Synthesis, characterization and polymerisation studies of cadmium(II) complexes containing N,N′,X-tridentate X-substituted (X = N, O) 2-iminomethylpyridines

The reaction of [CdBr₂·4H₂O] with N¹,N¹-dimethyl-N²-(pyridin-2-ylmethylene)ethane-1,2-diamine) (L_A), 2-methoxy-N-(pyridin-2-ylmethylene)ethanamine (L_B), 2-(piperidin-1-yl)-N-(pyridin-2-ylmethylene)ethanamine (L_C), 2-morpholino-N-(pyridin-2-ylmethylene)ethanamine (L_D), N¹,N¹-dimethyl-N³-(pyridin-2-ylmethylene)propane-1,3-diamine (L_E) and 3-methoxy-N-(pyridin-2-ylmethylene)propan-1-amine (L_F) in methanol produced the tridentate [(NN′X)CdBr₂] complexes, namely [L_ACdBr₂], [L_BCdBr₂], [L_CCdBr₂], [L_DCdBr₂], [L_ECdBr₂] and [L_FCdBr₂], respectively. The molecular structures of the Cd(II) complexes revealed that the cadmium atom in [L_nCdBr₂] (L_n = L_A, L_C-L_E) has a distorted square pyramidal geometry involving two nitrogen atoms and one nitrogen or oxygen atom of the N,N′,X-tridentate ligands and two bromo ligands. The dimethyl derivatives, generated in situ, [L_nCdMe₂] (L_A-L_F) initiated the polymerisation of rac-Lactide (rac-LA) and yielded heterotactic PLA. Notably, the substituent attached to ligand architecture affects the activities towards the rac-LA polymerisation, whereas the stereoselectivities remained unchanged. Moderate activities towards the polymerisation of methylmethacrylate (MMA) polymerisation in the presence of modified methylaluminoxane (MMAO) at 60 °C were observed for [L_nCdBr₂] (L_A-L_F). The preliminary results showed that these complexes yielded syndio-rich poly(methylmethacrylate) (PMMA) ([rr] = 0.66).