Binuclear CuII complexes as catalysts for hydrocarbon and catechol oxidation reactions with hydrogen peroxide and molecular oxygen

Article abstract of DOI:10.1590/S0103-50532010000700009

The tridentate ligands HL1, [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)] amine, and HL2, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine, were used to synthesize binuclear Cu^II complexes, [Cu₂(L1) ₂]Cl₂·2H₂O, complex 1, and [Cu ₂(L2)₂](ClO₄)₂·1.5H ₂O, complex 2, in order to obtain catalysts for oxidative processes. Both complexes were characterized by elemental analysis, IR, UV-Vis and EPR spectroscopies. In addition, they were studied by cyclic voltammetry and potentiometric titration in order to investigate their behavior in solution. The crystal structure of complex 1 revealed a binuclear cation where the metal centers are bridged by two phenoxo groups. This arrangement provides a Cu...Cu distance of 3.043(10) A?, which is similar to the observed for catechol oxidase (2.90 A?). The catalytic reactivities of both complexes were investigated for hydrocarbon and catechol oxidations. Complexes 1 and 2 led to low overall hydrocarbon oxidation conversion values of 6.34 percent and 7.15 percent, respectively. However, for complex 1, only cyclohexanol (Cy-OH) and cyclohexanone (Cy=O) were isolated as reaction products, with selectivities of 68.1percent for Cy-OH. This low overall conversion is tentatively attributed to steric hindrance effects produced by the non-coplanar aromatic rings of the ligand scaffolds, which suggest that the access of the hydrocarbon molecule to the binuclear active center is a determinant step in the reaction mechanism. Investigation of catecholase activities has shown high efficiencies, with complex 2 being more active than complex 1. It indicates that the pyridine-containing ligand is able to stabilize the intermediate Cu ^ICu^I center which is proposed to be formed in this process. This is corroborated by the strong participation of pyridine in the LUMO (lowest unoccupied molecular orbital) of complex 2, which can help to accommodate the additional negative charge when the complex is reduced from Cu^IICu^II to Cu^ICu^I.

Full text of DOI:10.1590/S0103-50532010000700009

J. Braz. Chem. Soc., Vol. 21, No. 7, 1218-1229, 2010.
Printed in Brazil - ©2010 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Binuclear CuII Complexes as Catalysts for Hydrocarbon and Catechol Oxidation
Reactions with Hydrogen Peroxide and Molecular Oxygen
Luciana R. Martins,a Elizabeth T. Souza,a Tatiana L. Fernandez,a Bernardo de Souza,b
Sílvio Rachinski,c Carlos B. Pinheiro,d Roberto B. Faria,a Annelise Casellato,a
Sérgio P. Machado,a Antonio S. Mangrich*,c and Marciela Scarpellini*,a
aDepartamento de Química Inorgânica, Instituto de Química, Universidade Federal do Rio de Janeiro,
21945-970 Rio de Janeiro-RJ, Brazil
bDepartamento de Química, Universidade Federal de Santa Catarina, 88040-900 Florianópolis-SC, Brazil
cDepartamento de Química, Universidade Federal do Paraná, 81531-970 Curitiba-PR, Brazil
dDepartamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais,
31270-901 Belo Horizonte-MG, Brazil
Dois ligantes tridentados, HL1, [(2-hidroxibenzil)(2-(imidazol-2-il)etil)]amina, e HL2, [(2-hidroxibenzil)(2-(piridil-
•
2-il)etil]amina, foram usados na síntese dos complexos binucleares [Cu2(L1)2]Cl2 2H2O, complexo 1, e [Cu2(L2)2]
•
(ClO4)2 1.5H2O, complexo 2, para serem empregados como catalisadores em processos de oxidação. Os complexos foram
caracterizados por análise elementar e espectroscopias na região do infravermelho, ultravioleta-visível e ressonância
paramagnética eletrônica. Foram também estudados por voltametria cíclica e titulação potenciométrica, a fim de caracterizar
seus comportamentos em solução.A resolução da estrutura cristalina do complexo 1 mostrou um cátion binuclear contendo
…
dois grupos fenóxido em ponte. Este arranjo possui uma distância Cu Cu de 3.043(10) Å, similar à observada na catecol
oxidase (2.90 Å). Os comportamentos catalíticos destes complexos foram investigados nas oxidações de cicloexano e
de catecol. Na oxidação de cicloexano observou-se baixa atividade para ambos os complexos, que pode ser atribuída ao
estereoimpedimento produzido pela falta de coplanaridade entre os anéis aromáticos do arcabouço dos ligantes, sugerindo
que a aproximação entre o substrato e o centro ativo binuclear é uma etapa determinante no mecanismo da reação. Com
relação à atividade de catecolase, foram observadas altas eficiências, com o complexo 2 sendo mais ativo que o complexo
1. Isto indica que o ligante piridina é capaz de estabilizar melhor o intermediário proposto para esse processo, que contém
o centro CuICuI. Isto é corroborado pela grande participação da piridina no LUMO (lowest unoccupied molecular orbital)
do complexo 2, que pode ajudar a acomodar a carga negativa adicional quando o complexo é reduzido da forma CuIICuII
para CuICuI.
The tridentate ligands HL1, [(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine, and HL2, [(2-hydroxybenzyl)
(2-(pyridil-2-yl)ethyl]amine, were used to synthesize binuclear CuII complexes, [Cu2(L1)2]Cl2 2H2O, complex 1,
•
•
and [Cu2(L2)2](ClO4)2 1.5H2O, complex 2, in order to obtain catalysts for oxidative processes. Both complexes were
characterized by elemental analysis, IR, UV-Vis and EPR spectroscopies. In addition, they were studied by cyclic
voltammetry and potentiometric titration in order to investigate their behavior in solution. The crystal structure of complex
1 revealed a binuclear cation where the metal centers are bridged by two phenoxo groups. This arrangement provides a
…
Cu Cu distance of 3.043(10) Å, which is similar to the observed for catechol oxidase (2.90 Å). The catalytic reactivities
of both complexes were investigated for hydrocarbon and catechol oxidations. Complexes 1 and 2 led to low overall
hydrocarbon oxidation conversion values of 6.34 % and 7.15 %, respectively. However, for complex 1, only cyclohexanol
(Cy-OH) and cyclohexanone (Cy=O) were isolated as reaction products, with selectivities of 68.1% for Cy-OH. This low
overall conversion is tentatively attributed to steric hindrance effects produced by the non-coplanar aromatic rings of the
ligand scaffolds, which suggest that the access of the hydrocarbon molecule to the binuclear active center is a determinant
step in the reaction mechanism. Investigation of catecholase activities has shown high efficiencies, with complex 2 being
more active than complex 1. It indicates that the pyridine-containing ligand is able to stabilize the intermediate CuICuI
center which is proposed to be formed in this process. This is corroborated by the strong participation of pyridine in the
LUMO (lowest unoccupied molecular orbital) of complex 2, which can help to accommodate the additional negative
charge when the complex is reduced from CuIICuII to CuICuI.
Keywords: binuclear copper complexes, molecular structure, hydrocarbon oxidation, catechol oxidase
*e-mail: mangrich@quimica.ufpr.br, marciela@iq.ufrj.br

Vol. 21, No. 7, 2010
Martins et al.
1219
Introduction
In addition to copper-containing laccase, tyrosinase and
catechol oxidase have also received special attention related
to their use as green catalysts because of their catecholase
activity, i.e., their ability to convert 1,2-dihydroxyphenols
(o-diphenol or catechol) to the respective o-quinones.
However, besides this feature, tyrosinase is also able to
promote the o-hydroxylation of phenols (cresolase activity)
and may contribute to bioremediation of phenol-containing
industrial residues.7 Unlike laccase, both tyrosinase and
catechol oxidase are binuclear (type 3) copper enzymes.
Despite tyrosinase crystal structure has not been solved,
several spectroscopic studies indicate a close similarity with
catechol oxidase. In the met form, catechol oxidase presents
two CuII ions coordinated to three histidine residues each,
bridged by a hydroxo group 2.87 Å apart.14
Considering the high academic and industrial interest
on these enzyme systems, and that their use is sometimes
limited mainly because of the optimal pH and temperature
ranges,15 model complexes are considered as an alternative.
Because of this, several compounds have been synthesized,
characterized and tested as catalysts for oxidative processes
involving molecular oxygen and hydrogen peroxide.16 It is
a matter of great concern to understand how small changes
on the ligand scaffold can interfere in the reactivity of
copper-containing coordination complexes, in order to
improve their efficiency.17
In view of our previous interest in copper model
complexes and in polipodal ligands,18-22 we present here
two new binuclear CuII complexes (1 and 2, Figure 1)
employing the tridentate N,O-donor ligands HL1,
[(2-hydroxybenzyl)(2-(imidazol-2-yl)ethyl)]amine, and
HL2, [(2-hydroxybenzyl)(2-(pyridil-2-yl)ethyl]amine.
These complexes were designed intending to develop
new catalysts for oxidative processes, and their reactivity
towards cyclohexane and catechol oxidation reactions
were investigated using hydrogen peroxide or molecular
oxygen as oxidants.
Bleaching processes are among the most outstanding
oxidative processes worldwide. They are largely employed
in household, hospitals, commercial installations and in
a variety of industries, such as textile, pulp and paper,
and detergents.1 Actually, chlorine-based bleaching
systems including chlorine gas, chlorites (Ca(ClO2)2
and NaClO2), hypochlorites (NaOCl, Ca(OCl)2) and
chlorine dioxide (ClO2) are largely employed.2 However,
environmental concerns have led to restrict their use
mainly because of the resulting chlorine-based residuals.3
This restriction focuses basically on their chlorinated
organic subproducts that are potentially hazardous,
present low biodegradability, are recalcitrant, and then
considered not environmentally friendly. In order to
overcome the disadvantages of chlorine-containing
products, totally chlorine free (TCF) systems emerged
as an alternative, including molecular oxygen, ozone,
hydrogen peroxide, perborates, percarbonates, enzymes
and others.4 Under the green chemistry concept, some
strategies are being spread out, as the use of enzymes
able to activate oxygen, or hydrogen peroxide, to perform
oxidation reactions.5,6 This class of enzymes is called
oxidoreductases and comprises several copper-containing
metalloenzymes such as laccases,7 tyrosinase,8,9 catechol
oxidase10 and Cu-containing quercetinase.11,12 Laccase is
probably the most employed in bleaching studies. It is a
multi-copper containing oxidoreductase (EC 1.10.3.2)
with four copper centers (one type 1, one type 2 and two
type 3 Cu atoms), which catalyzes the oxidation of a
variety of phenols to quinones through the activation of
molecular oxygen.13 Laccase has been studied in several
organic transformations such as the preparation of phenol-
derivatives, aldehydes, ketones, lactones, oxidations
of azo-dyes, hormones, polymerization reactions, and
others.13
2+
2+
HN
H
N
N
N
O
O
N
O
HN
N
NH
N
N
Cu
Cu
Cu
Cu
H
H
NH
NH
N
N
O
N
H
OH
OH
HL1
complex 2
HL2
complex 1
Figure 1. Schematic views of HL1, HL2 and complexes 1 and 2.

1220
Binuclear CuII Complexes as Catalysts for Hydrocarbon and Catechol Oxidation
J. Braz. Chem. Soc.
Experimental
point:229°C.FTIR(CsI,cm-1):n(NHsec)3240;n(CHar/CHalif)
3072-2941;n(C=N/C=C)1610-1423;n(C-O)1259;n(Cl-O)
1130-1028 and d(CHar) 775. Elemental analysis calculated
Materials and measurements
•
(found) for C28H30Cl2Cu2N4O10 1.5H2O: C 41.64 (41.61);
-1
HL1 and HL2 were synthesized and purified as
previously described.23,24 All chemicals for syntheses
and analyses were of analytical grade and used without
further purification. Infrared spectra (CsI pellet or film)
were recorded using a NICOLET, MAGNA-IR 760 (4000
to 200 cm-1) spectrophotometer. Elemental analyses were
performed using a Perkin-Elmer 2400 analyzer coupled to
anAD-4 Perkin-Elmer microbalance. Electronic absorption
spectra were recorded using a Perkin-Elmer Lambda-19
spectrophotometer. Cyclic voltammetry studies were
performed with a Princeton Applied Research (PAR) 273
potentiostat, at room temperature (25 ± 1 °C), in acetonitrile
solutions kept under argon atmosphere. The standard
three-electrode cell was composed by the following
electrodes: a glassy carbon working, a platinum auxiliary
and a Ag/AgCl pseudo-reference. Hexafluorophosphate
of tetrabutylammonium (tba(PF6), 0.1 mol L-1) was used
as supporting electrolyte and the ferrocenium-ferrocene
couple25 was employed to monitor the reference electrode
potential. Molar conductivities were measured on a
Digimed CD-21 conductivity meter in methanol solutions.
H 4.12 (3.79); N 6.94 (6.54)%. LM = 162 Ω mol-1 cm2
(electrolyte 2:1 in methanol).26
Warning: perchlorate salts are potentially explosive and
must be handled very carefully and only in small quantities.
Potentiometric titration
Potentiometric studies were carried out in CH3CN/H2O
(1:1 v/v) solution using a Micronal B375 pHmeter fitted
with blue-glass and calomel reference electrodes calibrated
to read –log[H+] directly, designated as pH. Bidistilled
water in the presence of KMnO4 was used to prepare
the CH3CN/H2O (1:1 v/v) solutions. The electrode was
calibrated using the data obtained from a potentiometric
titration of a known volume of a standard 0.0100 mol L-1
HCl solution (0.1 mol L-1 in KCl) with a standard CO2-
free 0.100 mol L-1 KOH solution. The measurements were
carried out in a thermostatized cell containing a solution of
the complex (0.05 mol/50 mL) with ionic strength adjusted
to 0.100 mol L-1 by addition of KCl, at 25.00 ± 0.05 °C.
The experiments were performed under argon flow to
eliminate the presence of atmospheric CO2. The samples
were titrated by addition of fixed volumes of a standard
CO2-free KOH solution (0.100 mol L-1). Computations were
carried out with the BEST program, and species diagrams
were obtained with SPE and SPEPLOT programs.27
Syntheses
•
[Cu2(L1)2]Cl2 2H2O, 1
Complex 1 was obtained by the slow addition of
•
CuCl2 2H2O (0.17 g, 1 mmol in 20 mL of methanol) to a
methanolic solution of HL1 (0.217 g, 1 mmol in 20 mL).
The reaction mixture was heated under stirring for ca.
15 min, filtered and left to crystallize on bench at room
temperature (near 25 °C). After a few days, dark green
single crystals suitable for X-ray crystallographic analysis
were collected from the mother liquor. Decomposition point:
195 °C. FTIR (CsI, cm-1): n(NHsec) 3134; n(CHar/CHalif)
3037-2909; n(C=N/C=C) 1596-1454; n(C-O) 1275 and
d(CHar) 771. Elemental analysis calculated (found) for
Crystal structure
X-ray diffraction data collection for compound 1
was performed on a Bruker-Kappa-CCD diffractometer
(LDRX) using graphite-monochromatized Mo-Ka
radiation (l = 0.71069 Å) at room temperature. Final unit
cell parameters were based on the fitting of all reflections
positions.28 Data integration and scaling of the reflections
were performed with the EVALCCD suite.29 Empirical
multiscan absorption corrections using equivalent
reflections were performed with the program SADABS.30
The structure was solved by direct methods using the
SHELXS31 program. The positions of all atoms could be
unambiguously assigned on consecutive difference Fourier
maps. Refinements were performed using SHELXL31
based on F2 through full-matrix least square routine.
All but hydrogen atoms were refined with anisotropic
atomic displacement parameters. Hydrogen atoms were
added to the structure and further refined according to the
riding model.32 No disordered groups have been found
•
C24H28Cl2Cu2N6O2 2H2O: C 43.25 (43.11); H 4.84 (4.61);
-1
N 12.61 (12.87)%. LM = 151 Ω mol-1 cm2 (electrolyte 2:1
in methanol).26
•
[Cu2(L2)2](ClO4)2 1.5H2O, 2
Complex 2 was synthesized by the same procedure
described for complex 1, but with the addition of excess
of sodium perchlorate at the end of reaction. Dark green
single crystals were also obtained from the mother liquor,
but none of them presented a satisfactory diffraction pattern.
Recrystallizations in other media failed. Decomposition

Vol. 21, No. 7, 2010
Martins et al.
1221
Table 1. Crystal structure data collection and refinement for compound 1
Complex 1
in the structure refinements. All attempts to localize the
hydrogen atoms around the water molecules failed. Thus,
the hydrogen bonds of the N–H group of the imidazole
towards the water molecules could not be properly assigned.
Crystal structure and refinement data for complex 1 are
summarized in Table 1. Selected bond distances and angles
are indicated in Table 2. Atomic coordinates and complete
crystal structure results are given as supplementary
information (see SI).
Empirical formula
Formula weight
Temperature (K)
Wavelength (l, Å)
Crystal system
Space group
C24H28Cl2Cu2N6O4
666.50
298(2)
0.71073
Monoclinic
Cc
Unit cell dimensions: a (Å)
b (Å)
16.524(3)
12.745(3)
15.735(3)
90
Reactivity
c (Å)
a (deg)
Cyclohexane oxidation
b (deg)
117.79(3)
90
The catalytic activities of complexes 1 and 2 towards
cyclohexane oxidation were determined following
previouslypublishedmethods.33 Thereactionwasperformed
in acetonitrile at room temperature and inert atmosphere,
using H2O2 as oxidant. The catalyst:substrate:oxidant
reactionratiowas1:1000:1000, withacatalystconcentration
of 7×10-4 mol L-1. In a typical experiment, the catalytic
reaction was triggered with the addition of cyclohexane to
a degassed acetonitrile solution containing the catalyst and
the oxidant. The reaction was quenched after 24 h with the
addition of an aqueous solution of Na2SO4 (0.4 mol L-1).
The products were extracted with diethyl ether; the organic
fractions were dried over anhydrous Na2SO4 and analyzed
by gas chromatography. The results are expressed as relative
yields.33
g (deg)
Volume (Å3)
2931.4(13)
4
Z
Density (rcalc, g cm-3)
Absorption coefficient (m, mm-1)
F(000)
1.501
1.673
1352
Crystal size (mm3)
Theta range for data collection (deg)
Index ranges
0.42 × 0.19 × 0.11
5.09 to 26.37
-20 ≤ h ≤ 20
-15 ≤ k ≤ 15
-19 ≤ l ≤ 19
Reflections collected
13418
5123 [R(int) = 0.0381]
98.3
Independent reflections
Completeness to q = 26.37° (%)
Refinement method
Full-matrix least-squares on F2
Data / restraints / parameters
Goodness-of-fit on F2
5123 / 2 / 345
Oxidation of 3,5-di-tert-butyl-catechol
1.160
Final R indices [I>2sigma(I)]
R indices (all data)
R1 = 0.0435, wR2 = 0.0841
R1 = 0.0792, wR2 = 0.1023
0.613 and -0.439
The cathecolase activities of complexes 1 and 2 were
measured by the oxidation of 3,5-di-tert-butylcatechol (3,5-
dtbc) to the respective quinone at 25 °C. The experiments
were performed with an Agilent 8453 spectrophotometer,
and the reactions were followed at 400 nm, which is the
characteristic absorption band of the oxidation product
(3,5-di-tert-butylquinone, 3,5-dtbq). The pH effect on the
reaction rate was determined over the pH range 5.5-10.0.
A typical experiment was performed using the following
conditions: 100 µL of freshly prepared aqueous buffer
solution, [buffer]final = 3×10-3 mol L-1 (buffers: MES
(2-(N-morpholino)ethanesulfonic acid), pH 5.5, 6.0 and 6.5;
HEPES (4-(2-hydroxyethyl)piperazine-1-ethanesulfonic
acid), pH 7.0 and 7.5; and CHES (2-(cyclohexylamino)
ethanesulfonic acid), 8.0, 8.5 , 9.0, 9.5 and 10.0), 100 µL
Largest diff. peak and hole (e Å-3)
were performed using 100 µL of freshly prepared aqueous
CHES buffer, 100 µL of a methanolic solution of the
complex ([complex]final = 2.4×10-5 mol L-1) and oxygen-
saturated methanol, at pH 8.5 ([buffer]final = 3×10-3 mol L-1).
The reaction was initiated by the addition of volumes
varying from 60 µL to 240 µL of a 3,5-dtbc solution ([3,5-
dtbc]final 3×10-3-12×10-3 mol L-1) and monitored for 20 min.
Correction for the spontaneous oxidation of the 3,5-dtbc
was carried out by subtracting the initial rate for the blank
experiment (without adding the catalyst). The initial rate
at each substrate concentration was obtained by fitting
a second degree polynomial to the absorbance vs. time
plot,34 using e(400 nm) = 1900 mol L-1 cm-1 for 3,5-di-tert-
butylquinone.35 A Michaelis-Menten approach was applied
using a non-linear fit to obtain Vmax and KM parameters.36
of a methanolic solution of the complex ([complex]final
=
2.4×10-5 mol L-1) and 3.0 mL of O2-saturated methanol. A
1-cm-path-length quartz cell was used as a reactor. The
kinetic experiments under conditions of excess of substrate

1222
Binuclear CuII Complexes as Catalysts for Hydrocarbon and Catechol Oxidation
J. Braz. Chem. Soc.
Table 2. Experimental (X-ray) and calculated (DFT) main bond distances
(Å) and angles (o) for complexes 1 and 2
of the complexes. Both ligands are able to stabilize CuII
complexes. Infrared spectra of complexes 1 and 2 have
shown characteristic bands of the ligands scaffold, and
are shifted when compared to free HL1 and HL2, which
is clear evidence of complexation. In order to help band
attribution, theoretical studies were carried out using DFT
(Figure S2). Considering the similarities of ligands and
complexes spectra, the attribution data are summarized on
Table S1, and only the main differences are discussed. In
both spectra of complexes 1 and 2, the out-of-the-plane OH
angular deformation band of the phenol group is absent,
indicating the presence of phenolate groups coordinated
to the metal centers. For complex 2, the presence of free
perchlorate anions is evidenced by a broad band from 1130
to 1028 cm-1 assigned to the Cl-O stretchings of this anion
as a counter ion.38 For both complexes, elemental analyses
indicate the 1:1 ligand:metal ratio, and the presence of
chloride or perchlorate anions. The binuclear arrangement
for both complexes is firstly suggested by conductivity
data obtained in freshly prepared methanol solutions
Complex 1
Complex 2
Calc
Exp
Calc
1.976
1.966
2.010
2.082
Cu(01)-N(010)
1.959(5)
1.980(4)
2.000(4)
2.030(5)
2.745(5)
4.430(5)
3.928
2.018
Cu(01)-O(006)
1.976
Cu(01)-O(005)
2.006
Cu(01)-N(009)
2.056
Cu(01)-Cl(03)
Cu(01)-O(01)
Cu(01)-O(02)
Cu(01)-Cu(02)
3.043 (10)
1.943(5)
1.950(4)
1.983(4)
2.019(5)
3.174(3)
2.899(4)
4.302
3.049
1.976
1.967
2.082
1.960
3.064
2.018
1.975
2.006
2.056
Cu(02)-N(012)
Cu(02)-O(005)
Cu(02)-O(006)
Cu(02)-N(007)
Cu(02)-Cl(04)
Cu(02)-O(02)
Cu(02)-O(01)
-1
(complex 1: LM = 151 Ω mol-1 cm2, and complex 2:
N(010)-Cu(01)-O(06)
N(010)-Cu(01)-O(005)
O(006)-Cu(01)-O(005)
N(010)-Cu(01)-N(009)
O(006)-Cu(01)-N(009)
O(005)-Cu(01)-N(009)
N(012)-Cu(02)-O(005)
N(012)-Cu(02)-O(006)
O(005)-Cu(02)-O(006)
N(012)-Cu(02)-N(007)
O(005)-Cu(02)-N(007)
O(006)-Cu(02)-N(007)
Cu(02)-O(005)-Cu(01)
Cu(01)-O(006)-Cu(02)
146.5(2)
93.8(2)
165.32
96.15
78.80
94.62
92.22
167.45
165.24
92.22
78.80
94.60
92.21
167.32
100.13
100.44
159.41
96.57
78.74
96.78
91.84
163.63
159.45
96.77
78.73
96.77
91.82
163.69
100.56
100.62
-1
LM = 162 Ω mol-1 cm2), which are in the typical range of
2:1 electrolytes.26
76.82(17)
95.7(2)
X-ray crystal structure
92.47(19)
169.25(19)
157.8(2)
92.61(19)
77.91(17)
96.9(2)
Crystallographic data and bond parameters for complex
1 are presented in Tables 1 and 2, respectively.An ORTEP39
drawing of the cation complex is shown in Figure 2. The
binuclear structure in the solid state is confirmed, where
each CuII atom is coordinated to a deprotonated L1, and
bridged by the two phenoxo groups provided by the
ligand. In close proximity, there are two chloride anions
and two water molecules (Figure 2). In addition to the two
94.18(19)
170.1(2)
100.79(18)
100.34(19)
Theoretical calculations
Geometry optimizations were performed as described
before,using Gaussian 03 package with the B3LYP hybrid
density functional theory combined with the 6-31G* basis
sets and LANL2DZ for the Cu atom.37
Results and Discussion
Synthesis and initial characterization
L1 and L2 were chosen in order to provide insights
about the influence of the substitution of pyridine by
imidazole rings on the electronic structure and reactivity
Figure 2. ORTEP39 representation of complex 1, showing the coordination
sphere atoms labeling and 50% probability ellipsoids.

Vol. 21, No. 7, 2010
Martins et al.
1223
oxygen atoms from the phenoxo bridges, each CuII atom is
coordinated to one imidazole and the amine nitrogen atoms.
Thus, the CuII atoms can be considered as tetracoordinated,
since their distances to the chloride anions and the water
molecules are longer than 2.745(5) Å (Table 2). In fact,
these Cu-Cl bond distances are longer than those reported
for coordinated chloride anions.19,40,41 The geometries
adopted by the CuII centers are both distorted square-planar,
with angles varying from 76.8(2)Å to 95.7(2)Å, for Cu(01),
and from 77.9(2) Å to 96.9(2) Å, for Cu(02).
solution.48 Based on the similarities of the spectral data
presented by complexes 1 and 2 we can conclude that they
might present the same kind of geometry. The very broad
shape of the spectra in the range of the low energy band
makes a precise geometry attribution difficult, but points
out to a distorted octahedron,47 which suggests interaction
of metal centers with solvent molecules.
In both CuII centers, the shorter bond distances are
Cu-Nimidazole [Cu(01)-N(10) = 1.959(5) and Cu(02)-N(12) =
1.943(5) Å], which are in the range observed for other CuII
complexes with imidazole-containing ligands.18-21,65 The
longer ones are Cu-Namine [Cu(01)-N(09) = 2.030(5) and
Cu(02)-N(07)=2.019(5)Å],whichalsoagreewiththistypeof
bonddistancesinCuII complexes.18-21,42,43 Alsointheexpected
rangearethedistancesCu-Ophenoxo [Cu(01)-O(006)=1.980(4),
Cu(01)-O(005) = 2.000(4), Cu(02)-O(005) = 1.950(4) and
Cu(02)-O(006) = 1.983(4) Å].24,44-46 Finally, the Cu Cu
…
distance is 3.043(10)Å and is in the range observed for other
binuclearCuII complexesbridgedbytwophenoxogroups.43,44
These distances are similar to that observed for the oxidized
form of catechol oxidase (2.90 Å).10,17
Figure 3. Electronic spectra of acetonitrile solutions of complexes 1 (line
a, C = 1.5×10-4 mol L-1) and 2 (line b, C = 2.1×10-4 mol L-1) and diffuse
reflectance spectra (inset) of 1 (line a) and 2 (line b) in KBr.
Spectroscopic analyses
EPR spectroscopy was used to give some insight on this
issue. X-band spectra of complexes 1 and 2 were collected
in frozen ethanol solutions at 77 K. Using the WINEPR
SimFonia51 program, the experimental data were simulated;
both experimental and simulated spectra are presented
in Figure 4. The following parameters were determined:
g⊥ = 2.068, g// = 2.268,A⊥ = 20×10-4 cm-1,A// = 175×10-4 cm-1
and g// / A// = 129 cm (for complex 1), and g⊥ = 2.0590,
g// = 2.261, A⊥ = 20×10-4 cm-1, A// = 182×10-4 cm-1 and
g///A// = 125 cm (for complex 2). The frozen solution spectra
of both complexes (Figure 4) are typically axial, presenting
four well-defined lines around g = 2, with g// > g⊥ > 2.0
andA// > A⊥. These features are characteristic of elongated
octahedral, square-pyramidal or square-planar geometries,52
and have been observed for other binuclear CuII complexes
with two phenoxide bridges.46,53 The empirical g// / A// ratio
can be employed to estimate the geometry distortion around
CuII centers, and values in the range of 105 to 135 cm are
attributed to square-planar or octahedral (with tetragonal
distortion) geometries.54,55 Considering the electronic
spectroscopy data and the values observed for complexes 1
(g// /A// = 129 cm) and 2 (g// /A// = 125 cm), it is possible to
infer that both complexes present interactions with solvent
molecules in the axial positions. Additionally, the g// / A//
ratio also provides evidence on the degree of covalency
The electronic spectra of complexes 1 and 2 were
recorded in the solid state and acetonitrile solutions
(Figure 3). In both cases, the two complexes present the
same electronic features, indicating that their structures are
maintained in solution. In acetonitrile, the spectra of both
complexes are quite similar and show bands at 635 nm
(e = 212 L mol-1 cm-1) and 398 nm (e = 3,340 L mol-1 cm-1)
for complex 1, and at 640 nm (e = 280 L mol-1 cm-1) and
408 nm (e = 2,620 L mol-1 cm-1) for complex 2. The low
molar extinction coefficients presented by the lower energy
bands classify them as typical ligand field transitions in the
CuII centers.47 The higher energy bands can be assigned
to ligand-to-metal charge transfer transitions (LMCT)
from the phenoxo bridges to the CuII ions, as proposed
for other phenolate-coordinated CuII complexes.24,40,46,48
A slight batochromic shift is observed for complex 2
when compared to complex 1. As observed before for
cobalt(III) complexes with these same ligands,49 this shift
is a consequence of substitution of an imidazole by a
pyridine ring in the ligand scaffold. In fact, we have also
observed this behavior in other systems and assigned it to
the greater basicity of 1-methylimidazole group compared
to pyridine.49,50 Finally, electronic spectroscopy has been
used to infer the geometry adopted by CuII complexes in

1224
Binuclear CuII Complexes as Catalysts for Hydrocarbon and Catechol Oxidation
J. Braz. Chem. Soc.
in the metal-ligand bond.21,55 Addison and Sakaguchi55
reported that the replacement of “hard” by “soft” donor
atoms around CuII centers results in a decrease of g//, and
consequently a decrease in the g// / A// ratio. This fact is
interpreted as an increase in the electron delocalization
away from the metal center, or an increase in covalency.
For complexes 1 and 2, the g// values are very similar, but an
increase in A// is observed when the softer base imidazole
(complex 1) is replaced by pyridine (complex 2), which
results in the decrease of the g// /A// ratio. This fact suggests
a slight increase of the ligand field strength around the metal
center for complex 2 compared to complex 1. In fact, as
imidazole is a better s-donor than pyridine,19-21,23,56 it was
expected that HL1 presented higher ligand field strength
than HL2, which is exactly the opposite behavior of the
observed here.
to complex 1 suggests that HL2 acts as a better electron
donor than HL1, despite the expected behavior based on
the s-donor ability of imidazole and pyridine groups.
As reported before,49 it is probably related to the LUMO
features of these complexes.
When cyclic voltammograms of complex 2 are recorded
at higher scan rates (125 to 250 mV s-1), an enhancement
of the system reversibility is observed (125 mV s-1:
E1/2 = –332 mV vs. NHE, DEp = 125 mV; 200 mV s-1:
E1/2 = –328 mV vs. NHE, DEp = 135 mV; 250 mV s-1:
E1/2 = –323 mV vs. NHE, DEp = 155 mV). This behavior
suggests that, at least on the time scale of the measurements,
the complex scaffold is maintained after reduction, and so a
quasi-reversible process is detected. This fact can tentatively
be rationalized in terms of the better p-acceptor properties
of the pyridine ring which, by withdrawing electron density
from the metal center after reduction, stabilizes the CuICuI
species under the time scale of the experiments.
Potentiometric titration
In order to examine the pKa of water molecules
coordinated to the metal centers, potentiometric studies
Figure 4. X-band experimental (——) and simulated (........) EPR spectra
for complexes 1 (black) and 2 (blue/gray), in frozen ethanol solutions
at 77 K.
Cyclic voltammetry studies
The cyclic voltammograms for complex 1 in acetonitrile
solution (Figure S1) do not undergo significant variation
upon several scan rate measurements, presenting a broad
irreversible peak at -315 mV vs. NHE (normal hydrogen
electrode). Considering that the coordination environments
around the CuII ions are identical, their reduction is expected
to occur at very similar potentials, which can explain the
broadening of the peak and allow us to consider it as a
CuIICuII → CuICuI process.20 This irreversibility indicates
that HL1 might not be able to stabilize the reduced complex
state leading it to break down (EC process). In contrast,
complex 2 presents a redox activity dependent on the scan
rate. As shown in Figure 5, from 50 and 100 mV s-1, an
irreversible wave is observed at –340 mV vs. NHE that is
also tentatively attributed to the CuIICuII → CuICuI process.
The more negative value observed for complex 2 compared
Figure 5. Cyclic voltammograms of complex 2 in methanol at different
scan rates.

Vol. 21, No. 7, 2010
Martins et al.
1225
were performed in acetonitrile/water mixture (1:1 v/v).
As can be seen in Figure 6, two pKa values were observed
for both complexes: for complex 1, pKa1 = 10.32 and
pKa2 = 11.36, and for complex 2, pKa1 = 10.25 and
pKa2 = 11.27.
Theoretical calculations
As mentioned earlier, the EPR and the voltammetric
data obtained for complexes 1 and 2 present an inverse
behavior of that expected considering only the substitution
of a pyridine by an imidazole group in the ligand scaffold.
As previously reported,49 this might be correlated to the
features of the complexes frontier orbitals. Since the crystal
structure of complex 1 revealed that the chloride anions
and the water molecules are only interacting with the metal
center, the geometry optimizations were carried out without
them.As shown in Table 2, a good agreement was achieved
between the experimental (X-ray) and the theoretical results
for complex 1 and, then, the same approach was used to
predict the geometry of complex 2. Figures 7 and 8 show
the optimized geometries and the graphical representations
of the frontier orbitals for complexes 1 and 2, respectively.
For complex 1, the HOMO (highest occupied molecular
orbital) representation shows a small participation of
the nitrogen atoms of the secondary amine and a strong
contribution of both phenolate bridges. On the other hand,
the LUMO has the participation of the nitrogen atoms of the
secondary amine and the imidazole, the phenolate groups
and the dx orbital of the Cu center. For complex 2, the
-
2
2
y
HOMO presents high similarity with that of complex 1, and
shows a small participation of the amine nitrogen atoms
and a large participation of the phenolate groups. However,
the LUMO of complex 2 has strong contribution of the
two pyridine rings. As the HOMO of both complexes are
quite similar, the behavior observed for complexes 1 and 2
might be related to the different atomic contributions to the
LUMO. While the LUMO of complex 1 is composed by
the contribution of several atoms and is delocalized all over
Figure 6. Diagram of species distribution for complexes 1 (up) and 2
(down).
Comparison of these results with those reported for
other copper complexes in which the water molecules are
considered completely coordinated to the metal center
(pKa ca. 8),19,36,40 reveals that these pKa values are much
higher. This fact can be tentatively explained by the
existence of a weak metal-water interaction, as observed
in the crystal structure of complex 1, in which the water
molecule is 2.899 Å away from the Cu(02) center. In fact,
a strong Jahn-Teller effect associated with the donating
ability of the phenolate groups may weaken the Cu–Ow
bond, not permitting a significant polarization on the O–H
bond of the closest water molecule and raising its pKa. It is
worth to mention that the phenolate protonation constants
could not be determined, probably because these groups
are coordinated in a bridge mode and have very low pKa.
Figure 7. (a) Geometry optimization, (b) HOMO and (c) LUMO for
complex 1.
Figure 8. (a) Geometry optimization, (b) HOMO and (c) LUMO for
complex 2.

1226
Binuclear CuII Complexes as Catalysts for Hydrocarbon and Catechol Oxidation
J. Braz. Chem. Soc.
the molecule, in complex 2 it has mainly the involvement
of the pyridine rings and is localized over these groups.
This fact can explain the more negative potential observed
for complex 2 compared to complex 1, since the increase
of electron density due to the reduction process might be
more easily transferred to the LUMO of complex 1 than
to the LUMO of complex 2.
Reactivity
Cyclohexane oxidation
Since our intention is to develop new catalysts for
oxidative processes, and alkane oxidations have great
industrial interest,58,59 the cyclohexane oxidation was
investigated using hydrogen peroxide at room temperature.
Complexes 1 and 2 lead to low overall conversion values
of 6.34 and 7.15%, respectively. For complex 1, only
cyclohexanol (Cy–OH) and cyclohexanone (Cy=O)
were isolated as reaction products, with selectivities of
68.1% for Cy–OH and 31.9% for Cy=O, and turnover
number of 70. For complex 2, the formation of 31.9%
of Cy–OH, 29% of Cy=O and 32% of Cy–OOH
(cyclohexylhydroperoxide) was observed, and turnover
number of 78. Comparing these values with other CuII
complexes presenting vacant positions on the metal
coordination sphere, the overall yields are fairly lower.60,61
This fact may be explained by the non-coplanarity of the
central square-plane core and the ligand aromatic rings,
which can make difficult the substrate approach, even
though both complexes (1 and 2) present two vacant
positions per CuII center.
Figure 9. pH dependence for the oxidation of 3,5-dtbc catalyzed
by complex 1, in methanol/water (30:1 v/v) solution. Experimental
conditions: [1]final 2.4×10-5 mol L-1, [3,5-dtbc]final 5×10-3 mol L-1,
[buffer]final 3×10-3 mol L-1, at 25 ºC.
for 1 and 8.0 for complex 2, which are the kinetic pKa.
The difference between these values and those obtained
by potentiometric titration can be explained by the
fact that the kinetic pKa represents the water molecules
deprotonation in the presence of substrate. In addition,
the potentiometric pKa was determined in CH3CN/H2O
(1:1 v/v) solution and the reactivity experiments were
carried out in methanol. Based on the pKa values, the
active species for 1 and 2 can be assigned to the aqua-
hydroxo complex.14,62-64 The substrate dependence was
carried out at pH 9, and a Michaelis-Menten profile was
obtained (Figure 10 for complex 1, and Figure S3 for
complex 2). The parameters obtained by a non-linear fit
are presented in Table 3. The values for complexes 1 and
2 indicate that they are very efficient compared to other
complexes in the literature.35,64,65 The kinetic efficiency
(kcat/KM) shows that complex 2 is approximately 10 times
more active than complex 1. Usually, the catecholase
activity of model complexes is largely attributed to the
Catechol oxidation
The most widely employed substrate to investigate
the catecholase activity of model complexes is 3,5-di-
tert-butylcatechol (3,5-dtbc). It is due to its low redox
potential that facilitates the oxidation to quinone, and
the presence of bulky substituents that prevents further
oxidation reactions.62
…
distance Cu Cu, but other effects such as redox potentials,
The pH dependence of the catecholase activities
promoted by complexes 1 and 2 was investigated in a range
(5.5 to 10) that includes the optimal pH activity range
observed for the enzyme.15 The plots of v0 (initial rate)
vs. pH (Figure 9 for complex 1, and S2 for complex 2)
show sigmoid-shape profiles and reveal pKa values of 9.1
neighboring groups, and the individual coordination spheres
can play important roles.66 For complexes 1 and 2, the
…
Cu Cu distances are very similar (Table 2) and may not
be the reason for their different activities. Since the first
step in the proposed mechanism is the oxidation of one
substrate molecule coupled to a two-electron reduction of
Table 3. Kinetic parameters for complexes 1 and 2
Complex
Kcat/KM (mol L-1 s-1)
Vmax (mol L-1 s-1)
1.84×10-6
KM (mol-1L)
7.72×10-3
0.86×10-3
Kcat (s-1)
7.69×10-2
7.85×10-2
Kass
129
1
2
10
92
1.88×10-6
1162

Vol. 21, No. 7, 2010
Martins et al.
1227
Supplementary Information
Crystallographic data have been deposited with the
CambridgeCrystallographicDataCentre(depositionnumber
CCDC 749493). Copies of the data can be obtained, free
of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html,
or by request to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax 44-1223-336033 or e-mail: deposit@ccdc.
cam.ac.uk). Tables with torsion angles and hydrogen bond
distances for complex 1, Tables S1 and S4, and Figures S1
to S3 are presented as supplementary information, available
free of charge at http://jbcs.sbq.org.br, as PDF file.
Acknowledgments
Figure 10. Dependence of the reaction rates on the 3,5-dtbc concentration
for the oxidation reaction catalyzed by complex 1, in methanol/water (30:1
v/v) mixture solution. Experimental conditions: [1]final 2.4×10-5 mol L-1,
[3,5- dtbc]final 1.6-5.0×10-3 mol L-1, [buffer]final 3×10-3 mol L-1, pH 9 (CHES
buffer), at 25 ºC.
Authors are grateful for the facilities of the LDRX
Laboratory (Laboratório de Difração de Raios X at UFF),
LABEPR (Laboratório Regional Sul de EPR at UFPR),
Prof. Octavio A. C. Antunes (in memorian), and grants
from CAPES, CNPq and FAPERJ.
the active site,67 it was expected that complex 1 presented
higher activity than complex 2, which has a more negative
reduction potential, but this kind of correlation has been
questioned.66
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53. Kruse, T.; Weyhermüller, T.; Wieghardt, K.; Inorg. Chim. Acta
2002, 331, 81.
54. Silva, L. A.; Andrade, J. B.; Mangrich, A. S.; J. Braz. Chem.
Soc. 2007, 18, 607.
61. Canhota, F. P.; Salomão, G. C.; Carvalho, N. M. F.; Antunes,
O. A. C.; Catal. Comm. 2008, 9, 182 and references therein.
62. Rompel, A.; Fischer, H.; Meiwes, D.; Buldt-Karentzopoulos,
K.; Magrini, A.; Eicken, C.; Gerdemann, C.; Krebs, B.; FEBS
Lett. 1999, 103, 445.
55. Sakaguchi, U.; Addison, A. W.; J. Chem. Soc., Dalton Trans.
1979, 600.
56. Scarpellini, M.; Toledo Júnior, J. C.; Neves, A.; Ellena, J.;
Castellano, E. E.; Franco, D. W.; Inorg. Chim. Acta 2004, 357,
707.
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35, 183.
57. Greatti, A.; Scarpellini, M.; Peralta, R. A.; Casellato, A.;
Bortoluzzi, A. J.; Xavier, F. R.; Jovito, R.; Brito, M. A.;
Szpoganicz, B.; Tomkowicz, Z.; Rams, M.; Haase, W.; Neves,
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Inorg. Chem. 2007, 46, 348.
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Received: October 1, 2009
Web Release Date: March 15, 2010

J. Braz. Chem. Soc., Vol. 21, No. 7, S1-S5, 2010.
Printed in Brazil - ©2010 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Binuclear CuII Complexes as Catalysts for Hydrocarbon and Catechol Oxidation
Reactions with Hydrogen Peroxide and Molecular Oxygen
Luciana R. Martins,a Elizabeth T. Souza,a Tatiana L. Fernandez,a Bernardo de Souza,b
Sílvio Rachinski,c Carlos B. Pinheiro,d Roberto B. Faria,a Annelise Casellato,a
Sérgio P. Machado,a Antonio S. Mangrich*,c and Marciela Scarpellini*,a
aDepartamento de Química Inorgânica, Instituto de Química, Universidade Federal do Rio de Janeiro,
21945-970 Rio de Janeiro - RJ, Brazil
bDepartamento de Química, Universidade Federal de Santa Catarina, 88040-900 Florianópolis - SC, Brazil
cDepartamento de Química, Universidade Federal do Paraná, 81531-970 Curitiba - PR, Brazil
dDepartamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais,
31270-901 Belo Horizonte - MG, Brazil
Table S1. Experimental and theoretical infrared data (cm-1) for HL1, HL2 and complexes 1 and 2
HL1
HL2
Complex 1
Complex 2
Attribution
n(NH)im
n(CH)Ar
n(NH)sec
n(C=N)
n(C=C)
d(O-H)ph
n(C-O)
Exp.
3313
-
Theor.
3647
-
Exp.
-
Theor.
-
Exp.
-
Theor.
Exp.
-
Theor.
-
3072-2941
3240
1610
1423
-
-
3071-2958
3297
1613
1416
-
2928-2638
3288
1715
1592-1458
1366
1258
755
3219-2977
3484
1669
1554
1378
1297
763
3134-3037
2909
3072-2941
3240
1610
1423
-
3124
1597
1574-1459
1398
1277
748
3498
1539
1555
1381
1295
761
1596
1596-1454
-
1275
1259
775
1259
775
1259
785
d(CH)Ar
n(Cl-O)
771
-
-
-
-
1130-1028
-
-
-
*e-mail: mangrich@quimica.ufpr.br, marciela@iq.ufrj.br

S2
Binuclear CuII Complexes as Catalysts for Hydrocarbon and Catechol Oxidation
J. Braz. Chem. Soc.
Table S2. Torsion angles (°) for complex 1
N(10)-Cu(1)-Cu(2)-N(12)
O(6)-Cu(1)-Cu(2)-N(12)
O(5)-Cu(1)-Cu(2)-N(12)
N(9)-Cu(1)-Cu(2)-N(12)
Cl(3)-Cu(1)-Cu(2)-N(12)
N(10)-Cu(1)-Cu(2)-O(5)
O(6)-Cu(1)-Cu(2)-O(5)
N(9)-Cu(1)-Cu(2)-O(5)
Cl(3)-Cu(1)-Cu(2)-O(5)
N(10)-Cu(1)-Cu(2)-O(6)
O(5)-Cu(1)-Cu(2)-O(6)
N(9)-Cu(1)-Cu(2)-O(6)
Cl(3)-Cu(1)-Cu(2)-O(6)
N(10)-Cu(1)-Cu(2)-N(7)
O(6)-Cu(1)-Cu(2)-N(7)
O(5)-Cu(1)-Cu(2)-N(7)
N(9)-Cu(1)-Cu(2)-N(7)
Cl(3)-Cu(1)-Cu(2)-N(7)
N(12)-Cu(2)-O(5)-C(15)
O(6)-Cu(2)-O(5)-C(15)
N(7)-Cu(2)-O(5)-C(15)
Cu(1)-Cu(2)-O(5)-C(15)
N(12)-Cu(2)-O(5)-Cu(1)
O(6)-Cu(2)-O(5)-Cu(1)
N(7)-Cu(2)-O(5)-Cu(1)
N(10)-Cu(1)-O(5)-C(15)
O(6)-Cu(1)-O(5)-C(15)
N(9)-Cu(1)-O(5)-C(15)
Cl(3)-Cu(1)-O(5)-C(15)
Cu(2)-Cu(1)-O(5)-C(15)
N(10)-Cu(1)-O(5)-Cu(2)
O(6)-Cu(1)-O(5)-Cu(2)
N(9)-Cu(1)-O(5)-Cu(2)
Cl(3)-Cu(1)-O(5)-Cu(2)
N(10)-Cu(1)-O(6)-C(27)
O(5)-Cu(1)-O(6)-C(27)
N(9)-Cu(1)-O(6)-C(27)
102.0(2)
-44.7(3)
159.4(3)
-25.5(3)
-123.59(19)
-57.3(3)
156.0(3)
175.1(3)
77.0(2)
Cl(3)-Cu(1)-O(6)-C(27)
Cu(2)-Cu(1)-O(6)-C(27)
N(10)-Cu(1)-O(6)-Cu(2)
O(5)-Cu(1)-O(6)-Cu(2)
N(9)-Cu(1)-O(6)-Cu(2)
Cl(3)-Cu(1)-O(6)-Cu(2)
N(12)-Cu(2)-O(6)-C(27)
O(5)-Cu(2)-O(6)-C(27)
Cu(1)-Cu(2)-O(6)-C(27)
N(12)-Cu(2)-O(6)-Cu(1)
O(5)-Cu(2)-O(6)-Cu(1)
N(12)-Cu(2)-N(7)-C(20)
O(5)-Cu(2)-N(7)-C(20)
Cu(1)-Cu(2)-N(7)-C(20)
N(12)-Cu(2)-N(7)-C(25)
O(5)-Cu(2)-N(7)-C(25)
Cu(1)-Cu(2)-N(7)-C(25)
N(10)-Cu(1)-N(9)-C(29)
O(6)-Cu(1)-N(9)-C(29)
O(5)-Cu(1)-N(9)-C(29)
Cl(3)-Cu(1)-N(9)-C(29)
Cu(2)-Cu(1)-N(9)-C(29)
N(10)-Cu(1)-N(9)-C(17)
O(6)-Cu(1)-N(9)-C(17)
O(5)-Cu(1)-N(9)-C(17)
Cl(3)-Cu(1)-N(9)-C(17)
Cu(2)-Cu(1)-N(9)-C(17)
O(6)-Cu(1)-N(10)-C(19)
O(5)-Cu(1)-N(10)-C(19)
N(9)-Cu(1)-N(10)-C(19)
Cl(3)-Cu(1)-N(10)-C(19)
Cu(2)-Cu(1)-N(10)-C(19)
O(6)-Cu(1)-N(10)-C(30)
O(5)-Cu(1)-N(10)-C(30)
N(9)-Cu(1)-N(10)-C(30)
Cl(3)-Cu(1)-N(10)-C(30)
Cu(2)-Cu(1)-N(10)-C(30)
-46.6(5)
-161.1(6)
-61.4(4)
15.3(2)
-165.6(2)
114.57(18)
-57.3(6)
143.0(6)
158.6(7)
144.1(2)
-15.6(2)
-139.0(5)
21.7(5)
146.7(3)
-156.0(3)
19.2(3)
-78.9(2)
-44.3(3)
169.0(3)
13.0(3)
13.3(6)
-8.3(5)
152.4(4)
144.0(4)
-1.3(5)
-171.9(3)
90.0(2)
138.5(6)
-155.1(5)
18.8(5)
146.2(5)
150.7(10)
-111.6(5)
134.1(4)
-132.9(5)
14.5(5)
-170.5(6)
-50.9(6)
15.5(2)
-170.6(2)
-57.8(5)
154.7(5)
150.2(10)
54.5(5)
19.0(14)
116.7(5)
2.4(5)
45.5(7)
-26.2(5)
148.8(5)
-130.3(5)
5.9(6)
170.3(6)
131.9(2)
-15.6(2)
-20.1(13)
-115.75(17)
137.4(5)
-145.9(5)
33.3(5)
-119.2(5)
169.1(5)
-16.0(5)
65.0(5)
-158.8(4)

Vol. 21, No. 7, 2010
Martins et al.
S3
Table S2. Cont.
O(5)-Cu(2)-N(12)-C(16)
O(6)-Cu(2)-N(12)-C(16)
N(7)-Cu(2)-N(12)-C(16)
Cu(1)-Cu(2)-N(12)-C(16)
O(5)-Cu(2)-N(12)-C(13)
O(6)-Cu(2)-N(12)-C(13)
N(7)-Cu(2)-N(12)-C(13)
Cu(1)-Cu(2)-N(12)-C(13)
C(16)-N(12)-C(13)-C(28)
Cu(2)-N(12)-C(13)-C(28)
C(16)-N(12)-C(13)-C(23)
Cu(2)-N(12)-C(13)-C(23)
C(22)-C(11)-C(15)-O(5)
C(22)-C(11)-C(15)-C(21)
Cu(2)-O(5)-C(15)-C(11)
Cu(1)-O(5)-C(15)-C(11)
Cu(2)-O(5)-C(15)-C(21)
Cu(1)-O(5)-C(15)-C(21)
C(13)-N(12)-C(16)-N(8)
Cu(2)-N(12)-C(16)-N(8)
C(28)-N(8)-C(16)-N(12)
C(29)-N(9)-C(17)-C(24)
Cu(1)-N(9)-C(17)-C(24)
C(30)-N(10)-C(19)-N(14)
Cu(1)-N(10)-C(19)-N(14)
C(31)-N(14)-C(19)-N(10)
C(25)-N(7)-C(20)-C(21)
Cu(2)-N(7)-C(20)-C(21)
C(11)-C(15)-C(21)-C(34)
O(5)-C(15)-C(21)-C(34)
C(11)-C(15)-C(21)-C(20)
O(5)-C(15)-C(21)-C(20)
N(7)-C(20)-C(21)-C(34)
N(7)-C(20)-C(21)-C(15)
C(15)-C(11)-C(22)-C(32)
C(28)-C(13)-C(23)-C(25)
N(12)-C(13)-C(23)-C(25)
N(9)-C(17)-C(24)-C(27)
34.1(8)
-29.6(5)
153.4(5)
-2.8(6)
N(9)-C(17)-C(24)-C(36)
-123.6(7)
179.9(5)
47.7(7)
C(20)-N(7)-C(25)-C(23)
Cu(2)-N(7)-C(25)-C(23)
C(13)-C(23)-C(25)-N(7)
Cu(1)-O(6)-C(27)-C(18)
Cu(2)-O(6)-C(27)-C(18)
Cu(1)-O(6)-C(27)-C(24)
Cu(2)-O(6)-C(27)-C(24)
C(33)-C(18)-C(27)-O(6)
C(33)-C(18)-C(27)-C(24)
C(36)-C(24)-C(27)-O(6)
C(17)-C(24)-C(27)-O(6)
C(36)-C(24)-C(27)-C(18)
C(17)-C(24)-C(27)-C(18)
C(16)-N(8)-C(28)-C(13)
N(12)-C(13)-C(28)-N(8)
C(23)-C(13)-C(28)-N(8)
C(17)-N(9)-C(29)-C(26)
Cu(1)-N(9)-C(29)-C(26)
C(30)-C(26)-C(29)-N(9)
C(19)-N(10)-C(30)-C(31)
Cu(1)-N(10)-C(30)-C(31)
C(19)-N(10)-C(30)-C(26)
Cu(1)-N(10)-C(30)-C(26)
C(29)-C(26)-C(30)-C(31)
C(29)-C(26)-C(30)-N(10)
N(10)-C(30)-C(31)-N(14)
C(26)-C(30)-C(31)-N(14)
C(19)-N(14)-C(31)-C(30)
C(11)-C(22)-C(32)-C(34)
C(27)-C(18)-C(33)-C(35)
C(22)-C(32)-C(34)-C(21)
C(15)-C(21)-C(34)-C(32)
C(20)-C(21)-C(34)-C(32)
C(18)-C(33)-C(35)-C(36)
C(33)-C(35)-C(36)-C(24)
C(27)-C(24)-C(36)-C(35)
C(17)-C(24)-C(36)-C(35)
-73.2(7)
137.1(5)
-17.3(9)
-41.8(8)
163.8(5)
-178.6(6)
0.3(10)
-130.9(6)
165.3(5)
-11.7(5)
-167.9(4)
0.4(7)
167.9(4)
-176.5(5)
-9.0(8)
176.0(6)
-5.6(9)
-178.4(6)
2.2(9)
-3.0(9)
175.4(6)
0.5(7)
152.7(5)
-15.1(8)
-27.8(8)
164.4(4)
-0.1(7)
-0.6(7)
175.9(6)
175.3(6)
41.3(7)
-167.4(4)
-0.2(7)
-72.5(7)
-0.1(7)
167.6(6)
-55.7(7)
0.1(7)
167.3(4)
-177.0(6)
-9.6(8)
-166.8(4)
-0.1(7)
-119.2(8)
56.8(8)
170.3(6)
-55.6(7)
-4.1(9)
0.0(7)
176.4(7)
0.0(7)
176.4(5)
171.5(6)
-7.9(9)
-2.1(10)
2.2(11)
0.1(10)
-131.1(6)
53.3(9)
3.0(10)
-172.8(6)
-2.0(11)
-0.7(12)
3.2(10)
1.0(10)
-123.8(7)
52.3(8)
58.1(8)
-175.2(7)

S4
Binuclear CuII Complexes as Catalysts for Hydrocarbon and Catechol Oxidation
J. Braz. Chem. Soc.
Table S3. Hydrogen bond distances and angles for complex 1 (Å and °)
Table S4. Experimental (X-ray diffraction data for HL123) and calculated
(DFT) main bond distances (Å) and angles (o) for HL1 and HL2
…
… …
d(D-H) d(H A) d(D A) <(DHA)
D-H
A
HL1
Exp.
Calc.
1.465
1.468
1.365
1.382
1.385
1.315
HL2
Calc.
1.462
1.458
1.396
1.395
1.344
1.338
…
N(8)-H(8) Cl(3)#1
0.86
0.86
2.29
2.24
3.149(5)
3.089(6)
173.9
172.2
N(8)-C(9)
1.70(3)
N(8)-C(9)
…
N(14)-H(14) Cl(4)#2
N(8)-C(7)
1.476(3)
1.331(3)
1.359(3)
1.363(3)
1.326(3)
N(8)-C(7)
Symmetry transformations used to generate equivalent atoms: #1 :
x-1/2,y+1/2,z ; #2 : x-1/2,-y+3/2,z-1/2.
N(14)-C(13)
N(14)-C(15)
N(12)-C(11)
N(12)-C(13)
C(9)-N(8)-C(7)
C(14)-C(13)
C(14)-C(15)
N(12)-C(11)
N(12)-C(13)
113.34(19) 114.55 C(9)-N(8)-C(7) 115.53
C(13)-N(14)-C(15) 107.31(18) 107.21 C(13)-C(14)-C(15) 117.95
C(13)-N(12)-C(11) 105.61(19) 105.72 C(13)-N(12)-C(11) 118.09
Figure S1. Cyclic voltammograms registered for complex 1 in methanol at different scan rates.

Vol. 21, No. 7, 2010
Martins et al.
S5
Figure S2. pH dependence for the oxidation of 3,5-dtbc catalyzed by complex 2, in methanol/water (30:1 v/v) solution. Experimental conditions: [2]final
2.4 × 10-5 mol L-1; [3,5-dtbc]final = 5 × 10-3 mol L-1; [buffer]final = 3 × 10-3 mol L-1; 25 ºC.
=
Figure S3. Dependence of the reaction rates on the 3,5-dtbc concentration for the oxidation reaction catalyzed by complex 2, in methanol/water (30:1 v/v)
solution. Experimental conditions: [2]final = 2.4 × 10-5 mol L-1; [3,5-dtbc]final = 2.33-5.0 × 10-3 mol L-1; [buffer]final = 3 × 10-3 mol L-1; pH 9 (CHES buffer); 25 ºC.