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

Treatment of o ‐ROC 6 H 4 NC (R = PhCH 2 , i Pr) with [Li{2‐CH(SiMe 3 )C 5 H 4 N}] afforded dimeric lithium complexes [Li{N( o ‐ROC 6 H 4 )C(SiMe 3 )CH(2‐C 5 H 4 N)}] 2 ( 3 , R = PhCH 2 ; 4 , R = i Pr). Reaction of the lithium complexes with 1 equiv. of (dme)NiCl 2 gave nickel complexes [Ni{N( o ‐ROC 6 H 4 )C(SiMe 3 )CH(2‐C 5 H 4 N)} 2 ] ( 5 , R = PhCH 2 ; 6 , R = i Pr). The stoichiometric reaction of complexes 3 and 4 with Et 3 NH + Cl – formed 2‐{ o ‐ROC 6 H 4 NHC(SiMe 3 )CH}C 5 H 4 N ( 7 , R = PhCH 2 ; 8 , R = i Pr) in quantitative yields. Reaction of 7 or 8 with metal halides, including (dme)NiCl 2 , NiBr 2 , FeCl 2 · 4H 2 O, and CoCl 2 yielded complexes [MX 2 {( o ‐ROC 6 H 4 )N=C(SiMe 3 )CH 2 (2‐C 5 H 4 N)}] ( 9 , R = PhCH 2 , M = Ni, X = Cl; 10 , R = i Pr, M = Ni, X = Cl; 11 , R = PhCH 2 , M = Ni, X = Br; 12 , R = i Pr, M = Ni, X = Br; 13 , R = PhCH 2 , M = Fe, X = Cl; 14 , R = i Pr, M = Fe, X = Cl; 15 , R = PhCH 2 , M = Co, X = Cl; 16 , R = i Pr, M = Co, X = Cl). For comparasion, nickel and cobalt complexes [MX 2 {( o ‐MeC 6 H 4 )N=C(SiMe 3 )CH 2 (2‐C 5 H 4 N)}] (M = Ni, X = Br, 18 ; M = Co, X = Cl, 19 ) were similarly synthesized through reaction of 2‐{ o ‐MeC 6 H 4 NHC(SiMe 3 )CH}C 5 H 4 N ( 17 ) with NiBr 2 and CoCl 2 , 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 × 10 2 to 18.2 × 10 2 kg/mol h atm for the nickel complexes upon activation with Et 2 AlCl and 4.3 × 10 2 to 8.1 × 10 2 kg/mol h atm for the iron and cobalt complexes upon activation with MMAO). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)