Experimental and theoretical studies of anions of transition-metal chelate complexes in alkylation reactions at a metal atom

Abstract

Electrochemical reduction of a number of chelate complexes of transition metals (Chel)2M or (Chel)2MXY (M=Co, Rh, Ir, or Ni; Chel are anions of dmgH (dmg is dimethylglyoxime), (3,5-di-tert-butyl-4-hydroxyphenyl)mgH (mg is methylglyoxime),N-aryl-3-methoxysalicylaldoxime,N-aryl-3-methyl-2-thiocarboxamidopyridine, or 2-acetylindan-1,3-dione; X=Y=py, Ph3P, or H2O or X=Cl and Y=Ph3P) in MeCN or DMF was studied using the cyclic voltammetry and rotating disk electrode techniques. Under the action of BunBr, some electrochemically generated anions [(Chel)2M]− enter into the rather fast alkylation reactions (apparently, at the metal atom) to form (Chel)2M—Alk. The geometries of four model neutral and anionic cobalt complexes were calculated using the semiempirical ZINDO/1 method. According to calculations, the transformation of the neutral complex (Chel)2M into the anion [(Chel)2M]− leads to a change in the configuration from square-planar to square-pyramidal or from tetrahedral to disphenoid. The effects of steric hindrances, the HOMO energies, and the charge of the metal atom in the anionic complexes on the alkylation reactions at the metal atom are discussed.