Metallative Reppe reaction

Scheme 9.7. Proposed reaction course for the metalative Reppe reaction.

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. 

Titanacydopentadiene 81 can also react with sulfonitrile 82 to lead to the pyri-dyltitanium 83before aqueous workup (Scheme 12.55) [73bj. The reaction, as the one described in Scheme 12.54 with alkynyl sulfone instead of sulfonitrile, proceeds via a metallative Reppe reaction. 

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

A. Mullen, Carbonylation Catalyzed by Metal Carbonyls-Reppe-Reactions, in J. Falbe, New Synthesis... 

The syntheses of carboxylic acids and esters are widely studied processes. Since the first examples of carboxylation in the presence of metal carbonyls were reported by Reppe, these reactions are sometimes referred to as the Reppe reactions. In his pioneering work125-127 stoichiometric or catalytic amounts of [Ni(CO)4] and ethylene or acetylene were reacted in the presence of water or alcohols to form saturated and unsaturated acids and esters. Commercial processes are practiced in the manufacture of propionic acid, acrylic acid and acrylates (see Section 7.2.4). 

Metal-catalyzed reactions of CO with organic molecules have been under investigation since the late 1930s and early 1940s, when Roelen (/) discovered the hydroformylation reaction and Reppe (2) the acrylic acid synthesis and other related carbonylation reactions. These early studies of the carbonyla-tions of unsaturated hydrocarbons led to extremely useful syntheses of a variety of oxygenated products. Some of the reactions, however, suffered from the serious problem that they produced isomeric mixtures of products. For example, the cobalt-catalyzed hydroformylation of propylene gave mixtures of n-butyraldehyde and isobutyraldehyde. 

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-... 

Walter Reppe (1892-1969) was the research director of Badische Anilin- Sodafabrik (BASF) at Ludwigshafen, Germany. His research included metal-catalyzed reactions of acetylene (1938) and of carbon monoxide (1939) (Section 2.1.2.2). High-pressure catalytic acetylene chemistry is nowadays named after him. He also discovered the metal carbonyl-catalyzed cyclooligomerization of acetylene to yield styrene, benzene, and cyclooctatetraene (1948) [10, 77]. 

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>. 

In Reppe reactions organic substrates are reacted with carbon monoxide in the presence of a metal carbonyl catalyst (or their precursors). Industrial chemicals such as acetic acid, methyl formate, formamide, di-methylformamide, formic acid, methyl methacrylate, and the emerging nonphosgene intermediates for isocyanates and dimethyl carbonate for polycarbonates are manufactured via Reppe reactions. 

Reppe reactions are the formation of carboxylic acids from olefins by reaction with carbon monoxide and water utilizing a metal carbonyl catalyst. The same reactants combine to form carboxylic acids in the presence of an acid catalyst. These acid catalyzed reactions are known as Koch Carbonyla-tion reactions. Commercial processes utilizing this route are the DuPont process for glycolic acid from carbon monoxide and formaldehyde and the carbonylation of olefins to neo acids practiced by Exxon and Shell. 

This is actually a crucial step in the carboxylation of olefins (Reppe reaction) with transition metal carbonyl catalysts Apart from these extreme cases, however, metal-carbon a-bonds as well as metal-hydride bonds are best described as moderately polarized covalent bonds, with negative charge on the carbon or hydrogen respectively ... 

A. Mullen, Carbonylations catalyzed by metal carbonyls-Reppe reactions, in New Syntheses with Carbon Monoxide, J. Falbe, ed., Springer-Verlag, Berlin/Heidelberg/New York(1980),pp. 243-308. 

J. W. Copenhaver, M. H. Bigelow, Acetylene and Carbon Monoxide Chemistry (New York, 1949) p 246 W. Reppe, Acetylene Chemistry, U.S. Dept. Commerce PB 18852-S (1949) Neue Entwicklungen auf dem Gebiet des Acetylens und Kohlenoxyds (Berlin 1949) H. Kroper, Houben-Weyl 4/II, 413-422 (1955) D. W. F. Hardie, Acetylene, Manufacture and Uses (New York, 1965) p 67 L. F. Fieser, M. Fieser, Reagents for Organic Synthesis (New York, 1967) pp 61, 183, 185, 190, 519, 720, 722, 723. Review of carbonylations A. Mullen, Carbonylations Catalyzed by Metal Carbonyls-Reppe Reactions in New Syntheses with Carbon Monoxide, J. Falbe, Ed. (Springer-Verlag, Berlin, 1980) pp 243-308. Mechanistic study of cyclooctatetraene synthesis R. E. 

Halide-promoted heterogeneous catalysts for carbonylation are analogues to homogeneous carbonylation catalyzed by metal carbonyls, that is, the Reppe reaction (11). The first step of the Reppe reaction involves the oxidative addition of alkyl halide promoter to carbonyl metal, for example, Rh(I) complex (Fig. 1). This step is followed by methyl migration, bonding of carbon monoxide to give a coor-dinatively saturated Rh(III) complex, and subsequent decomposition of this complex in the presence of methanol to yield a carbonylated product and regenerate the promoter and the catalyst. 

Reppe [83] developed the Reppe reaction of carbonylation, vinylation, ethy-nylation and cyclization by reaction of acetylene with carbon monoxide, water, alcohols, amines, aldehydes and ketones, etc. In 1952, the reaction of olefins in place of acetylene, in the presence of metal carbonyl catalysts, produces alcohols. This process is called the new Reppe process, and butanol has been industrially produced by this process since around 1960. 

W. Reppe starts working on the transition metal catalyzed reaction of acetylene. Reppe reactions [83]. 

Metal Carbonyl Catalyzed Carbonylation Reppe Reactions... 

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