Reactivity towards dioxygen of a copper(I) complex of tris(2-benzylaminoethyl)amine

Article abstract of DOI:10.1016/S0020-1693(01)00588-6

The reaction of dioxygen with the copper(I) Bz₃tren complex (Bz₃tren = tris(2-benzylaminoethyl)amine) complex has been investigated using low temperature stopped-flow techniques. The formation of a superoxo as well as a peroxo complex as intermediates was detected spectroscopically. The copper(II) complexes [Cu(Bz₃tren)H₂O](ClO₄)₂ and [Cu(Bz₃tren)Cl]Cl were synthesized and structurally characterized. Both complexes react with dioxygen in solution and formation of benzaldehyde was observed.

Full text of DOI:10.1016/S0020-1693(01)00588-6

www.elsevier.com/locate/ica
Inorganica Chimica Acta 324 (2001) 173–179
Reactivity towards dioxygen of a copper(I) complex of
tris(2-benzylaminoethyl)amine
Markus Schatz a, Michael Becker a, Olaf Walter b, Gu¨nter Liehr a, Siegfried Schindler a,*
a Institut fu¨r Anorganische Chemie, Uni6ersita¨t Erlangen-Nu¨rnberg, Egerlandstraße 1, 91058 Erlangen, Germany
b Forschungszentrum Karlsruhe GmbH, ITC-CPV, Postfach 3640, 76021 Karlsruhe, Germany
Received 9 April 2001; accepted 1 August 2001
Abstract
The reaction of dioxygen with the copper(I) Bz3tren complex (Bz3tren=tris(2-benzylaminoethyl)amine) complex has been
investigated using low temperature stopped-flow techniques. The formation of a superoxo as well as a peroxo complex as
intermediates was detected spectroscopically. The copper(II) complexes [Cu(Bz3tren)H2O](ClO4)2 and [Cu(Bz3tren)Cl]Cl were
synthesized and structurally characterized. Both complexes react with dioxygen in solution and formation of benzaldehyde was
observed. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Copper complexes; Tripodal ligands; Dioxygen activation; Peroxo/superoxo complexes
elucidate the factors that govern the (reversible) binding
and activation of dioxygen with copper(I) complexes.
1. Introduction
The first example of a structurally characterized cop-
Copper ions are found in the active sites of a large
per peroxo complex was obtained by Karlin and
number of metalloproteins involved in important bio-
coworkers from the reaction of [Cu(tmpa)(CH3CN)]PF6
logical electron transfer reactions, as well as in redox
(tmpa=tris[(2-pyridyl)methyl]amine, Fig. 1) with O2 at
processing of molecular oxygen [1–6]. Many low
molecular weight model complexes for copper proteins
have been synthesized and their reactions with dioxygen
have been investigated [2–12]. These model compounds
low temperatures [14,15]. A detailed kinetic investiga-
tion of the reversible reaction of [Cu(tmpa)(CH3CN)]+
(1) with O2 was performed in propionitrile which al-
lowed the spectroscopic observation of a superoxo
not only provide better understanding of the biological
complex prior to formation of the peroxo complex [16].
molecules but furthermore, they assist in the develop-
Furthermore, the influence of sterical hindrance as well
ment of new homogeneous catalysts for selective oxida-
as different donor atoms on the formation of the
tions under mild conditions [2,6,10,13]. A key step in
these redox reactions is the activation of dioxygen upon
binding at the active site prior to the reaction with a
substrate. It was discovered that a whole variety of
copper dioxygen adducts form when simple copper(I)
complexes are reacted with dioxygen [10,11]. The
course of these reactions depends on temperature, lig-
and and solvent. Therefore, it is of great interest to
* Corresponding author. Tel.: +49-9131-852 8383; fax: +49-
9131-852 7387.
E-mail address: schindls@anorganik.chemie.uni-erlangen.de (S.
Schindler).
Fig. 1. Tripodal ligands tmpa, tren, Me6tren, Bz3tren and L.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00588-6

174
M. Schatz et al. / Inorganica Chimica Acta 324 (2001) 173–179
peroxo complexes was studied [16–18,10,19]. More re-
cently we have investigated the effect of chelate ring
size on the properties of these complexes [20].
Dioxygen saturated solutions for the measurements
were obtained by passing dioxygen through the solvent
for 20 min as described earlier [16,28,29].
To further elucidate the factors that influence the
reactions of dioxygen with Cu(I) complexes we have
started to use tripodal ligands derived from the parent
compound tris(2-aminoethyl)amine (tren, Fig. 1), an
amine produced in industrial quantities [10,21]. Tren is
a versatile tetradentate ligand, known to form trigonal
bipyramidal complexes with copper(II) ions in the solid
state as well as in solution (similar to copper(II) tmpa
complexes). One of the axial positions is occupied by
the tertiary amine nitrogen, the other by water or some
other monodentate ligand [10,22–25]. Unfortunately, in
contrast to [Cu(tmpa)(CH3CN)]PF6 the copper(I) tren
complex does not form a stable dioxygen adduct on O2
exposure [10,21]. In contrast, the fully methylated form
of tren, Me6tren (tris(2-dimethylaminoethyl)amine, Fig.
1) supports formation of a copper superoxo and peroxo
complex in a similar manner to tmpa [21].
Caution! Perchlorate salts are potentially explosi6e
and should be handled with great care.
2.1.1. [Cu(Bz3tren)(H2O)](ClO4)]2
To a solution of 209 mg (0.5 mmol) Bz3tren in 5 ml
of methanol was added under inert conditions a solu-
tion of 185 mg (0.5 mmol) Cu(ClO4)2×6H2O in 5 ml of
methanol. Blue crystals suitable for X-ray characteriza-
tion were obtained by diffusion of diethyl ether into
this solution (yield: 140 mg, 40%). Anal. Calc. for
C27H38N4CuCl2O9: C, 46.52; H, 5.49; N, 8.04. Found:
C, 46.80; H, 5.97; N, 8.05%.
2.1.2. [Cu(Bz3tren)(Cl)]Cl
To a solution of 220 mg (0.53 mmol) Bz3tren in 5 ml
of methanol was added under inert conditions a solu-
tion of 90 mg (0.53 mmol) CuCl2×2H2O in 5 ml of
methanol. Green crystals suitable for X-ray characteri-
zation were obtained by diffusion of diethyl ether into
this solution (yield: 175 mg, 60%). Anal. Calc. for
C27H36N4CuCl2: C, 58.85; H, 6.58; N, 10.17. Found: C,
58.98; H, 7.16; N, 10.04%.
Therefore, we became interested in how monoalkyla-
tion of tren could influence the reactivity of its cop-
per(I) complexes towards dioxygen. Herein we describe
the properties and reactions of copper complexes of
Bz3tren (tris(2-benzylaminoethyl)amine, Fig. 1).
2.2. X-ray data collection and structure refinement
2. Experimental
Crystal data and experimental conditions are listed in
Table 1. The molecular structures are illustrated in
Figs. 3 and 4. Selected bond lengths and angles with
standard deviations in parentheses are presented in
Table 2. Intensity data were collected with graphite
2.1. Materials and methods
Reagents and solvents used were of commercially
available reagent grade quality. Bz3tren was either syn-
thesized according to a published procedure [26] or
obtained from Aldrich. [Cu(CH3CN)4)]+ salts were syn-
thesized and characterized according to literature meth-
ods [27]. Copper(I) Bz3tren complexes for the time
resolved UV–Vis spectra were prepared in situ by
mixing stoichiometric amounts of [Cu(CH3CN)4]+ and
Bz3tren in propionitrile or acetone under inert condi-
tions. Preparation and handling of air-sensitive com-
pounds was carried out in a glove box filled with argon
(Braun, Garching, Germany; water and dioxygen less
than 1 ppm). UV–Vis spectra were measured on a
Hewlett Packard 8452 A spectrophotometer. Cyclic
voltammetry was performed with an EG&G Poten-
tiostat (Model 263) at 25 °C with a scan rate of 100
,
monochromated Mo Ka, radiation (u=0.71073 A).
X-ray diffraction data for [Cu(Bz3tren)(H2O)](ClO4)2
were collected on a Nonius CAD4 MACH3. The inten-
sities were corrected for Lorentz and polarization ef-
fects (but not for absorption). The structure was solved
by direct methods [30] and refined by full-matrix least
squares methods on F2 [31]. Hydrogen atoms of
[Cu(Bz3tren)(H2O)](ClO4)2 were calculated for idealized
geometries and allowed to ride on their preceeding
atoms, their isotropic displacement parameters were
tied to those of the adjacent atoms by a factor of 1.5.
X-ray diffraction data for [Cu(Bz3tren)(Cl)]Cl were
collected on a Siemens SMART 5000 CCD-diffrac-
tometer. The exposure time was 10 s per frame col-
lected with the ꢀ-scan technique (Dꢀ=0.3°). The
collected reflections were corrected for Lorentz polar-
ization and absorption effects. The structures were
solved by direct methods and refined by full-matrix
least-squares methods on F2 [32–34]. [Cu(Bz3tren)-
(Cl)]Cl crystallises in the orthorhombic chiral space
group P2 ,2 ,2 as a racemic twin. The high residual
mV s−1
.
Time resolved spectra of the reactions of dioxygen
with copper(I) complexes were recorded on a modified
Hi Tech SF-3 L low temperature stopped-flow unit
(Salisbury, UK) equipped with a J&M TIDAS 16-500
diode array spectrophotometer (J&M, Aalen, Ger-
many). Data fitting was performed using the integrated
J&M software Kinspec or the program Specfit (Spec-
trum Software Associates, Chapel Hill, NC, USA).
1
1
electron density in the final Fourier difference map was
found to be located very close to the Cu(II) ion.

M. Schatz et al. / Inorganica Chimica Acta 324 (2001) 173–179
175
Table 1
Crystal data and structure refinement for [Cu(Bz3tren)(H2O)](ClO4)2 and [Cu(Bz3tren)Cl]Cl
Complex
[Cu(Bz3tren)(H2O)](ClO4)2
[Cu(Bz3tren)Cl]Cl
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
C27H38Cl2CuN4O9
695.04
293(2)
C27H36Cl2CuN4
548.01
200(2)
Triclinic
Orthorhombic
P2 ,2 ,2 (No. 19)
(
P1
1
1
,
a (A)
9.982(5)
15.114(5)
11.569(5)
91.711(5)
9.65530(10)
15.39400(10)
18.3699(2)
90
,
b (A)
,
c (A)
h (°)
i (°)
115.399(5)
90
k (°)
94.341(5)
1568.4(12)
2
1.438
0.919
706
90
3
,
V (A )
2730.39(4)
4
1.333
1.018
Z
Dcalc (mg m−3
)
Absorption coefficient (mm−1
F(000)
)
1144
Crystal size (mm)
2q Range (°)
0.36×0.29×0.14
2.53–24.96
0.2×0.2×0.4
1.73–28.34
Index ranges
−115h511, −175k517, −135l513
11 020
5510 [Rint=0.0449]
Full-matrix least-squares on F2
5510/240/388
−125h512, −205k520, −245l524
28 376
6672 [Rint=0.1210]
Full-matrix least-squares on F2
6672/0/313
Reflections collected/unique
Independent reflections
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
1.040
0.998
R1=0.0543, wR2=0.1371
R1=0.0957, wR2=0.1594
0.851 and −0.766
R1=0.0760, wR2=0.1714
R1=0.1243, wR2=0.1935
2.702 and −0.819
Completeness to q=28.3/99.2%
Absolute structure parameter 0.48(2)
−3
,
Largest difference peak and hole (e A
)
3. Results and discussion
Small changes in the ligand environment can have a
dramatic effect on the reaction behavior of copper(I)
complexes towards dioxygen and make it necessary to
study systematically varied systems [10,20]. In that re-
gard the ligand tmpa and its derivatives (as well as
many other ligands described in the literature) have the
disadvantage that chemical modification of these com-
pounds can be difficult and/or time consuming. In
contrast modifying the amine tren is quite facile and a
whole family of new tripodal ligands can be obtained.
For example, tren readily reacts with aldehydes to
form Schiff base derivatives that can be used as new
ligands for metal ions (this approach has been espe-
cially useful for the synthesis of dinuclear macrocyclic
complexes and cryptands) [35–40]. Imine nitrogen
donor atoms are well suited to stabilize the ‘soft’ cop-
per(I) ion but so far only a few mononuclear copper(I)
complexes with such ligands have been structurally
characterized [41–44].
Table 2
,
Selected bond lengths (A) and bond angles (°) for
[Cu(Bz3tren)(H2O)](ClO4)2 and [Cu(Bz3tren)Cl]Cl
Bond lengths for [Cu(Bz3tren)(H2O)](ClO4)2
CuꢀO(9)
CuꢀN(1)
CuꢀN(4)
1.964(4)
2.005(4)
2.087(4)
CuꢀN(2)
CuꢀN(3)
2.095(4)
2.171(4)
Bond lengths for [Cu(Bz3tren)Cl]Cl
CuꢀCl(1)
CuꢀN(1)
CuꢀN(4)
2.276(2)
2.042(4)
2.085(5)
CuꢀN(2)
CuꢀN(3)
2.137(5)
2.139(4)
Bond angles for [Cu(Bz3tren)(H2O)](ClO4)2
O(9)ꢀCuꢀN(1)
O(9)ꢀCuꢀN(4)
N(1)ꢀCuꢀN(4)
O(9)ꢀCuꢀN(2)
N(1)ꢀCuꢀN(2)
179.0(2)
94.4(2)
85.2(2)
95.4(2)
85.5(2)
N(4)ꢀCuꢀN(2)
O(9)ꢀCuꢀN(3)
N(1)ꢀCuꢀN(3)
N(4)ꢀCuꢀN(3)
N(2)ꢀCuꢀN(3)
132.1(2)
94.3(2)
85.0(2)
112.1(2)
113.6(2)
Bond angles for [Cu(Bz3tren)Cl]Cl
N(1)ꢀCu(1)ꢀN(2) 83.86(19)
N(1)ꢀCu(1)ꢀN(3) 84.6(2)
N(2)ꢀCu(1)ꢀN(3) 127.7(2)
N(1)ꢀCu(1)ꢀN(4) 84.32(18)
N(2)ꢀCu(1)ꢀN(4) 113.5(2)
N(3)ꢀCu(1)ꢀN(4) 115.7(2)
N(1)ꢀCu(1)ꢀCl(1) 178.05(15)
N(2)ꢀCu(1)ꢀCl(1)
N(3)ꢀCu(1)ꢀCl(1)
N(4)ꢀCu(1)ꢀCl(1)
At the beginning of our investigations we synthesized
the now commercially available amine Bz3tren by react-
ing benzaldehyde with tren followed by reduction with
sodium borohydride [26]. This prompted us, as well as
94.28(15)
96.15(14)
96.97(13)

176
M. Schatz et al. / Inorganica Chimica Acta 324 (2001) 173–179
Fig. 2. Time resolved spectra. Reaction of [Cu(Bz3tren)(CH3CN)]PF6 with dioxygen at −80 °C in dry acetone ([complex]=0.2 mM, [O2]=0.92
mM, Dt=39 s).
others, to investigate copper(I) complexes of the ini-
tially formed imine ligand (L, Fig. 1) [41,44,45]. The
synthesis of this complex is facile and it was structurally
characterized by X-ray crystallography [41,44]. How-
ever, when this complex was reacted with dioxygen in a
variety of solvents at different temperatures dioxygen
intermediates were not detected [44,45]. This finding is
well in line with our earlier results on the reaction of
dioxygen with different copper imine complexes. All
our kinetic investigations suggest the formation of a
copper peroxo (or superoxo) complex, but we were
unable to spectroscopically detect these compounds
[46,47]. Most likely, the dioxygen intermediate immedi-
ately reacts further to yield a decomposition product
(steady state conditions). So far, we are unable to
explain why this especially seems to be the case for
copper(I) imine complexes.
In contrast to the trivial synthesis of copper(I) com-
plexes with the imine ligand L, our efforts to isolate
copper(I) complexes using Bz3tren proved unsuccessful.
In all the experiments (performed in a glove box)
disproportionation of the copper(I) complexes to cop-
per metal and copper(II) was observed at higher con-
centrations as described earlier for other copper(I)
amine complexes [10,21]. It was not possible to synthe-
size a copper(I) complex of Bz3tren as a solid. However,
it can be easily prepared in situ by mixing equimolar
amounts of the ligand with the appropriate copper(I)
salts in propionitrile or acetone under inert conditions
(concentrations upto 1 mM were possible but solutions
needed to be freshly prepared because disproportiona-
tion occurred over longer time intervals). These solu-
tions were reacted with dioxygen at low temperatures in
a stopped-flow unit equipped with a diode array detec-
tor. A typical example of time resolved spectra for this
reaction at −80 °C in acetone is shown in Fig. 2.
These spectra provide evidence for the formation of
[(Bz3tren)CuO2]+ and [(Bz3tren)CuO2Cu(Bz3tren)]2+
because the spectral features are very similar to known
UV–Vis spectra of copper superoxo and peroxo com-
plexes [16,21]. We assigned the absorbance maxima of
the superoxo [(Bz3tren)CuO2]+ (umax=406 nm) and
peroxo [(Bz3tren)CuO2Cu(Bz3tren)]2+ (umax=506 nm)
complexes accordingly. Therefore, in Fig. 2 the forma-
tion of [(Bz3tren)CuO2Cu(Bz3tren)]2+ can be observed
by the increase of the absorbance maximum at 506 nm.
Under these conditions the total reaction time of 1000
s is not long enough for the complete formation of the
peroxo complex to be observed. The increase of the
absorbance of [(Bz3tren)CuO2Cu(Bz3tren)]2+ is accom-
panied by a decrease of the absorbance attributable to
the superoxo complex. From these results we conclude
that the reaction pathway follows Eqs. (1)–(3) as de-
scribed previously for [(tmpa)Cu(CH3CN)]+ and
[Cu(Me6tren)(CH3CN)]+. Clear differences in the rate
of formation and the stability of the dioxygen adducts
of the three complexes were observed and therefore, a
detailed kinetic study on the reactions of [Cu(Me6tren)-
(CH3CN)]+ and [Cu(Bz3tren)(CH3CN)]+ with dioxygen
is in progress to gain more insight into these differ-
ences.
[(Bz3tren)Cu(RCN)]++O2
X [(Bz3tren)Cu(O2)]++RCN
(1)
(2)
[(Bz3tren)Cu(RCN)]++[(Bz3tren)Cu(O2)]+
X [(Bz3tren)Cu(O2)Cu(Bz3tren)]2+ +RCN
[(Bz3tren)Cu(O2)Cu(Bz3tren)]2+ “ irreversible decay
(3)

M. Schatz et al. / Inorganica Chimica Acta 324 (2001) 173–179
177
[(Bz3tren)CuO2]+ and [(Bz3tren)CuO2Cu(Bz3tren)]2+
could only be observed spectroscopically at low temper-
atures. Increasing the temperature showed faster reac-
tion rates and at higher temperature only the
decomposition of the peroxo complex could be ob-
served. Similar to the reactions of dioxygen with
[(tmpa)Cu(CH3CN)]+ and [Cu(Me6tren)(CH3CN)]+ it
was found that acetone had a ‘stabilizing’ effect on
[(Bz3tren)CuO2]+ and [(Bz3tren)CuO2Cu(Bz3tren)]2+
indicating that nitrile is coordinated to the copper(I)
Bz3tren complex [21,48].
Efforts to isolate crystals of [(Bz3tren)CuO2Cu-
(Bz3tren)]2+ at low temperatures for structural charac-
terization were unsuccessful. In comparison to the spec-
tral data for [(tmpa)CuO2Cu(tmpa)]2+ it is most likely
a trans-v-1,2-peroxo complex [14,15]. It was observed
earlier that [(tmpa)CuO2Cu(tmpa)]2+ is structurally
very similar to other copper(II) tmpa complexes e.g.
[Cu(tmpa)Cl]ClO4 [15,49]. Therefore, synthesis and
characterization of simple copper(II) complexes with
Bz3tren as ligand can also provide valuable information
on [(Bz3tren)CuO2Cu(Bz3tren)]2+. According to the
Cambridge Structural Data Base no metal complexes
with Bz3tren as ligand have been characterized so far.
Only a zinc complex with a substituted Bz3tren ligand
and chloride as an additional ligand was reported that
is similar to [Cu(Bz3tren)Cl]Cl described below [50].
Furthermore, some mononuclear copper(II) complexes
with cryptands as ligands include Bz3tren in its coordi-
nation sphere [51,52].
The copper(II) complexes, [Cu(Bz3tren)(H2O)](ClO4)2
and [Cu(Bz3tren)Cl]Cl were obtained from a reaction
mixture of the ligand with the appropriate copper(II)
salts. ORTEP plots of the crystal structures of their
cations are shown in Figs. 3 and 4. The geometry of
both complexes is best described as trigonal bipyrami-
dal and the bond lengths and angles are similar to those
found in [Cu(Me6tren)Cl]ClO4 and [Cu(Me6tren)-
(H2O)](ClO4)2 [21,53]. The main difference between
[Cu(Bz3tren)(H2O)](ClO4)2 and [Cu(Bz3tren)Cl]Cl is the
bond distance of the Cuꢀaxial ligand. As expected the
,
CuꢀO bond length of 1.964(4) A is much shorter than
,
the CuꢀCl bond length of 2.276(2) A and is very similar
,
to the CuꢀO bond length of 1.973(4)
A
in
[Cu(Me6tren)(H2O)](ClO4)2 [53]. The CuꢀO bond length
2+
,
of 1.852(5) A in [(tmpa)CuO2Cu(tmpa)]
is slightly
shorter than in [Cu(Bz3tren)(H2O)](ClO4)2 [14] The
CuꢀCl bond distances of the three complexes
[Cu(Bz3tren)Cl]Cl, [Cu(Me6tren)Cl]ClO4 and [Cu-
(tmpa)Cl]ClO4 are very similar [21,49].
The trigonal bipyramidal geometry of [Cu(Bz3tren)-
(H2O)](ClO4)2 is retained in solution as was confirmed
by the UV–Vis spectrum in methanol (umax=857 nm,
m=292 M−1 cm−1) typical for trigonal bipyramidal
copper(II) complexes [54,55]. [Cu(Bz3tren)(H2O)]-
(ClO4)2 and [Cu(Bz3tren)Cl]Cl as well as Cu(II) Me6tren
complexes show irreversible cyclic voltammograms in
contrast to [Cu(tmpa)(H2O)](ClO4)2 supporting the
finding that the Cu(I) complexes have a high tendency
towards disproportionation.
Surprisingly it turned out to be problematic to obtain
pure copper(II) complexes of Bz3tren if the synthesis
was not performed under inert conditions. If air had
access to the reaction vessels the solutions started to
become cloudy after a few hours and the characteristic
odor of benzaldehyde could be detected. Most likely
this process can be divided into two separate parts. In
the first part the imine bonds are formed while in the
second part hydrolysis of the imine occurs releasing
benzaldehyde. Oxidations of amine complexes to imine
complexes are well known and an excellent discussion
on these reactions is described in the literature [56].
From these findings most likely the reaction sequence
(shown only for one amine arm) presented in Scheme 1
occurs.
Fig. 3. ORTEP drawing of the cation of [Cu(Bz3tren)(H2O)](ClO4)2.
The first step is deprotonation of the NH groups
caused by the coordination of the Cu(II) ion that
lowers the pKa of the NH groups in Bz3tren. Formal
electron transfer leads to a Cu(I) complex with radical
ligand. Cu(I) can be oxidized by air, now leading to a
Fig. 4. ORTEP drawing of the cation of [Cu(Bz3tren)Cl]Cl.

178
M. Schatz et al. / Inorganica Chimica Acta 324 (2001) 173–179
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Acknowledgements
The authors gratefully acknowledge financial support
from the Deutsche Forschungsgemeinschaft and the
Volkswagenstiftung. Furthermore, they thank Professor
Rudi van Eldik for the support of this work.
Scheme 1.
References
[1] R.H. Holm, P. Kennepohl, E.I. Solomon, Chem. Rev. 96 (1996)
2239.
[2] J. Reedijk, E. Bouwman (Eds.), Bioinorganic Catalysis, Marcel
Dekker, New York, 1993.
[3] S. Fox, K.D. Karlin, in: J.S. Valentine, C.S. Foote, A. Green-
berg, J.F. Liebman (Eds.), Active Oxygen in Biochemistry,
Blackie Academic and Professional, Chapman & Hall, Glasgow,
1995, pp. 188–231.
[4] W. Kaim, J. Rall, Angew. Chem. 108 (1996) 47.
[5] N. Kitajima, Adv. Inorg. Chem. 39 (1992) 1.
[6] K.D. Karlin, Z. Tyekla´r (Eds.), Bioinorganic Chemistry of Cop-
per, Chapman & Hall, New York, 1993.
Cu(II) complex with a radical ligand. Further reduction
of Cu(II) to Cu(I) and loss of a proton leads to a Cu(I)
imine complex. As described above the Cu(I) imine
complex will be again oxidized by air to the according
Cu(II) complex. But this complex is unstable towards
hydrolysis (similar to some related copper complexes;
[56] e.g. the copper complex of the ligand derived from
tren and pyridine-2-aldehyde [57]) and the copper
amine complex and benzaldehyde is formed. This reac-
tion scheme can be completely suppressed if the com-
plexes are synthesized and kept under inert conditions.
[7] E. Spodine, J. Manzur, Coord. Chem. Rev. 119 (1992) 171.
[8] H.-C. Liang, M. Dahan, K.D. Karlin, Curr. Opin. Chem. Biol.
3 (2) (1999) 168.
[9] K.D. Karlin, Science 261 (1993) 701.
[10] S. Schindler, Eur. J. Inorg. Chem. (2000) 2311.
[11] A.G. Blackman, W.B. Tolman, in: B. Meunier (Ed.), Structure &
Bonding, vol. 97, Springer, Berlin, 2000, pp. 179–211.
[12] W.B. Tolman, Acc. Chem. Res. 30 (1997) 227.
[13] R.A. Sheldon, J. Mol. Cat., A: Chem., Special Ed. 117 (1997).
[14] R.R. Jacobson, Z. Tyekla´r, A. Farooq, K.D. Karlin, S. Liu, J.
Zubieta, J. Am. Chem. Soc. 110 (1988) 3690.
4. Conclusions
An exciting finding of this work is that complete
alkylation of tren is unnecessary to obtain amine lig-
ands that support formation of copper peroxo com-
plexes; monoalkylation of each amine arm is enough to
stabilize such intermediates. As discussed above this
allows facile modification of tren to obtain a series of
new amine ligands for a study of systematically varied
systems.
Furthermore, it is interesting to note that the intro-
duction of the three benzyl groups did not provide any
sterical hindrance to suppress formation of [(Bz3tren)-
CuO2Cu(Bz3tren)]2+. The benzyl groups are oriented in
a propeller like fashion, away from the copper(II) ion.
[15] Z. Tyekla´r, R. Jakobson, N. Wei, N. Murthy, J. Zubieta, K.D.
Karlin, J. Am. Chem. Soc. 115 (1993) 2677.
[16] K.D. Karlin, N. Wei, B. Jung, S. Kaderli, P. Niklaus, A.
Zuberbu¨hler, J. Am. Chem. Soc. 115 (1993) 9506.
[17] T.N. Sorrell, D.L. Jameson, Inorg. Chem. 21 (1982) 1014.
[18] N. Wei, N.N. Murthy, Z. Tyekla´r, K.D. Karlin, Inorg. Chem. 33
(1994) 1177.
[19] N. Wei, N.N. Murthy, Q. Chen, J. Zubieta, K.D. Karlin, Inorg.
Chem. 33 (1994) 1953.
[20] M. Schatz, M. Becker, F. Thaler, F. Hampel, S. Schindler, R.R.
Jacobson, Z. Tyekla´r, N.N. Murthy, P. Ghosh, Q. Chen, J.
Zubieta, K.D. Karlin, Inorg. Chem. 40 (2001) 2312.
[21] M. Becker, F. Heinemann, S. Schindler, Chem. Eur. J. 5 (1999)
3124.
[22] P.C. Jain, E.C. Lingafelter, J. Am. Chem. Soc. 89 (1967) 6131.
[23] M. Duggan, N. Ray, B. Hathaway, G. Tomlinson, P. Brint, K.
Pelin, J. Chem. Soc., Dalton Trans. (1980) 1342.
[24] A. Marzotto, A. Ciccarese, D.A. Clemente, G. Valle, J. Chem.
Soc., Dalton Trans. (1995) 1461.
[25] F. Thaler, C.D. Hubbard, F.W. Heinemann, R. van Eldik, S.
Schindler, I. Fa´bia´n, A.M. Dittler-Klingemann, F.E. Hahn, C.
Orvig, Inorg. Chem. 37 (1998) 4022.
[26] A.A. Naiini, W.M.P.B. Menge, J.G. Verkade, Inorg. Chem. 30
(1991) 5009.
[27] G.J. Kubas, B. Monzyk, A.L. Crumbliss, Inorg. Synth. 19 (1979)
90.
5. Supplementary material
Crystallographic data (excluding structure factors)
for the structural analysis have been deposited with the
Cambridge Crystallographic Data Center, CCDC No.
161783 for compound [Cu(Bz3tren)(H2O)](ClO4)2 and
CCDC No. 161192 for compound [Cu(Bz3tren)Cl]Cl.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336-033;

M. Schatz et al. / Inorganica Chimica Acta 324 (2001) 173–179
179
[28] J.A. Halfen, S. Mahapatra, E.C. Wilkinson, S. Kaderli, V.G.
Young, L. Que Jr., A.D. Zuberbu¨hler, W.B. Tolman, Science
271 (1996) 1397.
[29] K.D. Karlin, M.S. Nasir, B.I. Cohen, R.W. Cruse, S. Kaderli,
A.D. Zuberbu¨hler, J. Am. Chem. Soc. 116 (1994) 1324.
[30] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M.C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 22
(1992) 389.
[31] G.M. Sheldrick, SHELXL-92, Universita¨t Go¨ttingen, Germany,
1992.
[32] Siemens Area Detector Absorption Correction, Siemens.
[33] G.M. Sheldrick, SHELX-97, Universita¨t Go¨ttingen, Germany,
1997.
[34] L. Zsolnai, XPMA, Zortep, Universita¨t Heidelberg, Germany,
1997.
[35] S.R. Collinson, D.E. Fenton, Coord. Chem. Rev. 148 (1996) 19.
[36] C.T. Brewer, G. Brewer, M. Shang, W.R. Scheidt, I. Muller,
Inorg. Chim. Acta 278 (1998) 197.
[37] V. McKee, J. Nelson, Acta Cryst., Sect. C 55 (1999) 1494.
[38] A. Al-Obaidi, G. Baranovic, J. Coyle, C.G. Coates, J.J. McGar-
vey, V. McKee, J. Nelson, Inorg. Chem. 37 (1998) 3567.
[39] M.G.B. Drew, D. Farrell, G.G. Morgan, V. McKee, J. Nelson,
J. Chem. Soc., Dalton Truns. (2000) 1513.
[40] H. Adams, N.A. Bailey, D.E. Fenton, M.B. Hursthouse, W.
Kanda, M. Kanesato, K.M.A. Malik, E.J. Sadler, J. Chem. Soc.,
Dalton Trans. (1997) 921.
[43] J.F. Gallagher, E.C. Alyea, G. Ferguson, X. Zheng, Acta Cryst.,
Sect. C 50 (1994) 16.
[44] D. Walther, K. Hamza, H. Go¨rls, W. Imhof, Z. Anorg. Allg.
Chem. 623 (1997) 1135.
[45] M. Becker, S. Schindler, unpublished results.
[46] M. Becker, S. Schindler, R. van Eldik, Inorg. Chem. 33 (1994)
5370.
[47] S. Ryan, H. Adams, D.E. Fenton, M. Becker, S. Schindler,
Inorg. Chem. 37 (1998) 2134.
[48] K.D. Karlin, D.-H. Lee, S. Kaderli, A.D. Zuberbu¨hler, Chem.
Comm. (1997) 475.
[49] K.D. Karlin, J.C. Hayes, S. Juen, J.P. Hutchinson, J. Zubieta,
Inorg. Chem. 21 (1982) 4106.
[50] P. Scrimin, P. Tecilla, U. Tonellato, G. Valle, A. Veronese, J.
Chem. Soc., Chem. Comm. (1995) 1163.
[51] D.K. Chand, P.K. Bharadwaj, Inorg. Chem. 35 (1996) 3380.
[52] D.K. Chand, P.K. Bharadwaj, Inorg. Chem. 37 (1998) 5050.
[53] S.C. Lee, R.H. Holm, J. Am. Chem. Soc. 115 (1993) 11 789.
[54] K.D. Karlin, J. Zubieta (Eds.), Copper Coordination Chemistry:
Biochemical and Inorganic Perspectives, Adenine Press, Guilder-
land, New York, 1983.
[55] A.M. Dittler-Klingemann, C. Orvig, F.E. Hahn, F. Thaler, C.
Hubbard, R. van Eldik, S. Schindler, I. Fa´bia´n, Inorg. Chem. 35
(1996) 7798.
[56] E.C. Constable, Metals and Ligand Reactivity, VCH, Weinheim,
1996.
[57] R.M. Kirchner, C. Mealli, M. Bailey, N. Howe, L.P. Torre, L.J.
Wilson, L.C. Andrews, N.J. Rose, E.C. Lingafelter, Coord.
Chem. Rev. 77 (1987) 89.
[41] E. Alyea, G. Ferguson, M. Jennings, Z. Xu, Tetrahedron 9
(1990) 739.
[42] E. Alyea, G. Ferguson, M. Jennings, L. Baolong, X. Zheng, X.
You, S. Liu, Tetrahedron 9 (1990) 2463.