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Free keywords:
bimetallic catalysts; bismuth; carbene complexes; cyclopropanation; rhodium
Abstract:
Cyclopropanation reactions of styrene derivatives with donor/acceptor carbenes formed in situ are significantly more enantioselective when catalyzed by the heterobimetallic bismuth‐rhodium complex 5a endowed with N‐phthalimido tert‐leucine paddlewheel ligands rather than by its homobimetallic dirhodium analogue 1a. This virtue is likely the result of two synergizing factors: the conical shape of 5a translates into a narrower calyx‐like chiral binding site about the catalytically active Rh center; the Bi atom, although fully solvent exposed, does not decompose aryl diazoacetates and is hence incapable of promoting a racemic background reaction. Moreover, ligand variation proved that successful catalyst design mandates that the anisotropy of the conical heterobimetallic core be matched by proper directionality within the ligand sphere.
