Oxidation encapsulated complexes

There are a few examples of 02 oxidations catalyzed by zeolite-encapsulated complexes. Encapsulated CoPc was active in the oxidation of propene to aldehyde, whereas the free complex was inactive.76 A triple catalytic system, Pd(OAc)2, benzoquinone, and a metal macrocycle, was used to oxidize alk-enes with molecular oxygen at room temperature.77,78 Zeolite-encapsulated FePc79-81 and CoSalophen80,82 complexes were used as oxygen-activating catalysts. 

The encapsulated complex with bulky alkyl groups was more active than the complex without alkyl groups. The catalytic activity increases on the addition of axial ligands as pyridine N-oxide, and the highest enantiomeric excess, 88%, was also achieved in the presence of the pyridine N-oxide. 

MPa O2). The role of the encapsulated [Co(salophen)] complexes is to catalyze the aerobic oxidation of hydroquinone to p-benzoquinone, which in turn oxidizes Pd(0). For the oxidation of 1,3-cyclohexadiene to l,4-diacetoxy-2-cyclohexene, the most active catalyst system involved the encapsulated complex [Co(tetra-tert-butyl-salophen)], which afforded product yields of 85-95% after 3 h at room temperature with greater than 90% trans-selectivity. This complex displayed significantly higher activity than the encapsulated [Co(salophen)] complex (72% yield in 3h) and the analogous homogeneous complex (86% yield in 5h). The increased activity of the t-butyl substituted catalyst was attributed to distortion of the bulky complex by the... 

FePc, it is less active, but more stable, than a FePc/NaY material. These differences between the encapsulated complexes were attributed to the possibilities that reaction could occur only at the pore mouths of VPI-5, where oxidatively degraded FePc catalyst molecules were replenished by the layer beneath and that the tighter fit of FePc in the NaY supercage required a saddle-type distortion of the molecule, which, while making it more reactive, made the catalyst more prone to oxidation. 

IR and UV-vis spectroscopy show that the majority of the encapsulated complexes still have structural integrity. As observed for many other oxidation catalysts, entrapment shows significantly enhanced activity. This effect is more pronounced when the degree of ligand substitution with Cl is higher. The simultaneous occurrence of two mechanisms is confirmed again, the selectivity of the encapsulated Mn(salen) complexes for the formation styrene epoxide is only 30%, the dominant product being benzaldehyde. 

In addition to the cryptates, which are synthesized apart from metal ions and then used to form complexes, there are other types of multicyclic ligands called encapsulating ligands, which are synthesized around the metal ion and cannot release it. Complexes of this sort are sometimes called sepulchrates. Two of these are (1-XXIII) and (1-XXIV). An encapsulation complex allows studies to be carried out under extremely acidic or basic conditions since the metal ion, though it cannot be removed, can be oxidized or reduced. Such ligands also can enforce unusual coordination geometries in the examples shown the coordination is much closer to trigonal prismatic than to octahedral. 

It is fairly apparent that encapsulation of the RuFiePc complex in NaX dramatically alters the catalytic activity and selectivity, however, that in itself is not evidence for the intrazeolite location of the complex. Therefore, we examined the oxidation of the much larger cyclododecane using the same reaction conditions as for cyclohexane. We found the homogeneous RuFisPc catalyst had virtually no preference for either cycloalkane, showing approximately the same number of turnovers per day. In contrast, the RuFiePc-NaX catalyst exhibited relatively low activity ( 300 tumovers/day) for the larger cyclododecane. The acti dty of the zeolite encapsulated complex was nearly 10 times greater for the smaller cyclohexane. This shape selectivity is consistent with the active sites located inside the zeolite. 

We have prepared the Fe Pc/ zeolite catalyst and used in the aerobic oxidation of 1-octene and cyclohexene. Zeohte-encapsulated iron phthalocyanine proved to be an active and stable catalyst in the oxidation of hydroquinone and in the triple catdytic oxidation of 1-octene and cyclohexene. Product distribution, selectivity and yield were similar to those obtained with free iron phthalocyanine. No decrease in catalytic activity was observed during the catalytic reaction. The zeohte-encapsulated complex is easier to handle than the non-supported one, it can be removed from the reaction mixture by simple filtration and it can be reused in several subsequent catalytic runs with similar catalytic activity. 

The discovery, in the mid-eighties, of the remarkable activity of TS-1 as a catalyst for selective oxidations with aqueous H2O2 fostered the expectation that this is merely the progenitor of a whole family of redox molecular sieve catalysts with unique activities. However, the initial euphoria has slowly been tempered by the realization that framework substitution/attachment of redox metal ions in molecular sieves does not, in many cases, lead to a stable heterogeneous catalyst. Nevertheless, we expect that the considerable research effort in this area, and the related zeolite-encapsulated complexes, will lead to the development of synthetically usefril systems. In this context the development of chiral ship-in-a-bottle type catalysts for intrazeolitic asymmetric oxidation is an important goal. Such an achievement would certainly justify the appellation mineral enzyme . 

Figure 4 shows the pinane s concentration profiles when the reaction is carried out in the presence of free and encapsulated FePc and CoPc complexes. The encapsulated complexes lead to slower rates of oxidation compared to the corresponding free complexes. 

Figure 4 - Concentration profiles of pinane for oxidation reactions carried out with free and encapsulated complexes O - FePcNaY - FePc X - CoPcNaY V -CoPc.

The same encapsulated complex is a good epoxidation catalyst, showing no evidence for allylic oxidation. It follows that heterolytic rather than homolytic dissociation of the V-peroxo species constitutes the dominating mechanism. Whereas with hydrogen peroxide in acetone the catalyst yields high diol selectivity, giving cis/trans isomers at equilibrium, with fBuOOH in tBuOOtBu mainly epoxide is obtained. Thus the role of residual acidity in such systems seems crucial. 

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. 

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