Palladium reaction with ethylene

Vinyl halides also enter into palladium-catalyzed reactions with ethylene. This will be dealt with under vinyl halides in Section 61.2.9.5. 

In fact, one important parameter is the water content of the medium, which causes the undesirable production of acetaldehyde by its reaction with ethylene in the presence of palladium chloride, or by the hydrolysis of the vinyl acetate formed. This operating variable can be adjusted to make the acetate production plant self-sufficient in terms of acetic acid. In this case, die acetaldehyde co-produced is oxidized to the arid in a separate section. It is the water content of the acetic arid employed, controlled by the degree of purification of the by-product arid which is recycled, which ultimately serves to determine the vinyl acetate to acetaldehyde ratio. Longer reridence time in the reactor or higher temperature also favors the formation of acetaldehyde. 

Nucleophilic attack of stabilized carbon nucleophiles on coordinated olefins is also known. Hegedus developed the alkylation of olefins shown in Equation 11.31. The (olefin)palladium(II) chloride complexes did not react with malonate nucleophiles, but the triethylamine adduct does react with this carbon nucleophile to provide the alkylation product. This reaction has recently been incorporated into a catalytic alkylation of olefins by Widenhoefer. - Intramolecular reaction of the 1,3-dicarbonyl compounds with pendant olefins in the presence of (GHjCNl PdCl occurs to generate cyclic products containing a new C-C bond (Equation 11.32). Some intermolecular reactions with ethylene and propylene have also been developed by this group. Deuterium labeling studies (Equation 11.32) have shown that the addition occurs by external attack on the coordinated olefin. ... 

Palladium chloride at 100 °C in anhydrous dimethyl formamide reacts in a stoichiometric reaction with ethylene producing vinyl chloride in 80% yield. Even though palladium chloride elimination is favored over hydride elimination, the addition recurs until the palladium is eliminated irreversibly as the hydride (Scheme 30). 

The palladium chloride reacts with olefins in a different course if water is present. Carbonyl compounds rather than chlorides are formed. The reaction with ethylene produces acetaldehyde and it can be done catalyticaUy in the presence of oxygen and cupric chloride, which is known as the Wacker process. The process is one of the most important commercially useful reactions employing transition metal catalysts. ... 

The reaction of methyl propionate and formaldehyde in the gas phase proceeds with reasonable selectivity to MMA and MAA (ca 90%), but with conversions of only 30%. A variety of catalysts such as V—Sb on siUca-alumina (109), P—Zr, Al, boron oxide (110), and supported Fe—P (111) have been used. Methjial (dimethoxymethane) or methanol itself may be used in place of formaldehyde and often result in improved yields. Methyl propionate may be prepared in excellent yield by the reaction of ethylene and carbon monoxide in methanol over a mthenium acetylacetonate catalyst or by utilizing a palladium—phosphine ligand catalyst (112,113). 

Dehalogenation of monochlorotoluenes can be readily effected with hydrogen and noble metal catalysts (34). Conversion of -chlorotoluene to Ncyanotoluene is accompHshed by reaction with tetraethyl ammonium cyanide and zero-valent Group (VIII) metal complexes, such as those of nickel or palladium (35). The reaction proceeds by initial oxidative addition of the aryl haHde to the zerovalent metal complex, followed by attack of cyanide ion on the metal and reductive elimination of the aryl cyanide. Methylstyrene is prepared from -chlorotoluene by a vinylation reaction using ethylene as the reagent and a catalyst derived from zinc, a triarylphosphine, and a nickel salt (36). 

Compounds prepared from naturally occurring nucleosides are of course more closely related to genetic material and may have a better chance of interacting with infected cells. Mercu-ration of the 2 -dcoxyuridine 113 leads to the organometallic derivative 114 reaction of that with ethylene in the presence dilithio palladium tetrachloride gives the alkylation product 115 this is reduced catalytically in situ. There is thus obtained the antiviral agent edoxudine (116) [25]. 

Quite recently Yasumori el al. (43) have reported the results of their studies on the effect that adsorbed acetylene had on the reaction of ethylene hydrogenation on a palladium catalyst. The catalyst was in the form of foil, and the reaction was carried out at 0°C with a hydrogen pressure of 10 mm Hg. The velocity of the reaction studied was high and no poisoning effect was observed, though under the conditions of the experiment the hydride formation could not be excluded. The obstacles for this reaction to proceed could be particularly great, especially where the catalyst is a metal present in a massive form (as foil, wire etc.). The internal strains... 

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at -20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects (54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3dic activity, in view of the current interest in polymer-sup-ported catalysts (51). 

The conversion of ethylene to acetaldehyde using a soluble palladium complex, developed in the late 1950s, was one of the early applications of homogeneous catalysis and the first organo-palladium reaction practised on an industrial scale [40], Typically this reaction requires stoichiometric amounts of CuCl under aerobic conditions. The use of copper represents not only an environmental issue, but often limits the scope of ligands that can be used in conjunction with Pd. 

The first example of a heterogeneously catalyzed hydroamination of an alkene appeared in a 1929 patent in which it is claimed that NHj reacts with ethylene (450°C, 20 bar) over a reduced ammonium molybdate to give EtNH2 [24]. An intriguing reaction was also reported by Bersworth, who reacted oleic acid with NH3 in the presence of catalysts like palladium or platinum black or copper chromite to give the hydroamination product in quantitative yields [25]. However, this result could not be reproduced [26]. 

Palladium(II) complexes possessing bidentate ligands are known to efficiently catalyze the copolymerization of olefins with carbon monoxide to form polyketones.594-596 Sulfur dioxide is an attractive monomer for catalytic copolymerizations with olefins since S02, like CO, is known to undergo facile insertion reactions into a variety of transition metal-alkyl bonds. Indeed, Drent has patented alternating copolymerization of ethylene with S02 using various palladium(II) complexes.597 In 1998, Sen and coworkers also reported that [(dppp)PdMe(NCMe)]BF4 was an effective catalyst for the copolymerization of S02 with ethylene, propylene, and cyclopentene.598 There is a report of the insertion reactions of S02 into PdII-methyl bonds and the attempted spectroscopic detection of the copolymerization of ethylene and S02.599... 

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

Over zinc oxide it is clear that only a limited number of sites are capable of type I hydrogen adsorption. This adsorption on a Zn—O pair site is rapid with a half-time of less than 1 min hence, it is fast enough so that H2-D2 equilibration (half-time 8 min) can readily occur via type I adsorption. If the active sites were clustered, one might expect the reaction of ethylene with H2-D2 mixtures to yield results similar to those obtained for the corresponding reaction with butyne-2 over palladium That is, despite the clean dideutero addition of deuterium to ethylene, the eth-... 

An initial step of orthometallation probably also occurs when aniline is allowed to react with ethylene in the presence of a rhodium(I) catalyst. 2-Methylquinoline (10 turnovers relative to the metal) and JV-ethylaniline (30 turnovers) are formed after 72 h in what are probably two independent reaction pathways (Scheme 144).216 It is interesting to note that the intramolecular cyclization step in the proposed216 mechanism (Scheme 144) has precedent in the palladium-promoted quinoline synthesis reported by Hegedus et al.16 (see Scheme 142), but the transformation 118->119 is unusual in the chemistry of organometallic insertion reactions.106... 

Catalysis experiments were performed to investigate the telomerization of butadiene with ethylene glycol in selected TMS systems (e.g. si toluene DMF 1 5 4 or sl 2-octanol DMSO 1.35 3 5.2). With Pd/TPPTS as the catalyst a maximum yield of only 10% of the desired products could be achieved. With Pd/TPPMS the yield increased up to 43% in the TMS system si toluene isopropyl alcohol, but additional water had to be added to obtain a phase split after the reaction. The catalyst leaching is very high and 29% of the palladium used is lost to the product phase. 

The details of the organic chemistry of the reaction of ethylene with PdCl2 (equation (1) above) are also known and are shown in Fig. 9.2. The palladium ion complexes with ethylene and water molecules and the water adds across the bond while still complexed to palladium. The palladium then serves as a hydrogen acceptor while the double bond reforms. Keto-enol tautomerism takes place, followed by release of an acetaldehyde molecule from the palladium. 

Vinyl acetate is produced by the oxidation of ethylene and acetic acid (4,5). Catalysts for the gas phase oxidation are made from palladium compounds with additional metal compounds on a porous support (6). Catalysts, preferably coated catalysts, can be used for many heterogeneously catalyzed reactions such as hydrogenations and oxidations. 

Comparison of these results with those presented for ethylene in Table 7 show that, for each catalyst, the two reactions show close similarities suggesting that the general features of the mechanisms are the same for both reactions. There are some important differences in detail between the two reactions, particularly with palladium and iridium. With palladium, olefin exchange occurs more readily with propene than with ethylene. This may be due to easier desorption of propene or possibly due to an alternative mechanism such as... 

C-Tracer studies of acetylene adsorption on alumina- and silica-sup-ported palladium [53,65], platinum [66] and rhodium [53] show the coexistence of at least two adsorbed states, one of which is retained on the surface, the other being reactive undergoing molecular exchange and reaction with hydrogen. Acetylene adsorption exhibits the same general characteristics as those observed with ethylene (see Sect. 3.2). However, there are important differences. The extent of adsorption and retention is substantially greater with acetylene than with ethylene. Furthermore, the amounts of acetylene retained by clean and ethylene-precovered sur-... 

---