(Pyrazol-1-ylmethyl)pyridine Nickel Complexes: Ethylene Oligomerization and Unusual Friedel−Crafts Alkylation Catalysts

The reactions of 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine ( L1 ) and 2,6-bis(3,5-di- tert- butylpyrazol-1-ylmethyl)pyridine ( L2 ) with NiCl 2 or NiBr 2 gave the nickel(II) complexes [NiCl 2 ( L1 )] ( 1 ), [NiBr 2 ( L1 )] ( 2 ), [NiCl 2 ( L2 )] ( 3 ), and [NiBr 2 ( L2 )] ( 4 ) in high yields. Compounds 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine ( L3 ) and 2-(3,5-di- tert -butylpyrazol-1-ylmethyl)pyridine ( L4 ) on the other hand gave either mononuclear or dinuclear nickel(II) complexes, depending on the steric bulk of the substituents on the pyrazolyl unit. While L3 gave the dinuclear complexes [Ni 2 (μ 2 -Cl) 2 Cl 2 ( L3 ) 2 ] ( 5 ) and [Ni 2 (μ 2 -Br) 2 Br 2 ( L3 ) 2 ] ( 6 ), L4 gave the mononuclear complexes [NiCl 2 ( L4 )] ( 7 ) and [NiBr 2 ( L4 )] ( 8 ). Activation of 1 − 8 with EtAlCl 2 resulted in the oligomerization of ethylene to C 4, C 6, and C 8 alkenes, followed by subsequent Friedel−Crafts alkylation of the toluene solvent. Activities as high as 15 660 kg of alkylated products/mol Ni/h were observed for 5 at 40 bar. However, when hexane was used as solvent, only trace amounts of alkylated toluene products were observed.