Ethylene reaction with platinum complexes

Attempt to prepare Jt-complexes of triafulvenes and related methylene cyclopro-parenes285,427 428 directly by ligand exchange reaction with transition metal complexes resulted in metal insertion into the sigma bond, forming metallacyclic complexes. Thus reaction of the electron-poor triafulvene l,2-diphenyl-3-dicyanomethylenecyclopropene with (ethylene)bis(triphenylphosphine)platinum in refluxing benzene gave two crystalline products whose platinacyclobutene structure was confirmed by X-ray structure analysis (equation 364)429. 

Reactions of 250 with four electrophiles are recorded in Scheme 31. In general, the products are more stable than those from complexes with monodentate ligands. Reaction of 249 with CS2, 249 or 250 with alkynes, and 249-251 with ethylene gives products in which the C6H8 has been lost but its fate has not been determined attempts to trap free cyclohexyne failed.93 Loss of the organic ligand appears to occur more readily in nickel complexes than in those with platinum. 

Braunstein et al. recently reported an interesting reaction of a base-stabilized mononuclear silylene complex with platinum-ethylene complexes [Eq. (35)]. In this reaction, the Pt-bound ethylene ligand is displaced by the base-free silylene complex, but the products can be also regarded as a dinuclear complex where two metals are bridged by a silylene unit.67... 

Di-jj-chloro-dichlorobis(ethylene)diplatinum(II) is customarily prepared by evaporating an aqueous solution of H[PtCl3(C2H4)] to dryness and then recrystallizing the dimer.1 However, this procedure has not been applied as a general synthesis of other related olefin complexes. The dimer has also been prepared, but with less success, by the reaction of Na2PtCl6 with boiling ethanol.2 The direct reaction of ethylene with platinum(IV) chloride also provides the dimer,3 but yield data are not available and presumably the method is unsatisfactory. 

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)... 

Scheme 4 shows a platinum catalyst 1 containing such a bis-SPO bidentate ligand anion, designed for the hydroformylation of ethylene and of 1-heptene, and various other, similarly built, platinum catalysts. Catalyst 1 has an activity comparable to that of the commercial cobalt catalysts that were used at the time and displays a higher selectivity for linear products than the cobalt-containing catalysts (66). Like the latter, the platinum complex exhibits hydrogenation activity to give, in part, alcohols in addition to aldehydes and also produces alkanes (an undesired reaction that implies a loss of feedstock). The catalysts are also active for isomerization, as are the cobalt complexes, and for internal heptene hydroformylation (Table 1), with formation of 60% linear products. 

The reaction could be carried out stepwise. First, reaction of the hydride complex 1 with ethylene under pressure at 90 °C gives the ethyl platinum complex 2 then, treatment of 2 with CO at ambient temperature and pressure rapidly gives the propionyl platinum complex 3. Reaction of... 

Platinum complexes incorporating an optically active amine have been employed for resolution of racemic mixtures of optically active olefins by reaction of the olefin with dichloro-platinum(II). The differing solubility of the diastereoisomers permits separation by fractional crystallization and the olefin can be recovered by reaction of the complex with aqueous alkali cyanide. Using either (-f)-l-phenyl-2-aminopropane (Dexedrine) or (-f)- or (—)-a-phenyl-ethylamine. Cope and co-workers have resolved the optical isomers of trans double bond coordinated and, with (—)-phenylethyl-amine)dichloroplatinum(II), a bridged complex with each double bond coordinated to a different platinum atom. 

In the presence of catalyst on the support, evidently being a platinum complex with diallylamine fixed on the porous glass, the reaction did not proceed at 70 - 80 °C, but at 90- 100 °C ethylene was actively absorbed and the ethyltriethoxysilane content in the mixture amounted to 94.3%. When the synthesis was repeated on the same catalyst, the reaction proceeded more slowly, but the triethoxysilane was completely consumed. 

Little is known about the chemical nature of the recently isolated carbon clusters (C o> C70, Cg4, and so forth). One potential application of these materials is as highly dispersed supports for metal catalysts, and therefore the question of how metal atoms bind to C40 is of interest. Reaction of C o with organometallic ruthenium and platinum re nts has shown that metals can be attached directly to the carbon framework. Ihe native geometry of transition metal, and an x-ray difi action analysis of the platinum complex [(CgHg)3P]2Pt( () -C6o) C4HgO revealed a structure similar to that known for [(C4Hs)3P]2Pt( n -ethylene). The reactivity of C40 is not like that of relatively electron-rich planar aromatic molecules su( as benzene. The carbon-carbon double bonds of C40 react like those of very electron-deficient arenes and alkcnes. 

The first metal complex identified as an organometallic compound was a salt, K(C2H4)PtCl3, obtained from reaction of ethylene with platinum (II) chloride by William Zeise in 1825. It was not until much later (1951-1952) that the correct structure of Zeise s compound (see Figure 1) was reported in connection with the structure of a metallocene compound known as ferrocene (see Figure 2). 

The migratory insertion (silyl migration) of alkene into the M—Si bond is a key step for the dehydrogenative silylation catalyzed by late transition metal complexes. The first convincing results for mechanistic pathways involving this step were presented by Seitz and Wrighton (45) and obtained in a photochemical study of the reaction with [(Me3Si)Co(CO)4] complex. The insertion of ethylene into the Co—SiMes bond was spectroscopically confirmed. In addition, as already mentioned, a theoretical study of the hydrosilylation of ethylene explained the preference of rhodium over platinum complexes as catalysts in these reactions (41,43). 

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