Air Stable, Sterically Hindered Ferrocenyl Dialkylphosphines for Palladium-Catalyzed C−C, C−N, and C−O Bond-Forming Cross-Couplings

Pentaphenylferrocenyl di-tert-butylphosphine has been prepared in high yield from a two-step
synthetic procedure, and the scope of various cross-coupling processes catalyzed by complexes
bearing this ligand has been investigated. This ligand creates a remarkably general palladium
catalyst for aryl halide amination and for Suzuki coupling. Turnovers of roughly 1000 were observed
for aminations with unactivated aryl bromides or chlorides. In addition, complexes of this ligand
catalyzed the formation of selected aryl ethers under mild conditions. The reactions encompassed
electron-rich and electron-poor aryl bromides and chlorides. In the presence of catalysts containing
this ligand, these aryl halides coupled with acyclic or cyclic secondary alkyl- and arylamines, with
primary alkyl- and arylamines, and with aryl- and primary alkylboronic acids. These last couplings
provide the first general procedure for reaction of terminal alkylboronic acids with aryl halides
without toxic or expensive bases. The ligand not only generates highly active palladium catalysts,
but it is air stable in solution and in the solid state. Palladium(0) complexes of this ligand are also
air stable as a solid and react only slowly with oxygen in solution.