Sapphyrin analogs

The second sapphyrin analog reported by Sessler and coworkers is derived directly from macrocycle 6.26. Here, subjecting the alkyne-containing macrocycle 6.26a to Lindlar reduction conditions was found to afford a near quantitative conversion to the partially reduced macrocycle 6.27a (Scheme 6.3.3). As inferred from H NMR spectroscopic analysis, the specific structure of this reduction product is the tra 5-alkene 6.27. This compound may formally be regarded as being a true isomer of pentaazasapphyrin, and is thus referred to as [22]sapphyrin-(2.1.0.0.1) or [22]pentaphyrin- 2.1.0.0.1). 

Corrole and sapphyrin analogs are exanqples of how the pocket sizes of imidazolium cyclophanes can be altered to accommodate different sized metals into the pockets. TTie corrole analog 16 would be best suited for first row transition metals because of its decreased size. The pocket cavity of the sapphyrin analog 17 is larger and would be potentially better suited for coordinating both second and third row transition metals. The synthesis of 16 and 17 is outlined below (72). Thermal ellipsoid plots of conq)ounds 16 and 17 are shown in Figure 6 and 7, respectively. 

The above results were later complemented by the observation that the monopro-tonated form of sapphyrin is also capable of chelating chloride anion in the solid state.Here, in analogy to what was seen in the case of the bishydrochloride salt, the single chloride counteranion was found to lie ca. 1.72 A above the macrocycle plane, being held there by four hydrogen bonds (Figure 3). 

Removal of one meso-carbon from the sapphyrin skeleton leads to relatively unstable non-sapphyrin 22ji smaragdyrin 144 (Scheme 59) (1983JA6429). These (1972JCSP(1)2111) bear a structural relationship analogous to that between a porphyrin and a corrole. The earlier attempts to... 

In order to confirm the structure of the heterosapphyrins that were presumed to have formed during the course of the above reactions, Johnson and coworkers carried out a 3 + 2 reaction analogous to that now commonly used to prepare pentaazasapphyrins (vide supra). Here, it was found that reacting diformylbifuran 5.51 with the dicarboxyl-substituted tripyrrane 5.58 did indeed produce the hexaalkyl sapphyrin derivative 5.60 (Scheme 5.3.2). Johnson, et al. also used this approach to prepare the thiasapphyrin analog 5,61. This sapphyrin was obtained in 19.5% yield from diformyl bipyrrole 5.9 and the dipyrrolylthiophene 5.59. 

Sapphyrins bearing peripheral substituents other than those present in 5.21 also react with uranyl cation in methanol to form complexes akin to 5.96. Analogous reactions, wherein the methoxide nucleophile is replaced by cyanide were also described by Sessler and coworkers. Unfortunately, when cyanide anion is used as the nucleophile, the reaction yield was very poor. It thus proved impossible to isolate and characterize fully the resulting uranyl complex. 

Out-of-plane anion chelation was also observed in the historically important structure of the sapphyrin bis-hydrochloride salt 10.6-2HC1 (Figure 10.5.12). Here, in analogy to what was seen in Franck s systems, the chloride anions were found to reside above and below the mean N5 plane of the doubly protonated macrocycle (at ca. 1.77 A and 1.88 A, respectively), being held there by a combination of electrostatic interactions and hydrogen bonds (either 3 or 2, as the case may be). Thus, while showing congruence with what was observed for the [22]porphyrins-(3.1.3.1), this result stands in marked contradistinction to what was observed in the case of the... 

Although only prepared quite recently,amethryin (10.42) and orangarin (10.43) are of interest in that they define smaller analogs of rubyrin and sapphyrin, respectively. One set of comparisons such congruence could allow is in terms of... 

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