Nickel bis-m-terphenylisocyanide dihalide complexes formed from 1,2-alkyl dihalides: probing for isolable β-haloalkyl complexes of square planar nickel

Abstract

The pentachloroethyl complex NiCl(CCl2CCl3)(CNArMes2)2 (ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3) was recently shown to be a unique example of an isolable β-chloroalkyl complex of square planar nickel. In an effort to generate additional β-haloalkyl complexes of square planar nickel, the reactivity of the precursor complex Ni(COD)(CNArMes2)2 with alkyl halides has been probed. Treatment of Ni(COD)(CNArMes2)2 with 1,2-dichloroethane results in the exclusive formation of the dichloride complex NiCl2(CNArMes2)2 without the buildup of detectable intermediates. Similarly, Ni(COD)(CNArMes2)2 reacts with either 1,2-dibromoethane or 1,2-diiodoethane to produce the dibromide, NiBr2(CNArMes2)2, and diiodide, NiI2(CNArMes2)2, species, respectively. Observable intermediates were also not detected in these latter reactions, indicating that either β-halo elimination is rapid or 1e− halogen-atom abstraction pathways are accessible to Ni(COD)(CNArMes2)2. The sterically and electronically modified m-terphenyl isocyanides CNArDipp2 and CNArClips2 (ArDipp2 = 2,6-(2,6-(i-Pr)2C6H3)2C6H3; ArClips2 = 2,6-(2,6-(Cl)2C6H3)2-4-(t-Bu)C6H2) were also investigated as ancillary ligands for stabilization of a β-chloroalkyl complex of square planar nickel. Treatment of the zero-valent precursors Ni(COD)(CNArDipp2)2 and Ni(COD)(CNArClips2)2 with either 1,2-dichloroethane or hexachloroethane resulted in rapid formation of the dichlorides NiCl2(CNArDipp2)2 and NiCl2(CNArClips2)2 as exclusive products. These results highlight the unique combination of steric and electronic properties that lead to the stability of the parent β-chloroalkyl complex NiCl(CCl2CCl3)(CNArMes2)2.