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Ferrocenyl macrocyclic conjugates involving 22pi oxasmaragdyrins and 18pi oxacorroles have been synthesized and characterized. The direct covalent linkage of the ferrocenyl moiety to the meso position of the macrocycle is achieved by simple oxidative coupling of appropriate precursors with trifluoroacetic acid as catalyst. The electronic coupling between the ferrocenyl moiety and the macrocyclic pi system is apparent from: a) the red shifts (293-718 cm(-1)) of the Soret and Q-bands in the electronic absorption spectra of ferrocenyl conjugates; b) the shift of oxidation potentials (50 130 mV) of both the ferrocene and the corrole rings to the positive potentials; and c) considerable shortening of the C-C bond which connects the ferrocene and the meso-carbon atom of the macrocycle. The single-crystal X-ray structure of oxasmaragdyrin-ferrocene conjugate 9 reveals the planarity of the 22pi skeleton with very small deviations of the meso-carbon atoms. The meso-ferrocenyl substituent has a small dihedral angle of 38degrees, making way for mixing of the molecular orbitals of the ferrocene and the macrocycle. However, the other two meso substituents are almost perpendicular to the mean plane, defined by the three meso carbon atoms. Classical C-(HO)-O-... and nonclassical C- H(...)pi interactions lead to a two-dimensional supramolecular network. Ferrocene-smaragdyrin conjugate 9 bonds to a chloride ion in the protonated form and a rhodium(i) ion in the free base form. Nonlinear optical measurements reveal a larger nonlinear refractive index (-5.83 x 10(-8) cm(2) W-1) and figure of merit (2.28 x 10(-8) cm(3)W(-1)) for the rhodium smaragdyrin-ferrocene conjugate 19 than for the others, suggesting its possible application in optical devices
An investigation of the conformational landscape of 1,3-dithian-2-yl bearing porphyrins and the rotational behavior of the dithianyl substituents in meso position was carried out by variable-temperature (VT) NMR spectroscopy. Additionally, theoretical results for alternative conformations and energy barriers were obtained by molecular modeling. The study revealed different NH trans tautomers with regard to the orientation of the dithianyl ligands for the free base porphyrins 1-3. Relatively ruffled porphyrin core conformations were established for the transition states of the dithianyl rotation, resulting in a lower rotational energy barrier for the nickel(II) complex 4 compared to that of the free base systems. The data obtained and the first depiction of a rotational transition state for the rotation of bulky meso-alkyl substituents illustrate the close structural interplay between meso-alkyl substituents and the macrocycle conformation in porphyrins.
Photodynamic therapy (PDT) is a developing modality for the treatment of certain tumorous and other diseases. Considerable progress has been made in recent years in the search for new photosensitizers, in particular elucidating the role of localization of the photosensitizer. Known successful photosensitizers of the tetrapyrrole type are amphiphilic molecules, preferably localizing in cellular membrane structures. Thus, the quest for new photosensitizers requires the synthesis of unsymmetrically Substituted (amphiphilic) tetrapyrroles. In this article. we describe strategies for the de novo synthesis of amphiphilic tetrapyrroles using a 3-hydroxyphenyl substituted tetrapyrrolic system (Temoporfin) as the lead structure. From an applied science-oriented approach, such a set of amphiphilic porphyrins is best synthesized by combining well-developed condensation methods with subsequent functionalization via organolithium compound or transition metal catalyzed coupling protocols. Starting from simple A(2)- or AB-porphyrins, the synthesis of A(2)B-, A(3)-, A(3)B-, and A(2)BC-porphyrins with a mixed hydrophilic/hydrophobic substitution pattern is described. Because of the versatility of this approach to unsymmetrically Substituted porphyrins it is also applicable to other areas where porphyryns with a tailor-made substitution patterns are needed. for example. catalysts or molecular electronic devices based on tetrapyrroles. (c) 2005 Elsevier Ltd. All rights reserved