Synthesis, structure, and catalytic activity of nickel complexes with new chiral binaphthyl-based NHC-ligands

Two new chiral NHC-nickel complexes have been prepared from the reactions between Ni(OAc)2, K2CO3 or K2CO3/NaBPh4, and imidazolium salts 3 or 4, which are derived from (R)-2,2′-diamino-1,1′-binaphthyl. Treatment of mono-imidazolium salt 3 with 1 equiv of Ni(OAc)2 in the presence of K2CO3 in 1,4-dioxane at 105 °C gives, after recrystallization from a CH2Cl2 solution, the chiral bis-ligated nickel complex (3)2Ni (5). Under similar reaction conditions, bis-imidazolium salt 4 affords a tetranuclear nickel complex [{(4)Ni}3Ni](BPh4)2 (6). All compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of compounds 3, 5, 6 have been further confirmed by X-ray diffraction analyses. Nickel complexes 5 and 6 show a good (106 g/mol h) norbornene polymerization activity upon activation with methylaluminoxane (MAO), leading to thermally very stable polynorbornenes.