Stable Subporphyrin meso‐Aminyl Radicals without Resonance Stabilization by a Neighboring Heteroatom

Most aminyl radicals studied so far are resonance‐stabilized by neighboring heteroatoms, and those without such stabilization are usually short‐lived. We report herein that subporphyrin meso ‐2,4,6‐trichlorophenylaminyl radicals and a bis(5‐subporphyrinyl)aminyl radical are fairly stable under ambient conditions without such stabilization. The subporphyrin meso ‐2,4,6‐trichlorophenylaminyl radical crystal structure displays a characteristically short C_meso −N bond and a perpendicular arrangement of the meso ‐arylamino group. The stabilities of these radicals have been ascribed to extensive spin delocalization over the subporphyrin π‐electronic network as well as steric protection around the aminyl radical center.     

Synthesis of β,β′‐Porphyrin Dimer Linked by Vinylene

Synthesis of a novel β,β′‐tetraalkylporphyrin dimer linked by vinylene was discribed, in which the dimer was readily prepared from a porphyrin‐derived Wittig reagent and a mono‐formylated porphyrin via Wittig reaction. No π‐conjugation between the two porphyrin rings was obserbed, and the dimer was in trans form.     

Synthesis of Direct β‐to‐β Linked Porphyrin Arrays with Large Electronic Interactions: Branched and Cyclic Oligomers

Direct β‐to‐β linked branched and cyclic porphyrin trimers and pentamers have been synthesized by the Suzuki–Miyaura coupling of β‐borylporphyrins and β‐bromoporphyrins. The cyclic porphyrin trimer, the smallest directly linked cyclic porphyrin wheel to date, and its twined pentamer, exhibit small electrochemical HOMO–LUMO gaps, broad nonsplit Soret bands, and red‐shifted Q‐bands, thus indicating large electronic interactions between the constituent porphyrin units.     

meso,β‐Oligohaloporphyrins as Useful Synthetic Intermediates of Diphenylamine‐Fused Porphyrin and meso‐to‐meso β‐to‐β Doubly Butadiyne‐Bridged Diporphyrin

The chlorination of β‐halo or β,β‐dihaloporphyrins with 2‐chloro‐1,3‐bis(methoxycarbonyl)guanidine (Palau′Chlor) proceeded selectively at the neighboring unsubstituted meso position to afford meso,β‐dihalo or meso,β,β‐trihaloporphyrins. Such oligohaloporphyrins are useful platforms for constructing more‐elaborate porphyrin‐based extended π systems. For example, meso‐chloro‐β,β‐diiodoporphyrin participated in an efficient single‐step synthesis of a diphenylamine‐fused porphyrin. In addition, meso‐chloro‐β‐iodoporphyrin was transformed in stepwise fashion into an efficiently conjugated meso‐to‐meso,β‐to‐β doubly butadiyne‐linked porphyrin dimer, a system which was previously difficult to access without such haloporphyrin precursors.     

A Waterwheel‐Shaped meso–meso‐Linked Porphyrin Pentamer

Wheels on water? A waterwheel‐shaped porphyrin pentamer has been synthesized by palladium‐catalyzed cross‐coupling reactions. The key intermediate is a boronate porphyrin, in which four boronic ester groups are directly attached to the meso‐positions.

     

meso‐Aryl [20]π Homoporphyrin: The Simplest Expanded Porphyrin with the Smallest Möbius Topology

An unstable conjugated homoporphyrin was successfully stabilized by introducing meso ‐aryl substitutents. It was evident from the moderate diatropic ring current found by NMR analysis that the newly formed 20π conjugated free base and its protonated form exhibited Möbius aromatic character. Furthermore, complexation as a ligand with an Rh^I ion afforded a unique binding mode and retained the Möbius aromaticity. Overall, these compounds are the smallest Möbius aromatic molecules, as confirmed by spectral and crystal‐structure analysis and supported by theoretical studies.     

meso–meso‐Linked Diarylamine‐Fused Porphyrin Dimers

A meso–meso‐linked diphenylamine‐fused porphyrin dimer and its methoxy‐substituted analogue were synthesized from a meso–meso‐linked porphyrin dimer by a reaction sequence involving Ir‐catalyzed β‐selective borylation, iodination, meso‐chlorination, and S_NAr reactions with diarylamines followed by electron‐transfer‐mediated intramolecular double C?H/C?I coupling. While these dimers commonly display characteristic split Soret bands and small oxidation potentials, they produced different products upon oxidation with tris(4‐bromophenyl)aminium hexachloroantimonate. Namely, the diphenylamine‐fused porphyrin dimer was converted into a dicationic closed‐shell quinonoidal dimer, while the methoxy‐substituted dimer gave a meso–meso, β‐β doubly linked porphyrin dimer.