Siamesisches Zwillingsporphyrin: ein Pyrazol‐expandiertes Porphyrin mit Bindungstaschen für Dimetallkomplexe

Abstract

Porphyrine an der Hüfte vereint: Ein expandiertes Porphyrin mit zwei Porphyrin‐ähnlichen {N4}‐Taschen, die durch verbrückende Pyrazole verbunden sind, wurde synthetisiert. Strukturelle und spektroskopische Daten belegen das Fehlen eines makrocyclischen aromatischen π‐Systems. In seinem Dikupferkomplex (siehe Bild) wird als Folge der fast orthogonalen magnetischen Kupfer(II)‐Orbitale erstmals eine ferromagnetische Kopplung in zweifach Pyrazolato‐verbrückten Komplexen beobachtet.

Siamese‐Twin Porphyrin: A Pyrazole‐Based Expanded Porphyrin of Persistent Helical Conformation

“…Its molecular structure showed the twist along the long axis also seen in the structure of the diprotonated free-base (and the dicopper complex; see below). [24] It thus again crystallized as a racemic mixture of two enantiomeric helimers. The compound exhibited crystallographic two-fold symmetry (D 2 molecular symmetry).…”

“…We thus named it the "Siamese-twin porphyrin". [24] This naming is descriptive of the framework structure but shall not evoke any implications about the presence of aromatic conjugation pathways. One of the goals of this target structure was to incorporate two metal ions in these highly preorganized binding pockets in close proximity to each other and to study the resulting metal-metal cooperativity.…”

“…[22] Guided by these experiences, our renewed efforts were finally successful and the twin porphyrin and its homobimetallic 22 Cu 2 complex were described in a preliminary report. [24] Following up on this, we provide here the details of the design and synthesis of the free-base twin porphyrin 22 H 4 and the formation and structure of its dicopper(II) complex 22 Cu 2 . Furthermore, we will firstly report the synthesis and crystal structure of the homobimetallic diamagnetic dinickel(II) complex 22 Ni 2 , as well as the crystal structure of the protonated form of free-base twin porphyrin 22 H 6 2 + , revealing the highly twisted chiral conformations already observed for the dicopper complex.…”

“…Furthermore, we will firstly report the synthesis and crystal structure of the homobimetallic diamagnetic dinickel(II) complex 22 Ni 2 , as well as the crystal structure of the protonated form of free-base twin porphyrin 22 H 6 2 + , revealing the highly twisted chiral conformations already observed for the dicopper complex. [24] A series of NMR and UV/Vis spectroscopic investigations allowed conclusions to be drawn on the protonation-and temperaturedependent conformational characteristics of the macrocycles and the prevailing conjugation pathways. Importantly, the helimeric conformations of the macrocycles were found to be persistent.…”

“…The resulting expanded porphyrin, consisting of four pyrroles and two pyrazoles, merges the structural characteristics of pyrazoles bearing chelating side‐arms with those of porphyrins; it can also be interpreted as the fusion of two porphyrin‐like coordination sites. We thus named it the “Siamese‐twin porphyrin” 24. This naming is descriptive of the framework structure but shall not evoke any implications about the presence of aromatic conjugation pathways.…”