En route to biferrocene based Walphos ligands: The synthesis of unsymmetrically 2,2″-disubstituted biferrocenes by Negishi coupling

Negishi coupling conditions were identified that allowed the synthesis of unsymmetrically 2,2″-disubstituted biferrocenes from non-identical ferrocene fragments. The coupling reaction of (R)-1-(N,N-dimethylamino)ethylferrocene (1) with enantiopure (S)-2-(p-tolylthio)-iodoferrocene (4) led to a diastereomerically pure 2-[1-(N,N-dimethylamino)ethyl]-2″-[(4-methylphenyl)thio]-1,1″-biferrocene (5) that could be further transformed into diphosphine 8, a biferrocene based analogue of Walphos ligand SL-W001.