Pyrazolyl iron, cobalt, nickel, and palladium complexes: Synthesis, molecular structures, and evaluation as ethylene oligomerization catalysts
Journal of Organometallic Chemistry
Department of Chemistry, University of Johannesburg, Auckland Park Kingsway Campus, Auckland Park 2006, South Africa; Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, United States; Department of Chemistry, Maseno University, Private Bag, Maseno 40105, Kenya
Reactions of [2-(3,5-dimethyl-pyrazol-1-yl)-ethanol] (L1) and [1-(2-chloro-ethyl)-3,5-dimethyl-1H-pyrazole] (L2) with Fe(II), Co(II), Ni(II), and Pd(II) salts gave the complexes [(L1)2FeCl2] (1), [(L1)2CoCl2] (2), [(L1)2NiBr2] (3), [(L1)2Pd(Me)Cl] (5), [(L2)2CoCl2] (6), and [(L2)2NiBr2] (7). Whereas L2 behaves as a monodentate ligand, L1 can behave as either a monodentate or bidentate ligand depending on the nature of the metal centre. For palladium, L1 is monodentate in the solid state structure of 5 but bidentate in the structure of 4, obtained during attempts to crystallize 3. While the activation of iron, cobalt and palladium complexes with EtAlCl2 did not produce active ethylene oligomerization catalysts, the nickel complexes 3 and 7 produced active ethylene oligomerization catalysts. Activities as high as 4329 kg/mol Ni h were obtained. Catalyst 3 produced mainly butenes (57%) and hexenes (43%); of which a combined 20% were converted to Friedel-Crafts alkylated-toluene. Catalyst 7, on other hand, produced mainly butenes (90%) and small amounts of hexenes (10%) which were then completely converted to the corresponding Friedel-Crafts alkylated-toluene products. This difference in product distribution in catalysis performed by complexes 3 and 7 is indicative of the role of the OH functionality in L1 on the EtAlCl2 co-catalysts. © 2010 Elsevier B.V. All rights reserved.
1H-pyrazole; Active ethylene; Bidentate ligands; Co catalysts; Ethylene oligomerization; Ethylene oligomerizations; Friedel-Crafts; Hexenes; Metal centres; Monodentate ligands; Monodentates; Nickel complex; Palladium complexes; Product distributions; Pyrazolyl; Solid-state structures; Butenes; Catalyst activity; Cobalt; Cobalt compounds; Ethanol; Ethylene; Iron compounds; Ligands; Metal complexes; Oligomerization; Oligomers; Palladium; Toluene; Palladium compounds