Immobilized metal complexes

In comparison with traditional biphasic catalysis using water, fluorous phases, or polar organic solvents, transition metal catalysis in ionic liquids represents a new and advanced way to combine the specific advantages of homogeneous and heterogeneous catalysis. In many applications, the use of a defined transition metal complex immobilized on a ionic liquid support has already shown its unique potential. Many more successful examples - mainly in fine chemical synthesis - can be expected in the future as our loiowledge of ionic liquids and their interactions with transition metal complexes increases. 

Conductive polymers are useful semiconductors or coating materials to construct solar cells. A new photodiode is proposed to be made from a film of a polymer metal complex. Immobilized catalysts on polymers are used for solar energy storage systems. 

Metal complexes immobilized on crosslinked polymer matrices are hard to characterize by the customary physicochemical techniques, which is why no quantitative studies have been made on the catalytic activity of polymer complexes. 

Insoluble polymer supports, for metal complex immobilization, 12, 665 Instrumentation specifications... 

Macropolyhedral thiaboranes, preparation, 3, 127 Macroporous polystyrene resins, for metal complex immobilization, 12, 665-666 Macroscale combustion calorimetry, limitations, 1, 611-612... 

The immobilization of metal complex catalysts on polymers and inorganic oxides has received considerable attention as a means of combining the best advantages of homogeneous and hetereo-geneous catalysis (1-6). The swelling layer lattice silicates known as smectite clay minerals have added an important new dimension to metal complex Immobilization. These compounds have mica-type structures in which two-dimensional silicate sheets are separated by monolayers of alkali metal or alkaline earth cations (7). The structure of a typical smectite, hectorite, is illustrated in Figure 1. 

Preparation of physically heterogeneous and chemically homogeneous catalysts on the base of metal complexes immobilized in polymer gels... 

Numerous studies have appeared in the literature in which transition metal complexes. Immobilized on functionalized-polymers, or in which sulfonated resins have been used as catalysts. Polystyrene is the most common polymer support and has been used in the gel-form and macroretlcular forms. Review articles on "immobilized catalysts" have presented the advantages and disadvantages of Immobilizing the catalytic site O- ). The primary motivation is to "hetrogenize" a homogenous catalyst and thereby avoid costly separations of the catalyst from the reaction mixture and, in the case of acids, to minimize contact of the corrosive catalyst with the reactor vessel. 

It should be mentioned that simple metal complexes immobilized on polymer supports were initially used for polymerization (1965/1966) in the Solvay catalysts based on titanium complexes bound to macromolecular ligands with C=0, C=N and C=N groups. Until now the data are mainly available in patent literature, and there are few kinetic studies of polymerization processes involving the action of macromolecular complexes. At the same time the use of metal complexes bound to inorganic supports has been extensively developed in polymerization catalysis. This indicates that there has been inadequate study of the application of metal complexes immobilized on polymer supports to the catalysis of polymerization and copolymerization of different monomers, mainly olefins. 

For many years now, researchers have been interested in using solid-state NMR to investigate atoms and molecules immobilized on surfaces.For example, Fyfe and co-workers demonstrated the feasibility of solid-state P CP/MAS NMR in investigating transition metal complexes immobilized on solid supports. In 1994, Reven... 

Asymmetric Hydrogenations over Chiral Metal Complexes Immobilized in SILCAs I 257... 

Metal complexes immobilized either in or on dendritic systems have the unique advantage of being soluble under the reaction conditions. However, they can be easily precipitated when the polarity of the solvent is changed. Astruc... 

Phosphine ligands and their transition-metal complexes immobilized on inorganic or organic supports have also been the subject of MAS studies. " ... 

Ogura K, Nakayama M, Kusumoto C (1996) In situ Fourier transform inlrared spectroscopic studies on a metal complex-immobilized polyaniline Pmssian blue modified electrode and the application to the electrorednction of CO2. J Electrochem Soc 143(11) 3606-3615... 

As described above, mesoporous materials can be used as supports for metals, oxides, acids, and bases. However, perhaps the most intriguing and exciting application is in catalysis involving large active molecules such as organometallics and transition metal complexes immobilized within the pores, as illustrated in Fig. 12. The large surface areas of mesoporous materials makes the materials very attractive as supports for such active phases. 

In what follows, the use of the PHIP technique in the studies of homogeneous catalytic processes such as hydrogenation and activation of Hj by transition metal complexes and clusters is briefly reviewed first to demonstrate the potential information content of such studies. Then, applications of PHIP to the studies of heterogeneous hydrogenations catalyzed by metal complexes immobilized on solid supports and by supported metal catalysts are discussed. 

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