On the structure of the Kagan-Modena catalysts for asymmetric oxidation ofsulfides

The reaction of Ti((OPr)-Pr-i)(4), diisopropyl (R,R)-tartrate and N,N'-di(t rifluoromethylsulfonyl)ethane- 1,2-diamine in 1:2:1 ratio provided a symmet ric, dinuclear complex of formula [Ti(eta(2)-dipt)(eta(2)-Hdipt)((OPr)-Pr-i )](2) (where H(2)dipt is diisopropyl tartrate), in which each metal bears o ne (OPr)-Pr-i ligand, a chelating tartrate diolate bridging the two metals, and a second, univalent tartrate unit in a novel binding mode, attached th rough alkoxy and ester carbonyl oxygens. This species appears to be stabili zed through hydrogen bonding with the disulfonamide. The configuration at T i deduced by NMR spectral information coincides with that calculated to be the most stable. In the absence of the disulfonamide, the data are consiste nt with an equilibrium between this complex, free tartrate and a condensati on product of formula Ti-4(dipt)(5)(Hdipt)(2)((OPr)-Pr-i)(4) which features an eta(2),eta(2)-tartrate linking two Ti-2(eta(2)-dipt)(2)(eta(2)-Hdipt)(( OPr)-Pr-i)(2) units. The relationship between these species and the Kagan a nd Modena catalysts for the asymmetric oxidation of sulfides is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.