Synthesis, Characterization and Catalytic Activity Studies of Rhenium Carbonyl Complexes Containing Chiral Diphosphines of the Josiphos and Walphos Families

Ten rhenium carbonyl complexes-[Re(H)(CO)(3)(1a)], [Re-3(mu-H)(3)(CO)(10) (1a)], [Re-2(CO)(9)(2a)], [Re-2(CO)(8)(2a)], [Re-2(CO)(9)(2b)], [{Re-2(CO)(9)}(2)(2b)], [Re-2 (CO)(8)(2b)], [Re-2(CO)(8)(1b)], [Re-2(mu-H)(2)(CO)(6)(2b)] and [Re-3(mu-H)(3)(CO)(11)(2b)]-containing different bidentate chiral phosphine ligands of the Josiphos (1a, 1b) and Walphos (2a, 2b) families have been synthesized and fully characterized (1a: (R)-1-{(S-P)-2-[Bis[3,5-bis(trifluoromethyl) phenyl] phosphino] ferrocenyl} ethyldi(3,5-xylyl) phosphine, 1b: (R)-1-{(S-P)-2-[Di(2-furyl) phosphino] ferrocenyl} ethyldi-tert-butylphosphine, 2a: (R)-1-{(R-P)-2-[2-[Bis(4-methoxy-3,5-dimethylphenyl) phosphino] phenyl] ferrocenyl} ethylbis[3,5-bis(trifluoromethyl) phenyl] phosphine and 2b: (R)-1-{(R-P)-2-[2( Diphenylphosphino) phenyl] ferrocenyl} ethyldicyclohexylphosphine). The phosphine-substituted clusters were tested for hydrogenation of tiglic acid [trans-2-methyl-2-butenoic acid]. The catalytic reactions gave reasonable conversion rates (15-88 %) under relatively mild conditions but relatively moderate enantiomeric excesses (8-57 %) were observed. The crystal structures of [ReH(CO)(3)(1a)], [Re-2 (CO)(9)(2a)], [{Re-2(CO)(9)}(2)(2b)] and [Re-2(mu-H)(2)(CO)(6)(2b)] are presented.