Shaping a Porphyrinoid Frame by Heteroatoms Extrusion: Formation of an Expanded [22]Triphyrin(6.6.0)

Abstract

An aromatic expanded triphyrin, [22]triphyrin(6.6.0) 2, containing a pyrrole unit, a bipyrrole moiety, and annulene links, was obtained from a tellurium‐containing precursor meso‐tetraaryl‐26,28‐ditellurasapphyrin 1. The reaction path proceeds through an acid‐promoted tellurium extrusion from 1 yielding directly 2, characterized in a dicationic form by X‐ray crystallography. In solution the neutral macrocycle 2 reveals flexibility typical for annulenes and it exists as a mixture of conformers that differ by the configuration of the annulene fragments, as proven by 1H NMR studies and analyzed by DFT methods. The conformation is controlled by protonation state, the nature of an interacting anion, solvent identity, and by interaction with water.

Conformation‐Dependent Response to the Protonation of Diphenanthrioctaphyrin(1.1.1.0.1.1.1.0): A Route to Pseudorotaxane‐Like Structures

“…Slightly elevated energy was found for M8 , whereas lower‐symmetry conformations M9 – M12 have the energy in a 12.7–23.6 kcal mol −1 range, suggesting their limited energetic accessibility. Nevertheless, it is worth underlining that the stability order, based on the calculated values, might be altered whenever additional intermolecular interactions start playing a role …”

Expanded Porphyrin Contraction: From [22]Triphyrin(6.6.0) to [22]Triphyrin(6.5.0)

“…5,10,15,20‐Tetraphenyl‐[22]triphyrin(6.6.0), 1 , (26,28‐divacatasapphyrin), reported recently subjected to a standard chromatographic workup on basic alumina underwent a macrocyclic transformation to 5,10,15,20‐tetraphenyl‐[22]triphyrin(6.5.0), 2 (Scheme ). The original product can be alternatively viewed as a sapphyrin with two pyrrole rings replaced by two different acyclic units: butadiene and a relatively rare in porphyrinoid skeletons allyl building block .…”

“…To get some insight into the macrocycle 1 contraction reaction, a specifically deuterated [D y ] 2 has been synthesized according to the known procedure from 5,10,15,20‐tetraphenyl‐26,28‐ditellurasapphyrin, 3 , with the use of DCl/D 2 O (Scheme , Figure S1 in the Supporting Information). The deuteration pattern is preserved during alumina‐promoted contraction of [D x ] 1 , allowing for unambiguous identification of the lost CH unit as C7/18‐H or C8/17‐H at the outer macrocycle rim of 2 .…”

“…Solution of 1 (20 mg, 0.03 mmol) in dichloromethane (10 mL) with one drop of HCl (conc.) was layered on a basic or neutral Al 2 O 3 (Brockmann I grade) column.…”

“…Thus, another approach, based on the post‐synthetic transformations of a macrocyclic skeleton may be more efficient and lead to structures difficult to obtain by assembly of small units . Skeletal rearrangements are encountered rather rarely; they may be exemplified by a core heteroatom replacement or extrusion, macrocyclic fusion, and ring expansion or contraction. For porphyrinoid aromatic macrocycles a contraction may take place at both—a meso ‐link or at a cyclic subunit, like a pyrrole in a regular porphyrin, a phenylene ring in benziporphyrin or naphthiporphyrin, or at the outer heptacyclic ring of azuliporphyrinoids as well .…”