Palladium complexes olefin

Chalk and Elarrod (11a) compared the above ethylene Pt(II) complex with chloroplatinic acid for hydrosilation, and found that each gave essentially the same results in terms of rate, yields, and products. Plati-num(II) complexes and rhodium(I) complexes were very much alike in their behavior. No system was found in which a palladium olefin complex brought about hydrosilation. In most systems the palladium complex was very rapidly reduced to the metal. 

My last comment concerns the reaction of palladium olefin complexes with carbon monoxide discovered by Tsuji. I agree that this is most likely to proceed by an insertion rather than an ionic mechanism. Chloride attack on coordinated olefin is rare however. Chloride ion is an inhibitor, for example in the palladous chloride catalyzed hydration of ethylene (0). I, therefore, wondered whether carbon monoxide was affecting the ease with which chloride attacks olefin. One can postulate that carbon monoxide participates in this insertion either as a gas phase reactant or by first forming a carbonyl olefin complex. Such complexes of the noble metals were unknown, but examining the reaction between carbon monoxide and the halogen bridged olefin complexes of platinum revealed that they are formed very readily... 

Palladium chloride or the chloropalladite ion catalyze the oxidation of olefins to aldehydes or ketones, presumably by forming unstable palladium-olefin complex intermediates 196). A reaction of great industrial importance is the palladium chloride/cupric chloride catalyzed oxidation of ethylene to acetaldehyde 195). The first stage is presumably the oxidative hydrolysis of ethylene,... 

New MM3+-based force fields for (p.3-allyl)palladium and palladium olefin complexes with various co-ligands, which are based on the points-on-a-sphere approach and do not require dummy atoms to define the connectivity, have been developed and validated with experimentally observed and quantum-mechanically computed data[454l... 

R. M. Atkins, R. Mackenzie, P. L. Timms, and T. W. Turney, The Preparation of Palladium-Olefin Complexes from Palladium Vapour, J. Chem. Soc., Chem. Comm. 1975, 764. 

Palladium olefin complexes are considerably less stable than the platinum analogues. The dibenzylideneacetone complex Pd2(dba)3 (18-H-IV), however, is air-stable it is a convenient source of Pd° for catalytic applications. 

Japan. Review of author s work on palladium-olefin complexes and nucleophiles... 

Nucleophilic attack of the arene on the palladium-olefin complex I with loss of HCI... 

Interestingly, Widenhoefer reported a similar palladium(II) catalyzed cycliza-tion of indoles onto alkenes (Scheme 58) [72]. This mild protocol for cyclization/ carboxylation of 2-alkenyl indoles makes possible catalytic addition of a carbon-nucleophile and carbonyl group across a C-C bond. The mechanism, however, is thought to involve outer-sphere attack of indole onto a palladium-olefin complex rather than the electrophilic C-H activation of the indole C(3)-H bond, exhibited by the Stoltz carbocyclization. 

The stereochemical outcome was in agreement with a mechanism for the palladium-catalyzed cyclization/carboalkoxylation of a substituted alkene (Scheme 47) that involves outer-sphere attack of the indole on the palladium-olefin complex I which, coupled with loss of HCI, would form the alkylpalladium intermediate II. 1,1-Migratory insertion of CO into the Pd-C bond of II with retention of stereochemistry would form the acyl-palladium complex III, which could undergo methanolysis to release c/.v-product and form a palladium(0) complex. Oxidation with Cu(II) would then regenerate the active Pd(II) catalyst. 

The crystal structures of Zeise s salt and of two analogous palladium-olefin complexes were published,shortly after the publication of the Chatt-Duncanson paper. They confirmed the structural proposals made by Chatt, but none of these papers cites Dewar,though metal-olefin bonding models were not discussed. Two short reviews on the history of Zeise s salt, (one part of a more general discussion of the history of organometallic chemistry) also only refer to Chatt s contribution, though neither specifically address questions of bonding. 

Kurosawa has shown that the related palladium(II) olefin complex [( ti -C5H5)Pd(Ph3P) (CHj=CHj)] undergoes clean trans attack by both methoxide and the anion of acety-lacetone. These examples of additions to iron- and palladium-olefin complexes occur by attack only at the ligand and lead to stable o-alkyl products because the metal center is coordinatively saturated. This coordinative saturation disfavors attack at the metal that would lead to either products from syn addition or displacement of the olefin. The cr-alkyl complexes that are products of these examples of nucleophilic attack are stable because the most common mode for decomposition of o-alkyl complexes, 3-hydrogen elimination, requires the presence of a vacant coordination site cis to the alkyl group, as noted in Chapters 8 and 9. Such a site is not present in these cr-alkyl products. 

Many reactions of amines with palladium- and platinum-olefin complexes have been reported. Akermark showed that nucleophiles add to palladium-olefin complexes to generate aminoalkyl complexes, as shown by the example in Equation 11.26. In this case, reactions of a bis-olefin dichloropalladium complex with amines occurs by splitting of the chloro-bridged dimer by the first equivalent of amine to give a neutral olefin-ligated palladium-amine complex that undergoes attack of the coordinated alkene by a second equivalent of amine. The stereochemistry of the amination is cleanly trans. Akermark and Zetterberg isolated and characterized by C NMR spectroscopy the a-alkyl complexes formed by the amination of both cis- and frans-2-butene, and the stereochemistry of the product alkyl complexes results from external attack by amines, as shown in Scheme 11.5. 

The organometallic chemistry of pahadium(II) is similar to that of platinum(II) except that the palladium compounds are less stable. This lability permits a wide variety of useful catalytic reactions (e.g., palladium olefin complexes in the Wacker process). Prominent examples are the formation and reaction of r-allyl complexes. The r-allyl complexes can be formed from an olefin bound to palla-dium(II) on heating or by the reaction of an allyl halide... 

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