C,C‐ and N,C‐Coupled Dimers of 2‐Aminotetraphenylporphyrins: Regiocontrolled Synthesis, Spectroscopic Properties, and Quantum‐Chemical Calculations

Abstract

β,β'-Bisporphyrins are intrinsically chiral porphyrin dimers with fascinating properties. The configurational stability at their axes can be directed by variation of the central metal atoms. Herein, we present a regioselective functionalization of the monomeric 2-amino-tetraphenyl-porphyrin as a versatile substrate for dimerization by oxidative coupling. By simple variation of the reaction conditions (solvent and oxidant), the oxidation selectively gave either the axially chiral C,C-coupled diaminobisporphyrin in high yields or, under Ullmann conditions, the twofold N,C-linked achiral dimer, also in good yields. A generalized mechanism for the coupling reaction is proposed based on DFT calculations. The axially chiral β,β'-coupled porphyrin dimers were isolated as racemic mixtures, but can be resolved by HPLC on a chiral phase. TDDFT and coupled-cluster calculations were used to explain the spectroscopic properties of the aminoporphyrins and their dimers and to elucidate the absolute configurations of the C,C-coupled bisporphyrins.

Good Computational Practice in the Assignment of Absolute Configurations by TDDFT Calculations of ECD Spectra

“…The resulting π‐stacking is correctly reproduced only by dispersion‐corrected functionals such as ωB97X‐D. The π‐stacking has a strong influence on the dihedral angle of the axis and thus on the ECD spectrum of the found conformers . Moreover, CAM‐B3LYP, B3LYP, and BHLYP predict quite different ECD spectra, with only the long‐range corrected functional CAM‐B3LYP reproducing the correct pattern, intensities, and signs of the experimental curve (Fig.…”

“…Another illustrative case is that of the bis(aminoporphyrin) 6 , for which both the geometry optimization and the TDDFT calculations were sensitive to the used functional . The phenyl rings adjacent to the interporphyrin axis lie above the neighboring porphyrinic macrocycle.…”

Optical Properties of Silver-Mediated DNA from Molecular Dynamics and Time Dependent Density Functional Theory

“…However, CAM-B3LYP is a functional built to overcome the deficiencies of B3LYP and to correctly describe charge transfer, local excitations, and Rydberg excitations [34]. It has been assessed for a broad set of small main group and organic molecules [44], and has been demonstrated to outperform B3LYP for chiral alkenes [45], chiral aromatic nitro compounds [46], and metal-porphyrin complexes [47]. It is very interesting to understand why for our Ag${}^{+}$-guanine system, CAM-B3YLP gives less accurate ECD spectra than B3LYP.…”

Chiroptical Sensing: A Conceptual Introduction

“…It is important to emphasize that relative Gibbs free energies, dipole, and rotational strength can be very sensitive to the choice of functional. The literature provides several cautionary tales of studies which demonstrate that popularly used B3LYP is not necessarily the most accurate functional for predicting structures and energies of standard organic molecules, especially when noncovalent interactions come into play [13,54,[58][59][60][61].…”