Structurally characterized, chiral heterobimetallic yttrocene derivatives L
i[Y(eta(5):eta(1)-C5R4SiMe2NCH2CH2OMe)(2)] (R = Me, H) have been shown to b
e active in the controlled ring-opening polymerization of L-lactide to give
poly(L-lactide)s with high molecular weights and moderately narrow molecul
ar weight distributions ((M) over bar(w)/(M) over bar(n) < 1.50). Both tran
sesterification and racemization appear to be less prominent. H-1 NMR spect
roscopic tetrad analysis of copolymers prepared using a mixture of L- and D
-lactide demonstrates the absence of any preference for one enantiomer duri
ng the polymerization.