Natasza Sprutta

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

The aromatic character of porphyrins, which has significant chemical and biological consequences, can be substantially altered by judicious modifications of the parent ring system. Expansion of the macrocycle, which is achieved by introducing additional subunits, usually increases the so-called free curvature of the ring, leading to larger angular strain. This strain is reduced by a variety of conformational changes, most notably by subunit inversion and p surface twisting. The latter effect creates a particularly convenient access to Möbius aromatic molecules, whose properties, predicted over 40 years ago, are of considerable theoretical importance. The conformational processes occurring in porphyrin analogues are often coupled to other chemical phenomena, and can thus be exploited as a means of constructing functional molecular devices. In this Review, the structural chemistry of porphyrinoids is discussed in the context of their conformational dynamics and p-electron conjugation.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications.

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

A tetraphenylthiaporphyrin with an inverted thiophene ring

Abstract A novel isomer of 5,10,15,20-tetraphenyl-21-thiaporphyrin with an inverted thiophene ring, i.e. 2-thia-5,10,15,20-tetraphenyl-21-carbaporphyrin (SCTPPH) has been produced by condensation of 2,4-bis(phenylhydroxymethyl)thiophene with pyrrole and benzaldehyde via a one pot, two-step reaction or by the [3 + 1] condensation of the thiophene precursor and 5,10-diphenyltripyrrin.

Hückel and Möbius Expanded para‐Benziporphyrins: Synthesis and Aromaticity Switching

The four expanded p-benziporphyrins A,C-di-p-benzi[24]pentaphyrin(1.1.1.1.1), N-fused A-p-benzi[24]pentaphyrin, A,D-di-p-benzi[28]hexaphyrin(1.1.1.1.1.1), and A,C-di-p-benzi[28]hexaphyrin(1.1.1.1.1.1) were obtained in three-component Lindsey-type macrocyclizations. These compounds were explored as macrocyclic ligands and as potential aromaticity switches. A BODIPY-like difluoroboron complex was obtained from the A,C-di-p-benzi[24]pentaphyrin, whereas A,C-di-p-benzi[28]hexaphyrin yielded a Möbius-aromatic Pd(II) complex containing fused pyrrole and phenylene subunits. Conformational behavior, tautomerism, and acid-base chemistry of the new macrocycles were characterized by means of NMR spectroscopy and DFT calculations. Free base N-fused A-p-benzi[24]pentaphyrin showed temperature-dependent Hückel-Möbius aromaticity switching, whereas the A,C-di-p-benzi[28]hexaphyrin formed a Möbius-aromatic dication.

Dithiaethyneazuliporphyrin - a contracted heterocarbaporphyrin

Dithiaethyneazuliporphyrin, the first contracted carbaporphyrinoid, has been synthesized; the molecule contains an azulene moiety embedded in the [18]dithiacarbatriphyrin(4.1.1) macrocyclic framework.

Thiaporphyrin with an Inverted Thiophene Ring – DFT Studies

The structure and electronic energy have been investigated applyingthe density functional theory (DFT) for two idealized 2-thia-21-carbaporphyrin, (SCP)H and (3H-SCP), 2-thia-21-carbaporphyrin anion (SCP)- and 21-thiaporphyrin (SP)H. The analysis of calculated total electronic energies, using the B3LYP/6-31-G* approach, demonstrates that the energy difference between 21-thiaporphyrin and its inverted isomer equals 10.34 kcal/mol [(SCP)H] and 52.08 kcal/mol [(3H-SCP)]. In contrast to 21-thiaporphyrin thethiophene fragments in (SCP)H and SCP- present a geometry resembling that one of an isolated thiophene molecule.

Protonation of 5,10,15,20-tetraphenylsapphyrin—identification of inverted and planar dicationic forms

5,10,15,20-Tetraphenylsapphyrin (TPSH3, I0) presents an unusual structural skeleton with an inverted pyrrole ring lying opposite to the bipyrrolic unit. The acid–base chemistry of sapphyrin, involving hydrogen chloride, dichloroacetic acid or trifluoroacetic acid in chloroform, dichloromethane (293 and 203 K) and DMSO (293 K) has been followed by means of UV–VIS electronic and 1H NMR spectroscopy. The protonation of TPSH3 proceeds stepwise via a mono- and a variety of di-cationic forms. The monoprotonated species (I1) preserves the inverted skeleton of I0. Two fundamental structures, inverted (I2) and expanded (P2), have been detected in the case of dications. The transformation of the macrocycle involves a reversible flip of a single pyrrole unit which relocates the 27-NH pyrrolic nitrogen between the periphery and the centre of macrocycle (I⇌P). The rearrangement is triggered by proton and/or anion addition and involves binding of anion(s) via a system of multiple NH-anion hydrogen bonds. The sequence of structural transformation is solvent dependent: I0→I1→P2→I2 in dichloromethane (chloroform) but I0→I1→I2→P2 in DMSO for all investigated acids.

Carbocations Confined in a Thiatriazuliporphyrin Frame

In the search for tricarbaporphyrinoids, a three-component acid-catalyzed condensation of azulene, 2,5-bis[(p-tolyl)hydroxymethyl]thiophene, and an aryl aldehyde has been elaborated, affording the appropriate thiatriazuliporphyrinogens. The subsequent oxidation yielded a rare example of a macrocyclic organic tetracation, which can be readily and reversibly converted into macrocyclic tri- and dicarbocations by addition of one or two hydroxides bound at the meso position(s). Further insight into the influence of carbocation formation on the geometry, electronic structure, and magnetic manifestation in (1) H NMR spectroscopy has been obtained by using density functional theory calculations. The charge distribution was evaluated by mapping electron density surfaces with electrostatic potential (ESP).

Retrieving aromaticity of dithiadiazuliporphyrin by oxidation: illustration by experimental and theoretical investigation

The photophysical properties of neutral, monocation radical, and dication of dithiadiazuliporphyrin have been examined with a particular focus on their aromaticity. Dithiadiazuliporphyrin exhibits significantly different characteristics depending on its oxidation state. From these features, we could conclude that the aromaticity of dithiadiazuliporphyrin is changed from nonaromatic to aromatic upon oxidation from neutral to monocation radical and dication by Br2.

Incorporation of a p-Phenylene Unit into the Azuliporphyrinogens Frame-Oxidation and Ruthenium Cluster Coordination

A porphyrinogen macrocycle incorporating two azulenes, phenylene and thiophene into the framework, joined by four C(sp3 ) atoms has been obtained as a mixture of six isomers. They were successfully separated and characterized spectroscopically. The identity of two of them was confirmed by X-ray crystallography. One isomer was tested in reaction with [Ru3 (CO)12 ] yielding exclusively π-complex with two clusters attached to azulenes. The partial oxidation of porphyrinogens yielded dication with two unmodified meso bridges. The stepwise oxidation followed by reaction with water as nucleophile afforded the dicationic species with two hydroxyl groups and a trication with one OH group. The hydroxy-dication can be reversibly transformed into hydroxy-trication by addition of HBF4 etherate.