Pyrrolylmethylene Appended Corrorin: Peripheral Coordination and Transformation to Pyridyl Incorporated Hemiporphycene Analogue

Dimerization of Hexaphyrin with an Appendant Pyrrole Possessing a Reactive Site to Alleviate the Steric Hindrance

Oxidative dimerization of π-conjugated molecules is a straightforward approach for effectively extending π-conjugation and absorption features. However, it is challenging to construct dimeric species of bulky π-conjugated frameworks because of the steric hindrances and/or poor regioselectivity. To address these issues, a pyrrole unit has been regioselectively appended to the α position of N-confused hexaphyrin (1.1.1.1.1.0) 1 by a facile acid-catalyzed condensation reaction, leading to the formation of pyrrole-appendant 2. Subsequent oxidation of 2 yielded an inner-fused monomer 2F and two fused dimeric species, namely, (2F)2a and (2F)2b. In contrast, oxidation of the corresponding Ni(II) complex 2Ni generated dimer (2Ni)2. Subsequent demetalation resulted in the formation of bipyrrole-linked freebase dimer (2)2, which could chelate Ni(II) and Cu(II) ions to furnish complexes (2Ni)2 and (2Cu)2, respectively. In comparison to the fused dimeric species (2F)2a and (2F)2b, the nonfused dimer (2)2 and its complexes (2Ni)2 and (2Cu)2 exhibit diminished local aromaticity, narrowed HOMO-LUMO gaps, and a red-shifted absorption profile that extends up to 2200 nm. These findings underscore a potent strategy for creating expanded porphyrin dimers, wherein the aromaticity and near-infrared absorption can be fine-tuned by incorporating an appendant pyrrole unit.

Syntheses of Variants of π(σ) Aromatic Modified N-Methyl N-Confused Porphyrinoids with Adaptive Properties

Retrosynthetically designed and syntheses of three unprecedented core modified N-confused porphyrinoids exhibiting vis-NIR absorption with tunable aromaticity is reported. Controlled modification of types of oxidants (chloranil vs. DDQ) has led to the isolation of 18π-aromatic porphyrinoid 7 (upon chloranil oxidation) while DDQ oxidation has led to 18 e σ-aromatic porphyrinoids 8 and 9. All the three SN3 hybrid N-confused porphyrinoids 7-9 have been thoroughly characterized via solution state spectroscopic measurements and in-depth DFT studies for concluding π-aromaticity of 7 and σ-aromaticity of 8 and 9. While 7 could recognize the fluoride anion with high selectivity via deprotonation rather than an anion recognition based mechanism, acetate anion binding studies clearly revealed NH⋅⋅⋅AcO- H-bonding interaction in the host-guest complex [7-AcO-] supporting an anion recognition based mechanism. Porphyrinoids 8 and 9 remain unsusceptible to anion recognition. The conformational preorganization and anion induced deprotonation leading to conformational reorganization have been extensively studied by solution state spectroscopic techniques and in depth DFT level theoretical calculations.

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

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.