Surface organometallic complexes

The participation of siloxane groups in the reaction increases with the temperature of dehydration of Si02 and quantity of organometallic compound introduced in the reaction. According to the data of infrared spectroscopy (139), the allyl ligands formed in the surface organometallic complexes of Ni and Cr keep the 7r-allyl character of the metal-ligand bond. 

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). 

Reaction of Organometallic Complexes with Oxide Supports the Controlled Formation of Surface Organometallic Complexes... 

The formation of a stable monobutyl species obtained at 50 °C is also further demonstrated by its hydrogenolysis at higher temperatures. Indeed, treatment under H2 of the grafted surface organometallic complex, Pts[SnBu]jy, at 300 °C for 4 h generates about one butane per Sn along with traces amounts of propane, ethane, and methane. 

Alumina is known to have more ionic character and its surface has a more complex structure than that of silica. Reaction of Bu3SnH with the surface of partially dehydroxylated aluminas was followed and it was found that the extreme sensitivity of tin chemical shifts to the molecular environment constitutes a method whereby surface organometallic complexes of tin can be used as molecular probes for determining surface structures of oxides.248... 

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... 

According to experimental evidence, the allyl ligands may be eliminated from the surface as either 1,5-hexadiene (by reductive elimination of two allyl ligands) or propene. Two tris(trimethylophosphine) complexes of rhodium are formed, only one of which retains the allyl ligand. This is in fact the 7i-o-allyl isomerization in a well-defined surface organometallic complex. 

The most commonly used grafting reaction in surface organometallic chemistry is the reaction of a surface silanol with an alkylmetal complex ([5-13] cf. Structures 1-12) which has led to the synthesis of a wide variety of surface organometallic complexes. In some cases the catalytic activity of these surface species can be studied directly [7,10,13] while in others the initially obtained species is converted to the desired catalytically active species by clean, quantitative reactions. 

Grafting, transformation, and application of a surface organometallic complex (Zr hydrides) will be described in detail, then summarized and augmented by some other applications of oxide-supported organometallic species in catalysis. 

New types of tin anchoring sites were created when both PSCs and CUPSCs were mildly oxidized to Oxidized Surface Organometallic Complex (OSOC), with general formula of -SUaRbOc. The addition of trace of oxygen led to the immediate formation of ethylene, i.e. surface chemistry involved in tin anchoring was altered. In this case as shown in Scheme 2 the lone pair of electrons of the... 

The decomposition of surface organometallic complexes formed in tin anchoring steps (see reactions (3) - (9)) was accomplished as a gas-solid reaction in the temperature range between 25-300 °C. The decomposition in a hydrogen atmosphere led to the formation of alloy-type bimetallic surface entities. More details on the decomposition of different surface organometallic complexes can be found elsewhere. These Sn-Pt catalysts will be referred as (H) type catalysts. 

However, the decomposition of surface organometallic complexes can also be... 

Y. I. Yermakov and B. N. Kuznetzov, Supported Metallic Catalysts Prepared by Decomposition of Surface Organometallic Complexes, J. Mol. Catal., 9, pp. 13-40, 1980. 

The grafting of Zr(Np)4 was not only restricted to silica surface but also to other well-defined oxide surfaces. Recently, amino-modified SBA-15 surfaces were prepared by the reaction of partially dehydroxylated SBA-15 at 1100°C with ammonia at 200 and 500°C to generate [(=Si-NH2)(=Si-OH)] (5) and [(=Si-NH2)2] (6). The advantage of this method is the preparation of adjacent groups in close vicinity. The surface organometallic complexes were prepared by the reaction of [Zr(Np)4] with [(=Si-NH2)(=SiOH)] and [(=Si-NH2)2l in pentane for 8 h at room temperature (Scheme 4) [20]. 

In conclusion, all the surface organometallic complexes synthesized and characterized so far are extremely electron deficient and between eight electrons to 12 electrons in the Green formalism [50]. The resulting complexes either alkyls... 

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. ... 

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