Low-valent Cobalt Complex Catalyzed Asymmetric Transformations in Thermal and Photochemical Conditions

Maji, Kakoli (2024) Low-valent Cobalt Complex Catalyzed Asymmetric Transformations in Thermal and Photochemical Conditions. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Kakoli Maji (16IP015)) 16IP015.pdf - Submitted Version Restricted to Repository staff only Download (45MB)

Abstract

One of the most efficient ways to meet the rising demand for non-racemic small molecules essential for medicine and pharmacy, nutrition, or material with optical properties is through asymmetric catalysis. It is exciting and challenging that one single molecule of chiral catalyst can transfer its chiral information to thousands of new chiral molecules in such processes. Though asymmetric catalysis is an evergreen emerging field, synthetic chemists are developing more reactive and selective catalysts to meet the needs of academia and industry. Transition metal-based enantioselective catalysis stands as one of the intricate yet extensively investigated domains in contemporary asymmetric catalysis. In this context, catalytic reductive coupling reactions have emerged as powerful carbon-carbon bond-forming tools in organic synthesis. Easily accessible, bench stable, and cheap π-component systems, including alkyne, alkene, diene, enone, allene, allyl halides, and eneal, were reductively coupled to build diverse chiral molecular libraries. Different low-valent transition metals such as rhodium, iridium, palladium, ruthenium, and nickel are employed as catalysts. Recently, there has been a growing application of first-row transition metal cobalt in the enantioselective reductive coupling reactions. The inexpensive and less toxicity increases its demand for use in various organic transformations. Early research into developing enantioselective transition-metal-catalyzed cross-coupling reactions was mainly centered on using configurationally labile organometallic species such as organomagnesium and organozinc reagents. They not only increase additional synthetic steps but also the metallic waste produced, burdening management and economics. In this context, reductive cross-coupling reactions sacrificing a benign reductant can be considered an alternative protocol for synthesizing various chiral structures. Thus, developing new catalytic pathways for asymmetric synthesis utilizing inexpensive 3d metal makes a process sustainable and brings an opportunity on different mechanistic fronts. This thesis's main aim will be to explore cobalt complexes for various reductive coupling reactions. The main focus will be constructing various carbon-carbon bonds asymmetrically using different cobalt complexes. This thesis is divided into five chapters.

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