Preparation of supported yttrium alkoxides as catalysts for the polymerization of lactones and oxirane

Two methods have been reported that allow yttrium alkoxides to be supported on porous silica and to be used afterward as heterogeneous catalysts in the ring-opening polymerization of oxirane and e-caprolactone. In the two methods, [tris(hexamethyldisilyl)-amide]yttrium [Y[N(SiMe3)(2)](3)} is the metal alkoxide precursor. It is directly reacted with the silanol groups of the support, in the first method, and this is followed by alcoholysis of the unreacted amide groups. The flexibility of this method seems to be limited because the grafting density and the structure of the grafted Y alkoxide (less than one alkoxide by metal) are independent of the experimental conditions. In the second method, Y[N(SiMe3)(2)](3) is first reacted with 1 or 2 equiv of alcohol with the formation of the mixed Y alkoxide/amide. The amide functions are used to attach Y to the support. This method is free from side reactions, quite reproducible, and well suited to support one type of active species (monoalkoxide or dialkoxide). Preliminary experiments with e-caprolactone polymerization have confirmed the activity of the supported Y alkoxide, whatever preparation method is used. (C) 2003 Wiley Periodicals, Inc.