Trineopentylphosphine: A Conformationally Flexible Ligand for the Coupling of Sterically Demanding Substrates in the Buchwald–Hartwig Amination and Suzuki–Miyaura Reaction

Trineopentylphosphine
(TNpP) in combination with palladium provides
a highly effective catalyst for the Buchwald–Hartwig coupling
of sterically demanding aryl bromides and chlorides with sterically
hindered aniline derivatives. Excellent yields are obtained even when
both substrates include 2,6-diisopropyl substituents. Notably, the
reaction rate is inversely related to the steric demand of the substrates.
X-ray crystallographic structures of Pd­(TNpP)2, [Pd­(4-t-Bu-C6H4)­(TNpP)­(μ-Br)]2, and [Pd­(2-Me-C6H4)­(TNpP)­(μ-Br)]2 are reported. These structures suggest that the conformational
flexibility of the TNpP ligand plays a key role in allowing the catalyst
to couple hindered substrates. The Pd/TNpP system also shows good
activity for the Suzuki coupling of hindered aryl bromides.