Quanquan Dai

Highly Active and Cis-1, 4 Selective Polymerization of 1, 3-Butadiene Catalyzed by Cobalt(II) Complexes Bearing Α-Diimine Ligands

A series of cobalt(II) complexes bearing α‐diimine ligands were synthesized and characterized by elemental and spectroscopic analysis. These complexes had the general formulas [ArN = C(Me)-(Me)C = NAr]CoCl2 (Ar = C6H5, 3a; 4‐MeC6H4, 3b; 4‐MeOC6H4, 3c; 4‐FC6H4, 3d; 4‐ClC6H4, 3e; 2‐MeC6H4, 3f; 2‐EtC6H4, 3g; 2‐iPrC6H4, 3h; 2, 4, 6‐Me3C6H2, 3i; 2, 6‐Et2C6H3, 3j; 2, 6‐iPrC6H3, 3k). 2,6‐Bis[(2,6‐diisopropylphenylimino)ethyl]pyridine CoCl2 (4a) was also synthesized for comparison. The structures of complexes 3i, 3k, and 4a were further analyzed by X‐ray crystallography. When the Co(II) complexes were activated with ethylaluminum sesquichloride, they exhibited high catalytic activity for 1,3‐butadiene polymerization. The polymers produced have high cis‐1,4 stereoregularity (up to 98.0%) and high molecular weights (Mn = 1×10^4 - 1×10^5). The substituent ligand affected both catalytic activity and stereoselectivity through an electronic effect while steric hindrance by the substituent was not important. The effects of the polymerization conditions, such as polymerization time, temperature, different alkylaluminum compounds used as cocatalyst, and [Al]/[Co] molar ratio, on polymerization behavior were investigated.

Iminopyridine-Based Cobalt(II) and Nickel(II) Complexes: Synthesis, Characterization, and Their Catalytic Behaviors for 1,3-Butadiene Polymerization

A series of iminopyridine ligated Co(II) (1a–7a) and Ni(II) (1b–7b) complexes were synthesized. The structures of complexes 3a, 4a, 5a, 7a, 5b, and 6b were determined by X-ray crystallographic analyses. Complex 3a formed a chloro-bridged dimer, whereas 4a, 5a, and 7a, having a substituent (4a, 5a: CH3; 7a: Br) at the 6-position of pyridine, producing the solid structures with a single ligand coordinated to the central metal. The nickel atom in complex 5b features distorted trigonal-bipyramidal geometry with one THF molecule ligating to the metal center. All the complexes activated by ethylaluminum sesquichloride (EASC) were evaluated in 1,3-butadiene polymerization. The catalytic activity and selectivity were significantly influenced by the ligand structure and central metal. Comparing with the nickel complexes, the cobalt complexes exhibited higher catalytic activity and cis-1,4-selectivity. For both the cobalt and nickel complexes, the aldimine-based complexes showed higher catalyst activity than their ketimine counterparts.