Nickel Catalysis in Halogen Exchange with Aryl and Vinylic Halides

Article abstract of DOI:10.1021/jo01298a035

Halogen exchange between haloarenes and inorganic halide salts is readily induced by catalytic amounts of certain nickel complexes.Exchange of cis- and trans-β-bromostyrenes with chloride is stereospecific.Although various nickel complexes with different formal oxidation states such as Ni⁰(PEt3)4, Ni^II(PEt3)3, and ArNi^IIBr(PEt3)2 may be employed as catalysts (or catalyst precursors), others such as Ni^IIBr2 or Ni^IIBr2(PEt3)2 are completely ineffective.The distinction between the two classes of nickel complexes lies in whether they are converted under reaction conditions to nickel(I) species, assigned as the active catalyst.The latter is supported by the study of direct halide exchange between haloarenes and arylnickel(II) halides, in which a radical-chain process showing an induction period and inhibition by quinones and nitro aromatics is attributed to a labile nickel(I) species.A mechanism for nickel(I) catalysis of halide exchange is proposed.