Synthesis, characterization, and catalytic oxidation of ethylbenzene over host (zeolite-Y)/guest (copper(II) complexes of tetraaza macrocyclic ligands) nanocomposite materials

Article abstract of DOI:10.1080/00958972.2010.510557

Cu(II) complexes of 14- and 16-membered tetraaza macrocyclic ligands have been encapsulated in nanopores of zeolite-Y by a two-step process in the liquid phase: (1) adsorption of [bis(diamine)copper(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, and 1,3-diaminobenzene); [Cu(N-N) ₂]²⁺-NaY; in the nanopores of the zeolite-Y and (2) in situ condensation of the copper(II) precursor complex with ethylcinnamate. The new host-guest nanocomposite materials were characterized by chemical analysis and spectroscopic methods. The neat and encapsulated complexes exhibit good catalytic activity in the oxidation of ethylbenzene at 333 K, using tert-butyl hydroperoxide as the oxidant. Acetophenone was the major product though small amounts of o- and p-hydroxyacetophenones were also formed revealing that C-H bond activation takes place both at benzylic and aromatic ring carbon atoms.

Full text of DOI:10.1080/00958972.2010.510557

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Synthesis, characterization, and
catalytic oxidation of ethylbenzene
over host (zeolite-Y)/guest (copper(II)
complexes of tetraaza macrocyclic
ligands) nanocomposite materials
Masoud Salavati-Niasari a b & Fatemeh Davar a
a Institute of Nano Science and Nano Technology, University of
Kashan , P.O. Box 87317-51167, Kashan, Islamic Republic of Iran
b Department of Inorganic Chemistry, Faculty of Chemistry ,
University of Kashan , P.O. Box 87317-51167, Kashan, Islamic
Republic of Iran
Published online: 19 Aug 2010.
To cite this article: Masoud Salavati-Niasari & Fatemeh Davar (2010) Synthesis, characterization,
and catalytic oxidation of ethylbenzene over host (zeolite-Y)/guest (copper(II) complexes of
tetraaza macrocyclic ligands) nanocomposite materials, Journal of Coordination Chemistry, 63:18,
3240-3255, DOI: 10.1080/00958972.2010.510557
To link to this article: http://dx.doi.org/10.1080/00958972.2010.510557
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Journal of Coordination Chemistry
Vol. 63, No. 18, 20 September 2010, 3240–3255
Synthesis, characterization, and catalytic
oxidation of ethylbenzene over host (zeolite-Y)/guest
(copper(II) complexes of tetraaza macrocyclic ligands)
nanocomposite materials
MASOUD SALAVATI-NIASARI*yz and FATEMEH DAVARy
yInstitute of Nano Science and Nano Technology, University of
Kashan, P.O. Box 87317-51167, Kashan, Islamic Republic of Iran
zDepartment of Inorganic Chemistry, Faculty of Chemistry,
University of Kashan, P.O. Box 87317-51167, Kashan,
Islamic Republic of Iran
(Received 5 January 2009; in final form 1 June 2010)
Cu(II) complexes of 14- and 16-membered tetraaza macrocyclic ligands have been encapsulated
in nanopores of zeolite-Y by a two-step process in the liquid phase: (1) adsorption of
[bis(diamine)copper(II)] (diamine ¼ 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminoben-
zene, and 1,3-diaminobenzene); [Cu(N–N)2]2þ–NaY; in the nanopores of the zeolite-Y and
(2) in situ condensation of the copper(II) precursor complex with ethylcinnamate. The new
host–guest nanocomposite materials were characterized by chemical analysis and spectroscopic
methods. The ‘‘neat’’ and encapsulated complexes exhibit good catalytic activity in the
oxidation of ethylbenzene at 333 K, using tert-butyl hydroperoxide as the oxidant.
Acetophenone was the major product though small amounts of o- and p-hydroxyacetophe-
nones were also formed revealing that C–H bond activation takes place both at benzylic and
aromatic ring carbon atoms.
Keywords: Nanocomposite materials; Copper(II); Tetraaza; Zeolite encapsulation; Oxidation
of ethylbenzene
1. Introduction
Studies on the isolation, characterization, and catalytic activity of transition metal
complexes encapsulated in various nanoporous materials have received considerable
attention because of their specific catalytic applications when compared to
homogeneous complexes [1–11]. The heterogenization process provides a rigid
framework to the metal complex inside the zeolite due to spatial restrictions,
Columbic interactions, and/or covalent bonding. It also facilitates reactions under
mild conditions [12]. Encapsulation of metal complexes in nanopores of zeolites alters
the redox properties; transition metal complexes encapsulated in various zeolites
resemble, to a certain extent, enzymes where the catalytically active centers might be
*Corresponding author. Email: salavati@kashanu.ac.ir
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.510557

Zeolite copper catalyst
3241
a transition metal ion and the protein sheath provides the stability and steric
constraints. Inorganic complexes encapsulated in such constrained environments can
therefore be termed as zeozymes [13].
Nanoporous materials are exemplified by crystalline framework solids, such as
zeolites, whose crystal structure defines channels and cages i.e., nanopores, of strictly
regular dimensions. They can impart shape selectivity for both the reactants and the
products in chemical reactions and processes. The large internal surface area and void
volumes with extremely narrow pore size distribution as well as functional centers
homogeneously dispersed over the surface make nanoporous solids highly active, and
there has been a dramatic increase in synthesis, characterization, and application of
nanoporous materials [1–16].
In this study, we chose tetraaza ligands and their encapsulated complexes (schemes 1
and 2) in oxidation reactions. Tetraaza copper(II) complexes have not been
encapsulated in the nanopores of zeolite-Y and have not been used in oxidation of
ethylbenzene. The use of these encapsulated complexes as nanocatalysts can enhance
selectivity in the oxidation. The host–guest nanocomposite materials (HGNM) can be
windows to selection of a suitable nanocatalyst for oxidation. In this article, we report
the synthesis and characterization of copper(II) complexes of 14- and 16-membered
tetraaza macrocyclic ligands; [14]aneN4: 1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcy-
clotetradecane; [16]aneN4: 1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane;
Bzo2[14]aneN4: dibenzo-1,5,8,12-tetraaza-2,9-dioxo-4,11-diphenylcyclotetradecane and
Bzo2[16]aneN4:
dibenzo-1,5,9,13-tetraaza-2,10-dioxo-4,12-diphenylcyclohexadecane;
and encapsulated within the nanopores of zeolite-Y by template condensation of
ethylcinnamate and [bis(diamine)copper(II)], [Cu([14]aneN4)]2þ–NaY, [Cu([16]ane
N4)]2þ–NaY, [Cu(Bzo2[14]aneN4)]2þ–NaY, and [Cu(Bzo2[16]aneN4)]2þ–NaY, shown
in schemes 1 and 2.
2. Experimental
2.1. Materials
2.1.1. Safety note. Copper perchlorate with organic ligands is often explosive and
should be handled with caution. All other reagents, solvents, and tert-butyl hydroper-
oxide (TBHP) (50% in ethylene dichloride; 0.42 mL) were purchased from Merck
˚
(pro-analysis) and dried using molecular sieves (Linde 4 A). NaY with the Si : Al ratio of
2.53 was purchased from Aldrich (Lot no. 67812). The complex [Cu(N–N)2](ClO4)2 was
prepared according to published procedures [17].
2.2. Physical measurements
Elemental analysis (carbon, hydrogen, and nitrogen) of the materials was obtained from
a Carlo ERBA Model EA 1108 analyzer. X-ray diffraction (XRD) patterns were
recorded on a Rigaku D-max C III, X-ray diffractometer using Ni-filtered Cu-Ka
radiation. Nitrogen adsorption measurements were performed at 77 K, using a Coulter
Ofeisorb 100CX instrument. The samples were degassed at 150ꢀC until a vacuum better

3242
M. Salavati-Niasari and F. Davar
Scheme 1. The 14- and 16-membered tetraaza dioxo diphenyl macrocyclic ligands.
than 10ꢁ3 Pa was obtained. Micropore volumes were determined by the t-method and
a ‘‘monolayer equivalent area’’ was calculated from the micropore volume [18, 19].
Electrochemical data were obtained in acetonitrile with 0.1 mol Lꢁ1 (n-Bu)4NClO4 as
supporting electrolyte. The working electrode was a platinum disc, the auxiliary
electrode was a coiled platinum wire, and the reference electrode was Ag/AgClO4
(0.1 mol Lꢁ1 in CH3CN), which showed þ0.24 V versus SCE. FAB mass spectra were
recorded on a Kratos MS50TC spectrometer. FTIR spectra were recorded on a
Shimadzu Varian 4300 spectrophotometer in KBr pellets. Electronic spectra of the neat
complexes were taken on a Shimadzu UV-Vis scanning spectrometer (Model 2101 PC).
The stability of the encapsulated catalyst was checked after the reaction by UV-Vis and
possible leaching of the complex was investigated by UV-Vis in the reaction solution

Zeolite copper catalyst
3243
Scheme 2. Encapsulation of copper complexes of the 14- and 16-membered tetraaza dioxo diphenyl
macrocycles within the nanopores of zeolite-Y.
after filtration of the zeolite. The amounts of metallocomplexes encapsulated in the
zeolite matrix were determined by elemental analysis and by subtracting the amount of
metallocomplex left in the solutions after the synthesis of the catalysts as determined by
UV-Vis spectroscopy, from the amount taken for the synthesis. Atomic absorption
spectra (AAS) were recorded on a Perkin-Elmer 4100–1319 spectrophotometer using a
flame approach, after acid (HF) dissolution of known amounts of the zeolitic material
and SiO2 was determined by gravimetric analysis. Diffuse reflectance spectra (DRS)
were recorded on a Shimadzu UV/3101 PC spectrophotometer in the range
1500–200 nm, using MgO as reference.
2.3. Synthesis of 14- and 16-membered tetraaza dioxo diphenyl macrocyclic ligands
Tetraaza macrocyclic ligands ([14]aneN4, [16]aneN4, Bzo2[14]aneN4, or Bzo2[16]aneN4)
were prepared by following the procedures reported [20]. Hot ethanol solution (20 mL)
of ethylcinnamate (3.52 g, 0.02 mol) and a hot ethanol solution (20 mL) of diamine
(0.02 mol) (1,2-diaminoethane (1.20 g), 1,3-diaminopropane (1.48 g), 1,2-diaminoben-
zene (2.16 g), and 1,3-diaminobenzene (2.16 g)) were mixed slowly with constant
stirring. This mixture was refluxed at 80ꢀC for 12 h with few drops of concentrated HCl.
On cooling, a white precipitate was formed, which was filtered, washed with cold
ethanol, and dried under vacuum over P4O10. The purity was checked by HPLC
technique. Anal. Calcd for [14]aneN4: C, 69.4%; H, 7.4%; and N, 14.7%; C/N, 4.7%.

3244
M. Salavati-Niasari and F. Davar
Found: C, 69.3%; H, 7.3%; and N, 14.9%; C/N, 4.7%; ꢀC¼O, 1624 cmꢁ1
,
ꢀ(C–N) þ ꢁ(N–H), 1593 cmꢁ1, ꢁ(N–H), 1249 cmꢁ1, ꢂ(C¼O), 780, and ꢀN–H, 3286.
Anal. Calcd for [16]aneN4: C, 70.6%; H, 7.9%; and N, 13.7%; C/N, 5.1%. Found:
C, 70.3%; H, 7.7%; and N, 13.9%; C/N, 5.1%; ꢀC¼O, 1620 cmꢁ1, ꢀ(C–N) þ ꢁ(N–H),
1590 cmꢁ1, ꢁ(N–H), 1248 cmꢁ1, ꢂ(C¼O), 780, and ꢀN–H, 3280. Anal. Calcd for
Bzo2[14]aneN4: C, 75.6%; H, 5.9%; and N, 11.8%; C/N, 6.4%. Found: C, 75.4%;
H, 5.7%; N, 11.8%; C/N, 6.4%; ꢀC¼O, 1630 cmꢁ1, ꢀ(C–N) þ ꢁ(N–H), 1596 cmꢁ1
,
ꢁ(N–H), 1252 cmꢁ1, ꢂ(C¼O), 782, and ꢀN–H, 3290. Anal. Calcd for Bzo2[16]aneN4:
C, 75.6%; H, 5.9%; and N, 11.7%; C/N, 6.5%. Found: C, 75.4%; H, 5.7%; and
N, 11.9%; C/N, 6.3%; ꢀC¼O, 1627 cmꢁ1, ꢀ(C–N) þ ꢁ(N–H), 1594 cmꢁ1, ꢁ(N–H),
1250 cmꢁ1, ꢂ(C¼O), 782, and ꢀN–H, 3288.
2.4. Preparation of tetraaza dioxo diphenyl copper(II) complexes
Copper(II) perchlorate hexahydrate (0.01 mol) dissolved in ethanol (20 mL) was reacted
with an ethanol (20 mL) solution of tetraaza ligands ([14]aneN4, [16]aneN4,
Bzo2[14]aneN4, or Bzo2[16]aneN4) (0.01 mol) by refluxing for 6 h until an orange
solution resulted. The solution was cooled to room temperature and filtered to remove
Cu(OH)2. Excess Li(ClO4)ꢂ3H2O dissolved in methanol was added to the filtrate, and
the mixture was kept in the refrigerator until a red solid was formed. The solids were
filtered, washed thoroughly with cold ethanol, and dried in vacuum. Anal. Calcd for
[Cu([14]aneN4)](ClO4)2: C, 41.1%; H, 4.4%; N, 8.7%, and Cu, 9.9%; C/N, 4.7%.
Found: C, 40.9%; H, 4.2%; N, 8.9%, and Cu, 9.8%; C/N, 4.6%; ꢀC¼O, 1620 cmꢁ1
,
ꢀ(C–N) þ ꢁ(N–H), 1591 cmꢁ1, ꢁ(N–H), 1248 cmꢁ1, ꢂ(C¼O), 779, ꢀN–H, 3258, and
ꢀM–N, 470. FAB mass (m/z): [Cu–ClO4]þ, 543, [Cu–2ClO4]2þ, 444; d $ d, 493
(in CH3CN), and 475 nm (in CH3NO2); ꢃB, 1.8 B.M; ÃM, 230 (ꢀꢁ1 cm2 (mol Lꢁ1 ꢁ1).
)
Anal. Calcd for [Cu([16]aneN4)](ClO4)2: C, 43.0%; H, 4.8%; N, 8.3%, and Cu, 9.5%;
C/N, 5.1%. Found: C, 42.7%; H, 4.7%; N, 8.4%; and Cu, 9.3%; C/N, 5.1%; ꢀC¼O,
1621 cmꢁ1, ꢀ(C–N) þ ꢁ(N–H), 1590 cmꢁ1, ꢁ(N–H), 1247 cmꢁ1, ꢂ(C¼O), 780, ꢀN–H,
3253, and ꢀM–N, 469. FAB mass (m/z): [Cu–ClO4]þ, 571, [Cu–2ClO4]2þ, 472; d $ d,
496 (in CH3CN), and 476 nm (in CH3NO2); ꢃB, 1.8 B.M; ÃM, 225 (ꢀꢁ1 cm2
(mol L )
ꢁ1 ꢁ1). Anal. Calcd for [Cu(Bzo2[14]aneN4)](ClO4)2: C, 48.8%, H, 3.8%;
N, 7.6%, and Cu, 8.6%; C/N, 6.4%. Found: C, 48.6%; H, 3.7%; N, 7.7%; and Cu,
8.5%; C/N, 6.3%; ꢀC¼O, 1633 cmꢁ1, ꢀ(CꢁN) þ ꢁ(N–H), 1594 cmꢁ1
, ꢁ(N–H),
1251 cmꢁ1, ꢂ(C¼O), 782, ꢀN–H, 3262, and ꢀM–N, 475. FAB mass (m/z): [Cu–
ClO4]þ, 639, [Cu–2ClO4]2þ, 540; d $ d, 490 (in CH3CN), and 470 nm (in CH3NO2); ꢃB,
1.8 B.M; ÃM, 220 (ꢀꢁ1 cm2 Mꢁ1). Anal. Calcd for [Cu(Bzo2[16]aneN4)](ClO4)2:
C, 48.8%; H, 3.8%; N, 7.6%; and Cu, 8.6%; C/N, 6.4%. Found: C, 48.6%; H,
3.7%; N, 7.7%; and Cu, 8.5%; C/N, 6.3%; ꢀC¼O, 1629 cmꢁ1, ꢀ(C–N) þ ꢁ(N–H),
1593 cmꢁ1, ꢁ(N–H), 1254 cmꢁ1, ꢂ(C¼O), 781, ꢀN–H, 3259, and ꢀM–N, 472. FAB mass
(m/z): [Cu–ClO4]þ, 639, [Cu–2ClO4]2þ, 540; d $ d, 491 (in CH3CN), and 473 nm
(in CH3NO2); ꢃB, 1.8 B.M; ÃM, 218 (ꢀꢁ1 cm2 (mol L
)
ꢁ1 ꢁ1).
2.5. Preparation of Cu(II)–NaY
Two grams of NaY zeolite was suspended in 100 mL of distilled water, which contained
Cu(NO3)2ꢂ6H2O (0.025 mol Lꢁ1). The mixture was then heated while stirring at 90ꢀC

Zeolite copper catalyst
3245
for 24 h. The solid was filtered, washed with hot distilled water till the filtrate was free
from any copper(II) (by AAS of filtrate) and dried for 10 h at 80ꢀC under vacuum.
The ionic exchange degree was determined by AAS. Anal. Found for NaY: Si, 21.8%;
Al, 8.6%; and Na, 7.5%; Si/Al, 2.5%; surface area, 545 m2 gꢁ1; pore volume,
0.3 cm3 gꢁ1. Anal. Found for Cu(II)NaY: Si, 21.5%; Al, 8.5%; Na, 3.3%; and Cu,
3.9%; Si/Al, 2.5%; surface area, 532 m2 gꢁ1; pore volume, 0.3.
2.6. Preparation of [Cu(N–N)2]2Y–NaY
Typically, a 4 g sample of NaY zeolite was mixed with 0.37 g of [bis(diamine)copper(II)]
perchlorate (diamine ¼ 1,2-diaminopropane, 1,3-diaminopropane, 1,2-diaminobenzene,
and 1,3-diaminobenzene) suspended in 100 mL of methanol and refluxed for 8 h. The
pale red solid consisting of [Cu(N–N)2]2þ exchanged with Naþ in NaY and denoted as
[Cu(N–N)2]2þ–NaY was collected by filtration and washed with ethanol. The resulting
zeolites were Soxhlet extracted with DMF (for 4 h) and then with ethanol (for 3 h) to
remove excess unreacted diamine and any copper(II) complexes adsorbed onto the
external surface of the zeolite crystallines. The resulting light blue solids were dried at
60ꢀC under vacuum for 24 h. Data for [Cu(N–N)2]2þ–NaY: surface area, 452 m2 gꢁ1
pore volume, 0.24 cm3 gꢁ1
;
.
2.7. Preparation of HGNM; [Cu([14 or 16]aneN4)]2Y–NaY and [Cu(bzo2[14 or
16]aneN4)]2Y–NaY
Ethylcinnamate was slowly added to a stirred methanol suspension (100 mL) of
[Cu(N–N)2]2þ–NaY (2 g) under N2. The mixture was heated under reflux for 24 h until a
pale red suspension resulted. The solution was filtered and the resulting zeolites were
Soxhlet extracted with DMF (for 6 h) and then with ethanol (for 5 h) to remove excess
unreacted products from amine–ester condensation and any copper(II) complexes
adsorbed onto the external surface of the zeolite. The resulting pale red solids were
dried at 70ꢀC under vacuum for 12 h. The remaining [Cu(N–N)2]2þ ions in the zeolite
were removed by exchanging with aqueous 0.1 mol Lꢁ1 NaCl solutions. The stability of
the encapsulated catalyst was checked after the reaction by UV-Vis; possible leaching of
the complex was investigated by UV-Vis in the reaction solution after filtration of the
zeolite. The amounts of copper(II) complexes encapsulated in the zeolite matrix were
determined by elemental analysis and subtracting the amount of copper(II) complex left
from the solutions after the synthesis of the catalysts as determined by UV-Vis
spectroscopy, from the amount taken for the synthesis. Anal. Found for
[Cu([14]aneN4)]2þ–NaY: C, 4.2; H, 1.6; N, 1.0; and Cu, 2.8; C/N, 4.2; Si, 21.1;
Al, 8.3; and Na, 5.2; Si/Al, 2.5; ꢀC¼O, 1625 cmꢁ1; ꢀN–H, 3256; d $ d, 477 nm; surface
area, 421 m2 gꢁ1; pore volume, 0.2 cm3 gꢁ1. Anal. Found for [Cu([16]aneN4)]2þ–NaY:
C, 4.3; H, 1.6; N, 0.9; and Cu, 2.8; C/N, 4.8; Si, 21.1; Al, 8.3; and Na, 5.2; Si/Al, 2.5;
ꢀC¼O, 1623 cmꢁ1; ꢀN–H, 3252; d $ d, 479 nm; surface area, 413 m2 gꢁ1; pore volume,
0.2 cm3 gꢁ1. Anal. Found for [Cu(Bzo2[14]aneN4)]2þ–NaY: C, 4.3; H, 1.6; N, 0.7; and
Cu, 2.7; C/N, 6.2; Si, 21.0; Al, 8.3; and Na, 5.2; Si/Al, 2.5; ꢀC¼O, 1633 cmꢁ1; ꢀN–H,
3260; d $ d, 473 nm; surface area, 374 m2 gꢁ1; pore volume, 0.1 cm3 gꢁ1. Anal. Found
for [Cu(Bzo2[16]aneN4)]2þ–NaY: C, 4.3; H, 1.6; N, 0.7; and Cu, 2.7; C/N, 6.2; Si, 21.0;

3246
M. Salavati-Niasari and F. Davar
Al, 8.3; and Na, 5.2; Si/Al, 2.5; ꢀC¼O, 1630 cmꢁ1; ꢀN–H, 3260; d $ d, 475 nm; surface
area, 361 m2 gꢁ1; pore volume, 0.1 cm3 gꢁ1
.
2.8. Oxidation of ethylbenzene; general procedure
The catalytic activities were conducted in a 25 mL round-bottom glass flask, placed in a
thermostated oil bath and fitted with a water cooled condenser. In a typical oxidation,
ethylbenzene (0.106 g, 1 mmol), catalyst (0.004 mmol in case of ‘‘neat’’ complexes and
0.004 mmol in case of HGNM), TBHP (50% in ethylene dichloride; 0.42 mL), and
CH3CN (1 mL) were taken and the reaction was conducted at 333 K for 10 h under Ar.
The progress of the reaction was monitored by HPLC and the products were identified
by GC–MS.
3. Results and discussion
3.1. Synthesis and characterization of HGNM
The C, H, and N analyses of the neat copper complexes showed close similar theoretical
values. The molecular formulae of the tetraaza complexes have been assigned on the
basis of their elemental analysis. Preliminary identification of the metal complexes was
made on the basis of their IR spectra, which exhibited no bands characteristic of free
primary amine, supporting the proposed macrocyclic skeleton (scheme 1). The copper
contents of the HGNM catalysts were estimated by dissolving known amounts of the
catalyst in concentrated HCl and from these solutions, the copper content was
estimated by using AAS. The chemical compositions confirmed the purity and
stoichiometry of the neat and encapsulated complexes. The chemical analyses of the
samples revealed the presence of organic matter with a C/N ratio similar to that for neat
complexes. The molar ratio of Si/Al obtained by chemical analysis for zeolites
Cu(II)–NaY and the zeolite complexes were almost in the same ratio, indicating little
change in the zeolite framework due to de-alumination in metal ion exchange.
The parent NaY zeolite has Si/Al molar ratio of 2.53, which corresponds to a unit cell
formula [Na56[(AlO2)56(SiO2)136]. The unit cell formula of metal-exchanged zeolites
showed a copper dispersion of 10.8 mol per unit cell [(Na33.8Cu10.8[(AlO2)56
(SiO2)136] ꢂ nH2O). The analytical data of each complex indicated Cu : C : N molar
ratios close to those calculated for the mononuclear structure. However, traces of free
[Cu(N–N)2]2þ in the lattice are higher than the stoichiometric requirement, and only a
small amount of [Cu(N–N)2]2þ has undergone complexation in exchange with zeolite
and the rest is expected to be removed through re-exchange with NaCl solution.
Synthesis of tetraaza copper(II) complexes encapsulated in the nanocavity
of zeolite-Y involves exchange of [Cu(N–N)2]2þ (diamine ¼ 1,2-diaminopropane,
1,3-diaminopropane, 1,2-diaminobenzene, and 1,3-diaminobenzene) with NaY in
methanol solution and reaction of [Cu(N–N)2]2þ–NaY with excess ethylcinnamate in
methanol where ethylcinnamate slowly enters into the nanocavity of zeolite-Y due to its
template nature and interacts with [Cu(N–N)2]2þ. Soxhlet extraction using methanol
finally purified the impure complexes. The remaining free metal ions in zeolite were
removed by exchanging with aqueous 0.01 mol Lꢁ1 NaCl solution. Thus, the formula of

Zeolite copper catalyst
3247
copper(II) complex may be written as [Cu([14]aneN4)]2þ–NaY, [Cu([16]aneN4)]2þ
–
NaY, [Cu(Bzo2[14]aneN4)]2þ–NaY, and [Cu(Bzo2[16]aneN4)]2þ–NaY. The percentage
of metal was determined before and after encapsulation by inductively coupled plasma
(ICP). After extraction with methanol, the metal ion content found after encapsulation
is only due to the presence of metal complexes in supercages of the zeolite-Y. The
molecular formula of the complexes are based on the neat complexes [Cu([14]aneN4)]2þ
,
[Cu([16]aneN4)]2þ, [Cu(Bzo2[14]aneN4)]2þ, and [Cu(Bzo2[16]aneN4)]2þ that have also
been prepared and characterized.
XRD patterns of encapsulated complexes are shown in figure 1. These complexes
exhibit similar peaks to those of zeolite-Y; except for a slight change in the intensity of
the peaks, no new crystalline pattern emerges, confirming that the framework and
crystallinity of the zeolite were not destroyed during the preparation, and that the
complexes were distributed in the cages. The relative peak intensities of the 220, 311,
and 331 reflections are correlated with the locations of cations. In zeolite-Y, the order of
peak intensity is in the order I331 ꢃ I220 4 I311, while in encapsulated complexes,
the order of peak intensity became I331 ꢃ I311 4 I220. The difference indicates that the
ion-exchanged Cu2þ, which substitutes at the location of Naþ, undergoes rearrange-
ment during complexation.
The surface areas and pore volumes of the catalysts were measured. The encapsula-
tion of [Cu([14]aneN4)]2þ–NaY, [Cu([16]aneN4)]2þ–NaY, [Cu(Bzo2[14]aneN4)]2þ–NaY,
Figure 1. X-ray diffractograms of (a) zeolite-Y and (b) [Cu([14]aneN4)]2þ–NaY.

3248
M. Salavati-Niasari and F. Davar
H
O
-
N
N
Cu
-
N
N
O
H
Scheme 3. Deprotonation of [Cu(Bzo2[14]aneN4)] in the presence of amine base.
and [Cu(Bzo2[16]aneN4)]2þ–NaY complexes in zeolite reduced the adsorption capacity
and the surface area of the zeolite. The lowering of the pore volume and surface area
indicated the presence of (Cu([14]aneN4)]2þ, [Cu([16]aneN4)]2þ, [Cu(Bzo2[14]aneN4)]2þ
,
and [Cu(Bzo2[16]aneN4)]2þ) within the zeolite nanocages and not on the external
surface.
3.2. Synthesis and characterization of ‘‘neat’’ complexes
The molecular formulae of the complexes have been assigned on the basis of their
elemental analyses and the molecular ion peaks in the mass spectra. All mass spectra
showed molecular ion peaks for the 1 : 1 metal-to-ligand stoichiometry with no further
peaks above them. A preliminary identification of the metal complexes was made on the
basis of their IR spectra, which exhibited no characteristic bands of free primary amine,
thus supporting the proposed macrocyclic skeleton (scheme 1). The deep red complexes
‘‘[Cu([14 or 16]aneN4)](ClO4)2 and [Cu(Bzo2[14 or 16]aneN4)](ClO4)2’’ readily dissolve
in polar solvents, such as H2O, CH3CN, CH3NO2, and (CH3)2SO2. The copper(II)
complexes are extremely stable in the solid state and in solution and are relatively stable
against ligand dissociation even in highly acidic solutions. The molar conductance
values of the complexes (218–230 ꢀꢁ1 molꢁ1 cm2) as measured in CH3NO2 correspond
to 1 : 2 electrolytes. The overall geometries of all macrocycles have been deduced on the
basis of the observed values of the magnetic moments and the band positions in the
electronic spectra. The magnetic moments (1.80–1.85 ꢃB) of the Cu(II) complexes
measured in the solid state correspond to square planar geometry.
The 14- and 16-membered tetraaza macrocyclic copper(II) complexes undergo
intense color changes due to deprotonation of the macrocyclic ligand in the presence of
amine bases, such as C5H5N and Et3N (Scheme 3). Similar N–H deprotonations have
been observed with other metal complexes containing N–H linkages. For the copper(II)
complex, Et3N is sufficiently basic to facilitate formation of the molecular complex.
For the preparation of the deprotonated form of [Cu(Bzo2[14]aneN4)](ClO4)2, Et3N
(0.5 mL) was added to a deaerated solution of 200 mg of [Cu(Bzo2[14]aneN4)](ClO4)2 in
15 mL of CH3CN. The shiny brown product, which began precipitating within minutes,
was filtered after 0.5 h under an N2 atmosphere, washed with anhydrous ethanol, and
dried in vacuum. IR (KBr, cmꢁ1): 3215 (ꢀN–H). [Cu(C30H26N4)]: Found: Cu, 11.7%;
C, 66.8%; H, 4.8%; and N, 10.5%. Calcd: Cu, 11.8%; C, 67.0%; H, 4.9%; and
N, 10.4%. The N–H stretching frequency of this compound [Cu(C30H26N4)], 3215 cmꢁ1
,

Zeolite copper catalyst
3249
is reduced significantly from its dicationic precursor, [Cu(Bzo2[14]aneN4)](ClO4)2,
3262 cmꢁ1
.
IR spectrum of the ligand does not exhibit any band for the free primary diamine and
hydroxyl group. The absorptions of tetraaza at 730–770 and 1415–1645 cmꢁ1 [21] are
due to the phenyl. Four new bands present in the spectrum of the free ligand in the
regions ꢄ1620, ꢄ1590, ꢄ1248, and ꢄ780 cmꢁ1 correspond to amide I [ꢀ(C¼O)], amide
II [ꢀ(C–N) þ ꢁ(N–H)], amide III [ꢁ(N–H)], and amide IV [’(C¼O)] bands, respectively
[22]. A sharp band at ꢄ3287 cmꢁ1 may be due to [ꢀ(N–H)] of the secondary amino
group [23]. The IR spectra of all the complexes showed a single sharp absorption
around ꢄ3250 cmꢁ1 which may arise from a secondary amine, ꢀN–H, although its
position is lower by ꢄ30 cmꢁ1 than the analogous metal-free tetraaza ligands [24–27].
This suggests that the secondary amine nitrogens coordinate confirmed by the
appearance of ꢀM–N bands at 340–350 cmꢁ1 in the complexes. The IR bands of all
encapsulated complexes are weak in comparison with the neat complexes due to their
low concentrations in zeolite nanocages. The four entrapped complexes exhibit very
similar IR spectra with bands at all regions that are shifted ꢄ2 cmꢁ1 relative to those of
the corresponding free complexes.
Copper(II) complexes with 14- and 16-membered tetraaza macrocyclic ligands
‘‘[14]aneN4; [16]aneN4; Bzo2[14]aneN4; Bzo2[16]aneN4’’ exist in aqueous solution as an
equilibrium mixture of a red square planar and a green octahedral species. Solution of
tetraaza macrocyclic copper(II) complexes in coordinating solvents (such as H2O,
CH3CN, etc.) show an absorption maximum at ꢄ470 nm, characteristic for square
planar red species and at ꢄ490 nm, characteristic for green octahedral species [24–28].
As shown above, the molar absorption coefficient of the ligand field transition band for
complexes measured in H2O or CH3CN is smaller than that in CH3NO2, a non-
coordinating solvent. This result is quite similar to those reported for other related
polyaza macrocyclic complexes, indicating that the complex dissolves in H2O or
CH3CN to produce an equilibrium mixture of square planar [Cu(Bzo2[14]aneN4)]2þ and
octahedral trans-[Cu(Bzo2[14]aneN4)(solvent)2]2þ (solvent ¼ H2O or CH3CN) [24–37].
The 14- and 16-membered tetraaza and some tetraaza macrocyclic Cu(II) complexes
exist in water as equilibrium mixture of red square planar [Cu(Bzo2[14]aneN4)]2þ and
green octahedral [Cu(Bzo2[14]aneN4)(H2O)2]2þ. The electronic spectra of copper(II)
complexes are comparable to other similar saturated tetraaza macrocyclic square planar
copper(II) complexes, indicating that the tetraaza ligands of this study do not differ
significantly from the tetraaza ligands with respect to ligand field strength [24–37].
The UV-Vis data of ‘‘neat’’ and zeolite-Y encapsulated complexes are shown in
figure 2. The ‘‘neat’’ complexes in MeNO2 showed a characteristic UV band of ligand
origin at 470–500 nm. A weak band due to copper-centered d $ d transitions was
observed in the visible range at ꢄ490 nm. The size of the macrocyclic ligand affected the
structure. As a consequence of this, the d $ d band shifted from 490 nm in
[Cu(Bzo2[14]aneN4)](ClO4)2 to 491 nm in [Cu(Bzo2[16]aneN4)](ClO4). This shift in the
band position to higher energy indicates that the 14-membered tetraaza ligands provide
greater stability than the 16-membered tetraaza ligands and the ligand field is stronger
in 14-membered than in 16-membered complexes. When the complexes were
encapsulated in zeolite-Y, the d $ d band shifted again to the higher energy side.
The stability of the complexes apparently increases when they are encapsulated in
zeolite-Y. The position of the d $ d band corresponds to square planar geometry for
tetraaza macrocyclic copper(II) complexes [38].

3250
M. Salavati-Niasari and F. Davar
Figure 2. UV-Vis and DRS spectra of (A): (a) [Cu([14]aneN4)](ClO4)2, (b) [Cu([14]aneN4)]2þ–NaY; (B):
(a) [Cu([16]aneN4)](ClO4)2, (b) [Cu([16]aneN4)]2þ–NaY; (C): (a) [Cu(Bzo2[14]aneN4)](ClO4)2, (b) [Cu(Bzo2
[14]aneN4)]2þ–NaY; and (D): (a) [Cu(Bzo2[16]aneN4)](ClO4)2, (b) [Cu(Bzo2[16]aneN4)]2þ–NaY.
Cyclic voltammetric data are summarized in table 1. Table 1 shows that oxidation
and reduction potentials of the copper(II) complexes of the tetraaza copper(II)
complexes do not differ significantly from other [14]aneN4 complexes. This suggests
that macrocycles have Lewis basicities and hole size similar to those of the [14]aneN4 in
spite of the structural differences. A pronounced shift in oxidation state stability occurs
when there is a change in macrocyclic ring size. An increase in ring size promotes
formation of Cu(I), while rendering the oxidation to copper(III) more difficult.
The difference between the [Cu([14]aneN4)]2þ and [Cu((CH3)6[16]1,4,12-trieneN4)]2þ
complexes amounts to 0.3 V. Busch et al. [39] suggested that this difference is primarily
due to deviations from the ideal metal donor distances accompanying the redox
changes. This concept of optimum fit between the coordinated metal ion and the
‘‘hole size’’ provided by the macrocyclic ligand is also in accord with theoretical
conclusions and electronic spectroscopic studies. The more common effect of ligand
unsaturation also favors the formation of the lower valent states of the complexes and
causes the copper(II) to copper(III) process to occur at higher energy. The effect of the
Bzo function on the reduction reactions of the copper macrocycles is very pronounced
and structures containing this moiety form stable complexes in lower valence states at
relatively mild potentials [40–43].

Zeolite copper catalyst
3251
Table 1. Cyclic voltammetric data for copper(II) complexes with 14- and 16-
membered tetraaza macrocycles.a,b
Oxidation
potential (V),
[Cu(polyaza)]2þ
Reduction
potential (V)
[Cu(polyaza)]2þ
/
/
Complexes
[Cu(polyaza)]3þ [Cu(polyaza)]þ References
[Cu(Bzo2[14]aneN4)](ClO4)2
[Cu([14]aneN4)](ClO4)2
[Cu([16]aneN4)](ClO4)2
1.34
1.36
1.40
1.41
1.52
1.53
1.54
1.55
1.55
1.49
1.31
1.32
1.35
1.43
1.42
ꢁ1.09
ꢁ1.07
ꢁ1.05
ꢁ1.04
ꢁ1.08
ꢁ1.07
ꢁ1.06
ꢁ1.03
ꢁ1.03
ꢁ1.11
ꢁ1.14
ꢁ1.07
ꢁ1.10
ꢁ1.03
ꢁ1.01
This study
This study
This study
This study
[39]
[Cu(Bzo2[16]aneN4)](ClO4)2
[Cu(H2Bzo2[14]aneN6)](ClO4)2
[Cu((CH3)2Bzo2[14]aneN6)](ClO4)2
[Cu(Et2Bzo2[14]aneN6)](ClO4)2
[Cu(Bu2Bzo2[14]aneN6)](ClO4)2
[Cu((Allyl)2Bzo2[14]aneN6)](ClO4)2
[Cu((Benzyl)2Bzo2[14]aneN6)](ClO4)2
[Cu((CH3)2Bzo2[14]aneN6)](ClO4)2
[Cu((Et2[14]aneN6)](ClO4)2
[Cu([14]aneN4)](ClO4)2
[39]
[39]
[39]
[39]
[39]
[40]
[40]
[41]
[Cu((CH3)2[16]aneN6)](ClO4)2
[Cu(Et2[16]aneN6)](ClO4)2
[42]
[42]
aMeasured in acetonitrile solutions; 0.1 mol Lꢁ1 (n-Bu)4NClO4 vs. SCE.
bRedox potential of this study and Ref. [38] were measured against a Ag/Agþ (0.1 mol Lꢁ1) reference
electrode and converted to the values measured against the SCE by adding þ0.24 V.
3.3. Catalytic activity
The N4-macrocyclic copper(II) complexes exhibited good activity in oxidation of
ethylbenzene using TBHP (table 2). Blank reactions performed over NaY zeolite under
identical conditions show only negligible conversion, indicating that zeolite host is
inactive for oxidation. Furthermore, TBHP alone is unable to oxidize the substrates in
the absence of any catalyst. Also, no reaction occurred when aqueous hydrogen
peroxide was used in place of TBHP, as the oxidant. In representative tests, zeolite
complex was filtered out and the filtrate was analyzed for copper content using AAS.
The absence of metal ions in solution phase indicates that no leaching of complexes has
occurred during reaction, as they are intact in the pores. These observations suggest
that the oxidations occur due to the catalytic nature of the encapsulated tetraaza
macrocyclic complexes, and no significant role is played by either the zeolite support or
free complexes.
Acetophenone is the major product; o-/p-hydroxyacetophenones and other products,
such as benzaldehyde are also formed in small quantities (table 3). The activity of
Cu(II)–NaY catalyst has also been included in table 3 to compare the effect of the
ligand on the activity of catalyst. Increase of conversion percentage from 31.4% to
50.3% comparing Cu(II)–Y with [Cu(Bzo2[14]aneN4)]2þ–NaY indicates that the ligand
has increased the activity of catalyst by a factor of 1.6. From the results indicated in
tables 2 and 3, it is evident that acetophenone has been formed selectively in the
presence of all catalysts. The trend observed in tables 2 and 3 can be explained by the
donor ability of ligand available in the complex catalysts. The type of the tetraaza
macrocyclic ring and encapsulation affected the activity and product selectivity.
Conversion for copper(II) complexes with different tetraaza dioxo diphenyl macrocyclic

3252
M. Salavati-Niasari and F. Davar
Table 2. Oxidation of ethylbenzene with TBHP catalyzed by copper(II) complexes.a
Selectivity (%)
Conversion
(%)
o-/p-
Hydroxyacetophenone
Other
products
Catalyst
Acetophenone
[Cu([14]aneN4)](ClO4)2
[Cu([16]aneN4)](ClO4)2
58.6
51.7
62.4
41.5
59.7
38.2
47.3
83.4
80.4
89.7
92.3
87.4
80.2
86.2
15.2
17.4
8.3
1.4
2.2
2.0
1.4
1.3
1.2
1.4
[Cu(Bzo2[14]aneN4)](ClO4)2b
[Cu(Bzo2[14]aneN4)](ClO4)2c
[Cu(Bzo2[14]aneN4)](ClO4)2d
[Cu(Bzo2[14]aneN4)](ClO4)2
[Cu(Bzo2[16]aneN4)](ClO4)2
6.3
11.3
18.6
12.4
aReaction conditions: ethylbenzene, 0.105 g (1 mmol); catalyst, 0.004 mmol; 50% TBHP in ethylenedichloride, 0.42 mL;
CH3CN, 1 mL; temperature, 333 K; and time, 10 h.
bCatalyst, 0.002 mmol.
cCatalyst, 0.006 mmol
dCatalyst, 0.008 mmol.
Table 3. Oxidation of ethylbenzene with TBHP catalyzed by HGNM.a
Selectivity (%)
Conversion
(%)
o-/p-
Hydroxyacetophenone
Other
products
Catalyst
Acetophenone
[Cu([14]aneN4)]2þ–NaY
[Cu([16]aneN4)]2þ–NaY
[Cu(Bzo2[14]aneN4)]2þ–NaY
[Cu(Bzo2[14]aneN4)]2þ–NaYb
[Cu(Bzo2[14]aneN4)]2þ–NaYc
[Cu(Bzo2[14]aneN4)]2þ–NaYd
[Cu(Bzo2[16]aneN4)]2þ–NaY
Cu2þ–NaY
46.1
40.2
50.3
49.7
49.1
48.3
36.4
31.4
90.7
93.6
97.3
96.5
96.1
95.0
96.4
62.7
4.9
4.2
2.7
3.5
3.9
5.0
3.6
3.2
4.4
2.2
–
–
–
–
–
34.1
aReaction conditions: ethylbenzene, 0.105 g (1 mmol); catalyst, 0.004 mmol; 50% TBHP in ethylenedichloride,
0.42 mL; CH3CN, 1 mL; temperature, 333 K; and time, 10 h.
bFirst reuse.
cSecond reuse.
dThird reuse.
ligands decreased in the order: Bzo2[14]aneN4 4 [14]aneN4 4 [16]aneN4 4 Bzo2
[16]aneN4 (for ‘‘neat’’ and encapsulated complexes). The encapsulated complexes
exhibited lower activity than the ‘‘neat’’ complexes.
Homogeneous catalysts are prone to deactivation by dimerization of active centers,
which is expected to be reduced by encapsulating them in zeolites. Comparing between
‘‘neat complexes’’ and HGNM as catalysts provides evidence that ‘‘neat complexes’’
gave higher conversion of ethylbenzene than their corresponding HGNM. For
homogeneously catalyzed reactions, the termination of catalytic cycle may occur
because of two factors, formation of Cu–O–Cu species, which has poor catalytic
activity, or due to oxidative degradation of metal complexes. [Cu(Bzo2[14]aneN4)]2þ
–
NaY was recyclable for oxidation of ethylbenzene with TBHP to establish the effect of
encapsulation on stability. The initial run shows a conversion of 50.3% and it is only
marginally reduced to 49.7% on recycling the catalyst. These results indicate that

Zeolite copper catalyst
3253
Table 4. Comparing catalytic activity of encapsulated tetraaza copper(II) complexes between this and other
study.
Selectivity (%)
o-/p-
Hydroxyaceto-
phenone
Conversion
(%)
Other
products
Catalyst
Acetophenone
References
[Cu(Bzo2[14]aneN4)]2þ–NaY
[Cu([H]2–N4)]2þ–NaY
[Cu(cyclen)a]2þ–NaY
50.3
58.2
30.5
27.8
44.4
97.3
96.4
80.2
85.9
98.0
2.7
3.6
4.3
6.3
2.0
–
–
This study
[43]
[45]
15.5
7.8
–
[Cu(Me4cyclen)b]2þ–NaY
[Cu(cyclam)c]2þ–NaY
[45]
[45]
aCyclen, 1,4,7,10-tetraazacyclononane.
bMe4cyclen, 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclodecane.
cCyclam, 1,4,8,11-tetrazacyclotetradecane.
[Cu(Bzo2[14]aneN4)]2þ–NaY complex is more recyclable than the neat complex for
oxidation of ethylbenzene without much loss in activity. Thus, encapsulation of
complexes in zeolites increases the life of the catalyst by reducing dimerization due to
the restriction of internal framework structure. IR spectrum of the recycled sample is
quite similar to that of fresh sample, indicating little changes in the coordination of
Bzo2[14]aneN4 after the oxidation reactions.
The results clearly suggest that [Cu(Bzo2[14]aneN4)]2þ–NaY are efficient catalysts for
the conversion of ethylbenzene to acetophenone with 97.3% selectivity. Comparison of
catalytic activity between encapsulated tetraaza copper(II) complexes in this study and
similar studies is shown in table 4. In 2005, when [Cu([H]2–N4)]2þ–NaY was applied as
a catalyst [43], reaction selectivity for acetophenone as a major product decreases about
1% compared with [Cu(Bzo2[14]aneN4)]2þ–NaY; however, the conversion increases to
about 8%. In other literature [44], when [Cu([H]2–N4)]2þ–NaY and [Cu(Me4cyclen)b]2þ
–
NaY were used as catalysts, selectivity and conversion decreased. In addition, these reactions
contained by-products while there were no other products except acetophenone and
hydroxyacetophenone. Also, [Cu(cyclam)c]2þ–NaY was applied as a catalyst in the literature
and the results showed decreased conversion and increased selectivity. More activity of the
Bzo2[14]aneN4 system arises from the electron-donating ligand which facilitates the electron
transfer rate, a process previously observed by us in other oxidation reactions [45, 46]. All
conversions in this study show a higher selectivity when compared to that obtained using
metal containing porous and nonporous materials.
4. Conclusion
In summary, Cu(II) complexes of 14- and 16-membered tetraaza macrocyclic complexes
have been encapsulated in the nanopores of zeolite-Y. The neat and encapsulated
copper complexes of 14- and 16-membered tetraaza dioxo diphenyl macrocycles within
the nanopores of zeolite-Y exhibited good catalytic activity in the oxidation of
ethylbenzene, using TBHP as an oxidant. The results clearly suggest that
[Cu(Bzo2[14]aneN4)]2þ–NaY is efficient for conversion of ethylbenzene to acetophe-
none with 97.3% selectivity. The encapsulated complexes exhibit enhanced stability and

3254
M. Salavati-Niasari and F. Davar
selectivity in the oxidation reaction. These encapsulated systems offer structural
integrity by having a uniform distribution of the metal complex in the pore structure of
the support. The zeolite framework keeps the guest complexes dispersed and prevents
their dimerization, leading to retention of catalytic activity. Future research on this
system is expected to explore its industrial applications for partial oxidation reactions.
Acknowledgment
The author is grateful to the Council of University of Kashan for providing financial
support to undertake this research.
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