Sterisch gespannte Porphyrine – Einfluß der Kernprotonierung und der peripheren Substituenten auf die Konformation bei tetra‐meso‐, octa‐β‐und dodecasubstituierten Porphyrin‐Dikationen

Abstract

Das am stärksten sattelförmig verbogene Porphyrin, das bislang charakterisiert wurde, ist das Dikation [H4obrtpp]2+ (H2obrtpp = Octabromtetraphenylporphyrin). Seine Pyrrolringe sind in der Verbindung [H4obrtpp][CF3COO]2.5 CHCI3im Kristall um 62° gegeneinander gekippt, und die β‐Pyrrol‐C‐Atome sind mehr als 1.5 Ä von der mittleren Ebene des Porphyrinrings entfernt. Diese extreme Verbiegung ist die Folge der sterisch anspruchsvollen Substituenten an der Porphyrinperipherie und der vier Protonen im Zentrum des Gerüstes.

Planar and Nonplanar Free‐Base Tetraarylporphyrins: β‐Pyrrole Substituents and Geometric Effects on Electrochemistry, Spectroelectrochemistry, and Protonation/Deprotonation Reactions in Nonaqueous Media

“…The assignment of macrocycle planarity to the neutral compounds in Scheme is based in part on structural data in the solid state and in part on the compound’s UV/Vis spectra that exhibit diagnostic patterns that indicate planarity or nonplanarity of the macrocycle, as described later in the manuscript. All of the porphyrins in Scheme are anticipated to have a nonplanar configuration after the addition of two more protons to the core nitrogen atoms, as was demonstrated for tetraphenylporphyrin [H 4 TPP] 2+ , octaethyltetraphenylporphyrin [H 4 OETPP] 2+ , and octabromotetraphenylporphyrin [H 4 TPPBr 8 ] 2+ which were structurally characterized as having a saddle‐type distortion ( D 2 d symmetry) 25…”

“…[22][23][24] Protonation of the central nitrogen atoms of a free-base porphyrin will also induce a nonplanar distortion of the macrocycle. [25] Under some conditions, the addition of two protons can occur in separate steps as shown in Equations (1) and (2), [8,[26][27][28][29] but in most cases the experimentally observed process actually occurs in a single step as illustrated in Equation (3). [8,[26][27][28][29][30][31] H 2 ðPÞ þ H þ Ð ½H 3 ðPÞ þ ð1Þ…”

“…All of the porphyrins in Scheme 1 are anticipated to have a nonplanar configuration after the addition of two more protons to the core nitrogen atoms, as was demonstrated for tetraphenylporphyrin [H 4 TPP] 2 + , octaethyltetraphenylporphyrin [H 4 OETPP] 2 + , and octabromotetraphenylporphyrin [H 4 TPPBr 8 ] 2 + which were structurally characterized as having a saddle-type distortion (D 2d symmetry). [25] A loss of protons from free-base porphyrins can occur in nonaqueous media containing added base, with the degree of deprotonation depending upon the porphyrin substituents, the solvent, the strength of the added base, and the planarity of the macrocycle. The deprotonation of H 2 (P) to give [H(P)] À and [(P)] 2À has been examined by UV/Vis spectroscopy in nonaqueous media [27,30,[37][38][39][40] but, to our knowledge, there has been no electrochemistry reported for the deprotonated porphyrins under these solution conditions.…”

Hermaphroditic Chirality of a D2‐Symmetric Saddle‐Shaped Porphyrin in Multicomponent Spontaneous Optical Resolution: Inclusion Cocrystals with Double‐Helical Porphyrin Arrays

“…Fully substituted porphyrins such as 1 are known to adopt a saddle shape owing to steric repulsion among the neighboring substituents on the porphyrin periphery. [6][7][8][9] Thus, porphyrin 1 with two different aryl groups at the adjacent meso positions exhibits molecular chirality (symmetry group D 2 ). [10][11][12] However, because of a rapid saddle-to-saddle macrocyclic inversion, 1 frequently switches back and forth between its two enantiomeric forms in solution.…”