The Design, Synthesis Of New Late Transition Metal Catalysts And The Study Of Their Catalytic Activity For Ethylene Oligomerization/Polymerization

Since the exceptionally active catalysts based on iron and cobalt have been reported independently by the groups of Brookhart and Gibson in 1998, following these species, a considerable amount of effort has been dedicated to design new catalysts based on these types of ligands.For the first time we have obtained the unsymmetry and symmetry compounds 2-Carbe-thoxy-6-acetylpyridine and 2,6-diacetylpyridine in the same reaction system, from which the mono(imino)pyridine ligands 2-carbethoxy-6-{l-[(2,6-dimethylphenyl)imino]ethyl}-pyridine, 2-carbethoxy-6-{l-[(2,4,6-trimethylphenyl)imino]ethyl}pyridine, 2-carbethoxy-6-{l-[(2,6-diethylphenyl)imino]ethyl}pyridine and the bis(imino)pyridine ligand 2,6-{l-[(2-methyl-4-methoxylphenyl)imino]ethyl}pyridine are synthesized respectively using microwave irradiation. The application of this microwave method to Schiff-base condensation reveals obvious advantages in terms of improved reaction rates, simple work-up procedure and formation of various products. Totally we have prepared 17 bis/mono(imino)pyridyl-transition metal (M=Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)) complexes. The structure of ligands and the corresponding complexes have been determined by the element analysis, 1H NMR, IR, MS and X-ray diffraction. The analysis results suggest that the components of these complexes are all in accord with the formula MLCl2 except the complex {2-carbethoxy-6-[l-[(2,6-dimethylphenyl)imino]ethyl] pyridine}2CoCl2 with the formula ML2. The crystal structure of complex {2-Carbethoxy-6-[l-[(2,6-diethylphenyl)-imino]ethyl]pyridine}CoCl2 indicates that the mono(imino) pyridine is coordinated to the cobalt as a tridentate ligand using [N, N, O] and the coordination geometry of the central cobalt can be best described as distorted trigonal bipyramid, with the pyridyl nitrogen atom and the two chlorin atoms forming theequatorial plane.The systematic studies are focused on the complexes' catalytic activity for the ethylene oligomerization/polymerization. The correlation among electronic property of central metal, the ligand structure, as well as reaction conditions and polymerization/polymerization activity are investigated. Bis(imino)pyridine-Fe(II), Co(II) catalysts show high ethylene polymerization and oligomerization activity up to 7.06x106g/mol-Fehatm and 3.98x105g/mol-Co-h-atm. While the Mono(irnino) pyridine-Fe(II), Co(II), Ni(II) catalysts give moderate activity between 0.35x104 and 5.9x104 g/mol-M-hatm. In the catalyst systems bearing mono(imino)pyridine ligand, it seems that the substitute attached to the ortho position of phenyl ring has a beneficial influence on the activity while substitute group in the para position has a negative effect. On the other hand, bulky ortho-substituted aryl groups attached to the imine nitrogens renders a less active catalyst. The reaction conditions also have a great influence on the productivity of catalyst system. To study these effects, we undertake a series of experiments under various reaction time, temperature and Al/M, from which the optimal reaction conditions have been chosen...