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Sapphyrin is a pentapyrrolic expanded porphyrin with a 22π aromatic character. Herein, we report the synthesis of a 20π antiaromatic sapphyrin isomer 1 by oxidative cyclization of a pentapyrrane precursor P5 with a terminal β‐linked pyrrole. The resulting isomer 1, containing a mis‐linked bipyrrole unit in the skeleton, exhibits a reactivity for further oxidation due to the distinct antiaromatic electronic structure, affording a fused macrocycle 2, possessing a spiro‐carbon‐containing [5.6.5.6]‐tetracyclic structure. Subsequent treatment with an acid afforded a weakly aromatic pyrrolone‐appended N‐confused corrole 3, and thermal fusion gave a [5.6.5.7]‐tetracyclic‐ring‐embedded 14π aromatic triphyrin(2.1.1) analog 4. The cyclization at the mis‐linked pyrrole moiety of P5 played a crucial role in synthesizing the antiaromatic porphyrinoid susceptible to facile transformation to novel porphyrinoids with variable aromaticity. [ABSTRACT FROM AUTHOR]

We present herein the synthesis of novel pseudo-metalla-carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N-confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well-known porphyrins, these species exhibit an unusually narrow HOMO-LUMO gap, resulting in an unprecedentedly low-energy absorption in the second near-infrared (NIR-II) region. Density functional theory (DFT) calculations revealed unique d π -p π -conjugated electronic structures involving the metal d π -ligand p π hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open-metal coordination site in the peripheral NN dipyrrin site, forming hetero-metal complexes (1Pd-BF 2 and 1Pt-BF 2 ) through boron difluoride complexation. The resulting hetero metalla-carbaporphyrinoid species displayed further redshifted NIR-II absorption, highly efficient photothermal conversion efficiencies (η; 62-65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of d π -p π -conjugated metalla-aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity-relevant NIR-II dyes., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

We report an unexpected rearrangement, controlled by the nature of the bridge, leading to the formation of novel, remarkably stable triply fused dinickel(II)/dicopper(II) chlorin-porphyrin dication diradical heterodimers in excellent yields. Here, a dipyrromethene bridge gets completely fused between two porphyrin macrocycles with two new C-C and one C-N bonds. The two macrocycles exhibit extensive π-conjugation through the bridge, which results in an antiferromagnetic coupling between the two π-cation radicals. In addition, the macrocyclic distortion also favours a rare intramolecular ferromagnetic interaction between the Cu II and π-cation radical spins to form a triplet state. The structural and electronic perturbation in the unconjugated dication diradical possibly enables the bridging pyrrolic nitrogen to undergo a nucleophilic attack at the nearby β-carbon of the porphyrin π-cation radical with a computed free energy barrier of >20 kcal mol -1 which was supplied in the form of reflux condition to initiate such a rearrangement process. UV-vis, EPR and ESI-MS spectroscopies were used to monitor the rearrangement process in situ in order to identify the key reactive intermediates leading to such an unusual transformation., (© 2023 Wiley-VCH GmbH.)

Ruthenium(iv) N-confused porphyrin μ-oxo-bridged complexes were synthesized via oxidative dimerization of a ruthenium(ii) N-confused porphyrin complex using 2,2,6,6-tetramethylpiperidine 1-oxyl. The deformed core planes in the dimers conferred a relatively high ring rotational barrier of ca. 16 kcal mol -1 . Rotation of the complexes was controlled by protonating the peripheral nitrogen., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)