Catalytic performance of tridentate versus bidentate Co(ii) complexes supported by Schiff base ligands in vinyl addition polymerization of norbornene

Abstract

A series of Co(II) complexes supported by Schiff base ligands, L_A–L_C, where L_A, L_B, and L_C are (E)-3-methoxy-N-(quinolin-2-ylmethylene)propan-1-amine, (E)-N¹,N¹-dimethyl-N²-(pyridin-2-ylmethylene)ethane-1,2-diamine, and (E)-N¹,N¹-dimethyl-N²-(thiophen-2-ylmethylene)ethane-1,2-diamine, respectively, were designed and synthesized. Structural studies revealed a distorted trigonal bipyramidal geometry for [L_BCoCl₂] and a distorted tetrahedral geometry for [L_CCoCl₂]. After activation with modified methyl aluminoxane (MMAO), all the Co(II) complexes catalyzed the polymerization of norbornene (NB) to yield vinyl-type polynorbornenes (PNBs) with activities of up to 4.69 × 10⁴ g_PNB mol Co⁻¹ h⁻¹ at 25 °C. High-molecular-weight (M_n of up to 1.71 × 10⁵ g mol⁻¹) soluble PNBs with moderate molecular-weight distributions (MWD) were obtained. The activity of the Co(II)/MMAO catalytic system is influenced by the steric hindrance and electronic properties of the ligands.