Acetylene, interaction with palladium

The figure shows the complex number of peaks that can be formed when acetylene interacts with palladium. 

Ab initio methods, 147-49 Acetate ion, decomposition, 135 Acetylene, interaction with palladium, tunneling spectroscopy, 435,437f Acid-dealuminated Y zeolites catalytical properties, 183 sorption, 175-78 Acid sites, on zeolites, 254 acidification effects, 266 Acoustic ringing, in NMR, elimination, 386 Active sites, nature, 104 Activity measurements, Co-Mo catalysts, 74 Adsorbed molecules,... 

Besides the interaction with CO, Figure 9 shows the most recent results of the simplest unsaturated hydrocarbon (acetylene) with alumina supported palladium. Here, however, the very small peak intensities indicate that tunneling spectroscopy shows little promise for studying complex hydrocarbons on supported metals. 

The nature of the unsaturated hydrocarbon has a very important role in the sulfur action Berenblyum et al. (83) have reactivated a palladium catalyst, poisoned with thiols, through the interaction with phenylacethyl-ene the presence of acetylenics together with low levels of sulfur even activate the nickel sites activity for acetylene hydrogenation (84, 85). 

There is a notable tendency to form oligomers when acetylenic substances interact with compounds of metals, and this tendency is also shown by butadiene 117) (see Section IV, B,d). This is particularly so with the carbonyls of iron and cobalt, and the oligomerization reactions are favored with nickel 121) and with palladium compounds 113, 122, 123). This phenomenon may be related to the hydropolymerization of acetylenes on metal surfaces, and it may be that such polymerization processes would be better described in terms of ir-complexes. 

We could thus expect that this reaction terminated the palladium- and nor-bornene-catalyzed reaction sequence in place of the acrylic ester or terminal olefins in general. Considerable difficulties were met, however, because the alkyne interacted with all the palladium complexes of the sequence, giving rise to a number of by-products. Starting from 1 equivalent of aryl iodide, 2 equivalents of alkyl bromide, 1 equivalent of norbornene, 0.3 equivalents of aryl-acetylene, 8 equivalents of KOAc, and 0.1 equivalent of Pd(OAc)2 and adding gradually 2 equivalents of alkyl bromide and 0.7 equivalents of arylacetylene (to keep the concentration of the latter low) satisfactory results were obtained. Equation 30 reports the reaction withp-fluoroiodobenzene, n-propyl bromide, and phenylacetylene, which gave a 79% yield (71% with iodobenzene) [37]. 

The reaction of methylenecyclopropanes with transition metal complexes is well known to promote a catalytic a-ir cycloaddition reaction with unsaturated compounds, in which a trimethylenemethane complex might exist71-76. Recently, much interest has been focused on the interaction of strained silicon-carbon bonds with transition metal complexes. In particular, the reaction of siliranes with acetylene in the presence of transition metal catalysts was extensively investigated by Seyferth s and Ishikawa s groups77-79. In the course of our studies on alkylidenesilirane, we found that palladium catalyzed reaction of Z-79 and E-79 with unsaturated compounds displayed ring expansion reaction modes that depend on the (Z) and (E) regiochemistry of 79 as well as the... 

In the alkyne dimerization catalyzed by palladium systems, all proposed mechanisms account for an alkynyl/alkyne intermediate with cis addition of the alkynyl C-Pd bond to the alkyne in a Markovnikov fashion, in which the palladium is placed at the less-substituted carbon, both to minimize steric hindrance and to provide the most stable C-Pd bond (Scheme 2a). The reverse regioselectivity in the palladium-catalyzed dimerization of aryl acetylenes has been attributed to an agostic interaction between the transition metal and ortho protons of the aromatic ring in the substrate (Scheme 2b) [7, 8],... 

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