Linkage Isomerism in Transition-Metal Complexes of Mixed (Arylcarboxamido)(arylimino)pyridine Ligands

The synthesis of a series of asymmetric mixed 2,6-disubstituted (arylcarboxamido)(arylimino)pyridine ligands and their coordination chemistry toward a series of divalent first-row transition metals (Cu, Co, and Zn) have been explored. Complexes featuring both anionic N,N',N″-carboxamido and neutral O,N,N'-carboxamide coordination have been prepared and characterized by X-ray crystallography, cyclic voltammetry, and UV-visible and EPR spectroscopy. Specifically, (R)LM(X) (M = Cu; X = Cl(-), OAc(-)) and (R)L(H)MX2 (M = Cu, Co, Zn; X = Cl(-), SbF6(-)) complexes that feature N,N',N″- or O,N,N'-coordination are presented. Base-induced linkage isomerization from O,N,N'-carboxamide to N,N',N″-carboxamido coordination is also confirmed by multiple forms of spectroscopy.