2,2 ',5,5 '-tetramethyl-4,4 '-bis(diphenylphoshino)-3,3 '-bithiophene: A new, very efficient, easily accessible, chiral biheteroaromatic ligand for homogeneous stereoselective catalysis

The four-step straightforward synthesis of enantiopure (+)- and (-)-2,2',5, 5'-tetramethyl-4,4'-bis-(diphenylphoshino)-3,3'-bithiophene (tetraMe-BITIOP ), a new C-2-symmetry chelating ligand for transition metals, is described, starting from 2,5-dimethylthiophene. The complexes of this electron-rich d iphosphine with Ru(II) and Rh(I) were used as catalysts in some homogeneous hydrogenation reactions of prostereogenic carbonyl functions of alpha- and beta-ketoesters, of prostereogenic carbon-carbon double bonds of substitut ed acrylic acids, and of N-acetylenamino acids. The enantiomeric excesses w ere found to be excellent in all the:experiments and comparable with the be st results reported in the literature for the same reactions, carried out u nder similar experimental conditions, with the metal complexes of the most popular chiral diphosphine ligands as catalysts.