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.