Amine and Imine Functionalized Azo-aromatic Pincer Type Complexes of Cobalt and Nickel: Synthesis, Characterization and Reactivity Studies

Goswami, Bappaditya (2023) Amine and Imine Functionalized Azo-aromatic Pincer Type Complexes of Cobalt and Nickel: Synthesis, Characterization and Reactivity Studies. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Bappaditya Goswami (17RS024)) 17RS024.pdf - Submitted Version Restricted to Repository staff only Download (20MB)

Abstract

Transition metal complexes with redox active non-innocent ligands and the correlation of reactivity with electronic structure has received significant research interest worldwide. This is because of the potential redox non innocent behavior of the ligand which significantly influence the electronic and structural properties of the complexes as well as the catalytic activity. Azo aromatic ligands are a typical redox non-innocent ligand with very mild reduction potential due to low-lying π*-antibonding orbitals. The research work presented here in this thesis describes the synthesis, characterization, coordination chemistry and catalytic activity of cobalt and nickel complexes with a series of redox active amine/imine functionalized azo-aromatic ligands. The synthesized complexes were mainly used for various catalytic applications like polymerization reaction, dehydrogenative quinoline formation and CO2 fixation reaction. This thesis comprises of five chapters. In view of this, a brief and concise literature review based on the work done in the subsequent chapter II-V has been documented in Chapter I. Chapter II describes the synthesis and characterization of amine functionalized azo-aromatic NNN-donor pincer like ligands and their cobalt complexes. The coordination chemistry of the complexes was studied and the complexes were further explored for catalytic styrene polymerization reaction. The mechanism of the reaction was investigated by various control experiments, spectroscopic and computational studies. The physicochemical properties of the polymers were also explored. In Chapter III, synthesis and characterization of four azo-aromatic cobalt complexes containing substitutionally variant ligands are described. A variety of substituted quinolines were prepared using these Co(II) complexes as catalysts via the dehydrogenative coupling of 2-aminobenzyl alcohol and acetophenones. To understand the mechanism several control experiments and spectroscopic studies were performed. In Chapter IV, we have reported the synthesis and characterization of alkyl amine functionalized azo-aromatic Co (II) complexes and their catalytic activities for CO2 fixation reaction. Electronic effect of ligand and reaction mechanism is also investigated using various control experiments, spectroscopic studies and DFT calculations. Chapter V reports the synthesis and characterization of homoleptic octahedral complexes of Ni(II) featuring amine/imine-functionalized azo-aromatic ligands. In addition, redox induced amine/imine hemilability was explored upon reduction. Detailed physicochemical characterization techniques were used to assign the electron transfer series of the complexes. Chapter VI discusses the overall conclusion of the work presented in the thesis. The future directions are also depicted in this chapter.

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