Enantioselective Synthesis of P-Chiral (η6-Arene)ruthenium(II) Complexes Using Enantiomerically Pure Orthometalated Palladium(II) Amine Complexes

• Published in: Organometallics 2003-07, Vol.22 (14), p.2977-2989
• Main Authors: Ghebreyessus, Kesete Y, Gül, Nizamettin, Nelson, John H
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om030172f

Enantiomerically pure, rigid, diphosphines [2-(dicyclohexylphosphino)-5,6-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-5-ene, [2-(diphenylphosphino)-5,6-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-5-ene, and the amidophosphine [2-(N,N-dimethylamido)-5,6-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-5-ene were prepared efficiently, by the asymmetric Diels−Alder reactions between dicyclohexylvinylphosphine (DCVP), diphenylvinylphosphine (DPVP), N,N-dimethylacrylamide (DMAA), and 3,4-dimethyl-1-phenylphosphole (DMPP) using chiral organopalladium(II) complexes containing orthopalladated (S)-1-α-(dimethylamino)ethylbenzene, (R)-1-α-(dimethylamino)ethylnaphthalene, or (S)-2-α-(dimethylamino)ethylnaphthalene as the reaction templates. Treatment of the diphosphine complexes with concentrated hydrochloric acid removed the chiral amine auxiliaries from the templates to give chelated dichloropalladium complexes. Then the ligands were displaced from the palladium chloride complexes with cyanide and reacted with [(η6-1,3,5-Me3C6H3)Ru)Cl2]2 in the presence of AgCF3SO3 to form enantiomerically pure [(η6-1,3,5-Me3C6H3)Ru(II)(P∼P)Cl]CF3SO3 complexes, chiral at ruthenium. Similarly, treatment of the amidophosphine palladium complexes with 1,2-bis(diphenylphosphino)ethane in dichloromethane liberated the enantiomerically pure P-chiral ligands, which reacted with [(η6-p-cymene)RuCl2]2 in the presence of AgCF3SO3 to form an inseparable mixture of two diastereomers of [(η6-p-cymene)Ru(II)(P∼O)Cl]CF3SO3, chiral at ruthenium. The complexes have been characterized by elemental analyses, circular dichroism, 1H, 31P{1H}, and 13C{1H} NMR spectroscopies, and in several cases X-ray crystallography.