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

Herein we report the synthesis of the mixed-ligand paddlewheel complex tris[N-phthaloyl-(S)-tertleucinate](triphenylacetate)dirhodium(II), Rh-2(S-PTTL)(3)TPA, the structure of which bears similarity to the chiral crown complex Rh-2(S-PTTL)(4). Rh-2(S-PTTL)(3)TPA engages substrate classes (aliphatic alkynes, silylacetylenes, alpha-olefins) that are especially challenging in intermolecular reactions of alpha-alkyl-alpha-diazoesters, and catalyzes enantioselective cyclopropanation, cyclopropenation, and indole C-H functionalization with yields and enantioselectivities that are comparable or superior to Rh-2(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.