Isotactic rac-Lactide Polymerization with Copper Complexes: The Influence of Complex Nuclearity.

Diiminopyrrolide copper alkoxide complexes, LCuOR (OR(1)=N,N-dimethylamino ethoxide, OR(2)=2-pyridyl methoxide), are active for the polymerization of rac-lactide at ambient temperature in benzene to yield polymers with M(w)/M(n)=1.0-1.2. X-ray diffraction studies showed bridged dinuclear complexes in the solid state for both complexes. While LCuOR(1) provided only atactic polylactide, LCuOR(2) produced partially isotactic polylactide (P(m)=0.7). The difference in stereocontrol is attributed to a dinuclear active species for LCuOR(2) in contrast to a mononuclear species for LCuOR(1).