Development of Chiral-At-Ruthenium Mesoionic Carbene Catalysts

Building on our previously established chiral-at-metal approach, in which the overall chirality of the transition metal catalyst is solely determined by a stereogenic metal center, we here present a new addition to the family of C₂-symmetric chiral-at-ruthenium catalysts. These are C₂-symmetric chiral ruthenium complexes featuring strongly σ-donating 1,2,3-triazol-5-ylidene mesoionic carbene (MIC) ligands. The complexes demonstrate excellent catalytic activity and enantioselectivity in a nitrene-mediated ring-closing C(sp³)-H amination of an aliphatic azide, leading to the formation of an N-Boc-protected chiral pyrrolidine. This study highlights the potential of this new class of chiral mesoionic carbene ruthenium complexes to further enhance or modify the reactivity of ruthenium-based chiral-at-metal catalysts.