Platinum olefin compounds

Platinum olefin compounds have long been known, the most familiar being Zeise s salt, K(PtCl2C2H4)Cl. The fundamental compound of such... 

Although the actual reaction mechanism of hydrosilation is not very clear, it is very well established that the important variables include the catalyst type and concentration, structure of the olefinic compound, reaction temperature and the solvent. used 1,4, J). Chloroplatinic acid (H2PtCl6 6 H20) is the most frequently used catalyst, usually in the form of a solution in isopropyl alcohol mixed with a polar solvent, such as diglyme or tetrahydrofuran S2). Other catalysts include rhodium, palladium, ruthenium, nickel and cobalt complexes as well as various organic peroxides, UV and y radiation. The efficiency of the catalyst used usually depends on many factors, including ligands on the platinum, the type and nature of the silane (or siloxane) and the olefinic compound used. For example in the chloroplatinic acid catalyzed hydrosilation of olefinic compounds, the reactivity is often observed to be proportional to the electron density on the alkene. Steric hindrance usually decreases the rate of... 

Arene and olefin compounds, pure or in admixture, are efficient ligands in promoting the aggregation of platinum atoms from mononuclear species to ligand-stabilized soluble clusters and solid-supported nanoparticles (Scheme 14). 

Olefin Oxidation Catalyzed by Platinum-Blue Compounds... 

PtBrs (arsine) 2, which are octahedral complexes of platinum(IV) in which the olefinic side chains of the ligands have been fully brominated. An alternative and more realistic formulation of these compounds is PtBr4 (arsine Bre) 2- These same compounds are formed by reaction of an excess (> 3 equivalents) of bromine with the original platinum(II) compounds. 

Significant advances in organonickel chemistry followed the discovery of frtzws,fraws,fraws-(l,5,9-cyclododecatriene)nickel, Ni(cdt), and bis(l,5-cycloocta-diene)nickel Ni(cod)2 by Wilke et. al.1 In these and related compounds, in which only olefinic ligands are bonded to the nickel, the metal is especially reactive both in the synthesis of other compounds and in catalytic behavior. Extension of this chemistry to palladium and to platinum has hitherto been inhibited by the lack of convenient synthetic routes to zero-valent complexes of these metals in which mono- or diolefins are the only ligands. Here we described the synthesis of bis(l,5-cyclooctadiene)platinum, tris(ethylene)-platinum, and bis(ethylene)(tricyclohexylphosphine)platinum. The compound Pt(cod)2 (cod = 1,5-cyclooctadiene) was first reported by Muller and Goser,2 who prepared it by the following reaction sequence ... 

In this paper, the effect of lead adatoms on the activity of platinum catalysts, in liquid phase hydrogenation of olefinic compounds, is presented. 

Dewar s landmark contribution [32] did not receive much attention at the time it was published, possibly because the author did not seek to establish the experimental evidence for his model in subsequent publications. He seemed not to be very interested in the field of transition metal chemistry and was probably not aware that his description of the bonding in olefin silver complexes was supported by Raman studies reported a decade previously. In 1941, Harvey Taufen and coworkers had found that the olefin remained largely unchanged in its coordination to Ag+ and that the C=C bond was weakened only slightly by the formation of the olefin silver complex [36]. In contrast to Dewar, Joseph Chatt knew this paper and mentioned the results in a review on the mercuration of olefins, which like Dewar s article was also published in 1951 [37], In his paper, Chatt made a clear distinction between the olefin silver and olefin platinum complexes and argued that, in contrast to the ionized olefin silver(I) salts, in the olefin platinum(II) compounds the metal is present in a covalent state and not as an ion. He also believed that for Ag+ the d-shell was core like and not available in the manner necessary to stabilize the olefin-platinum bond [37]2. 

Stone and the Family of Olefin Palladium(O) and Platinum(O) Compounds... 

It was somewhat puzzling that while olefin compounds of platinum(II) were well established, acetylene complexes were virtually unknown. Acetylene gives red intractable materials on reaction with potassium chloroplatinate(II) in aqueous solution, presumably acetylides and dimethylacetylene does not react, in marked contrast to ethylene, which forms [PtCl3(C2H4)] . However, Gel man, Bukhovets, and Meilakh (44)... 

Catalytic reactions of olefins with 7 platinum metal compounds (17)... 

Tris- and tetrakis (triphenylphosphine) platinum (0) are the source of many platinum compounds. They react with carbon monoxide, acids/ methyl iodide/ fluoroalkyl derivatives/ carbon disulfide/ oxygen/ chloro/ fluoro/ and activated olefins/ hydrogen sulfide and selenide/ and sulfur dioxide/ yielding many platinum (II) or platinum (0) compounds which cannot be obtained easily by other routes. 

The olefin complexes of platinum(II) resemble those of rhodium(I) in being very effective catalysts for addition of silanes to olefinic compounds (66). The following results have been found for the hydrosilylation of hexene-1 ... 

From the present available data, the formation constants for platinum(II)-olefin complexes are approximately 2 log units higher than those for palla-dium(II)-olefin complexes, although since different olefinic compounds have been used, a true comparison is not possible. 

An MO treatment of the platinum-olefin p/ -bond was applied by Chatt and Dun-canson in 1953 131>. It is similar to Dewar s explanation of bonding in silver complexes but o-bond overlap is between a filled ligand 7r-orbital and an empty 5d6s6p2 hybrid orbital of the metal. Back co-ordination from the filled metal 5d6p hybrid orbital to the empty olefin jt orbital assists in restoring a more favourable charge distribution as demonstrated in E.II. A result of the mixing in of a 6p with the Sd orbital of the metal is that the C=C bond will be perpendicular to the co-ordination plane of the metal atom if overlaps are to be maximised. The orientation of ethylene in Zeise s salt and related compounds... 

The use of complexes as stationary phases is well developed in gas chromatography. For example, Cartoni et al. [87] studied the properties of nickel, palladium, platinum and copper N-dodecylsalicylaldimines (MSal2) and those of nickel, palladium and platinum methyl-N-octylglyoximes (MGly2). It was shown that the stationary phases studied showed specific retention of amines, alcohols and olefinic compounds. Table 6.3... 

Some kinetic parameters for restricted rotation in rhodium-olefin complexes were reported some time ago. These values have recently been revised, and parameters for related rhodium compounds determined. Activation parameters have also been determined for some platinum-olefin complexes. Here intramolecularity of mechanism is proved by the persistence of Pt- H coupling and the lack of change in the n.m.r. spectra of the non-olefinic ligands with varying temperature. The roles of p and d orbitals both in fixing the preferred orientation of the olefin perpendicular to the co-ordination square around the platinum and in the rotational process, are discussed. Wide-line n.m.r. spectra indicate some... 

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