Bis(amidinate) tin(II) complex (1) was reported as active catalyst for ring-opening copolymerization of cyclic anhydrides and epoxides via a binary catalyst system. Polymerizations of six combinations of epoxides and cyclic anhydrides were carried out giving highly alternating poly(anhydride-alt-epoxide) with narrow dispersities, except for cyclohexene oxide where significant amount of ether linkage up to 62 % was observed. This ether linkages could be diminished by increasing the amount of cocatalyst to over 3 equiv. Six well-known cocatalysts were screened where PPNCl was found to be the best cocatalyst.
