Fluoro-substituted 2,6-bis(imino)pyridyl iron and cobalt complexes: High-activity ethylene oligomerization catalysts

Six five-coordinate difluoro-substituted 2,6-bis(imino)pyridyl iron and cobalt complexes, [12,6-(2,X-F2C6H3N=CCH3)(2)C5H3N}MCl2] (X = 6, M = Fe (1), Co (2); X = 5, M = Fe (3), Co (4)); X = 4, M = Fe (5), Co (6), were synthesized by reactions of the corresponding bis(imino)pyridyl ligands with FeCl2.4H(2)O or COCl2 in tetrahydrofuran (THF). However, a reaction between 2,6-diacetylpyridinebis(2,6-difluoroanil) and FeCl2.4H(2)O in CH3CN provided the ion-pair complex [Fe{2,6-(2,6-F2C6H3N=CCH3)(2)C5H3N}(2)](2+)[FeCl4](2-) (7) instead of a five-coordinate complex. The molecular structures of complexes 3 and 6 were determined by X-ray diffraction. The catalytic activities of complexes 1-7 for ethylene oligomerization were studied using modified methylaluminoxane (MMAO) as cocatalyst. At 60 degreesC and 10 atm of ethylene pressure, the iron complexes 1, 3, and 5 show very high activities: 4.07 x 10(7), 9.33 x 10(7), and 11.1 x 10(7) g/((mol of cat.) h), respectively. The oligomers formed consist mainly of dimer, trimer, and tetramer, with approximately 90% of the products being in the range of C-4-C-8. The complexes 1, 3, and 5 also exhibit high selectivity for linear alpha-olefins: >98% (complex 1) and >93% (complexes 3 and 5). The cobalt complexes 2, 4, and 6 and the ion-pair iron complex 7 are inactive for ethylene oligomerization.