Cobalt(III) complexes of monobenzyl-cyclam macrocycle derivatives

Article abstract of DOI:10.1071/CH01032

The synthesis and structural characterization of dichlorocobalt(III) of monobenzyl-cyclam macrocycle derivative were studied. The x-ray crystal structure of the trans derivative showed a distorted octahedral stereochemistry. The cyclam moieties confirmed a trans-III structure for both derivatives. The complexes were used as synthons for electron acceptors in donor-acceptor systems.

Full text of DOI:10.1071/CH01032

P u b l i s h i n g
publishing research papers from all fields of chemical
Volume 54, 2001
© CSIRO 2001
science, including synthesis, structure, new materials,
macromolecules, supramolecular chemistry, biological
chemistry, nanotechnology, surface chemistry, and
analytical techniques.
All enquiries and manuscripts should be directed to:
Dr Alison Green
Australian Journal of Chemistry–
an International Journal for Chemical Science
CSIRO
PUBLISHING
PO Box 1139 (150 Oxford St)
Collingwood, Vic. 3066, Australia
Telephone: +61 3 9662 7630
Fax: +61 3 9662 7611
E-mail: ajc@publish.csiro.au
CSIRO
Published by
PUBLISHING
for CSIRO and the Australian Academy of Science
w w w. p u b l i s h . c s i r o . a u / j o u r n a l s / a j c

Short Communications
Aust. J. Chem. 2001, 54, 101–104
Cobalt(III) Complexes of Monobenzyl-Cyclam Macrocycle Derivatives
Kenneth P. Ghiggino,A Martin J. Grannas,A,B,C Melissa S. Koay,A Andrew W. A. Mariotti,A
W. David McFadyenA,B and Peter A. TregloanA
A School of Chemistry, The University of Melbourne, Vic. 3010, Australia.
B Authors to whom correspondence should be addressed (e-mail: d.mcfadyen@chemistry.unimelb.edu.au).
C New address: Kodak (Australasia) Pty Ltd, Bld 17, 173 Elizabeth Street, Coburg, Vic. 3058, Australia.
Two dichlorocobalt(III) complexes of ligands L1 and L3 in which 4-R-benzyl moieties (R = NO2, NH2) are either
N-bonded (1-position) or C-bonded (6-position) to the 1,4,8,11-tetraazacyclotetradecane (cyclam) macrocycle have
been prepared and characterized: L1 = 1-(4-nitrobenzyl)cyclam; L3 = 6-(4-aminobenzyl)cyclam. The X-ray crystal
structure of trans-[Co(L1)Cl2]ClO4 {M 564.73, monoclinic P21/c (No. 14); a 13.1987(14), b 11.7701(11), c
14.9305(14) Å, β 97.692(9)°; V 2298.6(4) Å3. Z 4. Dc 1.632 g cm–3; final R1 0.0282, wR2 0.0671 (3438 refls Fo >
4σFo), [for all 4022 unique data R1 0.0366, wR2 0.0717]} shows a distorted octahedral stereochemistry at Co, with
a Cl–Co–Cl angle of 174°. The X-ray crystal structure of trans-[Co(L3)Cl2]Cl·H2O {M 488.77; monoclinic P21/n
(No. 14); a 10.5781(12), b 13.536(2), c 15.065(3) Å, β 101.027(13)°; V 2117.3(6) Å3. Z 4. Dc 1.207 g cm–3; final
R1 0.0284, wR2 0.0727 (5296 refls Fo > 4σFo), [for all 7928 data R1 0.0345, wR2 0.0762]} shows a less distorted
octahedral stereochemistry. The Cl–Co–Cl angle is essentially linear, 179.80(14)°. The cyclam moieties in both
structures display the trans-III conformation.
Manuscript received: 11 April 2001.
K
e
n
e
t
th032P.
G
unci
h
i
g
i
n
o
M
r
t
n
J
.
G
a
n
n
a
s
M
l
i
s
S
.
o
a
y
,
n
r
e
W
.
A
.
M
a
r
i
t
i
W
.
D
a
v
d
M
c
Fady
e
nand
P
e
e
A
.T
r
ge
l
oan
S
h
o
C
om
m
a
i
o
n
Introduction
As part of our investigations of photochemically-activated
electron donor–acceptor complexes we are examining
cobalt(III) complexes of the well-known macrocyclic ligand
1,4,8,11-tetraazacyclotetradecane (cyclam) that are
appended with one para-substituted benzyl group. It is
proposed to use these complexes as synthons for electron
acceptors in more elaborate donor-acceptor systems. Two p-
benzyl attachment positions to the cyclam framework have
been examined: attachment at a nitrogen atom (1- or N-
substituted), and attachment at the central carbon of one of
the trimethylene bridges (6- or C-substituted). Whilst the N-
substituted derivatives are more synthetically accessible,
they have two salient disadvantages: the uncomplexed
ligands are reported to be prone to acid-catalysed
debenzylation under reducing conditions;[1] and more
importantly, substitution at N may introduce steric bulk into
the coordination environment of a cyclam-complexed metal
ion, potentially restricting/influencing the accessibility of
exogenous ligands. Herein, we report the syntheses and
structural characterizations of the trans-dichlorocobalt(III)
complexes of the macrocycles 1-(4-nitrobenzyl)cyclam (L1)
and 6-(4-aminobenzyl)cyclam (L3).
Scheme 1. Reagents and conditions: (i) cyclam/CHCl3/K2CO3; (ii)
3 atm. H2/Pd/C/MeOH; (iii) diethyl malonate/NaH/(MeOCH2)2; (iv)
2,3,2-tetraamine/EtOH/reflux 2 weeks; (v) H3B.SMe2/THF.
aminobenzyl tetraoxocyclam has been reported in the patent
literature.[2] Our preparation involved the reduction of the
known precursor 6-(4-nitrobenzyl)cyclam.[3]
Syntheses
Literature procedures were used to obtain cyclam derivatives
L1 and L2,[1] and are summarized in Scheme 1. The
synthesis of the C-alkylated macrocycle L3 from an
The dichlorocobalt(III) complex of L1 was prepared by
aerobic oxidation of the cobalt(II) complex and, so as to avoid
the possibility of debenzylation, subsequent acidification
© CSIRO 2001
10.1071/CH01032
0004-9425/01/020101

102
Short Communications
(with aq. HCl) of the reaction mixture to no further than ca.
pH 3. The perchlorate salt separated in good yield from the
reaction mixture upon addition of NaClO4. The
corresponding complexes of L2 could not be obtained to an
acceptable level of purity by this route. The ESI mass
spectrum (positive-ion mode) of this complex in methanol
solution showed a parent-ion isotopic distribution consistent
with the expected [Co(L1)Cl2]+ cation. The lack of
symmetry in this cation was manifested in the 13C NMR
spectrum where all the aliphatic carbons appeared at
different chemical shifts. The 1H NMR spectrum was
complex due to the presence of four chemically different
rigid chelate rings: the salient features of the spectrum were
the AX system of the nitrobenzyl group at δ 8.26 and 7.63,
three broad peaks at δ 7.24, 6.80, and 6.43, assigned to the
three different amino hydrogens, and the benzylic methylene
AB system centered around δ 3.9. The cyclam-derived peaks
were not assigned fully.
Fig. 1. Diagram of the cation in the structure of trans-
[Co(L1)Cl2]ClO4. Ellipsoids are scaled to 35% probability
amplitudes. Selected bond lengths (Å): Co–N(1) 2.080(2); Co–N(2)
1.975(2); Co–N(3) 1.975(2); Co–N(4) 1.974(2). Selected angles (deg):
Cl(1)–Co–Cl(2) 174.22(2); N(1)–Co–N(2) 86.80(7); N(1)–Co–N(3)
178.75(7); N(1)–Co–N(4) 93.44(7); N(2)–Co–N(3) 93.39(8); N(2)–
Co–N(4) 177.74(8); N(3)–Co–N(4) 86.32(8); N(1)–Co–Cl(1)
92.42(5); N(2)–Co–Cl(1) 86.46(6); N(3)–Co–Cl(1) 86.36(6); N(4)–
Co–Cl(1) 91.28(6); N(1)–Co–Cl(2) 93.26(5); N(2)–Co–Cl(2)
92.82(6); N(3)–Co–Cl(2) 87.96(6); N(4)–Co–Cl(2) 89.42(6).
The dichlorocobalt(III) complex of L3 was formed by
reaction of cobalt(II) chloride hexahydrate with L3 in
aqueous methanol containing a small amount of HCl,
followed by atmospheric oxidation. Subsequent addition of
excess lithium chloride led to the formation of the chloride
salt of the dichloro cobalt(III) complex that was obtained in
low yield as green prismatic crystals by slow evaporation of
a mainly aqueous solution. The 13C NMR spectrum of the
complex was measured in (D6)Me2SO and it exhibits only 5
aliphatic resonances (the solvent multiplet either obscures 2
aliphatic peaks or some of these peaks coincide), indicating
that the cation is of Cs symmetry. In the 1H NMR spectrum
in (D4)MeOH, two broad signals at δ 6.12 and 6.22 were due
to the two different types of coordinated macrocyclic amino
hydrogens. These did not exchange with solvent deuterium
under neutral conditions, behaving like those in the
In a motif similar to that observed for the cation in the
complex [CuII(L4)Cl2] {L4 = 4-(1-cyclamylmethyl)benzoic
acid},[7] the benzyl moiety is oriented away from the metal
center. This Cu complex also displays the pattern of differing
M–N distances observed in the Co(III) complex of L1.
Diffraction-quality crystals of [Co(L3)Cl2]Cl·H2O were
obtained by the slow evaporation of the reaction mixture in
which the complex was formed. A diagram of the cation
determined from a single-crystal X-ray anaylsis of a
representative crystal is shown in Fig. 2. The cobalt atom is
octahedrally coordinated with the macrocycle in an
equatorial position. The macrocyclic nitrogens are
1
[Co(L1)Cl2]Cl H NMR spectrum. The aromatic amino
hydrogens exchanged with solvent in (D4)MeOH solution
but were observed as a broad signal at δ 5.92 in the spectrum
of a (D6)Me2SO solution of the complex.
Crystal Structures
Crystal data for both structures are presented in the
experimental section. Crystals of trans-[Co(L1)Cl2]ClO4
suitable for X-ray crystal studies were grown by Et2O-vapour
diffusion into a N,N-dimethylformamide solution of the
complex. The structure of a representative crystal contains
trans-[Co(L1)Cl2]+ cations and orientationally disordered
+
–
ClO4 anions. A diagram of the trans-[Co(L1)Cl2] cation is
presented in Fig. 1. The cation has a distorted octahedral
geometry typically seen for Co(III) complexes of cyclam.[4]
The macrocycle is in the most stable trans-III
conformation.[5,6] The Cl atom closest to the benzyl group
[i.e. Cl(2)] displays a shorter Co–Cl distance by 0.04 Å than
Cl(1). The Cl–Co–Cl angle is 174.22(2)°, with the Cl atoms
bent away from the nitrobenzyl group—both N(1)–Co–Cl
bond angles are obtuse. The Co–N distances are similar to
those observed for the [CoIII(cyclam)Cl2]+ cation[4] (ca. 1.97
Å) but with a longer Co–N(1) distance (2.08 Å) which
reflects the relative steric bulk of the tertiary amino nitrogen.
Fig. 2. Diagram of the cation in the structure of trans-
[Co(L3)Cl2]Cl·H2O. Ellipsoids are scaled to 35% probability
amplitudes. Selected bond lengths (Å): Co–N(1) 1.9786(14); Co–
N(2) 1.9760(15); Co–N(3) 1.9746(15); Co–N(4) 1.9741(14).
Selected angles (deg): Cl(1)–Co–Cl(2) 178.11(2); N(1)–Co–N(2)
86.67(6); N(1)–Co–N(3) 179.58(6); N(1)–Co–N(4) 93.53(6); N(2)–
Co–N(3) 93.26(6); N(2)–Co–N(4) 179.54(6); N(3)–Co–N(4)
86.54(6); N(1)–Co–Cl(1) 91.95(5); N(2)–Co–Cl(1) 89.56(5); N(3)–
Co–Cl(1) 87.64(5); N(4)–Co–Cl(1) 90.01(5); N(1)–Co–Cl(2)
88.45(5); N(2)–Co–Cl(2) 92.30(5); N(3)–Co–Cl(2) 91.97(5); N(4)–
Co–Cl(2) 88.12(5).

Short Communications
103
trans-[(6-(4-Aminobenzyl)cyclam)dichlorocobalt(III)] Chloride
sesquihydrate [Co(L3)Cl2]Cl·1.5H2O
coordinated in a coplanar equatorial manner and the chloro
ligands are coordinated axially. The macrocycle adopts the
trans-III configuration. The Cl–Co–Cl angle is essentially
linear, at 178.11(2)°, which is close to the exactly linear Cl–
Co–Cl geometry observed for the unsubstituted
[Co(cyclam)Cl2]+ cation.[4]
A solution of cobaltous chloride hexahydrate (238 mg, 1.00 mmol) and
6-(p-aminobenzyl)cyclam (305 mg, 1.00 mmol) in methanol (20 mL)
was heated to boiling, a small amount of green amorphous solid
separated, then 1.0 M aq. HCl (1.0 mL, 1 mmol) was added and the
mixture clarified. Air was bubbled through the green solution for 2 h,
the mixture was again heated to boiling and a solution of lithium
chloride (850 mg, 20 mmol) in water (5 mL) was added in small
portions. The mixture was concentrated on a steambath to ca. 15 mL
and allowed to evaporate at room temperature. Uniformly green
prismatic crystals of the monohydrate were collected when the volume
was ca. 10 mL, and were washed with a minimum of cold water. Drying
under vacuum at 110°C and subsequent re-exposure to the atmosphere
produced the sesquihydrate (74 mg, 15%), m.p. 330°C (dec.) (Found:
C, 41.2; H, 7.2; N, 14.5; Cl, 21.0. C17H31CoCl3N5·1.5H2O requires C,
41.0; H, 6.9; N, 14.1; Cl, 21.4%). IR (KBr) 1633 (ArNH2), 3437 (H2O)
cm–1. 1H NMR ((D4)MeOH) δ 7.00, d, J 8.3 Hz, 2H, Ar; 6.74, d, J 8.3
Hz, 2H, Ar; 6.22, br, 2H, NH; 6.12, br, 2H, NH; 1.98, m, 1H, CCH2C;
1.90, m, 1H, CCH2C. 13C NMR ((D6)Me2SO) δ 145.1, 129.6, 126.7,
115.1, 53.1, 52.5, 47.9, 36.6, 27.4.
Conclusion
In the absence of packing effects that might influence the
geometry around Co, the presented results confirm the
expectation that methylene substitution at the 6-position of
cyclam is sterically undemanding when compared with
substitution at the 1-position.
Experimental
All solvents for synthesis were AR grade and used as received
unless otherwise specified. Cyclam,[8] L1, L2,[1] and 6-(4-
nitrobenzyl)cyclam·4HCl[3] were all prepared by published procedures.
1H and 13C NMR spectra were recorded on Varian Unity 300, and
UnityPlus 400 spectrometers: shifts are given in ppm relative to the
solvents used [CDCl3 δH 7.26, δC 77.0; (D4)MeOH δH 3.30 (Me), δC
49.0; (D6)Me2SO δH 2.49, δC 39.5]. IR spectra were recorded on
samples dispersed in KBr disks using a Bio-Rad FTS 165 FT-IR
spectrometer. Elemental analyses were performed by the Campbell
Microanalytical Laboratory, University of Otago, New Zealand.
Crystallography
Crystals of [Co(C17H29N5O2)Cl2]ClO4 for diffraction studies were
grown by Et2O-vapour diffusion into a solution of the complex in N,N-
dimethylformamide. Crystals of [Co(C17H31N5)Cl2]Cl were grown
from aqueous solution by slow evaporation. Both crystals were attached
to small glass fibers by epoxy cement. Data was collected using ω: 2θ
scans at 20°C using an Enraf–Nonius CAD4MachS diffractometer
fitted with MoKα radiation (graphite monochromator, λ 0.71073 Å).
[Co(C17H29N5O2)Cl2]ClO4. M 564.73; Monoclinic P21/c (No. 14); a
13.1987(14), b 11.7701(11), c 14.9305(14) Å, β 97.692(9)°; V 2298.6(4)
Å3. Z 4. Dc 1.632 g cm–3; F(000) 1168. µMo 11.40 cm–1. Dark green,
prismatic specimen 0.40 × 0.23 × 0.19 mm, 4588/4022 measured/unique
data, 2θmax 50°, Rint = 0.0128. All non-hydrogens anisotropically
modelled, hydrogens modelled at calculated positions with a common
isotropic thermal parameter. The perchlorate anion was orientationally
disordered and modelled as two ClO4 tetrahedra that shared a common
centre (Cl3) and vertex (O3)—a parameter was refined for the
complementary occupancies of these two orientations. Max., min.
transmission factors 0.8255, 0.7353.[9] Final R1 0.0282, wR2 0.0671
(3438 data Fo > 4σFo), [all data R1 0.0366, wR2 0.0717], GoF (S) 1.027.
Max., min. residual electron density 0.339 and –0.315 e Å–3.
[Co(C17H31N5)Cl2]Cl·H2O. M 488.77; Monoclinic P21/n (No. 14);
a 10.5781(12), b 13.536(2), c 15.065(3) Å, β 101.027(13)°; V 2117.3(6)
Å3. Z 4. Dc 1.207 g cm–3; F(000) 1024. µMo 12.07 cm–1. Dark green,
prismatic specimen 0.53×0.50×0.30 mm, 9540/7928 measured/unique
data, 2θmax 55° Rint = 0.0295. Hydrogens attached to the anilino
nitrogen and the solvent water molecule were clearly evident in
difference maps and their positions and individual isotropic thermal
motion coefficients were included as parameters refined in the model.
Max., min. transmission factors 0.8273, 0.7812.[10] Final R1 0.0284,
wR2 0.0727 (5296 refls Fo > 4σFo), [for all data R1 0.0345, wR2
0.0762], GoF (S) 1.100. Max., min. residual electron density 0.397 and
–0.357 e Å–3.
Synthesis of Ligands and Complexes
Caution! Perchlorate salts of organic ligand complexes are potentially
explosive. Due care must be exercised in their preparation and handling.
trans-[Dichloro(1-(4-nitrobenzyl)cyclam)cobalt(III)] Perchlorate
[CoIII(L1)Cl2]ClO4
A solution of CoCl2·6H2O (238 mg, 1.00 mmol) in MeOH (10 mL) was
added to a solution of L1 (335 mg, 1.00 mmol) in MeOH (20 mL),
initially forming a brown solution that became green soon after heating
it to its b.p. Hydrochloric acid solution (0.5 M, 2.2 mL) was added and
the mixture was oxidized at room temperature for 4 h using a gently
bubbling air stream. A solution of NaClO4·H2O (562 mg, 4.00 mmol)
in MeOH (2 mL) was then added, the mixture became opalescent, and
H2O (10 mL) was added. The mixture was evaporated to a small volume
under a gentle air stream, yielding a uniformly green microcrystalline
solid. The solid was collected, washed with water, then dried at the
pump (413 mg, 73%) (Found: C, 36.2; H, 5.3; N, 12.3; Cl, 18.7.
C17H29CoCl3N5O6 requires C, 36.2; H, 5.2; N, 12.4; Cl, 18.8%). Mass
spectrum (ESI): m/z 488 ([Co(L1)37Cl2]+, 10%). 1H NMR ((D6)Me2SO)
δ 8.26, d, J 8.3 Hz, 2H, Ar; 7.63, d, J 8.3 Hz, 2H, Ar; 7.24, br, 1H, NH;
6.80, br, 1H, NH; 6.43, br, 1H, NH; 4.26, d, J 14.4 Hz, 1H, ArCH2; 3.94,
d, J 14.4 Hz, 1H, ArCH2; 3.39, m, 1H, NCH; 3.03–2.33, m, 14H, NCH2;
2.07, m, 5H, NCH2 and CCH2C. 13C NMR ((D4)Me2SO) δ 147.5,
139.1, 134.0, 123.2, 55.8, 55.1, 53.3, 52.9, 52.1, 50.9, 48.9, 47.7, 47.2,
27.2, 24.2.
Both structures. Corrections were applied for Lorentz and polariza-
tion effects. Face-indexed analytical absorption corrections were ap-
plied.[10] Structures were solved using direct methods;[11] full-matrix
least-squares refinement against F2,[9] all non-hydrogen atoms aniso-
tropic, hydrogens attached to carbon atoms and coordinated nitrogens of
the macrocycles at calculated positions with common isotropic thermal
parameters. Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the Cambridge Crys-
tallographic Data Center as supplementary publications, Nos CCDC
163332 (for [Co(C17H29N5O2)Cl2]ClO4) and CCDC 163333 (for
[Co(C17H31N5)Cl2]Cl·H2O). Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: +44 (0)1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
6-(4-Aminobenzyl)cyclam (L3)
6-(4-Nitrobenzyl)cyclam (1.00 g, 2.98 mmol) was hydrogenated in
methanol (50 mL) using 5% Pd/C catalyst (0.30 g) under 3 atm. H2 for
18 h. The mixture was then filtered through Filter Aid, the filter pad was
washed thoroughly with methanol and the combined filtrate and
washings were reduced to dryness by rotary evaporation to obtain the
product (886 mg, 97%), m.p. 155–157°C (lit.[2] 156–158°C), which was
1
used without further purification. H NMR (CDCl3/D2O) δ 6.92, d,
J 8.3 Hz, 2H, Ar; 6.59, d, J 8.3 Hz, 2H, Ar; 2.81–2.34, m, 18H, CH2Ar
and 8 × CH2N; 1.94, m, 1H, CH; 1.70, m, 2H, CCH2C. 13C NMR
(CDCl3) δ 144.3, 130.3, 129.7, 115.1, 55.7, 50.7, 49.1, 40.7, 38.0, 29.0.

104
Short Communications
[4] M. E. Sosa-Torres, R. A. Toscano, Acta Crystallogr. 1997, C53,
1585.
[5] B. Bosnich, C. K. Poon, M. L. Tobe, Inorg. Chem. 1965, 4, 1002.
[6] I. I. Creaser, T. Komorita, A. M. Sargeson, A. C. Willis, K.
Yamanari, Aust. J. Chem. 1994, 47, 529.
Acknowledgments
We thank Sheena Wee for measuring ESI mass spectra, and
the Australian Research Council for financial support.
[7] M. Manzetti, L. Macko, M. Neuberger-Zehnder, T. A. Kaden,
Helv. Chim. Acta 1997, 80, 934.
[8] E. K. Barefield, F. Wagner, A. W. Herlinger, A. R. Dahl, Inorg.
Synth. 1976, 16, 220.
[9] G. M. Sheldrick, ‘SHELXL-97. Program for Crystal Structure
Refinement’ (Universität Gottingen: Germany 1997).
[10] G. M. Sheldrick, ‘SHELX-76. Program for Crystal Structure
Determination’ (University of Cambridge: UK 1976).
[11] G. M. Sheldrick, ‘SHELXS-86. Program for Crystal Structure
Solution’ (Universität Gottingen: Germany 1986).
References
[1] I. M. Helps, D. Parker, J. R. Morphy, J. Chapman, Tetrahedron
1989, 45, 219.
[2] W. J. Kruper, Jr, D. K. Pollock, W. A. Fordyce, M. J. Fazio, M. N.
Inbasekaran, R. Muthyala, US Patent 5489425, 1996.
[3] P. Moreau, M. Tinkl, M. Tsukazaki, P. S. Bury, E. J. Griffen, V.
Snieckus, R. B. Maharajh, C. S. Kwok, V. V. Somayaji, Z. Peng,
T. R. Sykes, A. A. Noujaim, Synthesis 1997, 1010.