Doping a Nanographene with a Formal NiIV 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 NiII cation to form organo-NiII complex 3. Notably, complex 3 was readily oxidized to formal NiIV 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 NiIV 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.