Cobalt(ll) and nickel(ll) complexes bearing mono(imino)pyridyl and bis(imino)pyridyl ligands: preparation, structure and ethylene polymerization/oligomerization behaviors

摘要

BACKGROUND: Ethylene oligomerization is the major industrial process to produce linear a-olefins. Recently much work has been devoted to late transition metal catalysts used in this process, especially those with 2,6-bis(imino)pyridyl dihalide ligands. Considering that most work has focused on simple modification to the substituents in imino-aryl rings based on the symmetric bis(imino)pyridyl framework, here we expand this work to the asymmetric mono(imino)pyridyl ligands.RESULTS: The preparation, structure and ethylene polymerization/oligomerization behavior of series of mono(imino) pyridyl-MCl2 and bis(imino)pyridyl-MX" complexes are presented. The systematic studies were focused on the relationship between the catalytic behavior of these complexes for ethylene polymerization/oligomerization and reaction conditions, ligand structures, metal centers and counter-anions. The influence of the coordination environment on catalyst behavior is also discussed.CONCLUSION: For mono(imino)pyridyl-Co(ll) and -Ni(ll) catalysts bearing the CI- counter-anion, good activities ranging from 0.513 x 105 to 1.58 x 10~5 g polyethylene (mol metal)~(-1) h~(-1) atm~(-1) are afforded, and the most active catalysts are those with methyl in both ortho- and para-positions of the imine W-aryl ring. For bis(imino)pyridyl-Co(ll) and -Ni(ll) catalysts bearing the SO_4~(2-) and NO_3~- counter-anions, the low activities for ethylene oligomerization are in sharp contrast to those of their chloride analogues.