Möbius Aromatic [28]Hexaphyrin Germanium(IV) and Tin(IV) Complexes: Efficient Formation of Triplet Excited States

Abstract

[28]Hexaphyrin Ge and Sn complexes were synthesized in high yields by reactions of [28]hexaphyrin with GeCl or SnCl in the presence of triethylamine. Both complexes display distinct 28π Möbius aromatic character and possess a trigonal bipyramidal geometry at the central Ge or Sn atom. The equatorial hydroxy group of the Ge complex was smoothly exchanged with neutral nucleophiles, such as phenol derivatives and thiophenol, with retention of configuration. In the Sn complex, intersystem crossing to the T state is remarkably enhanced owing to the effective heavy-atom effect, thus allowing the formation of the T state in high yield. The T states of the Ge and Sn complexes were found to be antiaromatic on the basis of the transient absorption features in line with the Baird rule.

Figure‐eight Octaphyrin Bis‐Ge(IV) Complexes: Synthesis, Structures, Aromaticity, and Chiroptical Properties

“…The sum of the angles in each equatorial plane was calculated as 359.9° and 359.9°, indicating its high trigonal bipyramidal character. This coordination fashion is similar to that of [28]hexaphyrin Ge(IV) complex . On the other hand, the structure of 5‐syn is somewhat different: two Ge(IV) atoms are also embedded in the NNNC cavity in which one Ge atom is bound to N6, N8, and O2 atoms in the equatorial positions, and N7 and C23 atoms in the apical positions.…”

Reversible π-system switching of thiophene-fused thiahexaphyrins by solvent and oxidation/reduction

“…Consequently, the torsion angle at C(5)–C(6) is the largest value (66°). Although the largest torsion angle in the conjugation circuit of 5 is larger than those of typical Möbius aromatic [28]hexaphyrins (26–49°), 6 it is virtually identical to that of a [28]hexaphyrin monophosphorus complex (65°). 8 b The 1 H NMR spectra of 5 were measured in various solvents.…”

“…Nevertheless, Herges and co-workers reported the synthesis of the first Möbius aromatic molecule in 2003. 5 After this seminal work, various porphyrinoids have been found to be Möbius aromatic 6 , 7 and antiaromatic 8 molecules.…”

Theoretical studies as a tool for understanding the aromatic character of porphyrinoid compounds

“…The current density and current pathways have been studied for doubly Möbius-twisted meso-trifluoromethyl-substituted hexaphyrins, which were synthesized by Shimizu et al, 208 which triggered a large number of experimental studies of twisted expanded porphyrins. 214,215,218,219,221,223,[237][238][239][240][241][242][243][244][245] NICS calculations as well as atom in molecules (AIM) and electron localization function (ELF) critical point approaches have been used in studies of the aromatic properties of the doubly-twisted [26]hexaphyrin and [28]hexaphyrin molecules. Topological studies showed that the synthesized hexaphyrin molecules are formally doubly-twisted molecules with a linking number L k of 2.…”