Bis(iminoethyl)pyridine Systems with a Pendant Alkenyl Group. Part A: Cobalt and Iron Complexes and Their Catalytic Behavior

The acid-catalyzed reaction of 2,6-diacetylpyridine with 2,6-diisopropylaniline yielded the monoiminoethylpyridine derivative 3. Its condensation reactions with allylamine or ω-aminobutene, -pentene, and -hexene furnished the unsymmetrically substituted 6-(N-(n-alkenyl)iminoethyl)-2-(N-(2,6-diisopropylphenyl)iminoethyl)pyridines 5a−d (5a−c were characterized by X-ray diffraction). Treatment of the chelate ligands 5a−d with CoCl2 or FeCl2 gave the respective cobalt (7a−d) and iron complexes (8a−d) in good yields (all cobalt complexes and 8b,c were characterized by X-ray crystal structure analyses). The reaction of the cobalt(II) complex 7a with 3 molar equiv of methyllithium gave the corresponding tridentate chelate ligand Co(I) methyl complex 11a (also characterized by X-ray diffraction). The complexes 7a−d, 8a−d, and 11a were activated with methylalumoxane (Al:M = 300). The resulting cobalt-complex-derived homogeneous Ziegler−Natta catalysts produced polyethylene, albeit with a rather low activity. The iron-complex-derived catalysts were more active and gave mixtures of linear polyethylene and low-molecular-weight oligoethylenes.