Design of base metal extractants. Part 1. Inter-ligand hydrogen bonding in the assembly of pseudo-macrocyclic bis(aminosulfonamidato)M(ii) complexes

Article abstract of DOI:10.1039/b515650p

Monosulfonyl derivatives of simple 1,2- and 1,3-diamines (R ²HN-R-NHSO₂R¹ = L) have been shown to be easily deprotonated to give neutral 2: 1 complexes, [M(L - H)₂], with Co(ii), Ni(ii), Cu(ii) or Zn(ii). The Ni

Full text of DOI:10.1039/b515650p

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
Design of base metal extractants. Part 1. Inter-ligand hydrogen bonding in the
assembly of pseudo-macrocyclic bis(aminosulfonamidato)M(II) complexes†
Clare Squires,a Christopher W. Baxter,a John Campbell,b Leonard F. Lindoy,*c Hamish McNab,a
Andrew Parkin,a Simon Parsons,a Peter A. Tasker,*a Gang Weic and David J. Whitea
Received 3rd November 2005, Accepted 17th January 2006
First published as an Advance Article on the web 1st February 2006
DOI: 10.1039/b515650p
Monosulfonyl derivatives of simple 1,2- and 1,3-diamines (R2HN–R–NHSO2R1 = L) have been shown
to be easily deprotonated to give neutral 2 : 1 complexes, [M(L − H)2], with Co(II), Ni(II), Cu(II) or
Zn(II). The Ni(II) and Cu(II) complexes with deprotonated N-tosyl-1,2-diaminoethane have a planar
2−
N4 donor set and a 14-membered pseudo-macrocyclic structure based on head-to-tail
=
S O · · · H–N(amine) bonding between the two bidentate ligands. In the related tetrahedral Zn(II) complex
−
the ends of the mutually perpendicular bidentate N2 units are too far apart to form a cyclic H-bonded
system. X-Ray structure determinations on five free ligands provide evidence for extensive
inter-molecular H-bonding, which in the case of N-tosyl-1,3-diaminopropane and its Nꢀ-tert-butyl
derivative involves formation of dimeric 16-membered pseudo-macrocycles. Despite favourable
inter-ligand H-bonding in the neutral 2 : 1 complexes, these ligands are relatively weak extractants,
showing >50% loading of Cu(II) in “pH-swing” equilibria, 2 L(org) + M2+ = [M(L − H)2](org) + 2 H+, only
when the pH of the aqueous phase is raised above 4.
Introduction
Phenolic oximes (I, Fig. 1) are one of the most important
types of metal solvent extractant1,2 and are currently used in
hydrometallurgical processes accounting for approximately one
third of the world’s production of copper.3
The efficacy of these reagents in pH-controlled extraction
processes4 is thought to depend on the formation of pseudo-
macrocyclic complexes (II in Fig. 1) involving H-bonding between
the oximic protons and the phenolate oxygen atoms.5 This
2−
generates an N2O2 donor set cavity which gives a very good
fit for planar Cu(II) ions and, coupled to the Irving–Williams
order,6 ensures a high selectivity of extraction over other di-
and tri-valent metals of the first transition series. The use of
inter-ligand hydrogen bonding represents an immediately practical
application of supramolecular chemistry, in principle providing a
way of assembling highly organized donor sets using very simple
ligands, thus allowing control of the “strength” and selectivity
Fig. 1 Commercial phenolic oxime extractants I and their pseudo-
of metal transport with inexpensive reagents. In this paper we
examine the option of using monosulfonamide derivatives of
simple a,x-diamines to achieve head-to-tail H-bonding in a pH-
swing equilibrium (Scheme 1). Deprotonation of the sulfonamido
nitrogen atoms on the formation of complexes with metal dications
generates7 neutral species which offer the possibility of good solu-
bility in hydrocarbon solvents of the types used commercially. The
geometry of the N42− donor set in these complexes is determined in
macrocyclic copper complexes II (a variety of R1 and R2 substituents
is used to impart kerosene-solubility and to tune reagent strength),1,2
and sulfonamide ligands related to those described in this paper; III, a
dansylamido-azamacrocycle Zn-fluorophore,11 IV, the LIX34 reagent,31
and V, 2-aminobenzophenoneoximes33 related to I.
part by the requirements of the two types of chelate rings. Rational
design of systems to present planar or tetrahedral donor sets of
differing cavity sizes requires an understanding of the preferred
geometry of the six-membered H-bonded ring and of effects of
variation of the bridge in mono-deprotonated aliphatic diamines,
neither of which have been extensively studied previously. It is also
of interest to consider whether pre-organization of the donor-sets
by formation of dimers (Scheme 1) occurs in a manner analogous
to the phenolic oxime reagents in hydrocarbon solvents.5
aSchool of Chemistry, The University of Edinburgh, Edinburgh, UK EH9
3JJ. E-mail: p.a.tasker@ed.ac.uk
bCytec Industries Ltd., Blackley, Manchester, UK M9 8ZS
cCentre for Heavy Metals Research, School of Chemistry F11, University of
Sydney, N.S.W., 2006, Australia
† Electronic supplementary information (ESI) available: Additional
preparative details and hydrogen bonding parameters. See DOI:
10.1039/b515650p
2026 | Dalton Trans., 2006, 2026–2034
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
this unit is linked via a pendant 2-aminoethyl- or 3-aminopropyl-
group onto an azamacrocycle, see for example III in Fig. 1, the re-
sulting reagents have a very high affinity for zinc.11 Disulfonamide
derivatives of aliphatic 1,2-diamines can function as dianionic
ligands, and form stable complexes with metals in higher oxidation
states. Titanium,12–15 aluminium,16–20 ruthenium,21–23 boron,19,24,25
magnesium,26 zinc,27,28 and lanthanide29 complexes of chiral 1,2-
diaminosulfonamides have been used as catalysts in a wide range
of asymmetric syntheses.
Reports on the use of sulfonamide ligands as metal extrac-
tants include 1,2-bis(n-octylsulfonamido)benzene, LH2, in the
presence of 4-benzylpyridine which extracts Cu(II) or Zn(II)
into toluene as the neutral complex [ML(4-Bzpy)2].30 The 8-
aminoquinoline reagent LIX34 (IV in Fig. 1) was considered31
as a “pH-swing” reagent for recovery of Cu(II) from sulfate
streams and subsequently complexes of sulfonyl derivatives of 2-
pyridylalkylamine were reported as models with N42− donor sets.32
Arylsulfonyl derivatives of 2-aminobenzophenone oxime (V in
Fig. 1) were suggested33 as alternatives to the commercial phenolic
oxime reagents, and subsequently shown34 to be strong extrac-
tants for Cu(II). Sulfonyl-thiosemicarbazides,35 2-aminophenols,36
aminothiadiazoles,37 pyridines and other N-heterocycles,38 and
hydrazines39 have all been claimed in patents to extract base metal
cations, but in most cases the coordination chemistry involved has
not been described.
Scheme 1 The formation of pseudo-macrocyclic complexes accompany-
ing uptake of M2+ ions by water-immiscible solutions of aminosulfon-
amidato ligands.
In this paper we describe the coordination chemistry of the
mono-sulfonyl derivatives of 1,2-ethane-, 1,3-propane- and o-
phenylene-diamines (Fig. 2) and compare the inter-ligand hydro-
gen bonding in assemblies of the ligands and in their complexes
with Co(II), Ni(II), Cu(II) and Zn(II) ions (Table 1).
Experimental
All operations were carried out in air. Chemicals and solvents
(reagent grade or better) obtained from Aldrich or Acros were used
without further purification. Melting points were determined with
a Gallenkamp apparatus and are uncorrected. Elemental analyses
were performed on a Perkin Elmer 2400 or Carlo Erba 1108
elemental analyser. IR spectra were obtained on a Perkin Elmer
Paragon 1000 FT-IR spectrometer as KBr discs or as thin films on
NaCl plates. 1H and 13C NMR spectra were run on Bruker WP200,
AC250 or AVANCE DPX360 spectrometers. Chemical shifts (d)
are reported in ppm with residual solvent signals as internal
standards. Electron impact (EI) mass spectra were obtained either
on a Finnigan MAT4600 quadrupole spectrometer or on a Kratos
MS50TC spectrometer, fast atom bombardment (FAB) spectra
on a Kratos MS50TC spectrometer in acetonitrile/3-nitrobenzyl
alcohol/thioglycerol matrices, and electrospray (ESI) spectra on
a Thermoquest LCQ spectrometer in methanol. Metal analyses
for solvent extraction experiments were carried out by inductively
coupled plasma optical emission spectroscopy on a Thermo Jarrell
Ash IRIS ICP-OES spectrometer. The pH-dependence of Cu-
loading of 4 and 8 was determined by stirring dichloromethane
solutions (10 ml, 0.1 M) of [Cu(4 − H)2] or [Cu(8 − H)2] with
aqueous solutions (10 ml) containing different concentrations of
sulfuric acid for 16 h. The equilibrium pH was recorded using
a Fisher Scientific AR50 pH meter and solutions analysed as
described previously.40 Potentiometric titrations were carried out
in a sealed double jacket glass cell using a Metrohm 665 automated
burette and a Corning 130 digital pH meter fitted with a Phillips
glass electrode and a calomel electrode. Titrations were fully
Fig. 2 Potentially bidentate aminosulfonamido ligands.
Co(II), Ni(II) and Cu(II) complexes with both the mono- and di-
tosyl derivatives of o-phenylenediamine have been reported8–10 and
[Cu(1 − H)2(dmf)] characterised by X-ray crystallography.8 Dan-
sylamide derivatives are very effective zinc-fluorophores, and when
Table 1 Neutral complexes of the deprotonated monosulfonamidodi-
amines 1, 2, 4, 5, 8 and 10
Abbreviation
Complex
Abbreviation
Complex
12
13
14
15
16
17
18
19
[Zn(1 − H)2]a
[Ni(1 − H)2]a
[Co(1 − H)2]
[Cu(1 − H)2]
[Cu(2 − H)2]a
[Ni(4 − H)2]
[Co(4 − H)2]
[Cu(4 − H)2]
20
21
22
23
24
25
26
27
[Co(5 − H)2]
[Cu(5 − H)2]a,b
[Cu(5 − H)2]a,b
[Zn(5 − H)2]
[Cu(8 − H)2]
[Ni(10 − H)2]
[Cu(10 − H)2]
[Zn(10 − H)2]
automated and performed at 25.0
0.1 ◦C at constant ionic
a X-Ray crystal structures are reported for the complexes. b This complex
exists in blue and green polymorphs.
strength (I = 0.1, Et4NClO4 in 95% methanol which was 2 ×
10−3 mol dm−3 with respect to HClO4) under purified nitrogen
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2026–2034 | 2027
©

View Article Online
on solutions of ligand (ca. 1–2 × 10−3 mol dm−3) alone and
in the presence of varying concentrations of metal ion against
0.1 mol dm−3 Et4NOH, as described previously.41 All quoted log K
values represent the mean of data from at least two (and up
to four) titrations performed at different metal to ligand ratios.
Equilibrium constants were calculated from the potentiometric
data with the program MINIQUAD.42
N-(2-Aminophenyl)-4-methylbenzenesulfonamide (10) was pre-
pared by the method of Cheng et al.8 and N-(2-aminophenyl)-
4-tert-butylbenzenesulfonamide (11) by an adaptation of this
method (ESI†).
Synthesis of metal complexes
Bis[N - (2 - aminoethyl) - 4 - methylbenzenesulfonamidato]zinc(II)
(12). A solution of 1 (0.15 g, 0.7 mmol) and sodium hydroxide (0.7
mmol) in hot methanol (10 cm3) was added to a solution of zinc(II)
acetate dihydrate (77 mg, 0.35 mmol) also in methanol (10 cm3).
The solution was set aside at room temperature and white crystals
of 12 were collected after 3 days, washed with methanol (3 × 5 cm3)
and dried in vacuo (0.14 g, 81%) (Found: C, 41.7; H, 4.9; N, 12.2.
Calc. for C18H26N4O4S2Zn: C, 41.58; H, 5.4; N, 11.50%); IR (KBr
disc)/cm−1: 710w, 1599m, 1636w, 2858w, 2940w, 3346m; FAB MS,
m/z 491 (MH+, 66.2%).
Bis[N-(2-aminoethyl)-4-methylbenzenesulfonamidato]nickel(II)
(13) was similarly prepared from nickel(II) acetate as a beige
crystalline solid (83%). Crystals for X-ray structure determination
were obtained by the diffusion of toluene into a concentrated
solution in DMF (Found: C, 44.4; H, 4.9; N, 11.5. Calc. for
C18H26N4NiO4S2: C, 44.55; H, 5.40; N, 11.55%); IR (KBr
disc)/cm−1: 1178m, 1148w, 1599m, 1654w, 3327m; FAB MS, m/z
485 (MH+, 72.9%).
Ligand synthesis
N-(2-Aminoethyl)-4-methylbenzenesulfonamide (1) and N-(3-
aminopropyl)-4-methylbenzenesulfonamide (5) were prepared as
described by Kirsanov and Kirsanova.43
N-(2-Aminoethyl)-4-tert-butylbenzenesulfonamide (2) was pre-
pared by an adaptation of the procedures for 1 and 5.43
A
solution of 4-tert-butylbenzenesulfonyl chloride (12 g, 0.05 mol)
in toluene (100 cm3) was added dropwise over 8 h to a solution
of 1,2-diaminoethane (9.34 g, 0.16 mol) in toluene (100 cm3). The
precipitate was collected, washed with toluene (3 × 20 cm3) and
after recrystallisation from toluene (250 cm3) and washing with
diethyl ether (3 × 20 cm3) gave 2 as a white crystalline solid
(5.39 g, 40%), decomposition temperature >205 ◦C (Found: C,
55.9; H, 7.9; N, 11.0. Calc. for C12H20N2O2S: C, 56.22; H, 7.86; N,
10.93%); dH (CDCl3, 250 MHz): 1.29 (s, 9H, CH3), 2.76 (m, 2 H,
CH2), 2.48 (m, 2 H, CH2), 3.02 (s, 2 H, NH2), 7.47 (d, 2 H, J 7.5,
Ar CH), 7.75 (d, 2 H, J 7.7, Ar CH); dC (CDCl3, 63 MHz): 31
(3 C, CH3), 35 (Ar C(CH3)3), 41 (CH2), 45 (CH2), 126 (Ar CH),
127 (Ar CH), 137 (Ar C), 156 (Ar C); IR (KBr disc)/cm−1: 2922s,
2677s, 1601s, 1511s, 1327m, 1161m; EIMS, m/z 256 (M+, 20.0%).
The N-benzyl, N-2-ethylhexyl and N-n-butyl ligands 3, 4, 7, 8
and 9 were prepared by reductive amination of 1 or 5 with the
appropriate aldehyde.
N-(N-Benzyl-2-aminoethyl)-4-methylbenzenesulfonamide (3).
A solution of benzaldehyde (7.43 g, 0.07 mol) and 1 (15 g, 0.07
mol) in ethanol (200 cm3) was stirred at room temperature for 1 h.
Sodium borohydride (10.59 g, 0.33 mol) and a catalytic amount of
anhydrous sodium tetraborate (0.2 g, 1 mmol) were added and the
solution stirred for a further hour. Distilled water (100 cm3) was
added, the methanol removed in vacuo, and the product extracted
into dichloromethane (200 cm3) which was washed with water
(3 × 200 cm3), dried over anhydrous magnesium sulfate and
filtered. The solvent was removed in vacuo to yield a white
precipitate which was recrystallised from ethanol (100 cm3) to give
Bis[N-(2-aminoethyl)-4-methylbenzenesulfonamidato]cobalt(II)
(14) was similarly prepared from cobalt(II) acetate tetrahydrate as
a brown crystalline solid (ESI†).
Bis[N-(2-aminoethyl)-4-methylbenzenesulfonamidato]copper-
(II) (15). A solution of 1 (0.15 g, 0.7 mmol) in hot methanol (10 cm3)
was added to copper(II) acetate monohydrate (70 mg, 0.35 mmol)
in methanol (10 cm3). Purple crystals of 15 were collected after
the mixture had been allowed to stand for 16 h and washed with
methanol (5 cm3) and dried (0.13 g, 78%) (Found: C, 44.1; H, 5.2;
N, 11.5. Calc. for C18H26N4CuO4S2: C, 43.75; H, 5.30; N, 11.33%);
IR (KBr disc)/cm−1: 710w, 1178w, 1348w, 1603w, 2946w, 2819w,
3316s; ESMS, m/z 490 (MH+, 82.5%).
Bis[N-(2-aminoethyl)-4-tert-butylbenzenesulfonamidato]copper-
(II) (16) was similarly prepared as a purple crystalline solid (ESI†).
Bis{N-[N-(2-ethylhexyl)-2-aminoethyl]-4-methylbenzenesulfo-
namidato}nickel(II) (17): A solution of 4 (0.15 g, 0.46 mmol)
in hot methanol (10 cm3) was stirred for 30 min with nickel(II)
acetate tetrahydrate (57 mg, 0.23 mmol) in methanol (10 cm3).
Removal of ca. 15 cm3 of methanol in vacuo yielded an orange
oil which was triturated with hexane to give 17 as an orange
solid which was washed with small quantities of methanol and
dried in vacuo (0.19 g, 45%) (Found: C, 57.5; H, 8.2; N, 7.8. Calc.
for C34H58N4NiO4S2: C, 57.46; H, 8.22; N, 7.88%); IR data (KBr
disc)/cm−1: 669s, 971m, 1137m, 1279m, 1466w, 2343m, 2361m,
2929m, 3191m; FAB MS, m/z 709 (MH+, 77.8%).
◦
3 as a white crystalline solid (9.7 g, 46%), mp 78–80 C (Found:
C, 63.1; H, 6.6; N, 9.2. Calc. for C16H20N2O2S: C, 63.13; H, 6.62;
N, 9.20%); dH (CDCl3, 360 MHz): 2.44 (s, 3 H, CH3), 2.73 (m, 2
H, CH2), 3.03 (m, 2 H, CH2), 3.67 (s, 2 H, CH2), 7.29 (m, 7 H, Ar
CH), 7.76 (d, 2 H, J 8.3, Ar CH); dC (CDCl3, 90 MHz): 22 (CH3),
43 (CH2), 48(CH2), 53 (CH2), 128 (2 C, Ar CH), 128 (Ar CH), 129
(2 C, Ar CH), 129 (2 C, Ar CH), 130 (2 C, Ar CH), 137 (Ar C),
140 (Ar C), 144 (Ar C); IR (KBr disc)/cm−1: 748m, 1162s, 1332s,
1598w, 2850m, 3060w, 3450m; FAB MS, m/z 305 (MH+,100%).
N -[N -(2-Ethylhexyl)-2-aminoethyl]-4-methylbenzenesulfona-
mide (4), N-(3-aminopropyl)-4-tert-butylbenzenesulfonamide (6),
N-(N-benzyl-3-aminopropyl)-4-methylbenzenesulfonamide (7),
N-[N-(2-ethylhexyl)-3-aminopropyl]-4-methylbenzenesulfonamide
(8) and N-(N-butyl-3-amino-propyl)-4-methylbenzenesulfona-
mide (9) were prepared similarly (ESI†).
Bis{N-[N-(2-ethylhexyl)-2-aminoethyl]-4-methylbenzenesulfona-
midato}cobalt(II) (18), bis{N-[N-(2-ethylhexyl)-2-aminoethyl]-
4-methylbenzenesulfonamidato}copper(II) (19) and bis[N-(2-
aminopropyl)-4-methylbenzenesulfonamidato]cobalt(II) (20) were
prepared similarly (ESI†).
Bis[N-(2-aminopropyl)-4-methylbenzenesulfonamidato]copper-
(II) as its blue (21) and green (22) polymorphs was prepared by
the method of Cronin et al.7
2028 | Dalton Trans., 2006, 2026–2034
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
Bis[N-(2-aminopropyl)-4-methylbenzenesulfonamidato]zinc(II)
(23) was prepared in a similar manner to 20 (ESI†).
Bis{N-[N-(2-ethylhexyl)-3-aminopropyl]-4-methylbenzenesul-
fonamidato}copper(II) (24). A solution of 8 (0.15 g, 44 mmol) and
copper(II) acetate monohydrate (44 mg, 0.22 mmol) in methanol
(20 cm3) was heated to reflux. Removal of most of the solvent gave
24 as a green oil (52 mg, 32%) which was washed with small
quantities of methanol and dried in vacuo; IR (CHCl3)/cm−1:
1173s, 1345s, 1683w, 2963m; ESMS m/z 742 (MH+, 80.1%);
HRMS m/z calc. for C36H63N4CuO4S2 743.3586, found 743.3561.
Bis[N-(2-aminophenyl)-4-methylbenzenesulfonamidato]nickel-
(II) (25) was prepared in a similar manner to 15 (ESI†).
Bis[N-(2-aminophenyl)-4-methylbenzenesulfonamidato]copper-
(II) (26). A solution of 10 (0.15 g, 0.58 mmol) and copper(II)
acetate monohydrate (57 mg, 0.28 mmol) in hot DMF (20 cm3)
was set aside for 16 h. Black crystals of 26 were collected, washed
with DMF (3 × 5 cm3) and dried in vacuo (0.15 g, 90%) (Found:
C, 52.1; H, 5.9; N, 12.3. Calc. for C26H26N4CuO4S2: C, 52.19;
H, 5.88; N, 12.17%); IR (KBr disc)/cm−1: 707w, 1137m, 1390m,
1655s, 2927w, 3036w, 3448m; ESMS m/z 586 (MH+, 100.0%).
Bis[N-(2-aminophenyl)-4-methylbenzenesulfonamidato]zinc(II)
(27) was prepared in a similar manner to 25 (ESI†).
X-Ray crystallography
Data were collected below ambient temperatures (see Table 2)
using an Oxford Cryosystems device44 with graphite-mono-
chromated Mo-Ka radiation, except for 13 for which Cu-Ka
radiation was used. Absorption corrections were applied to the
data for 1, 5 and 16 obtained on a Bruker SMART APEX CCD
diffractometer using the program SADABS,45 based on the multi-
scan method of Blessing.46 Data for the other compounds were
collected on a Stoe Stadi-4 diffractometer. Absorption corrections
based on azimuthal measurements47 were applied to 12, whilst no
corrections were applied to 7, 9, 10 and 13.
Structures were solved by Patterson methods in SHELXTL48
for 1 and by direct methods in SHELXTL48 for 5, 7, 9, 10, 13 and
16, and in SIR9248,49 for 12, and were refined using full-matrix
least squares refinement against F2 in SHELXTL.48 All non-
hydrogen atoms were refined anisotropically. All H-atoms were
placed in geometrically calculated positions, and refined as riding
or rotating/riding groups, except for those involved in hydrogen
bonds in the sulfonamide groups. These were located in difference
maps and their coordinates and temperature factors refined, except
in 1 and 7, where they were refined with distance restraints on the
N–H bonds and with the temperature factor riding on the parent
nitrogen. Both 1 and 12 exhibit twinning by pseudo-merohedry.
Each is monoclinic with a b angle of approximately 90◦, such
that the metric symmetry of the cell is higher than the symmetry
of the space group.50,51 This frequently observed problem in such
systems was simply dealt with in these cases by refining a twin
law based on the higher cell symmetry—in both cases here a two-
fold axis down the a-axis (although the c-axis is equally valid).
The minor twin components in 1 and 12 refined to 0.3628(13) and
0.3470(18) respectively. A Flack parameter52 was refined for all
non-centrosymmetric structures, although only 10 and 16 could
be determined reliably. Final refinement parameters are given in
Table 2.
CCDC reference numbers 233475–233482.
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2026–2034 | 2029
©

View Article Online
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b515650p
Results and discussion
Extensive inter- and intra-molecular hydrogen bonding between
the sulfonamide R–NH–SO2R1 and amine R2–NH–R units is
observed in the solid-state structures of the free ligands 1, 5, 7,
9 and 10. In most cases this secondary bonding does not appear
to pre-organise the ligands to provide planar or tetrahedral N4
donor sets. Only 5 and 9 contain pseudo-macrocyclic structures
(Fig. 3) formed by “head-to-tail” dimerisation of the type shown
in Scheme 1. These rings have an “exo” conformation of the amino
nitrogen atom, and, unlike the phenolic oximes (Fig. 1) the acidic
(sulfonamido) hydrogen atom does not form a hydrogen bond
within a chelate ring to establish a conformation very similar to
that required to form the metal complex. Consequently the N4
“hole-size”53 in the free ligand 5 is significantly greater than that
observed in its Cu(II) complexes 21 and 22 (Table 3) and all the
N · · · N bite distances in the bidentate free ligands are significantly
longer than those in the metal complexes. Given the high density
of strong H-bond donor and acceptor groups in these ligands
(Table 4) complicated networks of intermolecular interactions
are expected in the solid state, in contrast to the phenolic oxime
extractants.5 The intermolecular H-bonds observed in 1, 5, 7, 9, 10
of the type needed to form head-to-tail dimers in 1–11 are relatively
Fig.
3
The pseudo-macrocyclic structures of the centrosymmetric
H-bonded dimers of 5 and 9. The symmetry-related half with atom labels
“AA” is generated by the operations 1 − x, −y, −z in 5 and by 1 − x, 1 −
y, 1 − z in 9.
weak,54 with the mean length of the shortest O · · · N distances for
˚
=
S O · · · H–N(amine) 3.05 A. This distance is significantly shorter
˚
in the pseudo-macrocyclic complexes, e.g. of 2.797(5) A in the
centrosymmetric [Ni(1 − 2H)2] and 2.785(3) and 2.834(3) A in
˚
sulfonyl oxygen atom (see ESI,† Table S1) which presumably
weakens the individual H-bonds.
The prolific intermolecular H-bonding in these structures ac-
counts for their observed low solubility in water-immiscible media,
[Cu(2 − 2H)2]. A common feature of the solid-state structures
of both the free ligands and the complexes is the tendency for
the amino proton(s) to make close contacts with more than one
Table 3 Bite distances (N · · · N) and hole sizes in the aminosulfonamido ligands and their metal(II) complexes
d
˚
˚
Compound
Bite distance/A
Hole size /A
e
e
1a
Molecule A
Molecule B
2.879(5)
3.767(5)
4.414(2)
4.895(6)
4.906(4)
2.793(4)
2.808(4)
2.718(11)
2.693(11)
2.716(11)
2.706(11)
2.605(4)
2.640(4)
2.614(3)
2.87f
5
3.14
e
7
9
3.50
e
10a
Molecule A
Molecule B
Zn(1) complex
e
12, [Zn(1 − H)2]b
2.00
—
2.00
—
1.91
1.99
—
Zn(2) complex
13, [Ni(1 − H)2]
16, [Cu(2 − H)2]
21, [Cu(5 − H)2]c green polymorph
22, [Cu(5 − H)2]b,c blue polymorph
1.98
2.90
Cu(1) complex
Cu(2) complex
2.85f
1.99
—
1.99
—
2.82
2.81
2.84
a Has two crystallographically independent ligands per asymmetric unit. b Has two crystallographically independent complexes per asymmetric unit
containing M(1) and M(2). c Exists in green and blue polymorphs.7 d Mean distance of N-donors from their centroid.53 e These free ligands do not show
the pseudo-macrocyclic structure (Scheme 1) in the solid state. f Standard uncertainties on the bite distance are quoted only for the structures determined
in this paper
2030 | Dalton Trans., 2006, 2026–2034
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
Table 4 Hydrogen bond donor and acceptor sites in ligands 1 to 11
compared with the commercial phenolic oxime extractants shown in Fig. 1
1, 2, 5, 6, 10, 11
3, 4, 7, 8, 9
Phenolic-oximes
H-Bond acceptors
H-Bond donors
6
3
6
2
3
2
an unfavourable feature in terms of their potential application
in commercial solvent extraction processes. The N-benzyl- and
N-2-ethylhexyl-derivatives, 5 and 8, of the ethane- and propane-
bridged ligands, prepared from the corresponding aldehydes by
reductive amination, and the tert-butyl-derivative, 11, of the
phenylene-bridged ligand were sufficiently soluble to allow studies
of aggregation and of metal loading to be undertaken.
Electrospray mass spectra of methanolic solutions (10−6 M) of
the free ligands 1, 4, 5 and 8 contain the dimer as the most intense
or second most intense peak. Aggregation numbers measured by
vapour phase osmometry for 1, 5 and 10 were observed to increase
from 1.0 to a maximum of 1.4 as the concentration in chloroform
was increased to 80 mM. For the more hydrophobic ligands 4
and 8 higher aggregation numbers were observed in non-polar
solvents, reaching maxima of 1.7 and 1.8 for 95 mM solutions in
cyclohexane.‡ This suggests that ligand–ligand association leading
to preorganisation of donor sets is not as pronounced as in the
phenolic oxime extractants (Fig. 1), but it is also clear that inter-
=
ligand S O · · · H–N(amine) hydrogen bonds are readily formed and
that they could also help to stabilise complexes of the type shown
in Scheme 1, reducing unfavourable ligand–ligand repulsion
enthalpy terms if the pseudo-macrocyclic structures provide N4
donor sets which meet the coordination requirements of the metal
ions. The planar complexes [Ni(1 − H)2] (13) and [Cu(2 − H)2]
(16) shown in Fig. 4 have the head-to-tail H-bonding arrangement
shown in Scheme 1 whilst in the pseudo-tetrahedral Zn(II) complex
(12) the mutually perpendicular bidentate ligands are too far apart
Fig. 4 The X-ray structures of (i) [Zn(1 − H)2], (ii) [Ni(1 − H)2] and
(iii) [Cu(2 − H)2]. The MN4 unit is planar in [Ni(1 − H)2] as Ni lies on
an inversion centre (with the ligand with atom labels “AA” generated
by the operation 1 − x, −y, −z), whilst the two chelate Cu, N(3),
N(6) planes are inclined at 9.8(2)◦ in [Cu(2 − H)2]. [Zn(1 − H)2] has
two pseudo-tetrahedral complexes per asymmetric unit with very similar
structures (that containing Zn(1) is shown). The Zn, N(3), N(6) planes
are inclined at 89.6(3) and 88.6(3)◦ in the complexes containing Zn(1) and
Zn(2), respectively.
2−
=
to allow a significant S O · · · H–N(amine) interaction within the
complex.
The pseudo-macrocyclic rings in 13 and 16 have different
conformations. Torsion angles in the ethane backbone (a, b and
c in Fig. 5) have similar values in the Ni(II) complex to those
observed in one of the free ligand molecules in the structure of 1.
The central bond delivers a syn-arrangement of the amino- and
amido-N-atoms in both the Ni(II) and Cu(II) complexes and in the
free ligand with a slight flattening of the chelate ring (torsion angles
c and j in the range 45.8–49.9◦) in the Ni(II) and Cu(II) complexes
relative to the free ligand (c, 59.7◦). These differences, and those
observed in the H-bonded segments, may be a consequence of
the pseudo-macrocycle providing a smaller hole size (Table 3)
and shorter amidato and amino to metal bonds in the low spin
In contrast to [Ni(1 − H)2], the Cu and Zn complexes have a more
planar disposition of the bonds about the sulfonamido N-atom
than in related free ligands (Table 5). However, the significance of
this in terms of strain energies is not clear as it has been shown
that N-atoms in sulfonamides show a greater “pyramidalization”
than in carboxamides,55 and ab initio calculations suggest that the
energy barrier for rotation about the N–S bond is smaller than
that in the N–C amide bond.56
The low solubility of the ligands and their metal complexes
in water restricted the measurement of pKa values and complex
formation constants in this solvent. Data obtained in 95%
methanol for 1, 5 and 10, and some of their metal complexes are
presented in Table 6. As might be expected, the anilino-groups in
10 give this ligand lower pKa1 and pKa2 values than its alkylamino
analogues 1 and 5. The formation constant for [Cu(1 − H)2] is
nearly 1010 times greater than that of [Ni(1 − H)2]. This unusually
large discrimination in favour of Cu(II) is consistent with the donor
set “hole-size” being too large for low spin Ni(II) in a flat “head-
to-tail” H-bonded arrangement of the deprotonated ligand (see
above and Table 3). The o-phenylene-bridged ligand 10 might be
˚
Ni(II) complex, 1.909(3) and 1.918(3) A in 13, than in the Cu(II)
˚
complex, 1.975(2) and 1.987(2), and 1.993(2) and 1.998(2) A in 16,
respectively.
The strain associated with providing a good fit for the smaller
Ni(II) ion may also be associated with the amido group being less
planar in [Ni(1 − H)2] than in the other complexes (see Table 5).
‡ The plots of aggregation number against concentration gave shallow
curves which did not permit equilibrium constants for association to be
calculated with confidence.
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2026–2034 | 2031
©

View Article Online
Table 5 The planarity of the sulfonamido N-atoms in 1, 5, 7, 9 and 10 and related metal complexes. Standard uncertainties are quoted only for those
structures published in this paper
Distance of N-atom from
MCS or HCS plane/A
Sum of 3 angles
around N/◦
Inclination of C–S bond
to the NCM planea/◦
˚
Ligand or complex
1b
Molecule A
Molecule B
0.250(19)
0.204(19)
0.300(7)
0.221(20)
0.272(16)
0.158(16)
0.208(18)
0.248(9)
0.012(9)
0.144(9)
0.074(9)
0.297(3)
0.269(3)
0.018(3)
0.013
350(3)
352(3)
344.0(16)
352(4)
346(3)
354(3)
349(4)
353.2(10)
360.0(10)
357.7(10)
359.4(10)
350.3(3)
352.2(3)
360.0(3)
360.0
359.9
355.7
357.1
353.7
—
—
—
—
—
—
—
47
29
43
30
53
57
28
2
5
7
9
10b
Molecule A
Molecule B
Zn(1) complex
[Zn(1 − H)2]c
Zn(2) complex
d
[Ni(1 − H)2
]
[Cu(2 − H)2]
e
[Cu(5 − H)2 ]
0.019
0.199
0.158
0.236
1
c,e
[Cu(5 − H)2
]
Cu(1) complex
Cu(2) complex
22
17
26
18
0.158
357.2
a Standard uncertainties are not quoted for these angles due to the difficulties involved in estimating their values. The angle is obtained by dropping a
line from the C1–S2 vector normal to the N3–C4–M plane to form a right-angled triangle, and the angle of intersection in the triangle calculated. b Has
two crystallographically independent molecules per asymmetric unit (molecules A and B). c Has two crystallographically independent complexes per
asymmetric unit containing M(1) and M(2). d This complex is centrosymmetric. e This complex exists in blue and green polymorphs.
Table 6 The pKa values of 1, 5 and 10 and corresponding formation
constants log KML and log bML of Ni(II), Cu(II) and Zn(II) complexes in
2
95% methanol, I = 0.1 mol dm−3, Et4NClO4 at 25.0 ◦Ca
Ligand
pKa1
8.89
pKa2
Complex
log KML
log bML
2
1
10.75
[Cu(1 − H)2]
[Ni(1 − H)2]
[Zn(1 − H)2]
[Cu(5 − H)2]
[Zn(5 − H)2]
[Ni(10 − H)2]
[Zn(10 − H)2]
10.3
5.7
5.8
10.0
6.3
9.5
∼ 19.4
9.8
b
—
—
—
b
5
9.49
3.17
10.89
9.83
b
10
14.4
14.7
9.8
a All pKa values are 0.05 and metal complex log K values 0.1 unless
otherwise indicated. b Precipitation prevented measurement of log bML for
these complexes and of both formation constants for [Ni(5 − H)2] 2and
[Cu(10 − H)2].
this, but unfortunately no crystals suitable for X-ray structure
determination could be obtained.
The “S-curve” plots for extraction of copper by the 2-ethylhexyl-
substituted reagents 4 and 8 (Fig. 6) indicate that the ethane-
bridged ligand 4 is a significantly “stronger” extractant with a pH
for 50% loading in the equilibrium
2 L(org) + M2+ = [M(L − H)2](org) + 2 H+
of ca. 4.2 compared with ca. 6.0 for 8. This order suggests that
the 14-membered pseudo-macrocycles assembled from 1 and 4
provide a better fit for Cu(II) than any 16-membered ring formed
from head-to-tail H-bonding of 5 or 8. It is also observed that the
formation constants KML for 1 : 1 complexes of this metal with the
related unsubstituted ligands 1 and 5 (see Table 6) are also slightly
larger for the ethane-bridged ligand. In a competitive extraction
experiment (Table 7) without pH-adjustment of the aqueous phase
both 4 and 8 discriminate strongly for Cu(II) over Co(II), Ni(II) and
Fig. 5 Torsion angles in the pseudo-macrocyclic complexes 13 and 16.
aThis complex has an inversion centre relating torsion angles such that a =
−h etc. Standard uncertainties are quoted only for those torsion angles
not involving a hydrogen atom in a calculated position.
2−
expected to deliver a smaller N4 cavity, and thus a more stable
[Ni(10 − H)2] complex. The measured log bML values support
2
2032 | Dalton Trans., 2006, 2026–2034
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
Table 7 Competitive uptake of Co(II), Ni(II), Cu(II) and Zn(II) by 4 or 8
(in CH2Cl2, 0.1 M, 25 ml) after contacting for 1 h at 20 ◦C with 25 ml of
an aqueous solution containing 0.85 M of each metal(II) sulfate
References
1 J. Szymanowski, Hydroxyoximes and Copper Hydrometallurgy, CRC
Press, Boca Raton, FL, 1993.
2 P. A. Tasker, P. G. Plieger and L. C. West, Comprehensive Coordination
Chemistry II, ed. J. A. McCleverty and T. J. Meyer, Elsevier, Oxford,
2003, ch. 9.17, pp. 759–808.
Ligand
M(II) concentration in dichloromethane/ppm
Co
Ni
Cu
Zn
3 G. A. Kordosky, Proc. Int. Solvent Extraction Conf., Cape Town, 2002,
4
8
2(2)
9(2)
31(1)
8(2)
400(2)
70(1)
2(2)
1(2)
p. 853.
4 N. Akkus, J. C. Campbell, J. Davidson, D. K. Henderson, H. A. Miller,
A. Parkin, S. Parsons, P. G. Plieger, R. M. Swart, P. A. Tasker and L. C.
West, Dalton Trans., 2003, 1932.
5 A. G. Smith, P. A. Tasker and D. J. White, Coord. Chem. Rev., 2003,
241, 61.
6 H. M. Irving and R. J. P. Williams, J. Chem. Soc., 1953, 3192.
7 D. J. White, L. Cronin, S. Parsons, N. Robertson, P. A. Tasker and A. P.
Bisson, Chem. Commun., 1999, 1107.
8 H. Y. Cheng, P. H. Cheng, C. F. Lee and S. M. Peng, Inorg. Chim. Acta,
1991, 181, 145.
9 P. H. Cheng, H. Y. Cheng, C. C. Lin and S. M. Peng, Inorg. Chim. Acta,
1990, 169, 19.
10 H. Y. Cheng, G. H. Lee and S. M. Peng, Inorg. Chim. Acta, 1992, 191,
25.
11 E. Kimura and T. Koike, Chem. Rev., 1998, 27, 179.
12 S. Pritchett, P. Gantzel and P. J. Walsh, Organometallics, 1997, 16,
5130.
13 L. T. Armistead, P. S. White and M. R. Gagne, Organometallics, 1998,
Fig. 6 The pH dependence of copper-loading of 4 and 8 determined by
contacting 0.1 M solution of [Cu(L − H)2] in dichloromethane with an
aqueous solution of sulfuric acid.
17, 216.
14 S. Pritchett, D. H. Woodmansee, P. Gantzel and P. J. Walsh, J. Am.
Chem. Soc., 1998, 120, 6423.
15 L. T. Armistead, P. S. White and M. R. Gagne, Organometallics, 1998,
17, 4232.
16 E. J. Corey and M. A. Letavic, J. Am. Chem. Soc., 1995, 117, 9616.
17 E. J. Corey, S. Sarshar and D.-H. Lee, J. Am. Chem. Soc., 1994, 116,
12089.
Zn(II). The observed selectivity orders Cu > Ni > Co ≈ Zn and
Cu > Co ≈ Ni > Zn for 4 and 8, respectively, must be interpreted
with caution because the errors on the uptakes of some of the
metals are close to the determined values.
18 E. J. Corey, S. Sarshar and J. Bordner, J. Am. Chem. Soc., 1992, 114,
7938.
19 E. J. Corey, R. Imwinkelried, S. Pikul and Y. B. Xiang, J. Am. Chem.
Soc., 1989, 111, 5493.
20 Y. Tamai, H. Yoshiwara, M. Someya, J. Fukumoto and S. Miyano,
J. Chem. Soc., Chem. Commun., 1994, 2281.
Conclusions
The simple aminosulfonamido ligands (Fig. 2) are cheap, very easy
to prepare and are good complexing agents, readily forming neu-
tral 2 : 1 complexes with Co, Ni, Cu and Zn, on deprotonation of
the sulfonamide group. Whilst they can form pseudo-macrocyclic
structures by head-to-tail H-bonding between coordinated ligands
in the same way as the phenolic oxime reagents,1 they are much
weaker “pH-swing” reagents and could not be used for efficient
recovery of base metals from acidic pregnant leach solutions
without pH-adjustment. Extensive intermolecular H-bonding in
the solid state leads to low solubilities in hydrocarbons of the
types used commercially in base metal recovery and extensive
alkyl-substitution would be needed to obtain high concentrations
of ligands and their metal complexes. The consequent high
molecular weights of the reagents will result in poor metal
transport efficiency (mass of metal transported per unit mass of
extractant) and high viscosity of reagents. The design, synthesis
and testing of extractants which yield more stable and soluble
pseudo-macrocyclic complexes and are better suited to base metal
recovery from acidic feeds, e.g. 4-ketopyrazolone oximes and
related heterocyclic ligands,57–59 will be reported shortly.
21 S. Hashiguchi, A. Fujii, J. Takehara, T. Ikariya and R. Noyori, J. Am.
Chem. Soc., 1995, 117, 7562.
22 K.-J. Haack, S. Hashiguchi, A. Fujii, T. Ikariya and R. Noyori, Angew.
Chem., Int. Ed. Engl., 1997, 36, 285.
23 A. Fujii, S. Hashiguchi, N. Uematsu, T. Ikariya and R. Noyori, J. Am.
Chem. Soc., 1996, 118, 2521.
24 E. J. Corey, C. M. Yu and S. S. Kim, J. Am. Chem. Soc., 1989, 111,
5495.
25 H. Ito, A. Sato and T. Taguchi, Tetrahedron Lett., 1997, 38, 4815.
26 D. A. Evans and S. G. Nelson, J. Am. Chem. Soc., 1997, 119, 6452.
27 S. E. Denmark, S. P. O’Connor and S. R. Wilson, Angew. Chem., Int.
Ed., 1998, 37, 1149.
28 S. E. Denmark and S. P. O’Connor, J. Org. Chem., 1997, 62, 584.
29 H. W. Goerlitzer, M. Spiegler and R. Anwander, Eur. J. Inorg. Chem.,
1998, 1009.
30 M. Takagi, T. Omori, S. Matsuo, S. Matsuno, K. Ueno and S. Ide,
Chem. Lett., 1980, 387.
31 G. A. Kordosky, K. D. MacKay and M. J. Virnig, Trans. Soc. Miner.
Eng. AIME, 1977, 262, 36.
32 E. Uhlig and M. Doering, Z. Anorg. Allg. Chem., 1982, 492, 52.
33 M. Doering, M. Rudolph, E. Uhlig, V. I. Nefedov and Y. V. Salyn,
Z. Anorg. Allg. Chem., 1987, 554, 217.
34 M. J. Virnig, US Pat., 4100163, 1978.
35 E. B. Spitzner, US Pat., 4237062, 1980.
36 K. D. MacKay, US Pat., 4239699, 1980.
37 R. K. Joffrion, US Pat., 4251644, 1981.
38 M. J. Virnig, US Pat., 4210759, 1980.
39 E. Spitzner, US Pat., 4252959, 1981.
Acknowledgements
40 P. G. Plieger, P. A. Tasker and S. G. Galbraith, Dalton Trans., 2004,
313.
We thank Mr J. Millar and Mr W. Kerr for obtaining NMR
spectra, Mr A. Taylor and Mr H. Mackenzie for mass spectra and
Ms L. Eades for elemental analysis. We gratefully acknowledge
the EPSRC and Avecia and Cytec Industries for funding.
41 M. Fainerman-Melnikova, A. Nezhadali, G. Rounaghi, J. C. McMur-
trie, J. Kim, K. Gloe, M. Langer, S. S. Lee, L. F. Lindoy, T. Nishimura,
K.-M. Park and J. Seo, Dalton Trans., 2004, 122.
42 P. Gans, A. Sabatini and A. Vacca, Inorg. Chim. Acta, 1976, 18, 237.
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2026–2034 | 2033
©

View Article Online
43 A. V. Kirsanov and N. A. Kirsanova, Zh. Obshch. Khim., 1962, 32, 887.
44 J. Cosier and A. M. Glazer, J. Appl. Crystallogr., 1986, 19, 105.
45 G. M. Sheldrick, SADABS, Program for area detector adsorption
correction, Institute for Inorganic Chemistry, University of Go¨ttingen,
Germany, 1998.
52 H. D. Flack, Acta Crystallogr., Sect. A, 1983, 39, 876.
53 K. Henrick, P. A. Tasker and L. F. Lindoy, Prog. Inorg. Chem., 1985,
33, 1.
54 G. A. Jeffrey, Introduction to Hydrogen Bonding, Oxford University
Press, Oxford, 1997.
46 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
47 C. T. North, D. C. Phillips and F. S. Mathews, Acta Crystallogr., Sect.
A, 1968, 24, 351.
55 T. Ohwada, I. Okamoto, K. Shudo and K. Yamaguchi, Tetrahedron
Lett., 1998, 39, 7877.
56 J. Elguero, P. Goya, I. Rozas, J. Catalan and J. L. G. De Paz, J. Mol.
Struct. (THEOCHEM), 1989, 53, 115.
57 A. G. Smith, PhD Thesis, University of Edinburgh, Edinburgh, 2000.
58 C. Squires, PhD Thesis, University of Edinburgh, Edinburgh, 2002.
59 L. C. Emeleus, PhD Thesis, University of Edinburgh, Edinburgh,
1999.
48 G. M. Sheldrick, Madison, WI, 1995.
49 A. Altomare, G. Cascarano, C. Giacovazzi and A. Guagliardi, J. Appl.
Crystallogr., 1994, 27, 1045.
50 S. Parsons, Acta Crystallogr., Sect. D, 2003, 59, 1995.
51 W. Massa, Crystal Structure Determination, Springer-Verlag, 2000.
2034 | Dalton Trans., 2006, 2026–2034
This journal is
The Royal Society of Chemistry 2006
©