Polymerization of Ethylene Catalyzed by Iron Complex Bearing 2,6-Bis(imine)pyridyl Ligand: 1H and 2H NMR Monitoring of Ferrous Species Formed via Catalyst Activation with AlMe3, MAO, AlMe3/B(C6F5)3 and AlMe3/CPh3(C6F5)4

Abstract

1H and 2H NMR spectroscopic monitoring of ferrous species formed via interaction of 2,6-bis[1-(2,6-dimethylphenylimino)ethyl]pyridineiron(II) chloride (1) with AlMe3, MAO, AlMe3/B(C6F5)3 and AlMe3/CPh3 (C6F5)4 is reported. At interaction of 1 with MAO in toluene solution, the new stable heterodinuclear neutral complexes with proposed structures LFe(II)(Cl)(μ-Me)2AlMe2 and LFe(II)(Me)(μ-Me)2AlMe2 are formed (L is initial tridentate ligand). Complex LFe(II)(Cl)(μ-Me)2AlMe2 predominates at low Al/Fe ratios (less than 50), while LFe(II)(Me)(μ-Me)2AlMe2 at high Al/Fe ratios (more than 500). Complex assigned to LFe(II)(Me)(μ-Me)2AlMe2 can be prepared via interaction of 1 with AlMe3. Activation of LFe(II)(Me)(μ-Me)2AlMe2 by B(C6F5)3 and CPh3B(C6F5)4 gives rise to formation of new complexes with proposed structures [LFe(μ-Me)2AlMe2]+[MeB(C6F5)3]– and [LFe(μ-Me)2AlMe2]+ [B(C6F5)4]–. Unexpectedly, the activity at ethylene polymerization was even higher for 1/AlMe3 than for 1/MAO catalytic system. The co-catalytic activity of MAO towards 1 dramatically decreased with the diminishing of AlMe3 content in the composition of MAO. Activity of the catalyst 1/AlMe3 and the molecular structure of polyethylene produced do not change noticeably at the addition of B(C6F5)3 to 1/AlMe3.These data allow to suggest, that active species of 1/AlMe3 and 1/MAO systems are neutral methylated ferrous complexes but not cationic intermediates. Probably, complex LFe(II)(Me)(μ-Me)2 AlMe2 is the closest precursor of these active species.