Catalytic Performance of Cobalt(II) Polyethylene Catalysts with Sterically Hindered Dibenzopyranyl Substituents Studied by Experimental and Methods.

Given the great importance of cobalt catalysts supported by benchmark bis(imino)pyridine in the (oligo)polymerization, a series of dibenzopyran-incorporated symmetrical 2,6-bis(imino) pyridyl cobalt complexes (-) are designed and prepared using a one-pot template approach. The structures of the resulting complexes are well characterized by a number of techniques. After activation with either methylaluminoxane (MAO) or modified MAO (MMAO), the complexes - are highly active for ethylene polymerization with a maximum activity of up to 7.36 × 10 g (PE) mol (Co) h and produced highly linear polyethylene with narrow molecular weight distributions, while is completely inactive under the standard conditions. Particularly, complex affords polyethylene with high molecular weights of 85.02 and 79.85 kg mol in the presence of MAO and MMAO, respectively. The H and C NMR spectroscopy revealed the existence of vinyl end groups in the resulting polyethylene, highlighting the predominant involvement of the -H elimination reaction in the chain-termination process. To investigate the mechanism underlying the variation of catalytic activities as a function of substituents, multiple linear regression () analysis was performed, showing the key role of open cone angle () and effective net charge () on catalytic activity.