Chan-Lam (CL) couplings, oxidative couplings between aryl boronic acids and various nucleophiles, offer an alternative to Buchwald-Hartwig couplings under much milder conditions. Typical catalysts are simple copper salts, copper acetate being the most commonly used. The solvent, the counteranion and added base/ligand all play various roles in the reaction mechanism. As a consequence, different and carefully optimized reaction protocols are required even for closely similar substrates such as anilines and amines. Incorporating the roles typically played by anion, solvent and added base in custom-designed ligands afforded coordination complexes, such as 1 and 2, which showed not only some of the highest activities in CL couplings, but also provided a general reaction protocol for a large variety of N-nucleophiles. Typical side reactions, such as deboration or homocoupling, were absent and quantitative conversion of amine can be achieved without using excess boronic acid. A detailed investigation of the reaction mechanism identified potential bottlenecks of the reaction and suggested improvements on catalyst design. Several pathways of increasing the efficiency of the Cu(II)-Cu(III) oxidation step, such as photocatalysis or an additional catalytic oxidant, were investigated.

Chan–Lam couplings with tridentate sulfonate ligands: Small steps toward more general catalysts

2019 Fall National Meeting

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