Anion selectivity in zwitterionic amide-functionalised metal salt extractants

FULL PAPER

DOI: 10.1002/chem.200601874

Anion Selectivity in Zwitterionic Amide-Functionalised Metal Salt

Extractants

Stuart G. Galbraith,^[a]Qiang Wang,^[b]Li Li,^[b]Alexander J. Blake,^[b]Claire Wilson,^[b]

[c]

Simon R. Collinson,^[b]Leonard F. Lindoy, Paul G. Plieger,^[d]Martin Schrçder,*^[b]and

Peter A. Tasker*^[a]

Abstract: Amide-functionalised salen

ligands capable of extracting metal

salts have been synthesised and charac-

terised. Single-crystal X-ray structure

determinations of complexes of NiSO₄,

tion studies show loading and stripping

pH-profiles that are suitable for the re-

covery of CuSO₄or CuCl₂from indus-

trial leach solutions. The copper-only

ty was evaluated for a number of other

mono-charged anions and interestingly

the ligands were found to display a

preference for the Br^ꢀion. To probe

the influence of the Hofmeister bias on

the selectivity of anion complexation,

single-phase potentiometric titration

experiments were employed to investi-

complexes, [Cu

A

[Ni(L)

A

for Cl^ꢀover SO₄in both solvent ex-

traction and bulk liquid membrane

transport experiments and were found

to bind Cl^ꢀin two steps via the forma-

phores are in a zwitterionic form with

Ni^IIbound in the deprotonated salen

moiety and the SO₄ion associated

gate the binding of SO₄and Cl^ꢀby

2ꢀ

with protonated pendant N’-amidopi-

perazine groups. Treatment of [Ni(L)-

tion of a 1:1:1 [Cu

A

one of the copper only complexes, [Cu-

followed by a 1:1:2 [Cu(L)Cl₂] assem-

bly as the pH of the aqueous phase is

lowered. The anion transport selectivi-

A

Under these conditions selectivity was

reversed (SO₄^2ꢀ>Cl^ꢀ) confirming that

the Hofmeister bias, which reflects the

relative hydration energies of the

anions, dominates the selectivity of

anion extraction from aqueous media

into CHCl₃.

from the pendant amido–amine group

2ꢀ

resulting in loss of the SO₄ion and

formation of metal-only complexes of

Keywords: anions · copper · extrac-

tive metallurgy · hydrogen bonds ·

type [Ni

A

characterized by single-crystal X-ray

diffraction. Three of the ligands with

solubilities suitable for solvent extrac-

nickel

·

receptors

extraction

Introduction

Cation-exchange reagents such as the phenolic oximes^[1,2]

are well suited to solvent extraction processes used for the

recovery of base metals from their oxidic ores after leaching

[a] Dr. S. G. Galbraith, Prof. P. A. Tasker

School of Chemistry, University of Edinburgh

Edinburgh, EH9 3JJ (UK)

with sulfuric acid, and such processes now account for

Fax : (+44)131-650-6543

[3]

around 30%of the worldꢀs copper production.

Different

[b] Dr. Q. Wang, Dr. L. Li, Prof. A. J. Blake, Dr. C. Wilson,

Dr. S. R. Collinson, Prof. M. Schrçder

types of hydrometallurgical flowsheets are needed for

metal-recovery from sulfide ores in order to exploit a range

of very efficient leaching processes that have been devel-

oped recently by the mining industry.^[4]Extraction of a

metal salt to achieve the unit operations of concentration

and separation (Figure 1) has been suggested as an approach

that will result in better materials balances, particularly

from pregnant leach solutions, which contain high concen-

trations of metal salts.^[2,5,6]Transport of a metal salt across a

flowsheet by means of a water-immiscible solvent can be fa-

cilitated through the use of zwitterionic heterotopic ligands

School of Chemistry, The University of Nottingham

University Park, Nottingham, NG7 2RD (UK)

Fax : (+44)115-951-3563

[c] Prof. L. F. Lindoy

Centre for Heavy Metal Research, School of Chemistry F11

University of Sydney, N.S.W. (Australia)

[d] Dr. P. G. Plieger

Institute of Fundamental Sciences, Massey University

Private Bag 11 222, Palmerston North (New Zealand)

Supporting information for this article is available on the WWW

under http://www.chemistry.org or from the author.

Chem. Eur. J. 2007, 13, 6091 – 6107

ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

6091

groups to bind a monohydrogen phosphate anion selective-

ly.^[24]

We report herein the incorporation of amide and urea

groups into the zwitterionic ditopic ligand framework of bis-

salicylaldimine (salen-type) ligands.^[25–29]It was anticipated

that the presence of hydrogen-bond donors in the target ion-

ophores Lⁿ(n=1–8; Scheme 1) would aid these derivatives

to address the solvation spheres of complexed anions and

hence influence the observed selectivity towards anion

transport.

Results and Discussion

Figure 1. Recovery of a base metal by selective transport of a metal salt

from a pregnant leach solution containing a complex mixture of cations

and anions

Synthesis of ligands and complexes: The ionophores Lⁿ(n=

1–8) were prepared from the appropriately substituted sali-

that have separate cation and

anion binding sites; the zwitter-

ionic nature of the reagent

allows the metal and anion to

be recovered separately by pH

adjustment of the strip solu-

tion.^[5,7]An efficient process re-

quires the reagent to show high

selectivity for both targeted

metal cation and anion.^[8]

Ligand design to achieve selec-

tive complexation of metal cat-

ions is well understood^[9]and

many highly selective solvent

extractants have been devel-

oped for use in extractive met-

allurgy.^[2]In contrast, selective

solvent extraction of anions, al-

though of great potential com-

mercial importance in extrac-

tive metallurgy especially for

Scheme 1. Preparation of salen derivatives with pendant anion-complexing groups ortho to the phenolate

donor atoms. Ligand L⁸has the same structure as L⁷, but with mixed isomer/multibranched nonyl groups re-

placing the tert-butyl substituents.

the recovery of precious metals

as their chlorometallate com-

plexes,^[10]is much less well de-

veloped. The design of selective

anion receptors is a rapidly ex-

panding area,^[11,12]and the simultaneous binding of both cat-

ionic and anionic moieties of metal salts by polytopic ligands

with chemically distinct binding sites is currently a very

active area of research.^[12–23]

Typically, many anion receptors use several non-covalent

interactions to achieve strong binding, and hydrogen-bond-

ing donor sites are most commonly incorporated into syn-

thetic receptors, because their directionality allows steric

and conformational control of the hydrogen-bond donors to

match the requirements of anions of different sizes and ge-

cylaldehyde by condensation with 1,2-diaminoethane

(Scheme 1). The secondary amines 1–3, which are precursors

for Lⁿ(n=1–3), respectively, were obtained by mono-deri-

vatisation of the appropriate diamine with benzoic anhy-

dride by using a modification of a literature method

(Scheme 2),^[30]followed by reaction with benzaldehyde and

reduction with NaBH₄. Compounds 1–3 were then treated

with paraformaldehyde and 2-hydroxy-5-tert-butylbenzalde-

hyde in a two-step Mannich reaction^[31]to give the corre-

sponding salicylaldehydes in typically 30–40%yields. Initial-

ly a conventional Mannich reaction^[31]between 5-tert-butyl-

2-hydroxybenzaldehyde^[32]and 1-acetylpiperazine was used

to generate the aldehyde 4 in 69%yield as a precursor for

A

system is the phosphate-binding protein (PBP), which uses

twelve hydrogen bonds including seven from amide NH

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Chem. Eur. J. 2007, 13, 6091 – 6107

Anion Selectivity

FULL PAPER

firmed by single-crystal X-ray diffraction and its structure is

compared to that of its NiSO₄complex below.

The neutral complexes [Cu

[Cu

(L³ꢀ2H)] were prepared by stirring a solution of the

ligand in CHCl₃with a solution of Cu(OAc)₂in MeOH. The

crude complex was washed with ammonia solution (pH 9) to

remove any excess Cu(OAc)₂and to ensure that the pen-

dant amine groups were fully deprotonated. These com-

A

N

AHCTREUNG

plexes, their copper(II) salt derivatives [Cu(L)X] (L=L¹–L³

and X=2Cl or SO₄) as well as the free ligands all showed

sufficient solubility in CHCl₃to allow solvent extraction ex-

periments to be carried out. The latter were employed to

probe the metal and anion binding properties of these iono-

phores and define the relative affinities of their complexes

for different anions (see below). Metal salt complexes of pi-

peridino- and piperazino-substituted ligands L⁴–L⁸were

much less soluble and consequently their coordination

chemistry and structures were studied largely in the solid-

state. Even the incorporation of multibranched/mixed

isomer nonyl groups as in L⁸failed to solubilize the CuSO₄

complex sufficiently in CHCl₃to allow comparisons to be

made with L¹–L³in solvent extraction experiments.

Scheme 2. Synthesis of 1–3 as the secondary amines precursors for the

preparation of L¹–L³. i) (PhCO)₂O/CH₂Cl₂; ii) PhCHO, NaBH₄; iii) paraf-

ormaldhehyde, K₂CO₃, EtOH, 08C, 72 h; iv) 5-tert-butyl-2-hydroxyben-

zaldehyde, MeCN, reflux, 72 h.

L⁴(Scheme 3). A significantly improved yield for 4 (85%)

was obtained by reaction of 5-tert-butyl-3-bromomethyl-2-

hydroxybenzaldehyde^[33](Scheme 3) with 1-acetylpiperazine;

Nickel(II) sulfate and copper(II) sulfate complexes

[M(L)SO₄] (L=L⁴–L⁸) were readily isolated from the reac-

tion of metal sulfate with the respective ligands in MeOH.

Complex formation was confirmed in each case by elemen-

tal analysis and electrospray mass spectrometry. The dia-

magnetism of the nickel(II) complexes is confirmed from

1

the sharpness of the peaks in their respective H NMR spec-

tra recorded in CDCl₃and is in accordance with the expect-

ed square-planar geometry for the nickel(II) centres; this

was confirmed also by single-crystal X-ray analysis (see

below).

Scheme 3. Synthesis of salicylaldehyde derivative precursors for L⁴–L⁷. i)

reference [33]; ii) appropriate piperazine or piperidine, K₂CO₃and KI in

CH₃CN. Aldehyde 9 has the same structure as 8, but with a mixed isomer

nonyl group replacing the tert-butyl substituent.

1

Complexation to nickel(II) leads to shifts of the H NMR

signals associated with the salen unit to higher field com-

pared to those of the metal-free ligands. For example, for

ligand L⁶the imine proton signal shifts from d=8.40 to

7.65 ppm upon reaction with nickel(II) sulfate. The spectra

similar methodologies were employed to obtain aldehydes

5–9 as precurors to Lⁿ(n=5–9).

of [Ni(L⁶)SO₄] and [Ni(L⁶)

(BF₄)₂] show differences that sug-

G

gest that the urea protons within each pendant arm interact

in different ways with the anions. Such interactions were

All ionophores were characterised by ¹H and ¹³C NMR

spectroscopy, by FTIR spectroscopy, mass spectrometry and

elemental analysis. Evidence for the complete formation of

products was confirmed by the presence of characteristic

resonances for the imine proton at d=8.2–8.5 ppm in the

¹H NMR spectrum and of the imine C centre at d=165–

168 ppm in the ¹³C NMR spectrum, coupled with the ab-

sence of resonances for aldehydic C and H centres. The

presence of amide linkages in the products Lⁿ(n=1–3) was

confirmed by a resonance for the NH proton at dꢁ6.9 ppm

and a peak in the ¹³C NMR spectra at dꢁ167 ppm corre-

sponding to the carbonyl carbon (NHCO). In the case of L⁶,

the urea linkage was characterised by the presence of reso-

nances for the NH protons at d=8.9 and 8.2 ppm, while for

L⁷the presence of an amide group was confirmed by the

presence of a resonance for the NH protons at dꢁ6.7 ppm.

The structure of the urea-substituted ligand L⁶was con-

later confirmed in the solid-state by single-crystal X-ray

2ꢀ

structures of the SO₄

complexes [Ni(L⁵)SO₄)] and

[Ni(L⁶)SO₄)]. A resonance due to one of the pendant amido

NH protons in L⁶is particularly sensitive to the nature of

the anion present and shifts from d=9.06 ppm in the nick-

el(II) sulfate complex to d=8.63 ppm in the tetrafluorobo-

rate complex. The other amido NH proton resonance shows

a smaller shift from d=8.28 to 8.19 ppm in the same com-

plexes. This is consistent with the observed solid-state struc-

ture for [Ni(L⁶)

of the amide NH centres interacting with the anion, N4H···

(OSO₃)^2ꢀ. In the solid-state, an additional intramolecular hy-

A

AHCTREUNG

drogen bond between the remaining amido NH group and a

carbonyl oxygen, N5H···O2, is observed.

Treatment of the metal sulfate complexes [M(L)SO₄] with

KOH in MeOH afforded the metal-only forms [M

ACHTREUNG

Chem. Eur. J. 2007, 13, 6091 – 6107

ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

P. A. Tasker, M. Schrçder et al.

These were isolated as solids and shown to be identical to

the products prepared directly from the corresponding met-

al(II) acetates. The deprotonation of the pendant amino

pH range 2–3 and both the metal and anion can be conven-

iently recovered by pH adjustment. This allows the metal

salt to be efficiently loaded and recovered and is therefore

1

2ꢀ

groups was followed by H NMR spectroscopy in CD₃OD

an ideal profile for base-metal recovery from SO₄

and CDCl₃. The SO₄^2ꢀ-free complex [Ni

A

feeds.^[5,7]

well-resolved resonances for the pendant amide arm and

methylene groups, which were found to have very similar

chemical shifts to those of the free ligand. Such studies dem-

onstrate that selective stripping/exchange of anions is possi-

ble with these polytopic complexing agents. The pH depen-

Leach solutions produced in base-metal recovery process-

2ꢀ

es typically contain SO₄and/or Cl^ꢀions. Consequently, we

monitored the uptake of HCl by the copper complex [Cu-

2ꢀ

A

to evaluate the anion selectivity of the extractant (Figure 3).

ACHTREUNG

Solvent extraction: New hydrometallurgical flowsheets for

the recovery of metal ions from their sulfidic ores require

the extraction and transport of metal salts. A practicable ex-

tractant needs to show selectivity for both the targeted

metal cation and anion as downstream electrolytic reduction

requires electrolytes of high purity. The anions most com-

monly found in the leach solutions produced in primary

2ꢀ

base-metal recovery are SO₄and Cl^ꢀ, so achieving selec-

2ꢀ

tivity of SO₄over Cl^ꢀ(or vice versa) is essential.

Figure 3. The pH dependence of H₂SO₄(circles) and HCl (triangles)

The selectivity of solvent extraction of metal cations into

the organic phase by organic acid extractants is directly re-

lated to the pH_1/2, the pH associated with 50%loading of

the extractant at a stated concentration and for a defined

composition of aqueous feed. We have recently described a

method for using the pH_1/2to also evaluate anion extraction

selectivities.^[29]In these two-phase experiments the uptake of

uptake by [Cu

A

[Cu

U

acids by the metal-only complexes [M

A

SO₄[pH_1/2values: 5.5Æ0.1 (Cl^ꢀ) and 3.8Æ0.1 (SO₄^2ꢀ)].

metal salt complexes is monitored over a range of pH in

order to yield the pH_1/2values for the anions [Eq. (1)].

Such Cl^ꢀ/SO₄selectivity is consistent with the Hofmeister

bias,^[34,35]which predicts that charge-diffuse anions (such as

mono-charged Cl^ꢀ) will in general be more favourably ex-

½MðLꢀ2HÞ_ðorgÞþ 2 HX ¼ ½MðLÞX₂

ð1Þ

ðorgÞ

tracted into low polarity solvents than more hydrophilic

2ꢀ

anions such as SO₄

.

ꢀ

This gives information on the strength and selectivity of

anion binding and if the metal concentrations in both the or-

ganic and aqueous phases are also recorded we can analyse

the effect of pH on the stability of the metal complex and

the strength of metal binding.

In Figure 3 a value of 100%for the extraction of Cl cor-

responds to formation of a 1:1:2 [Cu

(Lꢀ2H)Cl₂] complex. In

involves a 1:1:1 [Cu-

AHCTREUNG

2ꢀ

contrast, 100%extraction of SO

4

A

pH-loading curves are expected. As the pH is lowered the

loading of Cl^ꢀis first observed at pH<7, but the curve then

flattens as the pH approaches 6, rising again sharply at pH<

5.5. This is consistent with a two-step process and the load-

ing of the second Cl^ꢀbeing less favourable.

The results of such an experiment with the copper-only

complex [Cu

A

Figure 2. The loading of Cu²⁺and SO₄is ꢁ100%in the

It was hoped that the use of ligands with shorter (L¹) or

longer (L³) alkyl chains between the teriary amine and

amide groups in the anion binding sites would provide an in-

sight into how such systems might be tuned for anion selec-

tivity. The uptake of H₂SO₄and HCl by [Cu

ACHTREUNG

[Cu

ACHTREUNG

AHCTREUNG

2ꢀ

groups, is more selective for Cl^ꢀover SO₄than the 1,3-

propane-linked analogue [Cu

G

A

2ꢀ

the 2Cl^ꢀ/SO₄DpH_1/2=2.3 (Figure 4), which compares with

Figure 2. The pH dependence of H₂SO₄uptake by [Cu

strength of copper-binding (circles and diamonds define S and Cu molar

(L²ꢀ2H)] and the

DpH_1/2=1.7 for [Cu

for Cl^ꢀ-loading is observed for [Cu

and pH 7 (Figure 4). [The solvent extraction experiments

ACHTREUNG

AHCTREUNG

concentrations, respectively, as percentage of the molar concentration of

L²).

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Chem. Eur. J. 2007, 13, 6091 – 6107

Anion Selectivity

FULL PAPER

the interaction of Cl^ꢀions with the complexes given that the

solvent extraction experiments indicated potential formation

of both 1:1 and 1:2 complex/anion species. The experiments

involved incremental addition of 0–5 equivalents of H₂SO₄

or HCl in isopropanol to 0.05 mm solutions of [Cu

A

in the same solvent. The addition of H₂SO₄to the complexes

resulted in clear isosbestic points until greater than one

equivalent of acid was added indicating that the initial com-

plex formed had

(Figure 6). Such behaviour was expected as this 1:1 complex

a

[Cu

A

Figure 4. The pH dependence of H₂SO₄(circles) and HCl (triangles)

uptake by [Cu

A

Figure 5. The pH dependence of H₂SO₄(circles) and HCl (triangles)

uptake by [Cu

(L¹ꢀ2H)].

(L¹ꢀ2H)] (0.05 mm) upon the ad-

ACHTREUNG

Figure 6. The absorption spectra of [Cu

dition of H₂SO₄in isopropanol at 208C; the number of equivalents of

H₂SO₄added are: a) 0; b) 0.2; c) 0.4; d) 0.6; e) 1.0.

were not conducted above pH 7, because CHCl₃becomes

unstable in the presence of hydroxide.]

The copper-only complex [Cu

C

appears to be the dominant form in the extraction experi-

ments, except at very low pH at which there is a predomi-

nance of mono-charged HSO₄ions. Upon addition of more

than one equivalent of acid the respective spectra did not

pass through the existing isobestic points, indicating that

new species were formed. It is interesting to note that the

band at l_max374 nm observed for the complexes [Cu-

at a lower pH (<6.0) than [Cu

lectivity for Cl^ꢀover SO₄^2ꢀ. For [Cu

C

ꢀ

drops to 5.1 for Cl^ꢀand 3.5 for SO₄^2ꢀ, which gives a value

for DpH_1/2of 1.6. Although this value for DpH_1/2is not much

lower than that recorded for [Cu

G

there is a significant reduction in the Cl^ꢀto SO₄selectivity

as no clear two-step loading of Cl^ꢀis observed with [Cu-

G

(L¹ꢀ2H)]. This result is important for Cl^ꢀ-stripping from

pared to only 3 nm for [Cu

(L¹ꢀ2H)] on addition of one

[Cu(L¹)Cl₂] as in contrast to the other two systems, all Cl^ꢀ

in [Cu(L¹)Cl₂] can be removed by raising the pH above 6.0.

It appears that as the alkyl chain between the amine ni-

trogen and amide group is made more flexible {1,2-ethane

equivalent of H₂SO₄. This may indicate that a different

anion binding mode might occur for the more flexible hosts.

Similar experiments to the above were performed with

HCl and the results are consistent with the formation of an

initial 1:1 species followed by a complex with a [Cu-

in [Cu

E

(L²ꢀ2H)]!1,6-hexane

[Cu

A

2ꢀ

SO₄increases. This may be a result of the longer arms fa-

cilitating the formation of more favourable binding environ-

ments by separating the two Cl^ꢀbinding sites and thus re-

ducing electrostatic repulsion between these two bound

anions. Conversely, an enhancement of SO₄^2ꢀover Cl^ꢀselec-

tivity might be achieved by the development of a rigid and

pre-organised anion binding site for SO₄^2ꢀ, which would

consequently disfavour incorporation of two monoanions.

equivalent of acid, a clear isosbestic point was observed.

This indicates that only the 1:1 complex is present and no

1:2 species has been formed at this stage. Upon the incre-

mental addition of two equivalents of acid the intial isosbes-

tic point is lost, but a new isosbestic point is generated re-

flecting formation of a 1:2 species from the already formed

1:1 complex. No further changes were observed in the spec-

tra on the further addition of more than two equivalents of

HCl. A plot of the formation of the 1:1 and 1:2 [Cu-

UV/Vis titrations: UV/Vis spectra were used to monitor the

N

stoichiometry of anion binding by the copper-only com-

shown in Figure 7. These results are consistent with the two-

step Cl^ꢀ-loading observed in the solvent extraction experi-

plexes [Cu

A

Chem. Eur. J. 2007, 13, 6091 – 6107

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6095

P. A. Tasker, M. Schrçder et al.

Table 1. Transport rates^[a]of H₂SO₄and 2HCl (10^ꢀ6mol).

Source phase^[b]

[Cu

(L¹ꢀ2H)]

[Cu

U

2ꢀ

SO₄only

39

37

1.0/37

33

27

0.3/29

Cl^ꢀonly^[c]

SO₄^2ꢀ/Cl^{ꢀ [c]}

[a] Across a CHCl₃BLM (50 mL), [carrier]=1 mm, for 23 h based upon

anion concentrations in the receiving phase {30 mL buffered at pH 7.0Æ

0.1 with NaH₂PO₄/Na₂HPO₄(50 mm)}. Experimental uncertainty in the

recorded rates is Æ5%. [b] 10 mL of

a 0.1m solution of anion(s),

pH 1.8Æ0.1. [c] The reported values for Cl^ꢀrepresent the moles of (Cl^ꢀ)₂

transported and is scaled in terms of charge balance.

efficiently stripped into the receiving phase at pH 7. This

may compensate for the lower strength of binding shown by

2ꢀ

the extractants for SO₄in the solvent extraction experi-

ments. This is supported by the lower transport rates ob-

served for [Cu

C

(L¹ꢀ2H)], with

2ꢀ

amount of SO₄was transported. The indication that Cl^ꢀ

anions are preferentially bound by the complexes in the

BLM is consistent with the solvent extraction data presented

earlier and the results indicate that solvent extraction pH

profiles can be used to define the conditions required for ef-

ficient transport of anions in BLM studies of the present

type.

Figure 7. Plot of the formation of the 1:1 and 1:2 [Cu

cies in isopropanol at 208C. The%composition was calculated from the

A

To gain a wider appreciation of the extraction selectivity

absorbances recorded at the peak formed at 365 nm in the absorption

spectra of [Cu

A

of the copper-only complexes [Cu

A

number of equivalents of HCl added are: a) 0, b) 0.4, c) 0.6, d) 0.8, e)

1.0, f) 1.2, g) 1.6, h) 1.8, i) 2.0.

source-phase membrane-transport experiments were per-

formed for a variety of anions including SO₄^2ꢀ, Cl^ꢀ, Br^ꢀ,

ꢀ

NO₃and H₂PO₄. Comparative transport experiments were

also performed by using dibenzylamine as a carrier so that

the selectivity and efficiency of transport by the complexes

could be compared to those of a simple protonatable amine

with an environment about the nitrogen atom that is similar

to that in the extractant ligands. These experiments were

performed using a pH 5.2 citrate buffer solution as the re-

ceiving phase rather than phosphate buffer solution since

phosphate was one of the anions present in the source

phase.

ments with [Cu

A

formation of a 1:1 complex followed by the subsequent for-

mation of the 1:2 complex on further addition of acid under

the conditions employed.

Membrane transport of anions: To gain further understand-

ing of anion extraction and transport, the copper-only com-

plexes [Cu

A

a CHCl₃bulk liquid membrane (BLM) system. The initial

experiments involved monitoring the rate of transport of

The observed transport employing dibenzylamine as the

carrier (Figure 8) followed the expected Hofmeister

2ꢀ

SO₄and Cl^ꢀthrough the BLM from an acidic source

ꢀ

phase (pH 1.8Æ0.1) to a neutral receiving phase (pH 7.0)

buffered with phosphate. It was assumed that transport

occurs by means of a symport mechanism^[36]in which

anion(s) and protons are co-complexed and co-transported.

These experiments are summarised in Table 1 and were per-

formed by either using source phases containing only one

anion or with mixed SO₄^2ꢀ/Cl^ꢀions.

order^[34,35]of hydrophobicity: NO₃^ꢀ>Br^ꢀ>Cl^ꢀ>H₂PO₄

>

2ꢀ

ꢀ

SO₄and neither SO₄nor H₂PO₄were detected in the

receiving phase. The amide-functionalised copper-only com-

plexes were found to transport Br^ꢀmore efficiently than the

other anions. This was particularly evident for [Cu

(L¹ꢀ2H)]

for which the bromide flux was close to double that ob-

ꢀ

tained for NO₃. This poorer transport of NO₃by [Cu-

2ꢀ

Both complexes showed a slightly higher rate of SO₄

G

transport compared to Cl^ꢀfrom source phases containing

only a single anion type. This modest increase in rate can be

rationalised by comparing the pH profiles obtained for

of the NO₃ion and the cis disposition of the anion-binding

groups making it less favourable for these arms to accom-

ꢀ

modate two NO₃ions on one “edge” of the salen unit.

2ꢀ

ꢀ

SO₄and Cl^ꢀextraction (Figures 3 and 5). The pH_1/2values

No SO₄or H₂PO₄ion transport occurred in the pres-

2ꢀ

ꢀ

are greater for Cl^ꢀso it seems likely that SO₄will be more

ence of Cl^ꢀ, Br^ꢀor NO₃. To evaluate the selectivity order

6096

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Chem. Eur. J. 2007, 13, 6091 – 6107

Anion Selectivity

FULL PAPER

½CuðL¹ꢀ2HÞÞ þ H₂SO₄¼ ½CuðL¹ÞSO₄

½CuðL¹ꢀ2HÞ þ 2 HCl ¼ ½CuðL¹ÞCl₂

ð2Þ

ð3Þ

ð4Þ

½CuðL¹ꢀ2HÞ þ 2 H^þ¼ ½CuðL¹Þ

2þ

A

conventional pH titration procedure in 95%/5%

ꢀ

MeOH/water [I=0.1m (C₂H₅)₄N⁺ClO₄] was employed

both in the absence of added anion and in the presence (see

2ꢀ

Table 2) of Cl^ꢀor SO₄added as tetraalkylammonium salts.

Figure 8. The transport rates of Cl^ꢀ, Br^ꢀ, and NO₃from a mixed anion

ꢀ

Table 2. Protonation constants for [Cu

U

source phase using [Cu

A

carrier. [The concentration of dibenzylamine was 2 mm in the membrane-

transport experiments, so that the results could be fairly compared to the

dibasic ligands.]

Anion added^[b]

–

C

LogK₁

LogK₂

8.96

9.11

8.98

7.02

7.28

7.06

ꢀ [d]

HSO₄

Cl^ꢀ

for these former anions, membrane-transport experiments

ꢀ

were run using a mixed SO₄^2ꢀ/H₂PO₄aqueous source

[a] K₁and K₂refer to the equilibria [Cu

and [Cu(L¹)]²⁺=[Cu

(L¹ꢀH)]⁺+H⁺—they relate to the basicity of the

pendant amine groups in the presence of the “conducting anion” ClO₄

A

ACHTREUNG

phase. The pH of the source phase was set at 3.3 to ensure

AHCTREUNG

ꢀ

AHCTREUNG

that H₂PO₄was the dominant phosphate species present

(L¹ꢀ2H)] and [Cu-

and with the addition of sulfate or chloride. All logK values are Æ0.05.

(pK_a1for phosphoric acid=2.12). [Cu

ꢀ

[b] HSO₄was added using tetrabutylammonium hydrogensulfate and

A

tetrapropylammonium chloride was used for the addition of Cl^ꢀ.

[c] Anion concentration. [d] Although hydrogen sulfate anion was added

for SO₄over H₂PO₄(Figure 9), providing another exam-

ple of anti-Hofmeister behaviour.^[34,35]Again, the cis disposi-

it is present as SO₄anion before the protonation constants are calculat-

2ꢀ

ed.

Addition of Cl^ꢀwas found to give no change within experi-

mental error in the stepwise logK values relative to the ab-

sence of this anion. This is in accord with little or no interac-

tion between Cl^ꢀand the protonated amine sites under the

somewhat polar conditions employed. In contrast, the addi-

2ꢀ

tion of SO₄resulted in a small, but significant increase in

both logK₁and logK₂and is in keeping with inhibition of

proton ionisation occurring through specific hydrogen-bond

formation with the SO₄ion. The increase is most notice-

Figure 9. Transport rates of sulfate and dihydrogenphosphate from a

ꢀ

mixed SO₄^2ꢀ/H₂PO₄source phase through a CHCl₃bulk liquid mem-

2ꢀ

brane using the copper complexes [Cu

A

T

A

benzylamine (dbza) as carrier. [The concentration of dibenzylamine was

2 mm in the membrane-transport experiments, so that the results could

be fairly compared to the dibasic ligands.]

sembly involving SO₄and [Cu(L¹)]²⁺, which is more fa-

vourable than formation of a 2:1 assembly with Cl^ꢀand

2ꢀ

[Cu(L¹)]²⁺

The above corresponds to the reverse of the selectivity

observed in the solvent extraction and BLM experiments,

but can be rationalised because the Hofmeister bias, which

favours the extraction of charge-diffuse anions, is not a

major factor in these single-phase experiments. The selectiv-

tion of the pendant anion-binding arms may be significant.

Such an arrangement is presumably more favourable for ac-

commodating a single dianion, (SO₄^2ꢀ) over two monoan-

ꢀ

2ꢀ

ions (2H₂PO₄).

ity of SO₄binding over Cl^ꢀin a single phase (95%/5%

MeOH/water) reflects the design features incorporated into

ionophores L¹–L⁸to allow formation of 1:1:1 assemblies of

SO₄^2ꢀ:L:Cu²⁺by exploiting a chelating arrangement of the

pendant anion complexing groups. Clearly, this preference is

not sufficient to overcome the relative solvation energy

terms involved in two-phase systems, reflecting the impor-

tance of the Hofmeister bias in developing successful recov-

ery processes.^[34]Also, formation of higher order assemblies

in solution involving pendant arms in different molecules as-

sociating with the same anions cannot be ruled out. Such ar-

Potentiometric titrations: The extent to which the observed

anion discrimination in two-phase solvent extraction and

three-phase BLM transport experiments reflects the differ-

ences in solvation energies was examined using potentiomet-

ric titrations in 95%/5% MeOH/water to probe anion bind-

ing corresponding to the equilibria in Equations (2) and (3).

This was achieved indirectly by determining the stepwise

protonation constants for the pendant amines in [Cu-

A

Chem. Eur. J. 2007, 13, 6091 – 6107

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6097

P. A. Tasker, M. Schrçder et al.

separations of N2 and N2’

being 4.80, 6.12 and 5.97 in

[Ni(L⁶)SO₄]·1.75H₂O·2.25Me-

A

graphically independent com-

plexes of [Ni(L⁶)SO₄]·7.5H₂O.

The proximity of the anion-

complexing groups in [Ni(L⁶)-

A

allows the protonated pipera-

zine hydrogen atoms to “che-

2ꢀ

late” a SO₄ion, although in

Figure 10. A view of the structure of L⁶, showing the atom labelling scheme. Intramolecular hydrogen bonds

are indicated by solid dashed lines. Displacement ellipsoids are drawn at the 50%probability level.

practice this ion is very exposed

and is able to form further hy-

drogen bonds to the urea

moiety of an adjacent complex

rangements predominate in the solid-state structures, which

are now described.

as well as to a lattice molecule of MeOH; there are also

weaker interactions with a poorly defined solvent region.

The urea fragments in this structure form intramolecular

NH···O bonds as is also observed in the structure of the free

Single-crystal X-ray structure determinations: In addition to

providing information on the modes of binding of anions to

the pendant amine groups in these ligands, single-crystal X-

ray structure determinations were undertaken to indicate

the extent to which incorporation of the Ni^IIdication into

2ꢀ

the salen N₂O₂donor set controls the disposition of the

functionalities at the respective anion binding sites. This is

exemplified by a comparison of the structures of L⁶and two

crystalline forms of [Ni(L⁶)SO₄].

The free ligand L⁶adopts an extended structure with the

pendant benzylamino N centres, N2 and N2ⁱ(i=3ꢀx, ꢀy,

ꢀz) being separated by 16.64 . The molecule adopts an

anti conformation at the central ethane link between the

imino N atoms (Figure 10), the torsion angle N1-C1a-C1aⁱ-

N1ⁱ(i=3ꢀx, ꢀy, ꢀz) of 1808 a consequence of the inversion

centre between C1a and C1aⁱ. The two phenol groups form

ꢀ

intramolecular hydrogen bonds to the imine N centres, O1

H1···N1, d

A

lecular hydrogen bond between an NH group and the O

ꢀ

centre of the urea in the pendant arm, N5 H5B···O2,

d

N

ilar intramolecular hydrogen bond forming a six-membered

ring with this pendant arm when attached to an aza-thioeth-

er macrocycles.^[13]

The single-crystal X-ray structures of two crystalline

forms

of

the

nickel

sulfate

complex

of

L⁶,

[Ni(L⁶)SO₄]·1.75H₂O·2.25MeOH and [Ni(L⁶)SO₄]·7.5H₂O

differing in their levels of solvation, were obtained. The

latter has two crystallographically independent [Ni(L⁶)SO₄]

units per unit cell. The incorporation of Ni^IIinto the salen

Figure 11. Top: The structure of [Ni(L⁶)SO₄]·1.75H₂O·2.25MeOH, show-

ing the atom labelling scheme and intramolecular hydrogen bonding.

Minor disorder components for the ethane bridge and one tBu group, all

H atoms except NH and all solvent molecules have been omitted. Dis-

placement ellipsoids are drawn at the 30%probability level. Bottom: In-

termolecular hydrogen bonding involving the sulfate anions. General

notes: The 1,2-diiminoethane links have an approximately syn conforma-

tion with an N-C-C-N torsion angles of 45.41 and 19.558 in the major and

minor disorder components. The RMS deviation of the N₂O₂donors and

the Ni^IIcation from their least-squares mean plane is 0.022 .

2ꢀ

unit leads to formation of very nearly planar N₂O₂donor

sets (Figures 11 and 12) with the deviation of Ni^IIfrom the

2ꢀ

plane defined by the N₂O₂donor sets being 0.036, 0.022,

0.363

and

0.10

for

[Ni(L⁵)SO₄]·8H₂O·2MeOH,

[Ni(L⁶)SO₄]·1.75H₂O·2.25MeOH, and for the two crystallo-

graphically independent molecules of [Ni(L⁶)SO₄]·7.5H₂O,

respectively. The complexation of Ni^IIbrings the pendant

amino/amido groups closer together, with the intramolecular

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Chem. Eur. J. 2007, 13, 6091 – 6107

Anion Selectivity

FULL PAPER

Figure 12. Views of the two independent [Ni(L⁶)SO₄] units in

[Ni(L⁶)SO₄]·7.5H₂O showing the atom labelling schemes. Minor disorder

components for the tBu group, all H atoms except NH and all solvent

molecules have been omitted for clarity. Displacement ellipsoids are

drawn at the 30%probability level. Hydrogen bonds are indicated by

dashed lines. General notes: The 1,2-diiminoethane links have approxi-

mately syn conformation with N-C-C-N torsion angles of ꢀ43.46 and

ꢀ38.938 The RMS deviation of the N₂O₂donors and the Ni^IIcation from

their least-squares mean planes in the two crystallographically independ-

ent complexes are 0.363 and 0.100 .

ligand. In addition, one of the urea groups forms two centro-

symmetrically related intermolecular hydrogen bonds with

an adjacent complex (see Supporting Information Table S1).

Ignoring interactions with solvent molecules, the combined

effect of the hydrogen-bonding interactions between the

Figure 13. Views showing selected hydrogen-bonding interactions in

[Ni(L⁶)SO₄]·7.5H₂O. Hydrogen bonds are indicated by dashed lines.

2ꢀ

SO₄ion and the complex cation is to generate a chain run-

ning parallel to the [011] direction. Supramolecular assem-

blies have also been found for metal sulfate complexes of

salen ligands bearing just simple tertiary amine

groups,^[7,26,27,37]but the more prolific intermolecular hydro-

complexes (see Supporting Information Table S2). The com-

plex cation centred on Ni1 interacts with two separate but

symmetry-equivalent SO₄ions through one N(piperazi-

2ꢀ

nium)H···O and one N(urea)H···O hydrogen-bonding inter-

R

2ꢀ

gen bonding in the SO₄complexes of the amido-substitut-

action. In this way each SO₄interacts with two adjacent

complexes to form a dimer containing two [Ni(L⁶)SO₄] units

(Figure 13). The remaining piperazinium NH hydrogen

bonds to a water molecule and there is further extensive hy-

drogen bonding involving many of the water molecules in

the structure. The complex cation containing Ni2 interacts

through a single N(piperazinium)H···O hydrogen bond with

ed ligand L⁶(and L⁵, see below) is consistent with their very

low solubility in non-polar water-immiscible solvents, and

underlines a problem in designing receptors for solvent ex-

2ꢀ

tractants for anions like SO₄that have very high hydration

energies.

2ꢀ

Quite different interactions with SO₄are observed in

2ꢀ

the other crystalline modification, [Ni(L⁶)SO₄]·7.5H₂O (Fig-

ures 12 and 13). The asymmetric unit contains two inde-

the SO₄centred on S2. The three remaining SO₄oxygen

atoms are involved in hydrogen bonding with lattice water

molecules. A ribbonlike motif is formed through a combina-

tion of these SO₄^2ꢀ–water interactions with the Ni2 centres

lying on alternate sides of the ribbon.

2ꢀ

pendent Ni^IIcomplexes, two SO₄ions and a total of fifteen

lattice water molecules, giving a stoichiometry of 7.5H₂O

per Ni^IIcentre. The structures of the Ni

(salen) units are sim-

A

ilar to each other as well as to that in

[Ni(L⁶)SO₄]·1.75H₂O·2.25MeOH. The hydrogen-bonding in-

teractions differ for the two crystallographically independent

The highly hydrated nickel sulfate complex of ligand L⁵,

[Ni(L⁵)SO₄]·8H₂O·2MeOH, shows similar structural fea-

tures (Figure 14) to those of the complexes of L⁶. Three of

Chem. Eur. J. 2007, 13, 6091 – 6107

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6099

P. A. Tasker, M. Schrçder et al.

Figure 15. View of one of the three independent [Ni

A

Figure 14. A view of the structure of [Ni(L⁵)SO₄]·8H₂O·2MeOH, showing

the atom labelling scheme. Displacement ellipsoids are drawn at the

30%probability level. Minor disorder components of tBu groups, and all

H atoms except NH, have been omitted for clarity. The two partially oc-

cupied orientations of the sulfate oxygen atoms are distinguished by solid

and open bonds. Hydrogen bonds are indicated by dashed lines. General

notes: The 1,2-diiminoethane link has an approximately syn conforma-

tion with N-C-C-N torsion angles of 39.0(6)8. The RMS deviation of the

N₂O₂donors and the Ni^IIcation from their least-squares mean plane is

0.036 . The N2···N2’ contact distance is 5.24 .

showing the atom labelling scheme (the numbering for the other two

complexes is analogous with the prefix 2 and 3 for the second and third,

respectively). The displacement ellipsoids are drawn at 30%probability

level and all hydrogens are omitted.

served between the amide groups of ligands bound to Ni1

and Ni2 (Figure 16) to form a dimeric structure. The com-

plex units containing Ni3 link through intermolecular hydro-

2ꢀ

the four SO₄oxygen atoms are disordered over two parti-

ally occupied sites; this results in two hydrogen-bonding in-

ꢀ

teractions, one from N2 H2a to O2S (65%occupancy), the

second to O2T (35%occupancy). All other oxygen atoms

2ꢀ

of the SO₄and other hydrogen-bond donor and acceptor

atoms, including the amide, phenolate and second piperazi-

nium groups are involved in an extensive hydrogen-bonding

network with the lattice water and methanol molecules (see

Supporting Information Table S3).

As might be expected the coordination geometry of the

Ni^IIcentres in these complexes is very similar (see Support-

ing Information Table S4). There are also no major differen-

ces from that observed in the nickel-only complex [Ni-

N

pendent neutral [Ni

(L⁷ꢀ2H)] moieties (Figure 15). The in-

corporation of Ni^IIinto the salen unit again leads to forma-

2ꢀ

tion of very nearly planar N₂O₂donor sets with the

deviation of the Ni^IIcation from the plane defined by the

2ꢀ

N₂O₂donor sets being 0.075, 0.083 and 0.020 for the

three crystallographically independent molecules. Addition-

ally, the complexation of Ni^IIbrings the pendant amino/

amido groups closer together, the intramolecular separations

of the benzylamines being 5.23, 5.13 and 5.51 in the three

crystallographically independent complexes. The solid-state

Figure 16. Hydrogen-bonding intermolecular interactions involving the

Ni1 and Ni2 centres (top) and the Ni3 centres (bottom) in the crystal

structure of [Ni

A

structure of [Ni

A

drogen bonding between the pendant amides. Firstly, both

the Ni1 and Ni2 complex moieties exhibit intramolecular hy-

drogen bonding between the carbonyl of one pendant arm

and the amide NH₂of the other pendant arm of the same

ligand; secondly, intermolecular hydrogen bonding is ob-

gen bonds to form a ribbonlike structure. There is no intra-

molecular hydrogen bonding and the pendant piperazine

arms lie on opposite sides of the square planar Ni^IIcentre.

There are also hydrogen-bonding interactions between the

amides on the Ni1 and those on the Ni3 fragments.

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Chem. Eur. J. 2007, 13, 6091 – 6107

Anion Selectivity

FULL PAPER

2 FeCl₂þ Cl₂! 2 FeCl₃

ð6Þ

Conclusions

The intermolecular hydrogen bonding between the pendant

amido groups in [Ni

(L⁷ꢀ2H)] illustrates a challenge which

2 FeCl₃þ MS ! MCl₂þ 2 FeCl₂þ S

ð7Þ

AHCTREUNG

we face in designing solvent extractants for metal salts that

will show high selectivity for the anion component. Whilst

amido groups form effective hydrogen bonds to anions, their

propensity for bonding to each other leads to the formation

of high-molecular-weight assemblies in solution and will

greatly reduce the solubilities of the unloaded extractants.

The other feature of the X-ray structure determinations

Experimental Section

Nuclear magnetic resonance spectra were obtained on Bruker AC 200

and Bruker AC 250 instruments, FAB mass spectra on a Kratos MS 50

machine, FTIR spectra on a Perkin–Elmer Paragon 1000 spectrometer as

oils on NaCl plates or as KBr discs and electronic absorption spectrosco-

py on a Perkin–Elmer l-900 spectrometer. Inductively coupled plasma

atomic emission spectroscopy (ICP-AES) analysis of copper and sulfur

was recorded on a Thermo Jarrell Ash IRIS ICP-AES spectrometer. The

measurement of pH was carried out on a Fisher Scientific AR 50 pH

meter. Concentrations of Cl^ꢀin the solvent extraction experiments were

measured using a Cl^ꢀ-selective Thermo Orion Ion Plus electrode. Anion

concentrations in the membrane transport experiments were determined

by using a Dionex DX-100 ion chromatograph. Unless stated to the con-

trary, commercial grade chemicals were obtained from Aldrich or Acros

and were used without further purification.

2ꢀ

which is clear for all the SO₄complexes is the propensity

for this anion to retain a coordination sphere which contains

water, consistent with the Hofmeister bias^[34,35](see solvent

extraction experiments). Whilst there is no reason in princi-

2ꢀ

ple why an extractant cannot incorporate hydrated SO₄

ions, it will make it more difficult to design ligands that

show a high selectivity of anion complexation, because a

much larger entity needs to be incorporated into the recep-

tor and the plasticity and flexibility of the hydration spheres

makes it more difficult to use the disposition of hydrogen-

bond donors in the receptor to control selectivity. Transport-

Ligand synthesis: 2-Hydroxy-5-tert-butylbenzaldehyde was prepared by

the methods of Levin or Lindoy and co-workers.^[32,39]3-Bromomethyl-2-

hydroxy-5-tert-butylbenzaldehyde and its 5-nonyl homologue were made

by the procedure described recently by Wang et al. (Scheme 3).^[33]N-(3-

Aminopropyl)benzamide, N-(2-aminoethyl)benzamide and N-(6-amino-

hexyl)benzamide were obtained using a modified version of the method

2ꢀ

ing hydrated SO₄ions into non-polar water-immiscible sol-

of Jacobson and co-workers and is described for N-(3-aminopropyl)

amide.^[30]The procedures employed for the preparation of L²were also

used for ligands L¹and L³.

benz-

vents will also be more difficult in terms of their incompati-

bility with these solvents.

AHCTREUNG

In the context of extractive metallurgy the solvent extrac-

tion studies have shown that the ligands L¹–L³have almost

ideal pH profiles for loading and stripping of copper(II) sul-

fate. The challenge in applying such ligands commercially is

N-(3-Aminopropyl)benzamide: Benzoic anhydride (8.0 g, 0.035 mol) in

CH₂Cl₂(200 mL) was added dropwise to a stirred solution of 1,3-diami-

nopropane (13.1 g, 0.18 mol) in CH₂Cl₂(400 mL) at ꢀ808C and stirred

overnight. The solution was concentrated in vacuo to 100 mL and extract-

ed with 5%HCl (250 mL). The two aqueous extracts were combined,

basified with 10%NaOH solution and concentrated in vacuo to 200 mL,

and the product extracted with CH₂Cl₂(350 mL). The combined organ-

ic extracts were dried over MgSO₄, filtered and evaporated in vacuo to

2ꢀ

to ensure that high selectivity of transport of SO₄over Cl^ꢀ

can be achieved to deliver a pure electrolyte for copper pro-

duction [Eq. (5)], because it is probable that most pregnant

leach solutions will contain significant concentrations of Cl^ꢀ

ion.

yield N-(3-amino-propyl)benzamide as

a colourless oil (4.92 g, 78%

yield). ¹H NMR (250 MHz, CDCl₃, TMS): d=7.85–7.79 (m, 2H; Ar-H),

7.46–7.38 (m, 3H; Ar-H), 3.58 (q, J=6 Hz, 2H; NHCH₂CH₂), 2.90 (t, J=

6.2 Hz, 2H; NH₂CH₂CH₂), 1.74 (quintet, J=6.2 Hz, 2H; CH₂CH₂CH₂),

1.45 ppm (s, 2H; NH₂); ¹³C NMR (60 MHz, CDCl₃, TMS): d=168.0

(CO), 135.4 (Ar C), 131.8 (Ar CH), 129.1 (Ar CH), 127.6 (Ar CH), 41.4

(CONHCH₂), 40.0 (NH₂CH₂), 32.0 ppm (CH₂CH₂CH₂); IR: n˜ =3286 (s),

2936 (s), 2869 (s), 1635 (s), 1541 (s), 1490, 1435, 1309, 700 cm^ꢀ1; MS

(FAB): m/z: 179 [M]⁺.

1

ð5Þ

CuSO₄þ H₂O ¼ Cu þ H₂SO₄þ = O₂

2

Whilst the incorporation of chelating amido/alkylammoni-

um groups into the structures of L¹–L³to favour the binding

of a single dianion over two monoanions leads to selective

N-(2-Aminoethyl)benzamide: This compound was prepared by a similar

procedure to that described for N-(3-amino-propyl)benzamide from 1,2-

diaminoethane. It was obtained as a colourless oil (69%yield). ¹H NMR

(250 MHz, CDCl₃, TMS): d=7.98–7.94 (2H; m, Ar-H), 7.65–7.55 (3H;

m, Ar-H), 3.58 (2H; t, J=6.4 Hz, CONHCH₂), 2.99 ppm (2H; t, J=

6.4 Hz, NH₂CH₂); ¹³C NMR (60 MHz, CDCl₃, TMS): d=170.0 (CO),

135.8 (Ar C), 132.8 (Ar CH), 129.6 (Ar CH), 128.4 (Ar CH), 43.7

(CONHCH₂), 42.1 ppm (NH₂CH₂); IR: n˜ =3275 (s), 2940 (s), 2843 (s),

1642 (s), 1542 (s), 1488, 1314, 687 cm^ꢀ1; MS (FAB): m/z: 165 [M]⁺.

2ꢀ

uptake of SO₄over Cl^ꢀin a single phase (95%/5%

MeOH/water), it is not sufficient to overcome the Hofmeis-

ter bias in solvent extraction experiments using CHCl₃as

the water-immiscible solvent. These results provide a strik-

ing example of how important the relative solvation ener-

gies are to the development of selective anion extractants.

An alternative strategy is to exploit ligands similar to L¹–

L³to transport metal chlorides in the flowsheet outlined in

Figure 1, and then to use the chlorine liberated in electro-

winning the metal to regenerate the leachant. This ap-

proach, recycling the chlorine to generate FeCl₃[Eq. (6)] for

oxidative leaching of sulfides [Eq. (7)] has been suggested

for the CUPREX process and has the advantage of generat-

ing elemental sulfur as a by product of metal recovery

rather than sulfuric acid.^[2,38]

N-(6-Aminohexyl)benzamide: This compound was prepared by a similar

procedure to that described for N-(3-amino-propyl)benzamide from 1,6-

diaminoethane. It was obtained as a colourless oil (77%). ¹H NMR

(250 MHz, CDCl₃, TMS): d=7.79–7.75 (m, 2H; Ar-H), 7.51–7.41 (m,

3H; Ar-H), 6.25 (br, 1H; NHCO), 3.48 (q, J=6.7 Hz, 2H; CONHCH₂),

2.70 (t, J=6.7 Hz, 2H; NH₂CH₂), 1.67 (quintet, J=7.0 Hz, 2H;

CONHCH₂CH₂), 1.45 (m, 6H; NH₂CH₂CH₂CH₂CH₂), 1.19 ppm (t, J=

6.7 Hz, 2H; NH₂CH₂); ¹³C NMR (60 MHz, CDCl₃, TMS): d=170.0

(CO), 136.0 (Ar C), 132.6 (Ar CH), 129.6 (Ar CH), 128.3 (Ar CH), 42.3

(CONHCH₂),

40.9

(NH₂CH₂),

33.2

(CONHCH₂CH₂),

30.5

(NH₂CH₂CH₂), 27.9 (CONHCH₂CH₂CH₂), 27.7 ppm (NH₂CH₂CH₂CH₂);

IR: n˜ =3286 (s), 2936 (s), 2869 (s), 1635 (s), 1541 (s), 1490, 1435, 1309,

Chem. Eur. J. 2007, 13, 6091 – 6107

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6101

P. A. Tasker, M. Schrçder et al.

704 cm^ꢀ1; MS (FAB): m/z: 221 [M]⁺; elemental analysis calcd (%) for

C₁₃H₂₀N₂O: C 70.9, H 9.2, N 12.7%; found: C 70.9, H 8.9, N 12.4.

N-[2-(Benzylethoxymethylamino)ethyl]benzamide (1a): This compound

was prepared by a similar procedure to that described for 2a from com-

pound 1. It was obtained as a colourless oil (98%yield). ¹H NMR

(250 MHz, CDCl₃, TMS): d=7.77–7.73 (m, 2H; Ar-H), 7.47–7.27 (m,

8H; Ar-H), 4.26 (s, 2H; NCH₂O), 3.92 (s, 2H; NCH₂Ar), 3.52 (m, 2H;

OCH₂CH₃), 3.51 (m, 2H; CONHCH₂), 3.05 (t, J=5.5 Hz, 2H;

CH₂CH₂N), 1.21 ppm (t, J=7 Hz, 3H; CH₂CH₃); ¹³C NMR (60 MHz,

CDCl₃, TMS): d=167.8 (CO), 139.4 (Ar C), 135.3 (Ar C), 131.6 (Ar

CH), 129.1 (Ar CH), 128.9 (Ar CH), 128.8 (Ar CH), 127.7 (Ar CH),

127.4 (Ar CH), 85.9 (NCH₂O), 63.8 (ArCH₂N), 55.7 (CH₃CH₂O), 51.5

(CONHCH₂), 37.5 (NCH₂CH₂), 15.7 ppm (CH₃CH₂); IR: n˜ =3334 (s),

3062, 3026, 2934 (s), 2855 (s), 1639 (s), 1537 (s), 1383, 1062, 704 cm^ꢀ1(s);

MS (FAB): m/z: 267 [MꢀEtO]⁺.

N-(3-Benzylaminopropyl)benzamide (2): N-(3-Aminopropyl)benzamide

(19.4 g, 0.109 mol) in EtOH (20 mL) was added dropwise to a stirred so-

lution of benzaldehyde (11.6 g, 0.109 mol) in EtOH (200 mL). The reac-

tion was refluxed for 1 h then cooled to room temperature. NaBH₄

(12.4 g, 0.327 mol) was added portion-wise to maintain a gentle efferves-

cence. The reaction was refluxed for a further 1 h and cooled to room

temperature. A solution of 10%NaOH (150 mL) was added, with cau-

tion, under N₂. The EtOH was removed in vacuo and CH₂Cl₂(2

150 mL) was then added to extract the product. The combined organic

extracts were dried over MgSO₄, filtered and evaporated in vacuo to

yield

2

as

a

viscous colourless oil (28.0 g, 96%yield).

¹H NMR

(250 MHz, CDCl₃, TMS): d=8.2 (br, 1H; NHCO), 7.79–7.70 (m, 2H;

Ar-H), 7.46–7.29 (m, 8H; Ar-H), 3.8 (s, 2H; NHCH₂Ar), 3.58 (q, J=

6 Hz, 2H; CONHCH₂), 2.90 (t, J=5.7 Hz, 2H; CH₂CH₂NHCH₂),

1.79 ppm (quintet, J=5.9 Hz, 2H; CH₂CH₂CH₂); ¹³C NMR (60 MHz,

CDCl₃, TMS): d=167.9 (CO), 139.8 (Ar C), 135.2 (Ar C), 131.8 (Ar

CH), 129.2 (Ar CH), 129.1 (Ar CH), 129.0 (Ar CH), 127.9 (Ar CH),

127.6 (Ar CH), 54.7 (ArCH₂NH), 49.3 (CONHCH₂), 40.7

(CH₂NHCH₂CH₂), 28.6 ppm (CH₂CH₂CH₂); IR: n˜ =3296 (s), 3060, 3028,

2931 (s), 1640 (s), 1539 (s), 1306 (s), 697 cm^ꢀ1(s); MS (FAB): m/z: 269

[M]⁺; elemental analysis calcd (%) for C₁₇H₂₀N₂O: C 76.1, H 7.5, N 10.4;

found: C 76.1, H 7.7, N 10.2.

N-[6-(Benzylethoxymethylamino)hexyl]benzamide (3a): This compound

was prepared by a similar procedure to that described for 2a from com-

pound 3. It was obtained as a colourless oil (37.1 g, 96%yield). ¹H NMR

(250 MHz, CDCl₃, TMS): d=7.74–7.70 (m, 2H; Ar-H), 7.46–7.24 (m,

8H; Ar-H), 4.09 (s, 2H; NCH₂O), 3.76 (s, 2H; NCH₂Ar), 3.39 (m, 2H;

OCH₂CH₃), 3.37 (m, 2H; CONHCH₂), 2.63 (t, J=7.2 Hz, 2H;

CH₂CH₂N), 1.52 (m, 4H; CH₂NHCH₂CH₂CH₂CH₂CH₂), 1.32 (m, 4H;

NHCH₂CH₂CH₂CH₂CH₂), 1.15 ppm (t, J=7.1 Hz, 3H; CH₂CH₃);

¹³C NMR (60 MHz, CDCl₃, TMS): d=167.8 (CO), 140.2 (Ar C), 135.3

(Ar C), 131.7 (Ar CH), 129.2 (Ar CH), 129.1 (Ar CH), 129.0 (Ar CH),

128.8 (Ar CH), 127.5 (Ar CH), 85.0 (NCH₂O), 63.8 (ArCH₂N), 56.6

(CH₃CH₂O), 51.9 (CONHCH₂), 40.4 (NCH₂CH₂), 30.1 (CONHCH₂CH₂),

28.5 (NCH₂CH₂), 27.4 (CONHCH₂CH₂CH₂), 27.3 (NCH₂CH₂CH₂),

15.7 ppm (CH₃CH₂); IR: n˜ =3321 (s), 3061, 3028, 2929 (s), 2863 (s), 1640

(s), 1541 (s), 1375, 1064, 699 cm^ꢀ1(s); MS (FAB): m/z: 323 [MꢀEtO]⁺.

N-(2-Benzylamino-ethyl)-benzamide (1): This compound was prepared

by a similar procedure to that described for 2 from N-(2-aminoethyl)-

A

N

(250 MHz, CDCl₃, TMS): d=7.80–7.76 (m, 2H; Ar-H), 7.50–7.42 (m,

8H; Ar-H), 6.95 (br, 1H; NHCO), 3.81 (s, 2H; NHCH₂Ar), 3.53 (q, J=

5.6 Hz, 2H; CONHCH₂), 2.87 (t, J=5.8 Hz, 2H; CH₂CH₂NHCH₂),

1.85 ppm (br, 1H; CH₂NHCH₂); ¹³C NMR (60 MHz, CDCl₃, TMS): d=

168.2 (CO), 140.7 (Ar C), 135.2 (Ar C), 132.0 (Ar CH), 129.4 (Ar CH),

129.1 (Ar CH), 128.7 (Ar CH), 127.7 (Ar CH), 127.6 (Ar CH), 54.1

(ArCH₂NH), 48.5 (CONHCH₂), 40.1 ppm (CH₂NHCH₂CH₂); IR: n˜ =

3256 (s), 3062, 3027, 2926 (s), 1638 (s), 1537 (s), 1311 (s), 693 cm^ꢀ1(s);

MS (FAB): m/z: 255 [M]⁺; elemental analysis calcd (%) for C₁₆H₁₈N₂O:

C 75.6, H 7.1, N 11.0; found: C 75.3, H 7.2, N 10.6.

N-{3-[Benzyl(5-tert-butyl-3-formyl-2-hydroxybenzyl)amino]propyl}benz-

amide (2b): A solution of 2a (33.7 g, 0.103 mol) and 5-tert-butyl-2-hy-

droxybenzaldehyde (18.4 g, 0.103 mol) in MeCN (400 mL) was refluxed

under N₂for 72 h. The reaction was cooled to room temperature and the

solvent evaporated in vacuo to yield a dark brown oil which was purified

by silica column chromatography (ethyl acetate/hexane 1:2) to yield 2b

as a yellow oil (18.2 g, 38%yield). ¹H NMR (250 MHz, CDCl₃, TMS):

d=10.15 (s, 1H; CHO), 7.58–7.25 (m, 12H; Ar-H), 6.42 (br, 1H;

NHCO), 3.78 (s, 2H; NCH₂CCOH), 3.66 (s, 2H; NCH₂Ar), 3.49 (q, J=

6.2 Hz, 2H; CONHCH₂), 2.64 (t, J=6.5 Hz, 2H; CH₂CH₂N), 1.91 (quin-

N-(6-Benzylaminohexyl)benzamide (3): This compound was prepared by

a similar procedure to that described for 2 from N-(6-aminohexyl)benz-

tet, J=6.3 Hz, 2H; CH₂CH₂CH₂), 1.27 ppm (9H; s, C

(CH₃)₃); ¹³C NMR

E

amide. It was obtained as a sticky white solid (98%yield). ¹H NMR

(60 MHz, CDCl₃, TMS: d=194.3 (CHO), 168.2 (NHCO), 159.2 (Ar C),

142.8 (Ar C), 138.3 (Ar C), 135.2 (Ar C), 134.8 (Ar CH), 131.9 (Ar CH),

130.0 (Ar CH), 129.2 (Ar CH), 129.0 (Ar CH), 128.2 (Ar CH), 127.5 (Ar

CH), 127.0 (Ar CH), 125.5 (Ar C), 121.8 (Ar C), 59.1 (NCH₂CCOH),

(250 MHz, CDCl₃, TMS): d=7.78–7.74 (m, 2H; Ar-H), 7.49–7.27 (m,

8H; Ar-H), 6.27 (br, 1H; NHCO), 3.78 (s, 2H; NHCH₂Ar), 3.42 (q, J=

6.7 Hz, 2H; CONHCH₂), 2.62 (t, J=7.1 Hz, 2H; CH₂CH₂NHCH₂), 1.62

55.2 (NCH₂Ar), 51.6 (CONHCH₂), 38.7 (CH₂NCH₂CH₂), 34.7 (C(CH₃)₃),

N

(m,

5H;

CH₂NHCH₂CH₂CH₂CH₂CH₂),

1.38 ppm

(m,

4H;

NHCH₂CH₂CH₂CH₂CH₂); ¹³C NMR (60 MHz, CDCl₃, TMS): d=168.2

(CO), 141 (Ar C), 135.5 (Ar C), 131.9 (Ar CH), 129.7 (Ar CH), 129.2

(Ar CH), 129.0 (Ar CH), 128.8 (Ar CH), 127.5 (Ar CH), 54.7

(ArCH₂NH), 49.9 (CONHCH₂), 40.6 (CH₂NHCH₂CH₂), 30.6

(CONHCH₂CH₂), 30.3 (NHCH₂CH₂), 27.6 (CONHCH₂CH₂CH₂),

27.5 ppm (CH₂NHCH₂CH₂CH₂); IR: n˜ =3296 (s), 3060, 3028, 2931 (s),

1640 (s), 1539 (s), 1306 (s), 697 cm^ꢀ1(s); MS (FAB): m/z: 311 [M]⁺; ele-

mental analysis calcd (%) for C₂₀H₂₆N₂O: C 77.4, H 8.4, N 9.0; found: C

77.4, H 8.4, N 8.9.

31.9 (C(CH₃)₃), 26.9 ppm (CH₂CH₂CH₂); IR: n˜ =3326, 3062, 3027, 2961

U

(s), 1651 (s), 1538 (s), 1479 (s), 1216, 753 cm^ꢀ1; MS (FAB): m/z: 459 [M]⁺

; elemental analysis calcd (%) for C₂₉H₃₄N₂O₃: C 76.0, H 7.5, N 6.1;

found: C 76.0, H 7.3, N, 6.1.

N-{2-[Benzyl(5-tert-butyl-3-formyl-2-hydroxybenzyl)amino]ethyl}benz-

A

described for 2b from compound 1a. It was obtained as a yellow oil

(30%). ¹H NMR (250 MHz, CDCl₃, TMS): d=9.99 (s, 1H; CHO), 7.74–

7.22 (m, 12H; Ar-H), 6.90 (br, 1H; NHCO), 3.74 (s, 2H; NCH₂CCOH),

3.62 (s, 2H; NCH₂Ar), 3.58 (q, J=5.6 Hz, 2H; CONHCH₂), 2.75 (t, J=

N-[3-(Benzylethoxymethylamino)propyl]benzamide (2a): Compound

2

5.8 Hz, 2H; CH₂CH₂N), 1.27 ppm (s, 9H; C

(CH₃)₃); ¹³C NMR (60 MHz,

C

(28 g, 0.104 mol) in EtOH (10 mL) was added dropwise to a stirred sus-

pension of paraformaldehyde (3.13 g, 0.104 mol) and K₂CO₃(28.75 g,

0.208 mol) in EtOH (120 mL) at 08C. The mixture was allowed to warm

to room temperature and continually stirred for 72 h. The solution was

filtered to remove the K₂CO₃and the solvent was then evaporated in

vacuo to yield compound 2a as a colourless oil, which was used in the

second step of the Mannich reaction without further purification (33.74 g,

99.4%yield). ¹H NMR (250 MHz, CDCl₃, TMS): d=7.76–7.66 (m, 2H;

Ar-H), 7.53–7.28 (m, Ar-H), 4.13 (s, 2H; NCH₂O), 3.78 (s, 2H;

NCH₂Ar), 3.53 (m, 2H; CONHCH₂), 3.43 (m, 2H; OCH₂CH₃), 2.85 (t,

J=6 Hz, 2H; CH₂CH₂N), 1.75 (quintet, J=6.1 Hz, 2H; CH₂CH₂CH₂),

1.15 ppm (t, J=6.1 Hz, 3H; CH₂CH₃); IR: n˜ =3321 (s), 3061, 3028, 2929

(s), 2863 (s), 1640 (s), 1541 (s), 1375, 1064, 699 cm^ꢀ1(s); MS (FAB): m/z:

281 [MꢀEtO]⁺.

CDCl₃, TMS): d=196.3 (CHO), 168.0 (NHCO), 159.0 (Ar C), 143.0 (Ar

C), 138.9 (Ar C), 135.8 (Ar CH), 135.3 (Ar C), 132.0 (Ar CH), 129.7 (Ar

CH), 129.1 (Ar CH), 129.0 (Ar CH), 128.4 (Ar CH), 128.1 (Ar CH),

127.5 (Ar CH), 126.3 (Ar C), 121.4 (Ar C), 59.1 (NCH₂CCOH), 54.4

(NCH₂Ar), 53.0 (CONHCH₂), 37.7 (CH₂NCH₂CH₂), 34.7 (C(CH₃)₃),

A

31.9 ppm (C(CH₃)₃); IR: n˜ =3339, 3062, 3027, 2963 (s), 1649 (s), 1535 (s),

R

1480 (s), 1217, 754 cm^ꢀ1; MS (FAB): m/z: 445 [M]⁺; elemental analysis

calcd (%) for C₂₈H₃₂N₂O₃·C₄H₈O₂: C 72.2, H 7.6, N 5.3; found: C 72.0, H

7.1, N 5.3.

N-{6-[Benzyl(5-tert-butyl-3-formyl-2-hydroxybenzyl)amino]hexyl}benz-

A

described for 2b from 3a. It was obtained as a light yellow oil (36%

yield). ¹H NMR (250 MHz, CDCl₃, TMS): d=10.35 (s, 1H; CHO), 7.78–

6102

www.chemeurj.org

ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2007, 13, 6091 – 6107

Anion Selectivity

FULL PAPER

7.28 (m, 12H; Ar-H), 6.28 (br, 1H; NHCO), 3.77 (s, 2H; NCH₂CCOH),

3.65 (s, 2H; NCH₂Ar), 3.40 (q, J=6.7 Hz, 2H; CONHCH₂), 2.52 (t, J=

7.2 Hz, 2H; CH₂CH₂N), 1.58 (m, 4H; CH₂NHCH₂CH₂CH₂CH₂CH₂),

(24300), 330 nm (9018 dm³mol^ꢀ1cm^ꢀ1); MS (FAB): m/z: 1025 [M]⁺; ele-

mental analysis calcd. (%) for C₆₆H₈₄N₆O₄·H₂O: C 76.0, H 8.3, N 8.1;

found: C 76.2, H 8.4, N 8.2.

Ligands L⁴–L⁸, which contain piperazino and piperidino groups as pend-

ant amines, were obtained by similar procedures from the parent alde-

hydes 4–9.

1.34 (m, 4H; NHCH₂CH₂CH₂CH₂CH₂), 1.30 ppm (s, 9H; C(CH₃)₃);

U

¹H NMR (60 MHz, CDCl₃, TMS): d=192.6 (CHO), 168.1 (NHCO),

159.9 (Ar C), 142.5 (Ar C), 137.7 (Ar C), 135.4 (Ar C), 133.5 (Ar CH),

132.0 (Ar CH), 130.0 (Ar CH), 129.2 (Ar CH), 129.0 (Ar CH), 128.2 (Ar

CH), 127.5 (Ar CH), 125.1 (Ar CH), 124.7 (Ar C), 122.7 (Ar C), 58.9

(NCH₂CCOH), 56.6 (NCH₂Ar), 53.9 (CONHCH₂), 40.6 (CH₂NCH₂CH₂),

5-tert-Butyl-2-hydroxy-3-(N’-acylpiperazinomethyl)benzaldehyde (4): 3-

Bromomethyl-5-tert-butyl-2-hydroxybenzaldehyde (1.00 g, 3.69 mmol)

and KHCO₃(0.56 g, 5.60 mmol) were added to a solution of 1-acetylpi-

perazine (0.47 g, 3.69 mmol) in dry MeCN (40 mL). The mixture was

heated to reflux under N₂for 6 h and then allowed to cool to room tem-

perature. The yellow solution was filtered and a yellow solid was ob-

tained after removal of the solvent under reduced pressure. The solid

was re-dissolved in CH₂Cl₂. The yellow solution was filtered, evaporated

to dryness and the bright yellow solid was purified by chromatography

upon silica gel (DCM:MeOH=95:5) as eluent and the first band was col-

lected. Removal of solvent afforded 4 as off-white solid (1.0 g, 85%

yield).

34.7 (C

N

27.3 (CONHCH₂CH₂CH₂), 27.0 ppm (NCH₂CH₂CH₂); IR: n˜ =3335,

3062, 3029, 2930 (s), 1735, 1653 (s), 1539 (s), 1472 (s), 1242, 894 cm^ꢀ1; MS

(FAB): m/z: 501 [M]⁺; elemental analysis calcd (%) for C₃₂H₄₀N₂O₃: C

76.8, H 8.0, N 5.6; found: C 77.2, H 8.2, N 5.8.

Ligand L²: 1,2-Diaminoethane (0.13 g, 0.0021 mol) in MeOH (50 mL)

was added to a stirred solution of 2b (1.93 g, 0.0042 mol) in CHCl₃

(50 mL). After stirring for 10 h the solvent was removed in vacuo to give

a yellow oil which was dissolved in CHCl₃(100 mL) and washed with

water (250 mL). The resulting solution was dried with MgSO₄, filtered

5-tert-Butyl-2-hydroxy-3-(piperazinomethyl)benzaldehyde (5): A solution

of compound 4 (0.55 g, 1.72 mmol) in HCl (2m, 15 mL) was heated under

reflux for 2 days. After cooling to room temperature, the mixture was

brought to pHꢁ7 with saturated Na₂CO₃, extracted with CHCl₃, dried

over Na₂SO₄and concentrated to yield 5-tert-butyl-2-hydroxy-3-(piperazi-

[1]

and evaporated in vacuo to yield L²as a yellow oil (1.93 g, 98%yield).

H NMR (250 MHz, CDCl₃, TMS): d=8.30 (s, 2H; N=CH), 7.57–7.52 (m,

4H; Ar-H), 7.42–7.20 (m, 20H; Ar-H), 7.07 (br, 2H; NHCO), 3.72 (s,

4H; NCH₂CCOH), 3.70 (s, 4H; CH=NCH₂), 3.64 (s, 4H; NCH₂Ar), 3.50

(q, J=6.5 Hz, 4H; CONHCH₂), 2.60 (t, J=6 Hz, 4H; CH₂CH₂N), 1.81

nomethyl)benzaldehyde as

a

yellow solid (70%yield).

¹H NMR

(quintet, J=5.8 Hz, 4H; CH₂CH₂CH₂), 1.26 ppm (s, 18H; C(CH₃)₃);

R

(300 MHz, CDCl₃, TMS): d=10.18 (s, 1H; CHO), 7.54 (s, 1H; aromatic),

7.30 (s, 1H; aromatic), 3.65 (s, 2H; CH₂), 2.97 (s, 4H; CH₂), 2.57 (s, 4H;

¹³C NMR (60 MHz, CDCl₃, TMS): d=167.8 (CONH), 167.3 (N=CH),

158.0 (Ar C), 141.5 (Ar C), 139.7 (Ar C), 135.4 (Ar C), 131.8 (Ar CH),

131.5 (Ar CH), 129.9 (Ar CH), 129.8 (Ar CH), 128.9 (Ar CH), 128.8 (Ar

CH), 128.7 (Ar CH), 127.7 (Ar CH), 126.4 (Ar C), 118.4 (Ar C), 60.2

(NCH₂CCOH), 59.5 (CH=NCH₂), 53.2 (NCH₂Ar), 52.5 (CONHCH₂),

CH₂), 2.07 (s, 3H CH₃), 1.22 ppm (s, 9H;

C

(CH₃)₃); ¹³C NMR

A

(67.93 MHz, CDCl₃, TMS): d=192.0, 159.3, 141.9, 133.1, 125.0, 122.8,

122.1, 60.6, 53.7, 45.9, 34.2, 31.4 ppm; MS (LR-ES): m/z: 277 [M+H]⁺; el-

emental analysis cacld (%) for C₁₆H₂₄N₂O₂·0.15CH₂Cl₂: C 67.09, H 8.47,

N 9.69: found: C 67.11, H 8.43, N 9.30.

39.8 (CH₂NCH₂CH₂), 34.6 (C

N

(CH₂CH₂CH₂); IR: n˜ =3325, 3060, 2952 (s), 1633 (s), 1538, 1273, 1026,

697 cm^ꢀ1

;

UV/Vis

(CHCl₃):

l_max(e)=261

(23342),

331 nm

5-tert-Butyl-2-hydroxy-3-{N’-(tert-butylurea)piperazinomethyl}benzalde-

hyde (6): tert-Butyl isocyanate (0.112 g, 1.1 mm) was dissolved in dry

(8616 dm³mol^ꢀ1cm^ꢀ1); FAB (MS): m/z: 941 [M]⁺; elemental analysis

calcd (%) for C₆₀H₇₂N₆O₄·2H₂O: C 73.7, H 7.8, N 8.6; found: C 73.6, H

8.0, N 8.2.

CH₂Cl₂(15 mL) and added to

a solution of compound 5 (0.183 g,

0.66 mmol) in dry CH₂Cl₂(25 mL), which was then stirred overnight at

room temperature under N₂. After removal of the solvent under reduced

pressure, the product was subjected to chromatography on silica gel

(EtOAc/hexane 8:2) to give 6 as a white solid (65%yield). ¹H NMR

(300 MHz, CDCl₃, TMS): d=10.22 (s, 1H; CHO), 7.61 (s, 1H; aromatic),

7.43 (s, 1H; aromatic), 4.32 (s, 1H; NH), 3.73 (s, 2H; CH₂), 3.40 (s, 4H;

Ligand L¹: This compound was prepared by a similar procedure to that

described for L²from 1b to give a yellow oil (95%yield). ¹H NMR

(250 MHz, CDCl₃, TMS): d=8.25 (s, 2H; N=CH), 7.76–7.72 (m, 4H; Ar-

H), 7.41–7.10 (m, 20H; Ar-H), 3.80 (s, 4H; NCH₂CCOH), 3.76 (s, 4H;

CH=NCH₂), 3.58 (s, 4H; NCH₂Ar), 3.57 (m, 4H; CONHCH₂), 2.69 (t,

CH₂), 2.57 (s, 4H; CH₂), 1.36 (s, 9H; C

(CH₃)₃).

N’-(1-tert-Butyl-3-acylurea)piperazine: A solution of 1-tert-butyl-3-(chlo-

roacetyl)urea (1.03 g, 5.24 mmol) in dry CH₃CN (10 mL) was added into

stirred mixture of piperazine (2.73 g, 31.44 mmol), K₂CO₃(1.10 g,

A

J=5.7 Hz, 4H; CH₂CH₂N), 1.22 ppm (s, 18H;

C

(CH₃)₃); ¹³C NMR

A

AHCTREUNG

(60 MHz, CDCl₃, TMS): d=167.7 (CONH), 167.6 (N=CH), 158.2 (Ar C),

141.5 (Ar C), 140.1 (Ar C), 135.7 (Ar C), 132.1 (Ar CH), 131.5 (Ar CH),

129.5 (Ar CH), 128.9 (Ar CH), 128.8 (Ar CH), 127.8 (Ar CH), 127.7 (Ar

CH), 127.6 (Ar CH), 126.3 (Ar C), 118.4 (Ar C), 60.2 (NCH₂CCOH),

58.9 (CH=NCH₂), 53.1 (NCH₂Ar), 52.4 (CONHCH₂), 37.5

A

a

7.92 mmol) and KI (25 mg) in dry CH₃CN (20 mL). The resulting mixture

was stirred at 808C under N₂for 3 h. The solvent was removed under re-

duced pressure and the residue was dissolved in water before extraction

with CH₂Cl₂, the extracts were dried over MgSO₄, and concentrated to

afford the product as a while solid (62%yield). ¹H NMR (300 MHz,

CDCl₃, TMS): d=8.92 (brs, 1H; NH), 8.22 (brs, 1H; NH), 3.04 (s, 2H;

(CH₂NCH₂CH₂), 34.5 (C

N

2962 (s), 1633 (s), 1479, 1277, 754 cm^ꢀ1; UV/Vis (CHCl₃): l_max(e)=263

(22800), 332 nm (8540 dm³mol^ꢀ1cm^ꢀ1); MS (FAB): m/z: 913 [M]⁺; ele-

mental analysis calcd (%) for C₅₈H₆₈N₆O₄·1.5H₂O: C 74.1, H 7.6, N 8.9;

found: C 74.2, H 7.6, N 9.0.

Ligand L³: This compound was prepared by a similar procedure to that

described for L²from 3b to give a light yellow oil (95%). ¹H NMR

(250 MHz, CDCl₃, TMS): d=8.36 (s, 2H; N=CH), 7.75–7.12 (m, 24H;

Ar-H), 6.30 (br, 2H; NHCO), 3.88 (s, 4H; NCH₂CCOH), 3.65 (s, 4H;

CH=NCH₂), 3.58 (s, 4H; NCH₂Ar), 3.35 (q, J=6.7 Hz, 4H; CONHCH₂),

CH₂), 2.95 (s, 4H; CH₂), 2.60 (s, 4H; CH₂), 1.40 ppm (s, 9H; C(CH₃)₃).

G

5-tert-Butyl-2-hydroxy-3-{N’-(1-tert-butyl-3-acylurea)piperazinomethyl}-

benzaldehyde (7): A solution of N’-(1-tert-butyl-3-acylurea)piperazine

(0.11 g, 0.45 mmol) in CH₃CN (10 mL) was added into a solution of 3-

bromomethyl-5-tert-butylsalicyclaldehyde (0.13 g, 0.48 mmol), K₂CO₃

(0.13 g, 0.94 mmol) and KI (ca 0.005 g) in CH₃CN (20 mL). The resulting

mixture was stirred at 808C under N₂overnight. After filtration, the sol-

vent was removed under reduced pressure and the residue was purified

by using preparative TLC on silica gel (EtOAc/hexane 8:2) to give 7 as a

yellow solid (63%yield). ¹H NMR (300 MHz, CDCl₃, TMS): d=10.24 (s,

1H; CHO), 8.85 (brs, 1H; NH), 8.21 (brs, 1H; NH), 7.62 (s, 1H; aromat-

ic H), 7.38 (s, 1H; aromatic H), 3.74 (s, 2H; CH₂), 3.10(s, 2H; CH₂), 2.65

2.44

CH₂NHCH₂CH₂CH₂CH₂CH₂), 1.29 (m, 8H; NHCH₂CH₂CH₂CH₂CH₂),

1.27 ppm (s, 18H; C

(CH₃)₃); ¹³C NMR (60 MHz, CDCl₃, TMS): d=168.1

(t,

J=7 Hz,

4H;

CH₂CH₂N),

1.53

(m,

8H;

ACHTREUNG

(CONH), 167.1 (N=CH), 157.5 (Ar C), 141.4 (Ar C), 140.7 (Ar C), 135.5

(Ar C), 131.9 (Ar CH), 130.7 (Ar CH), 129.3 (Ar CH), 129.1 (Ar CH),

128.7 (Ar CH), 127.5 (Ar CH), 127.3 (Ar CH), 127.1 (Ar C), 126.7 (Ar

CH), 118.3 (Ar C), 60.6 (NCH₂CCOH), 59.2 (CH=NCH₂), 54.3

(brs, 8H; CH₂), 1.31 (s, 9H;C

C

G

(NCH₂Ar), 52.3 (CONHCH₂), 40.6 (CH₂NCH₂CH₂), 34.6 (C

ACHTREUNG

(C(CH₃)₃), 30.2 (CONHCH₂CH₂), 27.7 (NCH₂CH₂),

A

(CONHCH₂CH₂CH₂), 27.5 ppm (NCH₂CH₂CH₂); IR: n˜ =3330, 3062,

2935 (s), 1630 (s), 1540, 1216, 745 cm^ꢀ1; UV/Vis (CHCl₃): l_max(e)=264

Chem. Eur. J. 2007, 13, 6091 – 6107

ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

6103

P. A. Tasker, M. Schrçder et al.

5-tert-Butyl-2-hydroxy-3-(N-isonipecotamidemethyl)benzaldehyde

(8):

50.2, 49.76, 32.89, 30.41, 27.79 ppm; IR: n˜ =3444 (NH, br), 1716 (C=O),

1633 (C=N), 1552 cm^ꢀ1(C=O); MS (LR-ES⁺): m/z: 890 [M+H]⁺; ele-

mental analysis calcd (%) for C₄₈H₇₆N₁₀O₆·CH₂Cl₂: C 64.84, H 8.62, N,

15.75; found: C 64.28, H 8.91, N 15.94.

Isonipecotamide (0.56 g, 4.43 mmol) was dissolved in dry MeCN (40 mL)

and to it was added 3-bromomethyl-5-tert-butyl-2-hydroxy-benzaldehyde

(1.20 g, 4.43 mmol) and KHCO₃(0.69 g, 6.9 mmol). The mixture was

heated to reflux under N₂for 6 h and then cooled to room temperature.

The yellow solution was filtered and a yellow solid obtained after remov-

al of solvent under reduced pressure. The solid was re-dissolved in

CH₂Cl₂, and the yellow solution was filtered. Removal of CH₂Cl₂from

the filtrate afforded the product as a yellow solid (98%yield). M.p. 150–

1538C (decomp); ¹H NMR (300 MHz, CDCl₃, TMS): d=10.24 ppm (s,

1H; CHO), 7.63 (d, J=2.49 Hz, 1H; aromatic H), 7.53 (d, J=2.49 Hz,

1H; aromatic H); 5.84 (br, 2H; NH₂), 3.84 (s, 2H; CH₂N), 3.18 (s, 1H),

3.14 (s, 1H), 2.37 (br, 3H), 1.98 (m, 4H), 1.32 ppm (s, 9H; CH₃);

¹³C NMR (67.93 MHz, CDCl₃, TMS): d=193.0 (CHO), 176.9 (CONH₂),

159.2, 142.3, 134.3, 126.4, 121.7, 58.8, 52.2, 41.3, 34.3, 31.4, 28.1 ppm; IR

(KBr): n˜ =1676 cm^ꢀ1(CHO, vs); MS (ES⁺): m/z: 319 [M+1]⁺; elemental

analysis calcd (%) for C₁₈H₂₆N₂O₃·0.45CH₂Cl₂: C 62.14, H 7.60, N 7.86;

found: C 62.21, H 7.63, N 7.60.

Ligand L⁷: A solution of 1,2-diaminoethane (0.035 g, 0.59 mmol) in dry

MeOH (10 mL) was added dropwise to

a solution of 8 (0.37 g,

1.16 mmol) in dried MeOH (15 mL). The yellow solution was stirred at

room temperature under N₂. After reaction for 24 h, the MeOH was re-

moved under reduced pressure to afford the product as bright yellow

solid (98%yield). M.p. 123–126 8C; ¹H NMR (300 MHz, CDCl₃, TMS):

d=8.41 (s, 2H; CH=N), 7.42 (d, J=2.40 Hz, 2H; aromatic H), 7.18 (d,

J=2.44 Hz, 2H; aromatic H), 5.69 (br, 2H; NH₂), 5.65 (br, 2H; NH₂),

3.93 (s, 4H; CH₂N=C), 3.63 (s, 4H; CH₂N), 3.05 (s, 2H; CH₂), 3.01 (s,

2H; CH₂), 2.15 (br, 4H; CH₂), 1.83 (m, 8H; CH₂), 1.30 ppm (s, 18H;

CH₃); ¹³C NMR (67.93 MHz, CDCl₃, TMS): d=177.9 (CONH₂), 166.4

(C=N), 157.2, 140.7, 131.0, 126.7, 117.8, 59.8, 56.3, 52.9, 42.6, 33.9, 31.4,

28.7 ppm; IR (KBr): n˜ =1665 (CONH₂, vs), 1632 cm^ꢀ1(C=N, vs); MS

(ES⁺): m/z: 661 [M+H]⁺; elemental analysis calcd (%) for

C₃₈H₅₆N₆O₄·2H₂O: C 65.49, H 8.68, N 12.06; found: C 65.36, H 8.44, N

11.68.

5-Nonyl-2-hydroxy-3-(N-isonipecotamidemethyl)benzaldehyde (9): Isoni-

pecotamide (0.51 g, 4.01 mmol) and KHCO₃(0.61 g, 6.10 mmol) were

added to 3-bromomethyl-5-nonyl-salicylaldehyde (1.37 g, 4.01 mmol) in

dry MeCN (30 mL) and KHCO₃(0.61 g, 6.1 mmol). The mixture was

heated at reflux for 6 h under N₂atmosphere. A similar work up to that

used for 8 afforded 9 as a yellow solid (88%yield). M.p. 85–88 8C;

¹H NMR (300 MHz, CDCl₃, TMS): d=10.16 (m, 1H; CHO), 7.53 (m,

1H; aromatic H), 7.26 (m, 1H; aromatic H), 6.13 (s, 1H; NH₂), 5.86 (s,

1H; NH₂), 3.75 (s, 2H; CH₂N), 3.04 (br, 2H; CH₂N), 2.24 (br, 1H;

CH₂CHCONH₂), 1.91 (br, 4H; CH₂CHCONH₂), 0.76–1.66 ppm (m, 19H;

nonyl-H); ¹³C NMR (67.93 MHz, CDCl₃, TMS): d=193.8, 176.8, 158.6,

158.5, 142.0, 139.3 (m), 135.8–136.4 (m), 121.0, 120.4, 57.3, 51.8, 51.3,

29.0–43.9 (m), 27.4–24.4 ppm (m); IR (KBr): n˜ =1663 cm^ꢀ1(CHO, vs);

MS (ES⁺): m/z: 389 [M+1]⁺; elemental analysis calcd (%) for

C₂₃H₃₆N₂O₃·0.75CH₂Cl₂: C 63.19, H 8.31, N 6.21; found: C 63.13, H 8.39,

N 6.32.

Ligand L⁸: This compound was prepared by a similar procedure to that

described for L⁷starting from 9. The isolated bright yellow solid was re-

dissolved in CH₂Cl₂and hexane added to precipitate the product which

was dried in vacuo (80%yield). M.p. 103–106 8C; ¹H NMR (300 MHz,

CDCl₃, TMS): d=8.42 (s, 2H; CH=N), 7.34 (m, 2H; aromatic H), 7.13

(m, 2H; aromatic H), 5.78 (br, 2H; NH₂), 5.70 (br, 2H; NH₂), 4.00 (s,

4H), 3.60 (s, 4H; CH₂N=C), 3.00, 2.98 (br, 2H each; CH₂N), 2.11 (m,

6H), 1.85 (m, 8H), 0.57–1.68 ppm (m, 38H; nonyl-H); ¹³C NMR

(67.93 MHz, CDCl₃, TMS): d=177.6, 166.7, 157.0, 140.0, 137.8, 132.5 (m),

128.0 (m), 124.2 (m), 117.6, 59.9, 56.2, 53.0, 42.8, 40.1–31.0 (m), 28.9,

24.0–8.0 (m) ppm; IR (KBr): n˜ =1632 cm^ꢀ1(C=N, vs); MS (ES⁺): m/z:

801 [M]⁺; elemental analysis calcd (%) C₄₈H₇₆N₆O₄·CH₂Cl₂·H₂O:

C

65.09, H 8.92, N 9.30; found: C 65.00, H 8.94, N 9.38.

General preparation of copper-only complexes [Cu

(L²ꢀ2H)] and [Cu(L³ꢀ2H)]: Solutions of the appropriate ligand

(1.4 mmol) in CHCl₃(30 mL) and Cu(CH₃COO)₂·H₂O (0.28 g, 1.4 mmol)

A

Ligand L⁴:

A solution of 4 (0.46 g, 1.44 mmol) with MgSO₄(0.27,

A

ACHTREUNG

2.25 mmol) and molecular sieves 4 (1 g) in dry CH₂Cl₂(20 mL) was

added into a solution of 1,2-diaminoethane (0.043 g, 0.72 mmol) in dry

CH₂Cl₂(3 mL). The resulting mixture was stirred at room temperature

under N₂overnight. After filtration, the mixture was recrystallized from

CHCl₃/Et₂O to give a yellow powder (84%yield). ¹H NMR (300 MHz,

CDCl₃, TMS): d=8.41(s, 2H; HC=N), 7.47 (s, 2H; aromatic), 7.19 (s,

2H; aromatic), 3.94 (s, 4H; CH₂N=), 3.64 (s, 8H; CH₂), 3.47 (s, 4H;

AHCTREUNG

in MeOH (50 mL) were mixed and stirred overnight. The solvent was re-

moved in vacuo to yield a black oil which was dissolved in CHCl₃

(60 mL) and washed with a pH 9 ammonia solution (230 mL). The re-

sulting organic phase was dried with MgSO₄, filtered and then concen-

trated in vacuo to yield the metal complex which was used without fur-

ther purification.

CH₂), 2.51 (s, 8H CH₂), 2.09 (s, 6H; CH₃), 1.31 ppm (s, 18H; C(CH₃)₃);

C

Data for [Cu

A

¹³C NMR (67.93 MHz, CDCl₃, TMS): d=169.0, 166.8, 157.4, 157.0, 140.9,

131.3, 127.2, 124.1, 117.9, 59.9, 56.2, 53.2, 52.8, 46.4, 41.5, 34.0, 31.5,

21.5 ppm; IR: n˜ =1636 (C=N), 1462 cm^ꢀ1(C=O); MS (LR-ES⁺): m/z:

661 [M+H]⁺; elemental analysis calcd (%) for C₃₈H₅₆N₆O₄: C 69.06, H

8.54, N 12.72; found: C 69.14, H 8.47, N 12.69.

a 0.001m solution in butan-1-ol: elemental analysis calcd (ppm) for

C₅₈H₆₆N₆O₄Cu: 78.9; found: 77.8; IR: n˜ =3337, 2962 (s), 1628 (s), 1539,

1444, 1216, 753 cm^ꢀ1; UV/Vis (CHCl₃): l_max(e)=280 (23600), 381 (9862),

572 nm (430 dm³mol^ꢀ1cm^ꢀ1); MS (FAB): m/z: 974 [M]⁺.

Data for [Cu

C

Ligand L⁵: This compound was prepared by a similar procedure to that

described for L⁴starting from 6 to give a bright yellow solid after recrys-

tallization from CHCl₃/Et₂O (70%yield). ¹H NMR (300 MHz, CDCl₃,

TMS): d=8.41(s, 2H; HC=N), 7.51 (s, 2H; aromatic), 7.14 (s, 2H; aro-

matic), 4.38 (s, 2H; NH), 3.94 (s, 4H; CH₂N=), 3.77 (s, 4H; CH₂), 3.37 (s,

8H; CH₂N), 2.52 (s, 8H; CH₂N), 1.35 (s, 18H; CH₃), 1.31 ppm (s, 18H;

CH₃); ¹³C NMR (67.93 MHz, CDCl₃, TMS): d=167.12 (C=N), 157.71,

157.50, 141.17, 131.60, 127.49, 124.23, 118.17, 60.17, 58.62, 56.47, 52.99,

51.13, 44.01, 31.78, 29.80 ppm; IR: n˜ =3417 (NH, br), 1636 (C=N),

1534 cm^ꢀ1(C=O); MS (LR-ES⁺): m/z: 776 [M+H]⁺; elemental analysis

calcd (%) for C₄₄H₇₀N₈O₄: C 68.18, H 9.10, N 14.46; found: C 68.28, H

9.19, N 14.44.

Ligand L⁶: This compound was prepared by a similar procedure to that

described for L⁴starting from 7 to give a yellow powder (34%yield).

¹H NMR (300 MHz, CDCl₃, TMS): d=8.92 (s, 2H; NH), 8.40 (s, 2H;

HC=N), 8.23 (s, 2H; NH), 7.40 (s, 2H; aromatic H), 7.18 (s, 2H; aromat-

ic H), 3.94 (s, 4H; CH₂N=), 3.64 (s, 4H; CH₂), 3.06 (s, 4H; CH₂), 2.60

a 0.002m solution in butan-1-ol: elemental analysis calcd (ppm) for

C₆₀H₇₀N₆O₄Cu: 157.9; found: 157.0; IR: n˜ =3310, 2958 (s), 1624 (s), 1536,

1442, 1261, 697 cm^ꢀ1

UV/Vis (CHCl₃): l_max(e)=278 (24460), 381

(11672), 573 nm (400 dm³mol^ꢀ1cm^ꢀ1); MS (FAB): m/z: 1003 [M]⁺.

Data for [Cu

a 0.001m solution in butan-1-ol: elemental analysis calcd (ppm) for

C₆₆H₈₂N₆O₄Cu: 78.9; found: 79.7; IR: n˜ =3313, 2933 (s), 1626 (s), 1538,

1443, 754 cm^ꢀ1; UV/Vis (CHCl₃): l_max(e)=281 (25800), 382 (10514),

565 nm (450 dm³mol^ꢀ1cm^ꢀ1); MS (FAB): m/z: 1086 [M]⁺.

Nickel(II) and copper(II) complexes of L⁴–L⁸: A solution of the appro-

priate ligand (0.3 mmol) in MeOH (5 mL) was added to a stired solution

of the appropriate nickel(II)/copper(II) salt (0.3 mmol) in MeOH

(5 mL). Colour changes due to complexation were rapid and after 12 h

water (5 mL) was added before the solutions were left to evaporate. The

powders obtained were collected by filtration and dried in vacuo.

Data for [Ni(L⁴)SO₄]: Red microcrystalline solid, which was recrystal-

lised by vapour diffusion of hexane into a solution of the complex in

CHCl₃(53%yield). ¹H NMR (300 MHz, CDCl₃, TMS): d=7.72 (s, 2H;

HC=N), 7.30 (s, 2H; aromatic), 7.25 (s, 2H; aromatic), 4.30 (s, 4H; CH₂),

(brs, 16H; CH₂), 1.39 (s, 18H; C

U

G

150.19, 139.65, 130.18, 126.07, 122.99, 116.81, 60.56, 58.85, 52.43, 51.78,

6104

www.chemeurj.org

ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2007, 13, 6091 – 6107

Anion Selectivity

FULL PAPER

3.94 (s, 8H; CH₂), 3.52 (s, 4H; CH₂), 3.04 (s, 8H; CH₂), 2.02 (s, 6H;

NH₂), 3.63 (s, 4H; C=NCH₂), 3.37 (s, 4H; NCH₂Ph), 3.01 (d, J=11.2 Hz,

4H; isonipecotamide protons), 2.16 (m, 6H; CH₂, isonipecotamide pro-

tons), 1.77 (m, 8H; CH₂, isonipecotamide protons), 1.24 ppm (s, 18H;

CH₃); ¹H NMR (300 MHz, CD₃OD, TMS): d=7.77 (s, 2H; N=CH), 7.42

(d, J=2.24 Hz, 2H; aromatic H), 7.13 (d, J=2.31 Hz, 2H; aromatic H),

3.65 (s, 4H; C=NCH₂), 3.43 (s, 4H; NCH₂Ph), 3.03, 3.29 (s, 2H each, iso-

nipecotamide protons), 2.21 (m, 6H), 1.79 (m, 8H), 1.27 ppm (s, 18H;

CH₃); IR: n˜ =1666 (CONH₂), 1619 cm^ꢀ1(C=N); MS (ES⁺): m/z: 717

[M]⁺; elemental analysis calcd (%) for C₃₈H₅₄N₆NiO₄·0.3CHCl₃·CH₃OH:

C 60.20, H 7.44, N 10.72; found: C 60.09, H 7.44, N 10.75.

CH₃), 1.26 ppm (s, 18H; C

C

A

analysis calcd (%) for C₃₈H₅₈N₆O₈NiS·CHCl₃: C 50.10, H 6.14, N 8.99;

found: C 49.49, H 6.63, N 8.85.

Data for [Ni(L⁵)SO₄]: Red microcrystalline solid (87%yield); ¹H NMR

(300 MHz, CDCl₃, TMS): d=7.58 (s, 2H; HC=N), 7.42 (s, 2H; aromatic),

7.07 (s, 2H; aromatic), 3.72 (brs, 4H; CH₂), 3.52 (brs, 8H; CH₂), 2.58 (s,

4H; CH₂), 1.75 (s, 8H; CH₂), 1.34 (s, 18H; C(CH₃)₃), 1.28 ppm (s, 18H;

G

C

(CH₃)₃); IR: n˜ =3452 (NH, br), 1624 (C=N), 1545 cm^ꢀ1(C=O); MS

A

Complex [Cu

lar to that used for [Ni

very dark red powder (90%yield). IR (KBr): n˜ =1664 (CONH₂),

1629 cm^ꢀ1(C=N); MS (ES⁺): m/z: 722 [M]⁺; elemental analysis calcd

(%) for C₃₈H₅₄N₆CuO₄·1.25CHCl₃·CH₃OH: C 53.50, H 6.61, N 9.30;

found: C 53.54, H 6.68, N 9.66.

(L⁷ꢀ2H)]: This complex was prepared by a procedure simi-

(LR-ES⁺): m/z: 831 [Ni

calcd (%) for C₄₄H₇₀N₈O₈NiS: C 56.83, H 7.59, N 12.05; found: C 56.86,

H 7.87, N 12.10.

(L⁵ꢀH)]⁺, 416 [Ni(L⁵)]²⁺; elemental analysis

ACHTREUNG

Data for [Ni(L⁶)SO₄]: Orange solid (90%yield); ¹H NMR (300 MHz,

CDCl₃, TMS): d=9.03 (s, 2H; NH), 8.28 (s, 2H; NH), 7.65 (s, 2H; HC=

N), 7.32 (s, 2H; aromatic H), 7.24 (s, 2H; aromatic H), 4.34 (s, 4H;

CH₂), 3.58 (s, 4H; CH₂), 3.50(s, 4H; CH₂), 3.27 (s, 8H; CH₂), 2.83 (brs,

Complex [Ni

lar to that used for [Ni

A

(L⁷ꢀ2H)] from [Ni(L⁸)SO₄]. It was obtained as an

8H; CH₂), 1.35 (s, 18H; C

N

orange solid (94%yield). ¹H NMR (300 MHz, CDCl₃, TMS): d=7.55 (s,

2H; N=CH), 6.83, 6.91, 7.24, 7.28 (br, 1H each; Ph-H), 6.33 (br, 2H;

NH₂), 5.90 (br, 2H; NH₂), 3.59 (s, 4H; C=NCH₂), 3.38 (s, 4H; NCH₂Ph),

2.85, 2.02, 2.19, 2.98 (br, 16H; CH₂isonipecotamide group), 0.60–

1.65 ppm (m, 38H; nonyl); IR: n˜ =1670 (CO, s), 1618 cm^ꢀ1(C=N, vs);

MS (ES⁺): m/z: 857 [M]⁺, 429 [M+H]²⁺; elemental analysis calcd (%)

for C₄₈H₇₄N₆NiO₄·0.8CHCl₃·CH₃OH: C 60.70, H 8.06, N 8.53; found C

60.72, H 8.00, N 8.24.

3452 (NH, br), 1706 (C=O), 1629 (C=N), 1557 cm^ꢀ1(C=O); MS (LR-ES⁺

): m/z: 946 [Ni(L⁶)]⁺, 473 [Ni(L⁶)]²⁺; elemental analysis calcd (%) for

C₄₈H₇₆N₁₀O₁₀NiS: C 55.22, H 7.34, N 13.42; found: C 55.08, H 7.44, N

13.34.

Data for [Ni(L⁶)(BF₄)₂]: Orange solid (82%yield); ¹H NMR (300 MHz,

G

CDCl₃, TMS): d=8.63 (s, 2H; NH), 8.19 (s, 2H; NH), 7.67 (s, 2H; HC=

N), 7.45 (s, 2H; aromatic H), 7.31 (s, 2H; aromatic H), 4.35 (s, 4H;

CH₂), 3.52 (s, 8H; CH₂), 3.18 (s, 8H; CH₂), 2.96 (brs, 8H; CH₂), 1.37 (s,

Complex [Cu

lar to that used for [Ni

A

18H; C

(C=O), 1624 (C=N), 1552 cm^ꢀ1(C=O); MS (LR-ES⁺): m/z: 946

[Ni(L⁶)]⁺, 473 [Ni(L⁶)]²⁺

elemental analysis calcd (%) for

A

G

(L⁷ꢀ2H)] from [Cu(L⁸)SO₄]. It was obtained as a

dark red solid (90%yield). n˜ =1664 (CO, s), 1624 cm^ꢀ1(C=N, vs); MS

(ES⁺): m/z: 432 [M+2H]²⁺, 862 [M]⁺.

;

Ni₁B₂F₈C₄₈H₇₆N₁₀O₆: C 51.41, H 6.83, N 12.49; found: C 51.50, H 6.73, N

12.51.

2ꢀ

Solvent extraction of SO₄or Cl^ꢀby the copper-only complexes [Cu-

A

Data for [Ni(L⁷)SO₄]: Orange-yellow solid (85%yield);

¹H NMR

were prepared with pH values in the range 0–7. An aliqout of each aque-

ous solution (10 mL) was intimately mixed with a 0.01m solution of the

copper-only complex in CHCl₃(10 mL), at 208C, for 16 h to ensure equi-

libration. The organic layers were separated and 2 mL aliquots were re-

moved from each for copper and sulfur or Cl^ꢀanalysis. The metal and

sulfur content of the organic phase was analysed by ICP-OES and the

Cl^ꢀcontent was determined using a chloride selective electrode.

(300 MHz, CD₃OD, TMS): d=7.90 ppm (s, 2H; CH=N), 7.50 (d, J=

2.41 Hz, 2H; Ph-H), 7.41 (d, J=2.35 Hz, 2H; Ph-H), 4.28 (s, 4H; C=

NCH₂), 3.48 (s, 4H; CH₂N), 2.81 (br, 4H; CH₂), 2.44 (br, 4H; CH₂), 2.16

(br, 6H; CH₂, CHCONH₂), 1.52 (br, 4H; CH₂), 1.32 (s, 18H; CH₃); IR:

n˜ =1664 (CONH₂), 1625

C

m/z: 717 [Ni

A

C₃₈H₅₆N₆NiO₈S·CH₃OH·4H₂O: C 50.93, H 7.45, N 9.14; found: C 51.02,

H 7.19, N 9.41.

UV/Vis titrations: Titration experiments followed by UV/Vis spectrosco-

py were performed using 0.05 mm solutions of the copper-only complexes

containing various concentrations (0–5 equiv) of HCl or H₂SO₄in isopro-

panol and recording the resultant spectra.

Data for [Cu(L⁷)SO₄]: A black solid (80%yield); n˜ =1664 (CONH₂),

1636 (C=N), 621 cm^ꢀ1(SO₄); MS (ES⁺): m/z: 722 [Cu(L⁷)]⁺, 820

[M+H]⁺;

elemental

analysis

calcd

(%)

for

Membrane transport of anions: [Cu

C

G

C₃₈H₅₆N₆CuO₈S·CH₃OH·4.5H₂O: C 50.17, H 7.45, N 9.00; found: C

50.12, H 7.05, N 9.17.

A

a CHCl₃(50 mL) bulk liquid membrane. Details of the cell design have

been reported previously.^[40]It was assumed that transport occurs by

means of a symport mechanism^[36]in which the anion(s) and protons are

co-complexed and co-transported. The source phase consisted of 10 mL

of a 0.1m solution of anion(s) at pH 1.8Æ0.1 except for the transport ex-

Data for [Ni

A

using the nickel(II) acetate salt to give an orange solid (95%yield).

¹H NMR (300 MHz, CDCl₃, TMS): d=8.96 (s, 2H; NH), 8.24 (s, 2H;

NH), 7.54 (s, 2H; HC=N), 7.32 (s, 2H; aromatic H), 6.98 (s, 2H; aromat-

ic H), 3.66 (s, 4H; CH₂), 3.39 (s, 4H; CH₂), 3.09 (s, 4H; CH₂), 2.64 (s,

ꢀ

periment employing a SO₄^2ꢀ/H₂PO₄mixture, which had a pH of 3.3Æ

16H; CH₂), 2.16 (brs, 6H; CH₃CO₂^ꢀ), 1.38 (s, 18H; C

(s, 18H; C

1547 cm^ꢀ1(C=O); MS (LR-ES⁺): m/z: 946 [Ni

(L⁶ꢀ2H)]²⁺; elemental analysis calcd (%) for C₄₈H₇₄N₁₀O₆Ni: C 60.95, H

7.89, N 14.81; found: C 61.05, H 7.75, N 14.83.

ACHTREUNG

0.1. The receiving phase (30 mL) was either a pH 5.2Æ0.1 citric acid/

ACHTREUNG

sodium citrate 0.01m buffer solution or

a

AHCTREUNG

Na₂HPO₄50 mm buffer solution. All three phases in the transport cell

were stirred at 258C, for 23 h, and the rate of transport was determined

by analysing the anion concentration(s) in the receiving phase by using a

Dionex DX-100 ion chromatograph. Experimental uncertainty in the re-

corded rates is Æ5%.

ACHTREUNG

Metal-only complexes of L⁷and L⁸: These complexes were prepared as

2ꢀ

follows for SO₄^2ꢀ-loading studies, but the solubilities of their SO₄com-

plexes in CHCl₃were too low to allow results to be compared with those

Potentiometric titrations: The protonation constants for the di-basic

of L¹–L³.

copper-only complex of ligand [Cu

C

2ꢀ

Complex [Ni

A

MeOH (3 mL) was added to [Ni(L⁷)SO₄] (0.061 g, 0.075 mmol) in dry

MeOH (8 mL). The mixture was stirred at room temperature for 4.5 h,

and the yellow precipitate was collected, washed with small amounts of

MeOH and Et₂O and extracted into CHCl₃. Evaporation gave the prod-

uct as a yellow solid which was dried in vacuo (65%yield). ¹H NMR

(300 MHz, CDCl₃, TMS): d=7.54 (s, 2H; N=CH), 7.39 (d, J=2.24 Hz,

2H; aromatic H), 6.98 (d, J=2.31 Hz, 2H; aromatic H), 5.81 (br, 4H;

conventional potentiometric (pH) titration procedure. HSO₄was added

as its tetrabutylammonium hydrogen sulfate salt and Cl^ꢀas its tetrapro-

pylammonium chloride salt to the respective solutions to be titrated. All

measurements were performed in 95%methanol at 25 Æ0.18C (I=0.1;

[Et₄N]ClO₄). The concentration of [Cu

A

1 mm. Analytical grade methanol was fractionated and distilled over mag-

nesium before use. The potentiometric titration apparatus consisted of a

Chem. Eur. J. 2007, 13, 6091 – 6107

ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemeurj.org

6105

P. A. Tasker, M. Schrçder et al.

water-jacketed titration vessel and a water-jacketed calomel reference

electrode, connected by a salt bridge. A Philips glass electrode (GA-110)

was used for all pH measurements. [Et₄N]ClO₄(0.1m), used as the back-

ground electrolyte, was also employed in the salt bridge, while the calo-

mel reference electrode contained [Et₄N]ClO₄(0.09m) and [Et₄N]Cl

19.037(2), b=19.768(2), c=22.353(3) , a=65.593(2), b=64.947(2), g=

73.545(2), V=6879.5(14) ³, 1_cald=1.129 gcm^ꢀ3, Z=6, T=150(2) K, m-

A

(R_int)=30905 (0.069), R₁=0.087 [F>4s(F)], wR₂=0.251 for all data;

crystal colour: orange; shape: sphenoid; size: 0.820.260.12 mm³.

(0.01m) in 95%methanol. Methanol-saturated N was bubbled through

2

CCDC-623271–623275 contain the supplementary crystallographic data

for this paper. These data can be obtained free of charge from The Cam-

bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_

request/cif.

the solution in the measuring cell and tetraethylammonium hydroxide so-

lution was introduced into the cell by using a Metrohm Dosimat 665 au-

tomatic titration apparatus under PC control. A Corning model 130 Re-

search pH meter was employed for the pH determinations. The data sets

obtained from these experiments were processed by using a local version

of MINIQUAD.^[41]Precipitation occurred at high pH (>10), but in each

case sufficient data had been obtained by this stage to allow the determi-

nation of the two protonation constants. All protonation constants are

the mean of at least three individual determinations.

Acknowledgements

X-ray structure determinations

Data collection and processing: Single-crystal diffraction data for L⁶,

We thank the EPSRC (UK), the University of Nottingham, and the Aus-

tralian Research Council for support, and the National Mass Spectrome-

try Service at the University of Wales, Swansea (UK) for mass spectra.

L.L. acknowledges receipt of a research fellowship from the Royal Soci-

ety/Sino-British Trust, and S.G.G. for an Outgoing Research Fellowship

from the Royal Society. We thank CCLRC for the award of the beam

time on Station 9.8 and Dr. John E. Warren for his assistance. M.S. grate-

fully acknowledges receipt of a Royal Society Wolfson Merit Award and

of a Royal Society Leverhulme Trust Senior Research Fellowship.

[Ni(L⁵)SO₄] and [Ni

A

a either a Bruker

SMART1000 CCD or APEX area detector diffractometer,^[42]equipped

with an Oxford Cryosystem open-flow nitrogen cryostat,^[43]using graph-

ite-monochromated Mo_Karadiation (l=0.71073 ). Data for both com-

plexes of [Ni(L⁶)SO₄] reported herein were collected on Station 9.8 at

the Daresbury SRS, using synchrotron radiation (l=0.6902 ). Integrat-

ed intensities, corrected for Lorentz and polarization effects, were ob-

tained using the Bruker SAINT package,^[44]as were the cell parameters.

Data were corrected for absorption using a multi-scan method.

[1] J. Szymanowski, Hydroxyoximes and Copper Hydrometallurgy,

CRC, London, 1993.

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tion Chemistry II (Ed.: J. A. McCleverty, T. B. Meyer), Elsevier,

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Structure solution and refinement: The crystal structures were solved by

direct methods except for that of [Ni

A

heavy atom methods and all structures were refined on F²using

SHELXL-97.^[46]All ordered non-hydrogen atoms were refined with ani-

sotropic thermal parameters. All hydrogen atoms were placed in geomet-

rically calculated positions, except NH and OH atoms, which were locat-

ed from difference Fourier maps and subsequently included as part of a

riding model, except those of the H₂O in Ni(5) for which the positional

parameters were refined. Disorder was present in a number of tBu

groups and solvent molecules in all structures of the complexes. Details

of the modelling are given in the deposited CIFs.

Crystal data for L⁶: Formula: C₄₈H₇₆N₁₀O₆, M_r=889.19, monoclinic, space

group P2₁/n (non-standard setting of P2₁/c, no. 14), a=6.3692(9), b=

21.174(3), c=19.273(3) , b=92.211(3), V=2597.2(10) ³, 1_cald

=

1.137 gcm^ꢀ3, Z=2, T=150(2) K, m(Mo_Ka)=0.076 mm^ꢀ1, reflections col-

A

lected=16237, unique reflections, (R_int)=5888 (0.036), R₁=0.041 [F>

4s(F)], wR₂=0.110 for all data; crystal colour: yellow; shape: tablet;

size: 0.330.250.09 mm³.

Crystal data for [Ni(L⁵)SO₄]·8H₂O·2MeOH: Formula C₄₆H₉₄N₈NiO₁₈S,

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2987.

Ni[C₄₄H₇₀O₄N₈]SO₄·8H₂O·2CH₃OH, M_r=1138.06, triclinic, space group

¯

P1, a=13.349(2), b=14.247(2), c=15.576(2) , a=92.161(2), b=

96.629(2), g=93.931(2)8, V=2932.5(7) ³, 1_cald=1.289 gcm^ꢀ3, Z=2, T=

150(2) K, m

(Mo_Ka)=0.439 mm^ꢀ1, reflections collected=26664, unique re-

G

flections (R_int)=13107 (0.030), R₁=0.065 [F>4s(F)], wR₂=0.188 for all

data; crystal colour: orange; shape: needle; size: 0.630.130.11 mm³.

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[14] R. Custelcean, L. H. Delmau, B. A. Moyer, J. L. Sessler, W.-S. Cho,

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Chem. 2005, 117, 2593; Angew. Chem. Int. Ed. 2005, 44, 2537.

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Crystal

data

for

[Ni(L⁶)SO₄]·1.75H₂O·2.25MeOH:

Formula:

¯

C

_50.25H_88.5N₁₀NiO₁₄S, M_r=1147.58, triclinic, space group P1, a=14.5518

(4), b=14.5716(4), c=15.3812(5) , a=71.5760(4), b=76.0602(4), g=

83.9082(4)8, V=3001.6(2) ³, 1_cald=1.270 gcm^ꢀ3, Z=2, T=150(2) K, m-

A

(R_int)=17445 (0.023), R₁=0.053 [F>4s(F)], wR₂=0. 158 for all data;

crystal colour: red; shape: plate; size: 0.130.130.02 mm³.

Crystal data for [Ni(L⁶)SO₄]·7.5H₂O: Formula: C₄₈H₉₁N₁₀NiO_17.5S, M_r=

¯

1179.08, triclinic, space group P1, a=10.733(2), b=19.913(4), c=

29.059(6) , a=75.732(3), b=87.738(3), g=81.260(3)8, V=5949(2) ³,

1_cald=1.310 gcm^ꢀ3

,

Z=2, T=150(2) K,

m , reflec-

(0.6902)=0.435 mm^ꢀ1

A

tions collected=50235, unique reflections (R_int)=24152 (0.110), R₁=

0.084 [F>4s(F)], wR₂=0.225; crystal colour: red; shape: lath; size:

0.2550.0570.014 mm³.

Crystal

data

for

[Ni

A

Formula:

¯

C

_39.08H_56.08Cl_1.25N₆NiO_4.17

,

M_r=779.67; triclinic, space group P1, a=

6106

www.chemeurj.org

ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Chem. Eur. J. 2007, 13, 6091 – 6107

Anion Selectivity

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Received: December 23, 2006

Published online: May 3, 2007

Chem. Eur. J. 2007, 13, 6091 – 6107

ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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6107

Article Doi

Anion selectivity in zwitterionic amide-functionalised metal salt extractants

DOI: 10.1002/chem.200601874

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Article abstract of DOI:10.1002/chem.200601874

Full text of DOI:10.1002/chem.200601874

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