Copper(II) complexes of three isomeric bis(tacn) ligands: Syntheses, structures and properties

Article abstract of DOI:10.1016/j.poly.2015.12.004

Two new isomeric bis(tacn) ligands, 3,5-bis(1,4,7-triazacyclonon-1-ylmethyl)-1-(hydroxymethyl)-benzene (HL^hyx) and 2,6-bis(1,4,7-triazacyclonon-1-ylmethyl)anisole (L^anx) have been synthesised. In addition, 2,6-bis(1,4,7-triazacyclono

Full text of DOI:10.1016/j.poly.2015.12.004

Polyhedron 105 (2016) 246–252
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Copper(II) complexes of three isomeric bis(tacn) ligands: Syntheses,
structures and properties
Campbell J. Coghlan a,1, Eva M. Campi a, Stuart R. Batten b,c, W. Roy Jackson a, Milton T.W. Hearn a,
⇑
a Centre for Green Chemistry, Monash University, Clayton, Australia
b School of Chemistry, Monash University, Clayton, Australia
c Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new isomeric bis(tacn) ligands, 3,5-bis(1,4,7-triazacyclonon-1-ylmethyl)-1-(hydroxymethyl)-
benzene (HLhyx) and 2,6-bis(1,4,7-triazacyclonon-1-ylmethyl)anisole (Lanx) have been synthesised. In
addition, 2,6-bis(1,4,7-triazacyclonon-1-ylmethyl)-4-methylphenol (HLohx) was also synthesised in a
considerably higher yield than the previously reported method. The ligands were reacted with two equiv-
alents of Cu(NO3)2ꢀ3H2O at pH 5 resulting in the formation of three binuclear complexes. The ligands Lanx
and HLhyx form complexes [Cu2Cl3(L)(H2O)](PF6) containing two unique Cu2+ centres coordinated to the
Received 1 October 2015
Accepted 1 December 2015
Available online 11 December 2015
Keywords:
Copper(II) complexes
Aza-macrocycles
Crystal structures
m-Xylene linkers
Immobilised metal ion affinity
chromatography
ligand. In contrast, the phenolic HLohx ligand forms a bridged complex [Cu2(
two Cu centres further linked by ( -Cl) and ( -O) bridges.
l
-Cl)(Lohx)](PF6)2, with the
l
l
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
arise from specific amino acid residues (e.g. histidine) which can
coordinate to the metal ion in a manner similar to those bound
to the bis(tacn) compound.
The study of bis(tacn) ligands is a growing area of research and
many different bridging groups have been synthesised [1–12].
Generally, these ligands have been synthesised using the orthoa-
mide route first described by Zompa [13]. However, some ligands
have been synthesised via different methods, such as tosyl pro-
tected bis(tacn) compounds [14,15] or through the Boc2(tacn)
intermediate [16]. The linker chain has been found to affect how
the ligand binds to various metals. The effects range from forming
polymeric cation compounds and dimers, to the formation of
molecular sandwiches and intermolecular bridges [1–12].
Uses for these bis(tacn) ligands have included, but are not lim-
ited to, advanced modes of protein purification [17,18]. For exam-
ple, these ligands have been used in immobilised metal affinity
chromatography (IMAC) which has become a widely used method
for protein purification. The technique relies upon a ligand being
immobilised onto a solid support matrix and coordinated with a
metal ion. The metal complex ideally then interacts with a peptide
tag genetically engineered into to the protein of interest [19–22].
Typically, the tag consists of a short peptide chain with multiple
metal-binding sites. The metal binding sites on the peptide chains
The interactions of bridged bis(tacn) ligands with borderline
metal ions [23–25], such as Cu(II), Ni(II) or Zn(II), have been inves-
tigated previously [26–34]. Moreover, in our previous studies with
various Cu2+ bis(tacn) complexes (as well as the corresponding
complexes generated with Ni2+, Zn2+ and other borderline metal
ions), we demonstrated that when these complexes are used as
immobilised ligands for the chromatographic purification of native
and recombinant proteins, even closely related bridged bis(tacn)
chelating compounds were found to behave differently in terms
of their affinity binding constants (Kassocs), binding capacities
(Qmaxs) or their on- and off-kinetics (kon’s or koff’s) associated with
their interaction with native or recombinant proteins. These differ-
ences resulted in profound changes in performance between differ-
ent members of this new class of immobilised metal ion affinity
chromatographic (IMAC) resins for use in protein purification
[35,36]. The current investigations were consequently designed
to gain further insight into the origins of this behaviour through
determination of the crystal structures of three such closely related
m-xylene bridged Cu2+ bis(tacn) complexes and, in particular,
determine the organisational arrangement around the Cu2+ ion(s)
in these coordinated structures.
⇑
Corresponding author. Tel.: +61 3 9905 4547; fax: +61 3 9905 4597.
E-mail address: milton.hearn@monash.edu (M.T.W. Hearn).
Current Address: School of Chemistry and Physics, Centre for Advanced
Potentially, the linker can have a large effect on how the metal
can be coordinated. For example, we recently documented that
bis(tacn) ligands bearing phenyl, carboxylic acid or nitro groups
1
Nanomaterials, The University of Adelaide, Adelaide 5005, Australia.
http://dx.doi.org/10.1016/j.poly.2015.12.004
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

C.J. Coghlan et al. / Polyhedron 105 (2016) 246–252
247
were isolated as their hydrochloride salts, Lꢀ6HCl. The bis(tacn)
ligands HLhyx, Lanx and HLohx were characterised by 1H and 13C
NMR spectroscopy, mass spectrometry and elemental analysis.
The previously reported HLohx hydrochloride salt had been pre-
pared in a low yield (28%) from tacn orthoamide [38]. Using the
methods discussed here, with Boc2tacn as the starting material,
the overall yield of the purified product was 74%, including the iso-
lation of the intermediate Boc4 bis(tacn) compound.
R
(HLhyx
)
)
R = H, R' = CH2OH
(Lanx
N
HN
NH
N
R = OMe, R' = H
R = OH, R' = Me (HLohx
)
N
H
N
H
R'
Fig. 1. Schematic representation and abbreviations of the bis(tacn) ligands.
Each ligand (as the Lꢀ6HCl salt) was reacted with 2 equivalents
of Cu(NO3)2ꢀ3H2O in water, and the pH adjusted to approximately
pH 5.0 with 4 M NaOH. This step was followed by the addition of
the counter ion PFꢁ6 (as NH4PF6). The products crystallised from
this mixture over several days and were characterised by X-ray
crystallography and spectroscopic and analytical methods.
on the bridging xylene ring give rise to copper(II) complexes with
different and distinct crystalline structures [34]. This current paper
reports on studies of how these new linkers, all containing
aromatic rings bearing oxygen-containing substituents, affect the
coordination of copper(II) metal ions. To this end, this study
has focused on the synthesis of two new ligands, 3,5-bis(1,4,7-
triazacyclonon-1-ylmethyl)-1-(hydroxy-methyl)-benzene (HLhyx
(containing a CH2OH group in the 1-position) and 2,6-bis(1,4,7-
triazacyclonon-1-ylmethyl)anisole (Lanx
(containing an OMe
group in the 1-position) and the known 2,6-bis(1,4,7-triazacy-
clonon-1-yl-methyl)-4-methylphenol (HLohx
(Fig. 1) using
)
2.1. The structure of [Cu2(Cl)3(Lanx)(H2O)](PF6)ꢀH2O (1)
The asymmetric unit of 1 contains a binuclear Cu2+ complex
cation (Fig. 2), a PF6 counterion, and two intercalated water mole-
cules (both with half occupancy). Within the complex there are
two crystallographically- and chemically-distinct five-coordinate
copper atoms; in addition to the tridentate tacn rings, the
Cu2+(1) is coordinated by a chloride anion and a water molecule,
whilst Cu2+(2) is coordinated by two chloride anions (Table 1).
The ligand adopts a U-shaped geometry, with the tacn groups ori-
entated in a divergent fashion, but with the metal atoms located on
the same side of the ligand. The metal to metal distance within the
complex is 10.315 Å. The aromatic methoxy substituent is not
involved in any interactions.
Adjacent complexes are bound together through a series of
hydrogen bonds (Table 2) between the Cl(1) and the N(6) hydrogen
as well as hydrogen bonds between the Cl(2) and Cl(3) chlorine
atoms with the O(1) hydrogen atoms as shown in Fig. 2B. These
interactions and weaker N–H. . .Cl interactions (Table 2) link the
complexes into 2D sheets that lie in a parallel (ꢁ101) plane. These
sheets alternate with layers of PF6 anions and intercalated water
molecules. The intercalated water molecules form discrete hydro-
gen-bonded squares. Hydrogen bonds between these tetra-aqua
squares, the PF6 anions, the amine groups of the ligands, and the
coordinated water molecules and chloride anions then link all
these components into a complicated 3D network.
)
)
Boc2tacn as the synthetic precursor. Following synthesis and char-
acterisation of the bis(tacn) ligand products, the binding behaviour
of these ligands with copper(II) ions was then investigated. It was
anticipated that the metal–metal distances and metal binding
characteristics of these macrocyclic complexes will give an
indication of what may occur when these ligands are immobilised
onto a solid support. Our objective was to ultimately establish the
structural requirements necessary for these new metal–ligand
complexes to exhibit enhanced binding to specifically tagged pro-
teins during their downstream processing and purification from
complex fermentation or cell culture feed-stocks. In addition, this
study also highlights the benefits of employing the relatively
underutilised Boc2tacn as the precursor for the synthesis of these
compounds and compares this alternative approach to the stan-
dard orthoamide route described by Zompa [13].
2. Results and discussion
The ligands HLhyx, HLohx and Lanx were prepared (Scheme 1)
using adaptations of a previously reported method described by
Kimura and co-workers [37] for the synthesis of the analogous
bridged cyclen compounds. The reaction of two equivalents of di-
tert-butyl-1,4,7-triazonane-1,4-dicarboxylate (Boc2tacn) with the
2.2. The structure of [Cu2(l
-Cl)(Lohx)](PF6)2 (2)
appropriate substituted
a,
a0-dibromo-m-xylene reagent gave the
corresponding Boc4 bis(tacn) compound (Scheme 1). The Boc
The asymmetric unit of 2 comprises a binuclear Cu2+ complex
groups were removed with conc. HCl and the bis(tacn) compounds
cation and two PF6 counterions (Fig. 3). The tacn groups of the
R
Boc
Boc
Boc
Boc
N
N
MeCN, Et3N
R
N
N
N
N
N
N
N
H
R'
HCl
Boc
Boc
Br
Br
R'
R
(HLhyx
)
)
R = H, R' = CH2OH
(Lanx
N
NH
HN
N
.6HCl
R = OMe, R' = H
N
H
N
H
R = OH, R' = Me (HLohx
)
R'
Scheme 1. Synthesis of the bis(tacn) ligands HLhyx, Lanx and HLohx
.

248
C.J. Coghlan et al. / Polyhedron 105 (2016) 246–252
Fig. 2. Ball and stick representation of 1 (A) and the hydrogen bonding between complexes in 1 (B) (hydrogen bonds represented by dotted lines; some atoms omitted for
clarity). Intercalated water molecules have also been omitted for clarity in both figures.
anion, leading to five-coordinate metal environments in which
each copper atom is coordinated to three tacn amine atoms, a
bridging phenoxy oxygen, and a chloride anion. The metal to metal
distance is only 3.12 Å. The analogous Zn2+ complex has been
reported recently [39]. Similar Cu2+ bis(tacn) complexes with a
hydroxide bridge in place of the chloride [40], and an analogous
manganese complex containing a pair of bridging acetates in place
of the chloride [1,38], have also been reported. Unlike 1, there is no
obvious separation of the complexes and the PFꢁ6 counterions in
the lattice. Furthermore, in the absence of the water molecules
found in 1, the most significant intermolecular interactions are
hydrogen bonds between the amine groups of the ligand and the
fluorines of the anions (Table 2). This hydrogen bonding connects
the components into a complicated 3D network.
Table 1
Selected bond distances (Å) in compounds 1, 2 and 3.
1
2
3
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(3)
Cu(2)–N(4)
Cu(2)–N(5)
Cu(2)–N(6)
Cu(1)–Cl(1)
Cu(1)–Cl(2)
Cu(1)–O(1)
Cu(2)–Cl(2)
Cu(2)–Cl(3)
Cu(2)–O(1)
2.274(5)
2.011(5)
2.028(5)
2.286(5)
2.025(5)
2.045(5)
2.2790(17)
–
2.010(4)
2.2942(18)
2.2484(18)
–
2.031(2)
2.179(2)
1.999(2)
2.035(2)
2.192(2)
1.990(3)
2.3134(8)
–
2.298(4)
2.017(5)
2.013(5)
2.281(4)
2.002(4)
2.035(5)
2.2679(18)
2.162(4)
–
1.9427(19)
–
–
2.2501(16)
–
2.003(5)
–
Table 2y
Selected hydrogen bond distances (Å) and angles (°) in compounds 1, 2 and 3.
2.3. The structure of [Cu2(Cl)3(HLhyx)(H2O)](PF6)ꢀ3H2O (3)
D–H
H. . .A
D. . .A
D–H. . .A
As for the previous ligands, the hydroxymethyl ligand
HLhyx forms
a dinuclear complex. The asymmetric unit of
1
O(1)–H(1W). . .Cl(3)I
O(1)–H(2W). . .Cl(2)II
O(3)–H(4W). . .O(4)III
O(4)–H(6W). . .O(3)IV
O(4)–H(5W). . .F(2)
N(5)–H(3N). . .F(5)V
N(2)–H(1N). . .Cl(2)VI
N(6)–H(4N). . .Cl(1)VI
N(3)–H(2N). . ..Cl(3)I
2
0.88(1)
0.88(1)
0.88(1)
0.88(1)
0.88(1)
0.87(2)
0.88(2)
0.87(2)
0.89(2)
2.21(2)
2.29(1)
2.40(11)
1.86(4)
2.07(6)
2.27(5)
2.54(4)
2.44(3)
2.76(6)
3.066(5)
3.168(5)
2.89(2)
2.72(2)
2.86(1)
3.022(7)
3.339(6)
3.278(5)
3.406(5)
164(5)
176(6)
116(9)
165(12)
150(10)
144(8)
152(6)
161(5)
131(6)
[Cu2(Cl)3(HLhyx)(H2O)](PF6)ꢀ3H2O (3) contains the dinuclear
complex, one PF6 counterion, and three lattice water molecules.
As for 1, the two five-coordinate copper atoms are different – in
addition to the tacn ligand, Cu(1) binds to two chloride anions,
while Cu(2) binds to one chloride and one water. Unlike 1, however,
the ligand adopts a Z-conformation, with complexes orientated on
different sides of the ligand. The same conformation is seen in
dinuclear copper complexes of very similar ligands [41,42]. In
contrast, however, to related complexes of the Lcax [34] and the
HLohx ligands, there is only a weak interaction between the
copper(II) centre and an adjacent Cl(1) atom (3.085 Å). The metal
to metal distance across the complex is 10.771 Å.
N(2)–H(2N). . .F(1)
N(2)–H(2N). . .F(5)
N(3)–H(3N). . .F(11)I
N(3)–H(3N). . .F(16)I
N(5)–H(5N). . .F(4)II
C(5)–H(5A). . .F(2)I
3
O(1)–H(1W). . .O(5)
O(1)–H(2W). . .O(2)I
O(2)–H(2C). . .O(4)
O(3). . .O(1)I
0.89(4)
0.89(4)
0.92(4)
0.92(4)
0.80(4)
0.99
2.46(4)
2.57(4)
2.09(4)
2.22(4)
2.28(4)
2.52
3.184(3)
3.359(4)
2.968(6)
3.095(7)
3.048(4)
3.374(4)
139(3)
147(3)
161(3)
160(3)
162(4)
144
These complexes pack in hydrophobic layers dominated by the
ligand backbone, which lie parallel to the (1ꢁ10) plane. These lay-
ers alternate with hydrophilic layers of PF6 counterions and inter-
calated water molecules. A chloride ligand bound to Cu(1), the
coordinated water ligand on Cu(2), and the hydroxyl group of the
ligand all project into this hydrophilic layer. Extensive hydrogen
bonding (Table 2) between the coordinated and lattice water mole-
cules, one of the ligand amine groups (N(5)), the ligand hydroxyl
group, and one of the PF6 fluorines (F(4)) link the components of
the hydrophilic layers together (see Fig. 4).
0.88(1)
0.88(1)
0.84
1.87(1)
1.86(1)
1.95
2.740(8)
2.700(8)
2.78(1)
3.18(1)
2.90(1)
3.00(2)
3.011(6)
169(2)
159(2)
169
–
–
–
O(3)–H(4W). . .O(5)
O(4)–H(5W). . .F(4)II
N(5)–H(5N). . .O(2)III
0.88(1)
0.88(1)
0.93
2.38(1)
2.40(13)
2.21
118(2)
126(13)
143
y Symmetry operations: For 1: I: x ꢁ 1/2, 3/2 ꢁ y, z ꢁ 1/2; II: 1/2 ꢁ x, y + 1/2, 1/2 ꢁ z;
III: 1 ꢁ x, 1 ꢁ y, ꢁz; IV: x, y ꢁ 1, z; V: 3/2 ꢁ x, y + 1/2, 1/2 ꢁ z; VI: 1/2 ꢁ x, y ꢁ 1/2,
1/2 ꢁ z. For 2: I: 1/3 ꢁ y, x ꢁ y + 2/3, z + 2/3; II: y, y ꢁ x, ꢁz. For 3: I: 1 ꢁ x, 1 ꢁ y, ꢁz;
II: x + 1, y, z; III: x ꢁ 1, y, z.
In each of the three new complexes, the Cu coordination
geometries are best described as square-based pyramidal, with
the degree of distortion varying across the metal atoms. This is
ligand are orientated in a convergent fashion, bringing the metal
ions close enough to be bridged by the oxygen substituent on the
bridging central ring. The metals are further bridged by a chloride
reflected in the
s values [43], which are 0.03 (Cu1) and 0.35
(Cu2) for 1, 0.25 (Cu1) and 0.20 (Cu2) for 2, and 0.01 (Cu1) and

C.J. Coghlan et al. / Polyhedron 105 (2016) 246–252
249
Fig. 3. Ball and stick representation of 2. Some hydrogen atoms and the lattice water molecule have been omitted for clarity. One of the PF6 anions is disordered over two
positions, however only one position is shown for clarity.
Fig. 4. Ball and stick representation of 3; intercalated water omitted for clarity.
0.07 (Cu2) for 3. A
s value of 0 indicates true square-based pyrami-
3. Conclusions
dal geometry, while a value of 1 indicates trigonal bipyramidal
geometry. The CuAN bonds for complexes 1 and 3 are consistent
with the general binding for bis(tacn) ligands, with the bond length
to the tertiary amine in the apical position being slightly longer
than the bond length to the secondary amines (Table 1). Complex
2 shows a shorter bond from Cu to the tertiary amine because of
the bridging between the metal ions.
Three ligands HLhyx, Lanx, and HLohx have been prepared and
their binding to copper(II) investigated in this study. These results
confirm that the functional group attached to the xylene linker has
a significant influence on the nature of the crystallised product. The
metal–metal distance in the solid state can vary from between
3.12 Å and 10.77 Å. Of particular interest is the observation that

250
C.J. Coghlan et al. / Polyhedron 105 (2016) 246–252
the phenolic ligand HLohx is deprotonated and forms a
l-O and
l
-Cl
data [16]. 3,5-Bis(bromomethyl)benzyl alcohol was prepared by
DIBAL-H reduction [47] of methyl 3,5-bis(bromomethyl)benzoate.
bridged structure whereas the alcohol in the related HLhyx remains
protonated and uncoordinated. The placing of the hydroxyl group
in the 2-position of the central aromatic ring in HLohx is clearly
the key; in HLhyx the pendant alkoxy group is in the 5-position
and binding to the tacn coordinated copper atoms is therefore
more geometrically difficult. In Lanx, of course, the pendant group
lacks a suitable donor atom to coordinate.
4.1. General method for formation of Boc4-bis(tacn) compounds
Triethylamine (20 mmol) and the substituted
a,
a0-dibromo-m-
xylene (8 mmol) were added to a solution of Boc2 tacn (16 mmol)
in CH3CN (100 mL) and the mixture was stirred for 3 days at reflux.
The mixture was concentrated to a dark amber gum which was
dissolved in CH2Cl2 (50 mL) and washed consecutively with 10%
aq. NaOH (2 ꢂ 50 mL), H2O (50 mL), and brine (50 mL). The aque-
ous phases were combined and back extracted with CH2Cl2
(2 ꢂ 20 mL). The combined organic layers were concentrated to
an amber gum which was redissolved in CH2Cl2 (4 mL) and chro-
matographed on a plug of silica (EtOAc/hexanes, 1:1 ? 2:1) to give
the Boc protected bis(tacn) compound.
These results thus provide structural insights into the origins of
the differences observed in the binding behaviour of recombinant
proteins containing histidine-rich tags incorporated at the N-ter-
minus of the target protein by recombinant DNA technologies,
with bridged bis(tacn) ligands, such as the HLhyx, Lanx and HLohx
ligands, when these ligands are immobilised onto support materi-
als and complexed with Cu(II) or other borderline metal ions to
generate IMAC resins [35,36,44–46]. As an important experimental
procedure in protein purification, many bi-, tri- and tetra-dentate
chelating compounds have been employed with various border-
4.2. 1,4-Di-tert-butyl-7,70-(4-methylphenol-2,6-diyl)bis(1,4,7-
triazonane-1,4-dicarboxylate)
line, e.g. Cu2+, Ni2+, Zn2+, etc, or hard metal ions, e.g. Fe3+, Al3+
,
Yb2+, etc, to generate IMAC adsorbents for use in protein purifica-
tion. Despite their widespread use, detailed information on the
structural requirements and geometries of the coordinated metal
ion(s) within a specific chelated metal ion complex of the gener-
ated IMAC resins is frequently lacking. Thus, the need exists to
establish better criteria to allow the selection of specific chelated
metal ion complexes to achieve improved binding performance
based on their structural complementarity to the primary and sec-
ondary structural features of the chosen histidine-rich tags. In this
manner, the binding attributes of a specific IMAC resin, in terms of
its Kassoc, Qmax and kon/koff, can be optimised. The current investiga-
tion related to the arrangement of the coordinated Cu2+ centres
present within the three closely related bis(tacn) chelating ligands,
thus provides knowledge relevant to these considerations. In par-
ticular, when each of these xylene-bridged bis(tacn) ligands was
immobilised onto the support gel, Sepharose 6 FFTM, the protein
binding performance of the derived IMAC resins in batch (static)
and dynamic binding modes with the hexa-histidine tagged green
fluorescent protein (His6-GFP) and hexa-histidine tagged glu-
tathione S-transferase (His6-GST), revealed significant differences.
For example, the IMAC resin derived from the HLohx (phenolic)
ligand, in contrast to the other two bridged xylene-based bis(tacn)
IMAC resins, exhibited very weak binding with His6-GFP and none
with His6-GST. These findings is consistent with the steric hin-
drance observed around the coordinated Cu2+ ion in the crystal
structure of the corresponding Cu2+–HLohx complex, an effect
which would prevent binding of a histidine-rich tag to the coordi-
nated Cu2+ ion.
Reaction of triethylamine (2 mL), 2,6-bis(bromomethyl)-4-
methylphenol (3.00 g, 10 mmol) and Boc2tacn (7.92 g, 21 mmol)
in CH3CN (100 mL) as described above gave the target compound
as a yellow oil. Yield 6.98 g (85%). 1H NMR (400 MHz, CDCl3), d
(ppm): 1.49 (36H, m, CH3), 2.04 (3H, s, ArCH3), 2.70 (8H, m, tacn
CH2), 3.31 (8H, m, tacn CH2), 3.47 (8H, m, tacn CH2), 3.73 (4H, s,
ArCH2), 6.86 (2H, m, ArH). 13C NMR (100 MHz, CDCl3), d (ppm):
20.6 (CH3), 28.6 (CH3), 49.6 (tacn CH2), 50.3 (tacn CH2), 53.0 (tacn
CH2), 57.1 (CH2), 79.8 (ArC), 153.7 (ArC), 155.3 (ArCH), 153.2 (ArC),
155.4 (ArC), 155.6 (C@O). ESI-MS m/z 791.4 [M+H]+.
4.3. 1,4-Di-tert-butyl-7,70-(1-(hydroxymethyl)benzene-3,5-diyl)bis
(1,4,7-triazonane-1,4-dicarboxylate)
The reaction of triethylamine (1 mL), 3,5-bis(bromomethyl)
benzyl alcohol (1.50 g, 5 mmol) and Boc2tacn (3.17 g, 10 mmol)
in CH3CN (60 mL) as described above gave the target compound
as a yellow oil. Yield 2.77 g (68%). 1H NMR (400 MHz, CDCl3), d
(ppm): 1.45 (36H, m, CH3), 2.70 (8H, m, tacn CH2), 3.24 (8H, m, tacn
CH2), 3.47 (8H, m, tacn CH2), 3.70 (4H, s, ArCH2), 4.67 (2H, s,
CH2OH), 7.10 (1H, m, ArH). 7.3 (2H, m, ArH). 13C NMR (100 MHz,
CDCl3), d (ppm): 28.6 (CH3), 49.8 (tacn CH2), 50.5 (tacn CH2), 54.6
(tacn CH2), 60.4 (ArCH2), 61.6 (CH2OH), 79.5 (ArC), 125.8 (ArCH),
128.4 (ArCH), 140.0 (ArC), 143.6 (ArC), 155.7 (C@O). ESI-MS m/z
791.4 [M+H]+.
4.4. 1,4-Di-tert-butyl-7,70-(anisole-2,6-diyl)bis(1,4,7-triazonane-1,4-
dicarboxylate)
The reaction of triethylamine (1 mL), 2,6-bis(bromomethyl)ani-
sole [48] (2.50 g, 8 mmol) and Boc2tacn (5.66 g, 20 mmol) in CH3CN
(100 mL) as described above gave the target compound as a yellow
oil. Yield 5.55 g (81%). 1H NMR (400 MHz, CDCl3), d (ppm): 1.40
(36H, m, CH3), 2.70 (8H, m, tacn CH2), 3.28 (8H, m, tacn CH2),
3.51 (8H, m, tacn–CH2), 3.70 (3H, s, OCH3), 3.74 (4H, s, ArCH2),
7.40 (1H, m, ArH). 7.48 (2H, m, ArH). 13C NMR (100 MHz, CDCl3),
d (ppm): 28.5 (CH3), 49.3 (tacn CH2), 49.7 (tacn CH2), 50.3 (tacn
CH2), 53.2 (ArCH2), 53.9 (OCH 3), 79.5 (ArC), 131.0 (ArCH), 132.3
(ArC), 155.5 (ArCH), 155.7 (C@O), 157.0 (CAO). ESI-MS m/z 791.4
[M+H]+.
4. Experimental
Reagent or analytical grade materials were obtained from com-
mercial suppliers and used without further purification. 1H and 13
C
NMR spectra were recorded on either a Bruker DPX 300 or a Bruker
DPX 400 spectrometer. The NMR spectra were recorded as solu-
tions in base washed CDCl3, D2O or d6-DMSO and are reported rel-
ative to TMS (tetramethylsilane d 0.00 ppm). Low resolution
electrospray ionisation mass spectra (ESI) were recorded on a
Micromass Platform ll API QMS Electrospray mass spectrometer
and all samples were run in methanol unless otherwise indicated.
The samples were run in positive (ESI)+ mode. Microanalysis of
samples sealed in glass ampoules under nitrogen were determined
by the Campbell Microanalytical Service at the University of Otago,
New Zealand. Boc2tacn was synthesised according literature prepa-
ration methods and the NMR data were consistent with literature
4.5. General method for formation of bis(tacn) salts
The Boc protected bis(tacn) compound (3 mmol) was dissolved
in conc. HCl (50 mL) and the mixture stirred for 12 h at ambient
temperature. The solution was concentrated under reduced

C.J. Coghlan et al. / Polyhedron 105 (2016) 246–252
251
pressure and the precipitate collected by filtration and washed
with cold absolute EtOH (50 mL) to give the HCl salt of the
bis(tacn) compound.
was collected by filtration and washed quickly with a small
amount of cold H2O. Yield 0.10 g (76%). Selected IR bands (cmꢁ1):
3636s, 3318s 3268s, 3244s, 3210s, 2946br s, 2860br s,1617br s,
1584br s, 1527s, 1489s, 1455s, 1350s, 1280s, 1243s, 1148s,
1094vs, 1039vs, 1010s, 822vs, 782s, 697s. Anal. Calc. for
4.6. 3,5-Bis(1,4,7-triazacyclonon-1-ylmethyl)-1-(hydroxymethyl)
benzeneꢀ6HClꢀ4H2O, (HLhyxꢀ6HClꢀsalt)
C
21H42Cl3Cu2F6N6O3P ([Cu2(Cl)3(Lanx)(H2O)](PF6)ꢀH2O): C, 31.3; H,
5.3; N, 10.4. Found: C, 31.4; H, 5.1; N, 10.5%.
1,4-Di-tert-butyl-7,70-(1-(hydroxymethyl)benzene-3,5-diyl)bis
(1,4,7-triazonane-1,4-dicarboxylate) (2.77 g, 3 mmol) was dis-
solved in conc. HCl (50 mL) and the mixture stirred for 12 h as
described above. The 6HCl salt of HLhyx was isolated as a white
solid. Yield 1.54 g (71%). 1H NMR (400 MHz, D2O), d (ppm): 3.06
(8H, m, tacn CH2), 3.28 (8H, m, tacn CH2), 3.68 (8H, s, tacn CH2),
3.98 (4H, s, CH2Ar), 4.71 (2H, s, ArCH2), 7.40 (1H, s, ArH), 7.46
(2H, s, ArH). 13C NMR (100 MHz, D2O), d (ppm): 42.2 (tacn CH2),
43.7 (tacn CH2), 47.4 (tacn CH2), 58.4 (ArCH2), 63.4 (CH2OH),
121.4 (ArCH), 128.8 (ArC), 131.5 (ArCH), 136.2 (ArC), Selected IR
bands (cmꢁ1): 3357br vs, 2963vs, 2660br vs, 1724s, 1444s,
1161br s, 1111s, 1077s, 876s, 764s. ESI-MS m/z 390.3 [M+H]+. Anal.
Calc. for C21H52Cl6N6O5 (HLhyxꢀ6HClꢀ4H2O): C, 37.0; H, 7.7; N, 12.3.
Found: C, 37.1; H, 7.1; N, 11.8%.
4.10. [Cu2(l
-Cl)(Lohx)](PF6)2 (2)
Cu(NO3)2ꢀ3H2O (0.08 g, 0.34 mmol) and HLohxꢀ6HCl (0.10 g,
0.17 mmol) were dissolved in H2O (10 mL). The pH of the solution
was adjusted to pH 5.0 with 4 M NaOH and the mixture stirred for
20 min. Ammonium hexafluorophosphate (0.08 g, 0.48 mmol) was
added and the solution was left to slowly evaporate overnight fol-
lowed by filtration to remove a precipitate. The solution was left to
evaporate over a number of days to yield green crystals. The solid
was collected by filtration and washed quickly with a small
amount of cold H2O. Yield 0.13 g (87%). Selected IR bands (cmꢁ1):
3635s, 3372 m, 3320s, 2864br s, 2084br s, 1890br, w, 1578s,
1527s, 1488vs, 1468s, 1347s, 1318s, 1278vs, 1255s, 1166s,
1147s, 1095s, 1083vs, 1026vs, 1008vs, 954vs, 925s, 827vs, 738s,
659s. Anal. Calc. for C21H37ClCu2F12N6O1P2 ([Cu2(Cl)(Lohx)](PF6)2):
C, 30.0; H, 4.4; N, 10.0. Found: C, 30.7; H, 4.6; N, 9.8%.
4.7. 2,6-Bis(1,4,7-triazacyclonon-1-ylmethyl)anisoleꢀ6HClꢀ3.5H2O,
(Lanxꢀ6HCl salt)
1,4-Di-tert-butyl-7,70-(anisole-2,6-dyl)bis(1,4,7-triazonane-1,4-
dicarboxylate) (5.55 g, 7 mmol) was dissolved in conc. HCl (50 mL)
and the mixture stirred for 12 h as described above. The 6HCl salt
of Lanx was isolated as a white solid. Yield 3.90 g (90%). 1H NMR
(400 MHz, D2O), d (ppm): 2.94 (8H, m, tacn CH2), 3.18 (8H, m, tacn
CH2), 3.46 (8H, s, tacn CH2), 3.86 (3H, s, CH3), 3.86 (4H, s, CH2Ar),
7.08 (1H, m, ArH), 7.30 (2H, m, ArH). 13C NMR (100 MHz, D2O), d
(ppm): 41.5 (tacn CH2), 42.7 (tacn CH2), 46.8 (tacn CH2), 52.5
(ArCH2), 62.7 (OCH3), 125.2 (ArCH), 128.0 (ArC), 132.9 (ArCH),
157.7 (ArC). Selected IR bands (cmꢁ1): 3369br vs, 2961vs, 2659br
vs, 1583s, 1498s, 1433br s, 1257s, 1216s, 990s, 822s. ESI-MS m/z
390.3 [M+H]+. Anal. Calc. for C21H51Cl6N6O4.5 (Lanxꢀ6HClꢀ3ꢀ5H2O):
C, 37.5; H, 7.6; N, 12.5. Found: C, 37.4; H, 7.6; N, 12.4%.
4.11. [Cu2(Cl)3(HLhyx)(H2O)](PF6)ꢀ3H2O (3)
Cu(NO3)2ꢀ3H2O (0.08 g, 0.32 mmol) and HLhyxꢀ6HCl (0.10 g,
0.16 mmol) were dissolved in H2O (10 mL). The pH of the solution
was adjusted to pH 5.0 with 4 M NaOH and the mixture stirred for
20 min. Ammonium hexafluorophosphate (0.08 g, 0.48 mmol) was
added and the solution was left to slowly evaporate overnight fol-
lowed by filtration to remove a precipitate. The solution was left to
evaporate over a number of days to yield blue crystals. The solid
was collected by filtration and washed quickly with a small
amount of cold H2O. Yield 0.13 g (94%). Selected IR bands (cmꢁ1):
3327s, 3238br s, 2930s, 2874s, 2113br w, 1605w, 1488s, 1453s,
1355s, 1296s, 1235s, 1168w, 1093s, 1010br s, 947s, 829vs, 739s.
Anal. Calcd for
H2O): C, 31.3; H, 5.5; N, 10.4. Found: C, 31.1; H, 5.1; N, 10.7%.
C
21H42Cl3Cu2F6N6O3P ([Cu2Cl3(HLhyx)H2O](PF6)ꢀ
4.8. 2,6-Bis(1,4,7-triazacyclonon-1-ylmethyl)-4-methylphenolꢀ
6HClꢀ4H2O, (HLohxꢀ6HCl salt)
4.12. Crystal structure determinations
1,4-Di-tert-butyl-7,70-(4-methylphenol-2,6-diyl)bis(1,4,7-tria-
zonane-1,4-dicarboxylate) (6.98 g, 9 mmol) was dissolved in conc.
HCl (100 mL) and the mixture stirred for 12 h as described above.
The HCl salt of HLohx was isolated as a white solid. Yield 5.19 g
(92%). 1H NMR (400 MHz, D2O), d (ppm): 2.32 (3H, s, CH3), 3.08
(8H, m, tacn CH2), 3.28 (8H, m, tacn CH2), 3.66 (8H, s, tacn CH2),
3.98 (4H, s, CH2Ar), 7.26 (2H, s, ArH). 13C NMR (100 MHz, D2O), d
(ppm): 19.5 (CH3), 42.5 (tacn CH2), 44.1 (tacn CH2), 48.1 (tacn
CH2), 54.1 (ArCH2), 124.6 (ArCH), 131.7 (ArC), 132.9 (ArCH),
150.5 (ArC). Selected IR bands (cmꢁ1): 3368br vs, 2960vs, 2654br
vs, 1582s, 1499s, 1426br s, 1111s, 1009s, 764s, 699s. ESI-MS m/z
390.3 [M+H]+. Anal. Calc. for C21H52Cl6N6O5 (HLohxꢀ6HClꢀ4H2O): C,
37.0; H, 7.7; N, 12.3. Found: C, 37.1; H, 7.1; N, 11.8%. The NMR data
were consistent with literature data [38].
Only very small crystals for compounds 1, 2 and 3 were
obtained. Consequently data for each were measured using the
MX1 beamline at the Australian Synchrotron, Victoria Australia.
The end station comprised a u goniostat with a Quantum 210r area
detector and data were collected at
a single wavelength
(k = 0.71068 Å) using the Blue Ice GUI [49] and processed using
the XDS software.[50] Due to hardware constraints (fixed detector
angle, minimum detector distance) the maximum obtainable
resolution at the detector edge was approximately 0.83 Å. All
structures were solved by standard methods and refined by full
matrix least squares on F2 (SHELX-97) [51] with anisotropic displace-
ment parameter forms for non-hydrogen atoms. Plausible posi-
tions of hydrogen atoms attached to N or O were located in the
difference Fourier map and were refined with N–H/O–H distances
restrained to reasonable values (0.88–0.98 Å); all other hydrogen
atoms were placed in calculated positions and constrained to ride
on the parent atoms with Uiso(H) = 1.2.Ueq(C).
4.9. [Cu2(Cl)3(Lanx)(H2O)](PF6)ꢀH2O (1)
Cu(NO3)2ꢀ3H2O (0.08 g, 0.32 mmol) and Lanxꢀ6HCl (0.10 g,
0.16 mmol) were dissolved in H2O (10 mL). The pH of the solution
was adjusted to pH 5.0 with 4 M NaOH and the mixture stirred for
20 min. Ammonium hexafluorophosphate (0.08 g, 0.48 mmol) was
added and the solution was left to slowly evaporate overnight fol-
lowed by filtration to remove a precipitate. The solution was left to
evaporate over a number of days to yield blue crystals. The solid
4.12.1. Crystal and refinement data
1 C21H42Cl3Cu2F6N6O3P, M = 805.01, blue prism, 0.03 ꢂ 0.02 ꢂ
0.02 mm3, monoclinic, space group P21/n (No. 14), a = 13.996(3),
b = 8.5970(17), c = 26.909(5) Å, b = 99.83(3)°, V = 3190.2(11) Å3,
Z = 4, Dc = 1.676 g/cm3, F000 = 1648, goniostat with quantum 210r

252
C.J. Coghlan et al. / Polyhedron 105 (2016) 246–252
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detector, synchrotron radiation, k = 0.71068 Å, T = 100(2)K, 2hmax
=
53.3°, 45021 reflections collected, 6631 unique (Rint = 0.1442).
Final GooF = 1.023, R1 = 0.0640, wR2 = 0.1510, R indices based on
4202 reflections with I > 2
13 restraints. Lp and absorption corrections applied,
= 1.699 mmꢁ1
21H37ClCu2F12N6OP2, M = 842.04, blue rectangular,
r
(I) (refinement on F2), 423 parameters,
l
.
2
C
0.04 ꢂ 0.03 ꢂ 0.02 mm3, trigonal, space group R-3 (No. 148),
a = b = 35.660(5), c = 13.209(3) Å, V = 14547(4) Å3, Z = 18, Dc =
1.730 g/cm3, F000 = 7668, goniostat with quantum 210r detector,
synchrotron radiation, k = 0.71068 Å, T = 100(2) K, 2hmax = 53.8°,
36055 reflections collected, 6762 unique (Rint = 0.0378). Final
GooF = 1.059, R1 = 0.0417, wR2 = 0.1160, R indices based on 6363
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69 (2014) 219.
reflections with I > 2
restraints. Lp and absorption corrections applied,
r
(I) (refinement on F2), 459 parameters, 0
= 1.595 mmꢁ1
l
.
3 C21H46Cl3Cu2F6N6O5P, M = 841.04, blue prism, 0.30 ꢂ 0.20 ꢂ
0.10 mm3, triclinic, space group P1 (No. 2), a = 11.440(2),
ꢀ
b = 12.180(2), c = 14.490(3) Å,
(3)°, V = 1791.1(6) Å3, Z = 2, Dc = 1.556 g/cm3, F000 = 860, goniostat
with quantum 210r detector, synchrotron radiation,
a = 72.05(3), b = 69.19(3), c = 80.11
k = 0.71068 Å, T = 100(2) K, 2hmax = 55.0°, 29199 reflections
collected, 7554 unique (Rint = 0.0417). Final GooF = 1.038,
R1 = 0.0907, wR2 = 0.2667, R indices based on 6839 reflections with
I > 2
absorption corrections applied,
r
(I) (refinement on F2), 415 parameters, 71 restraints. Lp and
l
= 1.521 mmꢁ1
.
The completeness of this structure is low due to the constraints
of using the goniometer (phi rotation) while utilising the syn-
chrotron radiation source. Multiple attempts to collect data were
undertaken however due to the small nature of crystal better data
could not be obtained.
Acknowledgements
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Part of this research was carried out on the MX1 beamline at the
Australian Synchrotron, Victoria, Australia. Financial support from
Novo Nordisk A/S and from the Australian Research Council for
Linkage Grant funding which included a scholarship (to C.J.C.) is
gratefully acknowledged.
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CCDC 1003839, 1003840 and 1003674 contains the supplemen-
tary crystallographic data for compound 1, 2 and 3 respectively.
These data can be obtained free of charge via http://www.
ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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