Metal-Stabilized Quinoidal Dibenzo[g, p]chrysene-Fused Bis-dicarbacorrole System

We report here a metal complexation-based strategy that permits access to a highly stable expanded porphyrin-type quinoidal polycyclic aromatic hydrocarbons (PAH). Specifically, double insertion of Pd(II) ions into a dibenzo[g,p]chrysene-fused bis-dicarbacorrole (bis-H3) gives rise to a bis-metalated species (bis-Pd) that undergoes a facile benzenoid-quinonoid transformation. In contrast to what is true for the corresponding mono-Pd(II) complex, which has organic radical character, well resolved 1H NMR and 19F NMR spectra are seen for bis-Pd. This complex is also electron paramagnetic resonance (EPR) silent over a range of temperatures. On the basis of crystallographic analyses, Raman spectroscopic studies, harmonic oscillator model of aromaticity (HOMA), and nucleus-independent chemical shift (NICS) calculations, we suggest that the dibenzo[g, p]chrysene bridge in bis-Pd has quinoidal character and that the system as a whole is a closed shell species. As expected for a quinoidal system, bis-Pd is charact...