Ruthenocenyl Phosphine Designed as Novel Class of Phosphine-Arene Ligand: Application to Suzuki-Miyaura Reaction of Electronically and Sterically Deactivated Aryl Halides with Aryl Boronic Acids

摘要

The use of bulky and electron-rich phosphines as supporting ligands is now a well-recognized strategy for generating highly active palladium catalysts for cross-coupling reactions. Excellent palladium catalysts have also been realized with the use of biarylphosphine ligands which serve as the bidentate phosphine-arene ligand resulting from a pi-interaction between Pd~0 and the lower arene ring. We anticipated that the phosphine-arene ligand derived from the bidentate bisphosphine ligand by the replacement of one phosphino group with an electronically as well as geometrically appropriate arene group would have the ability to adopt the chelate geometry in the complex, as has the parent bisphosphine ligand. Thus, we designed the biphenylene ring-containing di-tert-butylruthenocenylphosphine (BUYRUTH-Phos) as the novel phosphine-arene ligand based on the 1,1'-bis(phosphino)ruthenocene, the well-precedented bidentate ligand. In order to take full advantage of the pi-interaction, we incorporated three phenyl groups along with biphenylene group the on the lower CP ring with the expectation that the stereochemistry favoring the chelate geometry would be controlled by their steric bulk which would allow for the phosphino group to locate upon the less sterically demanding biphenylene ring. In this paper we demonstrate that BUYRUTH-Phos is the exceptionally excellent ligand for the Pd-catalyzed Suzuki-Miyaura reaction (eq 1 and Table 1).