FePc complexes

The FePcY-PDMS supramolecular catalyst resembles the architecture of natural enzymes. In this system the PDMS membrane takes over the role of the phospholipid double layer likewise, the zeolite imitates the protein and the FePc complex the Fe-protoporphyrin. Zeolite-encaged Cu-histidine complexes were also studied as mimics of natural Cu-enzyme complexes.173... 

The water-soluble iron tetrasulfophthalocyanine (FePcS) complex, which is cheap and available on an industrial scale, was also a very active and selective catalyst for the oxidation reaction. Starches of different origin (potatoes, rice, wheat, com) were oxidized by H202 following two operating modes, viz. oxidation in aqueous suspension and oxidation by incipient wetness. 

At this stage of the work, two possible explanations can be advanced to rationalize the higher activity of FePcY and the superior stability of FePcVPI-5. As a result of the tubular nature of the pores of VPI-5 and eventual diffusion limitations of the reaction, only the FePc complexes at the external rim of the crystals are active initially but are gradually consumed during reaction. Consequently, FePc complexes located more towards the centre of the crystals become active. Secondly, it can be speculated that the saddle-conformation of FePc in NaY changes the electronic environment of the active iron, thus increasing not only its catalytic activity but also its vulnerability towards self-oxidation. 

A FePc complex encaged in the zeolite Y supercages, in its turn, can be wrapped in a polydimethylsiloxane membrane, thus acting not only as a mechanistic but also as a formal mimic of Cytochrome P450 often found in cell membranes.[57] Such membranes, contacted on one side with substrate and on the other side with oxidant, catalyse oxygenation reactions in a membrane reactor in the absence of any solvent, the majority of the product amount being recovered from the more polar phase. 

The expected structural transformation of VPI-5 into the more stable AIPO4-8 structure upon dehydration no longer occurred, while the porosity disappeared almost completely. This was attributed to presence of stacks of FePc complexes, filling the pores. No such effects were found upon adsorption of pre-synthesized complex into the VPI-5 voids. Indeed, application of the washing procedures that remove FePc from the external surface of zeolite crystals1591 do not result in any extraction of FePc from VPI-5. 

At the same time, one has to consider that the FePc complex is only a finely dispersed powder in the reaction mixture and the reaction most likely occurs via heterogeneous catalysis. It means that it is also possible that not the zeolite encapsulated catalyst has increased specific catalytic activity but the poor solubility of the free complex decreases its efficiency in homogeneous circumstances. 

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... 

The complex iron(ll) phthalocyanine, [FePc], supported onto activated CBs [55a] by the impregnation method, was used as a heterogeneous catalyst in the oxidation of alkanes, with TBHP as an oxygen source. Carbon black proved to be an appropriate support for [FePc] complex within the framework of the oxidation of alkanes. The hydrophobicity of the support surface induced the alkane adsorption, leading to a more ideal substrate/oxidant ratio near the active center, which explained the high activity and efficiency reached with the immobilized [FePc],... 

Romanovsky et al (19-22,32) have used this method extensively. The decomposition of Fe(C0)5 is critical according to the work of Bein et al. (33). There exist specific conditions in which it is possible to decompose adsorbed ironpentacarbonyl quantitatively into occluded iron metal particles. The major disadvantage of this method is the easy formation of extra-zeolitic iron clusters. Moreover, it is impossible to isolate a single Fe atom per supercage and consequently to transform Fe in a quantitative way into isolated and zeolite occluded FePc complexes. 

Ichikawa et al (36,45) from the temperature dependence of the recoil-free" fraction in Mossbauer spectroscopy were able to extract evidence about the uniform distribution of FePc complexes in zeolite Y. 

Fig. 4. Molecular graphics representation of a FePc complex into the supercage of zeolite Y (after ref. 23).

Mossbauer spectra of FePc on carbon supports after thermal treatment and have concluded that high activity is exhibited only by those FePc complexes in which the iron is directly bonded to the carbon substrate through an Fe-C bond. It is not completely clear, however, what spin state to expect for such Fe species. Melendres " has also compared the Mossbauer and Raman spectra of carbon-supported FePc and the pure complex and finds evidence of catalyst-support interactions with the former. 

Although X-Fe(ni)Pcs complexes were generally synthesized and characterized for the potential functional materials, there are a few examples for Fe(II)Pcs complexes. It was reported that synthesis of Fe(II)Pcs complexes was very difficult and these complexes were unstable, thus they preferred in less extent [55, 65-71]. Even though a FePc complex has Fe(III) or Fe(ll) oxidation states, they illustrated similar electrochemical and in situ SEC responses. They generally gave a metal-based... 

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