Cyclic ester insertion into a bismuth-amide bond: isolable molecular models for ROP initiation.

Reaction of a bismuth amide with L-lactide, ε-caprolactone and γ-butyrolactone gives isolable ring-opened products which are also observed during polymerisation studies, including rare crystallographically authenticated amidolactate and γ-butyrolactone-derived complexes. Monomer-dependent divergence between post-insertion transesterification, delayed propagation and arrested insertion provides insight into ROP initiation.