Syntheses of Organozinc Enolates and Their Reactivities in Polymerization Reactions

Abstract

Syntheses and reactivities of organozinc enolates, having same structure as that of the chain end of growing poly(vinyl ketone) molecules, were studied. An addition reaction of ZnEt2 with ethyl styryl ketone gave an organozinc enolate, ethylzinc 5-phenyl-3-heptene-3-olate (ZE), fairly quantitatively. In the polymerization of ethyl isopropenyl ketone initiated with ethylzinc 1,3-diphenyl-1-pentene-1-olate (ZC), a second-order rate law with respect to ZC was established, suggesting a coordination-addition mechanism plausible for this reaction in a way similar to the previous result with phenyl styryl ketone. At the same time as the above studies, the chemical behavior of ZC and ZE toward carbon dioxide (CO2) was also examined. Through the measurements of time course of IR and NMR spectra of the reaction system, it was concluded that a polymeric form of organozinc enolates should be the final product formed in the reaction between ZC (or ZE) and CO2. This polymeric organozinc compound was able to catalyze the reaction of methyloxirane with CO2 to give rise to poly(propylene carbonate) and propylene carbonate.