Phthalocyanines in zeolites

Ray, S. and Vasudevan, S. (2003). Encapsulation of cobalt phthalocyanine in zeolite-Y evidence for nonplanar geometry. Inorg. Chem. 42, 1711-1719... 

An example for subtle control by substitution of the phtallocyanine structure is reported by Pattons et al. [193] comparing the activity of FePcY with nitro substituted Fe phthalocyanines in zeolite Y. The electron withdrawing effect of the nitro substiment on the benzene ring was expected to enhance the electrophilic character of the active oxygen species and so to increase the activity. For the oxidation of cyclohexane to cyclohexanone and cyclohexanol with tBHP a 10 fold increase in the turnover frequency (TOF)was found for the nitro substituted complex in zeolite Y in comparison to the unsubstituted [204]. However the nitro substimted Fe phthalocyanines were found to be located at the outer surface of the... 

The in-s rtu synthesis of metalio-phthalocyanines in zeolites can be done via three distinct literature procedures (Scheme 1). The required amount of a given transition metal is brought into the zeolite via a simple ion exchange (procedure A), through adsorption of a TM-carbonyl (B) or a metallocene (C). After removal of the respective TM ligands (water, CO and cyclopentadiene, respectively), 1,2-dicyanobenzene (DCB) is adsorbed onto the TM-zeolite and the mixture heated to form the MePc compiex. Rnally, the sample has to be purified in such a way that oniv occiuded MePc complex remains in the zeolite. The association of DCB with the supercage TM ions in Y zeolite, are schematically shown in Fig. 3. 

Ship-in-Bottle Synthesis of Sterically Crowded Fe-Phthalocyanines in NaY Zeolite Hosts and Their Catalytic Behavior in Regioselective Oxidation of Alkanes... 

The use of heterogeneous catalysts in the synthesis of urethanes from aliphatic and aromatic amines, C02 and alkyl halides has been explored only recently. Titanosilicate molecular sieves [60a], metal phthalocyanine complexes encapsulated in zeolite-Y [60a], beta-zeolites and mesoporous silica (MCM-41) containing ammonium cations as the templates [60b, c], and adenine-modified Ti-SBA-15 [60d, e] each function as effective catalysts, even without any additional base. 

Metal phthalocyanines are easily synthesized by vapor-phase condensation of four molecules of dicyanobenzene in the presence of molecular sieves such as faujasites or A1PO-5 (123-126). This results in direct entrapment of the macrocycle inside the molecular sieve s channels and cages. There are also reports of ship-in-a-bottle synthesis of porphyrins in zeolites, but since porphyrin synthesis requires a mixture of pyrrole and an aldehyde instead of a single compound, porphyrin synthesis is a much less clean process than phthalocyanine preparation (127). Alternatively, soluble porphyrins or phthalocyanines can be added to the synthesis gel of, for example, zeolite X. This also results in entrapped complexes (128). 

The same holds for t-BuOOH and Fe phthalocyanines encapsulated in zeolites or adsorbed on carbon black (121, 124). On the other hand, hydroperoxides have been detected as products in the oxidation of ds-pinane by t-BuOOH in the presence of zeolite Y-encapsulated FePc (133). This is irrefutable evidence of trapping of a radical by dissolved O2. Superior hydroperoxide yields are obtained with FePc in zeolite NaY in comparison with the homogeneous reaction, particularly at subambient temperature ... 

The immobilization of Ru-phthalocyanines follows routes similar to those employed for the analogous Fe complexes. Particularly, the perfluorinated Ru phthalocyanines were immobilized in zeolites by ship-in-a-bottle synthesis or by template synthesis, or in MCMs after surface modification. The materials display extremely high activities for the oxygenation of paraffins with r-BuOOH as the oxidant (128,288). 

Figure 4. Structures of several ligands eomplexes synthesized in zeolite Y by the ship-in-a-bottle strategy (a) tetren (b) pyren (c) Co(salen) (d) Fe(phthalocyanine) (e) [Ru(bpy)2daf] + (f) [Ru(bpy)3] + (g) [Ru(bpz)3] +. Y,iV -Ethylenebis(salicylideneiminato) (2-) ion = salen, tetra-ethylenepentamine = tetren, 2,2 -bipyridine = bpy, 4,5-diazafluorene = daf, 2,2 -bipyrazine = bpz.

A recent elegant example of the tailoring the chemical properties of encapsulated metal complexes is the work of Balkus etal. who prepared and studied perfluorinated phthalocyanine complexes of Fe, Co, Cu and Ru (Scheme 25)[230] in NaX. Perfluorinating the complexes enhances the stability and catalytic activity of the catalysts in the oxyfiinctionalisation of light alkanes. The rapid deactivation of the catalysts based on Fe, Co and Cu Fj Pc complexes was overcome by using Ru as the metal center. Similar catalysts, i.e.,Co-phthalocyanine (Co-Pc) encapsulated in zeolite Y, are active catalysts for cyclohexene and 1-hexene epoxidation (Scheme 27)[231]. Comparison of the activity of free and encapsulated Co-Pc has shown that the interaction with the zeolite stabilizes the complex. Co-Pc is still active after 24 hrs reaction whereas the free complex in solution is virtually inactive after 15 minutes. 

A type c catalytic membrane was developed and tested by Jacobs et al. [91]. It consisted of a polydimethylsiloxane polymer matrix loaded with 30 wt% of iron phthalocyanine-containing zeolite Y crystals (see Figure 33). The membrane (thickness 62 pm) is m between two liquid streams cyclohexane and 7 wt% t-butyl hydroperoxide in the membrane and the iron sites inside the zeolite catalyze the oxidation of cyclohexane towards cyclohexanol and cyclohexanone. The oxidation products are distributed over the two phases. 

Over iron-phthalocyanine encaged in zeolite Y and using tertiary-butylhydroperoxide (t.-BHP) as oxidant, even cyclohexane can be converted to adipic acid. Selectivities of up to 35 % at conversions around 85 % have been reported. Unfortunately, however, a reaction time of 33 hours at 60 °C was required to achieve this conversion. Although the activity of the latter catalyst is certainly much too low to compete with the conventional catalytic systems for adipic acid synthesis, it provides interesting prospects for further developments. For the near future, we perceive that more and more groups will be working in this interesting field of catalysis by zeolite inclusion compounds. 

We have shown that perfluorination of the phthalocyanine ligand enhances the stability and catalytic activity of RuFiePc. Encapsulation of this complex in zeolite NaX by the synthesis method dramatically improves the activity and selectivity of RuFiePc. These results suggest that RuFi Pc-NaX is one of the best alkane oxidation catalysts of its kind. Although cycloalkanes are readily oxidized, the complete range of possible substrates is uncertain at this point. The oxidation of other alkanes and olefins will be the subject of continuing studies. 

Iron phthalocyanine encapsulated in zeolite. FePc/Z catalysts were prepared by two... 

K) has been observed for the composite formed by loading of phthalocyanine dye in zeolites.[74] It is worthwhile to point out that only in zeolites with water molecules can dye molecules exhibit apparent spectral hole-burning properties. This may be because the interactions between water molecules and the dye molecules in the pores of zeolites render the chromophoric groups of the dye molecules solvated, thus facilitating the electron-phonon interactions. 

The macrocycle phthalocyanine contains 8 N atoms, but usually only the four N-atoms on the inner side of the cycle are able to coordinate. In fact, in most cases the synthesis of phthalocyanine is realized in the presence of a metal ion as the template. It is also possible to attach various substituents on the phthalocyanine macrocycle. As for porphyrin, when coordinating to a metal ion, the H-atoms of the two NH groups on the inner side of the phthalocyanine cycle are replaced. The incorporation of metal porphyrin and phthalocyanine complexes into porous crystals has been gaining increasing interest. The properties of the complexes located in zeolite channels or cages are usually different from those of the compounds in solution, and they may find applications in areas such as catalysis, photochemistry, electrochemistry, and biomimetics. 

Pioneering studies of zeolite-encapsulated iron phthalocyanine (FePc) complexes were performed by Herron [73] who coined the term ship-in-a-bottle complex. He studied the Oxidation of alkanes with iodosylbenzene catalyzed by FePc encapsulated in zeolites Na-X... 

METALLO-PHTHALOCYANINES IN FAUJASITE-TYPE ZEOLITES 2.1. Encapsulation of MePc... 

The hydroxylation reaction of phenol with hydrogen peroxide and zeolite encapsulated MePc has received considerable attention. With the perchlorinated phthalocyanine (ClnPc) and tetra-nitro ((N02)4Pc) substituted ligands, catalysts with superior activity have been obtained [32], Such catalysts have been prepared via the zeolite synthesis method around the individual complexes. With the former more bulky complex only the slimmer hydroquinone (HQ) has been obtained, while with the encapsulated perchloroPc equal ratios of catechol (CAT) and the para-isomer have been obtained (see table). The unsubstituted Pc in zeolite Y both with Co and Cu as metallating ion, show an excess of the ortho-isomer (CA T) [32J, corresponding to the approximate thermodynamic ratio. This points to the critical importance of the available space close to the encapsulated Pc as selectivity determining parameter when there is more space, the catalyst yields more catechol. 

Iron phthalocyanine encapsulated in zeolites was used as oxygen activating catalysts in the triple catalytic aerobic oxidation of hydroquinone to benzoquinone, in the allylic oxidation of olefins and in the selective oxidation of terminal olefins to ketones. The catalyst proved active in the above reactions. It is stable towards self-oxidation and can be recovered and reused. 

Zeolites are well suited for the preparation of encapsulated complexes by virtue of the large supercages. Metallo-phthalocyanines encaged in zeolites have been proposed as enzyme mimics [7,8 Zeolite-encapsulated iron phthalocyanine catalysts have been used in hydrocarbon oxidations it was found that the resistance of the zeolite-encaged complexes against oxidative destruction by far exceeded that of free iron phthaTocyanines [9,10]. In the present work, zeolite-encaged phthalocyanine catalysts were studied in the triple catalytic oxidation of olefins. 

Iron phthalocyanine encaged in zeolite, Fe(Pc)/Z, was prepared by adding 5 g of air-dried NaY to 50 ml of a solution of 84 mg of ferrocene in acetone, followed by air-drying at 343 K [10]. The dried solid was mixed with 5 g of 1,2-dicyanobenzene and 15 ml of decalin, and was heated in an argon atmosphere. The solid material was soxhiet extracted with acetone, pyridine and again with acetone, until a colorless extract was obtained. Finally, the catalyst was dried at 343 K. 

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