Alpha-diimine Nickel (II) and Palladium (II) Complexes in Cross-coupling Reactions




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Cross-couplings reactions are the most versatile synthetic tools and extensively applied for organic syntheses in the industrial production plants. Traditionally established cross-coupling reactions, including Suzuki–Miyaura, have been investigated over the last two decades because of synthetic applicability for manufacturing valuable functionalized building blocks in organic electronics, natural products, and drug discovery. Apart from Suzuki–Miyaura carbon-carbon cross-coupling, carbon-sulfur cross-coupling has been established as a potential synthetic method for synthesizing biologically and pharmaceutically active compounds. Remarkably, the introduction of heteroaromatics through carbon-sulfur cross-coupling added a new dimension to the pharmaceutical industries. Recently, direct arylation has gained much popularity for making πconjugated monomers and polymers through carbon-carbon bond formation that is an alternative tool to the Suzuki–Miyaura cross-coupling technique. Nonetheless, these useful synthetic procedures are facing enormous challenges arising from the catalytic systems. A significant portion of the catalysts employed in these cross-coupling reactions are air- and moisture-sensitive. Moreover, thermal instability is another drawback of implementing in elevated temperature. Notably, ligand design plays a crucial role in catalytic outcomes. The existing ligand design for the cross-coupling reactions lacks essential features, including steric and electronic requirements. Consequently, these shortcomings are subject to the poor catalytic performance that significantly hinders the industrial-scale application. In this dissertation, ligand design based on α-diimine frameworks is investigated in the Suzuki–Miyaura cross-coupling, carbon-sulfur cross-coupling, and direct arylation methods. Both nickel and palladium complexes with α-diimine cores were synthesized and applied to examine their potential scope in the cross-coupling reactions. Recent advances in the nickel and palladium-based catalytic systems in the cross-coupling reactions are described in chapter 1. In situ and well-defined nickel and palladium catalytic systems are discussed in this chapter. Moreover, existing challenges and possible solutions are also explained. Chapter 2 is designed to investigate the potential application of α-diimine-based nickel (II) and palladium (II) complexes in the Suzuki–Miyaura cross-coupling reaction. Notably, ligand design is extensively examined for making four different complexes by varying the ligand structure and metal center. Notably, a wide variety of substrates having challenging functional moieties are synthesized through carbon-carbon cross-coupling. Chapter 3 describes the synthesis and application of α-diimine-based nickel (II) and palladium (II) complexes in the carbon-sulfur cross-coupling. Both mono- and dinuclear complexes are synthesized and practiced for making aryl/alkyl sulfides. Mostly, pharmaceutically relevant heteroaryl moieties both from thiols and aryl halides are coupled. Chapter 4 is dedicated to examining the α-diimine-based nickel (II) and palladium (II) complexes in making valuable functionalized π-conjugated monomers through the direct arylation method. Mainly, five-membered heteroaromatics, including thiazole and thiophene derivatives, are applied with a wide variety of aryl halides. Moreover, the findings propose that α-diimine-based complexes can deliver direct arylation as an alternative technique to the carbon-carbon bond formation through Suzuki–Miyaura cross-coupling.



Chemistry, General