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

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 (L_A), 2-methoxy-N,N-bis(pyridin-2-ylmethyl)ethan-1-amine (L_B), and 3-methoxy-N,N-bis(pyridin-2-ylmethyl)propan-1-amine (L_C), yielded [L_nCoCl₂] (L_n = L_A, L_B and L_C), respectively. The Co(II) centre in [L_nCoCl₂] (L_n = L_A, and L_C) 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 [L_BCoCl₂] 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. [L_CCoCl₂] (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).