Divalent Nickel, Cobalt and Iron Complexes of an Amide‐Appended N2S2 Ligand: Synthesis, Characterization and Reactivity with Hydroxide Anion

Abstract

AbstractDivalent nickel, cobalt and iron complexes {[(bmppa)Ni(CH3CN)](ClO4)2 (1), [(bmppa)Co(CH3CN)](ClO4)2 (2), [(bmppa)Fe(CH3CN)](ClO4)2 (3)} of an amide‐appended N2S2‐donor ligand {bmppa = N,N‐bis(2‐methylthio)ethyl‐N‐[(6‐pivaloylamido‐2‐pyridyl)methyl]amine} have been prepared and characterized using 1H NMR, IR, UV/Vis, elemental analysis and magnetic moment measurements. The complexes 2 and 3 were also characterized by X‐ray crystallography. When treated with 1 equiv. of Me4NOH·5H2O in methanol, 1 and 2 form deprotonated amide complexes {[(bmppa–)Ni]ClO4 (4), [(bmppa–)Co]ClO4·H2O (5)} which were isolated and characterized by 1H NMR, IR, UV/Vis, elemental analysis and magnetic moment measurements. Treatment of the FeII complex 3 with 1 equiv. of Me4NOH·5H2O in methanol produced the free bmppa chelate ligand and a precipitate of an unidentified iron species. Heating of 5 at 50 °C in methanol for 5 d resulted in a ca. 50 % yield of amide methanolysis products and a small amount of products resulting from oxidative N‐dealkylation of the bmppa ligand. It has been previously shown that a zinc analog of 5 undergoes quantitative amide methanolysis under milder conditions. Complex 4 does not undergo amide cleavage upon heating at 50 °C in methanol for 5 d. A rationale for the metal‐dependent amide methanolysis reactivity of these complexes is proposed on the basis of structural differences in the “parent” protonated complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)