Porphyrins perfluorination

A biomimetic oxidation with perfluorinated porphyrin complexes [(F20TPP) FeCl] showed high catalytic activity with secondary alcohols with over 97% yield in all cases [144]. Furthermore, this catalyst is able to oxidize a broad range of alcohols under mild conditions with wCPBA as terminal oxidant. Here, an a-hydroxyalkyl radical species is proposed as central intermediate. 

The highly evolved catalyst 20 combines several features that have proved successful in simpler cases. The ionic sulfonate groups make the substrate sufficiently soluble for the reaction to be run in water. (The four hydrophilic cyclodextrins perform the same service for the catalyst.) The target reaction, the seledive oxidation of the steroid skeleton, goes back to the early days of enzyme models,1711 and the choice of porphyrin and of manganese as the metal cation are based on many years experience. The aryl groups are perfluorinated because an earlier version of the catalyst suffered self-oxidation. 

Oxidation reactions are not limited to those that occur at a carbon centre. The perfluorinated Ni(F-acac)2-benzene-CgFi7Br system described above was also active for the oxidation of sulfides to sulfoxides and sulfones [28], A sacrificial aldehyde is required as co-reductant, but the reaction may be tuned by changing the quantity of this aldehyde. If 1.6 equivalents of aldehyde are used, the sulfoxide is obtained, whereas higher quantities (5 equivalents) lead to sulfones. Fluorous-soluble transition metal porphyrin complexes also catalyse the oxidation of sulfides in the presence of oxygen and 2,2-dimethylpropanal [29],... 

The difficulty of perfluorinating pyrrole is enhanced in the porphyrins, which have reduced 7r-density on the a-carbons. Although direct fluorination appears promising, it is not yet fully developed [88JCS(P1)1735 89CL263 90TL6847]. The use of N-fluoropyridinium triflate resulted only in meso-fluorination (92TL1069). 

Two other interesting papers should also be mentioned. Perfluorination of porphyrin was achieved with AgF resulting in a robust catalyst (equation 41), capable of performing around 50 cycles of benzene oxidation or olefin epoxidation with H20281. The second work deals with photolytic reactions of AgF in the presence of Ti02. The formally nucleophilic fluoride behaves as an electrophile and replaces protons in quite a few cases (equation 42)82. 

Vasil ev V, Borisov SM. Optical oxygen sensor based on phosphorescent metal porphyrins immobilized in perfluorinated ion-exchange membrane. Sens Actuators 2002 B82 272-6. 

Zeolite-encapsulated perfluorinated ruthenium phthalocyanines catalyze the oxidation of cyclohexane with t-BuOOH [146]. A dioxoruthenium complex with a D4-chiral porphyrin ligand has been used for the enantioselective hydroxylation of ethylbenzene to give a-phenylethyl alcohol with 72% e.e. [147]. 

DiMagno and coworkers reported an efficient route to 58 that also employs a double elimination step, but this is performed on the readily available tetrafluor-opyrrolidine 10 (see Section 3.2.1 above) (Fig. 3.27). Optimization of conditions provided 58 in good yield in a reaction that is readily scaled up, thus providing ready access to this fluorinated building block. This has been particularly valuable for the synthesis of perfluorinated porphyrins (see the discussion below). 

An early report described the preparation in low yield of two isomeric meso-monofluorinated derivatives of porphyrins using the Schiemann reaction. Electrophilic fluorinating agents have been a more effective way to carry out direct fluorination of the porphyrin system. For example, reaction of octaethylporphyrin with A-fluoropyridinium salts such as A-fluoro-2,3,4,5,6-pentachloropyridinium triflate gave a mixture of mono, di, tri, and tetrafluoro derivatives 88 (Fig. 3.41). The perfluorinated derivative was formed in 20% yield. mew-Fluorination of octaethylporphyrin had minimal effects on oxidation potential and spectral properties. 

Condensation of pyrroles with carbonyl compounds under Lewis acid catalysis followed by oxidation provides an efficient route to the porphyrin ring system. This has been effectively used to prepare polyfluorinated porphyrins from 3-fluoro and 3,4-difluoropyrroles, as well as pyrroles substituted with fluorinated side chains in these positions. For example, DiMagno and coworkers extended their studies of highly electron-deficient porphyrins to a series of 2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraarylporphyrins 96, including the perfluorinated compound, by BFs-catalyzed condensation of 3,4-difiuoropyrrole with benzaldehydes followed by dichloro dicyano quinone (DDQ) oxidation (Fig. 3.46). A similar approach was used by Leroy and coworkers. ... 

Naruta, Y Tani, R Mamyama, K. mci o-Perfluorination of porphyrins with A-fluor-opyridinium triflate. Tetrahedron Lett. 1992, 33, 1069-1072. 

One problem with our system was that the catalyst itself was oxidized fairly easily, so we did not get many catalytic turnovers. Others working on cytochrome models had shown that the catalyst was much more oxidatively stable when the phenyl rings were perfluorinated. Thus we synthesized a perlluorinated version (24) of our previous compound, easily prepared from the porphyrin with four pentafluorophenyl groups by simple reaction with j8-cyclodextrin 6-thiol, which selectively replaced the para fluorines in the phenyl rings. While with the previous catalyst we only achieved three to five turnovers before the catalyst was destroyed, the new fluorinated catalyst performed the same selective hydroxylation of C-6 in the steroid with 187 turnovers. 

Novel nanoscale discotic liquid crystalline porphyrins 14 with partial alkyl chain perfluorination has been designed and synthesized in our group which exhibits exceptionally enhanced tendency to spontaneously self-assemble into homeotropically ordered nanostructures [107]. The defect-free homeotropically aligned fluorinated porphyrin thin films were fabricated and characterized. In the films thinner than 10 pm in glass cells, it shows strong tendency towards homeotropic... 

Epoxidation of olefins was catalyzed by the ruthenium(II) complex of the above perfluorinated y3-diketone in the presence of 2-methylpropanal (Scheme 50). Unfunctionalized olefins were epoxidized with a cobalt-containing porphyrin complex, and epoxidation of styrene derivatives was catalyzed by chiral salen manganese complexes (248) (Scheme 50). In the latter case, chemical yields were generally high, however, the products showed low enantiomeric excess with the exception of indene (92% ee). [Pd(C7Fi5COCHCOC7Fi5)2] efficiently catalyzed the oxidation of terminal olefins to methyl ketones with f-butylhydroperoxide as oxidant in a benzene-bromoperfluoro-octane solvent system (Scheme 50). In all these reactions, the product isolation and efficient catalyst recycle was achieved by a simple phase separation. 

Two novel complexes have been reported as aetive catalysts for both inter-and intra-molecular C( p )-H aminations of hydrocarbons. While perfluorinated dichlororuthenium(IV) porphyrin (171) proved efifieient using phosphoryl azides as... 

Reaction of 3,4-difluoropyrrole 391 with benzaldehydes 470 followed by oxidation with DDQ led to tetraarylporphyrins 471. On the base of that reaction sequence a convenient and common pathway towards p-octafluoroporphyrins 471, bearing meso-tetraaryl substituents, including perfluorinated tetraarylporphyrin was elaborated [153], In the case of AI2O3 catalysis the first step of above mentioned sequence afforded p-octafiuorocorroles 472 instead of porphyrins 471 [154],... 

Naruta Y, Tani F, Maruyama K (1992) Meso-perfluorination of porphyrins with N-fluoropyridinium Inflate. Tetrahedron Lett 33(8) 1069-1072... 

Li G, Chen Y, Missert JR, Rungta A, Dougherty TJ, Grossman ZD, Pandey RK (1999) Application of Ruppert s reagent in preparing novel perfluorinated porphyrins, chlorins and bacteriochlorins. J Chem Soc Perkin Trans 1 Org Bio-Org Chem 13 1785-1787... 

Stuzhin PA, Goryachev MYu, Ivanova SS, Nazarova A, Pimkov I, Koifmem OI (2013) Perfluorinated porphyrazines 1 Synthesis and UV-vis spectred study of perfluorinated octaphenylporphyrazine and its indium(III) complex, [MPA(F5Ph)8](M = 2H, In" (OH)) J Porphyrins Phthalocyanines 17 905-912... 

Li, G., Chen, Y., Missert, J.R., Rungta, A., Dougherty, T.J., and Pandey, R.K., AppHcation ofRuppert s reagent in preparing novel perfluorinated porphyrins, chlorins and bacteriochlorins, /. Chem. Soc. Perkin. Trans. 1,1785,1999. 

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