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

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)-N(1),N(1)-dimethyl-N(2)-(pyridin-2-ylmethylene)ethane-1,2-diamine, and (E)-N(1),N(1)-dimethyl-N(2)-(thiophen-2-ylmethylene)ethane-1,2-diamine, respectively, were designed and synthesized. Structural studies revealed a distorted trigonal bipyramidal geometry for [L(B)CoCl(2)] and a distorted tetrahedral geometry for [L(C)CoCl(2)]. 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 × 10(4) g(PNB) mol Co(−1) h(−1) at 25 °C. High-molecular-weight (M(n) of up to 1.71 × 10(5) 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.