In situ selective N-alkylation of pendant pyridyl functionality in mixed-valence copper complexes with methanol and copper(ii) bromide

Abstract

The reactions of CuBr₂ with pyridyl 2,2′:6′,2′′-terpyridine ligands in methanol yielded four copper complexes under solvothermal conditions. The self-assembly processes were accompanied by designing bitopic precursor ligands and increasing the stoichiometric metal–ligand ratio. In the four resulting complexes, the pendant pyridyl groups of pyridylterpyridine were selectively in situ N-methylated and yielded the 4′-(N-methylpyridinium)-2,2′:6′,2′′-terpyridine cations, including the 2-position pyridyl group which is difficult to be N-alkylated due to the steric problem. Partial divalent copper atoms were reduced to cuprous ones in the solvothermal reactions, which made the mixed-valence copper atoms coexist in each compound. The mixed-valence complexes have a varied dimensionality (from 2D to 0D) and the Cu^IBr cluster, which can be controlled by changing the metal–ligand ratio. Theoretical studies show that the nucleophilic attack of the nitrogen atom in the pendant pyridyl is more facile than others of terpyridine. A possible mechanism was also proposed.