Synthesis of New Bis(amidine)-Cobalt Catalysts and Their Application to Styrene Polymerization

초록

Two new bis(amidine) cobalt(II) complexes were rationally designed and efficiently synthesized. The first synthesized cobalt complex was based on a cyclic bis(amidine) ligand with chiral vicinal diphenyl groups. The structure was verified by single-crystal X-ray crystallography. As expected from the ligand structure, the Co-N bonds in this complex were significantly shorter than those found in the corresponding 1,2-diimine cobalt complex. This indicates that the bis(amidine) ligand has better electron-donating capability than the 1,2-diimine ligand. Upon test polymerization of styrene, the complex exhibited a moderate activity of 5.88 x 10(5) g PS/(mol Co h). On the basis of this encouraging result, a new 1,2-diaminobenzene-derived bis(amidine) ligand was efficiently synthesized and used to make the corresponding cobalt(II) complex. When subjected to styrene polymerization, the resulting complex showed unusually high polymerization activity [164 x 10(5) g PS/(mol Co h)] and high conversion (>99%). The resulting polymer was identified as atactic polystyrene by C-13 NMR spectroscopy analysis. The significantly enhanced styrene polymerization activity of the 1,2-diaminobenzene-originated bis(amidine) cobalt(II) complex is attributed to the improved electron-donating capability of the ligand.

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