Non-ligated Nickel Chloride-Catalyzed Cross-Coupling of Aryl Grignard Reagents with Haloarenes-Syntheses of Asymmetric Teraryls -

Abstract

The reaction between aryl Grignard reagents and aryl halides in the presence of non-ligated nickel (II) chloride (NiCl₂) affords the cross-coupling products in high yields. It is found that NiCl₂ effectively catalyzes the coupling of aryl Grignard reagents with bromoarenes, but it has a low catalytic activity towards chloroarenes. The high halogen-selectivity which was not found in the reactions using phosphine-ligated nickel complexes is a unique feature of the NiCl₂-catalysis for the cross-coupling reaction. By the halogen-selectivie NiCl₂-catalyzed cross-coupling, we synthesized unsymmetrical terphenyls, which are important materials for a heat-stable polymer. On the other hand, for the crosscoupling reactions of heteroaromatics, NiCl₂ was not act as an active catalyst, but the cross-coupling reaction of thienylmagnesium halides with chloroiodobenzene proceeded selectively to give (chlorophenyl)thiophenes.