The Activation of Tertiary Carboxamides in Metal Complexes: An Experimental and Theoretical Study on the Methanolysis of Acylated Bispicolylamine Copper(II) Complexes

It is a well-established concept that the C−N bond cleavage of carboxamide functions is facilitated by the coordination
of a metal ion to the carbonyl oxygen atom. In contrast, the alternative C−N bond activation by coordination of a
neutral tertiary carboxamide nitrogen atom has not been studied. We present the first results on the effect of
nitrogen pyramidalization in N-coordinated metal complexes on the methanolysis of tertiary carboxamide groups.
An analysis of the reactions products obtained from the methanol cleavage of [(N-Acyl-bpa)Cu]2+ (bpa = N,N-bispicolylamine) complexes is presented together with experimental and high-level theoretically calculated structures.
The strong effect of different anions on the amide pyramidalization and subsequent C−N-bond cleavage is evaluated.
We show that dichloro complexes [(N-Acyl-bpa)CuCl2] have much less activated amide groups than the corresponding
triflate species. They should therefore be less reactive. However, [(N-Acyl-bpa)CuCl2] complexes dissociate in
solution to give cationic monochloro complexes [(N-Acyl-bpa)Cu(S)Cl]+ (S = solvent molecule). Theoretical calculations
show that the amide pyramidalization in the monochloro complexes is equal to that in the corresponding CF3SO3-
salts. Consequently, chloro and triflato complexes are cleaved with similar rates and efficiencies. Parallels to and
differences in the reactivity of purely organic distorted amides are discussed.