Arun,V; Dr.Mohammed Yusuff,K K(Cochin University of Science & Technology, June , 2009)
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Abstract:
The thesis deals with studies on the synthesis, characterisation and catalytic
applications of some new transition metal complexes of the Schiff bases derived from 3-hydroxyquinoxaline 2-carboxaldehyde.. Schiff bases which are considered as ‘privileged ligands’ have the ability to stabilize different metals in different oxidation states and thus regulate the performance of metals in a large variety of catalytic transformations. The
catalytic activity of the Schiff base complexes is highly dependant on the environment about
the metal center and their conformational flexibility. Therefore it is to be expected that the
introduction of bulky substituents near the coordination sites might lead to low symmetry complexes with enhanced catalytic properties. With this view new transition metal
complexes of Schiff bases derived from 3-hydroxyquinoxaline-2-carboxaldehyde have been
synthesised. These Schiff bases have more basic donor nitrogen atoms and the presence of
the quinoxaline ring may be presumed to build a favourable topography and electronic
environment in the immediate coordination sphere of the metal. The aldehyde was condensed
with amines 1,8-diaminonaphthalene, 2,3-diaminomaleonitrile, 1,2-diaminocyclohexane,
2-aminophenol and 4-aminoantipyrine to give the respective Schiff bases. The oxovanadium(IV), copper(II) and ruthenium(II)complexes of these Schiff bases were synthesised and characterised.
All the oxovanadium(IV) complexes have binuclear structure with a square pyramidal geometry.
Ruthenium and copper form mononuclear complexes with the Schiff base derived from 4-
aminoantipyrine while binuclear square planar complexes are formed with the other Schiff
bases. The catalytic activity of the copper complexes was evaluated in the hydroxylation of
phenol with hydrogen peroxide as oxidant. Catechol and hydroquinone are the major products. Catalytic properties of the oxovanadium(IV) complexes were evaluated in the
oxidation of cyclohexene with hydrogen peroxide as the oxidant. Here allylic oxidation
products rather than epoxides are formed as the major products. The ruthenium(II)
complexes are found to be effective catalysts for the hydrogenation of benzene and toluene.
The kinetics of hydrogenation was studied and a suitable mechanism has been proposed.
Description:
Department of Applied Chemistry, Cochin
University of Science and Technology