In bimetallic palladium catalyst for asymmetric allylic substitution reactions

With 1,1'-diacetylruthenocene (9) as starting material, the preparation of 1,1'-bis[1-(1-{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethy})-1H-pyrazol-3-yl]ruthenocene ((R,R)-(S,S)-12) is attained in three steps. 12 coordinates to two independent Pd(II)-pi-allyl units to form the dicationic complex 15, isolated as a bis(hexafluorophosphate) salt. This has been characterized by X-ray and 2D NMR methods in solution, along with the analogous derivative 14, which contains 1-{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}-3-ruthenocenyl-1H-pyrazole ((R)-(S)-8b). The three Pd(II)-allyl fragments in these two complexes show very similar conformational features. In the Pd-catalyzed substitution reaction of ethyl (1,3-diphenylallyl)carbonate (1) with benzylamine, the bimetallic catalyst containing ligand 12 and the mononuclear catalyst formed by 8b afford the same high enantioselectivity (99.3%).