Supported immobilizing organometallic complexe

A third approach (Figure 6.14.9c) uses organometaDic catalysts in sohd modifications, for example, covalently bonded (see above) or immobilized in supported liquid form (see below). Here the reaction remains a sohd/supercritical fluid biphasic system during reaction and again the SCCO2 is used as the mobile phase to contact the reactant intimately with the immobilized organometallic complex. 

Figure 2.27 Concept of immobilizing organometallic complexes in supported films of IL, and transmission electron micrograph of the catalyst EMIm/Pd.

The above example outlines a general problem in immobilized molecular catalysts - multiple types of sites are often produced. To this end, we are developing techniques to prepare well-defined immobilized organometallic catalysts on silica supports with isolated catalytic sites (7). Our new strategy is demonstrated by creation of isolated titanium complexes on a mesoporous silica support. These new materials are characterized in detail and their catalytic properties in test reactions (polymerization of ethylene) indicate improved catalytic performance over supported catalysts prepared via conventional means (8). The generality of this catalyst design approach is discussed and additional immobilized metal complex catalysts are considered. 

The method of catalyst immobilization is one for the reasons for the success of the SAPC approach. Rather than covalently linking an organometallic complex to a support—which usually leads to loss of catalytic efficiency and leaching of the metal—it is the catalyst-philic phase that is immobilized. 

A new immobilization method designed specifically to convert liquid-phase reactants has been developed [7, 8], The catalytic materials consist of a thin film that resides on a high-surface-area support, such as controlled-pore glass or silica, and is composed of a hydrophilic liquid and a hydrophilic organometallic complex (see Figure 1). 

The most used polymer support (resin) both for organic synthesis and for immobilization of catalysts is cross-linked polystyrene. Numerous types of polystyrene resin are commercially available and can be obtained in different sizes, loading capacities (level of functionalization), and degrees of cross-linking. This makes immobilization of organometallic complexes a reasonably simple operation since the metal complex bearing a suitably functionalized ligand can be attached directly to a commercially available polymer backbone or, if necessary, built up on the support. 

An immobilized catalyst concept has been described in a recent patent application (25). The catalyst, used for the dehydrogenation of organic compounds, comprises an organometallic pincer complex bonded to a TUD-1 support. The pincer complex possesses catalytic activity for alkyl group dehydrogenation. This catalyst can be used for various refining and petrochemical processes, such as paraffin dehydrogenation. 

Several rhodium-allyl complexes were immobilized on to solid supports. For example, the reaction of Rh( j -03115)3 with the surface hydroxyl groups of partially dehydroxylated silica led to the formation of the surface organometallic complex (=SiO)(=SiOX)Rh(77 -C3Hs)2 (where X is H or Si=), with the evolution of propene. ... 

It is interesting to explore the structure when an organometallic complex is involved in the supported IL thin film. Catalyst models were prepared by immobilization of [Pd(DPPF)-(CF3C02)2] (DPPF, l,l -bis(diphenylphosphino)ferrocene) and CF3SO3H in imidazolium salts [(MeRR lmljfCFjSOj] supported on silica (R=H, Me R = Et, Bu, and hexyl) [62]. For comparison, a series of reference... 

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