Rh2(S-PTTL)3TPA—a mixed-ligand dirhodium(ii) catalyst for enantioselective reactions of α-alkyl-α-diazoesters

Abstract

Herein we report the synthesis of the mixed-ligand paddlewheel complex tris[N-phthaloyl-(S)-tert-leucinate](triphenylacetate)dirhodium(II), Rh₂(S-PTTL)₃TPA, the structure of which bears similarity to the chiral crown complex Rh₂(S-PTTL)₄. Rh₂(S-PTTL)₃TPA engages substrate classes (aliphatic alkynes, silylacetylenes, α-olefins) that are especially challenging in intermolecular reactions of α-alkyl-α-diazoesters, and catalyzes enantioselective cyclopropanation, cyclopropenation, and indole C–H functionalization with yields and enantioselectivities that are comparable or superior to Rh₂(S-PTTL)₄. Mixing ligands on paddlewheel complexes offers a versatile handle for diversifying catalyst structure and reactivity. The results described herein illustrate how mixed-ligand catalysts can create new opportunities for the optimization of catalytic asymmetric processes.