Doping a Nanographene with a Formal Ni^IV Center

A new nanographene ligand (2) was synthesized by incorporating a meso-oxo substituted carbaporphyrin(1.1.1.0) unit into the hexa-peri-hexabenzocoronene (HBC) backbone. Compound 2 features an adj-CCNN dianionic core and coordinates with a Ni^II cation to form organo-Ni^II complex 3. Notably, complex 3 was readily oxidized to formal Ni^IV species 4 after treating with CuCl₂, as confirmed with X-ray photoelectron spectroscopy (XPS) and theoretical calculations. Complex 4 showed substantial stability in the solid state but reacted rapidly with water at room temperature to yield inner oxygen-inserted complex 5. Demetalation of complex 5 with trifluoroacetic acid afforded an inner oxygen doped free base 6 containing a quinonoid-type ring. These new nanographene-containing compounds 2-6 were thoroughly characterized and studied using NMR spectroscopy, single-crystal X-ray diffraction analysis, UV-vis-NIR spectroscopy, and cyclic voltammetry as well as density functional theory (DFT) calculations. To the best of our knowledge, complex 4 represents the first example of a highly reactive Ni^IV nanographene complexes. The present work advances the development of metal doping chemistry of nanographenes, which in turn provide new access to postsynthetic heteroatom doping within the carbon networks of nanographenes.