Copper(II) complex of new non-innocent O-aminophenol-based ligand as biomimetic model for galactose oxidase enzyme in aerobic oxidation of alcohols

Article abstract of DOI:10.1016/j.molstruc.2016.11.076

Mononuclear copper(II) complex of tetra-dentate o-aminophenol-based ligand (H₂L^BAPP) has been synthesized and characterized. The three dentate precursor (HL^BAP) of the final ligand was synthesized first, while the title four-dentate copper bound ligand was synthesized in situ, isolated only in the final copper species [CuL^BAPP]. This copper coordination complex reveals a distorted square-planar geometry around the copper(II) centre by one oxygen and three nitrogen atoms from the coordinating ligand. The ligand is thus twice deprotonated via hydroxy and amine groups. The complex is red, non-typical for copper(II), but the effective magnetic moment of 1.86 B?M. and a single isotropic symmetry EPR signal with g 2.059 confirm a S?=?1/2 diluted spin system, without copper-copper magnetic coupling. Electrochemical oxidation of this complex yields the corresponding Cu(II)–phenyl radical species. Finally, the title complex CuL^BAPP has shown good and selective catalytic activity towards alcohol to aldehyde oxidation, at aerobic room temperature conditions, for a set of different alcohols.

Full text of DOI:10.1016/j.molstruc.2016.11.076

Accepted Manuscript
Copper(II) complex of new non-innocent O-aminophenol-based ligand as biomimetic
model for galactose oxidase enzyme in aerobic oxidation of alcohols
Elham Safaei, Hadiseh Bahrami, Andrej Pevec, Bojan Kozlevčar, Zvonko Jagličić
PII:
S0022-2860(16)31263-7
10.1016/j.molstruc.2016.11.076
MOLSTR 23177
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 2 October 2016
Revised Date: 24 November 2016
Accepted Date: 25 November 2016
Please cite this article as: E. Safaei, H. Bahrami, A. Pevec, B. Kozlevčar, Z. Jagličić, Copper(II)
complex of new non-innocent O-aminophenol-based ligand as biomimetic model for galactose
oxidase enzyme in aerobic oxidation of alcohols, Journal of Molecular Structure (2016), doi: 10.1016/
j.molstruc.2016.11.076.
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ACCEPTED MANUSCRIPT
Copper(II) Complex of New Non-innocent 0-aminophenol-based Ligand as Biomimetic
Model for Galactose oxidase Enzyme in Aerobic Oxidation of Alcohols
3
Synthesis and characterization of copper complex of N O 0-aminophenol based ligand as
model for galactose oxidase in aerobic oxidation of alcohols have been investigated.

ACCEPTED MANUSCRIPT
Copper(II) Complex of New Non-innocent O-aminophenol-based Ligand as
Biomimetic Model for Galactose oxidase Enzyme in Aerobic Oxidation of Alcohols
a
b
c
c
d, e
Elham Safaei* , Hadiseh Bahrami
,
Andrej Pevec , Bojan Kozlevčar , Zvonko Jagličić
b
Department of Chemistry, College of Sciences, Shiraz University, Shiraz, 71454, Iran
Institute for Advanced Studies in Basic Sciences (IASBS), 45137-66731, Zanjan, Iran
Faculty of Chemistry and Chemical Technology, University of Ljubljana,Večna pot 113, SI-1000
a
c
Ljubljana, Slovenia
d
Institute of Mathematics, Physics and Mechanics, Jadranska c. 19. SI-1000, Ljubljana, Slovenia
e
Faculty of Civil and Geodetic Engineering, Jamova c. 2. SI-1000, Ljubljana, Slovenia
Correspondence to: Elham Safaei
E-mail:e.safaei@shirazu.ac.ir
Abstract
BAPP
Mononuclear copper(II) complex of tetra-dentate o-aminophenol-based ligand (H2L
) has
BAP
been synthesized and characterized. The three dentate precursor (HL ) of the final ligand
was synthesized first, while the title four-dentate copper bound ligand was synthesized in
BAPP
situ, isolated only in the final copper species [CuL
]. This copper coordination complex
reveals a distorted square-planar geometry around the copper(II) center by one oxygen and
three nitrogen atoms from the coordinating ligand. The ligand is thus twice deprotonated via
hydroxy and amine groups. The complex is red, non-typical for copper(II), but the effective
magnetic moment of 1.86 B.M. and a single isotropic symmetry EPR signal with g 2.059
confirm a S =1/2 diluted spin system, without copper-copper magnetic coupling.
Electrochemical oxidation of this complex yields the corresponding Cu(II)–phenoyl radical
BAPP
species. Finally, the title complex CuL
has shown good and selective catalytic activity
towards alcohol to aldehyde oxidation, at aerobic room temperature conditions, for a set of
different alcohols.
Keywords: Galactose oxidase; Biomimetic copper complexes; Phenoxyl radical; Alcohol
oxidation.
1

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1
. Introduction
Galactose oxidase (GO) is an important example of oxidoreductase enzymes that catalyze
oxidation of D-galactose with simultaneous reduction of molecular oxygen to water or hydrogen
peroxide. Within the active site of this enzyme, the synergistic action between copper and
phenoxyl radical of cysteine-modified Tyrosine 272 residue has a critical role in the
catalytic cycle (Scheme 1) [1-4].
Scheme 1.Galactose oxidase (GO)active site [5]
It has been shown that GO passes three important oxidation levels, including metal
radical species, during the catalytic cycle (Schemes 2, 3) [5-9].
Scheme 2. Proposed mechanism for alcohol catalysis to aldehyde and
hydrogen peroxide byGO [4].
2

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Scheme 3: Redox states of phenolate/copper in GO active site [7]
•
The discovery of the mentioned unusual biological entities, namely M…R such as copper
-
phenoxyl radical of Tyrosine 272 residue , in the active site of GO and similar species in
other enzymes such as cytochrome P , has encouraged scientists to mimic the oxidative
4
50
chemistry of complexs involving o-aminophenolates [10-14]. The involved ligands are
known as a class of redox-active, ‘non-innocent’ ligands, the later term being focused
onto metal-ligand coordination via different oxidation states (Scheme 4) [15-17]. O-
aminophenols are one of the most common classes of redox active ligands. They can be
bound to the transition metal ion with three oxidation forms, either as an o-
aminophenolate dianion, o-iminobenzosemiquinonate π radical monoanion and neutral
iminoquinonate ligand.
N
N
O
N
-
e
e
-e
CuII
CuII
CuII
+
+e
O
O
aminophenole
iminosemiquinone
iminoquinone
Scheme 4: Redox state of redox active ligands [17]
3

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Copper complexes based on ‘non-innocent’ catecholate and semiquinones ligands have also
been identified as GO-like reactive [17-20]. The oxidation of alcohols to aldehydes is one of
the considerably interest reactions in organic chemistry [21-23]. A ligand–assisted Cu
catalytic system containing copper employing pyridine or bipyridine ligands [24] was
reported to catalyze the selective aerobic oxidation of alcohols to aldehydes. The catalytic
oxidation of alcohols to aldehydes, based on the isolated Cu complexes, has been also
reported by several groups [25-32].
In this work, we reveal a design of a mononuclear copper complex with in situ prepared ‘non-
innocent o-aminophenole N O based ligand (Scheme 5). Subsequently, its performance as
3
efficient catalytic system for the aerobic oxidation of benzyl alcohols was investigated.
NH2
OH
tBu
N
tBu
N
N
N
Cu
But
O
tBu
BAP
BAPP
Scheme 5 . Structure of the precursur ligand HL
and copper complex CuL
2
. Experimental
.1. Materials and physical measurements
2
Reagents or analytical grade materials were obtained from commercial suppliers and used
without further purification, except those for electrochemical measurements. Elemental
analyses (C, H, and N) were performed by the Elementar, Vario EL III . Fourier transform
infrared spectroscopy with KBr pellets was performed on a FT IR Bruker Vector 22
instrument. NMR measurements were performed on a Bruker 400 instrument. UV-Vis
absorbance digitized spectra were collected using a CARY 100 spectrophotometer. The
electronic absorption spectra of complexes have been measured in dichloromethane in the
2
00-800 nm range.
4

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BAPP
Crystal data and refinement parameters of complex CuL
are listed in Table 1. The X-ray
diffraction data were collected at room temperature on an Agilent Technologies SuperNova
Dual source diffractometer with an Atlas detector using mirror-monochromatized Mo Kα
radiation (λ = 0.71073 Å). The data were processed using CRYSALIS PRO[33]. The
structures were solved by direct methods implemented in SIR–92 [34] and refined by a full-
2
matrix least-squares procedure based on F using SHELXL–97 [35]. All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms bonded to carbon (except C1 and C8) were
included in the model at geometrically calculated positions and refined using a riding model.
The N–bound hydrogen atoms were located in a difference map and refined with the using
distance restraints (DFIX) with N–H = 0.86 and with Uiso(H) = 1.2U (N). The C1– and C8–
eq
bound hydrogen atoms were located in a difference map and refined with the using distance
restraints (DFIX) with C–H = 0.98 and with Uiso(H) = 1.2U (C).
eq
Table 2
Magnetic susceptibility was measured with powder sample in the temperature range 2-300 K
by using a SQUID magnetometer (Quantum Design MPMS-XL-5) in a magnetic field of
1
000 Oe. EPR spectra were collected using a Bruker EMX plus spectrometer operating with a
premium X X-band (∼9.5 GHz) microwave bridge. Low temperature measurements of frozen
solutions used a Bruker helium temperature-control system and a continuous flow cryostat.
Voltammetric measurements were made by a computer controlled electrochemical system
(ECO Chemie) equipped with a PGSTA 30 model and driven by GPES (ECO Chemie). A
2
glassy carbon electrode, with a surface area of 0.035 cm , was used as a working electrode,
while a platinum wire served as a counter electrode. The reference electrode was a silver wire
as the pseudo reference electrode. Ferrocene was added as an internal standard after
completion of a set of experiments, and potentials are referenced vs. the
+
ferrocenium/ferrocene couple (Fc /Fc).
5

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2
.2. Synthesis
Synthesis of HL
A synthesis of ligand precursor HL
BAP
BAP
(Scheme 6) was already previously described [16, 36].
A solution of 3,5-DTBQ (3,5-di tert butyl quinone; 0.22 g, 1.0 mmol) in acetonitrile (4 mL)
was prepared, to which 2-aminobenzyl amine (0.122 g, 1.0 mmol) was added. The reaction
solution was stirred for 30 min at the room temperature in the presence of air. The yellow
BAP
precipitate of HL
was filtered off and dried in air.
(
0.278 g, 85% yield). Anal. Calcd. for C H N O (324.46 g/mol) C, 77.74; H, 8.70; N,
21 28 2
1
8
9
1
.63%. Found: C, 76.93; H, 8.55; N, 8.48%. H NMR (400 MHz, CDCl , 298 K): δ 1.4(s,
3
H), 1.5(s, 9H), 6.3(s, 2H), 6.7 (s, 1H), 6.8(m, 2H), 7.0 (d, 1H), 7.3(d, 2H), 7.4 (d, 1H), 8.7(s,
-1
H). νmax(KBr)/cm : 3421 (O−H, N−H); 2951(C−H); 1466 (C−H), 1212 (C−O), 1607 (C=N)
BAP
+
6
51(C-H, methylene). ESI-MS m/z (%): 325.5 [MHL +1] .
NH2
O
NH2 NH2
OH
tBu
O
tBu
CH CN (4 ml)
N
tBu
3
+
tBu
BAP
Scheme 6. Synthesis pathway of the precursor ligand H2L
.
BAPP
Synthesis of the complex [CuL
]
Methanol (50 mL) was added to powdered 1 (0.324 g, 1.0 mmol) and proline (0.115 g, 1.0
mmol). After one minute of stirring, Cu (OAc) ⋅(H O) (0.199 g, 1.0 mmol) and of NEt
3
2
2
(0.199 g, 1.0 mmol) were added into the initial reaction mixture, while the color turned to
BAPP
red-brown. After 4 h at 298 K, a red-brown microcrystalline precipitate of CuL
was
filtered off. It was dried under air. (0.351 g, 72% yield). X-ray quality dark red single
crystals were grown from a 1:1 (V:V) dichloromethane/ethanol. Elemental Analysis:
6

ACCEPTED MANUSCRIPT
calculated (found) for C H CuN O (489.1 g/mol): C; 72.34, H; 7.31, N; 8.61, Cu; 10.2;
2
8
31
3
-1
Found: C; 71, H; 7.24, N; 8.57, Cu; 9.7. νmax(KBr)/cm : 2949 (C-H), 1628 (C=N), 1612
+
(
C=N), 1466 (C=C), 808 (=C-H bending). ESI-MS m/z (%): 489.5 [MHL+Cu
]
, 878.5
+
[
M
]
.(Figure 4S).
HL+Cu 2
BAPP
Catalytic activity of [CuL
]
BAPP
In a typical experiment, alcohol (1.0 mmol), [CuL
] (4 mmol%), Cs CO (0.650 g, 2
2
3
mmol) and 5 mL THF (oxygen saturated) were inserted in a 25 mL two-necked round-bottom
flask, equipped with an oxygen balloon. The solution was stirred at room temperature, after
which the mixture was filtered through a plug of silica, and then diluted with THF (2 mL).
The progress of the reaction was monitored by gas chromatography. For a comparison, blank
tests were performed, with the identical flask and amounts of Cs CO , THF (oxygen
2
3
BAPP
saturated) and oxygen balloon. Instead of CuL
, only copper(II) acetate, or precursor
BAP
ligand HL
were used.
3
. Results and Discussion
BAPP
The copper(II) complex CuL
was synthesized by the reaction of the precursor ligand
BAP
HL
with copper acetate in the presence of proline in methanol (Scheme 7). During the
synthesis, several possible reactions seem to appear (Scheme 8), with the final in situ ligand
BAPP
BAPP
H2L
, being found only coordinated in CuL
, where it is in a double deprotonated
BAPP
form. It is worth to note that in the absence of proline, the product CuL
wasn’t isolated
pure, but the insoluble solid mixture precipitated instead, which we were unable to
characterize. Therefore, we decided to add other ligand as capping agent prevent a possible
polymerization process. In addition, in the presence of glycine and tyrosine amino acids the
same product as proline was produced.
Cu(OAc) (1 mmol) , Proline
HLBAP
2
CuLBAPP
1
mmol
CH OH
3
NEt (2 mmol)
3
7

ACCEPTED MANUSCRIPT
BAPP
Scheme 7. The synthesis pathway of copper(II) complex CuL
O
O
Prolin
N
Cu
NH2
N
NH2
N
OH
OH
OH
H
H
2
N
tBu
NH2
H
tBu
H O
2
tBu
O
H
O
tBu
tBu
tBu
HO
N
H
NH2
NH2
OH
O
H
OH
N
tBu
H
H N
N
tBu
+
2
tBu
tBu
H
OH
N
Cu(OAc)2
HN
N
N
Cu
N
O
N
H
BAPP
Scheme 8. The suggested reaction pathway for the synthesis of CuL
and
BAPP
BAP
the in situ ligand H2L
from HL
BAPP
3
.1. The crystal structure description for CuL
BAPP
The complex [CuL
] crystallizes in the monoclinic space group C2/c, with one formulae
within the asymmetric unit (Figure 1). The geometry of the coordination sphere is square-
BAP
planar, with tetradentate o-aminophenol-based ligand HL
binding the central Cu(II)
through one oxygen atom and three nitrogen atoms. A coordination of the asymmetric [N O]
3
ligand to the copper(II) ion generates three chelate rings, two of them composed by six atoms
and the other one by five atoms. The C–C, C–O and C–N distances in the six- and five-
8

ACCEPTED MANUSCRIPT
BAPP
membered rings within the structure of CuL
are in accordance with the distances in the
complex with the similar structural fragment thus indicating delocalization of electron density
over these rings. There is also no evidence for any significant non-covalent interactions.
BAPP
Selected bond lengths and angles for the CuL
are given in Table 2.
Figure 1
Table 2
BAPP
BAPP
In the IR spectrum of CuL
, a deprotonation and coordination of the ligand H2L
phenol and amine groups are in agreement by the replacement of the strong and sharp bands
BAP
BAPP
-1
seen in the spectrum of HL
(precursor ligand to H2L
) around 3300-3500 cm , by a
BAPP
BAPP
broad band found in the spectrum of CuL
. The ν(C = N) band found for CuL
at 1612
-1
BAP
cm is shifted to higher frequencies from 1607 in HL , also indicating the ligand
coordination via the azomethine nitrogen atom .
BAPP
In the UV-Vis spectrum of CuL
, two absorption bands at 508, 409, 340 and 273 nm are
seen. The visible region band is assigned to phenolate (π) -to- Cu(II) (dπ*) charge transfer
LMCT). On the other hand the UV region band is assigned to ligand π→π* transitions of
(
phenolate units (Figure 2) [37].
Figure 2
BAPP
The MS spectrum of CuL
shows an intense ion peak with molecular weight of 489.5
BAP
related to a complex containing copper and a rearranged ligand so as three dentate HL
ligand reacts with 2-amino benzaldehyde species(from hydrolysis of aminobenzyl amine) and
BAPP
produce four dentate H2L
ligand which clearly indicated the formation of 1:1 complex
+
BAPP
[
M
2
+Cu] . X-ray analysis confirms this proof. Another peak placed at 878.5 is related to
H L
a dimeric form of copper complex. The molecular peak of the complex ion is shown in the
BAPP
supplementary materials. The suggested reaction pathway for the synthesis of CuL
has
been shown in Scheme 8. We didn’t observe proline or other above mentioned amino acids in
9

ACCEPTED MANUSCRIPT
the structure of complexes and all synthesized complexes show the same mass spectrum
BAP
pattern. It considers that amino acids play a catalytic rule in hydrolysis of HL
and
BAPP
formation of H2L
.
3
.2. Magnetic susceptibility
BAPP
Temperature variation of measured molar magnetic susceptibility χM(T) for CuL
is
shown in Figure 3. The presented data were corrected for the temperature-independent
Larmor diamagnetic susceptibility obtained from Pascal’s tables [38] and for the sample
BAPP
holder contribution. The susceptibility of CuL
increases with decreasing temperature,
following a Curie 1/ T law, which indicates a paramagnetic behavior (Figure 4). Almost
temperature independent effective magnetic moment of copper complex confirms proposed
paramagnetic property of this mononuclear species. The effective magnetic moment (Figure
3
) at room temperature is around 1.86 BM, being very close to the measured values for the
other diluted copper complexs (reported values in [39] are 1.77–1.83 BM). This is in
agreement with the presence of one unpaired electron and quantum spin number S = ½ in the
-1
copper center of complex. Susceptibility graph χM (T) shows a straight line of slope 1/C
passing through the origin (0 K). Only a small downturn of the effective magnetic moment
below 20 K may indicate a weak antiferromagnetic interaction between the Cu(II) centers.
Figure 3
Figure 4
3
.3. EPR spectroscopy
Frozen solution EPR shows a single isotropic symmetry signal with a g value of 2.059. It is
9
more than the free electron g value (2.0023) attributed to a single-electron copper(II) d
BAPP
configuration. A typical EPR spectrum of CuL
has been shown in Figure 5.
Figure 5
1
0

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3
.4. Electrochemistry
BAPP
Cyclic voltammogram (CV) of CuL
has been recorded by CH Cl solution containing
2 2
0
.1 M [(n-Bu) N]ClO as a supporting electrolyte. It displays two pseudo-reversible anodic
4 4
redox processes at 0.630 and 0.825 V, indicating a ligand-centered oxidation to form
phenoxyl radical species (vide infra). Both oxidation potentials are comparable to the first
II
oxidation potential reported for a large number of Cu -imino-phenolate complexes (~0.45 V
+
vs. Fc /Fc in CH Cl ), that exhibit ligand radical formation [40-44]. The redox process at -
2
2
II
I
1
.25 V could be a Cu /Cu reduction process based on previously reported data [40-44].
BAPP
Cyclic voltammogram (CV) of CuL
, is presented in Figure 6.
Figure 6
BAPP
3
.5. The catalytic activity of CuL
BAPP
To study the application of CuL
for the aerobic oxidation of alcohols to corresponding
aldehydes, benzyl alcohol was chosen as a model complex and the reaction conditions were
optimized accordingly. The initiation time was around half an hour (Fig. 7).
Figure 7
Various organic solvents were used to determine the optimal one. The THF appeared to be
the most favorable for the described transformation (Table 3) and not fluorinated solvents,
which are usually used in such cases [45].
Table 3
BAPP
The catalyst CuL
optimal quantity was 4.0 mmol%, when 4 h were needed for the
complete transformation (Table 4).
Table 4
Additionally, different bases for oxidation of benzyl alcohol were checked, with. 2
equivalents of Cs CO optimally used Cs CO (Table 5).
2
3
2
3
Table 5
1
1

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The ligand-free copper(II) acetate/Cs CO blank test shows an appearance of aldehyde in low
2
3
yield (Scheme 6, Table 6). On the other hand, copper(II) acetate/Cs CO , in the presence of
2
3
BAP
ligand precursor HL , increases the aldehyde yield. This suggests the ligand effect on
increasing alcohol conversion. Comparing these results with the analogous for
BAPP
[
CuL
/Cs CO ], suggests us to include the metal-ligand synergy role into the oxidation of
2 3
BAPP
alcohols. Under optimized reaction conditions (4 mmol % of CuL
, 2 mmol Cs CO THF
2 3,
as solvent), namely, various substituted benzaldehydes were obtained from their
corresponding, alcohols (Table 7).
1
2
. THF (5ml)
. [CuLBAPP] (4 mmol%)
OH
3. Cs
2
CO
3
(2 mmol, 0.65 g)
O
H
R
1
R
R'
4
. RT, Oxygen
R'
mmol
BAPP
Scheme 6. Catalytic activity of CuL
at the aerobic oxidation of alcohols
Table 6
These results also reveal that unsubstituted benzylic alcohols are oxidized more efficiently
than aliphatic alcohols. Further oxidation towards the corresponding acids was not observed
(Scheme 6).
Table 7
4
. Conclusion
BAPP
In summary, a new square-planar copper(II) complex CuL
with the in situ prepared
BAPP
aminophenol-based ligand H2L
was synthesized and characterized. Electrochemical
oxidation of this copper complex yields the corresponding Cu(II)–phenyl radical species. In
addition, highly efficient and eco-friendly oxidation of alcohol to aldehyde was achieved with
BAPP
molecular oxygen as an oxidant and non-expensive catalyst system CuL
/Cs CO . This
2 3
1
2

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system is found to be very efficient for a wide range of benzylic alcohols, enabling high
selectivity under mild reaction conditions (room temperature). Thus, it clearly mimics the
Galactose oxidase natural performance. Unfortunately, the system show weaker activity
against aliphatic primary and secondary alcohols, and copper complex yield should be
reduced as well.
BAPP
Appendix A. The structural data for CuL
have been deposited with the Cambridge
Crystallographic Data Centre, the deposition number being CCDC 1494302
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgments
Authors are grateful to the Institute for Advanced Studies in Basic Sciences (IASBS), Shiraz
and the Slovenian Research Agency (Grant P1-0175) for their valuable help. AP also thank
EN-FIST centre of Excellence, Ljubljana, Slovenia for using SuperNova diffractometer.
1
3

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[
[
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Table 1. Crystal data and structure refinement for CuL
BAPP
formula
C H CuN O
28 31 3
489.10
0.10 x 0.04 x 0.04
red
monoclinic
C2/c
25.9272(9)
6.8885(3)
28.5350(9)
90
-1
Fw (g mol )
crystal size (mm)
crystal color
crystal system
space group
a (Å)
b (Å)
c (Å)
α (º)
β (º)
95.634(3)
90
5071.7(3)
8
1.281
2056
γ (º) 3
V (Å )
Z
-3
Calcd. density (g cm )
F(000)
θ range (º)
2.87 – 27.48
23947
5805
0.0777
3408
313
0.0585
0.1284
1.009
No. of collected reflns.
No. of independent reflns.
Rint
no. of reflns used
no. parameters
a
R[I > 2σ(I)]
b
wR (all data)
2
c
Goof , S
Max./min. residual electron
+0.30/-0.26
1

ACCEPTED MANUSCRIPT
0
BAPP
Table 2. Selected bond lengths [Å] and angles [ ] for CuL
Cu1–O1
Cu1–N1
Cu1–N2
Cu1–N3
N1–C1
N2–C7
N2–C8
N3–C14
C1–C2
1.935(2)
1.940(3)
1.972(3)
1.878(3)
1.280(4)
1.420(4)
1.328(4)
1.324(4)
1.441(5)
1.408(5)
O1–Cu1–N1
O1–Cu1–N2
O1–Cu1–N3
N1–Cu1–N2
N2–Cu1–N3
N1–C1–C2
83.93(10)
173.64(11)
89.74(11)
94.09(11)
93.23(12)
125.9(3)
121.5(3)
126.1(2)
122.6(2)
130.2(3)
N2–C7–C2
Cu1–N1–C1
Cu1–N2–C7
Cu1–N3–C14
C2–C7
Table 3. The solvent effect (5 mL) at the benzyl alcohol oxidation with
BAPP
CuL
/Cs CO (4/2 in mmol).
2 3
Solvent
t / h
yield / %
CH CN
6
4
6
6
49
100
37
3
THF
n-Hexane
Toluene
89
2

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BAPP
Table 4. The CuL
equivalencesCs CO ratio influence (mmol) in THF (5 mL)
2
3
at the benzyl alcohol oxidation.
Solvent
t / h
yield / %
n(CuLBAPP)/n(Cs2CO3)
THF
THF
THF
THF
4
4
4
4
4
5
2
3
4
5
/2
/2
/2
/2
62
100
100
BAPP
Table 5. Different basic agents at the alcohol oxidation with 4 mmol of CuL
in THF.
n/mmol Base
Solvent
t / h
yield / %
2
4
2
1
NaNO2
KOH
THF
THF
THF
THF
THF
THF
6
47
22
1
1
1
2
3
24
NEt3
4
48
Cs CO
2
3
4
100
100
Cs CO
2
3
4
Cs CO
2
3
Table 6. The result of blank test for oxidation of benzyl alcohol with
similar catalytic system
Catalytic system
t / h
24
4
yield / %
Cu(OAc) /Cs CO
26
85
2
2
3
BAP
Cu(OAc) /Cs CO /HL
2
2
3
3

ACCEPTED MANUSCRIPT
Table 7. Different alcohols applied for their oxidation to corresponding aldehyde in THF,
BAPP
catalyzed by CuL
in a presence of Cs CO as a base and O as an oxidant.
2 3 2
t / h
4
yield / %
100
Substrate
1
2
3
4
90
OH
Cl
6
8
96
92
4
5
6
7
24
24
81
75
OH
O N
2
OH
24
24
76
64
OH
8
9
MeO
Br
OH
24
24
23
1
0
-
4

ACCEPTED MANUSCRIPT
BAPP
Figure 1. Electronic absorption spectra of CuL
BAPP
Figure 2. ORTEP diagram and atom labeling scheme for complex CuL
Ellipsoids are plotted at 30% probability level. Hydrogen atoms are omitted for clarity.
1

ACCEPTED MANUSCRIPT
Figure 3. Temperature dependent susceptibility χ(T) and the effective magnetic moment
BAPP
µeff(T) (inset) of CuL
measured in a magnetic field of H = 1 kOe.
-1
BAPP
Figure 4. χ (T) of CuL
measured in a magnetic field of H = 1 kOe.
2

ACCEPTED MANUSCRIPT
BAPP
-1
Figure 5. Cyclic voltammogram of CuL
in CH Cl at RT. (sc 25 mVs ).
2
2
BAPP
Figure 6. EPR spectrum of CuL
3

ACCEPTED MANUSCRIPT
BAPP
Figure 7. Time screening of benzyl alcohol oxidation alcohol with CuL
4

ACCEPTED MANUSCRIPT
Research Highlights
‹
‹
Copper(II) complex of tetra-dentate o-aminophenol-based.
Excellent galactose oxidases mimic system.
Aerobic oxidation of alcohols.
‹