The NMR and X-ray crystallographic studies clarified that planar-chiral alkenylene-bridged (phosphino-π-arene)(phosphine)chromium complexes (R)-1 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 phosphine-olefin chelate coordination of (R)-1 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 of the arylboron nucleophiles. The control experiments demonstrated that the (η2-olefin)-Rh interaction as well as the bridging structure in (R)-1 played the pivotal roles in the high enantioselectivity of the Rh-catalyzed asymmetric reactions. Homologous (phosphino-cyclopentadienyl)(phosphine)manganese(I) species (S)-2 show the better robustness as well as the higher enantioselectivity over chromium-based ligands (R)-1. Complexes (S)-2 are 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 up to 99.9% ee. They are also highly effective in the rhodium-catalyzed asymmetric 1,2-addition reactions of the arylboron nucleophiles to imines or aldehydes showing up to 99.9% ee.

Design and synthesis of phosphine-olefin ligands with planar-chiral metal complex scaffold and application in asymmetric catalysis

253rd National Meeting (2017)

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