Rationale Behind the Resistance of Dialkylbiaryl Phosphines toward Oxidation by Molecular Oxygen

Electron-rich dialkylbiaryl phosphines, which comprise a common class of supporting ligands for Pd-catalyzed cross-coupling reactions, are highly resistant toward oxidation by molecular oxygen. Presented herein are possible reasons why this class of phosphine ligands manifests this property. Experimental and theoretical data suggest that the two alkyl substituents on the phosphorus center and the 2' and 6' positions of the biaryl backbone play an important role in inhibiting oxidation of this class of ligands.