Surface organometallic fragment

The surface species produced by this reaction are real surface organometallic fragments (15 in Fig. 7.13). 

Scheme 1.3 Initial description of a surface organometallic fragment.

Scheme 1.8 Selected examples of thermally stable surface organometallic fragments [43].

Heterogeneous catalysis is primarily a molecular phenomenon since chemical bonds are created and/or broken (between the molecule and the surface) this implies that surface organometallic fragments are intermediates in any catalytic reaction on a surface. If one can design and synthesize surface organometallic fragments and study their reachvity, especially elementary steps, then one possesses in principle a crihcal tool to better understand the mechanisms of heterogeneous catalysis. 

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. 

Figure 2.14 Schematic representation of the various stages of the grafting of a surface organo-tin complex on a platinum particle (as demonstrated by EXAFS, NMR, chemical analysis, IR). From left to right starting platinum particle with the surface organometallic fragment [(Pts)3(Tl -snBu]i adatoms of Sn, [(Pt4(ri -Sn]) surface PtSn alloy [sphere color-code orange (Pt), blue (H), white (C), green (Sn)].

Figure 1. Representation of a surface organometallic fragment on an oxide (left) and on a metal particle.

Scheme 55 Structures of surface organometallic fragments resulting from the reaction of [Rh(allyl)3] and various oxide supports (silica, alumina, and titania).

At low temperature, there is less than 1.5 Ce evolved by reacted AsPhs on the NiD18 sample and the coverage of the metallic surface does not exceed 1 (table 3). We can conclude that there is formation of grafted surface organometallic fragments which can be formulated as Nis(AsPhx)y. 

A material in which a surface organometallic fragment is linked to the metaUic nanoparticle via covalenf bonds. 

Fig. 18.6 EXAFS data (at the Sn K-edge) used for the determination of the distances between Sn and its surface neighbors and the coordination number of Sn in the surface organometallic fragment (Pts)3(ri -SnBu) .

Fig. 18.25 Various pathways for the hydrogenation of citral (top) application to the hydrogenation of citral with Rh covered with various amounts of tin (left) for Sn/Rh 0.3, only adatoms are present (right) for Sn/Rh 0.8, Rhs [=Sn(n-Bus)] surface organometallic fragment is present.

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