Organometallic complexes bimetallic complex

An example of particular interest is the two-fold introduction of M(CO)n moieties at silicon to give HMPA adducts of organometallic analogues of silaallene. It has been shown that this reaction proceeds through the dichlorosilylene complex as intermediate. Both the iron 22 and ruthenium 23 compound and also the bimetallic complex 24 are accessible. 

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... 

In this chapter, SOMC/M will be used to study the reactivity of organometallic complexes with the surface of supported metals. In 1984, Travers [31] and Margit-falvi [32] simultaneously described this application of SOMC for the preparation of bimetallic catalysts. 

Behr A, Von Ilsemann G, Keim W, Kruger C, Tsay Y (1986) Octadienyl-bridged bimetallic complexes of palladium as intermediates in telomerization reactions of butadiene. Organometallics 5 514—518... 

Bimetallic Complexes. There are two types of bimetallic organometallic thorium complexes those with, and those without, metal—metal interactions. Examples of species containing metal—metal bonds are complexes with Fe or Ru carbonyl fragments. Cp ThX(CpRu(CO)2), where X = Cl or I, and Cp 3Th(CpM(CO)2), where M = Fe or Ru, have both been prepared by interaction of Cp2ThX2 or Cp ThCl [62156-90-5], respectively, with the anionic metal carbonyl fragment. These complexes contain very polar metal—metal bonds that can be cleaved by alcohols. 

The two ideas are not incompatible. The Ti—C bond is activated by monomer coordination to the unoccupied d orbital of alkylated Ti, perhaps also with a contribution of the bimetallic complex with the organometal. Catalytic activity as well as the regularity, tacticity or stereoregularity (see Chap. 5, Sect. 4) of the polymer produced depend on the structure and concentration of the organometallic compound used. Its change affects the degree of alkylation other reactions, e.g. reduction of TiCl3, may also occur. 

From an applied perspective, metals are probably the most important surfaces in SOMC. Whereas in SOMC on oxides we introduce the active site, in SOMC on metals the metals themselves are the active catalysts. Organometallic chemistry provides the means to modify the often unselective metal surface by introduction of organometallic complexes (most often chemically inert) to the surface and eventually by transforming the initially obtained species by thermal or chemical means. For example, the hydrogenolysis of cyclic hydrocarbons, in particular cyclohexane, on the surface of unmodified Ir particles supported on a silica carrier has been studied and clearly indicated to bimetallic mechanism of C-C bond cleavage (Scheme 4) [24, 25]. 

Surface organometallic chemistry (SOMC) has shown high potential for the preparation of supported metal catalysts with desired composition and good dispersion [3]. For example, the controlled hydrogenolysis of tetra-n-butyltin (Sn(/i-C4H9)4) on the surface of group VIII metals leads to well-defined bimetallic catalysts [3-6]. In SOMC on metal supported on oxide, judicious selection of reaction conditions (temperature, initial complex concentration etc.) allows the reaction to occur preferentially between organometallic complexes and metal surface [3,5,6]. 

In this section, selected examples are described of dipolar second-order NLO chromophores in which an organometallic or coordination moiety may act as the donor (D), the acceptor (A) or even as the n-bridge connecting D to A. Representative examples of noncentrosymmetric bimetallic complexes containing metal-based fragments used as electron-donating and electron-accepting moieties, are also discussed. 

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. 

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