AN UNEXPECTEDLY STABLE CHIRAL HYDRIDO-SOLVENT COMPLEX OF RU-II - A MECHANISTIC LINK IN THE ENANTIOSELECTIVE HYDROGENATION OF PYRONES

The ligand l-2,2'-diyl)bis[3,5-di(tert-butyl)phenylphosphine] (1) form s an unexpectedly stable hydrido-bis-solvento complex of composition [ RuH(isopropanol)(2)(I)]BF4, (2) under the conditions used in the enant ioselective hydrogenation of pyrones. The structure of 2, determined b y X-ray diffraction, represents the first well-characterized chiral fi ve-coordinate bis-phosphine ruthenium-hydride complex stable as a solv ento complex, and provides a structural link in the enantioselective p yrone hydrogenation cycle catalyzed by [Ru(OAc)(2)(1)]. Using the aren e complex [RuH(p-cymene)(1)]BF4 (3), the chiral pocket of coordinated 1 is shown to be relatively rigid, via NMR spectroscopy. This is refle cted in restricted rotation about one of the four P-[3,5-di(tert-butyl )phenyl] P-C-ipso bonds at room temperature.