Quinoxaline and Triazole Based Sulfur:/Selenium Ligands: Metal Complexes for Catalytic Activation

The focus of thesis is on (i) designing of bidentate chalcogenoether ligands (ii) exploring their coordination chemistry with Pd(II), (η-benzene)Ru(II) and (ηpentamethylcyclopentadiene) Rh(III) / Ir(III) and (iii) investigating the designed metal complexes for C−C coupling reactions, NMO based oxidation of alcohols, Oppenauer-type oxidation of alcohols and transfer hydrogenation of carbonyl compounds. The bidentate 2,3-di[(phenylthio/-seleno)methyl]quinoxaline (L1 / L2) synthesized by the reaction PhS / PhSe with 2,3-bis(bromomethyl)quinoxaline, on reaction with Na2PdCl4, results in complexes [Pd2(L1−H)2Cl2] (1) / [PdL2Cl2] (2) respectively. Structures of Single crystals by X-ray diffraction of ligands and complexes have been determined. The 1 is a palladacycle, formed by external base free activation of benzyl group’s C(sp)−H of L1 whereas L2 behaves in 2 as a bidentate. Complexes 1 and 2 were explored to catalyzed Suzuki−Miyaura coupling reactions of several aryl bromides (including deactivated ones). The palladacycle1 shows better catalytic efficiency than complex 2. The catalysis with 1 / 2 has been found to proceed via in situ generated nanoparticles (size < 2 nm) composed of palladium and sulfur or selenium and protected by L1 or L2. The bidentate 1-benzyl-4-((phenylthio)-/(phenylseleno)methyl)-1H-1,2,3triazole (L3 / L4) and 4-phenyl-1-((phenylthio)-/(phenylseleno)-methyl)-1H-1,2,3triazole (L5 / L6) were synthesized by the 1,3-dipolar cycloaddition of azides to terminal alkynes (click reaction). Their metal complexes (3−8) are formed by direct reaction with [Pd(CH3CN)Cl2] and [{(η-benzene)RuCl(μ-Cl)}2].The coordination There is a "pseudo-octahedral" half sandwich “Piano-Stool” geometry around the Ru center in 7−8. The Pd(II) complexes were explored for C−C coupling reactions (Suzuki-Miyaura and Heck), whereas Ru(II) complexes were investigated to catalyze oxidation of alcohols and transfer hydrogenation of ketones. Complexes efficient for Suzuki than Heck coupling are pre-catalysts and dispense catalytically active Pd NPs in the course of reaction. NPs (size 3−11 nm) appear to havea role in the catalysis, as they show catalytic activity after isolation also. Catalytic oxidation of alcohols appears to involve the formation of Ru(IV)=O species, whereas catalytic transfer