Synthesis and characterization of iron, cobalt, and nickel complexes bearing novel N,N-chelate ligands and their catalytic properties in ethylene oligomerization

Article abstract of DOI:10.1002/ejic.200700020

Treatment of o-ROC₆H₄NC (R = PhCH₂, iPr) with [Li{2-CH(SiMe₃)C₅H₄N}] afforded dimeric lithium complexes [Li{N(o-ROC₆H₄)C(SiMe ₃)CH(2-C₅H₄N)}]₂ (3, R = PhCH ₂; 4, R = iPr). Reaction of the hthium complexes with 1 equiv. of (dme)NiCl₂ gave nickel complexes [Ni{N(o-ROC₆H ₄)-C(SiMe₃)CH(2-C₅H₄N)} ₂] (5, R = PhCH₂; 6, R = iPr). The stoichiometric reaction of complexes 3 and 4 with Et₃NH⁺Cl^- formed 2-{o-ROC₆H₄NHC(SiMe₃)CH}C₅H ₄N (7, R = PhCH₂; 8, R = iPr) in quantitative yields. Reaction of 7 or 8 with metal halides, including (dme)NiCl₂, NiBr₂, FeCl₂·4H₂O, and CoCl₂ yielded complexes [MX₂{(o-ROC₆H₄)N=C(SiMe ₃)CH₂(2-C₅H₄N)}] (9, R = PhCH ₂, M = Ni, X = Cl; 10, R = iPr, M = Ni, X = Cl; 11, R = PhCH ₂, M = Ni, X = Br; 12, R = iPr, M = Ni, X = Br; 13, R = PhCH ₂, M = Fe, X = Cl; 14, R = iPr, M = Fe, X = Cl; 15, R = PhCH ₂, M = Co, X = Cl; 16, R = iPr, M = Co, X = Cl). For comparasion, nickel and cobalt complexes [MX₂{(o-MeC₆H ₄)N=C(SiMe₃)CH₂(2-C₅H ₄N)}] (M = Ni, X = Br, 18; M = Co, X = Cl, 19) were similarly synthesized through reaction of 2-{o-MeC₆H₄NHC(SiMe ₃)CH}C₅H₄N (17) with NiBr₂ and CoCl₂, respectively. These compounds were characterized by NMR (for 3, 4, 7, 8, and 17) and IR (for 5-19) spectroscopy, elemental analyses and HRMS (for 5, 6, and 9-19). The molecular structures of complexes 3, 6, 12, and 14 were characterized by single-crystal X-ray diffraction techniques. The catalytic behavior in ethylene oligomerization of complexes 5, 6, 9-16, 18, and 19 was investigated. Under optimal conditions, the complexes showed good catalytic activities upon activation with appropriate aluminum co-catalysts (8.72 × 10² to 18.2 × 10² kg/mol h atm for the nickel complexes upon activation with Et₂AlCl and 4.3 × 10² to 8.1 × 10² kg/mol h atm for the iron and cobalt complexes upon activation with MMAO). Wiley-VCH Verlag GmbH & Co. KGaA, 2007.