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.