A new class of bis-phospholane ligands for asymmetric catalys

The class of the bis-phospholane ligands were introduced by Mark Burk in rhodium-catalyzed asymmetric hydrogenation reactions of prostereogenic carbon-carbon double bonds in 1990. The most successful ligands of this series are the dialkyl-DuPHOSes (1). Their most outstanding e. peculiarities are the dialkyl substitution at the phosphorus atoms which improves their electronic availability at phosphorus and the rigidity of the structure surrounding the metal core, which improves the efficiency of the chirality transfer during the reaction. The brealcdowns of these very e powerful mediators are their complex synthesis and the difficulty in tuning their electromc properties. We have recently given the preliminary examples of a new class of C2-bis(phospholane) ligands having the general formula 2,[h1 characterized by a five-membered heteroaromatic system as scaffold for the phospholane groups. The eterocyclic five-membered system allows a fine tuning of of the electromc availability at phosphorus either by changing the supporting heterocyclic system, or the position of the phosphorus atoms on it. The synthetic approach to the thiophene- and Iofl pyrrole-based bis-phospholanes 3 and 4, their chemical and electrochemical characterization and preliminary applications as ligands of Rh(I) in the asymmetric hydrogenation of functinalized carbon-carbon and carbon-oxigen double bond are discussed. The results have been compared ng, with those obtained with allcyl-DuPHOS (i).