09-11-2012, 02:18 PM
Three Component Mannich Reaction and 1,5-Benzodiazepine Synthesis Catalyzed by a Tetranitrile-Silver Complex
[attachment=38741]
INTRODUCTION
The search for novel catalysts, which show atom efficiency
and environmental friendliness, is continuing in academic
and industrial laboratories due to the rising concern
over environmental issues and the need for more efficient
catalysts. Homogeneous catalysis using organometallic complexes
is advancing into the modern fine chemical and bulk
chemical industry [1]. In this paper we describe a novel homogeneous
catalyst derived from silver complex of a tetranitrile
ligand. Polydentate ligands have found extensive application
in molecular and crystal engineering [2]. Among the
polydentate ligands, polynitrile ligands have received particular
attention due to their special property to co-ordinate
with silver ions. This property was exploited in the synthesis
of silver complexes having excellent properties and beautiful
topologies [3]. But catalysis using these polynitrile-silver
complexes is a less explored area.
The synthetic utility of Mannich reaction is evident from
its application in the synthesis of many natural products and
biologically important compounds [4]. Recently the focus
has been shifted to catalyst assisted three component Mannich
reaction because of the simplicity and atom economy of
the reaction [5, 6]. Snapper and Hoveyda [7] have exploited
catalytic properties of some silver complexes in Mannich
reactions of enol ethers and silylketene acetals with various
imines, while Asao [8] used AgOTf as the catalyst in Mannich
and nitro Mannich reactions of pre-formed alkynylaryl
aldimines.
RESULTS AND DISCUSSION
The tetranitrile ligand used to prepare the catalyst was
propylenediaminetetrapropionitrile (1). The ligand was derived
from 1,3-diaminopropane and acrylonitrile according
to a standard procedure (Scheme 1) [13].
The complex (2) was prepared by stirring the ligand and
AgNO3 (1:2 ratio) in methanol. The formation of the complex
was indicated by the development of a reddish brown
color. On evaporation of the solvent, a brownish mass was
formed which in turn changed to black on exposure to light
and air. Even if the complex underwent blackening upon
exposure to light and air, there was no reduction in the catalytic
activity. UV-Vis-NIR spectra of the complex, ligand
and silver nitrate in methanol were compared.
CONCLUSION
In summary, a tetranitrile silver complex was prepared
and used as homogeneous catalyst for one pot three component
Mannich reaction and benzodiazepine synthesis from ophenylene
diamine and ketones. The reactions proceeded
efficiently with good yields. The catalyst can be separated
from the product by changing the solvents. The catalyst is
reusable.
[attachment=38741]
INTRODUCTION
The search for novel catalysts, which show atom efficiency
and environmental friendliness, is continuing in academic
and industrial laboratories due to the rising concern
over environmental issues and the need for more efficient
catalysts. Homogeneous catalysis using organometallic complexes
is advancing into the modern fine chemical and bulk
chemical industry [1]. In this paper we describe a novel homogeneous
catalyst derived from silver complex of a tetranitrile
ligand. Polydentate ligands have found extensive application
in molecular and crystal engineering [2]. Among the
polydentate ligands, polynitrile ligands have received particular
attention due to their special property to co-ordinate
with silver ions. This property was exploited in the synthesis
of silver complexes having excellent properties and beautiful
topologies [3]. But catalysis using these polynitrile-silver
complexes is a less explored area.
The synthetic utility of Mannich reaction is evident from
its application in the synthesis of many natural products and
biologically important compounds [4]. Recently the focus
has been shifted to catalyst assisted three component Mannich
reaction because of the simplicity and atom economy of
the reaction [5, 6]. Snapper and Hoveyda [7] have exploited
catalytic properties of some silver complexes in Mannich
reactions of enol ethers and silylketene acetals with various
imines, while Asao [8] used AgOTf as the catalyst in Mannich
and nitro Mannich reactions of pre-formed alkynylaryl
aldimines.
RESULTS AND DISCUSSION
The tetranitrile ligand used to prepare the catalyst was
propylenediaminetetrapropionitrile (1). The ligand was derived
from 1,3-diaminopropane and acrylonitrile according
to a standard procedure (Scheme 1) [13].
The complex (2) was prepared by stirring the ligand and
AgNO3 (1:2 ratio) in methanol. The formation of the complex
was indicated by the development of a reddish brown
color. On evaporation of the solvent, a brownish mass was
formed which in turn changed to black on exposure to light
and air. Even if the complex underwent blackening upon
exposure to light and air, there was no reduction in the catalytic
activity. UV-Vis-NIR spectra of the complex, ligand
and silver nitrate in methanol were compared.
CONCLUSION
In summary, a tetranitrile silver complex was prepared
and used as homogeneous catalyst for one pot three component
Mannich reaction and benzodiazepine synthesis from ophenylene
diamine and ketones. The reactions proceeded
efficiently with good yields. The catalyst can be separated
from the product by changing the solvents. The catalyst is
reusable.