Catalyst surface organometallic

The application of these catalysts in the initial state (without any special treatment of the surface organometallic complexes of such cata-lysts) for ethylene polymerization has been described above. The catalysts formed by the reaction of 7r-allyl compounds with Si02 and AUOj were found to be active in the polymerization of butadiene as well (8, 142). The stereospecificity of the supported catalyst differed from that of the initial ir-allyl compounds. n-Allyl complexes of Mo and W supported on silica were found to be active in olefin disproportionation (142a). 

Some data have been obtained on the activity of the catalyst in a reduced state [for nickel (141,143,144), palladium (144°), and molybdenum (145, 145a). In the case of nickel catalysts the formation of nickel in the zero oxidation state takes place during the reduction of the surface organometallic compound by H2. The infrared spectrum shows the total restoration of the concentration of Si—OH groups (139), so the reduction proceeds according to the scheme ... 

To rationally govern the selectivity of a catalytic process, the elementary reaction steps on real catalyst surfaces must be identified. The use of well-defined organometallic compounds (possible intermediates in surface reactions) can be very useful in the determination of these steps. The use of kinetic modelling techniques combined with statistical analysis of kinetic... 

Metalloporphyrinosilicas as a new class of hybrid organic-inorganic materials were prepared by polymerization of 3- er -butyl-5-vinylsalicylaldehyde with styrene and divinylbenzene and used as selective biomimetic oxidation catalyst.27 Synthesis and structural characterization of rare-earth bisfdimethyl-silyl)amides and their surface organometallic chemistry on mesoporous silicate MCM-41 have been reported.28... 

The reaction of organometallics with metal surfaces is a very promising aspect of surface organometallic chemistry related to fine chemicals. The precise understanding of the reactions between organometallics and metal surfaces is essential to obtain highly selective catalysts by this route.292,293... 

Surface Organometallic Chemistry as a Tool for Tailor-Made Catalysts... 

A bimetallic catalyst can be obtained by the reaction of tetrabutyltin with Rh/Si02 catalyst. The partial hydrogenolysis leads to the Rhs[Sn(n-C4H9)2]/ Si02 surface organometallic complexes, which proved to be fully selective in the hydrogenation of unsaturated aldehydes into the corresponding unsaturated alcohols.318... 

Heterogeneous Catalysts Prepared via Surface Organometallic Chemistry... 

J. R Candy, B. Didillon, E. L. Smith, T. M. Shay, and J. M. Basset, Surface organometallic chemistry on metals A novel and effective route to custom-designed bimetallic catalysts, J. Mol. Catal. 86, 179-204 (1994). 

This is a major achievement, mainly due to Basset and his group, in surface organometallic chemistry because it has been thus possible to prepare single site catalysts for various known or new catalytic reactions [53] such as metathesis of olefins [54], polymerization of olefins [55], alkane metathesis [56], coupHng of methane to ethane and hydrogen [57], cleavage of alkanes by methane [58], hydrogenolysis of polyolefins [59] and alkanes [60], direct transformation of ethylene into propylene [61], etc. These topics are considered in detail in subsequent chapters. 

Preparation of Single Site Catalysts on Oxides and Metals Prepared via Surface Organometallic Chemistry... 

If by chance one discovers that the rules of molecular chemistry apply to these surface organometallic fragments then it must be possible to transpose the concepts of modern molecular chemistry to design heterogeneous catalysts and especially the single sites that are necessary to get higher activities, better selec-tivities and higher life times, and eventually to discover new catalytic reactions. 

---