Synthesis and application of diphenyl sulfide linked bis(imidazoline) ligands: Dramatic electronic effect of ligands on catalytic behavior

Diphenyl sulfide linked bis(imidazoline) ligands with electron-withdrawing N-Ts substitution and electron-donating N-alkyl or N-H substitutions were synthesized through different routes. The electronic effects of the ligands were tuned rationally, and dramatic variation in their catalytic behavior was observed. N-Alkyl and N-H ligands demonstrated much higher catalytic activity and improved enantioselectivity than N-Ts ligands in Pd-catalyzed asymmetric allylic alkylation reactions. Diphenyl sulfide linked bis(imidazoline) ligands were synthesized. The electronic effects of the ligands were tuned rationally, and dramatic variation in their catalytic behavior was observed. N-Alkyl and N-H ligands showed much higher catalytic activity and improved enantioselectivity over N-Ts ligands in Pd-catalyzed asymmetric allylic alkylation reactions.