BDI ∗ MgX(L) where X= n Bu and O t Bu and L=THF, py and DMAP. The rates of kinetic exchange of L where BDI ∗ =CH{C( t Bu)N-2,6- i Pr 2 C 6 H 3 } 2

BDI∗MgX(L), where X=nBu or OtBu and L=THF, 2-MeTHF, py and DMAP, undergo the reversible reaction shown above by a dissociative process involving the loss of the ligand, L. This process is involved in the rate of polymerization of rac-LA to give heterotactic PLA.