Steric and Electronic Effects of Benzoferrocenyl Phosphine Ligands on Palladium-Catalyzed Allylic Alkylation and Suzuki Coupling Reactions

Five benzoferrocenyl phosphine ligands with the phosphorus atom attached to the 5-position of the benzoferrocene and some ligand-Mo(CO)5 complexes were prepared and fully characterized; the structure of one ligand was confirmed by X-ray crystallography. These ligands were applied in palladium-catalyzed allylic alkylation and Suzuki coupling of chlorobenzene with phenylboronic acid. Results were compared with those reported previously using ligands having the phosphorus atom attached to the 4-position of benzoferrocene. This structural modification resulted in an increase of activity of the ligands in allylic alkylation reaction but a decrease of activity in Suzuki coupling reactions. The underlying reasons are analyzed with the help of X-ray single crystal determined structures and CO stretching frequencies in the IR spectra of complexes between the ligands and Mo(CO)5.