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 mu-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.