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

Abstract

The reaction of [CdBr2·4H2O] with N1,N1-dimethyl-N2-(pyridin-2-ylmethylene)ethane-1,2-diamine) (LA), 2-methoxy-N-(pyridin-2-ylmethylene)ethanamine (LB), 2-(piperidin-1-yl)-N-(pyridin-2-ylmethylene)ethanamine (LC), 2-morpholino-N-(pyridin-2-ylmethylene)ethanamine (LD), N1,N1-dimethyl-N3-(pyridin-2-ylmethylene)propane-1,3-diamine (LE) and 3-methoxy-N-(pyridin-2-ylmethylene)propan-1-amine (LF) in methanol produced the tridentate [(NN′X)CdBr2] complexes, namely [LACdBr2], [LBCdBr2], [LCCdBr2], [LDCdBr2], [LECdBr2] and [LFCdBr2], respectively. The molecular structures of the Cd(II) complexes revealed that the cadmium atom in [LnCdBr2] (Ln = LA, LC-LE) 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, [LnCdMe2] (LA-LF) 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 [LnCdBr2] (LA-LF). The preliminary results showed that these complexes yielded syndio-rich poly(methylmethacrylate) (PMMA) ([rr] = 0.66).