Catalytic reactions involving acetylenes

Carbonylation of the parent acetylene via stoichiometric or catalytic reactions involving transition-metal carbonyl complexes has been extensively studied. Various types of carbonylation reactions of acetylene were discovered. In 1968, Pino et al. [30] reported on the synthesis of hydroquinone via a Ru3(CO)12-cat-alyzed carbonylation of acetylene with H2 or H20. The product formally consisted of two molecules of acetylene and CO, and one molecule of H2 (Eq. 14). To achieve a good yield of hydroquinone, the H2 pressure must be kept under... 

The accepted papers cover every aspect of catalysis on microporous materials. A significant number of contributions describe the synthesis, modification, instrumental and chemical characterisation of zeolites and other micro- and mesoporous materials. Catalytic reactions involve hydrocarbon cracking, nucleophilic aromatic substitution, methanol to hydrocarbon conversion, hydration of acetylene, various alkylation reactions, redox transformations, Claisen rearrangement, etc. A whole range of appealing chemistry can be enjoyed by reading the contributions. 

The reactivity of arylhalides in the acetylenic condensation sharply decreases in the series Ar—I, Ar—Br, Ar—Cl. The rate of reaction of phenylacetylene with iodo derivatives is 800 times higher than that of the reaction with bromo derivatives and is 10 higher than that of the reaction with corresponding chlorides (75JOM253). Taking into account the very low activity of halogenopyrazoles (66AHC347), the catalytic variant of acetylenic condensation mainly involves the most active iodo derivatives. 

A significant part of the examples of transition metal catalyzed formation of five membered heterocycles utilizes a carbon-heteroatom bond forming reaction as the concluding step. The palladium or copper promoted addition of amines or alcohols onto unsaturated bonds (acetylene, olefin, allene or allyl moieties) is a prime example. This chapter summarises all those catalytic transformations, where the five membered ring is formed in the intramolecular connection of a carbon atom and a heteroatom, except for annulation reactions, involving the formation of a carbon-heteroatom bond, which are discussed in Chapter 3.4. 

It has been found in the meantime that reaction (1) is generalizable (752), and that oxidative additions of this type occur for such widely differing substrates H2Y as ethylene, benzene 130), cyclic olefins, alkyl and aryl phosphines, aniline 337, 406), and H2S 130), ail of which give the same product structure with a triply-bridging Y ligand. The stability of these third-row transition metal clusters has stiU prevented catalytic reactions of these species, but it is likely that similar ones are involved in olefin and acetylene reactions catalyzed by other metal complexes. 

Currently available chiral Diels-Alder catalysts have major limitations with regard to the range of dienes to which they can be applied successfully. Indeed, most of the reported catalytic enantioselective Diels-Alder reactions involve reactive dienes such as cyclopentadiene, but 1,3-butadiene and 1,3-cyclohexadiene have not been successfully utilized without reactive 2-bromoacrolein. To solve this problem, a new class of super-reactive chiral Lewis acid catalysts has been developed from chiral tertiary amino alcohols and BBr3 [24] (Eq. 8A.13). This type of chiral super Lewis acid works well for a,fj-acetylenic aldehydes [25],... 

The time is ripe for truly exciting developments in the reactivity of dinuclear transition metal compounds. The potential for cyclic sequences of reactions, as is required for catalytic reactions, has already been realized. (1) It has been shown, by Muetterties, et al. (53), that alkynes can be selectively hydrogenated to alkenes (cU 2H-addition) by Cp2Mo2(C0) the rate determining step involves CO dissociation from the acetylene adducts Cp2MO2(C0) (R2C2). (2) We have found that... 

The adsorption of small unsaturated hydrocarbons, such as ethylene and acetylene, on transition metal surfaces is of considerable scientific interest due to their involvement in several elementary catalytic reactions. One of the prerequisites to a... 

The C-H bond cleavage of active methylene compounds with a transition metal catalyst is another method for the functionalization of these C-H bonds. To date, several reactions have been developed. In particular, the asymmetric version of this type of catalytic reaction provides a new route to the enantioselective construction of quaternary carbon centers. One of the most attractive research subjects is the catalytic addition of active methylene C-H bonds to acetylenes, allenes, conjugate ene-ynes, and nitrile C-N triple bonds. The mthenium-catalyzed reaction active methylene compounds with carbonyl compounds involving aldehyde, ketones, and a,y3-unsatu-rated ketones and esters is described in this section. 

Shown in Table 8.6 arc some literature data on the use of dense membrane reactors for liquid- or multi-phase catalytic reactions. Compared to gas/vapor phase application studies, these investigations are relatively few in number. Most of them involve hydrogenation reactions of various chemicals such as acetylenic or ethylenic alcohols, acetone, butynediol, cyclohexane, dehydrolinalool, phenylacetylene and quinone. As expected, the majority of the materials adopted as membrane reactors are palladium alloy membranes. High selectivities or yields are observed in many cases. A higher conversion than that in a conventional reactor is found in a few cases. 

The following describes results of three, relatively simple chemical reactions involving hydrocarbons on model single crystal metal catalysts that illustrate this general approach, namely, acetylene cyclotrimerization and the hydrogenation of acetylene and ethylene, all catalyzed by palladium. The selected reactions fulfdl the above conditions since they occur in ultrahigh vacuum, while the measured catalytic reaction kinetics on single crystal surfaces mimic those on reahstic supported catalysts. While these are all chemically relatively simple reactions, their apparent simplicity belies rather complex surface chemistry. 

Bonding and Adsorbed Species.—Broden et al. have investigated geometric and electronic effects in the chemisorption and reaction of acetylene, ethylene, and benzene on Ir(lOO) surfaces. Though not a paper on catalysis, the study represents primary information on adsorption processes for molecules which may or may not be involved in catalytic changes. The physical techniques used were LEED, AES, and UPS. 

For the Reppe carbonylation, it is proposed that the reaction involves the initial oxidative addition of a nucleophile to the transition metal complex, followed by the complexation of an unsaturated hydrocarbon to the metal and insertion into a metal-H bond. Subsequently, migration of hydrocarbon species to CO followed by a reductive elimination afford the corresponding product." Scheme 1 illustrates the formation of ester from acetylene, CO, and methanol in the presence of a catalytic amount of Pd[CO]4. In addition, a mechanism analogous to that of Hydroformylation is proposed and displayed in Scheme 2 for the Reppe formylation. 

A [4+2] benzannulation between acetylenic ketones 248 and a benzenediazo-nium 2-carboxylate proceeds effectively in the presence of a catalytic amount of AuCl, yielding functionalized anthracenes 250 in good yields (Scheme 12.67) [137]. It is suggested that the reaction involves a reverse electron demand Diels-Alder reaction between benzyne and the benzopyrylium aurate complex 249. 

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