Novel Cobalt(II) complexes containing N,N-di(2-picolyl)amine based ligands; Synthesis, characterization and application towards methyl methacrylate polymerisation

• Co(II) complexes with N′-substituted N,N-di(2-picolyl)amine ligands are synthesized.
• Co(II) complexes exhibited diverse coordination geometries around the metal centre.
• Co(II) complexes yielded syndiotactic PMMA in the presence of MMAO.

The reaction of [CoCl2·6H2O] with N′-substituted N,N-di(2-picolyl)amine ligands such as 1-cyclohexyl-N,N-bis(pyridin-2-ylmethyl)methanamine (LA), 2-methoxy-N,N-bis(pyridin-2-ylmethyl)ethan-1-amine (LB), and 3-methoxy-N,N-bis(pyridin-2-ylmethyl)propan-1-amine (LC), yielded [LnCoCl2] (Ln = LA, LB and LC), respectively. The Co(II) centre in [LnCoCl2] (Ln = LA, and LC) adopted distorted bipyramidal geometries through coordination of nitrogen atoms of di(2-picolyl)amine moiety to the Co(II) centre along with two chloro ligands. The 6-coordinated [LBCoCl2] showed a distorted octahedral geometry, achieved through coordination of the two pyridyl units, two chloro units, and bidentate coordination of nitrogen and oxygen in the N′-methoxyethylamine to the Co(II) centre. [LCCoCl2] (6.70 × 104 gPMMA/molCo h) exhibited higher catalytic activity for the polymerisation of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) compared to rest of Co(II) complexes. The catalytic activity was considered as a function of steric properties of ligand architecture and increased steric bulk around the metal centre resulted in the decrease catalytic activity. All Co(II) initiators yielded syndiotactic poly(methylmethacrylate) (PMMA).

Novel Co(II) complexes, [LnCoCl2] (Ln = LA, LB, and LC), bearing tridentate N′-substituted N,N-di(2-picolyl)amine based ligands were synthesized and characterized by X-ray crystallography. These monomeric Co(II) complexes exhibited diverse coordination geometries around the metal centre. These Co(II) complexes polymerise methyl methacrylate in the presence of MMAO at 60 °C and resulted in syndiotactic poly(methylmethacrylate).Figure optionsDownload as PowerPoint slide