A Binaphthyl-Based Scaffold for a Chiral Dirhodium(II) Biscarboxylate Ligand with α‑Quaternary Carbon Centers

A chiral dirhodium­(II) paddlewheel
complex has been synthesized
from biscarboxylate ligands derived from BINOL, and the resulting
complex has been used in enantioselective carbene/alkyne cascade reactions.
The ligand design was guided by requirements of α,α-dimethyl
substituted carboxylates and bidentate ligands to ensure high levels
of catalytic activity. Previously disclosed chiral complexes lack
these features, resulting in low product yields. The design successfully
replicated or exceeded the yields of the unusually effective achiral
catalyst for the cascade reaction, Rh2(esp)2, which often shows unique reactivity. Promising enantioselectivity
was observed for aldehyde-derived hydrazone substrates (29–96%
ee), showing that the new scaffold has significant potential.