COMPARING CHIRAL FERROCENYL AND RUTHENOCENYL LIGANDS - HOW SUBTLE STRUCTURAL-CHANGES INFLUENCE THEIR PERFORMANCE IN ASYMMETRIC CATALYSIS

A route to enantiopure heteroleptic ruthenocenyl derivatives has been found; the diastereoselective addition of MeLi to (R)-CyCH(Me)N(Me)CH= C5H4 (de = 74%), followed by a transmetalation reaction with either [C pRU(mu(3)-Cl)](4) or [(p-cymene)RUCl(2)](2)/KPF6, afforded the hetero leptic complexes (S,R)-[CpRu(eta(5)-C5H4CH(Me)N(Me)CH(Me)Cy)], 6, or ene)Ru(eta(5)-C5H4CH(Me)N(Me)CH(Me)Cy)](PF6-)-P-+, 5, in 93% and 72% y ields, respectively. Whereas 5 displayed a somewhat inert behavior, 6 reacted with NHMe(2), in acetic acid, to afford its dimethylamino cong ener (S)-7 in 93% yield. The latter was converted in two steps into th e bis(phosphine) derivatives (S)-(R)-CpRuC5H3CH(Me)PCy(2)PPh(2)-2, (S )-(R)-9, and (S)-(R)-CpRuC5H3CH(Me)PC(8)H(14)PPh(2)-2, (S)-(R)-10, an d into the P,N derivative R)-CpRuC5H3CH(Me){N(2)C(3)HMe(2)-3,5)PPh(2) }-1,2, (S)-(R)-11. These products were obtained in >99% ee after recry stallization. The ruthenocenyl derivatives were probed for their use a s chiral ligands for the palladium-catalyzed enantioselective allylic alkylation and the rhodium catalyzed hydroboration reactions. By emplo ying the ruthenocenylpyrazole (S)-(R)-11, styrene was converted to (S) -1-phenylethanol with 87% ee, whereas its isostructural ferrocenyl con gener (S)-(R)-16 afforded 94% ee. The following compounds were charact erized by X-ray diffraction: (S,R)-5, (S)-(R)-9, (S)-(R)-10, R)-14)Pd (eta(3)-C3H5)](+)-[OTf](-)((S)-(R*)-12), and [((S*)-(R*)-9)Pd(eta-C3H 5)](+)OTf(-) ((S)-(R*)-13).