Chiral atropisomeric five-membered biheteroaromatic diphosphines: new ligands of the bibenzimidazole and biindole series

Two new chiral atropisomeric biheteroaromatic diphosphines are described: 2,2′-bis(diphenylphosphino)-1,1′-bibenzimidazole (3a) and 3,3′-dimethyl-1,1′-bis(diphenylphosphino)-2,2′-biindole (4a). Structural characterization is given and configurational stability at room temperature demonstrated. The oxidation potential was recognized as a good tool to evaluate the electronic availability of the phosphorus atom in the series of biheteroaromatic diphosphines. Its value increases parallel to the electronic demand of the heterocyclic system and also depends on the position of the diphenylphosphino group.