Copper coordination to the aldehyde and hemiacetal form of 4-bromo-2-[(2-diethylaminoethyl)ethylaminomethyl]-6-formylphenol: Synthesis and structure of [Cu(H2L)2(X)2] X2 · nH2O (X=NO3−,CIO4−) and [Cu(L′)]2 · 2CH3OH

The coordination behaviour of Cu2+ towards 4-bromo-2-[(2-diethylaminoethyl)ethyl-aminomethyl]-6-formylphenol (HL) having phenolate, amine and aldehyde donor sites has been studied. In aqueous, weakly acidic solution Cu2+ coordinates to the phenolate and aldehyde oxygen giving rise to the complexes [Cu(H2L)2X2]X2 (X=NO3− (1a) and CIO4− (1b)), while in alkaline solution a complex of composition [CuL2] (2) is formed. In methanol, the aldehyde groups in 1 and 2 suffer nucleophilic attack from the solvent resulting in the formation of the hemiacetal form of the ligand and in the isolation of [Cu(L′)]2 · 2CH3OH (3). X-ray structures of 1a, 1b and 3 are reported, the latter featuring a rare example of a coordinated methyl-hemiacetal.

Graphical abstractIn aqueous, weakly acidic solution Cu2+ coordinates to the phenolate and aldehyde oxygen of HL. In methanol, HL is converted into the hemiacetal and the corresponding Cu complex providing a rare example of a coordinated methyl-hemiacetal has been structurally characterized.Figure optionsDownload full-size imageDownload as PowerPoint slide