A01 • 3d Transition-Metal-Catalyzed Borylations

Organoboron reagents are invaluable in modern synthetic chemistry due to their diverse applications in medicinal, agrochemical, and materials science. Transformation of C‒B bonds into C‒X (X = C, N, and O) bonds in a stereo-controlled fashion has become invaluable in medicinal, agrochemical, and natural products chemistry, as well as in materials science. Traditional borylation reactions have relied on expensive precious metals, but recent advances highlight the potential of inexpensive, more abundant and less toxic 3d metals. This project aims to develop novel 3d metal catalyzed borylation reactions using diborane(4) esters, with a focus on mechanistic understanding and synthetic applications. Specifically, the goals of this project are: (1) to develop new and efficient methods for 3d metal catalyzed borylations using diborane(4) esters; (2) to build up chiral advanced building blocks readily convertible into a diversity of enantiopure molecules, with potential applications for material science; and (3) to gain a detailed mechanistic understanding of transition metal boryl complexes and catalytic borylations. These goals will be achieved by leveraging previous results from the Radius group on nickel-catalyzed borylation reactions for new reactivity and radical borylations as well as developing novel protocols for enantioselective borylations, capitalizing the expertise of the Wencel-Delord group on asymmetric synthesis. The Hierlmeier group contributes with their knowledge on titanium chemistry and catalysis, in general. Initially, the synthesis and reactivity of 3d-metal boryl complexes of nickel and titanium will shed new light on bonding and reactivity of boryl complexes, which are the key intermediates in catalytic borylations. In parallel, new synthetic methods using nickel- and titanium-based catalysts will be developed. This will include (chiral) NHC nickel complexes for borylation of aryl halides and C‒C bonds, exploiting the expertise of the Wencel-Delord group. Stereoselective nickelcatalyzed borylations will provide access to enantioenriched structures. Furthermore, novel radical borylation protocols based on Ti(III/IV) catalytic cycles will be developed. The combination of titanium radical catalysis and nickel couplings will deliver novel dual catalysis protocols for borylation reactions.