Perimeter Coordinated Diastereomeric Rh(I) Complex of Helically Twisted Weakly Aromatic Hybrid Singly N‑Confused β–β Fused Ferrocenoporphyrinoids

Expedient synthesis, spectroscopic,
solid state structural proof,
and theoretical study of helically twisted weakly aromatic hybrid
singly N-confused ferrocenoporphyrinoids and the peripheral coordinated
Rh­(I) complex are reported. The X-ray crystal structure of the macrocycles
reveals an ambiguously inverted pyrrole ring reinforcing regioselective
β,β-linkage with the spatially adjacent N-confused N-methyl pyrrole ring leading to endocyclic extension of
macrocyclic π-conjugation via tricyclic [5.5.5] moiety. The
three-dimensional structure with built-in fused tricyclic [5.5.5]
moiety has paved way to three-dimensional weak diatropicity with vis–NIR
absorptions. The peripheral coordinated Rh­(I) complex owing to helical
chirality about the macrocyclic ring and planar chirality about the
square planar Rh coordination site exists as a mixture of diastereomers
(5:3) with well resolved 1H NMR spectra anticipating weak
aromaticity. The experimental spectroscopic measurements are in agreement
with theoretically determined electronic structure and properties
strongly elucidating sustained weak diatropic ring currents in twisted
macrocycles both in neutral form and in the metalated complex. Further
fragment molecular orbital approach and molecular orbital theory gave
insights on the stability of N-confused β–β fused
oxo-ferrocenoporphyrinoids and formation of the selective peripheral
coordinated Rh­(I) complex.