Unsymmetrical Naphthyridine-Based Dicopper(I) Complexes: Synthesis, Stability, and Carbon–Hydrogen Bond Activations

Two unsymmetrical dinucleating naphthyridine-based
ligands with
di­(pyridyl) and phosphino side arms were employed in the synthesis
of dicopper­(I) chloride cores that activate NaBPh4 to afford
bridging phenyl organocopper complexes. In these compounds, the bridging
ligand binds symmetrically, as observed in previously described symmetrical
dicopper­(I) complexes supported by naphthyridine-based ligands with
two di­(pyridyl) side arms. Unlike the symmetrical systems, however,
these complexes undergo quasireversible electrochemical reductions,
and chemical reduction yields a diamagnetic product resulting from
the coupling of naphthyridine-based radicals of two complexes. The
μ-Ph complexes activate the C–H bonds of terminal alkynes
and the electron-poor arene C6F5H. By DFT calculations,
the mechanism of terminal alkyne activation involves H-atom transfer
at the cationic dicopper center and is sensitive to subtle changes
in copper-ligand interactions as well as the position of the anion.