Synthesis and Characterisation of New Transition Metal Complexes of Schiff Bases Derived from 3-hydroxyquinoxaline-2- carboxaldehyde and Application of Some ofthese Complexes as Hydrogenation and Oxidation Catalysts

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.

Synthesis and Characterization Of Some Transition Metal Complexes Of Multidentate Ligands

Coordination chemistry of schiff bases is of considerable interest due to their various magnetic, catalytic and biological applications. Here it describes the spectral characterization of schiff bases and its Mn (II), Cu (II) and Ni (II) complexes. Then synthesis and spectral characterization of Zn (II), Cd (II) and Co (II) complexes of schiff base derived from 3-Formylsalicilic Acid and 1,3-diaminopropane. Then it discusses the synthesis and spectral studies of Copper (II) complexes of 2-Hydroxyacetophenone N-phenyl semicarbazone. Finally it discusses the synthesis and spectral characterization of Co (III) complexes of salicylaldehyde N-phenyl semicarbazone. The preparation and characterization of Cobalt (III) complexes of salicylaldehyde, N-phenylthiosemicarbazone containing hetrocyclic bases phenalthroline and bipyridine. Thiocyanate, azide and perchlorate ions act as coligands. Elemental analysis suggests +3 state for Cobalt. HNMR, IR and UV-visible spectra characterize the complexes.

Ruthenium complexes of Schiff base ligands as efficient catalysts for catechol–hydrogen peroxide reaction

Zeolite Y-encapsulated ruthenium(III) complexes of Schiff bases derived from 3-hydroxyquinoxaline-2-carboxaldehyde and 1,2- phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYqpd, RuYqap and RuYqab, respectively) and the Schiff bases derived from salicylaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYsalpd, RuYsalap and RuYsalab, respectively) have been prepared and characterized. These complexes, except RuYqpd, catalyze catechol oxidation by H2O2 selectively to 1,2,4-trihydroxybenzene. RuYqpd is inactive. A comparative study of the initial rates and percentage conversion of the reaction was done in all cases. Turn over frequency of the catalysts was also calculated. The catalytic activity of the complexes is in the order RuYqap > RuYqab for quinoxaline-based complexes and RuYsalap > RuYsalpd > RuYsalab for salicylidene-based complexes. The reaction is believed to proceed through the formation of a Ru(V) species.

Thermochemistry of Charge-Transfer Complexes of 7,7,8,8-Tetracyanoquinodimethane with Benzene and Its Chloro Derivatives

The enthalpies of formation of charge-transfer complexes of benzene, chlorobenzene, and 1,3-dichlorobenzene as donors with 7,7,8,8-tetracyanoquinodimethane as acceptor were determined. The thermochemical data show an increased stability of charge-transfer complexes of donors with permanent dipole moment. The results confirm the importance of electrostatic forces in bonding and stabilizing weak complexes. The approximate formation constants of the complexes are also reported.

Chemistry of molecular and supramolecular structures of vanadium(IV) and dioxygen-bridged V(V) complexes incorporating tridentate hydrazone ligands

Four hydrazone ligands: 2-benzoylpyridine benzoyl hydrazone (HBPB), di-2-pyridyl ketone nicotinoyl hydrazone (HDKN), quinoline-2-carbaldehyde benzoyl hydrazone (HQCB), and quinoline-2-carbaldehyde nicotinoyl hydrazone (HQCN) and four of their complexes with vanadyl salts have been synthesized and characterized. Single crystals of HBPB and complexes [VO(BPB)(l2-O)]2 (1) and [VO(DKN)(l2-O)]2 ½H2O (2) were isolated and characterized by X-ray crystallography. Each of the complexes exhibits a binuclear structure where two vanadium(V) atoms are bridged by two oxygen atoms to form distorted octahedral structures within cis-N2O4 donor sets. In most complexes, the uninegative anions function as tridentate ligands, coordinating through the pyridyl- and azomethine-nitrogen atoms and enolic oxygen whereas in complex [VO(HQCN)(SO4)]SO4 4H2O (4) the ligand is coordinated in the keto form. Complexes [VO(QCB)( OMe)] 1.5H2O (3) and 4 are found to be EPR active and showed well-resolved axial anisotropy with two sets of eight line pattern