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-1,10-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 degrees C gives, after recrystallization from a CH2Cl2 solution, the chiral bis-ligated nickel complex (3)(2)Ni (5). Under similar reaction conditions, bis-imidazolium salt 4 affords a tetranuclear nickel complex [{(4) Ni}(3)Ni](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 (10(6) g/mol h) norbornene polymerization activity upon activation with methylaluminoxane (MAO), leading to thermally very stable polynorbornenes. (C) 2013 Elsevier B.V. All rights reserved.