Trineopentylphosphine: A Conformationally Flexible
Ligand for the Coupling of Sterically Demanding Substrates in the
Buchwald–Hartwig Amination and Suzuki–Miyaura Reaction
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Abstract
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)<sub>2</sub>, [Pd(4-<i>t</i>-Bu-C<sub>6</sub>H<sub>4</sub>)(TNpP)(μ-Br)]<sub>2</sub>, and [Pd(2-Me-C<sub>6</sub>H<sub>4</sub>)(TNpP)(μ-Br)]<sub>2</sub> 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
