From four to five and six coordinated sparteine and α-isosparteine mononuclear Cu(II) complexes through the carboxylate donors

Cu[(C15H26N2)(OCOR)2] complexes, where OCO is a fragment of either formato or acetato group and C15H26N2 is sparteine or α-isosparteine have been synthesized and structurally characterized. The bis-formato complexes (1 and 2) display a distorted 4 + 1 coordination resulting from variable metal binding stereochemistry and function of the two formato units. The syn formato group acts as a pseudochelating bidentate while the anti conformer as a monodentate ligand. This inequivalence of the two formate ligands seems deliberate for it allows formation of the stabilizing intramolecular hydrogen bond between the CH donor belonging to the monodentate formate ligand and equatorially coordinated oxygen atom belonging to the pseudo-chelating formate ligand. At variance, the C2 symmetrical bis-acetato complex (3) displays tetragonally elongated octahedral geometry of the CuN2O2O′O′ with long off-axis coordination of the second O atom from each acetate ligand in the axial position.Complexes 1–3 have been also characterized by elemental analysis, IR, UV–Vis and MS spectroscopy.

Sparteine and α-isosparteine form distinctly different metal complexes with Cu(HCOO)2 and Cu(CH3COO)2. The bis-acetato complexes display tetragonally elongated octahedral geometry and the syn/syn coordination mode of the two acetato ligands, while the formato analogues display the square pyramidal geometry and the syn/anti coordination mode of the two formato ligands. The stereochemical role of the intramolecular formato C–H⋯O hydrogen bond is discussed.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of Cu(II) diformato and diacetato complexes of sparteine or α-isosparteine.
► The bis-formato complexes display a distorted 4 + 1 coordination.
► Bis-acetato complex displays tetragonally elongated octahedral geometry.