Dirhodium Complexes Heterochiral-at-the-Metal Centers: An Alternative Type of Paddlewheel Catalyst for Asymmetric Synthesis

The prototype of an entirely new class of dirhodium paddlewheel complexes is disclosed, which is chiral at both inequivalent metal centers although it carries just three different achiral μ-bridging equatorial ligands. One of them is a carboxamidate, which ensures selective carbene formation at the Rh[O₃N] face of the catalyst; moreover, the -NH group engages the ester carbonyl of the emerging rhodium carbene intermediate derived from α-stannylated α-diazoacetate in interligand hydrogen bonding, which is critically important for controlling the stereochemical course of the ensuing [2 + 1] cycloaddition. The new heterochiral catalyst furnished stannylated cyclopropane derivatives with excellent diastereo- and enantioselectivity; moreover, a cyclopropane with a quaternary trifluoromethylated stereocenter was obtained with an unprecedented level of asymmetric induction.