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, LA-LC, where LA, LB, and LC 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 [LBCoCl2] and a distorted tetrahedral geometry for [LCCoCl2]. 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 gPNB mol Co−1 h−1 at 25 °C. High-molecular-weight (Mn 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.