Transition Metal Complexes of Azo-aromatic and Phosphine Derived Pincer Like Ligands: Synthesis, Characterization and Reactivity Studies

Khatua, Manas (2022) Transition Metal Complexes of Azo-aromatic and Phosphine Derived Pincer Like Ligands: Synthesis, Characterization and Reactivity Studies. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Manas Khatua (15RS064)) 15RS064.pdf - Submitted Version Restricted to Repository staff only Download (18MB)

Abstract

This thesis comprises five chapters. Primarily, the reactivity of transition metal complexes containing non-innocent ligand have been explored. In view of this, a brief and concise literature review has been sketched in Chapter 1. Considering the works done in the thesis focuses have been given to the complexes and their reactivity containing redox non-innocent ligand(s), cooperative ligands, phosphine donor non-innocent ligand containing complexes that heterolytically cleave a bond for sustainable catalytic application. The reactions like oxidative addition, reductive elimination, C-C bond formation, C-N bond formation reaction as well as small molecule activation, hydrogenation and dehydrogenation reactions of organic substrates were considered in this chapter. Chapter 2 is focused on the synthesis and characterization of a series of new class of tridentate NNN-donor pincer-like amine functionalized azo-aromatic ligands and their Ni(II) complexes. A ligand redox mediated dehydrogenative imine formation from amine has been demonstrated using these Ni(II) complexes which has led to the isolation of a new pincer like azo-imine ligand. The mechanism of the reaction was investigated thoroughly by various experiments. In Chapter 3, we have synthesized and characterized a series of Cu(II) complexes containing aryl and aliphatic amine-functionalized NNN-donor tridentate ligands. Using sodium-L-ascorbate as reductant to the Cu(II) complexes, a highly efficient (ppm level) [2+3] azide-alkyne cycloaddition reaction is demonstrated. Mechanistic investigations have showed that the amine side arm in ligand backbone played a significant role in determining the efficiency of the catalyst. In Chapter 4, employing secondary alkyl amine-functionalized tridentate azo-aromatic pincer-like ligand containing Cu(II) complexes, aerobic oxidation of alcohols have been explored in presence of reductant cobaltocene, N-methyl imidazole and TEMPOH. The Cu(II) complex by the reduction of cobaltocene in the presence of NMI activates the dioxygen for oxidation of alcohol in presence of TEMPOH. The amine side arm of the ligand was hemilabile and showed significant role in enhancing the catalytic efficiency of the complexes. A plausible mechanism has been proposed experimentally as well as by computational studies. Chapter 5 deals with the synthesis and characterization of a new phosphine donor pincer like, PN³ and its phosphine oxide, PN³O pincer-like ligands and their Co(II) complexes. These complexes were explored for base-promoted dearomatization through deprotonation of the NH proton. These dearomatized PN³-Co and PN³O-Co complexes have been explored in the dehydrogenative coupling reaction between alcohols and amines for the sustainable synthesis of imines and quinolines. A detailed reaction mechanism has been proposed experimentally as well as theoretically.

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