Ship-in-the-bottle synthesis

The capture of metal complexes is achieved in the synthesis of clusters within the porous network of zeolites, where the reactants are small enough to enter the large cavities, but the clusters formed are too large to escape ( ship- in-the-bottle synthesis). The cages limit the size of the cluster compounds that can be formed and the entrance to the porous channels prevents the departure from the cages. Other methods of encapsulating metal complexes utilize polymerization or polycondensation reactions such as the sol-gel process. The metal complex is dissolved in the medium to be polymerized and is therefore trapped in the matrix formed [93] (cf. Section 3.2.2). The limitations clearly arise from the porosity of the polymer formed. A pore structure with pores that are too wide cannot prevent the leaching of the complex, whereas a pore diameter that is too small results in mass-transfer limitations. 

Examples of building up large molecules inside a zeolite structure via a reaction were frequently reported under the term ship-in-the-bottle synthesis . For instance, very early Romanowski et al. [844] and, somewhat later, Schulz-Ekloff et al. [845] produced phthalocyanines in faujasite-type zeolites and investigated the pro ducts, inter alia, by IR spectroscopy. Cobalt-phthalocyanine encapsulated in zeolite EMT was prepared and, inter alia, characterized via IR spectroscopy by Ernst et al. (cf. [846] and references to related work therein). A number of typical bands of CoPc-EMT in the mid infrared (1600-1200 cm ) were observed and interpreted. 

Different synthetic approaches have been described for the formation of zeolite inclusion compounds, including direct adsorption, impregnation, ion-exchange from solutions or solid-state ion-exchange, ship-in-the-bottle synthesis, formation of large molecules (e.g., by polymerization reactions), and zeolite synthesis around the metal complex. Some examples of these approaches are given in the next sections. 

The synthetic route followed in the encapsulation of [Ru(bpy)3] + in ZeoliteY is referred as ship-in-a-bottle synthesis due to non-extractability of the [Ru(bpy)3] complex, once encapsulation has taken place within the cages of the zeolite Y. Nanoparticles of TiO was then introduced through TiClj in ethylene glycol mixture under argon, with sintering at 200°C. A schematic diagram of the synthesis is shown in Fig. 16.1 [1]. 

Ship-in-a-bottle" synthesis of netal complexes inside zeolite cages has gained growing attention for the purpose of obtaining the catalytically active precursors surrounded with configurationally constrained circumstances [3]. 

A promising unprecedented application of the chiral enecarbamates Ic in asymmetric synthesis is based on the ship-in-the-bottle strategy, which entails the oxidation of these substrates in zeolite supercages . In this novel concept, presumably dioxetanes intervene as intermediates, as illustrated for the oxidation of the chiral enecarbamate Ic in the NaY zeolite (Scheme 6). By starting with a 50 50 mixture of the diastereomeric enecarbamates (45, 3 R)-lc and (45, 3 5 )-lc, absorbed by the NaY zeolite, its oxidation furnishes the enantiomerically enriched (ee ca 50%) S -methyldesoxybenzoin, whereas the (4R,3 R)-lc and (4R,3 S)-lc diastereomeric mixture affords preferentially (ee ca 47%) the R enantiomer however, racemic methylbenzoin is obtained when the chirality center at the C-4 position in the oxazolidinone is removed. Evidently, appreciable asymmetric induction is mediated by the optically active oxazolidinone auxiliary. 

Semen, reactive oxygen species, 612 Sensorial quaUty appreciation, oxidation stabihty, 664 Semm protein oxidative damage, 614 see also Human seram Sesquiterpenes, stractural chemistry, 133-6 SET see Single electron transfer Sharpless epoxidation, allylic alcohols, 789 Shelf durability, peroxide value, 656 Ship-in-the-bottle strategy, chiral dioxetane synthesis, 1176-7... 

Fig. 15. Ship-in-a-bottle synthesis of the trityl cation 16 from 13CCU and benzene inside the HY supercage. (Reprinted with permission from Tao and Maciel (118). Copyright 1996 American Chemical Society.)...

The formation of these dinuclear complexes can be impeded by entrapment of the Mn(BPY)22+ complexes in the structure of zeolite Y. Preferably, Mn(BPY)2+ is assembled via ship-in-a-bottle synthesis in zeohte Y, through BPY adsorption on a NaY zeolite partially exchanged with Mn2+. Because a single zeolite Y supercage can contain only one Mn(BPY)2+ complex, the formation of dinuclear complexes is impossible for steric reasons. The reaction of H2C>2 with the zeolite-entrapped Mn(BPY)2+ complex does not lead to the same vigorous peroxide decomposition as occurs in solution. Instead, H2O2 is heterolytically activated on the Mn complex with civ-bipyridine ligands to form a Mn(IV)=0 or Mn(V)=0 species. The latter is a... 

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 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). 

Each zeolite type can be easily obtained over a wide range of compositions directly by synthesis and/or after various post synthesis treatments. Moreover, various compounds can be introduced or even synthesized within the zeolite pores (ship in a bottle synthesis). This explains why zeolites can be used as acid, base, acid-base, redox and bifunctional catalysts, most of the applications being however in acid and in bifunctional catalysis. 

Ship-in-a-bottle synthesis of organometallic clusters (usually within porous hosts) followed by denuding of the organic ligands [2],... 

Figure 6. Synthesis of adipic acid over ship-in-the-bottle catalysts (t.-BHP tertiary-butylhydroperoxide).

From the seminal work of Lunsford et al. in the early 1980s (DeWilde et al., 1980 Quayle and Lunsford, 1982), ship-in-a-bottle synthesis of metal complexes in the zeolite supercages, encapsulation of catalytically, optically, and/or electrochemically active species within micro- and mesoporous aluminosilicates, has received considerable attention (Alvaro et al., 2003). Site isolation of individual guest molecules, combined with shape and size restrictions imposed by the supercage steric limitations. 

Domenech, A., Ferrer, B., Fomes, V., Garcia, H., and Leyva, A. 2005b. Ship-in-a-bottle synthesis of triphenylamine inside faujasite supercages and generation of the triphenylam-minium radical ion. Tetrahedron 61, 791-796. 

Transition metal complexes of phthalocyanine encaged in faujasite type zeolites have been reported as efficient catalysts in the oxidation of alkanes at room temperature and atmospheric pressure [6-13]. These catalysts constitute potential inorganic mimics of remarkable enzymes such as monooxygenase cytochrome P-450 which displays the ultimate in substrate selectivity. In these enzymes the active site is the metal ion and the protein orientates the incoming substrate relative to the active metal center. Zeolites can be used as host lattices of metal complexes [14, 15]. The cavities of the aluminosilicate framework can replace the protein terciary structure of natural enzymes, thus sieving and orientating the substrate in its approach to the active site. Such catalysts are constructed by the so-called ship in a bottle synthesis the metal phthalocyanine complexes are synthesized in situ within the supercages of the zeolite... 

Mukai and co-workers [105] used Keggin-type heteropolyacids immobilized in the network structure of resorcinol-formaldehyde carbon gels as catalysts for the synthesis of methyl tert-butyl ether from methyl alcohol and tert-butyl alcohol. Large amounts of 12-tungstophosphoric and 12-molybdophosphoric acids were immobilized into the support by two methods, pore shrinkage and the ship-in-the-bottle method, which are essentially impregnation methods. The authors reported that these catalysts showed activity in the reaction studied and could be of practical utility as solid acid catalysts in various reactions. 

During the last decade a variety of mctluxloiogies have been developed to immobili/e molecular homogeneous catalysts on the surface of heterogeneous organic as well as inorganic polymeric materials (a) adsorption of the catalyst into the pores of the support, (b) encapsulation of the catalyst within the confines of cavities of the support, the Sii-callcd ship in the bottle technique", (c) attachment of the catalyst to the support by covalent bond formation and (d) direct synthesis into the final composite material [7. ... 

Figure 2. Some examples of micro- and mesoporous materials as the template micro reactors for ship-in-a-bottle synthesis of metal clusters in micropores and mesoporous channels.

Figure 3. Pictorial illustration of ship-in-a-bottle synthesis of metal clusters, Rh6(CO)i6 assembled in NaY cages by the suecessive carbonylation of Rh ions using CO + H2O or CO + H2 as building blocks, which are introduced by the ion-exchange methods and gas admission.

Furthermore, Ichikawa et. al. recently extended the ship-in-a-bottle synthesis for some other metal elusters such as Ru3(CO)i2/NaY, H4Ru4(CO)i2/NaY,f ... 

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