Synthesis and Characterization of Iron, Cobalt, and Nickel Complexes Bearing Novel N,N‐Chelate Ligands and Their Catalytic Properties in Ethylene Oligomerization

Abstract

AbstractTreatment of o‐ROC6H4NC (R = PhCH2, iPr) with [Li{2‐CH(SiMe3)C5H4N}] afforded dimeric lithium complexes [Li{N(o‐ROC6H4)C(SiMe3)CH(2‐C5H4N)}]2 (3, R = PhCH2; 4, R = iPr). Reaction of the lithium complexes with 1 equiv. of (dme)NiCl2 gave nickel complexes [Ni{N(o‐ROC6H4)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}C5H4N (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(SiMe3)CH2(2‐C5H4N)}] (9, R = PhCH2, M = Ni, X = Cl; 10, R = iPr, M = Ni, X = Cl; 11, R = PhCH2, M = Ni, X = Br; 12, R = iPr, M = Ni, X = Br; 13, R = PhCH2, M = Fe, X = Cl; 14, R = iPr, M = Fe, X = Cl; 15, R = PhCH2, M = Co, X = Cl; 16, R = iPr, M = Co, X = Cl). For comparasion, nickel and cobalt complexes [MX2{(o‐MeC6H4)N=C(SiMe3)CH2(2‐C5H4N)}] (M = Ni, X = Br, 18; M = Co, X = Cl, 19) were similarly synthesized through reaction of 2‐{o‐MeC6H4NHC(SiMe3)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, 69451 Weinheim, Germany, 2007)