Ship-in-a-bottle complexes

Schuster, C. and Holderich, W. F. Modification of faujasites to generate novel hosts for ship-in-a-bottle complexes, Catal. Today, 2000, 60, 193-207. 

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... 

Selective Oxidation of Benzyl Alcohol on a Zeolite Ship-in-a-bottle Complex... 

In yet another approach metal complexes are encapsulated in zeolite cages to give so-called ship-in-a-bottle complexes [35] or, alternatively, in polydimethyl-siloxane membranes [36]. 

Zeolites were used as well-defined hosts with well-defined nanospaces that can be filled or used as reactors long before nanotechnology achieved its current popularity. Ship-in-a-bottle complexes, laser dyes and chromophore species, nanoparticulate oxides and sulfides and conducting wires and polymers have all been assembled in regular arrays within the pores. At present, cata-lytically active nanoparticles of supported metals remain the most widely applied of such composites. 

In ZEOlite based enZYME mimics (ZEOZYMES), the function of the protein mantle is replaced by the inorganic framework, which imposes geometric and steric constraints on the reaction of substrate molecules. Strictly speaking, ZEOZYMES are only mimics of enzymes with rigid protein mantle. Such materials are often denoted as ship-in-a-bottle" complexes (1). However, this notation is too limitative as it only refers to complexes physically encaged in bottle-type zeolite pores and does not take into account any physical and chemical interaction of the pore or cage wall with the complex. 

For example, MPc complexes are synthesized in the zeolite framework by subjecting the zeolite to metal ion exchange and then treating it with molten dicyanobenzene. These "ship-in-a-bottle complexes cannot leave the zeolite without destroying the framework. Such zeolite catalysts, whose super-cages serve as a sort of reaction flask with molecular dimensions, continue to possess shape selectivity, reactant selectivity, regioselectivity and stereoselectivity. 

Balkus KJ, Khanmamedova AK, Dixon KM, Bedioui F. Oxidations catalyzed by zeolite ship-in-a-bottle complexes. Appl Catal A 1996 143 159-73. 

The application of zeolite encapsulated metal chelate complexes in catalysis is a promising area of research. In particular shape selective oxidations catalyzed by metallophthalocyanines (MPc), shown in Figure 1, included in synthetic faujasite (FAU) type zeolites (2-10) appear to be competitive with other molecular sieve based catalysts that may have commercial potential. The restricted apertures ( 7.4 A) to the supercages (12A) in FAU type zeolites precludes removal of the large MPc complex unless the zeolite lattice is destroyed. Such physically trapped complexes have been termed ship-in-a-bottle complexes as well as zeozymes (to reflect the biomimetic reactivity that is often associated with these catalysts). 

Zeolites have ordered micropores smaller than 2nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique (Figure 1) [1,2], and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16 [3,4], MCM-41 [5], and SBA-15 [6] have been used as catalyst supports, because they have large pores (2-10 nm) and high surface area (500-1000 m g ) [7,8]. The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications [9]. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noble-metal nanoclusters in mesoporous silicas. 

Another way of immobilizing catalyst complexes might be to trap them in the pores of solid particles, for instance by synthesizing the complex inside the pores of a zeolite ( ship in a bottle ). Another method could be to trap catalyst complexes in porous materials and deposit a membrane at the outer. surface. These methods of immobilizing a homogeneous catalyst do not involve chemical linkage between the catalyst and the carrier. The fixation is the result of steric hindrance. 

Figure 2 Ship in a bottle synthesis of encapsulated salen complexes.

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]. 

When entrapment methods are being used for heterogenization, the size of the metal complex is more important than the specific adsorptive interaction. There are two different preparation strategies. The first is based on building up catalysts in well-defined cages of porous supports. This approach is also called the ship in a bottle method [29]. The other approach is to build up a polymer network around a preformed catalyst. 

In Fig. 2.1.6.6, the FTIR spectra of the Jacobsen ligand (a), the Jacobsen catalyst (bj, and the immobilized manganese salen complex in the cages of dealuminated faujasite zeolite (c) are compared. While spectra a and b have been measured using the standard KBr technique, the spectrum c of the ship in a bottle catalyst has been recorded using a self-supported wafer. The bands at wavenumbers 1466 cm, 1434 cm" , 1399 cm" and 1365 cm" in spectrum c can be assigned to the... 

The second example demonstrated immobilization via ship in a bottle , ionic, metal center, and covalent bonding approaches of the metal-salen complexes. Zeolites X and Y were highly dealuminated by a succession of different dealumi-nation methods, generating mesopores completely surrounded by micropores. This method made it possible to form cavities suitable to accommodate bulky metal complexes. The catalytic activity of transition metal complexes entrapped in these new materials (e.g, Mn-S, V-S, Co-S, Co-Sl) was investigated in stereoselective epoxidation of (-)-a-pinene using 02/pivalic aldehyde as the oxidant. The results obtained with the entrapped organometallic complex were comparable with those of the homogeneous complex. 

Another option is encapsulating the homogeneous complex in an (inorganic) cage, creating a ship-in-a-bottle hybrid catalyst. Zeolites are often used for trapping large... 

Zsigmond, A., Bogar, K. and Notheisz, F. (2003) Comparative study of ship-in-a-bottle and anchored heterogenized Rh complexes./. Catal., 213, 103. 

In microporous supports or zeolites, catalyst immobilization is possible by steric inclusion or entrapment of the active transition metal complex. As catalyst retention requires the encapsulation of a relatively large complex into cages only accessible through windows of molecular dimensions, the term ship-in-a-bottle has been coined for this methodology. Intrinsically, the size of the window not only determines the retention of the complex, but also limits the substrate size that can be used. The sensitivity to diffusion limitations of zeolite-based catalysis remains unchanged with the ship-in-a-bottle approach. In many cases, complex deformation upon heterogenization may occur. 

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). 

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