Synthesis, crystal structures, and electrochemistry of CuII complexes with tetradentate N2O2 ligands derived from 3,7-diazabicyclo[3.3.1]nonan-9-one

Article abstract of DOI:10.1007/s11172-006-0044-2

New copper(II) complexes with tetradentate ligands derived from 1,5-diphenyl-3,7-diazabicyclo[3.3.1]nonan-9-one and containing the N,N′-2-hydroxyethyl, 2-methoxyethyl, and carboxymethyl substituents were synthesized. The crystal structures of the complexes were established and the complexes were studied by cyclic voltammetry. The ligands are preorganized for complexation and are highly complementary for a divalent copper cation.

Full text of DOI:10.1007/s11172-006-0044-2

Russian Chemical Bulletin, International Edition, Vol. 54, No. 8, pp. 1825—1835, August, 2005
1825
Synthesis, crystal structures, and electrochemistry
of CuII complexes with tetradentate N2O2 ligands
derived from 3,7ꢀdiazabicyclo[3.3.1]nonanꢀ9ꢀone
a
b
b
S. Z. Vatsadze,a V. S. Tyurin,a N. V. Zyk, A. V. Churakov, L. G. Kuz´mina,
ꢀ
E. V. Avtomonov,c R. D. Rakhimov,a and K. P. Butina†
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 939 0290. Eꢀmail: tv@org.chem.msu.ru
bN. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
31 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 954 1279
cA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (495) 135 5085
New copper(II) complexes with tetradentate ligands derived from 1,5ꢀdiphenylꢀ3,7ꢀ
diazabicyclo[3.3.1]nonanꢀ9ꢀone and containing the N,N´ꢀ2ꢀhydroxyethyl, 2ꢀmethoxyethyl,
and carboxymethyl substituents were synthesized. The crystal structures of the complexes were
established and the complexes were studied by cyclic voltammetry. The ligands are preorganized
for complexation and are highly complementary for a divalent copper cation.
Key words: diazabicyclononane, bispidine, copper complexes, amino acids, structure, elecꢀ
trochemistry.
3,7ꢀDiazabicyclo[3.3.1]nonane (DABCN, bispidine)
is a functional building block, which has been extensively
studied in organic chemistry and is widespread in living
nature.1 It combines the complexation properties of the
nitrogen atoms included in the chelating configuration
and rigid geometry of the bicyclic moiety, which fixes the
directionality of the lone pairs of heteroatoms and the
volume of the coordination sphere.2,3 This provides seꢀ
lectivity and strength of complexation with appropriate
metal cations and even neutral atoms fitting into the coꢀ
ordination sphere.4 A wide range of possible modificaꢀ
tions, varying the nature of substituents in the skeleton,
and controlling the conformational equilibrium between
the constituent sixꢀmembered rings allow one to make
bispidine derivatives suitable for solving certain problems.
In particular, diazabicyclononaneꢀbased pharmaceuticals,
which control signal transduction in synapses and are
used for the treatment of certain diseases, were designed.5
It is conceivable that complexation of bispidines with
metal cations in heart tissues plays a decisive role in the
management of cardiac arrhythmia with the use of approꢀ
priate pharmaceuticals.6 Complexes with (–)sparteine,
which is a naturally occurring chiral alkaloid containing
DABCN as the key fragment, have been studied most
thoroughly. Sparteine complexes with transition and
mainꢀgroup metals have found use as enantioselective
catalysts.7 An essential drawback, which limits the synꢀ
thetic potential of the natural alkaloid, is that the (+)enanꢀ
tiomer is inaccessible, resulting in the formation of only
one type of stereoisomers. This has stimulated a search for
synthetic analogs of sparteine.8 Although bispidines have
been studied inꢀdepth, data on their complexes are surꢀ
prisingly scarce. Studies in this field have been intensified
in the past decade because of diversity of bispidines and
prospects of their use as ligands.
As part of our continuing studies of the complexation
properties of 1,5ꢀdiphenylꢀ3,7ꢀdiazabicyclo[3.3.1]noꢀ
nanes containing various substituents at the nitrogen
atoms,9 we turned our attention to N2O2ꢀtype tetradentate
ligands, which, like N4ꢀtype bispidine ligands,2,3,10 are
expected to possess a pronounced chelating effect and
high affinity for divalent copper cations. At the same time,
the presence of oxygen atoms lowers the symmetry of the
coordination environment of the copper cations and opens
up possibilities for the synthesis of innerꢀcomplex salts.
The steric volume of the environment of the oxygen atoms
is smaller than that of the nitrogen atom because it has
only two substituents. As a result, additional ligands can
† Deceased.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1773—1782, August, 2005.
1066ꢀ5285/05/5408ꢀ1825 © 2005 Springer Science+Business Media, Inc.

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Vatsadze et al.
more easily approach the copper atom, which is of imporꢀ
tance in catalytic processes.
acids (in which this effect is smaller) do not afford the
expected condensation products as well.17 Earlier,18 we
have succeeded in performing the Mannich reaction with
alanine to prepare bispidone 4 containing chiral substituꢀ
ents at the nitrogen atoms.
Results and discussion
We synthesized ligands 1—4 using procedures deꢀ
scribed in the studies11—13 and in our earlier publicaꢀ
tions.18 Complex compounds 5 and 6 were synthesized
from copper(II) chloride and perchlorate, respectively, by
heating mixtures of solutions of the corresponding salt
and the ligand followed by crystallization of the product
upon cooling of the reaction mixture. Chelated salt 7 was
prepared by deprotonation of chloride complex 5 with
alkali. Compounds 8 and 9 were synthesized by heterogeꢀ
neous reactions of solutions of the ligands with copper
hydroperoxide.
R = H (1, 3), Me (2, 4)
We used the simplest αꢀamino acids, such as glycine
and alanine, and their reduced derivatives, such as ethaꢀ
nolamine and 2ꢀmethoxyethylamine, as bicyclononaneꢀ
bridged chelating moieties. These DABCN ligands were
synthesized by double Mannich condensation with the
use of the corresponding primary amine, dibenzyl ketone,
and paraformaldehyde. The reactions with ethanolamine
and its methyl ether afforded ligands 1 and 2, respecꢀ
tively.11,12 The glycine derivative of bispidone 3 has been
described for the first time by Stetter,13 who prepared its
complex salts with CoII, NiII, and CuII and measured
their stability constants. However, the structural data were
lacking. Attempts to incorporate other amino acids into
the bicyclononane structure failed, except for α,αꢀdiꢀ
methylglycine.14 The Mannich reaction of amino acids
are difficult to perform because of the influence of the
carboxy group, which is manifested, in particular, in low
nucleophilicity of the amino group. This is confirmed by
the fact that reactions with amino acid esters, as well as
with aromatic amines,15 proceed even more difficultly.16
The yields of the reaction products are very low. The
influence of the carboxy group of amino acids on the
Mannich reaction cannot be attributed exclusively to the
(–I ) effect, because the reactions with βꢀ and γꢀamino
Structures of complexes
The crystal structures of complexes 5—7 and 9 were
established by Xꢀray diffraction analysis. The crystalloꢀ
graphic data are given in Table 1. Selected bond lengths,
bond angles, and torsion angles are listed in Tables 2—4.
The structures of complexes 5—7 and 9 are shown in
Figs 1—4. Since we failed to grow single crystals of comꢀ
pound 8 suitable for Xꢀray diffraction study, the geometry
of 8 was calculated by two quantumꢀchemical methods,
the semiempirical PM3(tm) method and the density funcꢀ
tional theory (DFT).
Generally, complexation of bispidine leads to the
transformation of the bicyclic moiety into the exclusively
rigid tricyclic skeleton, in which only slight variations in
C(12)
C(13)
C(12´)
O
C(11)
C(10)
C(11´)
C(13´)
C
C(10´)
C(5´)
C(5)
C(14´)
C(15´)
C(14)
C(15)
C(4)
C(3´)
C(4´)
C(3)
N(1´)
C(2´)
N(1)
C(2)
O(2)
Cu
C(1)
RNH2
=
(1),
(3),
(2),
C(1´)
Cl(1)
O(1)
O(1´)
Fig. 1. Structure of complex 5.
(4)

Copper(II) complexes with N2O2 bispidines
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
1827
Table 1. Crystallographic data for compounds 5—7 and 9
Parameter
5
6
7
9
Molecular formula
Molecular weight
Temperature
Radiation
Wavelength/Å
Crystal dimensions/mm
Crystal system
Space group
a/Å
b/Å
c/Å
α/deg
β/deg
C
25H36Cl2CuN2O5 C25H32Cl2CuN2O11
C23H36CuN2O8
532.08
C50H52Cu2N4O14
1060.04
579.00
293(2)
670.97
213(2)
293(2)
298(2)
MoꢀKα
MoꢀKα
CuꢀKα
MoꢀKα
0.71073
0.4×0.1×0.1
Monoclinic
Cc
14.472(1)
21.792(1)
8.768(1)
90.00
119.38(1)
90.00
2409.5(4)
4
0.71073
1.54178
0.71073
0.2×0.2×0.2
Orthorhombic
P212121
9.164(2)
17.558(4)
29.392(6)
90.00
90.00
90.00
4729.2(18)
4
1.489
0.4×0.2×0.2
0.6×0.1×0.1
Triclinic
Triclinic
–
–
P1
P1
8.991(1)
12.725(1)
13.232(1)
114.37(1)
95.89(1)
103.54(1)
1306.4(2)
2
10.636(1)
10.646(1)
13.258(1)
104.15(1)
91.77(1)
108.09(1)
1374.4(2)
2
γ/deg
V/Å3
Z
dcalc/g cm–3
1.472
1.621
1.467
0.957
µ/mm–1
1.079
3.479
0.973
F(000)
606
694
1124
2200
θ Scan range
Ranges of indices of measured
reflections
2.39—25.12
–10 < h < 10
–15 < k < 13
0 < l < 15
4837
3.46—64.99
–12 < h < 13
–13 < k < 12
0 < l < 16
3472
2.52—25.00
–12 ≤ h ≤ 17
–5 < k < 25
–10 < l < 10
3622
2.32—27.50
0 < h < 12
0 < k < 24
0 < l < 41
6026
Number of measured reflections
Number of independent
4619 (0.0366)
3334 (0.0489)
2841 (0.0448)
6023 (0.0025)
reflections (Rint
)
Number of parameters in refinement
R1 [I > 2σ(I )]
wR2 (based on all reflections)
Goodnessꢀofꢀfit on F 2
Flack absolute structure parameter
Residual electron density
(max/min)/e Å–3
317
0.0789
0.2185
1.044
—
333
0.1065
0.3746
1.033
—
452
0.0282
0.0710
1.036
634
0.0359
0.1100
1.013
–0.01(1)
–0.01(2)
1.263/–2.364
1.441/–0.762
0.450/–0.545
0.469/–0.300
Table 2. Selected geometric parameters of molecules 1 and 4
determined by Xꢀray diffraction analysis
as a result of deviation of the metal atom from the mean
N2O2 plane. In addition, the ethanolamine and αꢀamino
acid fragments differ in both the electronic and steric
properties.
Parameter
1
4a
4b
4c
The available structural data19,20 for ligands 1 and 4
provide a possibility of comparing these ligands with the
corresponding complexes 5, 7, and 9. In the crystal, molꢀ
ecules 1 adopt a chair—boat conformation, which is, apꢀ
parently, the major conformation in solution as well.17
Upon complexation, the ligand molecule is forced to adopt
a chair—chair conformation. Molecules 4, like other
amino acids, exist in the zwitterionic form. The proton
bound to the nitrogen atom forms an intramolecular
hydrogen bond with another nitrogen atom, thus fixing a
chair—chair conformation. Therefore, the bicyclic skelꢀ
eton of 4 is spatially preorganized for complexation, i.e.,
minimal changes in the geometry of the ligand are reꢀ
quired for the complex formation. Correspondingly, the
change in the entropy of the reaction is small. An analoꢀ
gous effect would be expected for molecule 3. The free
Bond
d/Å
N(1)—N(2)
O(1)—O(2)
Angled
3.476(4)19 2.713(4) 2.665(4)20
7.650(4)19 6.050(4) 6.108(4)20
ω/deg
2.689
6.079
11.5(3)18 13.2(3)
7.9(3)19
10.5
a,b Two crystallographically independent molecules.
c The average value for two molecules.
d The N(1)—N(2)—O(1)—O(2) dihedral angle.
structural parameters at the Cu atom are possible, primaꢀ
rily, due to asymmetry of the bonds between the nitrogen
atoms and the metal. The presence of additional carbon
bridges between the oxygen atoms and the diazabiꢀ
cyclononane skeleton provides alternative conformational
possibilities for the ligand and, correspondingly, gives rise
to additional types of coordination geometry, for example,

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Vatsadze et al.
Table 3. Selected bond lengths (Å) in the ligand molecules and complexes 5—11 (XDA is Xꢀray diffraction analysis)
Parameter
5
6
7
8,
DFT
8,
PM3
9a
9b
9c
10,
XDA21
11,
XDA22
XDA
XDA
Cu—N(1)
Cu—N(2)
Cu—Nd
Cu—O(1)
Cu—O(2)
Cu—Od
2.008(3)
2.012(4)
2.010
1.993(3)
2.012(3)
2.003
2.017(12)
1.965(13)
1.991
1.975(12)
1.979(11)
1.977
2.776(16)
3.012(15)
2.51(1)
O(ClO4)
2.54(1)
2.015(2) 2.03
2.030(3) 2.06
1.90
1.96
1.93
1.86
1.86
1.86
2.71
2.39
2.02
2.027(4)
1.989(4)
2.008
1.922(3)
1.952(4)
1.937
2.841(5)
2.821(5)
2.218(4)
2.025(4) 2.026
1.983(4) 1.986
1.979(8) 1.984(10)
1.979(8) 2.021(11)
2.023
2.05
2.004
2.006
1.979
2.003
1.926(3) 1.93
1.928(2) 1.96
1.911(4) 1.917
1.958(3) 1.955
1.944(7) 1.946(9)
1.950(7) 1.957(9)
1.927
1.95
1.936
1.936
1.947
1.952
N(1)—N(2) 2.771(4)
2.760(4) 2.90
2.871(4) 3.09
2.408(3) 2.49
2.808(5) 2.825
2.818(5) 2.820
2.213(4) 2.216
3.000(9) 2.989(14)
2.804(9) 2.831(12)
2.390(7) 2.404(11)
O(OCO) O(H2O)
O(1)—O(2)
Cu—X(1)
X(1)e
2.958(5)
2.416(1)
Cl
3.826(7)
O(H2O)
0.369(2)
O(H2O) O(H2O) O(H2O) O(OCO)
O(H2O)
—
—
—
—
—
Cu—X(2)
X(2)e
—
—
—
—
—
—
0.26
—
—
—
—
O(ClO4)
0.019(6)
—
—
f
∆
0.201(2) 0.08
0.345(2)
0.343(2) 0.344
0.13(1)
0.05(1)
a,b Two crystallographucally independent molecules.
c The average value for two molecules.
d The average value.
e The extra ligand.
f The deviation of the copper atom from the N(1)—N(2)—O(1)—O(2) plane.
Table 4. Selected bond angles (deg) in the ligand molecules and complexes 5—11 (XDA is Xꢀray diffraction analysis)
Parameter
5
6
7
8,
DFT
8,
PM3
9a
9b
9c
10,
11,
XDA21 XDA22
XDA
XDA
N(1)—Cu—N(2)
O(1)—Cu—O(2)
X(1)—Cu—X(2)
Cu—N—Cexo
NCuN/OCuO
Dihedral angle
87.21(13)
95.24(14)
162.5(1) 158.3(4)
104.4(3) 105.9(10) 103.9(2)
30.6(1)
1.38(1)
88.8(5) 86.05(11) 90.083 89.155 90.1(2) 89.0(2)
99.2(5) 102.23(13) 105.15 80.113 93.5(2) 93.5(2)
89.6 98.6(3) 96.6(4)
93.5 92.1(3) 92.9(4)
—
—
—
—
—
—
—
—
103.9
29.86
27.89
104.4 105.4(3) 105.6(3) 105.5 108.1(4) 109.4(5)
23.95 29.4(2) 29.5(1) 29.5 11.04(3) 4.82(4)
9.99 4.28(15) 6.45(15) 5.37 1.0(3) 2.2(4)
7.3(3)
7.2(5)
16.9(3)
1.97(13)
N(1)—N(2)—O(1)—O(2)
a,b Two crystallographycally independent molecules.
c The average value for two molecules in the asymmetric unit.
energies of complexation for 3 and 4 decrease due to an
increase in the entropy term, thus increasing stability of
the resulting complexes. To estimate the geometric
complementarity for copper(II) and preorganization of
the ligands for complexation with copper(II), it is necesꢀ
sary to compare the structural parameters of the comꢀ
plexes with those of the free complexation agents and
with the ideal values for the bonds with the metal atom.
The latter can be determined, on the one hand, by ab initio
calculations of the geometry of the appropriate model
molecules and, on the other hand, from experimental
data for related compounds, whose structures can be conꢀ
sidered as unstrained. It is reasonable to compare the
compounds under study with complexes, in which the
bicyclononane skeleton linking two chelate fragments is
absent, i.e., there are no restrictions imposed by the bicyꢀ
clic fragment on the coordination sphere of the metal
atom. The structures of copper alanine (10) and glycine
(11) complexes and the structure of compound 9 have
been established earlier.21—23 The copper complexes with
ephedrine24 and trisꢀhydroxymethylaminomethane25 are
the closest analogs of compound 7. The crystallographic
data for copper ethanolaminate and analogs of complexes
5 and 6 are lacking. In addition, the copper(II) complex
with an alanine derivative of urotropine26 and the nickel(II)
complex with a glycine derivative of urotropin27 were
documented.
The principal bond lengths and bond angles for comꢀ
pounds 1, 4, and 5—11 are given in Tables 2—4. It should
be noted that the diazabicyclononane backbone remains
virtually unchanged upon complexation, and the main
difference is observed in the orientation of the substituꢀ

Copper(II) complexes with N2O2 bispidines
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
1829
C(12´)
C(11´)
C(13´)
C(13´)
C(12´)
C(11´)
C(14)
O
C(14)
C(15)
C(13)
C(15)
C(10)
O
C(13)
C
C(10´)
C(14´)
C(15´)
C(12)
C(11)
C(14´)
C(15´)
C
C(10)
C(12)
C(5´)
C(4´)
C(10´)
C(5´)
C(3´)
C(3)
C(5)
C(5)
C(11)
C(4)
C(4´)
C(4)
C(3´)
C(3)
N(1´)
C(2´)
N(1)
C(2)
O(2)
N(1´)
O(23)
C(2´)
N(1)
C(2)
O(21)
Cu
Cu
C(1´)
C(1´)
O(14)
Cl(1)
O(12)
C(1)
C(1)
O(1)
Cl(2)
O(1´)
Fig. 3. Structure of complex 7.
O(1´)
O(1)
O(13)
O(24)
O(11)
O(22)
C(16´)
C(16A)
C(16)
The coordination environment of the metal atoms in
complexes 5, 7, and 9 can be considered as a distorted
tetragonal pyramid. The coordination environment of the
metal atom in complex 6 can be described as a tetragonal
bipyramid or as an elongated octahedron. The apical poꢀ
sitions of the bipyramid are occupied by the oxygen atoms
of the ClO4– anions. In this interpretation, the coordinaꢀ
tion environment of copper in 6 has a distorted squareꢀ
planar geometry, because the perchlorate anions are at a
large distance from the metal atom (2.5 Å) and form weak
Fig. 2. Structure of complex 6.
ents at the nitrogen atoms. The substituents can adopt
different conformations in the free ligand depending on
the crystal packing. Apparently, several stable conformers
exist in solution, but both substituents in the complex
adopt similar conformations fixed by the fiveꢀmembered
chelate rings.
O(2#)
C(12)
C(13)
C(6)
C(11)
O(2)
C(1)
C(1#)
C(2#)
C(6#)
C(4)
C(3)
C(2)
N(1)
C(10)
C(5)
C(5´)
O
C(14)
O(1#)
O(3)
N(1#)
C(4#)
Cu#
C(15)
C(11´)
C(12´)
C
C(3#)
O(1´´)
C(15´)
C(10´)
O(1)
C(11´´)
C(12´´)
C(13´´)
C(6´´)
C(14´)
Cu
C(1´´)
C(3´)
C(13´)
C(10´´)
C(5´´)
C(4´´)
N(1´)
C(4´)
C(2´)
O(2´)
N(1´´)
O(2´´)
C(2´´)
O(1´)
C(1´)
C(15´´)
C(5#)
C(3´´)
C#
C(14´´)
C(11#)
O#
C(6´)
C(10#)
C(12#)
C(13#)
C(15#)
C(14#)
Fig. 4. Structure of complex 9.

1830
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
Vatsadze et al.
tances in 9 differ by 0.042(6) Å, whereas these distances
in 10 are identical, both Cu—N bonds in 9 being longer
than those in 10 but being similar to the Cu—N distance
in bisglycinate 11. The Cu—O bond lengths in 9 are, on
the average, slightly shorter than those in 10 and 11
(~0.01 Å). However, the average difference in the bond
lengths in two complexes is substantially smaller than the
asymmetry of the bonds in 9. The bonds between the
copper cation and the apical ligands in 9 are substantially
shorter (by more than 0.17 Å), and the Cu atom is located
above the plane of the base of the coordination pyramid.
The N—Cu—N bond angle in 9 is close to 90o (89.6°) and
is substantially larger in 10 (98.6°), whereas the O—Cu—O
bond angles in both compounds have similar values
(93.5(2) and 92.1(2)°, respectively). An essential differꢀ
ence is observed only in the geometric parameters of the
alanine fragments of complexes 9 and 10. The amino acid
substituents in 10 are characterized by considerable asymꢀ
metry of the bond lengths and bond angles with respect to
each other. In both complexes, two alanine fragments
adopt different conformations. In one fragment, the Me
substituent is in an equatorial position, whereas this subꢀ
stituent in another fragment is in an unfavorable axial
position. It should be noted that the bond with the Me
group in the axial position in 10 is substantially longer
than the other bonds,21 whereas all analogous bonds in 9
are virtually equal in length.22
The molecules of all complexes have symmetry C1.
However, molecule 6 has the pseudosymmetry axis C2
passing through the copper atom and the keto group,
whereas molecule 5 has a pseudosymmetry plane, which
relates two sixꢀmembered rings of the bicyclic skeleton
and two βꢀhydroxyethyl substituents to one another. Comꢀ
plex 7 also has pseudosymmetry Cs. In this complex, the
coordinated water molecule slightly violates the almost
ideal symmetry Cs. The geometry of complex 8 in the gas
phase optimized by the semiempirical PM3 method is
close to Cs, whereas calculations by the DFT method gave
symmetry C2 characteristic of the tetrahedrally distorted
tetragonal symmetry of the ligand environment, i.e., for
fourꢀ and sixꢀcoordinate copper. This is attributed to an
increase in the bond length between the copper atom and
the water molecule, which is transferred into the second
coordination sphere. Apparently, these two coordination
polyhedra with different symmetry are energetically simiꢀ
lar, because both type of complexes exist, and the existꢀ
ence of a particular coordination mode depends primarily
on the crystal forces. In all complexes, the Cu—N bond
lengths, as well the parameters of the bicyclononane skelꢀ
eton, have very similar values. In all compounds, the
N—Cu—N angle is close to 90°. The Cu—O bond length
varies depending on the charges of the oxygen atoms and
additional ligands. The shortest Cu—O bonds are obꢀ
served in the anionic ligands, the bond lengths being virꢀ
tually equal for the oxide and carboxy binding centers.
bonds determined, apparently, by electrostatic forces. The
coordination plane is slightly tetrahedrally distorted, which
is typical of fourꢀcoordinate copper(II). The N—N—O—O
dihedral angle is 7.25°, which corresponds to the angle
between the N—Cu—N and O—Cu—O planes (7.33°).
The tetrahedral distortion characteristic of fourꢀcoordiꢀ
nate copper(II) (unlike sixꢀcoordinate copper) argues in
favor of considering complex 6 as having a squareꢀplanar
–
structure and the bonds between Cu and ClO4 as secꢀ
ondary bonds. In complex 5, the apical position of the
pyramid is occupied by the Cl– anion. In other structures,
the fifth coordination site in the coordination sphere of
copper is occupied by the water molecule. The structure
of dimeric compound 9 is somewhat different. In one
molecule of 9, the copper cation is coordinated by the
water molecule, whereas the carbonyl oxygen atom of the
carboxylate group of the first molecule is present as the
fifth ligand in another molecule of 9. The base of the
pyramid is virtually undistorted, and the metal atom is at
a distance of 0.20—0.35 Å from the base of the pyramid.
The geometry of the coordination sphere in 9 is simiꢀ
lar to that in copper cisꢀbisalaninate complex 10. The
following differences can be mentioned: the Cu—N disꢀ

Copper(II) complexes with N2O2 bispidines
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
1831
The longest Cu—O bond is observed for the hydroxy bindꢀ
ing center, whereas the analogous bond for the methoxy
center is somewhat shorter. This is associated with the
fact that the copper atom in complex 6 is less coorꢀ
dinatively saturated, because it has four atoms in the first
coordination sphere rather than five atoms involved in
the first coordination sphere in complex 5.
hedron differs substantially from that in complex 9 and is
characterized by tetrahedral distortion of the N2O2 plane
with the simultaneous displacement of the water molꢀ
ecule to a distance corresponding to secondary interacꢀ
tions. Therefore, the calculated structure of single molꢀ
ecule 8 in vacuo can be described as a tetrahedrally disꢀ
torted planar square. The geometry optimization by the
semiempirical method (PM3tm) retains the pyramidal
geometry of the coordination polyhedron but underestiꢀ
mates the bond lengths of the metal atom, the parameters
of the organic moiety of the molecule corresponding to
standard values. The calculated structure of 8 is shown
in Fig. 5.
Complexes with the amino acid bispidine ligands can
be related to their methylpyridine analogs. To date,
copper(II) complexes with 3,7ꢀbis(2ꢀpyridylmethyl)ꢀ3,7ꢀ
diazabicyclo[3.3.1]nonane are the most stable of comꢀ
plexes with acyclic tetramines.29 This is associated with
rigidity and preorganization of the ligand and its compleꢀ
mentarity for CuII. Compounds 3 and 4 have a similar
geometry. However, there are no van der Waals repulꢀ
Taking into account that the structure of copper
glycinate 11 is unstrained, its parameters can be used as a
model for estimating the deviations of the coordination
polyhedra in 8 and 9 from the model values. The paramꢀ
eters of the ligand in complex 11 are virtually equal to
those of free glycine, except for the carboxy group, in
which the C—O bonds differ in length due to complexꢀ
ation. The average Cu—O and Cu—N bond lengths in
complex 9 are similar to those observed in 11. The deviaꢀ
tion of the copper atom from the plane passing through
the donor atoms, apparently, indicates that the size of the
CuII dication does not match the size of the the coordinaꢀ
tion cavity. This assumption is confirmed by an increase
in the distance between the nitrogen atoms (by 0.16 Å)
upon complexation and by the longer N—N distances in
complexes 10 and 11. However, the deviation of the geoꢀ
metric complementarity between the ligands and the diꢀ
valent copper cation from the ideal case is small and is
compensated by the displacement of the metal atom from
the N2O2 plane. Since the bond angles at the metal atoms
in the complexes are rather flexible,2 the above fact does
not cause strain in the coordination sphere of the cation.
Therefore, all ligands are characterized by high geometric
complementarity for copper(II). Electronic complemenꢀ
tarity, i.e., complementarity at the level of electronic inꢀ
teractions, reflects complementarity of electron distribuꢀ
tion responsible for the interaction energy.28 The generalꢀ
ized double complementarity is responsible for stability of
the complexes,28 which was studied by electrochemical
methods.
O
O
N
N
O
Cu
O
O
O
DFT
The geometry of molecule 8 was calculated using the
atomic coordinates of one of molecules 9 determined by
Xꢀray diffraction analysis. In this model, the copper atom
is coordinated by the water molecule, and the Me group is
replaced with the hydrogen atom. The geometry optimiꢀ
zation was carried out by the DFT method with the use of
the hybrid functional B3LYP. To accelerate calculations,
we used the twoꢀlevel ONIOM approach, in which the
copper atom and its closest environment are represented
with the use of the LanL2DZ basis set, whereas the bicyꢀ
clic skeleton and the Ph groups are described using the
minimal STOꢀ3G basis set. The bond lengths in the coorꢀ
dination sphere of complex 8 calculated by the nonꢀ
empirical method are similar to those for copper(II)
bisglycinate. The parameters of the bicyclononane moiꢀ
ety differ substantially from the experimental data known
for other compounds, which is reasonable considering the
minimal basis set used. The type of the coordination polyꢀ
O
O
N
O
O
O
Cu
O
N
PM3
Fig. 5. Calculated structures of complex 8.

1832
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
Vatsadze et al.
sions in complexes 8 and 9, whereas such repulsions beꢀ
tween the αꢀhydrogen atoms of the pyridine rings conꢀ
tribute to strain in the structures of the pyridine comꢀ
plexes. Hence, complexes 8 and 9 would also be expected
to be highly thermodynamically stable.
A
5 µA
1
E
2
C
Electrochemistry
–1
0
1
E/V
Earlier,30 we have studied the redox properties of a
series of CuII complexes with general formula LCuCl2
(12; L is 3,7ꢀdialkylꢀ3,7ꢀdiazabicyclo[3.3.1]nonanꢀ
9ꢀone).
It was hypothesized that oxidation of these complexes
occurs at the lone pairs of the nitrogen atoms giving rise
to CuCl2, whereas reduction leads to electron transfer
from the electrode to the copper atom, both leading to
decomposition of the complex.
B
D
Fig. 6. The CV curves for oxidation (1) and reduction (2) of
complex 9 at a Pt electrode in MeCN against 0.05 M Bu4NBF4
at 20 °C.
In the present study, we examined the electrochemiꢀ
cal properties of complexes 5—9 by cyclic voltammetry
(CV) in MeCN at Pt and glassyꢀcarbon electrodes against
0.05 M Bu4NBF4.
in the reverse anodic scan. This peak has a triangular
shape without a diffusion tail, which is characteristic of
oxidative desorption of metal deposited on the surface of
the electrode. Earlier, we have observed an analogous
behavior for copper complexes with 3,7ꢀdialkylꢀ3,7ꢀ
diazabicyclo[3.3.1]nonanꢀ9ꢀone.30
Oxidation
The complexes under consideration are irreversibly
oxidized at high anodic potentials (Table 5), except for
complex 8, which is not oxidized under these conditions.
Apparently, the ligand is oxidized in the anodic scan
analogously to complexes 12.30 The CV curves for soluꢀ
tions of complex 9 in MeCN at a Pt electrode are shown
in Fig. 6 (curve 1). Electrochemical oxidation of this
compound (peak A) affords a product, which gives rise to
a reduction peak (peak B) in the reverse cathodic scan of
the CV curve at –0.68 V, which is 180 mV less negative
than the reduction peak of compound 9 (peak D). Reducꢀ
tion at the peak B is accompanied by elimination of copꢀ
per metal, as evidenced by the appearance of the peak C
Reduction
As can be seen from Table 5, the complexes under
consideration behave differently at the cathode. At a platiꢀ
num electrode, complexes 7—9 are reduced in one oneꢀ
electron quasireversible step (see Fig. 6, curve 2). The
difference between the potentials of the reverse and direct
peaks (EpE – EpDRed; E and D are the cathodic and
Ox
anodic peaks, respectively, of the quasireversible redox
pair 9/9•– in Fig. 6) is rather large (450 mV for comꢀ
plex 9, 350 mV for complex 8, and 330 mV for 7), which
may be indicative of a structural rearrangement of the
initially formed radical anion. No anodic peaks, which
could be assigned to oxidation of copper metal, were obꢀ
served in the CV curves of complexes 7 and 8 during
the reverse potential scan, whereas the oxidation peak
Cu0/CuI (–0.29 V) was observed upon reduction of comꢀ
plex 9 in the reverse anodic branch of the CV curve after
six—eight potential scans from 0.0 to –1.3 V and in the
opposite direction. The anodic branch of the CV curves
Table 5. Oxidation potentials (EpOx) and reduction potentials
(EpRed) of complexes 5—9 at a Pt electrode (MeCN, Bu4NBF4,
Ag/AgCl,KClsat, 20 °C, scan rate was 200 mV s–1
)
Ox
Red a
Red
Comꢀ
pound
Ep
E1/2
Ep
V
Ox
1.84b
2.23
2.31
—
0.48; –0.53
1.09
0.50; –0.60; –1.40
0.23; –0.52; –1.55
–0.89
also has an anodic peak (Ep = 0.15 V) corresponding,
5
6
7
8
apparently, to the CuI/CuII transition. When the potenꢀ
tial was scanned from –1.3 to +0.4 V and then in the
opposite direction, both anodic peaks virtually disapꢀ
peared. This fact can be explained as follows. The formaꢀ
tion of copper metal by oneꢀelectron reduction of the CuII
complex occurs, apparently, due to disproportionation of
the complexꢀfree CuI, as was observed in aqueous media.31
Presumably, interactions between the d orbitals of the
Sharp oxidation
waves are absent
1.81; 1.76
1.14
–1.18
9
1.05
–0.87; –2.46c
a The halfꢀwave potentials at a rotating disk Pt electrode.
b At a glassyꢀcarbon electrode.
c A small peak was also observed at –1.01 V.

Copper(II) complexes with N2O2 bispidines
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
1833
copper atom and the n orbitals of the nitrogen atoms in
radical anion 9–• become weaker. However, oxidation of
copper metal to Cu2+ is accompanied by regeneration of
the starting complex. Stability of radical anion 9•– apꢀ
peared to be dependent on the material of the working
electrode. In experiments with the use of a glassyꢀcarbon
electrode, oxidation peaks of copper metal were observed
neither after the first reduction peak of complex 9 nor
after the second reduction peak at high cathodic potenꢀ
tials (–2.46 V, see Table 5).
onstrated that these ligands are characterized by high geoꢀ
metric complementarity for copper(II). Electrochemical
investigation revealed high electronic complementarity of
chelated salts 7—9 and substantially lower complemenꢀ
tarity of complexes 5 and 6.
Experimental
Single crystals were grown by crystallization from ethanol.
Xꢀray diffraction data sets were collected on an Enraf—Nonius
CAD4 diffractometer (graphite monochromator, ω scanning
technique). The crystallographic data, characteristics of Xꢀray
data collection, and details of structure refinement for comꢀ
pounds 5—7 and 9 are given in Table 1. The absorption correcꢀ
tions were applied using experimental azimuthal scan curves.
The structures were solved by direct methods (SHELXSꢀ86)34
and refined anisotropically by the fullꢀmatrix leastꢀsquares
method against F2 (SHELXLꢀ93).35 The hydrogen atoms in the
structures of 5, 6, and 9 were placed in geometrically calculated
positions and refined using a riding model. The hydrogen atoms
in the structure of 7 were refined isotropically. In compound 6,
one of the Me groups is disordered over two positions with
occupancies of 0.55 and 0.45. The structure of 5 contains ethaꢀ
nol solvate molecules. In the structures of 7 and 9, water molꢀ
ecules were revealed.
Quantumꢀchemical calculations of the geometry of comꢀ
pound 8 were carried out by the DFT method with the use of the
B3LYP hybrid functional and the twoꢀlevel ONIOM procedure
implemented in the Gaussianꢀ98 program package.36 The geoꢀ
metry optimization was performed using the Berny algorithm
and intrinsic coordinates. The PM3(tm) calculations were carꢀ
ried out using the Hyperchem 7.5 program.37
Electrochemical measurements were performed with the use
of a PIꢀ50ꢀ1.1 potentiostat, a platinum electrode (3.5 mm in
diameter), and a glassyꢀcarbon electrode (50 nm in diameter).
A silver chloride electrode was used as the reference electrode,
and Bu4NBF4 was used as the supporting electrolyte. All meaꢀ
surements were carried out in MeCN, which was purified by
successive treatment with a nitrating mixture, potassium hyꢀ
dride, and phosphorus pentoxide. The potentials are given takꢀ
ing into account iR compensation. The numbers of electrons
were determined by comparing the oxidation peaks of ferrocene
taken at an equal concentration.
Reduction of complexes 5 and 6 occurs analogously to
reduction of complexes 12.30 Two oneꢀelectron reducꢀ
tion peaks are observed. The first peak is quasireversible
Ox
Red
(Ep – Ep
= 80 mV for complex 5 and 190 mV for
complex 6). The transfer of the second electron results in
deposition of copper metal on the electrode. The third
cathodic peak (see Table 5) corresponds, apparently, to
reduction of the ligand.
High negative reduction potentials of chelated salts
7—9 compared to those of complexes 5 and 6 are indicaꢀ
tive of high stability of these compounds and high
complementarity of metal—ligand interactions. Data obꢀ
tained under the same conditions are necessary for a direct
comparison with other ligands. Complexes 5 and 6 have
positive first reduction potentials, which may be indicative
of their lower stability. The reduction peaks are nearly
Ox
Red
thermodynamically reversible (when Ep – Ep
=
60 mV). Apparently, copper(I) complexes formed in the
first step are much better stabilized by neutral ligands
than those in the case of complexes 7—9 containing the
dianions as ligands. Therefore, the electronic compleꢀ
mentarity for CuII ions in complexes 5 and 6 is lower than
that in complexes 7—9, whereas the complementarity for
CuI ions is higher, the steric parameters being similar.
Since bispidines based on substituted αꢀamino acids
have chiral centers near the nitrogen atoms, their comꢀ
plexes can be used as catalysts for enantioselective reacꢀ
tions. The accessibility of the starting reagents, viz., natuꢀ
ral amino acids, and the ease and simplicity of the oneꢀ
pot synthesis of ligands based on these compounds hold
promise for the design of this type of enantioselective
catalysts. Only N4ꢀtype ligands derived from dipeptide
Schiff bases, which also contain αꢀamino acids as the key
fragments, are characterized by a comparable combinaꢀ
tion of useful structural parameters, the ease of the synꢀ
thesis, and accessibility of the starting reagents.32 In the
study,32 the authors called these ligands "privileged"
ligands without data on the catalytic activity at their disꢀ
posal. The efficiency of the use of complexes analogous to
those described in the present study was demonstrated for
bicyclononanes, which are derivatives of substituted ethaꢀ
nolamine and which catalyze the addition of diethylzinc
to aldehydes with enantiomeric excess of 83—98%.33
To summarize, we synthesized copper(II) complexes
with tetradentate ligands 1—4. The structural study demꢀ
The complexes and ligands were synthesized with the use
of solvents purified according to standard procedures.38
Ligands 1—4 were synthesized according to procedures deꢀ
scribed earlier.11—13,18
N,N´,O,O´ꢀ3,7ꢀBis(2ꢀhydroxyethyl)ꢀ9ꢀoxoꢀ1,5ꢀdiphenylꢀ
3,7ꢀdiazabicyclo[3.3.1]nonanocopper(II) dichloride (5). Comꢀ
pound 1 (1.6 g, 4.2 mmol) was dissolved in ethanol (40 mL) and
heated to boiling. Then a warm solution of anhydrous copper(II)
chloride (0.56 g, 4.2 mmol) was added. The solution was reꢀ
fluxed for 3 h and then allowed to stand for 18 h. The blue
crystals that precipitated were filtered off, washed with ethanol,
and recrystallized from ethanol. The product was obtained
in a yield of 1.9 g. After recrystallization from aqueous ethaꢀ
nol, the solvate with one ethanol molecule and one water molꢀ
ecule was obtained. M.p. 176—179 °C. Found (%): C, 51.57;
H, 6.29; N, 4.89. C25H36Cl2N2O5Cu. Calculated (%): C, 51.86;
H, 6.27; N, 4.84.

1834
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 8, August, 2005
Vatsadze et al.
N,N´,O,O´ꢀ3,7ꢀBis(2ꢀmethoxyethyl)ꢀ9ꢀoxoꢀ1,5ꢀdiphenylꢀ
3,7ꢀdiazabicyclo[3.3.1]nonanocopper(II) diperchlorate (6). Cauꢀ
tion! This procedure uses explosive perchlorates! Compound 2
(0.61 g, 1.5 mmol) was dissolved in chloroform (5 mL) and
mixed with a solution of copper(II) perchlorate hexahydrate
(0.55 g, 1.5 mmol). The reaction mixture was heated to boilꢀ
ing and then allowed to stand for 18 h. The blue crystals that
precipitated were filtered off. The product was obtained in a
yield of 1.01 g. Complex 6 is stable up to 210 °C. Heating at
high temperature may cause explosion! Found (%): C, 44.60;
H, 4.70; N, 4.25. C25H32Cl2N2O11Cu. Calculated (%): C, 44.75;
H, 4.81; N, 4.17.
7. J. Spieler, O. Huttenloch, and H. Waldmann, Europ. J. Org.
Chem., 2000, 391.
8. J.ꢀP. R. Hermet, D. W. Porter, M. J. Dearden, J. R. Harrison,
T. Koplin, P. O’Brien, J. Parmene, V. Tyurin, A. C.
Whitwood, J. Gilday, and N. M. Smith, Org. Biomol. Chem.,
2003, 1, 3977.
9. S. Z. Vatsadze, V. K. Bel´skii, S. E. Sosonyuk, N. V.
Zyk, and N. S. Zefirov, Khim. Geterotsikl. Soedin., 1997,
356 [Chem. Heterocycl. Compd., 1997, 33, 300 (Engl.
Transl.)].
10. G. D. Hosken, C. C. Allan, J. C. A. Boeyens, and R. D.
Hancock, J. Chem. Soc., Dalton Trans., 1995, 3705.
11. Z.ꢀY. Kyi and W. Wilson, J. Chem. Soc., Abstracts,
1951, 1706.
12. S. Chiavarelli, H. F. Toeffler, R. LandiꢀVittory, and
P. Mazzeo, Ist. Super. Sanita, Rome. Farmaco, Edizione
Scientifica, 1965, 20, 421.
13. H. Stetter and K. Dieminger, Chem. Ber., 1959, 92, 2658.
14. S. Chiavarelli, G. P. Valsecchi, F. Toffler, and
L. Gramiccioni, Bollettino Chimico Farmaceutico, 1967,
106, 301.
15. A. Gogoll, H. Gernnberg, and A. Axen, Organometallics,
1997, 16, 1167.
16. D. S. C. Black, G. B. Deacon, and M. Rose, Tetrahedron,
1995, 51, 2055.
17. S. Z. Vatsadze, Ph. D. (Chem.) Thesis, Department of
Chemistry of the M. V. Lomonosov Moscow State Univerꢀ
sity, Moscow, 1995, 146 pp. (in Russian).
18. N. S. Zefirov, N. V. Zyk, S. Z. Vatsadze, and V. S. Tyurin,
Izv. Akad. Nauk, Ser. Khim., 1992, 2687 [Bull. Russ. Acad.
Sci., Div. Chem. Sci., 1992, 41, 2131 (Engl. Transl.)].
19. N. S. Zefirov, V. A. Palyulin, S. V. Starovoitova,
K. A. Potekhin, and Yu. T. Struchkov, Dokl. Akad.
Nauk, 1996, 347, 637 [Dokl. Chem., 1996, 347, 98 (Engl.
Transl.)].
20. A. N. Chekhlov, Zh. Strukt. Khim., 2000, 41, 140 [Russ.
J. Struct. Chem., 2000, 41, 116 (Engl. Transl.)].
21. R. D. Gillard, R. Mason, N. C. Payne, and G. B. Robertson,
J. Chem. Soc. (A), 1969, 1864.
22. H. C. Freeman, M. R.Snow, I. Nitta, and K. Tomita, Acta
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Copper(II)
β,β´ꢀ(9ꢀoxoꢀ1,5ꢀdiphenylꢀ3,7ꢀdiazabicyꢀ
clo[3.3.1]nonꢀ3,7ꢀylene)diethylate (7). A solution of potassium
hydroxide (0.096 g, 1.72 mmol) in water (10 mL) was added to a
solution of complex 5 (0.5 g, 0.86 mmol) in water (30 mL), and
the reaction mixture was kept for 5 days. The crystals that formed
were filtered off. The product was obtained in a yield of 0.45 g.
M.p. 215—218 °C. Found (%): C, 51.85; H, 6.62; N, 5.13.
C23H36N2O8Cu. Calculated (%): C, 51.92; H, 6.82; N, 5.26.
Copper(II) 9ꢀoxoꢀ1,5ꢀdiphenylꢀ3,7ꢀdiazabicyclo[3.3.1]nonꢀ
3,7ꢀylenediacetate (8). Compound 3 (3.0 g, 7.3 mmol) was disꢀ
solved in a mixture of DMF (100 mL) and isopropyl alcohol
(30 mL). Then freshly precipitated copper hydroxide (1.5 g,
15 mmol) was added and the mixture was stirred at 30—40 °C
for 3 h. The precipitate was filtered off, washed with diethyl
ether, and dried in a vacuum desiccator for 10 h. Purple crystals
of complex 8 were obtained in a yield of 3.5 g. M.p. 276—278 °C.
Found (%): C, 58.51; H, 4.79; N, 6.20. C23H22N2O5Cu. Calcuꢀ
lated (%): C, 58.78; H, 4.72; N, 5.96.
Copper(II) (+)ꢀ(S,S´)ꢀα,α´ꢀ(9ꢀoxoꢀ1,5ꢀdiphenylꢀ3,7ꢀdiazaꢀ
bicyclo[3.3.1]nonꢀ3,7ꢀylene)dipropionate (9). Compound 4
(4.8 g, 11 mmol) was dissolved in a mixture of DMF (15 mL)
and methanol (150 mL). Then freshly precipitated copper hydrꢀ
oxide (1.5 g, 15 mmol) was added and the mixture was stirred at
30—40 °C for 3 h. The precipitate was filtered off, washed with
diethyl ether, and dried in a vacuum desiccator. Darkꢀblue crysꢀ
tals, which were obtained in a yield of 5.0 g, were recrystallized
from aqueous DMF. M.p. 284—286 °C. Found (%): C, 58.02;
H, 5.61; N, 5.46. C25H28N2O6Cu. Calculated (%): C, 58.19;
H, 5.47; N, 5.43.
23. A. N. Chekhlov, Zh. Strukt. Khim., 2000, 41, 359 [Russ.
J. Struct. Chem., 2000, 41, 294 (Engl. Transl.)].
24. J. F. Malone, M. Miskelly, and M. Parvez, Proc. R. Ir. Acad.
Sect. B, 1978, 77, 499.
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 04ꢀ03ꢀ32845
and 03ꢀ03ꢀ32401).
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26. Z. Travnicek and J. Marek, Acta Crystallogr., Sect. C (Cr. Str.
Commun.), 1994, 50, 1211.
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Received September 21, 2004