Metal-free and dicopper(II) complexes of schiff base [2 + 2] macrocycles derived from 2,20-iminobisbenzaldehyde: Syntheses, structures, and electrochemistry

Article abstract of DOI:10.1021/ic200059n

Three new bis-terdentate Schiff base [2 + 2] macrocycles (H₂LEt, H₂L^Pr, and H₂L^Bu) have been prepared in high yields by 1:1 condensation of 2,20- iminobisbenzaldehyde with 1,2-diaminoethane, 1,3-diaminopropane, and 1,4-diaminobutane, respectively. Metalation of these macrocycles yields the corresponding dicopper(II) acetate (1, 2, and 3) and tetrafluoroborate (4, 5, and 6) complexes. The structures of H₂Et^Pr, H₂L^Pr, H₂L ^Bu, [CuII ₂Li(OAc)₂] 3 solvents (where i is Et, Pr or Bu) and [Cu^II ₂L^Pr(DMF)₄] (BF₂)₂ 3 0.5H₂Oare reported. Intramolecular hydrogen bonding is a feature of the metal-free macrocycles. The copper(II) centers in [Cu^II ₂Li(OAc)₂] 3 solvents are four coordinate, and the macrocycles have U-shaped (Et, Bu) or stepped (Pr) conformations. Complex 5 crystallizes with two dimethylformamide (DMF) molecules bound per five coordinate copper(II) center. Electrochemical studies revealed ligand based oxidations for all of the macrocycles and complexes. Complexes 1 and 2 undergo two quasi-reversible oxidations in DCM which are associated with the deposition of a visible film on the electrode after multiple scans in this oxidative region, suggestive of electropolymerization. Complexes 4-6, studied in MeCN, have CuII f CuI redox potentials at more positive potentials than for 1-3.

Full text of DOI:10.1021/ic200059n

ARTICLE
pubs.acs.org/IC
Metal-Free and Dicopper(II) Complexes of Schiff Base [2 þ 2]
Macrocycles Derived from 2,20-Iminobisbenzaldehyde: Syntheses,
Structures, and Electrochemistry
Scott A. Cameron and Sally Brooker*
Department of Chemistry and the MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, P.O. Box 56,
Dunedin 9054, New Zealand
S Supporting Information
b
ABSTRACT: Three new bis-terdentate Schiff base [2 þ 2] macrocycles (H2LEt,
H2LPr, and H2LBu) have been prepared in high yields by 1:1 condensation of 2,20-
iminobisbenzaldehyde with 1,2-diaminoethane, 1,3-diaminopropane, and 1,4-dia-
minobutane, respectively. Metalation of these macrocycles yields the corresponding
dicopper(II) acetate (1, 2, and 3) and tetrafluoroborate (4, 5, and 6) complexes. The
structures of H2LEt, H2LPr, H2LBu, [CuII Li(OAc)2] solvents (where i is Et, Pr or
2
3
Bu) and [CuII LPr(DMF)4] (BF4)2 0.5H2O are reported. Intramolecular hydrogen
2
3
bonding is a feature of the metal-free macrocycles. The copper(II) centers in
[CuII Li(OAc)2] solvents are four coordinate, and the macrocycles have U-shaped
2
3
(Et, Bu) or stepped (Pr) conformations. Complex 5 crystallizes with two dimethyl-
formamide (DMF) molecules bound per five coordinate copper(II) center. Elec-
trochemical studies revealed ligand based oxidations for all of the macrocycles and
complexes. Complexes 1 and 2 undergo two quasi-reversible oxidations in DCM
which are associated with the deposition of a visible film on the electrode after
multiple scans in this oxidative region, suggestive of electropolymerization. Com-
plexes 4-6, studied in MeCN, have CuII f CuI redox potentials at more positive
potentials than for 1-3.
’ INTRODUCTION
decided to focus our attention on new Schiff base macrocycles
based on this head unit, and report here the first examples of
dinucleating [2 þ 2] N6 macrocycles derived from this head unit,
obtained by condensation with simple nonsubstituted R,ω-diami-
noalkanes (H2LEt, H2LPr, and H2LBu, Scheme 1).
We demonstrate that the resulting, metal-free, 22-, 24-, and
26-membered macrocycles can be easily deprotonated at the
amine groups, forming dianionic macrocycles with two terden-
tate binding pockets that each bind a copper(II) ion (Scheme 1).
The synthesis and characterization of these dinuclear copper(II)
complexes was targeted to investigate the viability and profit-
ability of employing such systems. The results of this study are
presented here.
There has been sustained interest in tetraimine [2 þ 2] macro-
cycles since the first report of such a system, the Robson macro-
cycle,1 in 1970 as they provide controlled access to dimetallic and
tetrametallic complexes.2-13 Many of the studies have focused on
dicopper complexes.10,14-22 Typically the structural, electrochemi-
cal and magnetic properties of these complexes have been investi-
gated; and more recently their application as (oxidation, hydrolysis
or esterification) catalysts;23-25 anion binders;26 or antimicro-
bial agents, DNA binding, or cleavage agents27-29 have also
been considered. These compounds have also been produced
in to model enzyme functional sites.30,31 Indeed there are
many dicopper containing proteins, with important roles in
oxygen activation and transport, electron transfer, methane
oxidation, and so on.32,33
’ RESULTS AND DISCUSSION
Schiff base [2 þ 2] macrocycles can be obtained by condensa-
tion of a suitable dicarbonyl containing species (“head unit”) with
a diamine (“lateral unit”).2-13 Head units derived from pyridine,
phenol, thiophenol, pyridazine, furan, thiophene, pyrrole, dipyrrole,
pyrazole, and triazole have been employed for such purposes,
with the pyridine and phenol based head units easily the most
heavily used. Surprisingly the 2,20-iminobisbenzaldehyde head unit
(Scheme 1), available since 1983,34 has been used only once, in the
synthesis of a family of [1 þ 1] macrocyclic complexes.34 We
Synthesis and Structure of 2,20-Iminobisbenzaldehyde
and Precursors. 2,20-Iminobisbenzaldehyde was prepared
according to the literature,34 in comparable yields. First, an
Ullmann coupling of ethyl 2-bromobenzoate and ethyl 2-ami-
nobenzoate, in the presence of potassium carbonate and
Received: January 10, 2011
Published: March 21, 2011
r
2011 American Chemical Society
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Figure 1. Perspective view of 2,20-iminobisbenzaldehyde. Hydrogen
Figure 2. Perspective view of H2LEt. The second half of the molecule is
generated by an inversion operation (-x, 1 - y, -z). Hydrogen atoms,
other than those involved in hydrogen bonds, are omitted for clarity.
atoms (except H1x) have been omitted for clarity. N(1) O(1)
3 3 3
2.7707(18) Å; N(1) O(11) 2.7510(17) Å. O(1) H(1X) O-
(11) 99.7(8)°.
3 3 3
3 3 3
3 3 3
N(1) N(2) 2.7113(13) Å.
3 3 3
To accommodate the hydrogen atoms present at the 6- and 60-
positions, the two phenyl rings of the diester and dialdehyde
precursors are not coplanar; the resulting twist angle between the
mean planes of these two phenyl rings is ∼43°. In both cases, the
carbonyl groups are conjugated to the phenyl rings to which they
are attached and do not deviate far from the mean planes of these
Scheme 1. Metal-Free Direct Synthesis of the Three [2 þ 2]
Schiff Base Macrocycles (n = 2, H2LEt; n = 3, H2LPr; n = 4,
H2LBu) Derived from 2,20-Iminobisbenzaldehyde, and
Synthesis of Dicopper(II) Complexes of These Macrocycles
As Acetate and Tetrafluoroborate Salts
rings. Strong intramolecular bifurcated hydrogen bonds (D
A
3 3 3
∼2.7 Å) are formed between the central amine hydrogen atom
and both of the carbonyl oxygen atoms of these groups, and
constrain the ester and formyl groups to be in a cis-like conformation
relative to the amine.
Synthesis and Structure of Imine [2 þ 2] Macrocyclic
Ligands. The formation of [2 þ 2] Schiff-base macrocycles is
usually metal-templated, often on a metal ion other than that of
interest thus necessitating a subsequent transmetalation reaction.
However, in some cases they can be prepared directly, metal-free,
usually by employing high dilution techniques or hydrogen
bonding to favor cyclization.35
The target macrocycles, H2LEt, H2LPr, and H2LBu (Scheme 1),
can be synthesized directly, in high yield and purity, by the Schiff-
base condensation of 2 equiv of 2,20-iminobisbenzaldehyde with 2
equiv of 1,2-diaminoethane, 1,3-diaminopropane, and 1,4-diamino-
butane, respectively (in a similar fashion to the selenium and
tellurium based macrocycles made by Singh and co-workers36,37).
These new [2 þ 2] macrocycles are particularly easily accessed as
they precipitate from the refluxing methanol solution as they form.
The resulting suspensions can be filtered after just 20 min, to give
yellow powders that after drying under vacuum are analytically clean
and air stable.
Light yellow single crystals (blocks) of H2LEt, H2LPr, and
H2LBu were obtained by recrystallization from ethyl acetate. The
ethylene and propylene linked macrocycles crystallized with
half a molecule in the asymmetric unit whereas the butylene
linked macrocycle crystallized with the entire molecule in the
asymmetric unit (Figures 2-3 and Supporting Information,
Figure S8). No solvent or disorder is present in these three
structures.
In all cases there are strong intramolecular hydrogen bonds
between the amine hydrogen atom and one or two imine
nitrogen atoms (Supporting Information, Table S3). For the
two macrocycles with an even number of methylene links (H2LEt
and H2LBu) there is one hydrogen bond per amine, and the
imines are in a trans-like conformation. In contrast, the macro-
cycle with an odd number of methylene links (H2LPr) forms two
hydrogen bonds per amine (a bifurcated hydrogen bond), resulting
in a cis-likeconformation. Theformationofthemacrocyclesislikely
being promoted by these strong intramolecular hydrogen bonds.
copper(I) iodide at 180 °C, is employed to form 2,20-iminobis-
(ethyl benzoate), in 80% yield. This diester is reduced to the
white diol, 2,20-iminobis(hydroxymethylbenzene), using lithium
aluminum hydride in dry diethyl ether, in 80% yield. Lastly, this
diol is oxidized to the desired bright yellow dialdehyde using
MnO2 in dry diethyl ether in 72% yield.
Single crystals of these compounds were obtained as follows:
light yellow blocks of the diester (Supporting Information,
Figure S7) by recrystallization from pentane/DCM; yellow
rods of the dialdehyde (Figure 1) by slow evaporation of
Et2O/MeOH.
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Figure 3. Perspective view of H2LPr. The second half of the molecule is
generated by an inversion operation (-x, 1 - y, 2 - z). Hydrogen
atoms, other than those involved in hydrogen bonds, are omitted for
clarity. N(1) N(2) 2.7867(16) Å; N(1) N(3A) 2.7922(16) Å.
3 3 3
3 3 3
N(2) H(1X) N(3A) 107.5(8)°.
Figure 5. Perspective view of [CuII2LPr(OAc)2] 1.5MeOH 0.5H2O.
The second half of the molecule is generated by an inversion operation
(2 - x, 1 - y, 1 - z). Hydrogen atoms, other than those involved in
hydrogen bonds, are omitted for clarity.
3 3 3
3 3 3
3
3
Figure 4. Perspective view of [CuII2LEt(OAc)2]. The second half of the
molecule is generated by a 2-fold rotation (y, x, -z). Hydrogen atoms
are omitted for clarity.
Figure 6. Perspective view of [CuII2LBu(OAc)2] 3MeOH. Hydrogen
atoms, other than those involved in hydrogen bonds, are omitted for
clarity.
3
The phenyl-phenyl twist angle for H2LEt is exceptionally low
(28°), compared to any of the other ligands, ligand precursors or
metal complexes (41-61°). In this structure the macrocycles
sit on top of one another and there is a short edge-to-face π
interaction from the C13-18 phenyl ring to the C1-6 ring of a
neighboring unit. This particular interaction is not observed in
any of the other structures and may be the cause of the low twist
Concentration of the resulting orange-brown solutions caused
precipitation of the desired product, which was filtered and dried
under vacuum. In all three cases, it appears that two solvent
molecules are bound per copper(II) center, one pyridine and the
other either water or iso-propanol, giving a square pyramidal
coordination environment. Diethyl ether vapor diffusion into a
dimethylformamide (DMF) solution of 5 yielded single crystals
angle (for details of π π interactions see Supporting Informa-
3 3 3
tion, Tables S5 and S6; Figures S10-S18).
of [CuII LPr(DMF)4] (BF4)2 0.5H2O.
2
3
The complexes [CuII LEt(OAc)2], [CuII LPr(OAc)2] 1.5
Synthesis and Structure of Macrocyclic Copper(II) Com-
plexes. The dicopper(II) macrocyclic complexes were synthe-
sized as acetate and tetrafluoroborate salts (Scheme 1). The
acetate compounds (1, 2, and 3) could be simply produced by
the addition of 2 equiv of copper(II) acetate monohydrate to a
refluxing suspension of the appropriate macrocycle in dry MeOH.
Upon addition the suspension immediately clarified and changed
to a yellow-brown color. By ceasing heating and removing
the condenser, dark orange-brown block-shaped single X-ray
2
2
3
MeOH 0.5H2O and [CuII LPr(DMF)4](BF4)2 0.5H2O crys-
2
3
3
tallized with half a macrocycle in the asymmetric unit whereas the
entire macrocycle was present in [CuII LBu(OAc)2] 3MeOH
2
3
(Figures 4-6 and Supporting Information, Figure S9). This is an
analogous pattern to that in the free macrocycles; the reduced
internal symmetry observed for the butylene linked macrocycle
and complex may be attributable to the increased length, and
hence flexibility, of the alkyl chain.
quality crystals of the ethylene, [CuII LEt(OAc)2], propylene,
The bond lengths and angles involving the copper(II) centers
in each of these complexes are provided in Supporting Informa-
tion, Table S4. In all cases, the macrocyclic ligands are deproto-
nated at both of the amines (N1/N4), and these make the
shortest Cu-N bond lengths. Despite the negative charge, the
equatorially coordinated acetate oxygen atoms make the longest
of the bonds to the copper centers. Nevertheless the Cu-X
distances fall in a narrow range (1.922-1.995 Å). Likewise, all of
2
[CuII LPr(OAc)2] 1.5MeOH 0.5H2O, and butylene [CuII LBu-
2
2
3
3
(OAc)2] 3MeOH linked macrocyclic dicopper(II) complexes
were obtained in high yield.
3
The tetrafluoroborate complexes (4, 5, and 6) were produced
in moderate yields by the addition of 2 equiv of copper(II)
tetrafluoroborate hydrate to a hot suspension of the approp-
riate macrocycle in iso-propanol with a few drops of pyridine.
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Table 1. Comparison of Selected Structural Parameters between the Ligand Precursors, Metal-Free Macrocycles, and the
Corresponding Dicopper(II) Complexes, [CuII2(OAc)2LEt], [CuII2(OAc)2LPr] 1.5MeOH 0.5H2O, [CuII2(OAc)2LBu] 3MeOH,
3
3
3
and [CuII2LPr(DMF)4] 0.5H2O
3
mean formyl/imine
oop deviation and
ranges (Å)b
copper
copper
measure of
metal
crystal system
R(Ph-Ph)
(deg)a
hydrogen bonding
3 3 3
(space group)
D
A (Å)
separation (Å)
geometry
3 3 3
0.366
monoclinic
BPhOEt
BPhCHO
H2LEt
45.55(4)
41.08(4)
27.84(5)
48.07(4)
N(1) N(2) 2.7113(13)
N/A N/A
3 3 3
0.266(2)-0.466(2)
(P21/n)
0.220
N(1) N(2) 2.7867(16)
orthorhombic
3 3 3
N/A
N/A
0.1743(3)-0.265(3)
N(1) N(3) 2.7922(16)
(P212121)
3 3 3
0.323
monoclinic
N(1) N(2) 2.7113(13)
N/A
N/A
3 3 3
0.259(2)-0.386(2)
(P21/c)
0.169
N(1) N(2) 2.7867(16)
monoclinic
3 3 3
H2LPr
N/A
N/A
0.161(2)-0.176(2)
N(1) N(3) 2.7922(16)
(P21/c)
3 3 3
50.20(11); 0.159
N(1) N(6) 2.670(3)
triclinic
3 3 3
H2LBu
N/A
N/A
53.06(10)
0.105(5)-0.270(5)
N(3) N(4) 2.683(3)
(P1)
3 3 3
0.288
trigonal
[CuII2(OAc)2LEt]
53.43(9)
nil
3.6072(8)
5.2650(17)
0.35 D4h:Td
0.41 D4h:Td
c
0.127(6)-0.449(6)
(P3221)
[CuII2(OAc)2LPr]
triclinic
0.359
O(41) O(50) 2.724(5)
3 3 3
c
54.91(12)
0.336-0.381(7)
O(50) O(60) 2.896(19)
1.5MeOH 0.5H2O
(P1)
3 3 3
3
3
O(41) O(60) 2.682(2)
3 3 3
c
c
[CuII2(OAc)2LBu
]
monoclinic
59.70(6);
55.25(5)
0.345
O(60) O(70) 2.785(2)
0.38 D4h:Td
0.31 D4h:Td
3 3 3
5.8384(3)
5.0207(5)
O(51) O(80) 2.744(3)
3MeOH
(Cc)
0.231(4)-0.461(4)
3 3 3
3
O(51) O(81) 2.739(8)
3 3 3
[CuII2LPr(DMF)4]
0.5H2O
triclinic
0.272
O(51)
O(61)
O(61) 2.864(7)
F(11) 2.607(7)
3 3 3
3 3 3
d
61.00(6)
0.29 C4v:D3h
(P1)
0.065(3)-0.479(4)
3
a The angle between the mean planes of the two phenyl rings making up the diphenylamine unit. b The mean, and range, of out of plane (oop) deviation
of the carbonyl oxygen and imine nitrogen atoms from the mean plane of the phenyl ring to which they are attached. c Tetrahedral distortion parameter
[ω/90]: Square Planar (D4h), 0; Tetrahedral (Td), 1, where ω is the dihedral angle between the chelate ring planes N-Cu-N and N-Cu-O.38
d Trigonality distortion parameter τ = [(β-R)/60]: Square Pyramidal(C4v), 0; Trigonal Bipyramidal (D3h), 1, where β is the largest of the basal angles
and R is the second largest.40
the cis X-Cu-X angles (89.2-98.3°) are quite close to 90°.
This is pleasing as these macrocycles were designed to form six-
membered chelate rings on binding, and hence angles close to
90°. It is anticipated that this should prove favorable for most
transition metal ions, so this is a very promising result with
regard to our intention to further our investigations of such
complexes.
In the acetate complexes the copper(II) ions are in a tetra-
hedrally distorted square planar N3O environment (0.31-0.41
D4h:Td ratio,38 see Table 1). This distortion is very noticeable
when a mean plane produced from any three of the four donor
atoms is considered, as in all cases the copper atom is somewhat
out of plane (0.106-0.452 Å) while the fourth donor atom is
even further out of plane (1.044-1.657 Å). The oxygen atom
(from the acetate ion) is strongly bound in what is approximately
the equatorial plane. This results in the second oxygen atom
of the same acetate weakly interacting with the otherwise
vacant “axial” site of the same copper center (Cu-Oax is ca.
0.5-0.9 Å > Cu-Oeq; Supporting Information, Table S4);
however, as expected,39 the resulting four-membered chelate
ring has a rather acute O-Cu-O angle (50.2-58.6°).
In the tetrafluoroborate complex, the copper ions are five,
not four coordinate, each binding two neutral monodentate
solvent molecules (rather than one acetate anion). The result
is a trigonally distorted square pyramidal N3O2 environment
(0.29 C4v:D3h ratio (τ),40 see Table 1). Two molecules of DMF
bond to each copper center, one at the remaining equatorial site
and one at the axial site. The latter DMF makes good angles to
the 4 donors in the basal plane and shows the axial elongation
expected for copper(II) (Cu-Oax being ∼0.38 Å longer than the
equatorial bond lengths, Supporting Information, Table S4).
The copper(II) centers are a significant distance apart (3.6-
5.8 Å, Table 1), and are not bridged by any group. This distance
increases with increasing chain length. Since the propylene linked
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Table 2. Comparison of the Anodic and Cathodic Peak Potentials for Macrocycles H2LEt, H2LPr, and H2LBu and Complexes with
Copper(II) Acetate (1, 2, and 3) and Tetrafluoroborate (4, 5, and 6), at 200 mV s-1 Scan Rate, Referenced against Internal Fc/Fcþ
Couple for Ease of Comparisona
EPA and/or [EPC], and where applicable {ΔEP, the absolute difference between EPC and EPA}, in V versus Fc/Fcþ
H2LEt H2LPr H2LBu
1
2
3
4
5
6
0.468
0.917
0.512, 0.682
0.856
0.454, 0.534
0.910
0.025
0.137
-0.102 0.276 [0.130] {0.14}
0.332 [0.161] {0.17} 0.236
0.506 [0.309] {0.20} 0.415
0.107
0.063 0.474 [0.297] {0.18}
[-0.296] [-0.933]
[-0.672]
0.145 [-1.695] -0.793, -0.479 [-1.703] -0.471
[-1.94] -0.521 [-1.254] [1.284] -0.500, -0.168 [-0.881] -0.520
[-1.411] [-1.611]
a The original data can be seen in Figures 7-9, in the discussion below, and in the Supporting Information. Note that for solubility reasons, complexes
4-6 were run in MeCN whereas all other samples were run in DCM.
macrocycle adopts a “stepped” conformation as opposed to the
“U shaped” conformation for the ethylene and butylene com-
crystallize in centrosymmetric space groups. For details of the
π interactions present in these complexes see the Support-
ing Information, Tables S5 and S6; Figures S15-S18.
There are multiple hydrogen bonds present in the structures of
the copper(II) acetate complexes. These occur between the
acetate groups and the solvent, and are quite strong (Table 1).
Similarly, in the tetrafluoroborate complex, a water molecule
hydrogen bonds to both an anion as well as the coordinated
oxygen atom in the axially bound DMF molecule.
π
3 3 3
plexes, the observed Cu Cu separation, while falling between
3 3 3
the values for the smaller and larger macrocycles, is slightly higher
than might be expected. The tetrafluoroborate complex of the
propylene linked macrocycle also exhibits the stepped conforma-
tion, and has a slightly shorter (0.24 Å) Cu Cu separation
3 3 3
than its acetate analogue.
As for the carbonyl groups in the precursors, the imine groups
in the metal-free macrocycles and the resulting complexes do not
deviate much from the mean plane of the phenyl ring to which
they are attached (Table 1). As for the metal-free macrocycles,
the phenyl rings are twisted away from coplanarity in all four
structurally characterized copper(II) complexes (Figures 4-6
and Supporting Information, Figure S9, Table 1). Upon coordi-
nation to copper(II) the twist angle between these phenyl rings
increases, by 5-26°, to a similar value for all complexes, R = 57 (
5°. Notably, all precursors, ligands, and complexes have twist
angles within a fairly small range (50 ( 10°), except for the
ethylene linked ligand, H2LEt, which has a significantly lower
twist angle of 27.8° (discussed above). It therefore exhibits
easily the largest increase in twist angle on complexation to
copper(II), 26°, while the rest increase by only 5-13°. All of
these compounds have significantly lower twist angles than those
reported for the tellurium and selenium macrocycles of Singh
and co-workers (63-83° free macrocycles; 67-87° when co-
ordinated to Ni, Co, Pd).36,37,41,42 This can be attributed to the
amine nitrogen atom being somewhat more conjugated with the
carbon atoms of the phenyl rings than is the case for the larger
selenium and tellurium atoms.
The conformation of the macrocyclic complexes is interesting
since the ethylene and butylene linked macrocyclic complexes
form “U-shaped” structures, where the acetate anions are both on
the same side of the macrocycle. In these structures, two of the
four phenyl rings on opposite sides of the macrocycles are close
to each other; the other two rings face outward. The ethylene
linked structure crystallizes in a chiral space group (P3221),
whereby these phenyl rings are offset π-stacked and are always on
the same side of the macrocycle. Presumably crystals of the
opposite chirality also crystallized.
Electrochemical Studies. The cyclic voltammograms (CVs)
of the macrocyclic ligands (H2LEt, H2LPr, and H2LBu) and
copper(II) acetate (1, 2, and 3) and tetrafluoroborate (4, 5,
and 6) complexes were investigated. For solubility reasons the
ligands and acetate complexes were run in DCM versus Ag/AgCl
(3 mol L-1 KCl) (Fc/Fcþ Em 0.64 V; ΔEp 0.17 V), whereas the
3
tetrafluoroborate complexes were run in MeCN versus Ag/0.01
mol L-1 AgNO3 (Fc/Fcþ Em 0.10 V; ΔEp 0.16 V). For ease of
3
comparison the peak potentials for the observed oxidative and
reductive processes, at a scan rate of 200 mV/s, have been conve-
rted to be referenced against internal Fc/Fcþ and are presented in
Table 2. However, in the following discussion and figures, it is
important to note that all quoted potentials are versus the original
reference electrode (not versus Fc/Fcþ). Various scan rate studies
were also carried out for which the scan rates investigated were
25, 50, 100, 200, 300, and 400 mV/s (Supporting Information,
Table S7).
Imine [2 þ 2] Macrocyclic Ligands. The electrochemistry of
the macrocycles H2LEt, H2LPr, and H2LBu was investigated
in DCM versus Ag/AgCl (3 mol L-1 KCl) (Figure 7) for
3
comparison with the corresponding macrocyclic dicopper(II)
complexes. In all three cases, irreversible oxidative processes
occurred with EPA values below 1 V (H2LEt, 0.66 and 0.77 V;
H2LPr, 0.74 V; H2LBu, 0.53, 0.70, and 0.78 V). For H2LEt, there is
one clear oxidation process and a lower current process at
slightly lower potentials, which appears as a shoulder. Like-
wise for H2LBu, there is one clear process, but it is flanked by
both lower and higher potential processes of low current. In
contrast, ligand H2LPr has only one distinguishable oxidative
process.
In all cases, on scanning to negative potentials first (0 f -1.7 f
0 V) there are no reductive processes, indicating that these ligands
cannot be reduced at potentials more positive than -1.7 V
(Supporting Information, Figures S24, S26 and S28). Scans to
positive potentials first (0 f 1.3 f -1.7 f 0 V) reveal a very
small reductive process having an EPC at slightly more positive
than -1 V (Figure 7), which is more obvious at higher scan rates
(Supporting Information, Figures S23, S25 and S27).
The butylene structure crystallizes in a non-centrosymmetric
space group (Cc), which also features one pair of opposite phenyl
rings close to each other, but forms a much weaker π-π
interaction. An n-glide generates the molecule of the opposite
handedness. In contrast, the propylene linked macrocyclic com-
plexes form “stepped” structures, where each acetate, or axial
DMF points towards opposite sides of the macrocycles, and
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Figure 7. CVs (0 f 1.3 f -1.7 f 0 V) of macrocycles H2LEt, H2LPr,
and H2LBu run at 200 mV/s in DCM versus Ag/AgCl (3 mol L-1 KCl).
3
Copper(II) Acetate Macrocyclic Complexes. The electro-
chemistry of the copper(II) acetate complexes 1, 2, and 3 was
investigated in DCM versus Ag/AgCl (3 mol L-1 KCl)
3
(Figure 8) since these compounds are only sparingly soluble in
MeCN. The CVs of the ethylene linked dicopper(II) complex 1
show two clear oxidation processes with EPA of about 0.91 and
1.11 V. These appear to be reversible as they have associated
reduction processes with EPC of about 0.76 and 0.93 V, and ΔEP
values of 0.15 and 0.18 V respectively, close to that observed for
the Fc/Fcþ couple in this cell system (ΔEP = 0.17 V; not 57 mV
due to IR drop which is particularly large in DCM). The ratio
iPA/iPC is almost unity for both processes. In principle these
processes could be due to copper oxidation (CuII f CuIII),
but they are more likely to be due to ligand oxidation, given
the results obtained on the free macrocycles (above). The shift
of these oxidations to more positive potentials compared to
the free macrocycle is expected because of the presence of
the copper(II) cations which likely outweighs the effect of
deprotonation.
Multiple scans of this oxidative region (0.3 f 1.5 f 0.3 V)
were carried out to investigate the chemical reversibility of these
oxidation processes (Supporting Information, Figure S35). Both
the oxidation and return reduction waves showed sustained
growth in peak current with each additional scan (without
cleaning of the platinum working electrode). Inspection of the
working electrode after 12 scans showed a bronze colored
material had been thinly deposited on the surface (Supporting
Information, Figure S39b). Further scans resulted in the two
oxidative processes merging into one broad process. The same
was observed for the two return reductive processes. After 100
scans the growth in peak current begins to slow, but it still
continues to grow (Supporting Information, Figure S40). Further-
more, the color of the deposited material darkens (Supporting
Information, Figure S39c). To ensure this electrodeposition was
not a consequence of the Pt working electrode surface used, a
glassy carbon (GC) electrode was also tried. The same behavior
of increasing current with each scan was observed (Supporting
Information, Figures S35 and S37) and a similar looking material
was seen on the electrode surface afterward. In a final experiment to
probe the nature of this behavior a small amount of MeCN was
added to the DCM solution and the same tests with Pt and GC
working electrodes were carried out. Under these conditions the
processes grew only very, very slowly and kept their peak shape
Figure 8. CVs (0 f 2.1 f about -1.4 f 0 V) of copper(II) acetate
macrocyclic complexes 1, 2, and 3 run at 200 mV/s in DCM versus Ag/
AgCl (3 mol L-1 KCl).
3
(Supporting Information, Figures S36 and S38). It therefore seems
that the product of this oxidative process is stabilized or solubilized
by the MeCN, whereas use of only DCM causes deposition onto the
electrode surface, modifying the electrode surface and resulting in
higher current flows. This voltammetric behavior is consistent with
ligand based oxidative polymerization and deposition.43
CVs of the propylene (2) and butylene (3) linked copper(II)
acetate macrocyclic complexes in DCM also show two clear
oxidation processes (2, EPA 0.96 and 1.14 V; 3, 0.87 and 1.04 V).
A further oxidation process in 3 could be distinguished at 1.17 V
at low scan rates (Supporting Information, Figure S48). As for 1,
return reduction processes having EPC of 0.95 and 0.80 V were
seen for 2, giving ΔEP values of 0.17 and 0.20 V, respectively,
similar to that seen for Fc/Fcþ in this system (0.17 V). These
return waves had even better peak shapes, giving an iPA/iPC ratio
of unity for both processes at all scan rates (Supporting Informa-
tion, Figure S43). These two redox processes are thus also
reversible. In contrast, 3 has no clear peaks on the return (even
when the direction of the scan is reversed at 0.93 V, that is, just
after the first oxidation) so these oxidations are chemically irrever-
sible. Multiple scans of this oxidative region (0.3 f 1.5 f 0.3 V)
were also carried for 2 and 3 (Supporting Information, Figures
S47 and S52). As for 1, complex 2 exhibited sustained peak
growth with each scan, and a similar colored material was
deposited. In contrast, for complex 3, the peak shape is destroyed
and the current falls. This is consistent with the normal expecta-
tion that repeated cycles will deplete the concentration of
nonoxidized compound at the surface, causing the current to
drop. No deposition onto the electrode is observed for compound 3.
This is consistent with the lack of increased current, but is puzzling
as a similar electropolymerization could have been expected. Inter-
estingly, the butylene linked ligand and the copper(II) acetate
complex of it have lower oxidation potentials than the ethylene
and propylene analogues.
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When scanning to negative potentials first (0 f -1.3 f 0 V)
there is a single, low current irreversible reduction process
observed for all complexes (1, EPC -1.06 V; 2, -1.07 V; 3,
-1.30 V), which results in an additional oxidation process
or processes being observed on the return (1, EPA -0.15 and
0.16 V; 2, 0.18 V; 3, 0.14 V; Supporting Information, Figures
S32, S45 and S51). Scans to positive potentials first (0 f 1.5 f
-1.3 f 0 V) result in additional reduction processes being
observed (1, EPC -0.06 and -0.43 V; 2, 0.74 and 0.59 V; 3, nil;
Supporting Information, Figures S31 and S46). The reductive
processes are likely to be the reduction either of the imines or of
the copper centers (CuII f CuI). Having acetate anions bound
to the copper ions (as they will be in DCM) is expected to help
make the reduction of these metal centers unfavorable, leading
to quite negative EPC values. The low current waves at about -
1.1 V might well correspond to such a copper reduction,
since imine reduction is expected to occur at even more
negative potentials.44 CVs following addition of a small amount
of MeCN (1 mL) to the DCM solution were carried out to
see if this copper(II) reduction could be shifted to more positive
potentials. No shifting of any reductive process was observed.
Presumably the acetate anions remain coordinated despite the
presence of MeCN.
Copper(II) Tetrafluoroborate Macrocyclic Complexes. The
electrochemistry of complexes 4, 5, and 6 was investigated in
Figure 9. CVs of copper(II) tetrafluoroborate macrocyclic complexes
4, 5, and 6 run at 200 mV/s in MeCN versus Ag/0.01 mol L-1 AgNO3.
3
MeCN versus Ag/0.01 mol L-1 AgNO3 (Figure 9; Supporting
Shown are two separate scans per complex, both starting from 0 V but
one initially scanning to negative potentials and the other to positive
potentials.
3
Information, Figures S53-54, S58-59 and S63-65) as, unlike
the DCM soluble and MeCN insoluble acetate analogues (1, 2,
and 3), these tetrafluoroborate complexes are insoluble in DCM.
The CVs of these complexes also exhibit distinct oxidation pro-
cesses, having one large current oxidation wave and a number of
smaller waves, sometimes seen as shoulders (4, EPA 0.56 and 1.01 V;
5, 0.61, 0.79, 0.95, and 1.45 V; 6, 0.45, 0.55, 0.63, and 1.02 V). Once
these values have been corrected for the differing cells, reference
systems and solvent employed, by using the Fc/Fcþ couple as the
internal reference in both cases, these EPA values are all con-
sistently higher than in the acetate complexes (1, 2, and 3). This
is expected since there is a higher positive charge on the
macrocyclic complex since the tetrafluoroborate is not bound,
meaning the oxidation process occurs at a higher potential. These
oxidation waves are almost entirely irreversible, as they were for
the ligands. Only the ethylene complex, 4, shows return reduction
processes, wherein the first process has two accompanying, much
smaller, peaks with EPC of 0.45 and 0.22 V on the return scan.
Multiple scans of this region (0/0.3 f 1.2/1.5 f 0/0.3 V) were
also carried out for these tetrafluoroborate complexes, but no peak
growth or deposition was observed (Supporting Information,
Figures S57, S62 and S68). The oxidation product (as seen for
the acetate analogues 1 and 2) either is not being produced or it is
being stabilized or solubilized by the MeCN solvent.
may be expected, and as neutral acetonitrile is bound, and is
known for its ability to stabilize CuI,45 such a reduction would be
significantly more favored than for the acetate complexes in
DCM (implies EPC expected to lie at higher potentials). Reduc-
tion of the copper(II) centers in the tetrafluoroborate complexes
appears to happen in two steps, whereby one of the copper
centers (EPC ca. -0.8 V) seems to influence the other, causing a
second reduction wave at slightly more negative potentials (EPC
ca. -1.2 V). If all of these reduction potentials are converted to
be against the internal Fc/Fcþ couple (Table 2), for ease of
comparison between the tetrafluoroborate complexes in MeCN
versus Ag/0.01 mol L-1 AgNO3 and the acetate complexes in
3
DCM versus Ag/AgCl (3 mol L-1 KCl), these reductions are
3
seen to occur at significantly more positive potentials, consistent
with the tetrafluoroborate macrocyclic complexes carrying a high-
er charge than when acetate is bound. The remaining reduction
processes in these complexes were not able to be explained.
’ CONCLUSION
A simple high yielding metal-free synthesis of three Schiff base
[2 þ 2] macrocycles, the first to be obtained from the 2,20-
iminobisbenzaldehyde head unit, is presented. These macro-
cycles can be complexed with copper(II) acetate and tetrafluor-
oborate to give the corresponding, highly colored, macrocyclic
complexes in good yields. The first structure determinations for
any complex of a macrocycle derived from this head unit are
reported. A square planar coordination environment is observed
in the three complexes with coordinating acetate anions, whereas
the use of the noncoordinating tetrafluoroborate anions led to a
square pyramidal environment because of two molecules of
solvent binding per copper(II) center. These new macrocycles
provide two anionic N3 terdentate binding pockets that we have
proven in this study produce near 90° bond angles on binding
In scans to negative potentials first (0 f -2 f 0 V), these
complexes also show several irreversible reduction processes (4, -
0.19, -0.75, -1.15, and -1.30 V; 5, -0.83 and -1.19 V; 6, -
0.57, -0.79, and -1.47 V). New oxidation waves are seen after
scans to such potentials (4, 0 V {after scan to -2 V}; 5, -0.45
and -0.05 V {after scan to lower than -1.19 V}; 6, -0.41 {after
scan to lower than -0.79 V}; Supporting Information, Figures
S56, S61, and S66). Scans to positive potentials first (0 f
1.3 f -2 f 0 V) show markedly different reduction waves
(Supporting Information, Figures S55, S60, and S67), likely a
consequence of the irreversible oxidation events occurring prior
to investigation of negative potentials. Reduction (CuII f CuI)
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copper(II) ions. This is most encouraging as we look to extend
this study to complexes of these macrocycles with other
transition metal ions. These studies will also be greatly facili-
tated by the ease with which the pure metal-free macrocycles
are isolated. This is a rare and advantageous situation, as most
large Schiff-base macrocycles are only stable in the presence of a
metal ion, necessitating considerably more synthetic effort to
produce complexes of the range of transition metal ions of
interest.
All of the compounds studied exhibited ligand based oxida-
tions under 1 V. In the ethylene and propylene linked macro-
cyclic dicopper(II) acetate complexes in DCM these processes
were quasi-reversible and generated a film on the electrode,
consistent with an electropolymerization reaction having oc-
curred. Practically nothing occurred in the reductive region of the
CVs of the acetate complexes, owing to the solvent employed
(DCM) and the bound anions. In contrast, the tetrafluoroborate
complexes, studied in MeCN, exhibited multiple irreversible
reductive steps, some of which are tentatively assigned to CuII f
CuI reductions.
Ph), 120.55 (4-Ph), 118.22 (6 Ph), 60.24 (NCH2), 33.20 (NCH2CH2).
IR (KBr): (cm-1) = 2920 (w), 2818 (m), 1641 (s), 1577 (s), 1515 (s),
1451 (s), 1385 (m), 1310 (s), 1197 (w), 1156 (m), 1015 (w), 971 (w),
744 (s), 607 (w), 463 (w).
Butylene Linked Imine [2 þ 2] Macrocycle (H2LBu). Using the
general method above, reaction of the dialdehyde (1.3845 g, 6.147
mmol) with butylene diamine (0.4415 M, 13.93 mL, 6.150 mmol) gave
isolated pure product (1.2709 g, 75%). ESI(þ) MS (m/z): 555.32
[C36H38N6H]þ. Anal. Calcd for C36H38N6: C, 77.95; H, 6.90; N, 15.15
Found: C, 78.07; H, 7.20; N, 15.34. 1H NMR (400 MHz, CDCl3) δ =
11.55 (NH, s, 2H), 8.53 (CHN, s, 4H), 7.64 (3 PhH, dd [J = 7.6, 1.2],
4H), 7.45 (6-PhH, d [J = 8.4], 4H), 7.28 (5-PhH, dt [J = 8.0, 1.6], 4H),
6.94 (4-PhH, t [J = 7.2], 4H), 3.65 (NCH2, s, 8H), 1.80 (NCH2CH2, s,
8H). 13C NMR (100 MHz, CDCl3) δ = 161.33 (CHN), 143.37 (1 Ph),
131.12 (3-Ph), 130.97 (5-Ph), 123.72 (2-Ph), 120.40 (4-Ph), 117.68 (6-
Ph), 61.94 (NCH2), 29.23 (NCH2CH2). IR (KBr): (cm-1) = 3010 (w),
2939 (w), 2826 (m), 1628 (s), 1605 (w), 1587 (s), 1524 (s), 1454 (s),
1378 (m), 1312 (s), 1255 (w), 1199 (w), 1156 (w), 1125 (w), 1035 (w),
978 (w), 745 (s), 681 (m), 481 (w).
General Method A: Synthesis of Dicopper(II) Acetate
Macrocyclic Complexes Derived from Imine [2 þ 2] Macro-
cycles. To a refluxing light yellow suspension of the appropriate imine
[2 þ 2] macrocycle (1 equiv) in dry MeOH (20 mL, distilled over
In summary, these results indicate that these new dinucleating
Schiff base macrocycles have great promise: our next step is to
explore other transition metal complexes of them.
CaH2) was added a light blue solution of Cu(OAc)2 H2O (2 equiv) in
3
dry MeOH (20 mL). The yellow suspension immediately changed to
yellow-brown solution. Refluxed for further 3 h. Turned off heating,
removed condenser, and left overnight, yielding X-ray quality crystals
(dark orange-brown blocks) which were collected from the reaction
vessel in good yields.
’ EXPERIMENTAL SECTION
General Procedures. 2,20-Iminobisbenzaldehyde and precursors
were synthesized as described in the literature.34 Diaminoalkanes and
the copper(II) salts were of analytical reagent grade and used without
further purification. Methanol for direct synthesis of the macrocycles
was HPLC grade. IPA and pyridine (Py) were reagent grade.
[CuII LEt(OAc)2] H2O (1). Using the general method A above,
2
3
reaction of H2LEt (28.4 mg, 0.0570 mmol, 1 equiv) with Cu(OAc)2
3
H2O (23.0 mg, 0.1152 mmol, 2.02 equiv) gave pure isolated product
(37.6 mg, 73%). ESI(þ) MS (m/z): 653.11 [C32H28N6Cu2 OMe]þ,
560.17 [C32H28N6CuH]þ. Anal. Calcd for C36H36N6Cu2O5: C, 56.91;
General Method for Direct Synthesis of Imine [2 þ 2]
Macrocycles. To a refluxing solution of 2,20-iminobisbenzaldehyde
(∼6 mmol, 1 equiv) in MeOH (120 mL) was added a standard solution
in MeOH of the appropriate diaminoalkane (∼6 mmol, 1 equiv). Within
20 min a bright yellow precipitate formed. The solution was refluxed for
a further 2 h. Precipitate filtered, washed with ice-cold MeOH, and dried
under vacuum (∼80%).
H, 4.78; N, 11.06 Found: C, 56.89; H, 4.62; N, 11.05. IR (KBr): (cm-1
)
= 3427 (m, br), 3244 (w), 2916 (w), 1635 (s), 1612 (s), 1580 (s), 1552
(s), 1463 (m), 1432 (s), 1401 (s), 1314 (s), 1227 (m), 1190 (m), 1156
(m), 1036 (m), 749 (m), 676 (w), 462 (w). UV-vis: λ/nm (ε/L mol-
1
cm-1) = 249 (20,400), 280 (sh., 12,500), 335 (4,200), 405 (3,600),
Ethylene Linked Imine [2 þ 2] Macrocycle (H2LEt). Using the
general method above, reaction of the dialdehyde (1.4191 g, 6.300
mmol) with ethylene diamine (0.9991 M, 6.31 mL, 6.304 mmol) gave
isolated pure product (1.3243 g, 84%). ESI(þ) MS (m/z): 499.26
[C32H30N6H]þ. Anal. Calcd for C32H301N6: C, 77.08; H, 6.06; N, 16.85
Found: C, 77.19; H, 6.00; N, 16.67. H NMR (300 MHz, CDCl3)
δ = 11.54 (NH, s, 2H), 8.49 (CHN, s, 4H), 7.58 (3-PhH, d [J = 7.5],
4H), 7.27 (6-PhH, d [J = 7.4], 4H), 7.21 (5-PhH, t [J = 7.6], 4H), 6.88
(4-PhH, t [J = 7.1], 4H), 3.96 (NCH2, s, 8H). 13C NMR (75 MHz,
CDCl3) δ = 163.14 (CHN), 143.44 (1-Ph), 131.30 (5-Ph), 131.07 (3-
Ph), 123.38 (2-Ph), 120.36 (4-Ph), 117.51 (6-Ph), 62.22 (NCH2). IR
(KBr): (cm-1) = 3010 (w), 2836 (w), 1630 (s), 1587 (s), 1534 (m),
1384 (m), 1456 (s), 1384 (m), 1316 (m), 1208 (w), 1150 (w), 1015 (w),
982 (w), 745 (s), 486 (w).
486 (6,700), 910 (514).
[CuII LPr(OAc)2] MeOH 1.2H2O (2). Using the general method
2
3
3
A above, reaction of H2LPr (25.7 mg, 0.0488 mmol, 1 equiv) with
Cu(OAc)2 H2O (19.9 mg, 0.0997 mmol, 2.04 equiv) gave pure isolated
3
product (26.2 mg, 70%). ESI(þ) MS (m/z): 709.14 [C36H35N6O2
Cu2]þ, 681.15 [C34H32N6Cu2OMe]þ. Anal. Calcd for C39H44.4N6Cu2
O6.2: C, 56.88; H, 5.43; N, 10.21 Found: C, 56.79; H, 5.24; N, 10.27. IR
(KBr): (cm-1) = 3419 (w, br), 2916 (w), 2854 (s), 1614 (s), 1552 (s),
1460 (m), 1435 (s), 1401 (m), 1323 (s), 1193 (m), 1162 (m), 1135 (m),
1020 (w), 749(m), 670(w), 474 (w). UV-vis: λ/nm (ε/L mol-1 cm-1) =
251 (19,500), 275 (sh., 13,900), 333 (3,700), 396 (3,300), 471 (6,500),
880 (540).
[CuII LBu(OAc)2] 1.2H2O (3). Using the general method A above,
2
3
reaction of H2LBu (40.5 mg, 0.0730 mmol, 1 equiv) with Cu(OAc)2 H2O
3
Propylene Linked Imine [2 þ 2] Macrocycle (H2LPr). Using
the general method above, reaction of the dialdehyde (1.3231 g, 5.874
mmol) with propylene diamine (0.5006 M, 11.74 mL, 5.877 mmol) gave
isolated pure product (1.2306 g, 80%). ESI(þ) MS (m/z): 527.29
[C34H34N6H]þ. Anal. Calcd for C34H341N6: C, 77.54; H, 6.51; N, 15.96
Found: C, 77.30; H, 6.81; N, 16.08. H NMR (300 MHz, CDCl3)
δ = 11.33 (NH, s, 2H), 8.52 (CHN, s, 4H), 7.59 (3 PhH, dd [J = 7.8, 1.8],
4H), 7.41 (6-PhH, dd [J = 8.4, 0.9], 4H), 7.27 (5-PhH, dt [J = 7.2, 1.8],
4H), 6.94 (4 PhH, dt [J = 7.5, 0.9], 4H), 3.73 (NCH2, t [J = 7.2], 8H),
2.06 (NCH2CH2, quin [J = 7.2], 4H). 13C NMR (75 MHz, CDCl3) δ =
161.56 (CHN), 143.48 (1 Ph), 131.43 (3-Ph), 130.94 (5 Ph), 124.20 (2-
(30.5 mg, 0.153 mmol, 2.09 equiv) gave pure isolated product (28.5 mg,
44%). ESI(þ) MS (m/z): 737.17 [C38H39N6O2 Cu2]þ, 709.14
[C36H36N6Cu2OMe]þ. Anal. Calcd for C40H44.4N6Cu2O5.2: C, 58.62; H,
5.46; N, 10.25. Found: C, 58.55; H, 5.36; N, 10.19. IR (KBr): (cm-1) = 3441
(w, br), 2914 (w), 2854(w), 1716 (w), 1618 (s), 1596 (s), 1554 (s), 1462
(m), 1435 (s), 1405 (s), 1318 (s), 1198 (m), 1153 (m), 1014 (w), 746 (m),
675 (w), 462 (w). UV-vis: λ/nm (ε/L mol-1 cm-1) = 249 (20,200), 280
(sh., 11,100), 331 (4,000), 396 (3,300), 476 (7,300), 850 (542).
General Method B: Synthesis of Dicopper(II) Tetrafluor-
oborate Macrocyclic Complexes Derived from Imine [2 þ 2]
Macrocycles. To a hot (70 °C) light yellow suspension of the
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appropriate imine [2 þ 2] macrocycle (1 equiv) in IPA (30 mL) and Py
volume was degassed by passing a stream of Ar through it for 15 min
prior to the measurements and then maintaining an inert atmosphere of
Ar over the solution during the measurements. Em is the midpoint
potential (approximately the reversible formal potential), calculated
from the average of EPA and EPC. ΔEP is the absolute value of the
(7 drops) was added a light blue suspension of Cu(BF4)2 xH2O
3
(2 equiv) in IPA (15 mL). The yellow suspension slowly changed to a
dark orange-brown solution over half an hour. Reduced the solvent
volume to 10 mL, cooled, and then filtered and washed the resulting
precipitate. The product was dried under vacuum.
difference between EPA and EPC
.
[CuII LEt(Py)2(OH2)2](BF4)2 0.5H2O (4). Using the general
2
3
method B above, reaction of H2LEt (50.5 mg, 0.101 mmol) with
’ ASSOCIATED CONTENT
Cu(BF4)2 xH2O (50.4 mg, 0.213 mmol) gave the desired orange-
3
brown product (58.5 mg, 58%). ESI(þ) MS (m/z): 560.172
S
Supporting Information. Further details are provided in
b
[CuLEtH]þ, 436.610 [Cu2LEt(Py)2F](H2O)4, 341.082 [Cu2LEt(IPA)]2þ
.
Figures S1-S68 and Tables S1-S7. This material is available
free of charge via the Internet at http://pubs.acs.org. Supple-
mentary crystallographic data can be obtained from the CCDC
using the following reference codes: 796910 {2,20-iminobis(ethyl
benzoate)}, 796911 {2,20-iminobisbenzaldehyde}, 796912 {H2LEt},
Anal. Calcd for C42H43N8Cu2 B2F8O2.5: C, 50.42; H, 4.33; N, 11.20. Found:
C, 50.52; H, 4.33; N, 10.85. IR (ATR):/cm-1 = 3538 (w, br), 3278 (w),
3054 (w), 2941 (w), 1611 (m), 1553 (m), 1527 (m), 1461 (m), 1433 (m),
1401 (w), 1307 (m), 1192 (m), 1157 (m), 1030 (s, br), 876 (w), 855 (w),
778(m), 745(s), 699(w), 658(w), 520(m), 499(m). UV-vis: λ/nm (ε/L
mol-1 cm-1) = 220 (33,800), 250 (33,000), 277 (sh., 13,300), 329 (3,610),
363 (4,390), 402 (4,780), 478 (6,830), 790 (413).
796913 {H2LPr}, 796914 {H2LBu}, 796915 {[CuII (OAc)2LEt]},
2
796916 {[CuII (OAc)2LPr] 1.5MeOH 0.5H2O}, 796917 {[CuII -
2
2
3
3
(OAc)2 LBu] 3MeOH} and 796918 {[CuII2(DMF)4 LPr]-
[CuII LPr(Py)2(OH2)1.5(IPA)0.5](BF4)2 (5). Using the general
3
2
(BF4)2 2H2O}. This data can be obtained free of charge from
the Cambridge Crystallographic Data Centre via www.ccdc.
method B above, reaction of H2LPr (53.9 mg, 0.102 mmol) with
3
Cu(BF4)2 xH2O (50.5 mg, 0.213 mmol) gave the desired brown product
3
(65.8 mg, 62%). ESI(þ) MS (m/z): 588.202 [CuLPrH]þ, 465.636
[Cu2LPr(Py)2(MeCN)3]2þ. Anal. Calcd for C45.5H49N8Cu2B2F8O2:
C, 52.50; H, 4.75; N, 10.77. Found: C, 52.50; H, 4.67; N, 10.65. IR
(ATR): (cm-1) = 3548 (w, br), 3268 (w), 2928 (w), 1609 (m), 1553 (m),
1536 (m), 1453 (m), 1434 (m), 1403 (w), 1313 (m), 1193 (m), 1157 (m),
1051 (s, br), 880 (w), 853 (w), 749 (s), 699 (w), 677 (w), 641 (w),
520 (m), 471 (m), 440 (w). UV-vis: λ/nm (ε/L mol-1 cm-1) = 213
(19,800), 249 (21,700), 275 (sh., 10,300), 327 (3,710), 363 (3,730), 392
(4,430), shoulder at about 825 (ca. 800).
cam.ac.uk/data_request/cif.
’ AUTHOR INFORMATION
Corresponding Author
*Fax: (þ64)-3-4797906. E-mail: sbrooker@chemistry.otago.
ac.nz.
’ ACKNOWLEDGMENT
[CuII LBu(Py)2(OH2)2](BF4)2 IPA (6). Using the general method
2
3
B above, reaction of H2LBu (47.7 mg, 0.0860 mmol) with Cu(BF4)2 xH2O
We are grateful to the University of Otago for funding this
research, including a Postgraduate Scholarship (to S.A.C.), and
to Professor Alan Bond (Monash) for helpful discussions and
suggestions regarding the electrochemistry results.
3
(42.3 mg, 0.1784 mmol) gave the desired golden-brown product (52.3 mg,
55%). ESI(þ) MS(m/z): 616.24 [CuLBuH]þ, 546.17 [Cu2LBu(Py)5F]2þ
.
Anal. Calcd for C49H58N8Cu2B2F8 O3: C, 53.27; H, 5.02; N, 10.14. Found:
C, 53.40; H, 4.78; N, 10.15. IR (ATR): (cm-1) = 3548 (w, br), 2936 (w),
2865 (w), 1607 (m), 1554 (m), 1537 (m), 1463 (m), 1435 (m), 1409 (m),
1347 (w), 1313 (m), 1303 (m), 1261 (w), 1233 (w), 1197 (m), 1156 (s),
1134 (w), 1053 (s, br), 990 (m), 856 (w), 754 (s), 709 (w), 641 (w),
520 (w), 456 (m), 394 (m). UV-vis: λ/nm (ε/L mol-1 cm-1) = 217
(28,700), 246 (23,100), 271 (17,100), 328 (3,800), 391 (3,800), 436
(5,200), 467 (7,200), 858 (450).
’ REFERENCES
(1) Pilkington, N. H.; Robson, R. Aust. J. Chem. 1970, 23, 2225–2236.
(2) Nelson, S. M. Pure Appl. Chem. 1980, 52, 2461–3476.
(3) Fenton, D. E. Pure Appl. Chem. 1986, 58, 1437–1444.
(4) Lindoy, L. F. The Chemistry of Macrocyclic Ligand Complexes;
Cambridge University Press: Cambridge, U.K., 1990.
(5) Atkins, A. J.; Black, D.; Blake, A. J.; Marin-Becerra, A.; Parsons,
S.; Ruiz-Ramirez, L.; Schroder, M. Chem. Commun. 1996, 457–464.
(6) Okawa, H.; Furutachi, H.; Fenton, D. E. Coord. Chem. Rev. 1998,
174, 51–75.
(7) Reiter, W. A.; Gerges, A.; Lee, S.; Deffo, T.; Clifford, T.; Danby,
A.; Bowman-James, K. Coord. Chem. Rev. 1998, 174, 343–359.
(8) Gerbeleu, N. V.; Arion, V. B.; Burgess, J. Template Synthesis of
Macrocyclic Compounds. Wiley-VCH: Weinheim, Germany, 1999.
(9) Brooker, S. Coord. Chem. Rev. 2001, 222, 33–56.
(10) Brooker, S. Eur. J. Inorg. Chem. 2002, 2535–2547 and front cover
feature.
Instrumentation and Measurements. As reported previously,46
except for the following.
See Supporting Information, Tables S1 and S2 for a summary of
selected crystallographic data, data collection and structure refinement
details.
All cyclic voltammetry (CV) experiments were carried out on
solutions containing 1 mmol L-1 compound and 0.1 mol L-1 TBAPF6
3
electrolyte (Fluka >99%, used as received). Ligands and acetate com-
plexes were run in DCM (filtered through a pad of neutral alumina) in
a mini-cell (2 mL working volume), using a platinum (1 mm diameter)
or glassy carbon (1.4 mm diameter) working electrode connected to a
Ag/AgCl (3 mol L-1 KCl) reference electrode (Cypress EE007 mini-
(11) Vigato, P. A.; Tamburini, S. Coord. Chem. Rev. 2004,
248, 1717–2128.
3
Electrode) and a platinum wire serving as counter electrode. The
tetrafluoroborate complexes were run in dry, distilled (over CaH2)
MeCN in a two-compartment three-electrode cell (5 mL working
volume), using a platinum working electrode (1 mm diameter)
(12) Lozan, V.; Loose, C.; Kortus, J.; Kersting, B. Coord. Chem. Rev.
2009, 253 (19-20), 2244.
(13) Love, J. B. Chem. Commun. 2009, 3154–3165.
(14) Gagnꢀe, R. R.; Koval, C. A.; Smith, T. J. J. Am. Chem. Soc. 1977,
99, 8367–8368.
(15) Acholla, F. V.; Takusagawa, F.; Mertes, K. B. J. Am. Chem. Soc.
1985, 107, 6902–6908.
(16) Bailey, N. A.; Fenton, D. E.; Moody, R.; Rodriguez de Barbarin,
C. O.; Sciambarella, I. N.; Latour, J.-M.; Limosin, D.; McKee, V. J. Chem.
Soc., Dalton Trans. 1987, 2519–2529.
connected to a Ag/0.01 mol L-1 AgNO3 reference electrode and a
3
platinum plate serving as counter electrode. Measurements were re-
corded with an EG&G Princeton Applied Research Potentiostat/
Galvanostat Model 273A unit at room temperature. The working
electrode surface was cleaned using 0.015 μm alumina, washed with
water and dried before every scan unless otherwise stated. The working
3705
dx.doi.org/10.1021/ic200059n |Inorg. Chem. 2011, 50, 3697–3706

Inorganic Chemistry
ARTICLE
(17) Brooker, S.; Hay, S. J.; Plieger, P. G. Angew. Chem., Int. Ed. 2000,
39, 1968–1970.
(18) Brooker, S.; Davidson, T. C.; Hay, S. J.; Kelly, R. J.; Kennepohl,
D. K.; Plieger, P. G.; Moubaraki, B.; Murray, K. S.; Bill, E.; Bothe, E.
Coord. Chem. Rev. 2001, 216-217, 3–30.
(19) Black, D.; Blake, A. J.; Finn, R. L.; Lindoy, L. F.; Nezhadali, A.;
Rougnaghi, G.; Tasker, P. A.; Schroder, M. Chem. Commun.
2002, 340–341.
(20) Depree, C. V.; Beckmann, U.; Heslop, K.; Brooker, S. Dalton
Trans. 2003, 3071–3081.
(21) Li, R.; Mulder, T. A.; Beckmann, U.; Boyd, P. D. W.; Brooker, S.
Inorg. Chim. Acta 2004, 357, 3360–3368.
(22) de Geest, D. J.; Noble, A.; Moubaraki, B.; Murray, K. S.; Larsen,
D. S.; Brooker, S. Dalton Trans. 2007, 467–475.
(23) Jagoda, M.; Warzeska, S.; Pritzkow, H.; Wadepohl, H.; Imhof,
P.; Smith, J. C.; Kr€amer, R. J. Am. Chem. Soc. 2005, 127 (43),
15061–15070.
(24) Torelli, S.; Belle, C.; Gautier-Luneau, I.; Pierre, J. L.; Saint-
Aman, E.; Latour, J. M.; Le Pape, L.; Luneau, D. Inorg. Chem. 2000, 39
(16), 3526–3536.
(25) Tai, A. F.; Margerum, L. D.; Valentine, J. S. J. Am. Chem. Soc.
1986, 108 (16), 5006–5008.
(26) Amendola, V.; Fabbrizzi, L.; Mangano, C.; Pallavicini, P.; Poggi,
A.; Taglietti, A. Coord. Chem. Rev. 2001, 219-221, 821–837.
(27) Anbu, S.; Kandaswamy, M.; Suthakaran, P.; Murugan, V.;
Varghese, B. J. Inorg. Biochem. 2009, 103 (3), 401–410.
(28) Raman, N.; Sakthivel, A.; Rajasekaran, K. J. Coord. Chem. 2009,
62 (10), 1661–1676.
(29) Sreedaran, S.; Shanmuga Bharathi, K.; Kalilur Rahiman, A.;
Jagadish, L.; Kaviyarasan, V.; Narayanan, V. Polyhedron 2008, 27 (13),
2931–2938.
(30) Collinson, S. R.; Fenton, D. E. Coord. Chem. Rev. 1996, 148
19–40.
(31) McKee, V. Adv. Inorg. Chem. 1993, 40, 323–399.
(32) Crichton, R. R. Biological Inorganic Chemistry: An Introduction;
Elsevier: New York, 2008; p 369.
(33) Itoh, S. Comprehensive Coordination Chemistry II 2004,
8, 369–393.
(34) Black, D. S. C.; Rothnie, N. E. Aust. J. Chem. 1983, 36 (12),
2387–2394.
(35) Borisova, N. E.; Reshetova, M. D.; Ustynyuk, Y. A. Chem. Rev.
2007, 107 (1), 46–79.
(36) Menon, S. C.; Singh, H. B.; Patel, R. P.; Kulshreshtha, S. K. J.
Chem. Soc., Dalton Trans. 1996, 7, 1203–1207.
(37) Panda, A.; Menon, S. C.; Singh, H. B.; Morley, C. P.; Bachman,
R.; Cocker, T. M.; Butcher, R. J. Eur. J. Inorg. Chem. 2005, 6, 1114–1126.
(38) Lever, A. B. P. Inorganic Electronic Spectroscopy, 2nd ed.; Else-
vier: New York, 1986; p 864.
(39) Hathaway, B. J. J. Chem. Soc., Dalton Trans. 1972, 1196–1199.
(40) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Vershoor,
G. C. J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
(41) Patel, U.; Singh, H. B.; Butcher, R. J. Eur. J. Inorg. Chem. 2006,
24, 5089–5097.
(42) Menon, S. C.; Panda, A.; Singh, H. B.; Butcher, R. J. Chem.
Commun. 2000, 2, 143–144.
(43) Waltman, R. J.; Bargon, J. Can. J. Chem. 1986, 58 (20), 76–95.
(44) Andrieux, C. P.; Saveant, J. M. J. Electroanal. Chem. 1971, 33
(2), 453–461.
(45) Kolthoff, I. M.; Coetzee, J. F. J. Am. Chem. Soc. 1957,
79, 1852–1858.
(46) Olguín, J.; Brooker, S. New J. Chem. 2011, DOI: 10.1039/
c0nj00774a.
3706
dx.doi.org/10.1021/ic200059n |Inorg. Chem. 2011, 50, 3697–3706