In Situ and Reactor Study of the Enantioselective Hydrogenation of Acetylacetone by Ruthenium Catalysis with the New Chiral Diphosphine Ligand (R)-(R)-3-Benzyl-2,4-bis(diphenylphosphino)pentane

The new optically pure C1-symmetric diphosphine ligand (R)-(R)-3-benzyl-2,4-bis(diphenylphosphino)pentane (BDPBzP) has been synthesized by enantioselective reduction of 3-benzyl-2,4-pentanedione with [((S)-BINAP)Ru(p-cymene)Cl]Cl, followed by the reaction of potassium diphenylphosphide with the bis(mesylate) intermediate (S)-(S)-PhCH2CH(CH(OMs)CH3)2. The Ru(II) complexes [(BDPBzP)Ru(p-cymene)I]I·2CH2Cl2 (5), [(BDPBzP)(DMSO)Ru(μ-Cl)3RuCl(BDPBzP)] (6a), and [(BDPBzP)RuCl(CH3CN)3]OTf (7) have been prepared and characterized by multinuclear NMR spectroscopy. The p-cymene complex 5 has been authenticated by a single-crystal X-ray analysis. All Ru(II) complexes are effective catalyst precursors for the enantioselective hydrogenation of acetylacetone to (R)-(R)-2,4-pentanediol. The best catalytic performance in terms of enantioselective discrimination (ee's up to 99%) has been observed for the dimer 6a. An in situ high-pressure NMR study in catalytic conditions has shown that the nonclassical polyhydride dimer [...