Isocyanide Insertion into the Palladium−Carbon Bond of Complexes Containing Bidentate Nitrogen Ligands: A Structural and Mechanistic Study

Abstract

Insertion of the isocyanides 2,6-dimethylphenyl isocyanide (DIC), tert-butyl isocyanide (TIC) and tosylmethyl isocyanide (TosMIC) into the Pd−Me bond of complexes (N⌒N)Pd(Me)Cl (N⌒N = 2,2‘-bipyridine (bpy), 1,10-phenanthroline (phen), 2,2‘-bipyrimidine (bpm)) afforded quantitatively (N⌒N)Pd(C(NR)Me)Cl (R = 2,6-Me2C6H3, t-Bu, CH2Tosyl). The course of the reaction has been shown to proceed via the intermediates [(N⌒N)Pd(CN−R)(Me)]Cl (N⌒N = bpy, phen; R = 2,6-Me2C6H3, t-Bu, CH2Tosyl), which have been characterized at 250 K by NMR and IR spectroscopies and conductivity measurements. The mechanism of the insertion reaction involves substitution of the halide by the isocyanide followed by a rate-determining methyl migration to the precoordinated isocyanide. Kinetic measurements of the isocyanide insertion reaction, which provided the reaction rate constants of the isocyanide association (k1), isocyanide dissociation (k-1), and methyl migration reaction (k2), have demonstrated that the migration rate of the meth...