Unlike common cross-coupling reaction examples using privilege substrates, the coupling processes employing highly steric congested electrophilic partners have been a lasting challenge. Here we report the first general examples of palladium-catalyzed Miyaura borylation of steric hindered aryl chlorides. Key to success of this reaction relies on the distinctive tailor-made phosphine ligand in which it features of smaller phosphine head and larger remote steric bulk. This concept is on contrary, yet complementary to the existing characteristic of common phosphines, e.g. Pt-Bu3 or biaryl-PCy2 and etc., where they consist of localized steric bulk at the phosphorous center. In fact, the smaller phosphine motif effectively allows coupling partner to approach Pd center at the initial stage. Our finding showed that even an extremely steric hindered 2,6-di-iso-propyl-substituted aryl chloride was applicable under this newly developed catalyst system. Nice functional group compatibility was observed under these reaction conditions and the catalyst loading down to 0.05 mol% Pd was able to be achieved for particular entry. The success of this ligand-enabled C-B bond formation is believed to offer unique fundamental knowledge in attaining catalyst establishments fit for other highly steric hindered cross-coupling reactions in relevance.

A Rational Ligand Design for Palladium-Catalyzed Miyaura Borylation of Highly Steric Hindered Aryl Chlorides

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