Reppe alkynes

Other references related to the Reppe alkyne cyclotrimerization are cited in the literature. 

This reaction is closely related to the Reppe Alkyne Cyclotrimerization. 

Alkyne complexes are essentially similar to the alkenes (p. 932) and those of Pt particularly when the alkyne incorporates the <-butyl group, are the most stable. Ni alkyne complexes are less numerous and generally less stable but are of greater practical importance because of their role as intermediates in the cyclic oligomerization of alkynes, discovered by W. Reppe (see Panel). 

In the metal-carbonyl catalysed hydrocarboxylation of alkynes ( Reppe reaction ) nearly exclusive cia-addition of H—COOH is found (Ohashi et al., 1952). 

Pioneering work involving the combinahon of an organosulfide, a C-C unsaturated organic compound and a transihon metal catalyst was reported by Reppe in 1953, in which Ni(CO)4-catalyzed hydrothiocarboxylahori of alkyne or ethylene by thiol and CO was briefly described to give the corresponding thioesters 1 or 2 (an application of one of the so-called Reppe reachons) (Eqs. 7.1 and 7.2) [12, 13]. 

The reactions are related to the incorporation of CO and H20 into alkenes or alkynes leading to the corresponding saturated or unsaturated carboxylic acids. The general equation is shown below. Equation lb is related to the synthesis of acrylic acid discovered by Reppe [11]. 

Reactions of Alkenes and Alkynes in Presence of Metal Carbonyls. Metal carbonyls—e.g., Ni(CO)4, Fe(CO)5, and Co2(CO)s—and hydrocarbonyls— HCO(CO)4 and H2Fe(CO)4—act as catalysts for the transformation of simple unsaturated materials into a wide variety of larger molecules. Perhaps the simplest example is that of hydroformylation (Equation 7). Reppe chemistry... 

In the 1930s, the Reppe group developed commercial processes for the production of carboxylic acids and esters by the carbonylation of alkynes and alkenes using metal carbonyls [4], In particular, an industrial process for producing acrylic acid or ester by the carbonylation of highly explosive acetylene, catalysed by extremely toxic Ni(CO)4, was established (eq. 1.3). 

Reppe and co-workers reported in 1948 the Ni-catalyzed cyclotetramerization of acetylene to give cyclooctatetraene (106) [58]. After this discovery, the reaction was expanded to monosubstituted alkynes. Monosubstituted alkyne 138 is cyclized smoothly to give tetrasubstituted cyclooctatetraene 139 [59]. Internal alkynes are... 

A much shorter route is the Reppe carbonylation [83] of propyne. Propyne is, together with propadiene (allene), part of the C3 stream of the cracking process. The order of metal substrate binding strength is allenes>alkynes>alkenes. Thus the desired reaction can only proceed if the propadiene has been removed from the feed, since it is an inhibitor of the Pd catalyst. Equally important, the alkyne complex reacts much faster than the alkene complex. Thus the product is neither a substrate nor an inhibitor for the catalyst (Scheme 5.46). 

Metallacycles have been claimed to play pivotal roles in many transition metal-mediated multi-component coupling reactions [1]. For example, [2 -i- 2 -i- 2] alkyne cyclo-trimerization leading to benzenes - the Reppe reaction - has been considered to proceed via metallacyclopentadiene and elusive metallacycloheptatriene intermediates ("common mechanism ), while metallacyclopentenes have been proposed as intermediates for the [2 -i- 2 -i- 1] cyclo-coupling reactions of an alkyne, an alkene, and CO leading to a cyclopentenone (the Pauson-Khand reaction). A metallacyclic compound - which is defined here as a carbocyclic system with one atom replaced by a transition metal element - can be generally formed by oxidative cyclization of two unsaturated molecules with a low-valent transition metal fragment [2-4]. Alter-... 

At the same time, Reppe (158) discovered the catalytic properties of tetracarbonyinickel and its derivatives in the carbonylation reactions and in the cyclization of alkynes, and this gave a tremendous thrust forward to the experimental research on the chemistry of carbonylnickel derivatives. In the beginning the development of the chemistry of low oxidation states proceeded concomitantly with the chemistry of zerovalent... 

Polymerization and Cyclization of Alkynes (163). In 1940 Reppe and Schweckendieck 163) discovered that the substitution derivatives of tetracarbonylnickel with phosphines, and particularly those of the type Ni(CO)2(PR3)2, catalyze the linear polymerization and the cyclization to benzene derivatives of alkynes. Schrauzer 167) more recently showed that stoichiometric amounts of bisacrylonitrilenickel give the cyclization reaction. The reaction becomes, on the contrary, catalytic in the presence of a tertiary phosphine. Meriwether and co-workers (57, 136, 137, I40) studied the possible mechanism of Reppe s reaction. They showed that both the polymerization and the cyclization reactions are particularly effective with monosubstituted acetylenes, and that the cyclization reaction is infiuenced by steric and electronic effects. They then proposed a mechanism by which the induction time is ascribed to this rather slow reaction ... 

W. Reppe / BASF (> 1938) catalytic transformations of alkynes 0. Roelen / RUHRCHEMIE (1938) hydroformylation... 

The carbonylation of alkynes has been known since the pioneering work of Reppe in the late 1930s [2] and has attracted considerable interest from industry and academia [3]. 

In recent years, attention has been focused on alkyne carbonylation catalysts based on the metals nickel, palladium, and platinum, modified with a variety of tertiary (bi)phosphines [5]. TTie main goal has been to develop chemo- and regio-selective carbonylation catalysts for application to higher alkyne substrates for the synthesis of certain fine chemicals. Many of these catalysts do allow the carbonylation to proceed under milder conditions than those applied in the catalytic Reppe process, and some of these catalysts do provide the branched regioisomer product from higher alkynes with good selectivity. However, in all cases reaction rates are very low, i.e., below 100 (and in most cases even below 10) mol/mol metal per h, as are the product yields in mol/mol metal (< 100). These catalyst productivities are far too low for large-scale industrial application in the production of commodity-type products, such as (meth)acrylates. 

Thermal cyclooligomerizations of olefins and alkynes require severe and often dangerous reaction conditions and the yields of cyclic products are usually very low. Acetylene ean be trimerized to benzene at 500 °C [1] and butadiene (BD) dimerizes at 270 °C and under high pressure to give small amounts of 1,5-cyclo-octadiene [2]. Reppe s discovery in 1940 that acetylene can be cyclotetramerized to cyclooctatetraene (COT) using a nickel catalyst [3] shows that transition metals can act as templates for the synthesis of cyclic hydrocarbons from acetylenic or olefinic building blocks (Scheme 1). 

Subsequent protic workup releases the aromatic compound. The metalative Reppe reaction can also be used to prepare iodo-substituted or homologated aromatics by treatment of the titanium aryl compound with iodine or an aldehyde, respectively. This procedure has recently been extended to include pyridine derivatives (254 and 255), where the titanacyclopentadiene intermediate can be treated with sulfonylnitriles to afford pyridines after protic workup.192 As with the alkyne cyclotrimerizations, treatment with the appropriate electrophiles affords iodo- and homologated pyridines. 

Compared with the Diels-Alder reaction, the [2+2+2]-cycloaddition is potentially more powerful since the number of new bonds as well as chirality centers that are formed is higher. Unfortunately, the reaction seems to be entropically or kinetically unfavorable. This disadvantage can, however, be overcome by the use of transition metal catalysts (templates). Among the most successful examples of this reaction type, the nickel(II) catalyzed Reppe reactions 96), the cobalt(I) catalyzed cocyclizations of a,to-diynes with alkynes 97), the cobalt(I) catalyzed pyridine synthesis 985 and last but not least the palladium(0) catalyzed cyclotrimerizations of 3,3-dialkylcyclopropenes to frans-cr-tris-homobenzenes must be mentioned. The latter has been known for ten years 99>. 

The reaction of an alkene (or alkyne), CO, and H2O to directly produce a carboxylic acid is called Reppe carbony-lation chemistry or, more recently, hydrocarboxylation see Reppe Reaction). An excellent review of palladium-catalyzed Reppe carbonylation systems has been published recently by Kiss, and coverage of this important material will not be repeated here. This catalytic reaction has been known for quite some time, although the stoichiometric Ni(CO)4-based carbonylation of acetylene was the first commercial carbonylation process implemented (equation 13). The extreme toxicity of Ni(CO)4, however, has limited practical applications see Nickel Organometallic Chemistr. Co, Rh, and Pd catalysts have certainly replaced Ni(CO)4 in smaller-scale laboratory reactions, though for historical reasons a number of the fundamental mechanisms discussed in this section are based on Ni(CO)4. 

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