Mono- and bis-Pd(ii) complexes of N-confused dithiahexaphyrin(1.1.1.1.1.0) with the absorption and aromaticity modulated by Pd(ii) coordination, macrocycle contraction and ancillary ligands

Abstract

To further enrich the coordination chemistry of hexaphyrins and probe the underlying property–structural correlations, N-confused dithiahexaphyrin(1.1.1.1.1.0) (1) with 26 π-electron Hückel aromaticity was synthesized. Based on its unprecedented two unsymmetrical cavities, five palladium complexes 2, 3, 4-Ph, 4-Cl and 5 have been successfully synthesized under various coordinations. Thus, two mono-Pd(II) complexes 2 and 3 with the Pd(II) atom coordinated in the two different cavities were obtained by treating 1 with palladium reagents PdCl₂, and (PPh₃)₂PdCl₂ respectively. On this basis, bis-Pd(II) complexes 4-Ph and 4-Cl were synthesized by treating 2 and 3 with (PPh₃)₂PdCl₂ and PdCl₂, respectively. As a result, both 4-Ph and 4-Cl contain two Pd(II) atoms coordinated within the two cavities, with one of the Pd(II) atoms further coordinated to a triphenylphosphine ligand in addition to an anionic ancillary ligand of Ph⁻ and Cl⁻, respectively. Notably, a further contracted mono-Pd(II) complex 5 was synthesized by treating 1 with Pd(PPh₃)₄ by eliminating one of the meso-carbon atoms together with the corresponding C₆F₅ moiety. These complexes present tunable 26 π aromaticity and NIR absorption up to 1060 nm. This work provides an effective approach for developing distinctive porphyrinoid Pd(II) complexes from a single porphyrinoid, without resorting to tedious syntheses of a series of porphyrinoid ligands.