Hybrid organic-inorganic Cu(II) iminoisonicotine@TiO2@Fe3O4 heterostructure as efficient catalyst for cross-couplings

PROFESSOR MOHAMED SHAKER S. ADAM (Orcid ID : 0000-0001-8826-3558)

Article type : Article

Hybrid organic-inorganic Cu(II) iminoisonicotine@TiO @Fe O heterostructure as

2

3

4

efficient catalyst for cross-couplings

1

,2

3

4,5

Mohamed Shaker S. Adam * | Farman Ullah | Mohamed M. Makhlouf *

1

Department of Chemistry, College of Science, King Faisal University, P.O. Box 380 Al Hofuf 31982 Al Ahsa, Saudi

Arabia.

2

Chemistry Department, Faculty of Science, Sohag University, Sohag-82534, Egypt.

3

Department of Chemistry, Winnipeg University 515 Portage Avenue, Winnipeg, Manitoba, R3B 2E9 Canada.

4

Department of Sciences and Technology, Rania University College, Taif University, Rania 12975, Saudi Arabia.

5

Department of Physics, Damietta Cancer Institute, Damietta, 34517, Egypt.

*

Correspondence

E-mail:

madam@kfu.edu.sa;

shakeradam61@yahoo.com

(M.S.S.

Adam)

and

m_makhlof@hotmail.com (M.M. Makhlouf)

Abstract

Two novel mononuclear copper (II) complex catalysts were synthesized from a new tridentate

iminoisonicotine ligand (HL) by coordination with Cu(II) ion, with (CuL@TiO @Fe O ) and

2

3

4

without (CuL) immobilization on TiO coated nanoparticles of Fe O . The ester moiety on the

2

3

4

back of the ligand was utilized for immobilization on nanoparticles of Fe O . Both ligand and CuL

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4

complex were fully characterized by alternative spectral techniques (nuclear magnetic resonance,

infrared, ultraviolet-visible and mass spectroscopy, and elemental analyses). Different analytical

techniques were used to identify the structural feature and morphology of the immobilized copper

catalyst (CuL@TiO @Fe O ) core-shell-shell system. The structural analysis revealed that the

2

3

4

This article has been accepted for publication and undergone full peer review but has not been

through the copyediting, typesetting, pagination and proofreading process, which may lead to

differences between this version and the Version of Record. Please cite this article as doi:

1

0.1111/JACE.17098

catalyst system is composed of both agglomerated nanospheres and deformed nanorods. Both

copper catalysts, immobilized CuL@TiO @Fe O and un-immobilized CuL were studied in

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4

heterogeneous and homogeneous catalysis, respectively, for Suzuki-Miyaura (C―C) and

Buchwald-Hartwig (C―N) cross-coupling reactions of various heteroaryl halides. Both catalysts

showed good catalytic potential under the controlled optimal reaction conditions. In contrast to the

homogeneous catalyst (CuL), the heterogeneous catalyst (CuL@TiO @Fe O ) showed slightly

2

3

4

better catalytic performance. The characteristic obtains supported the catalytic potential of the

current samples. Reusability/recycling of both catalysts was also investigated in C―C cross-

coupling reactions. It was found that the homogeneous catalyst (CuL) could be only recycled up to

3

times, whereas the heterogeneous one (CuL@TiO @Fe O ) could be reused up to 7 times with

2 3 4

good efficiency.

1

| INTRODUCTION

Enormous organic syntheses catalyzed by metals, as homogeneous metal-chelates¹or

heterogeneous metal-oxides,²^,³are extensively developed, which are pivotal in the industrial

4

application. The vast catalytic applications of various metal species, as metal ion chelates, are

5

limited only to the homogeneous phase, with coagulating features and non-recyclability. The

immobilized metal nanoparticles on the surface of supporting material are a spectacular way to

enhance their catalytic sufficiency and reactivity. Moreover, the metal species agglomeration in

the homogeneous phase could be reduced with alternative immobilization processes that could

also increase their recyclability power in the catalytic systems. In most of the electrocatalysis⁶^-⁸

and cross-coupling reactions, the immobilized copper nanoparticles, as complexes, are of strong

interest than the other high-cost transition metal nanoparticles, e.g. palladium and platinum.

Consequently, there are many published works regarding various applications, of copper

9

-16

nanoparticles in catalysis, supported on SiO coated Fe O nanoparticles.

2

3

C ―C and C ―N cross-coupling reactions are a facile approach to synthesize biaryls

sp2

1

7

molecular collection, which are highly valuable as intermediates for materials manufacturers in

pharmaceutical and biochemical industries.¹⁸Many comprehensive studies reported various

approaches to synthesize biaryl molecular collections from heteroaryl bromides and chlorides via

C―C and C―N bond formation reaction utilizing various transition metal complexes as catalysts

homogeneously or heterogeneously supported on various supporting reagent. The most well-

known supporting materials are Fe O nano-particles and Fe O nano-particles coated by SiO ,

3

4

3

4

2

whereas Fe O nanoparticles coated by TiO are not enough studied for such cross-coupling

3

4

2

reactions, however, it is well documented that TiO coated Fe O nano-spindles could be used for

2

3

different proposes.¹⁹^,²⁰Indeed, titanium dioxide as an important example of viable support, like

SiO , ZrO and ZnO, which has gained much importance with specific characteristics such as cost-

2

effectiveness, nontoxicity, good biological applicability and easy preparation.²¹^,²²The TiO₂

2

1,22

modified Fe O nano-spindles are well documented for various applicable proposes,

e.g. in

2

3

photochemistry and photocatalysis.²³^-³⁰

Substituted imines (―CH=N―), are considered as the most active chelating ligands with many

transition metal ions at different oxidation states giving high stable metal pincer chelates.³¹^,³²

Copper (II)-imine complexes have appeared as flourished structures due to their widespread

activities against a variety of targets,³³including high corrosion inhibition,³⁴^,³⁵photosynthetic

inhibition,³⁶DNA/RNA binding cleavage³⁷^,³⁸and antioxidants.³⁹Copper as a cheap 3d group

element has alternative oxidation states and unequaled features in tuning the Cu nanoparticles

size.⁴⁰^,⁴¹The electrochemical features of Cu(II)-chelates for the Cu(II)/Cu(I) the electron transfer

4

2

couple realized that many Cu(II)-complexes were applied as homogeneous and heterogeneous

catalysts in alternative catalytic processes.⁴³^-⁴⁸Vast and enormous applicability of metal-imine

framework complexes are explored in wide areas, e.g. in the bio- and pharmaceutical industry,⁴⁹^-⁵²

sensors,⁵³organic photovoltaics⁵⁴and in catalysis.⁵⁵^-⁵⁸C―C, C―S, C―O and C―N cross-

coupling reactions in various organic syntheses are achieved by using imine complexes as

5

9

catalysts. To emphasize the organocatalysts immobilization on coated Fe O could be enhanced

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4

6

0

with functional active reagents, as a linker, e.g. CPTMS (3-chloroopropyltrimethoxysilane) or

APTES (3-aminopropyltriethoxysilane).⁶¹^,⁶²To save cost and reduce the number of synthetic steps

for such immobilized metal complexes on Fe O -NPs, significant functional groups in the

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4

backbone of the coordinated ligands to the central metal ion of the catalyst could interact with

Fe O -TiO nanoparticles to be immobilized through those groups, e.g. ―OH (hydroxyl

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4

2

group)⁶³^,⁶⁴and ―OR (alkoxy group).⁶⁵^,⁶⁶The presence of such groups in the coordinated ligand

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7

could considerably support metal complexes on Fe O and/or TiO .

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4

2

Building on those efforts, it is a motivation to design and synthesize novel copper (II) imine

complex as a homogeneous (CuL) and heterogeneous (CuL@TiO @Fe O ) catalysts for C―C

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4

and C―N cross-coupling systems. The ester moiety on the back of ligand could be a benefit for

immobilization on Fe O nanoparticles coated by TiO . A comparative study on the catalytic

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4

2

potential of these two Cu(II)-catalysts was examined under various reaction conditions.

Additionally, the limit of the reusability of both catalysts was also examined.

2

| EXPERIMENTAL

.1 | Materials and physical measurements

Starting materials, reagents and solvents used in this study are commercially available. The

supplementary materials include a subsection listing of all chemicals, purchase companies, purity

grades and their melting or boiling points (Table S1). Elemental analyses of the samples were

measured by GMBH varioEI model V2.3 of the CHN machine at room temperature. Nuclear

magnetic resonating spectroscopy was measured by Bruker ARX400 as FT-NMR multinuclear

spectrometric machine at 25 °C using 400.1 MHz for hydrogen nuclei and 100.6 MHz for carbon

nuclei. Melting point and the decomposition temperatures of the prepared copper chelating

complex and its coordinated ligand were estimated using a Gallenkamp (Sanyo) machine.

Magnetic features of the studied copper complex were evaluated on magnetic susceptibility

balance (Sherwood Scientific, Cambridge, UK). The IR spectra of the prepared samples were

measured with an FT-IR spectrophotometer (Agilent Technologies Cary 630 FT-IR

spectrophotometer). IR spectra were measured at room temperature over solid samples in 4000-

-1

4

00 cm . Electronic transition spectra of the coordinated ligand and its corresponded Cu-complex

were measured in UV-1800 SHIMADZU UV-spectrophotometer within a 10 mm matched quartz

cell. Moreover, data were determined in λ_m_a_x(nm) in the region 190-800 nm using an aqueous

solution at room temperature. Moreover, mass spectroscopy of CuL was recorded in m/z using

waters Qtof Micro YA263 mass spectrometer at room temperature.

2

.2 | Synthesis

.2.1 Synthesis of (E)-ethyl-2-((2-methoxyethylimino)methyl)isonicotinate (HL)

Ligand (HL) was prepared according to the general Schiff base preparing procedure: ethyl 2-

formylisonicotinate (1.30 g, 7.26 mmol) was treated with 2-methoxyethanamine (0.653 g, 8.72

mmol) in toluene (15 mL) provided orange red gummy solid of HL (Yield = 1.35g with 0.03 g

error, 92%), Scheme 1.

1

H NMR (400.6 MHz, CDCl ): δ = 8.72 (d, J = 3.6 Hz, 1H), 8.46 (s, 1H), 8.42 (s, 1H), 7.83 (m,

3

2

1

H), 4.40 (q, J = 7.2, J = 14.4 Hz, 2H), 3.85 (t, J = 5-1 Hz, 2H), 3.71 (t, J = 5-1, 2H), 3.33 (s,

H), 1.38 ppm (t, J = 6.9Hz, 3H).

3

1

3

C NMR (100.1 MHz, CDCl ): δ = 164.80, 162.75, 155.39, 150.1, 138.45, 123.76, 120.71, 71.78,

3

6

1.85, 60.85, 58.83 and 14.20 ppm.

-1

FT-IR (KBr taplet, 휈, cm ): 3066 (C―H_a_r_o_m_a_t_i_c), 2919 (C―H_a_l_i_p_h_a_t_i_c), 1718 (C=O), 1682

-1

(

CH=N_S_c_h_i_f_f_b_a_s_e), 1625 (CH=N_p_y_r_i_d_i_n_e), 1344 (C―O), 1208 (C―O_c_a_r_b_o_x_l_a_t_e) and 1110 cm (C―N).

2

.2.2 | Synthesis of Cu(II)-complex (CuL)

Copper chloride dihydrate (0.17 g, 1.0 mmol, in 10 mL water) was added dropwise to a

methanolic solution of ligand (HL) (0.22 g, 1.0 mmol, in 10 mL methanol) at room temperature.

The reaction mixture was heated at 80 °C for 1 h. The colour of the reaction mixture was slowly

changed to dark green with the formation of precipitate upon cooling down to room temperature.

The crude product of the complex was collected by filtration. The complex was purified by

recrystallization in hot methanol awarding 77% (0.26 g with 0.04 g error) of CuL, Scheme 2.

-1

FT-IR (KBr taplet, 휈, cm ): 3056 (C―H_a_r_o_m_a_t_i_c), 2925 (C―H_a_l_i_p_h_a_t_i_c), 1724 (C=O), 1611

(

CH=N_S_c_h_i_f_f_b_a_s_e), 1559 (CH=N_p_y_r_i_d_i_n_e), 1282 (C―O), 1211 (C―O_c_a_r_b_o_x_l_a_t_e), 1111 and 1017 cm^-¹

-1

(

C―N), 687 (Cu―O), 463 and 439 cm (Cu―N).

2

.2.3 | Synthesis of Fe O

3 4

2

5,26,68

The nanoparticles of Fe O were prepared according to the reported method

by mixing

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4

FeCl .4H O with FeCl .6H O in a ratio of 2 : 1, respectively, in a mixture of water (98 mL) and

2

3

2

EtOH (2 mL) in a Schlenk line. The mixed contents were kept with stirring for about a half-hour,

then 20 mL of an aqueous NaOH (2.0 N) was added dropwisely to get a pH of the solution about

1

0–12. The reaction mixture was turned to dark brown colour upon pH 10-12. Then 0.3 mol of an

aqueous solution of urea was slowly added to the reaction mixture, followed by stirring for 5 h at

room temperature. The resulted mixture was kept for 30 min at 70 °C and then slowly cooled

down to 25 °C. The mixture was centrifuged for a few minutes as a result of black precipitate. The

black precipitate was collected by filtration and washed with H O and ethanol multiple times until

2

pH became ≈ 7. The final nanoparticles of Fe O were collected and dried in an oven at 40 °C for

3

4

3

h.

2

.2.4 | Synthesis of TiO @Fe O

4

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3

2

5,26,68

The preparation of TiO @Fe O was carried out according to the reported method.

A solid

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Fe O (0.05 g) was kept in a sonicated both in 20 mL of ethanol. In another beaker, 0.2 g of CTAB

3

4

was dissolved in 15 mL of an aqueous media. The CTAB solution was added dropwisely to the

suspended ethanolic solution of Fe O . After that TiO (0.05 g) in isopropanol (8 mL) was added

3

4

2

to the previous solution. The resulted reaction mixture was treated by ammonia until the pH of the

reaction mixture was between 8 to 9 to afford a white gel. The final reaction mixture was stirred

magnetically for almost 24 h at the ambient temperature to give a well uniform dispersed

precipitate. The fine precipitate was extracted by filtration washed within water and ethanol. The

final precipitate was dried in an oven at 60 °C awarding nanoparticles of paramagnetic

TiO @Fe O .

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3

4

2

.2.5 | Immobilization of HL on Fe O @TiO

3 4 2

The solid-supported ligand (HL@TiO @Fe O ) was prepared by mixing a solution of ligand (HL)

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4

1

.0 g in acetonitrile (20 mL) to a suspension of TiO @Fe O in acetonitrile (20 mL), and then the

2 3 4

mixture was stirred for 12 h at room temperature. The colour of the suspension of TiO @Fe O

4

2

3

was changed from dark-gray to dark brown. The final product was collected by filtration, washed

with acetonitrile and then dried in an oven at 50 °C for 12 hours.

2

+

2

.2.6 | Supporting of Cu ions on HL@TiO @Fe O

2 3 4

HL@TiO @Fe O (0.5 g) was suspended in acetonitrile (25 mL) and sonicated for 30 min. The

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3

4

sonication process was carried out with an ultrasonic bath (Elmasonic S150 - TEVOTECH) using

ultrasound waves with frequencies of ~ 20 kHz. During sonication, the solution keeps on ice to

stop heating up and degrading of the sample. Then, 0.5 g of copper chloride dihydrate in

acetonitrile (15 mL) was added dropwise to the resulted suspended of HL@TiO @Fe O . The

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3

4

colour of the suspended HL@TiO @Fe O was slowly changed from dark brown to dark green,

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3

4

which was left on stirring for 24 h at room temperature. The final product was collected by

filtration, washed few times with acetonitrile and water then s dried in an oven at 50 °C for 12 h.

2

.3 | Characterization of CuL@TiO @Fe O nanoparticles

2 3 4

Fe O -nanoparticles, which coated by TiO and CuL@TiO , were characterized by FT-IR spectra

3

4

2

and with a VSM-9600 LDJ vibrating sample magnetometer with a 1T magnet. The phase

morphology of the materials was investigated by XRD using a Brucker Axs-D8 Advance-

diffractometer with Cu–K radiation at 0.154178 nm within a range of 2θ from 10.0 to 90.0 in a

a

continual scan type. The elemental composition of the surface morphology of the TiO and

2

CuL@TiO coated Fe O -nanoparticles were measured by SEM, Model JEOL JSM 5410 machine

2

3

4

using FE-SEM and with EDS (FE-SEM/EDS-Germany) detector (at 15 kV). TEM analyses

Transmission electron microscope machine-model: Jeol-1230) was applied with an acceleration

voltage (200 kV) to evaluate the size of Fe O -nanoparticles, TiO @Fe O and

(

3

4

2

3

4

CuL@TiO @Fe O . The suspended material sizes in an aqueous media were measured with Cilas

2

3

4

dual scattering particle size analyzer Nano DS. The Brunauer-Emmett-Teller (BET) specific

surface area of the new nanoparticles of CuL@TiO @Fe O was evaluated by nitrogen gas

2

3

4

adsorption isotherms at 77.38 K within relative pressures range from 0.05 to 0.30 atm.

Micrometrics ASAP2010 as a volumetric adsorption apparatus was used for the adsorption

isotherm studies. Nanoparticles of CuL@TiO @Fe O were investigated under degassed

2

3

4

conditions at 40 °C for 20 h.

2

.4 | Catalytic procedures

.4.1 | C―C and C―N cross-coupling reaction

Homogeneous and heterogeneous cross-coupling reactions of Suzuki-Miyaura or Buchwald-

Hartwig amination reactions were carried out in two-necked 50 mL round bottom flask with water

circulation condenser. Loaded with phenylboronic acid (1.1 mmol) in 10 mL solvent (toluene,

chloroform, ethanol, water and water-ethanol mixture), Cu(II)-complex (CuL, homogeneously,

0

.01, 0.02, 0.05 and 0.1 mmol) or CuL@TiO @Fe O (heterogeneously, 0.05, 0.1 or 0.2 and 0.5

2 3 4

g), and base 2.0 mmol (K CO , tBuOK, K PO and KOH). The reaction was initiated by the

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4

addition of aryl halide (1.0 mmol) under the aerobic condition and the mixture was stirred under

reflux conditions at 100 °C for given reaction time.

The progress of the reaction was monitored by Shimadzu Gas Chromatography mass spectrometer

(GC-MS model QP2010 SE, Rxi-5 Sil MS capillary column (30 m length × 0.25 mm ID × 025

um film thickness). The sample was injected into the GC-MS at room temperature. The initial

oven temperature was 40 °C and hold for 1 min. The temperature rate was increased with 10 °C

min⁻¹up to 200 °C. The carrier gas was Helium with high purity up to 99.999%, which was

applied with a flow rate of 1 mL/min. Lab solution software was used to analyze the percentages

yields of the obtained products.

2

.5 | Reusability of CuL homogeneously and heterogeneously

The recycling of homogeneous catalyst (CuL) at 0.02 mmol scale and heterogeneous catalyst

CuL@TiO @Fe O ) at 0.05 g scale were investigated in C―C coupling reaction using optimized

(

2

3

4

reaction condition (phenylboronic acid, 1.1 mmol, 2-pyridyl bromide, 1.0 mmol, K CO , 3.0

2

3

mmol, and toluene 10 mL, at 100 °C). The catalyst from homogeneous catalysis (CuL) was

simply collected by filtration after cooling down to the room temperature and re-subjected in

catalysis under the same reaction condition. While the heterogeneous catalyst

(

CuL@TiO @Fe O ) was collected by a magnet from the reaction mixture, washed with toluene,

2 3 4

dried in an oven and then re-subjected in the next trill under the same reaction condition.

3

| RESULTS AND DISCUSSION

.1 | Synthesis and characterization of ligand (HL) and copper complex (CuL)

The novel neutral tridentate pincer ligand (HL) was prepared by using Schiff base general

procedure from ethyl 2-formylisonicotinate and 2-methoxyethanamine in toluene provided HL in

good yield (92%). The copper complex (CuL) was synthesized by the treatment of HL with

CuCl .2H O in methanol under mild condition afforded CuL in good yield (77%) (Scheme 1). The

2

+

complex was obtained by coordination of ligand with Cu metal ion in a 1 : 1 molar ratio. Both

HL and its corresponding Cu-chelate were characterized by various spectral techniques including

¹H-NMR, ¹³C-NMR, infrared, electronic and mass spectra, CHN analysis and magnetic

susceptibilities. CuL was found to be highly stable in the air as a solid and in liquid phases. The

thermal stability of CuL was tested at a high temperature (211 °C). No decomposition was

observed, which showed very high thermal stability. Both ligand (HL) and complex (CuL) were

highly soluble in polar organic solvents e.g. methanol, ethanol and acetonitrile. Low solubility was

observed in less polar solvents (CHCl , CH Cl and benzene), whereas, DMF and DMSO showed

3

2

fair solubility. Various attempts were made to crystallize the complex to get a single-crystal for X-

ray analyses but no luck so far. The C, H, N-elemental analysis data for HL and its Cu-chelate are

documented in Table 1. The measured values are agreed with the calculated values of their

tentative structures, with the slight acceptable differences (about ± 0.4 %) referring to the high

purity of ligand (HL) and complex (CuL). The magnetic features of CuL showed that CuL is

9

paramagnetic with a magnitude 2.77 B.M. confirming that copper ion is divalent with d electronic

1

13

configuration. H NMR and C NMR spectra of HL are presented in Figs. S1 and S2.

O

Cl

O

N

Cu

Cl

N

CuCl2.2H2O

MeOH

N

O

OEt

O

OEt

CuL

HL

Scheme

1.

Synthesis

of

Cu(II)-complex

(CuL)

from

(E)-ethyl-2-((2-

methoxyethylimino)methyl)isonicotinate (HL)

1

In H-NMR spectra (Fig. S1), the HL showed a characteristic peak for —CH=N— proton which

appeared at 8.72 ppm as a doubled. The other three signals in the aromatic region belong to the

pyridine ring appeared at 8.46, 8.42 and 7.83 ppm. Two protons signals appeared at 4.38 and 3.85

ppm with two proton integration each, belong to the neighbors ―CH ― of —CH=N— group. A

2

signal at 3.33 ppm with the integration of three protons belongs to the methoxy group. The ethyl

ester protons showed signals at 3.71 and 1.38 ppm for the ―CH ― and ―CH protons,

2

3

1

3

respectively. The most distinguished signal in C NMR spectra is at 164.80 ppm, which assigned

to —CH=N— group (Fig. S2, in the supplementary materials).

FT-IR absorption frequencies of the ligand (HL) were measured for comparison with complex

upon coordination. The ligand Schiff base group (—CH=N—), which showed the IR spectral band

-1

at 1682 cm was strongly shifted to 1611 cm in the complex (CuL) due to nitrogen lone pair

2

+

coordination to Cu ion. The second distinguished vibrational band of the ―CH=N― group of

-1

the pyridine ring was also shifted from 1625 to 1559 cm upon coordination of pyridine nitrogen

6

9

to the central metal ion. Moreover, the C―O vibrational band of the coordinated methoxy group

-1

was also strongly shifted from 1344 cm to low frequencies region 1282 cm , as shown in

-1

Scheme 2. Importantly, there were a number of new weak bands observed at 687 and 439 cm ,

which considered for the vibrational spectra of the coordination bonds Cu—O and Cu—N,

respectively.⁷⁰

O

Cl

Cu

O

N

O

Cl

O

N

CuCl .2H O

TiO2

2

TiO2

Fe O

TiO2

3

4

MeOH

TiO2

O

OEt

TiO2

TiO @Fe O

TiO2

2

3

4

Fe O

3

4

TiO2

Fe O

TiO2

Fe O

HL

3

4

TiO2

Fe O

TiO2

3

TiO2

HL@TiO @Fe O

4

2

3

CuL@TiO @Fe O

4

2

3

Scheme 2. The absorbed progressed steps of Cu-complex (CuL) on the Fe O @TiO .

3

4

2

The electronic transitions of HL and CuL were investigated in methanolic solution at room

temperature with the assignment of their maximum absorption wavelength (λ_m_a_x) and molar

absorptivity, which summarized in Table 1 and presented in Fig. 1. In the UV-region, HL

displayed one specific high-energy band for π→π* and/or n→π* transitions in the molecule at 321

nm. Furthermore, an additional electronic absorption band at 334 nm, which interpreted the

electronic ligand charge transition.⁷¹Considerably, the coordination bonding between HL and

2

+

Cu ion caused newly observable shifts of the π→π* and/or n→π* characteristic bands of the

ligand. Particularly, that transition was shifted to lower energy magnitudes at 301 nm for CuL.

2

+

Indeed, the ligand charge transfer band was disappeared after complexation with Cu ion with the

presence of a novelty band in the visible region due to the d→d transition, which appeared at 647

nm (Fig. 1).

The mass spectra of HL and CuL were measured in methanolic media. The mass spectroscopic

results are shown in Fig. S3 and S4. Mass spectra of HL presented distinguished peaks at 236.9,

2

58.9, 265.9 and 291.1 (high intense) m/z confirming the molecular structure of the ligand. CuL

established two mass peaks one at 368.6 and the other was 369.9 m/z for the molecular mass of the

complex and a high intense base peak at 299.2 m/z for the complex molecular mass without the

two chloride ions [M – 2 Cl^-].

3

.2

|

Structural formation and characterization of Fe O , TiO @Fe O and

3 4 2 3 4

CuL@TiO @Fe O nanoparticles

2

3

4

CuL was immobilized on Fe O -NPs coated by TiO within the ethoxy group, as reported

3

4

2

3

2

previously. Sadeghzadeh et al. reported that manganese (II) complex of imine complex has been

supported on Fe O -NPs within the ethoxy moiety as an effective heterogeneous catalyst for

3

4

benzopyranopyrimidines syntheses.⁷²Also, Eftekhari-Sis et al. synthesized immobilized

Oxoperoxo tungsten (VI) Schiff base complex within the ethoxy moiety, as a catalyst for alcohol

7

3

oxidation. The significant FT-IR spectral bands for CuL and its support on TiO @Fe O are

2

3

4

-1

assigned in Fig. 2. A significant vibrational band at 550 cm was remarked for the free Fe O pure

3

4

7

4

magnetic nanoparticles for the Fe—O bond. Water molecules exhibited characteristic bands at

-1

3

177 and 1617 cm for the O—H group in Fe O (Fig. 2a) and also at 3196 and 1635 cm for

3 4

7

0,75

TiO @Fe O (Fig. 2b).

The stretching band of the Fe—O bond was lower shifted due to the

2

3

4

-1

coating of TiO to appear at 485 cm . Particularly, other distinguished bands at 2117 and 1345

2

-1

cm for Fe O and at 2919 to 2850 cm for TiO @Fe O were characterized for the N≡C―O

3

4

2

3

4

7

6

bonding of urea which used as a chelating agent in preparing process of Fe O . The presence of

3

4

-1

77

new vibrational bands at 718 and 555 cm were characteristic for the Ti—O—Ti bonding mode.

The specific stretching bands of un-supported free CuL, which displayed at 1724 and 1282 cm^-¹

for the C=O and C―O bonds, respectively, were little influenced by the immobilization on

-1

TiO @Fe O nanoparticles to appear at 1735 and 1291 cm (Figs. 2c,d). A high remarkable

2

3

4

-1

disappearance of the aliphatic C―H band at 2925 and the C―O band at 1211 cm could be

proven for the Cu-complex immobilization on TiO @Fe O with lose of ethyl group of the para-

2

3

4

ethyl ester group, as detected previously.⁷⁷Indeed, the intensity of the absorption bands of

-1

―

CH=N― Schiff base, ―CH=N― pyridine and CH―N groups at 1611, 1559 and 1111 cm ,

respectively, were reduced from moderate and strong bands in the free CuL to be weak bands after

7

8

its supporting on TiO @Fe O (Fig. 2d). Moreover, the Ti—O—Ti bonding mode assigned

2

3

4

-1

vibrational stretching bands at 725 and 523 cm , which also small influenced by the insertion of

high magnetic particles of Fe O and CuL, as shown in Scheme 2.

3

4

The energy-dispersive X-ray spectroscopy analysis (EDS) was applied to investigate the chemical

composition of the prepared material in addition to the degree of its purity. Fig. 3 presents the

obtained EDS spectra of prepared Fe O , TiO @Fe O and CuL@TiO @Fe O samples. Figure

3

4

2

3

4

2

3

4

3

a reveals high contents of Fe and O ions which reflect the high purity of the prepared Fe O

3

4

sample. Figure 3b exhibits high peaks attributed to the presence of Ti in the shell of the Fe O

3

nanoparticles core. However, there are some small signal peaks of Fe ions were detected as a

consequence of an irregular coating of TiO @Fe O . Likewise, it was seen that there are clear

2

3

4

peaks located at well-defined positions attributed to Fe, O, Ti, C, N and Cu atoms as shown in Fig.

c. This could be a shred of evidence for the presence of all mentioned elements in the structural

formation of the CuL@TiO @Fe O prepared sample.

3

2

3

4

The surface morphology of Fe O , TiO @Fe O and CuL@TiO @Fe O samples were analyzed

3

4

2

3

4

2

3

4

using FE-SEM and HR-TEM techniques. The FE-SEM images represented in Figs. 3a-c show the

surface morphology of the target samples. Figure 3a exhibited Fe O composed of a uniform

3

4

nanoparticles-like spherical structure. While the image of Fig. 3b revealed the surface morphology

of Fe O nanospheres after coated by TiO . This coated layer of TiO causes the accumulation of

3

4

2

nanospheres of Fe O forming the bigger ones, which lead to an increase in the degree of the

3

4

crystalline nature of the TiO @Fe O samples. Figure 3c displayed the surface of the morphology

2

3

4

of Fe O after coated by both of TiO and CuL complex to form heterostructure of

3

4

2

CuL@TiO @Fe O . It could be observed that the structure of the sample is composed of both

2

3

4

agglomerated nanospheres and deformed nanorods. Irregular agglomeration of TiO @Fe O

4

2

3

nanoparticles was cross-linked with deformed nanorods shaped structures of CuL organic

framework. This imperfection of structure compared to the structure of Fe O nanoparticle was

3

4

considerably due to the changes in the atomic coordination, dangling bonds and lattice disorder,

7

9

which resulted from coated layers of TiO and CuL.

2

Figs. 4 represent the HR-TEM micrographs of Fe O , TiO @Fe O and CuL@TiO @Fe O

4

3

4

2

3

4

2

3

samples. These images supported the result obtained from FE-SEM images. A seen in Fig. 4a, a

uniform nanospheres shaped structure of Fe O was formed, whereas Fig. 4b shows nanoclusters

3

4

of Fe O nanoparticles coated by TiO form core-shell of TiO @Fe O . The amorphous shell of

3

4

2

3

4

TiO covered Fe O nanoparticles reduced the degree of crystallization of Fe O and enhanced

2

3

4

3

4

disorders, defects and porosity of its surface morphology, which has improved the degree of

adsorption capacity. Figure 4c revealed Fe O coated by two layers of TiO and CuL complex.

3

4

2

The structure morphology of the heterostructure CuL@TiO @Fe O formed an irregular shape of

2

3

4

texture composed of aggregates of clusters of TiO @Fe O cross-linked with deformed nanorods

2

3

4

of CuL complex.

An X-ray diffraction (XRD) analysis of Fe O nanoparticles, TiO @Fe O and

3

4

2

3

4

CuL@TiO @Fe O samples are depicted in Figs. 5. As shown in Fig. 5a, the multiple diffraction

2

3

4

8

0

peaks indicated the observed planes of Fe O . With the aid the standard JCPDS database of

3

4

8

1

Fe O (JCPDS, card No. 75-1609), the peaks locate at 2θ of 20.5°, 35.4°, 37.2° and 57.1°

3

4

preferred orientations planes at (1 1 1), (3 1 1) and (5 1 1), respectively.

Figure 5b exhibits the XRD pattern of Fe O after coated by TiO (TiO @Fe O ), which existed

3

4

2

3

4

in anatase crystallographic phase and presented many peaks referring to the different planes. The

o

peaks at 2θ of 20.5 , and 37.2 , with preferred orientations planes at (1 1 1) and (3 1 1),

respectively, were related to Fe O cores, which confirmed its magnetite phase. Whereas, the

3

4

o

peaks at 2θ of 24.3 , 26.9.2 and 36.9 with preferred orientations planes at (1 0 1), (1 1 0) and (0 0

8

1

4

), respectively, were attributed to the TiO shell. Figure 5c shows the XRD pattern of Fe O

2 3 4

after coated by a double layer of TiO and Cu(II)-complex (CuL@TiO @Fe O ). The XRD

2

3

4

spectrum of the sample revealed more multiple new peaks related to the CuL coated shell. This

could assign that Fe O cores are coated completely with externally two shells of TiO and CuL.

3

4

2

The present result of XRD analysis exhibited well agreement with that of FE-SEM and HR-TEM

micrographs.

Figure 6 presents the applied magnetic field dependence of the magnetization characteristics (M–

H curves) at 25 °C for Fe O purely nanoparticles, TiO @Fe O and CuL@TiO @Fe O samples.

3

4

2

3

4

2

3

4

It could be seen that there was no hysteresis loops are detected. Hence, the remnants

magnetization and coercivity were absent for those samples leading to the superparamagnetic

behavior. The saturation magnetization of Fe O nanoparticles was about 60 emu/g, which could

3

4

be much greater than those of the TiO @Fe O (40 emu/g) and CuL@TiO @Fe O (22 emu/g).

2

3

4

2

3

4

The stable ferrite phase in the presence of the Fe O layer revealed the superparamagnetic

3

4

properties of Fe O -NPs. However, the reduction in magnetization values of Fe O @TiO was

3

4

3

4

2

most likely attributed to the nonmagnetic shell of TiO coated cores of the magnetic Fe O

4

2

3

nanoparticles. Further reduction in the magnetization of CuL@TiO @Fe O was remarked since

2

3

4

the presence of an additional shell of nonmagnetic species of CuL complex coated TiO @Fe O

2

3

4

8

2

sample rapidly decreased its magnetic properties compared to Fe O and TiO @Fe O samples.

3

4

2

3

4

TGA of CuL and CuL@TiO @Fe O depicts two different degradation steps, as shown in Fig. 7.

2

3

4

CuL presented distinguished three degrading steps, whereas, CuL@TiO @Fe O did not show any

2

3

4

characteristic decomposition steps. The loss within 180–200 °C was probably due to the loss of

2

,3

moisture and CO in the Cu-complex with 9.1%. The second weight loss was found in the region

2

from 250–300 °C gradually presumed to the degradation of the organic moiety in CuL with

8

3

1.2%. The weight loss in the third stage was observed at the range 300 to 320 with gradual

degradation and with a loss percentage of 39.9%. Comparatively, the supported CuL on the

surface of TiO @Fe O showed high thermal stability compared to the free CuL. This result could

2

3

4

propose that CuL@TiO @Fe O is highly stable and could be utilized as a heterogeneous catalyst

2

3

4

up to 340 °C without any observable degradation.

The Brunauer-Emmett-Teller (BET) method is a widely applicable tool to characterize the pore

structure and the physical and chemical adsorption of gas molecules on the specific surface area of

materials. Figure

8

reveals the characteristic adsorption-desorption isotherms of

CuL@TiO @Fe O core-shells, which taken for N at 77.4 K. Based on BET classifications, the

2

3

4

2

isotherm curve of the core-shells sample exhibited a type IV profile with an H3-type hysteresis

loop, which reflected the mesoporous nature for CuL@TiO @Fe O sample. The adsorption-

2

3

4

desorption isotherm curve revealed an evident hysteresis loop at the relative pressure (P/P ) >

o

0

.34, which was a characteristic porous material. Whereas, the adsorption and desorption curves

almost coincided under the low value of P/P ≤ 0.34. This process was associated with capillary

o

condensation in mesopores. According to the IUPAC classifications, the pores within porous

materials could be classified into micropores (< 2nm), mesopores (2 – 50 nm) and macropores (>

5

0 nm). The average pore radius for CuL@TiO @Fe O sample was found to be 2.12 nm, which

2 3 4

reflected the mesopores nature. Additionally, the total pore volume was also estimated to be 0.043

cc/g. Therefore, it well-known that the Fe O powder had negligible N -adsorption and it was

3

4

2

8

4

called a non-porous material. The porosity of CuL@TiO @Fe O core-shells enhanced and thus

2

3

4

leading to the significantly improved its adsorption capacity.

Furthermore, the BET specific surface of the sample can be estimated via the well-known BET

equation as the following Eq. 1⁸⁵^,⁸⁶

:

1

푐 ― 1 푃

1

= _푣_푚_푐( )

+

(1)

푃

푃표

푣푚푐

푣₍

) ^―¹

푃

표

where, P and P are equilibrium and saturation pressure of adsorbents, respectively, v is the

o

adsorbed gas quantity and v is the monolayer adsorbed gas quantity and c is the BET constant.

m

Eq. 1 could be applicable at P/P = 0.05 − 0.3 for the surface area of macro- and mesoporous

o

materials.

Figure 9 revealed the BET surface area plot of CuL@TiO @Fe O . The best fit result exhibited

2

3

4

straight line and according to Eq. 1, the value of v and c could be extracted from the value of the

m

slope ~ 17.96 and the y-intercept of that line ~ 0.805 in Fig. 9. The value of the BET constant (c)

was found to be 23.3. Moreover, the BET specific surface area (S_B_E_T) could be given in terms of

the total surface area S_T_o_t_a_l, as shown in Eqs. 2 and 3:

푆푇표푡푎푙

(2)

푆퐵퐸푇 =

푎

and

푣푚푁푠

푉

푆_푇_표_푡_푎_푙

=

(3)

²

w here, s is the adsorption cross-section of the adsorbing species ~ 16 Å /molec, N is Avogadro's

number, V is the molar volume of the adsorbate gas and a is the mass of the solid sample ~ 0.0216

2

g. The value of S_B_E_Twas estimated to be ~ 185.54 m /g.

The present value of S_B_E_Twas comparable with those obtained by other works in literatures⁸⁷^,⁸⁸for

analogy core-shell systems. It could be observed that the value of S_B_E_Tof CuL@TiO @Fe O

4

2

3

8

7

core-shell-shell system was the largest value. Zhang et al. reported the value of S of Fe O -C-

BET

3

4

2

88

TiO was found to be ~ 40 m /g. Likewise, Lee et al. prepared a Fe O -SiO sample with S of

2

3

4

2

BET

2

89

2

~

41 m /g. Whereas, Costa et al. synthesized Fe O -SiO -TiO with S

of ~ 141 m /g. Here,

BET

3

4

2

the largest S_B_E_Twas the benefit of adsorption, influenced by its large surface area with large

adsorption. This result indicated that the surface area of Fe O -nanoparticles was increased by

3

4

coating with TiO and CuL. Hence, the CuL@TiO @Fe O core-shell-shell system obtained in the

2

3

4

present work could be considered as a potential candidate to be used as a heterogeneous catalyst.

3

.3 | Catalytic cross-coupling reactions

Exploring the catalytic potential of the novel prepared catalysts, CuL and CuL@TiO @Fe O

4

2

3

were devoted to the C―C cross-coupling reaction (Suzuki-Miyaura) of phenylboronic acid with 2-

pyridyl bromide and chloride, and to the C―N cross-coupling reaction (Buchwald-Hartewig) of 2-

aminopyridine with 2-pyridyl bromide and chloride. Utilized optimized reaction conditions using

K CO as a base and ethanol as a solvent at 100 °C for the given time. The kinetics of the

2

3

homogeneously and heterogeneously catalyzed reaction using CuL and CuL@TiO @Fe O

4

2

3

catalysts, respectively, were determined by the yield percentages of the chemoselective C―C and

C―N biaryl synthesis, as listed in Table S2. Reaction progress was monitored by TLC (thin

column chromatography) and the yield percentages of the C―C and C―N biaryl products were

determined by GC-MS. The results, which plotted in Figs. 10a,b, showed that both catalysts

consumed coupling reagents in different times frames. CuL took 4 h to afford the highest yield of

the C―C coupling product provided 89% yield while the CuL@TiO @Fe O catalyst took 6 h

2

3

4

with the highest yield 91%of the reaction completion. Similarly, for C―N coupling, CuL took 3 h

with 91% yield and CuL@TiO @Fe O took one hour longer (4 h) with 94% yield to complete the

2

3

4

cycle. The slight variation in consumption time for both catalysts, 2 h difference for C―C

coupling and 1 h for C―N coupling could be the less homogenicity of CuL@TiO @Fe O in the

2

3

4

3

9

reaction media. The slightly higher percentage yield of the desired products (C―C and C―N

biaryls) with CuL@TiO @Fe O catalyst than that with CuL catalyst could be interpreted by the

2

3

4

presence of the supporting materials of TiO and Fe O , which enhanced the catalytic reactivity of

2

3

the immobilized CuL catalyst within increase in the surface area of TiO @Fe O , as detected

2

3

above.¹⁹^,²⁰During optimization, various reaction conditions were examined including different

solvents, e.g. ethanol, chloroform, toluene, water and ethanol-aqueous equimolar mixture, various

bases (K CO , tBuOK and K PO ) and reaction time at 100 °C.

2

3

4

The yield percentages for both C―C and C―N cross-couplings are represented in Tables 2 and

, respectively. The results from Tables 2 and 3, it could be noted that the C―N coupling product

3

yield percentages were better than those of C―C coupling products, which could be estimated

from the low stability of boronic acid derivatives in an aerobic atmosphere compared to that of

1

amino group of 2-aminopyridine, as a precursor. In a blank reaction, i.e. in absence of any

catalyst, Suzuki-Miyaura reaction was tested obtaining low yield product percentages, i.e. 16 and

2

8% (Table 2, entries 1 and 2), respectively.

It is well documented that the inorganic bases give usually the best results of yield percentages for

9

0

2

the C―C and C―N chemoselectivities. K CO was found to be the best base for such catalytic

2

3

systems, in contrast to other used bases, i.e. tBuOK, K PO and KOH. The reason could be that

3

4

K CO is more compatible with the catalyst and solvent than the other tested bases, as observed

2

3

9

1

previously. With various solvents K CO showed better performance (Tables 2 and 3) than

2

3

other used bases. KOH was found to be the least active base in both catalytic reactions provided

low yield for C―C biaryls synthesis (entires 7 and 8 in Table 2, 37 and 44% catalyzed by CuL

and CuL@TiO @Fe O , respectively). Similarly, for the C―N cross-coupling, the yield was also

2

3

4

low with KOH, as observed in Table 3 (entries 5 and 6, giving 42 and 49 % catalyzed by CuL and

CuL@TiO @Fe O , respectively). The high basicity of the reaction media could cause base

2

3

4

9

2

93,94

hydrolysis, with formation probably of Cu(OH) precipitate.

2

The other applied base, i.e. tBuOK presented appreciable potential towards the formation of the

C―C biaryls from the aryl bromide in various solvents e.g. toluene, water, ethanol and ethanol-

water binary mixture (Table 2, entries 7, 21, 29, and 37 catalyzed by CuL offered 65, 62, 76 and

7

0%, and also entries 9, 23, 31 and 39 catalyzed by CuL@TiO @Fe O awarding 72, 59, 80 and

2 3 4

2% of the chemoselective product, respectively). Likewise, the catalytic system with K PO

3

4

displayed good potential with good yield percentages of the C―C biaryls in various solvents, in

toluene (entry 8, 53%), water (entry 22, 55%), ethanol (entry 30, 81%) and ethanol-water binary

mixture (entry 37, 70%) with homogeneous catalyzed system (CuL). In heterogeneous reaction

condition (CuL@TiO @Fe O ), the yield percentages were clearly influenced by the solvent, in

2

3

4

toluene (entry 10, 66%), water (entry 24, 51%), ethanol (entry 32, 79%) and ethanol-water binary

mixture (entry 40, 70%).

By using K PO in C―N cross-coupling system, the obtained yields were moderate to good with

3

4

CuL (Table 3), as 69% in toluene (entry 6), 55% in water (entry 20), 75% in ethanol (entry 28)

and 70% in EtOH-H O mixture (entry 36). K PO , also reflected good behavior towards the

2

3

4

catalytic potential of CuL@TiO @Fe O , as 75% in toluene (entry 8), 59% in water (entry 22),

2

3

4

7

2% in ethanol (entry 30) and 74% in EtOH-H O mixture (entry 38). It could be concluded that

2

9

5

K PO is a relatively good base, as reported recently.

3

4

The reactivity of the homogeneous (CuL) and heterogeneous (CuL@TiO @Fe O ) catalyst in

2

3

4

various tested solvents in C―C and C―N bond formation was found to be in order ethanol >

chloroform > toluene > ethanol-water mixture > water. For both homogeneous and heterogeneous

phases, ethanol was found to be the best choice, the reason could the better solubility of the

reaction contents and their miscibility could improve their catalytic sufficiency towards C―C and

1

7

C―N cross-couplings. Interestingly, after ethanol, chloroform also showed good compatibility

with these catalytic systems (Tables 2 and 3). In ethanol-water mixture and in water alone, the

probed reactions demonstrated lower yield percentages of the target products (Table 2, entries 17-

2

3 for water and entries 33-40 for ethanol-water equimolar mixture) (Table 3, entries 15-22 for

water and entries 31-38 for ethanol-water equimolar mixture). Water as a high polar inorganic

solvent did not show the desired performance, the reason could be the poor solubility of the

organic contents in the reaction media.⁷⁹^,⁹⁶For that reason, the catalytic potential of CuL and

CuL@TiO @Fe O were remarkably reduced and offered the lowest yield (Tables 2 and 3).

2

3

4

As a more reactive coupling partner 2-pyridyl bromide offered better coupling results then 2-

pyridyl chloride, as summarized in Tables 2 and 3. The high bond dissociation energy of the

Ar―Cl bond could be the reason for the lower reactivity of 2-pyridyl chloride.⁹⁷

To demonstrate the role of feeding of CuL complex to TiO @Fe O , separated probes of catalytic

2

3

4

tests of C―C cross-coupling reactions of phenylboronic acid with 2-pyridyl bromide at the

optimized reaction conditions (in presence K CO , in ethanol at 100 °C for 6 h) using Fe O and

2

3

4

TiO @Fe O were accomplished and their results of the product yields are represented in Table 4.

2

3

4

The yield percentages of the C―C biaryl product catalyzed by Fe O (only) awarded 71% and

3

4

within TiO @Fe O (as a heterogeneous catalyst) gave 83% (Table 4). Comparatively, the

2

3

4

immobilized CuL to the TiO @Fe O nanoparticles promoted its surface area and hence improved

2

3

4

its catalytic sufficiency (affording 91% of the desired product).

Using the best base (K CO ) solvent (ethanol) combination, the reaction was further investigated

2

3

for catalytic loading using 0.01, 0.02, 0.05 and 0.1 mmol of CuL and 0.05, 0.1 0.2 and 0.5 g of

CuL@TiO @Fe O in C―C cross-coupling of phenylboronic acid with 2-pyridyl bromide. The

2

3

4

results are summarized in Table 5. For CuL, the increased loaded amounts of the catalyst from

0

8

.01, 0.02 to 0.05 mmol, showed observable performance in the yield percentages from 78, 89 to

9%, similarly, the increased loaded amounts of CuL@TiO @Fe O catalyst (0.1 mmol of CuL

2

3

4

and 0.5 g) also showed prominent improvement in the yield percentages (73, 90 and 91 of C―C

product), Table 5. The highest loaded amounts of both catalysts (0.1 mmol of CuL and 0.5 g of

CuL@TiO @Fe O ) indicated rejection by the catalytic system, which awarded lower yield

2

3

4

compared to the lower loaded amounts (81 and 89%, respectively). The high loaded amount of

both catalysts could observably catalyze the reaction for further by-products.⁹⁸^,⁹⁹

Tables 6 and 7 display the yield products of Suzuki-Miyaura and Buchwald-Hartwig cross-

couplings of phenylboronic acid or 2-aminopyridine with alternative heterocyclic bromides, as

coupling partners, under optimized conditions catalyzed by either CuL or CuL@TiO @Fe O .

2

3

4

Interestingly, the biaryls and secondary diaryl amines were obtained within single regioisomers,

which afforded good yields. With 2-bromothiophene and 2-bromofuran, the catalysts worked with

lower activity and the yields were good (60 and 67% for CuL and CuL@TiO @Fe O ,

2

3

4

respectively) for the Suzuki-Miyaura reaction (Table 6). Whereas, in respect of the Buchwald-

Hartwig reactions, the reactivity of CuL andCuL@TiO @Fe O was somewhat lower and gave

2

3

4

lower yield (53 and 64% for 2-bromothiophene and 2-bromofuran, as small heterocyclic reagents,

respectively, Table 7). As a consequence, overall, the more electron-withdrawing aryl bromides

gave a better yield of C―C and C―N products more than those of the less electron-withdrawing

aryl bromides with both catalysts, as for particularly for 2-pyridyl bromide, 3-pyridyl bromide, 4-

pyridyl bromide, 2-quinolyl bromide and 8-quinolyl bromide.

For understanding the tolerance of the electronic effects of the heterocyclic attached ring to

bromide Ar―Br, the heterocyclic bromides with more electron-withdrawing more resonance

character would increase the nucleophilic power of bromide and hence, reinforce it reactivity

towards cross-couplings.¹⁰⁰

Comparatively, the catalytic yield results of the C―N cross-coupling reaction catalyzed by new

magnetic Cu(0)-amino acid catalyst immobilized on Fe O -TiO -L-dopa afforded 80% of the

3

4

2

biaryls between aniline and phenylboronic acid in water and in presence of K CO at 80 °C for 24

2

3

h.²

3

.4 | Reusability of the homogeneous and heterogeneous CuL

The recyclability of the Cu-catalysts homogeneously (with CuL) and heterogeneously (with

CuL@TiO @Fe O ) were examined in C―C cross-coupling reaction, using phenylboronic acid

2

3

4

with 2-pyridyl bromide in the presence of K CO , at the optimum conditions in toluene. The

2

3

obtained results are displayed in Fig. 11. The homogeneous catalyst (CuL) was separated easily

from the reaction mixture by extracting and filtration after cooling down to the room temperature

and washed by toluene. While, the heterogeneous catalyst (CuL@TiO @Fe O ) was extracted

2

3

4

easily by a magnet from the reaction mixture, washed with toluene, dried in an oven and reused in

the next trial using fresh solvent and reagents. The reusability of homogeneous catalyst (CuL) was

found to be limited up to 3 times only, whereas the heterogeneous catalyst (CuL@TiO @Fe O )

2

3

4

showed better catalytic performance in cycling up to 7 times. In the homogeneous phase catalysis,

the catalyst lost its potential dramatically on the fourth consecutive run. It lost more than half of its

reactivity that could be explained by its decomposition or loss of little quantity in the extraction

process.

After 8 times, in the heterogeneous CuL@TiO @Fe O showed remarkable inhibition of its

2

3

4

reactivity is almost ~10% without loss of its composition. Figure 12 presents the EDS analyses of

1

01

the reused CuL@TiO @Fe O after 7 times, as observed elsewhere. Clearly, there was no

2

3

4

considered change in the morphology of CuL@TiO @Fe O to lose its catalytic potential, so,

2

3

4

there is no obvious reason for its deactivation, which could be found elsewhere or could explain

that behavior.

4

| CONCLUSIONS

N,N,O-tridentate pyridyl-imine ligand (HL) was synthesized and then treated with CuCl to give a

2

novel mononuclear copper complex (CuL). Both ligand (HL) and its complex (CuL) were

characterized by various spectral tools, i.e. NMR, IR, UV-Vis. and EI spectra, and elemental

analyses. For heterogeneous catalysis, the novel complex was synthesized afresh by immobilizing

the ligand on TiO coated Fe O nanoparticles, provided solid-supported copper catalyst

2

3

(

HL@TiO @Fe O ). The different analytical techniques (FT-IR, XRD, SEM, TEM, EDS, TGA

2 3 4

and magnetism) were used to confirm the elemental compositions and morphological structure of

CuL@TiO @Fe O core-shell-shell system. The surface morphology of Fe O , TiO @Fe O and

2

3

4

3

4

2

3

4

CuL@TiO @Fe O were analyzed by using FE-SEM and HR-TEM techniques, which exhibited

2

3

4

agglomerations of TiO @Fe O nanoparticles, which are cross-linked with deformed nanorods

2

3

4

shaped structure of CuL organic framework. The BET isotherm curve of the CuL@TiO @Fe O

4

2

3

exhibited a type IV profile with an H3-type hysteresis loop, which reflected the mesoporous nature

2

with an average pore radius ~ 2.12 nm and BET specific surface S_B_E_T~ 185.54 m /g. Both

catalysts were investigated in catalysis for Suzuki-Miyaura (C―C bond formation) and

Buchwald-Hartwig amination (C―N bond formation) reactions. Both catalysts CuL and

CuL@TiO @Fe O showed prominent catalytic potential under the optimized reaction conditions.

2

3

4

The solid supported catalyst (CuL@TiO @Fe O ) showed a slightly dominant catalytic reactivity

2

3

4

over a homogeneous catalyst system (CuL). Hence, the characteristic obtains interpreted the

catalytic potential of the current samples, in which the increase of the surface area of TiO @Fe O

2

3

4

with immobilized CuL, progressed its catalytic reactivity. In C―C cross-coupling reaction the

heterogeneous catalyst (CuL@TiO @Fe O ) was recycled up to 7 times, while homogeneous

2

3

4

catalyst (CuL) up to 3 times only.

ACKNOWLEDGMENTS

The authors acknowledge the Deanship of Scientific Research at King Faisal University for the

financial support under Nasher Track (Grant No. 186374).

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[

3

4

2

catalyst for the Chan-Lam cross-coupling reaction in ligand free conditions. Catal. Commun.

018;107:68-73.

3] Anuma S, Mishra P, Bhat BR/Copper complex with N-,O-architecture grafted graphene

2

[

oxide nanosheet as a heterogeneous catalyst for Suzuki cross coupling reaction. J. Taiwan

Inst. Chem. Eng. 2019;95:643-651.

[

4] Dutta DK, Borah BJ, Sarmah PP/Recent Advances in Metal Nanoparticles Stabilization

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Article Doi

Hybrid organic-inorganic Cu(II) iminoisonicotine@TiO2@Fe3O4 heterostructure as efficient catalyst for cross-couplings

DOI: 10.1111/jace.17098

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Article abstract of DOI:10.1111/jace.17098

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