Incorporation of transition metals

In the search to develop new materials for immobilization of homogeneous transition metal catalyst to facilitate catalyst-product separation and catalyst recychng, the study of dendrimers and hyperbranched polymers for application in catalysis has become a subject of intense research in the last five years [68], because they have excellent solubility and a high number of easily accessible active sites. Moreover, the pseudo-spherical structure with nanometer dimensions opens the possibility of separation and recycling by nanofiltration methods. Although dendrimers allow for controlled incorporation of transition metal catalysts in the core [69] as well as at the surface [70], a serious drawback of this approach is the tedious preparation of functionalized dendrimers by multi-step synthesis. 

The chlorination of alkyl aromatics by sulfuryl chloride promoted by free-radical initiators, which was originally discovered by Kharasch and Brown990, can be modified by incorporation of transition metal complexes. Matsumoto and coworkers have observed that, upon addition of Pd(PPh3)4, in place of a radical initiator, the side-chain monochlorination of toluene is substantially more selective991. Davis and his colleagues992 have extended this study and report that Pt(0) and Pd(0) are effective initiators for side-chain chlorination of toluene by sulfuryl chloride and dichlorine. Mn, Re, Mo and Fe complexes, on the other hand, behave more like Friedel-Crafts catalysts. Gas-phase chlorination of olefins to allyl chlorides is catalyzed by PdCl2 or by PtCl2993. 

Hosseini have devoted a lot of effort to aza crown complexes with ATP 48, showing them to be true yet weak ATPase mimics [24], Schmidtchen reported tetrahedral zwitterions 49 to discriminate between spherical anions [25]. Reetz was able to show that ditopic receptor 50, which includes both Lewis-acidic and basic centers will complex a whole ion pair [26]. Incorporation of transition metals into anion receptors such as 51 renders neutral species positively charged and susceptible to spectroscopic and electrochemical manipulations [27]. 

Incorporation of transition metals into the Zintl anions described above has been somewhat snccessful, althongh in many cases, the emphasis has been on the solntion chemistry of the metal chalcogenides. The heavier gronp 14/15 anion clnsters, snch as 809", Sb7, and Asu , have received mnch less attention bnt have proved to be eqnally interesting. More recently, there has been renewed interest... 

While the incorporation of transition metal oxides into complexes with materials such as alumina can lower their volatilities by factors from 10 (CuO) to 1000 (BaO) depending primarily upon the heat of reaction between the two oxides, it is also likely that formation of very stable complex metal oxides, such as aluminates, can also greatiy lower the chemical activity of the transition metal. As mentioned above, Mn, Ni, and Co may requite stabilization in complex oxides for long catalyst life, but the complex oxides generally have inferior activity. The most active transition metal oxides (Ru and Cu) may still have unacceptable volatility as relatively active complex oxides. As a consequence, there may be a technology-limiting trade-off between the catalytic activity of metals and metal oxides and their chemical and thermal stability in combustion environments. 

Since the incorporation of transition metals into the frameworks of zeolites or micro-porous ahiminophosphates to form heteroatom-containing molecular sieves with important application values, the synthesis, structure, and characterization of microporous transition metal phosphates have been extensively studied in the last decade. In particular, because transition metal cations possess redox and coordination features, they are a kind of catalytic material with useful applications, and promise potential... 

J. Evans, A.B. Zaki, M. El-Sheikh, and S.A. El-Safty, Incorporation of Transition-metal Complexes in Functionalized Mesoporous Silica and their Activity toward the Oxidation of Aromatic Amines. J. Phys. Chem., B, 2000, 104, 10271-10281. 

Metallosilicate mesoporous catalysts prepared by incorporation of transition metals in the MCM-41 molecular sieves and their catalytic activity in selective oxidation of aromatics (styrene and benzene)... 

The use of microporous solid catalysts such as zeolites and related molecular sieves has an additional benefit in organic synthesis. The highly precise organization and discrimination between molecules by molecular sieves endows them with shape-selective properties [12] reminiscent of enzyme catalysis. The scope of molecular sieve catalysis has been considerably extended by the discovery of ordered mesoporous materials of the M41S type by Mobil scientists [13,14]. Furthermore, the incorporation of transition metal ions and complexes into molecular sieves extends their catalytic scope to redox reactions and a variety of other transition metal-catalyzed processes [15,16]. 

Investigation of transition metal cations and their reactions fall in the realm of ESR spectroscopy. Such studies benefit by the high sensitivity of that spectroscopic technique. Moreover, ESR spectroscopy of cations in zeolites provides in many cases deeper insight into their coordination state. Thus, Clearfield et al. [4] were also the first to successfully apply ESR spectroscopy to prove the incorporation of transition metal cations into a zeolite structure by solid-solid interaction. In Figure 10, ESR spectra of Cu,Na-Y... 

The incorporation of transition-metal atoms into post-transition clusters may be a relatively new area of research, but the opposite process i.e. the incorporation of... 

Highly ordered tnesoporous silicas synthesis using deca-(oxyethylene) oleylether as surfactant variation of the weight percentage of surfactant and incorporation of transition metal cations... 

PPy films containing transition-metal complexes should find applications in areas similar to those in which conventional PPy films are used [1]. In addition, the films discussed in this chapter may possess unique biosensing/chemical sensing properties. This area of research is being actively pursued at Monash University [101]. A different approach for the incorporation of transition-metal complexes into PPy, that has already received some attention [25,35], involves using chemically modified pyrrole monomers. This method should enable a wider range of transition-metal complexes to be incorporated into PPy than has been possible previously. 

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