title: Phosphine-olefin ligands based on a planar-chiral (π-arene)chromium scaffold: design, synthesis, and application in asymmetric catalysis.
abstract: The NMR and X-ray crystallographic studies clarified that planar-chiral alkenylene-bridged (phosphino-π-arene)(phosphine)chromium complexes 3 were capable of coordinating to a rhodium(I) cation in a bidentate fashion at the (π-arene)-bound phosphorus atom and at the olefin moiety. The P-olefin chelate coordination of 3 constructs the effective chiral environment at the metal center, and thus, these rhodium complexes display high performances in various rhodium-catalyzed asymmetric 1,4- and 1,2-addition reactions with arylboron nucleophiles. The control experiments demonstrated that the (η(2)-olefin)-Rh interaction as well as the bridging structure in 3 played the pivotal roles in the high enantioselectivity of the Rh-catalyzed asymmetric reactions. To enhance the synthetic utilities of these phosphine-olefin ligands, an enantiospecific and scalable synthetic method was developed. The novel synthetic method is flexible in terms of the substituent variation, and a library of the planar-chiral (arene)chromium-based phosphine-olefin ligands was established by the combinatorial approach. Among the newly prepared ligand library, compound 3g, which is with a bis(3,5-dimethylphenyl)phosphino group on the η(6)-arene ring, was found to be a far better chiral ligand in the rhodium-catalyzed asymmetric reactions showing excellent enantioselectivity and high yields.
authors.affiliation: Catalysis Research Center and Graduate School of Life Science, Hokkaido University , Kita-ku, Sapporo 001-0021, Japan.
authors.forename: Masamichi
authors.initials: M
authors.lastname: Ogasawara
authors.forename: Ya-Yi
authors.initials: YY
authors.lastname: Tseng
authors.forename: Sachie
authors.initials: S
authors.lastname: Arae
authors.forename: Tomotaka
authors.initials: T
authors.lastname: Morita
authors.forename: Takeshi
authors.initials: T
authors.lastname: Nakaya
authors.forename: Wei-Yi
authors.initials: WY
authors.lastname: Wu
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Takahashi
authors.forename: Ken
authors.initials: K
authors.lastname: Kamikawa