Reactivity of (Dicarboxamide)MII–OH (M = Cu, Ni) Complexes – Reaction with Acetonitrile to Yield MII–Cyanomethides

Abstract

The complexes (Bu4N)(LMeM(II)-OH) (LMe = 2,6-dimethylphenyl-substituted pyridine(dicarboxamide); M = Cu or Ni) react with CH3CN to yield (Bu4N)(LMeM-CH2CN), novel cyanomethide complexes that were fully characterized, including by X-ray crystallography. These conversions contrast with the usual reactions of metal-hydroxide complexes with nitriles, which typically involve attack at the nitrile carbon and formation of amides or carboxylic acids. Kinetic studies (M = Cu) revealed a first-order dependence on the complex and a kinetic isotope effect (k(CH3CN)/k(CD3CN) of 4. Various mechanisms involving either intra- or intermolecular deprotonation steps are proposed. In addition, (Bu4N)(LMeCu-OH) was oxidized by Fc+PF6- to a proposed Cu(III) complex LMeCuOH at low temperature, and comparisons of its stability and reactivity with dihydroanthracene were drawn to its previously described congener having isopropyl substituents on the phenyl rings of the supporting ligand. The cyanomethide complex (Bu4N)(LMeCu(CH2CN)) also was reversibly oxidized both electrochemically (E1/2 = -0.345 V vs. Fc/Fc+) and chemically (Fc+PF6-, -25 °C). The product was formulated as LMeCu(III)(CH2CN), a novel Cu(III)-alkyl complex relevant to such species proposed during copper-catalyzed organic reactions.