Pd‐PEPPSI‐IPent: An Active, Sterically Demanding Cross‐Coupling Catalyst and Its Application in the Synthesis of Tetra‐Ortho‐Substituted Biaryls

Incredible Bulk: A series of N-heterocyclic carbene catalysts (see picture) were prepared and evaluated in the Suzuki-Miyaura reaction. A variety of sterically encumbered tetra-ortho-substituted biaryl products were formed from unreactive aryl chlorides using the isopentyl-substituted catalyst at temperatures ranging from 65 degrees C to room temperature. The cyclopentyl-substituted catalyst was virtually inactive, demonstrating that "flexible bulk" is essential to promote these transformations.