Macrocyclic oxidation

Nolle, Rowan, and coworkers prepared cavity-functionalized porphyrin catalysts with diameter of about 9 A. The catalytic macrocycles strongly bound viologen derivatives in their own cavities through electrostatic and n-n stacking interactions K = 10 to 10 M ). The catalytic macrocycle with manganese porphyrin strongly binds a polymer substrate (polybutadiene) that is included in the cavity, and the macrocycle oxidizes polymer substrate complexes. 

Although it has been known for many years that ethylene oxide and formaldehyde ean form statistical copolymers, it was not until the interest in crown ethers developed that the potential of macrocyclic formals as complexing agents was recognized. 

Oxidation of /U-cresol afforded a triphenol 22 which is approximately half the molecule. The central hydroxyl of the triphenol could be selectively methylated and then the compound was ort/ro-brominated and bridged using 1,3-dibromopropane to give 23. Metallation with butyllithium followed by iron catalyzed coupling afforded the macrocycle as indicated. 

Gentle oxidation of thiols leads generally to disulfides When tetrafluoro-1,4-benzeneditliiol is added to dimethyl sulfoxide, a macrocyclic tetradisulfide is formed [102] (equation 94)... 

Treatment of macrocycle 278 with an excess of Caro s acid resulted in oxidation of all the sulfur atoms to sulfones and the azo group to an azoxy group (Scheme 181) (99MI4). The oxidation product 279 was formed in 42% yield. Products with smaller oxygen contents were obtained using weaker oxidizing agents. 

Oxidation of thiol 287 with air in glyme gave disulfide 288, which on intramolecular oxidative coupling with A,)V-dibromoisocyanurate formed macrocycle 289 in 42% yield (Scheme 188) (99MI3). 

A number of oxepin derivatives with alkano bridges across the 3- and 6-positions and across the central C-C double bond have been oxidized with ruthenium(VIII) oxide. Usually, all of the double bonds of the heterocycle are cleaved and a macrocycle 5 is formed that contains two 1,2-diketone functions.142,199... 

The high stability of porphyrins and metalloporphyrins is based on their aromaticity, so that porphyrins are not only most widespread in biological systems but also are found as geoporphyrins in sediments and have even been detected in interstellar space. The stability of the porphyrin ring system can be demonstrated by treatment with strong acids, which leave the macrocycle untouched. The instability of porphyrins occurs in reduction and oxidation reactions especially in the presence of light. The most common chemical reactivity of the porphyrin nucleus is electrophilic substitution which is typical for aromatic compounds. 

In the case of the osmium(VIII) oxide oxidation of 5,10,15,20-tetraphenylchlorin,3b the metal-free macrocycle gives the bacteriochlorin 6, whereas the corresponding zinc derivative leads to an isobacteriochlorin. 

Similiar problems of regioselectivity as in reduction reactions are encountered in oxidation reactions of porphyrins and chlorins. The oxidation of chlorins to isobacteriochlorins can be directed by insertion of zinc(II) or nickel(II) into the macrocycle. Again here, the metal-free chlorins give the bacteriochlorins whereas the metal chlorins, e.g. 1, give isobacteriochlorins, e.g. 3.15a,b I 7... 

The condensation gives the orange-colored macrocycle 39 in reasonable yield with a fully cyclically conjugated, but nonaromatic, 2071 electron chromophore. The cyclic conjugation is formed directly upon condensation so that no further oxidation is required. 

The isosmaragdyrins have been prepared1 -14 by a McDonald-type strategy. On acid-catalyzed condensation between an a-unsubstituted terpyrrole 3713 and a dipy rrylmethanedicarbaldehyde 43 the macrocycle 44 is formed directly without the requirement of an oxidation step. In the primarily formed diprotonated form of isosmaragdyrin 44, the cyclic conjugation is disrupted. 

The approach makes use of a bipyrroledicarbaldehyde 54 and a tripyrranedicarboxylic acid 55 which are condensed with subsequent decarboxylation in the presence of acid and oxygen. The presence of oxygen, as in many other syntheses of porphinoid macrocycles, is necessary to adjust the oxidation level of the chromophore which is in sapphyrins a 2271-aromatic cyclically conjugated system. Many sapphyrins 56 with different substitution patterns have been synthesized according to this general scheme. As in all McDonald-type condensations at least one of the components has to be symmetric because otherwise mixtures of constitutional isomers would be formed. 

The name amethyrin refers to the fact that the dull-purple color of the protonated form of the macrocycle is that of amethyst stones, Formal oxidation or reduction products are the aromatic [22]hexaphyrin(l.0.0.1.0.0) or the [26]hexaphyrin(l.0.0,1.0.0), respectively. However, none of these products could be observed either as reaction products or as direct products of oxidation or reduction reactions. 

In marked contrast to what is usually observed with porphinoid macrocycles under these oxidation conditions and therefore surprisingly, the rosarins are obtained as 2471 cyclically conjugated, but nonaromatic species, an observation which was also made in the amethyrin series vide supra). 

Almost every metal atom can be inserted into the center of the phthalocyanine ring. Although the chemistry of the central metal atom is sometimes influenced in an extended way by the phthalocyanine macrocycle (for example the preferred oxidation state of ruthenium is changed from + III to + II going from metal-free to ruthenium phthalocyanine) it is obvious that the chemistry of the coordinated metal of metal phthalocyanines cannot be generalized. The reactions of the central metal atom depend very much on the properties of the metal. 

Although the substitution of a preformed phthalocyanine always leads to a complex mixture of more- or less-substituted products, the reaction is of major industrial importance. Besides the chloro- and bromocopper phthalocyanines, also polysulfonated phthalocyanines, which are used as water-soluble dyes, are produced by the reaction of copper phthalocyanine with the respective reactant. While typical aromatic reactions of the Friedel-Crafts type are also possible,333 direct nitration of the macrocycle commonly results in oxidation of the phthalocyanine. However, under mild conditions it is possible to introduce the nitro group directly into several phthalocyanines.334... 

The oxidation of the macrocycle in phthalocyanines does not generally lead to stable molecules. One-electron oxidations of the macrocyclc(s) in bis(phthalocyanines) leading to species which can be isolated have been carried out chemically or electrochemically,... 

Porphyrin complexes have been the most intensively studied macrocyclic complexes of these metals [129]. They are formed in a wide range of oxidation states (II-VI) and they are, therefore, treated together under this heading, though most of the chemistry for ruthenium lies in the II-IV states. Octaethylporphyrin (OEP) complexes are typical. 

---