Chiral N-heterocyclic biscarbenes based on 1,2,4-triazole as ligands for metal-catalyzed asymmetric synthesis.

A facile and straightforward synthetic procedure for the preparation of new chiral bis-1,2,4-triazolium salts and their corresponding rhodium(I) biscarbene complexes are reported. It is widely applicable for the synthesis of 1,2,4-triazolium salts. The new chiral biscarbenes represent promising ligands for transition metal-catalyzed asymmetric syntheses. Their first successful application is demonstrated by the rhodium-catalyzed hydrogenation of dimethylitaconate and methyl-2-acetamidoacrylate which yielded enantioselectivities of up to 61% ee.