Molybdenum-Catalyzed Enantioselective Synthesis of Planar-Chiral (η⁵‑Phosphacyclopentadienyl)manganese(I) Complexes and Application in Asymmetric Catalysis

Enantioselective desymmetrization of C_s-symmetric (η⁵-2,5-dialkenylphospholyl)­(allyldiphenylphosphine)­manganese­(I) dicarbonyl complexes 1 was realized by molybdenum-catalyzed asymmetric ring-closing metathesis (ARCM), and the corresponding bridged planar-chiral phosphacymantrene derivatives 2 were obtained in good yields with excellent enantioselectivity. The enantioselectivity of the ARCM reaction was strongly influenced by the structures of the phospholyl-bound alkenyl groups, and the highest enantioselectivity of up to 99% ee was achieved in the reaction of 1d,e, which possess the 2-methylpropenyl substituents at the 2- and 5-positions of the η⁵-phospholides. Single-enantiomeric planar-chiral 2d, which was obtained by the recrystallization of the highly enantiomerically enriched ARCM product, can serve as a chiral ligand for the palladium-catalyzed asymmetric allylic alkylation to show good enantioselectivity in up to 74% ee.