Abstract
HETEROGENEOUS TRANSITION METAL CATALYSTS FOR CC AND C-N BOND FORMING REACTIONS
The work in the thesis has been presented in five chapters.
Chapter-I describes a detailed introduction on the state of the art of
heterogeneous catalysts preparation, uses and advantages as well as the disadvantages.
Chapter-II
describes
the preparation, characterization and catalytic
application of nanocrystalline magnesium oxide supported palladium catalyst (NAPMg-Pd0). The catalyst was synthesized by counter ion stabilization of PdCl42- on to the
high surface area aerogel prepared nanocrystalline magnesium oxide followed by
reduction with hydrazine hydrate (Scheme 1). The NAP-Mg-Pd0 was characterized by
using FTIR, XRD, XPS, TEM, ICP-AES, UV-VIS DRS, SEM-EDX etc. NAP-MgPd0 was the employed in different carbon-carbon bond forming reactions namely
Heck, Suzuki, Stille, and Sonogashira coupling reactions (Scheme 2). The catalyst
showed excellent reusability over several cycles.
HO
HO
HO
HO
Mg+
HO
+
Na2PdCl4,
Mg
Mg+ H O, 12 h, N
2
2
O
HO
OH
O-
+
PdCl42-
O-
Na +
Mg
Mg+
+
Mg O+
Na
OH
Scheme 1. Preparation of NAP-Mg-Pd0.
i
HO
H2NNH2.H2O
HO
Mg+
OMg+ Pd
Mg+
OOH
Abstract
R
K2CO3, water, rt
NaOAc, DMAc, TBAB
130 0C
or DMAc, K3PO4, 130 0C
B(OH)2
R''
k
ec
H
Su
zu
ki
R'
R
R'
R''
X
R
NAP-Mg-Pd0 R
X
X= I, Br, Cl
X= I, Br, Cl
e
hi
H
ra
NMP, KOAc,
R
R
s
ga
Bu3Sn R'''
R'''= Ph
ill
St
no
So
R'''
Ph
THF-water, Et3N, rt
0
or DMF, Et3N, 80 0C
50 C
Ph
Scheme 2. Catalytic applications of NAP-Mg-Pd0 in Heck, Suzuki, Stille, and
Sonogashira reactions.
Chapter-III describes the preparation, characterization and catalytic
application of layered double hydroxides (LDHs) supported rhodium catalyst (LDHRh0). The catalyst was synthesized by grafting of Rh3+ on to the LDHs followed by
reduction with molecular hydrogen at 250 °C. The thus synthesized catalyst was
characterized by using different techniques such as UV-VIS DRS, XPS, XRD, TEM,
SEM-EDX, TPR, ICP-AES etc. LDH-Rh0 was employed in Heck, Suzuki, and Stille
coupling of aryl halides (iodo- and bromoarenes). The catalyst is easily separated by
filtration and recycled with almost consistent activity.
Chapter-IV describes the preparation, characterization and catalytic
application of modified silica supported nanorhodium catalyst (SiO2-Rh0). The
catalyst was synthesized by complexation of RhCl3 with 3-aminopropyl
functionalized silica gel followed by reduction with aqueous NaBH4. SiO2-Rh0 was
characterized by using ICP-AES, XPS, FTIR, XRD etc. SiO2-Rh0 was employed in
the Heck-type coupling of alkenes and arylboronic acids to afford the corresponding
ii
Abstract
Heck product in moderate to excellent yields (Scheme 3). SiO2-Rh0 was separated by
simple filtration and reused for 5 cycles with slightly diminished activity.
B(OH)2
+
CO2Bu
SiO2-Rh0 ( 1.1 mol%)
CO2Bu
Toluene-water (5:1), 100 0C, 10h
NH2
NH2
SiO2
NH2
NH2
NH2
SiO2-Rh0
Scheme 3. Heck-type coupling of alkenes with arylboronic acids catalyzed by SiO2Rh0.
Chapter-V is divided into two sections. Section-A describes the preparation,
characterization and catalytic activity of silica immobilized copper complexes in Narylation of N(H)-heterocycles and benzyl amines with aryl halides and arylboronic
acids (Scheme 4).
iii
Abstract
Ar-X +
Ar-N-heterocycle
N(H)-heterocycle Catalyst (5 mol%)
0
Cs2CO3, solvent, 100-135 C
Ar-X +
Ar1-CH2-NH2
X=I, Br
Ar-B(OH)2+
Catalyst (5 mol%)
Cs2CO3, solvent, 100-135 0C
N(H)-heterocycle
Catalyst (2 mol%)
Ar1-CH2-NH-Ar
Ar-N-heterocycle
0
MeOH, 80 C
SiO2
N
AcO Cu
N
CatalystOAc
Scheme 4. N-arylation of N(H)-heterocycles and benzyl amine.
In Section-B, the three component coupling of aldehyde, amine and terminal
alkyne catalyzed by silica immobilized copper(I) iodide was described (Scheme 5).
The catalyst is easily separated by simple filtration and reused with consistent activity
for several cycles.
2
R1CHO +
R2R3NH
+
4
R
Catalyst (5 mol%)
R
N
R3
R1
R4
R1, R2, R3, R4 = aryl, alkyl, H
N
SiO2
I
Cu N
Catalyst
Scheme 5. Three component coupling of aldehyde, amine, and alkyne catalyzed by
silica immobilized CuI.
iv