Synthesis of aliphatic polyesters has been studied intensively due to their biocompatible and biodegradable properties and their potential applications in medical and agricultural fields. There has been particular emphasis over the past decade on the synthesis of discrete, well-characterized complexes that are active polymerization initiators for the ring-opening polymerization (ROP) of lactide (LA) and beta-butyrolactone (BBL) to give, respectively, poly(lactide) (PLA) and poly(3-hydroxybutyrate) (PHB). These recent advances in catalyst design have led to a variety of polyester microstructures. This tutorial review focuses on the use of metal-based complexes for the stereoselective ROP of rac-LA and rac-BBL.

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CO2 is an ideal feedstock for chemical synthesis; unfortunately its thermodynamic stability is a barrier to widespread use. Active cobalt catalysts for the copolymerization of propylene oxide and CO2 are reported (see scheme; L=N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine), which have excellent regioselectivity for polycarbonate synthesis without concomitant production of cyclic carbonate by‐products.