Preparation and structural characterization of bis(acetylacetonato)ruthenium(II)-BINAP: an efficient route to an effective asymmetric hydrogenation catalyst precursor

A simple one-pot synthesis of Ru(acac)2(S-BINAP) in near quantitative yield was achieved by the reduction of Ru(acac)3 (acac = acetylacetonate) with activated Zn in the presence of S-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (S-BINAP). The X-ray diffraction study revealed the presence of two independent molecules of Ru(acac)2 (S-BINAP) as well as three acetone molecules (solvent of crystallization) in the unit cell (monoclinic, space group P21 with a = 15.681(5), b = 12.765(4), c = 25.607(9)A, β = 98.16(3)°, V = 5074(3) A3, Z = 2, R = 0.059 and Rw = 0.067). Each ruthenium(II) complex has a distorted octahedral geometry involving two phosphorus atoms of BINAP and four atoms of oxygen from two η2-acac ligands. Although the conformation of the BINAP-containing seven-membered ring is δ in each molecule, both Λ and Δ metal configurations are observed. The molecular structure has been compared with Ru(OCOR)2(BINAP) (OCOR = pivalate, tiglate) structures. Ru(acac)2(S-BINAP) was used to catalyze the asymmetric hydrogenation of 2-(6′-methoxy-2′-naphthyl)acrylic acid to yield Snaproxen in high optical purity.