, N 8.37.
ACHTUNGTRENNUNG
[(L10 H)2PtCl6]: This compound was prepared in a similar manner to that
[1] F. Bernardis, R. A. Grant, D. C. Sherrington, React. Funct. Polym.
2005, 65, 205–217, and references therein.
[2] P. A. Tasker, P. G. Plieger, L. C. West in Comprehensive Coordina-
tion Chemistry II, Vol. 9 (Eds.: J. A. McCleverty, T. J. Meyer), Elsev-
ier, Oxford, 2004, pp. 59–808, and references therein.
described for [(L2H)2PtCl6] and precipitated as a yellow powder. Yield=
55%; 1H NMR (300 MHz, [D6]DMSO): d =9.87 (br, 2H; NH+), 8.81 (t,
3J
(t, 3J
3.72 ppm (d, 3J
ACHTUNGTRENNUNG(H,H)=5.5, 12H; CH2) (CH2 peak obscured by broad
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=5.2 Hz, 6H; NH), 7.81 (d, 3J
A
ACHTUNGTRENNUNG
[3] J. B. Love, J. M. Vere, M. W. Glenny, A. J. Blake, M. Schrçder,
Chem. Commun. 2001, 2678–2679; M. W. Glenny, M. Lacombe, J. B.
Love, A. J. Blake, L. F. Lindoy, R. C. Luckay, K. Gloe, B. Antonioli,
C. Wilson, M. Schrçder, New J. Chem. 2006, 30, 1755–1767; D.
Black, A. J. Blake, R. L. Finn, L. F. Lindoy, A. Nezhadali, G. Roug-
naghi, P. A. Tasker, M. Schrçder, Chem. Commun. 2002, 340–341;
Q. Wang, C. Wilson, A. J. Blake, S. R. Collinson, P. A Tasker, M.
Schrçder, Tetrahedron Lett. 2006, 47, 8983–8987; S. G. Galbraith, Q.
Wang, L. Li, P. G. Plieger, A. J. Blake, C. Wilson, S. R. Collinson,
L. F. Lindoy, M. Schrçder, P. A. Tasker, Chem. Eur. J. 2007, 13,
6091–6107, and references therein; S. G. Galbraith, L. F. Lindoy,
P. A. Tasker, P. G. Plieger, J. Chem. Soc. Dalton Trans. 2006, 1134–
1136, and references therein.
H2O signal); IR (solid): n¯ =3371 (NꢀH), 3221 (NꢀH), 1637 cmꢀ1 (C=O);
elemental analysis calcd (%) for C54H62Cl6N8O6Pt: C 48.88, H 4.71, N
8.44; found: C 49.15, H 4.63, N 8.37.
ACHTUNGTRENNUNG
[(L11H)2PtCl6]: This compound was prepared in a similar manner to that
described for [(L2H)2PtCl6], but no precipitate formed so the reaction
was repeated in [D3]MeCN to study complexation in solution. 1H NMR
(300 MHz, [D3]MeCN): d=9.83 (br, 2H; NH+), 7.87 (br, 6H; NH), 7.31
(d, 3J(H,H)=6.6 Hz, 6H; HAr), 7.18 (s, 6H; HAr), 6.73 (d, 3J
ACHTUNGTRENNUNG AHCTUNGTRNEN(UGN H,H)=
6.4 Hz, 6H; HAr), 3.81 (s, 18H; OCH3), 3.65 (s, 18H; OCH3), 2.39 (br,
6H; CH2), 2.07 ppm (br, 6H; CH2); IR (solid): n¯ =3340 (NꢀH),
1634 cmꢀ1 (C=O).
ACHTUNGTRENNUNG
[(L12H)2PtCl6]: This compound was prepared in a similar manner to that
described for [(L2H)2PtCl6]. Crystals precipitated from the solution over
[4] B. K. O. Leung, M. J. Hudson, Solvent Extr. Ion Exch. 1992, 10, 173–
190; E. Benguerel, G. P. Demopoulos, G. B. Harris, Hydrometallurgy
1996, 40, 135–152.
24 h. Yield=58%; 1H NMR (300 MHz, [D6]DMSO): d=9.68 (br, 2H;
NH+), 8.79 (t, 3J
ACHTUNGTRENNUNG(H,H)=4.9 Hz, 6H; NH), 7.00 (s, 12H; HAr), 6.68 (s,
[5] M. J. Deetz, M. Shang, B. D. Smith, J. Am. Chem. Soc. 2000, 122,
6201–6207; P. D. Beer, P. A. Gale, Angew. Chem. 2001, 113, 502–
532; Angew. Chem. Int. Ed. 2001, 40, 486–516; K. Choi, A. D. Ham-
ilton, Coord. Chem. Rev. 2003, 240, 101–110; P. A. Gale, Coord.
Chem. Rev. 2003, 240, 191; F. P. Schmidtchen, Coord. Chem. Rev.
2006, 250, 2918–2928; K. Wichmann, B. Antonioli, T. Sçhnel, M.
Wenzel, K. Gloe, J. R. Price, L. F. Lindoy, A. J. Blake, M. Schrçder,
Coord. Chem. Rev. 2006, 250, 2987–3003; R. Custelcean, L. H.
Delmau, B. A. Moyer, J. L. Sessler, W.-S. Cho, D. Gross, G. W.
Bates, S. J. Brooks, M. E. Light, P. A. Gale, Angew. Chem. 2005, 117,
2593–2598; Angew. Chem. Int. Ed. 2005, 44, 2537–2542; J. L. Sess-
ler, P. A. Gale, W. S. Cho, Anion Receptor Chemistry, RSC, Cam-
bridge, 2006.
[6] K. Gloe, H. Stephan, M. Grotjahn, Chem. Eng. Technol. 2003, 26,
1107–1117; B. A. Moyer, P. V. Bonnesen, R. Custelcean, L. H.
Delmau, B. P. Hay, Kem. Ind. 2005, 54, 65–87; P. A. Tasker, C. C.
Tong, A. N. Westra, Coord. Chem. Rev. 2007, 251, 1868–1877.
[7] L. Brammer, J. K. Swearingen, E. A. Bruton, Proc. Natl. Acad. Sci.
USA 2002, 99, 4956–4961.
6H; HAr), 3.78 (s, 36H; OCH3), 3.70 (br, 12H; CH2), 3.50 ppm (br, 12H;
CH2); 195Pt NMR (500 MHz, [D3]MeCN): d=244 ppm; IR (solid): n¯ =
ꢀ
3368 (NꢀH), 1641 (C=O), 1592 (C=C), 1155 cmꢀ1 (C O); MS (ES ):
ꢀ
m/z: 936 [(L12-ꢀ2H)PtCl3]ꢀ, 972 [(L12ꢀH)PtCl4]ꢀ, 1044 [(L12H)PtCl6]ꢀ,
1378 [(L12H)(PtCl5)2]ꢀ, 1682 [L12(L12H)PtCl6]ꢀ; elemental analysis calcd
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
(%) for C66H86Cl6N8O18Pt: C 46.98, H 5.14, N 6.64; found: C 47.05, H
5.11, N 6.57.
ACHTUNGTRENNUNG
[(L13H)2PtCl6]: This compound was prepared in a similar manner to that
described for [(L2H)2PtCl6], but no precipitate formed so the reaction
was repeated in [D3]MeCN to study complexation in solution. 1H NMR
(300 MHz, [D3]MeCN): d=9.96 (br, 2H; NH+), 8.34 (br, 6H; NH), 7.03
(s, 6H; HAr), 6.73 (d, 3J
ACHTUNGTRENNUNG(H,H)=6.4 Hz, 6H; HAr), 4.01 (br, 12H; CH2),
3.90 (br, 12H; CH2), 3.73 (s, 36H; OCH3), 3.72 ppm (s, 18H; OCH3);
13C NMR (75 MHz, [D3]MeCN): d=170, 153, 128, 117, 105, 60, 56, 55,
36 ppm; IR (solid): n¯ =3364 (NꢀH), 1650 cmꢀ1 (C=O).
ACHTUNGTRENNUNG
[(L14H)2PtCl6]: Yield=52%; 1H NMR (400 MHz, CDCl3): d=9.70 (br,
2H; NH+), 7.96 (br, 6H; NH), 7.82 (d, 3J
ACHTNUTRGNE(UNG H,H)=8.0 Hz, 12H; HAr),
7.61–7.71 (m, 18H; HAr), 3.68 (br, 12H; CH2), 3.07 ppm (br, 12H; CH2);
13C NMR (101 MHz, CDCl3): d=139.5, 132.8, 129.4, 126.6, 51.9,
37.0 ppm; IR (solid): n¯ =3248 (NꢀH), 1329 cmꢀ1 (S=O).
[8] K. J. Naidoo, A. S. Lopis, A. N. Westra, D. J. Robinson, K. R. Koch,
J. Am. Chem. Soc. 2003, 125, 13330–13331.
ACHTUNGTRENNUNG
[(L15H)2PtCl6]: This compound was prepared in a similar manner to that
[9] L. Brammer, E. A. Bruton, P. Sherwood, Cryst. Growth Des. 2001, 1,
277–290; see also: J. C. Mareque Rivas, L. Brammer, Inorg. Chem.
1998, 37, 4756–4757; B. Dolling, A. G. Orpen, J. Starbuck, X.-M.
Wang, Chem. Commun. 2001, 567–568; M. Felloni, P. Hubberstey,
C. Wilson, M. Schrçder, CrystEngComm 2004, 6, 87–95.
described for [(L2H)2PtCl6] and precipitated as an orange-yellow powder.
Yield=46%; 1H NMR (270 MHz, CDCl3): d=8.19 (s, 2H; NH+), 7.51
(dd, 3J(H,H)=8.5, 4J(H,H)=2.2 Hz, 6H; HAr), 7.38 (d, 4J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG ACTUHNGTRENNNGU
6H; HAr), 6.91 (d, 3J
ACHTUNGTRENNUNG
3.87 ppm (m, 60H; OCH3, NHCH2); IR (CDCl3): n¯ =3009 (CꢀH, Ar),
2935 (CꢀH), 2855 (CꢀH), 1590 (C=C), 1510 (C=C), 1331 (S=O), 1264
(CꢀO), 1185 (S=O), 1157 cmꢀ1 (CꢀO); elemental analysis calcd (%) for
C48H62Cl6N8O12PtS6: C 37.36, H 4.05, N 7.26; found: C, 38.07, H 4.19, N
7.33.
[10] The compositions of Alamines are proprietary but are thought be
mixtures of octyl and decyl tertiary amines (see reference [2]).
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Bowman-James, Inorg. Chem. 2004, 43, 3751–3755.
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[14] M. K. Zart, T. N. Sorrell, D. Powell, A. S. Borovik, Dalton Trans.
2003, 1986–1992.
[15] C. Raposo, M. Almaraz, M, Martꢄn, V. Weinrich, L. Mussꢅns, V.
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Angew. Chem. 1993, 105, 942–944; Angew. Chem. Int. Ed. Engl.
1993, 32, 900–901.
Acknowledgements
We thank the EPSRC, the Chemistry Innovation Programme, the Nation-
al Research Foundation of South Africa for financial support and the
EPSRC National Mass Spectrometry Service at the University of Wales,
Swansea (UK) for mass spectra. Special thanks are due to Professor An-
tonio Bianchi and his group at the University of Florence, Italy who per-
formed the potentiometry experiments. M.S. gratefully acknowledges re-
[17] P. D. Beer, P. Hopkins, J. D. McKinney, Chem. Commun. 1999,
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Chem. Eur. J. 2009, 15, 4836 – 4850
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4849

M. Schrçder, P. A. Tasker et al.
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Received: November 17, 2008
Published online: April 15, 2009
4850
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Chem. Eur. J. 2009, 15, 4836 – 4850