Iso-dibenzo[g,p]chrysene-Fused Bis-dicarbaporphyrin: Pd Coordination-Induced Global Aromaticity and Stabilization of Double In-Plane Pd(IV) Cations

An iso-dibenzo[g,p]chrysene (DBC)-fused bis-dicarbaporphyrin (4) with two adj-CCNN cores was synthesized. This bis-dicarbaporphyrin can be regarded as an isomer of the previously reported DBC-fused bis-dicarbacorrole obtained by tuning the orientation of the DBC bridge. This subtle change has significant impacts on structure and properties. As prepared, 4 has a highly twisted figure-eight conformation, whereas DBC-fused bis-dicarbacorrole adopts roughly a planar conformation with slight distortion. The incorporation of two Pd(II) cations can induce a transformation in the molecular framework, resulting in a curved, arch-shaped π-system. Utilizing crystallographic data, along with the electron density of delocalized bonds (EDDB), electron localization function-π (ELF-π), harmonic oscillator model of aromaticity (HOMA), the anisotropy of the induced current density (ACID), and nucleus-independent chemical shift (NICS) calculations, a 34π-electron global aromatic pathway was elucidated for the bis-Pd(II) complex (5). The Pd coordination-induced global aromaticity is a distinctive feature that has not been observed in the previously reported bis-Pd complexes of DBC-fused bis-dicarbacorrole. Moreover, the treatment of 5 with CuCl2 leads to the formation of a rare in-plane bis-Pd(IV) complex 6 with two axial coordinated Cl anions. The bis-Pd(IV) complex retains the global aromatic feature and arch-shaped conformation. To our knowledge, this is the first well-defined in-plane bis-Pd(IV) organometallic complex using a porphyrinoid-type macrocyclic ligand.