Certain organoboronic acids, particularly those with heteroaryl and polyfluoroaryl groups, are prone to fast decomposition in the presence of base and have long been challenging, though attractive, substrates for Suzuki-Miyaura coupling (SMC) and other coupling reactions. This talk will describe a mild yet rapid method for coupling bromoarenes with any polyhaloarylboronic acid. These reactions are complete within one to five hours at room temperature using 1 mol% Pd. The analogous pinacol ester reagents also react equally fast in this method, which contrasts their typically sluggish reactivity in many other catalytic processes. Key to these fast reactions is a bench-stable, coordinatively-unsaturated precatalyst, Pd(PAd<sub>3</sub>)(Ar)(Br) (Ad = 1-adamantyl; Ar =aryl), that can be prepared from commercial reagents in one step and good yields. While typical palladium precatalysts do not initiate under the exceedingly mild conditions of this method, the “on-cycle” precatalyst is a catalytic intermediate that reacts with no induction period. Preliminary mechanistic experiments aimed at understanding the origin of this high catalytic reactivity characteristic of PAd<sub>3</sub>-Pd complexes will be discussed.

Unstable boronic acid and pinacol ester cross-coupling enabled by an “on-cycle” precatalyst

255th National Meeting (2018)

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