Electronic and Steric Effects on the Reductive Elimination of Diaryl Ethers from Palladium(II)

Arylpalladium aryloxide complexes containing sterically and electronically varied phosphine ligands were prepared, and the rates for reductive elimination of diaryl ethers from these complexes were studied to determine the ligand properties that most strongly accelerate this unusual reaction. Electronic and steric effects were probed by preparing monomeric palladium complexes of the type (L)Pd(Ar)(OAr‘), in which L = DPPF (1,1‘-bis-diphenylphosphinoferrocene), CF3-DPPF (1,1‘-bis[di(4-(trifluoromethyl)phenyl)phosphino]ferrocene), and D-t-BPF (1,1‘-bis(di-tert-butylphosphino)ferrocene) and Ar = electron-deficient and electron-neutral aryl groups. Direct C−O bond-forming reductive elimination to form diaryl ethers in high yield was observed after warming the complexes that contained an electron-deficient aryl group bound to palladium. The rate constant for C−O bond-forming reductive elimination from the CF3-DPPF-ligated palladium complex was twice that obtained for the analogous DPPF-ligated complex. Reducti...