Copper tetradentate N2Py2 complexes with pendant bases in the secondary coordination sphere: improved ligand synthesis and protonation studies

An improved preparation for a tetradentate neutral N2Py2 ligand with two dimethylamine functionalities in the secondary coordination sphere (LDMA) is reported. This synthetic route uses cheaper and more readily available precursors with fewer steps and greater overall yield. The synthesis and characterization of the corresponding Cu(II) and Cu(I) complexes of this ligand and its analog lacking pendant bases (LH) are also described. The cyclic voltammograms indicate that the Cu(II/I) couple for the LDMA complex is over 400 mV positive of the quasi-reversible Cu(II/I) couple for the LH complex. Structural characterization indicates this is likely a result of steric effects in [Cu(LDMA)]2+ that are not present in the [Cu(LH)]2+ complex. Protonation of both diamagnetic Cu(I) complexes is cleanly reversible. 1H NMR spectroscopic studies of the protonated complexes reveals that protonation occurs on the tertiary amines in the ligand backbone for both complexes.