Tartrates polymer-linked

Polymer-linked tartrate esters have been prepared and used for asymmetric epoxidation in efforts to simplify reaction workup procedures and to allow recycling of the chiral tartrate [21]. The tartrates were linked through an ester bond to either a hydroxymethyl or a hydroxyethyl group on the polymer backbone to form 4 and 5, respectively. 

Epoxidation catalysts were prepared from these polymer-linked tartrates by combination with 0.5 equiv. of Ti(0-i-Pr)4, based on the weight of tartrate ester, which had been added to the polymer. Epoxidation of geraniol with 4 or 5 gave epoxy alcohol with 49 and 65% ee, respectively. Recycling of the polymer-linked tartrate was possible, but the subsequent epoxidation suffered from significant loss in enantioselectivity [21 ]. 

Obviously, the way to heterogeneous enantioselective catalysis is open when chiral ligands are introduced into the polymers. This idea was first proposed by Okamoto and Still (231). However, the first catalytic results were published by Cazaux and Caze (235). These authors use the asymmetric Mo(VI) complex (9) covalently bound to a cross-linked polystyrene resin for the enantioselective epoxidation of geraniol. Unfortunately, the enantiomeric excess obtained was low—far below that obtained with the Ti-tartrate catalyst (Section II,B). Moreover, the polymeric structure appeared to be unstable. 

An unbranched polymer composed of 1,4 )9-linked glucopyranose units. Polymeric. Minimum formula given. The most abundant organic material found in plants forming the principal constit. of their cell walls giving them structural strength. Cotton is almost pure cellulose. Wood is the most important industrial source. Basic material for textile and paper manuf. Used in the isoln. of heavy metals. Insol. H2O, most solvs., but forms sol. complexes in cone. aq. ZnCl2, copper-amine solutions and with Fe sodium tartrate solution. 

---