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Chiral Mn(iii) salen complexes S-1, R-1, S-2, R-2, S-3 and R-3 derived from the respective chiral salen ligands, viz., (1S,2S)-N,N'-bis-[3-tert-butyl-5-chloromethyl-salicylidine]-1,2-cyclohexanediamine S-1'/(1R,2R)-N,N'-bis-[3-tert-butyl-5-chloromethyl-salicylidine]-1,2-cyclohexanediamine R-1'/(1S,2S)-N,N'-bis-[3-tert-butyl-5-N,N'N'triethylaminomethyl-salicylidine]-1,2-cyclohexanediamine dichloride S-2'/(1R,2R)-N,N'-bis-[3-tert-butyl-5-N,N'N'triethylaminomethyl-salicylidine]-1,2-cyclohexanediamine dichloride R-2'/(1S,2S)-N,N'-bis-[3,5-di-tert-butylsalicylidene]-1,2-cyclohexanediamine S-3' and (1R,2R)-N,N'-bis-[3,5-di-tert-butyl-salicylidene]-1,2-cyclohexanediamine R-3', were synthesized. Characterization of the complexes was done by microanalysis, IR, LC-MS, UV-vis. and circular dichroism (CD) spectroscopy. Binding of these complexes with calf thymus DNA (CT-DNA) was studied by absorption spectroscopy, competitive binding study, viscosity measurements, circular dichroism measurements, thermal denaturation study and observation of their different antioxidant activities. Among all the complexes used, the best result in terms of binding constant (intercalative) (130.4 x 10(4)) was achieved with the complex S-1 by spectroscopic titration. The complex S-1 showed strong antioxidant activity as well.

A convenient approach to the asymmetric Strecker reaction was established by synthesizing chiral, mono‐ and dinuclear, macrocyclic MnIII–salen complexes possessing achiral and chiral linkers (trigol, piperazine, and diethyl tartarate). This group of macrocyclic complexes has emerged as improved metal‐based catalysts for the enantioselective Strecker reaction of aldimines, giving high enantioselectivity (up to 99 %) for a wide range of substrates. The macrocylic complex 6 a with trigol linker works very well with TMSCN (trimethylsilyl cyanide) as a source of cyanide, using 4‐phenyl pyridine N‐oxide (4‐PPyNO) as a co‐catalyst in toluene at −40 °C. However, the macrocyclic complex 6 b with diethyl tartarate as a linker affected excellent chiral induction for both aromatic and aliphatic imines with a safer cyanide source (ethyl cyanoformate) in toluene at −20 °C in the presence of N,N‐diisopropylimine as a co‐catalyst. Complexes 6 a and 6 b used in the present study were recoverable and recyclable (five times) with retention of their performance at gram level. The kinetic study with complex 6 a for the enantioselective Strecker reaction of N‐benzyl benzylimine revealed a first‐order dependence on catalyst, substrate, and TMSCN concentration. This protocol with catalyst 6 b was further extended for the synthesis of D‐homophenyl alanine, an important analogue in factor Xa inhibitors.

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Recyclable copper(II) chiral amino alcohol based Schiff base complexes smoothly catalysed the Friedel-Crafts alkylation of indole with aryl aldimine in good yields (98%) and with enantioselectivities up to 97%. The effects of ligand structure, solvent, metal source and temperature on the reaction were also studied. The catalytic system worked very well several times retaining its performance. To understand the mechanism of the catalytic Friedel-Crafts addition reaction, a kinetic investigation was carried out with different concentrations of the catalyst Cu(II)-L 2 , indole and N-(3-nitrobenzylidene)-4-methylbenzene sulfonamide as a model substrate. The Friedel-Crafts alkylation reaction of N-(3-nitrobenzylidene)-4-methylbenzene sulfonamide was first order with respect to the concentration of the catalyst and the nucleophile but did not depend on the initial concentration of the substrate (aryl aldimine). An appropriate mechanism of the Friedel-Crafts alkylation reaction is proposed.

A series of amino alcohol-derived, Schiff-base ligands L1-L4 were synthesised and characterized. Iron complexes of these ligands [FeL1(acac)], [FeL2(acac)], [FeL3(acac)] and [FeL4(acac)] were generated in situ to catalyze the asymmetric oxidation of prochiral sulfides using aqueous H 2 O 2 as a terminal oxidant. One of these complexes [FeL1(acac)] was identified as a very efficient catalyst for the enantioselective oxidation of a series of alkyl aryl sulfides with excellent enantioselectivity (75-96% ee), conversion (up to 92%) and chemo selectivity (up to 98%). During the optimization process, a series of electron-donating benzoic acid derivatives were found to favour both conversion and enantioselectivity.

A diethyl tartrate linked chiral macrocyclic manganese(III)–salen (salen=N,N′‐ethylenebis(salicylimine)) complex has been used for the enantioselective epoxidation of nonfunctionalized alkenes, namely, indene and chromenes, as well as oxidative kinetic resolution of racemic alcohols. For the epoxidation reaction, a 2.5 mol % catalyst loading in the presence of pyridine N‐oxide as an axial ligand and urea–H2O2 adduct as an oxidant gave respective epoxides in high yield (>97 %) and enantiomeric excess (ee, up to 92 %). The same catalyst at a loading of 1.5 mol % has provided enantioenriched (ee up to 97 %) secondary alcohols through oxidative kinetic resolution of racemic alcohols. The catalyst can be recovered and reused up to four times with no loss in performance.