Iron and Cobalt Ethylene Polymerization Catalysts: Variations on the Central Donor

Three classes of ligands, designed to explore the effect of variations on the central pyridine donor core in bis(imino)pyridine iron and cobalt ethylene polymerization catalysts of the general formula [LMCl2] (M = Fe or Co),
have been prepared. The first class comprises six-membered N-heterocycles (pyrimidine and triazine) and the
second class five-membered heterocycles (furan and thiophene) as the central donor core. In the third class of
ligands, the imine donor arm has been extended by one carbon to give anionic tridentate ligands based on carbazole
and neutral analogues based on dibenzofuran and dibenzothiophene. The coordination behavior of these ligands
upon reaction with FeCl2 or CoCl2 has been investigated, whereby only in the case of the neutral pyrimidine or the
anionic carbazolide unit as the central donor core have stable complexes been obtained. Ethylene polymerization
results are compared with the parent bis(imino)pyridine iron and cobalt catalyst systems.