title: Planar-Chiral Phosphine-Olefin Ligands Exploiting a (Cyclopentadienyl)manganese(I) Scaffold To Achieve High Robustness and High Enantioselectivity.
abstract: A series of 2-methyl-1,3-propenylene-bridged (η5-diarylphosphinocyclopentadienyl)(phosphine)manganese(I) dicarbonyl complexes 2 have been developed as a new class of phosphine-olefin ligands based on a planar-chiral transition-metal scaffold, which show better robustness as well as higher enantioselectivity over phosphine-olefin ligands 1 with a planar-chiral (η6-arene)chromium(0) framework. The practical enantiospecific and scalable synthesis of 2 has been established. Phosphine-olefin ligands 2 enable construction of an effective chiral environment around a transition-metal center upon coordination, and thus their rhodium(I) complexes exhibit excellent catalytic performance in the various asymmetric addition reactions of arylboron nucleophiles. Complex 2b, which has a bis(3,5-dimethylphenyl)phosphino group on the cyclopentadienyl ring, is found to be a superior chiral ligand in the rhodium-catalyzed asymmetric 1,4-addition reactions of arylboronic acids to various cyclic/acyclic enones giving the corresponding arylation products in over 99% ee. On the other hand, 2c and 2d, which have bis[3,5-bis(trifluoromethyl)phenyl]phosphino and bis(3,5-di-tert-buthyl-4-methoxyphenyl)phosphino groups, respectively, are highly efficient chiral ligands in the rhodium-catalyzed asymmetric 1,2-addition reactions of the arylboron nucleophiles to imines or aldehydes showing up to 99.9% ee. The X-ray crystallographic studies of (R)-2b and [RhCl((S*)-2b)]2reveal the absolute configuration of 2b and its phosphine-olefin bidentate coordination to a rhodium(I) cation. Structural comparison with [RhCl((R*)-1b)]2postulates the origins of the higher enantioselectivity of newly developed phosphine-olefin ligands 2.
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka Prefecture University , Sakai, Osaka 599-8531, Japan.
authors.forename: Ken
authors.identifier: 0000-0002-7844-4993
authors.initials: K
authors.lastname: Kamikawa
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka Prefecture University , Sakai, Osaka 599-8531, Japan.
authors.forename: Ya-Yi
authors.initials: YY
authors.lastname: Tseng
authors.affiliation: Institute for Catalysis, Hokkaido University , Kita-ku, Sapporo 001-0021, Japan.
authors.forename: Jia-Hong
authors.initials: JH
authors.lastname: Jian
authors.affiliation: Institute for Catalysis, Hokkaido University , Kita-ku, Sapporo 001-0021, Japan.
authors.forename: Tamotsu
authors.identifier: 0000-0003-4728-6547
authors.initials: T
authors.lastname: Takahashi
authors.affiliation: Institute for Catalysis, Hokkaido University , Kita-ku, Sapporo 001-0021, Japan.|Department of Natural Science, Graduate School of Science and Technology, Tokushima University , Tokushima 770-8506, Japan.
authors.forename: Masamichi
authors.identifier: 0000-0002-1893-3306
authors.initials: M
authors.lastname: Ogasawara