Organometallic compounds acetylene, reactions with

It occurs with the alkyls, aryls or acetylides of metals more electropositive than magnesium, but including Grignard reagents, and is often carried out by adding a solution of the organometallic compound in an inert solvent to a large excess of powdered, solid C02 it is a particularly useful method for the preparation of acetylenic acids. The Kolbe-Schmidt reaction (p. 291) is another example of carbanion carbonation. 

A solulion of CuCl in HCI absorbs carbon monoxide, forming copperil) carbonyl chloride. Cu(CO)Cl H 0. This reaction, which is used In gas analysis, is Indicative of the ability of copper to combine with carbon monoxide. Evidence for a true carbonyl is limited to the observation that if hot carbon monoxide is passed over hot copper, a metallic mirror is produced in the hotter parts of the tube. Other organometallic compounds include Ihe very unstable methyl copper, CHiCu. phenyl copper. C<,H5Cu, and bixchlurucopper acetylene CjHrtCuCIi . 

Fig. 16.17. Mechanism of the carbocupration of acetylene (R = H) or terminal alkynes (R H) with a saturated Gilman cuprate. The unsaturated Gilman cuprate I is obtained via the cuprolithiation product E and the resulting carbolithiation product F in several steps—and stereoselectively. Iodolysis of I leads to the formation of the iodoalkenes J with complete retention of configuration. Note The last step but one in this figure does not only afford I, but again the initial Gilman cuprate A B, too. The latter reenters the reaction chain "at the top" so that in the end the entire saturated (and more reactive) initial cuprate is incorporated into the unsaturated (and less reactive) cuprate (I). - Caution The organometallic compounds depicted here contain two-electron, multi-center bonds. Other than in "normal" cases, i.e., those with two-electron, two-center bonds, the lines cannot be automatically equated with the number of electron pairs. This is why only three electron shift arrows can be used to illustrate the reaction process. The fourth red arrow—in boldface— is not an electron shift arrow, but only indicates the site where the lithium atom binds next.

Catalytic liquid phase semihydrogenation of acetylenes is an important industrial and laboratory reaction, especially in fine chemical synthesis [1]. The use of supported metal catalysts for this selective hydrogenation readily facilitates the separation of organic products from the catalyst. However, liquid phase reactions with supported catalysts tend towards mass transport limitation [2] and, therefore, the support particles should be between 1 and 10 pm in size this avoids transport limitations and separation problems. With support particles of this size high temperature reduction in a flow of H2 gas is very difficult and to avoid this step it is possible to prepare supported metal particles by decomposing organometallic compounds under mild conditions [3-5]. 

Risse and S. Breunig, Transition metal catalyzed vinyl addition polymerizations of norbor nene derivatives with ester groups, Makromol. Chem. 193, 2915 (1992) C. Mehler and M. Risse, Addition polymerization of norbornene catalyzed by palladium(2- -) compounds. A polymerization reaction with rare chain transfer and chain termination, Macromol. 25, 4226 4228 (1992) R.G. Schulz, Polym. Lett. 4, 541 (1966). C. Tanielian, A. Kiennemann, and T. Osparpucu, Influence de differents catalyseurs abase d elements de transition du groupe VIII sur lapol3mierisation du norbor nene, Can. J. Chem. 57, 2022 (1979) A. Sen and T. W. Lai, Catalytic polymerization of acetylenes and olefins by tetrakis(acetonitrile)palladium(II) ditetrafluoroborate, Organometallics 1, 415 (1982) C. Mehler and W. Risse, Pd(II) catalyzed polymerization of norbornene derivatives, Mak romol. Chem. Rapid Commun. 12, 255 (1991). 

The reactivity of metal-silylene complexes is more limited than the reactivity of carbene complexes. The cationic base-stabilized ruthenium-silylene complex in Equation 13.37 does not react with olefins or alkynes to undergo [2-1-2] addition reactions. However, a related complex did undergo [2-1-2] addition reactions with isocyanates, as shown in Equation 13.46. Other reactions of silylene complexes are distinct from those of carbene complexes or those of other conventional organometallic compounds. For example, the reaction of the silylene hydride with an acetylene generates a p-silylvinylarene complex... 

Dicobalt-hexacarbonyl-alkyne complexes are another class of organometallic compounds with good stability imder physiological conditions. Complexation of the alkyne proceeds smoothly under mild conditions by reaction with Co2(CO)g imder loss of two molecules of CO [79]. The applicability of this reaction to peptides was shown by Jaouen and coworkers by the reaction of Co2(CO)g with protected 2-amino-4-hexynoic acid (Aha) and dipeptides thereof (Boc-Phe-Aha-OMe and Ac-Aha-Phe-OMe) [80]. Similarly, Cp2Mo2(CO)4 complexes of these alkynes were obtained. It has been shown that the C-terminal Met" in SP can be replaced by isostere analogs without appreciable loss of physiological activity. The same is true for the C-terminal Met in neurokinin A (NKA), another tachykinin peptide hormone (Scheme 5.16). Alkyne analogs of SP and NKA were obtained by replacement of these methionines with norleucine acetylene residues. Alternatively, Lys in NKA may be replaced by an alkyne derivative which can also be complexed to Co2(CO)g as shown in Scheme 5.16. Complexation with Co2(CO)g proceeds smoothly in about 50% yield for all derivatives [81]. After HPLC purification, these cobalt alkyne peptides were comprehensively characterized spectroscopically. Most notably, they exhibit typical IR absorptions for the metal carbonyl moieties between 2000-2100 cm [3]. Recently, there is renewed interest in Co2(CO)5(alkyne) complexes because of their cytotoxicity [82-84]. 

Transition metal compounds of diverse types undergo reactions with alkynes to yield a large variety of organometallic and organic products. In some cases, simple acetylene complexes are obtained. Often, however, more complex ligands result from insertion or oligomerization reactions. Undoubtedly, the formation of the latter products in most cases proceeds by way of initially formed acetylene complexes, but these are often undetectable. 

Condensation reactions of alkyl halides and carbonyl compounds with organometallic derivatives of acetylene or with acetylene itself are quite useful in the laboratory and in industry. 

Prior to the development of methods for caiTving out the direct reaction of fomialdehyde vdth acetydene or monosubstituted acetylenes (page 237), the only satisfactory procedime for preparing acetylenic alcohols from formaldehyde involved the intennediate preparation of organometallic compounds. Substituted pi Opargyl alcohols are obtained in yields of 70 per cent or better by reaction of monosubstituted acetylenic Grignard compounds with gaseous formaldehyde ... 

The experimental conditions for the syntheses starting from acid chlorides of hydroxamic acids and from nitrile oxides are somewhat different. In the former case the other component of the reaction is organometallic, usually an organomagnesium derivative of an acetylene or, less frequently, a sodium enolate of a /8-diketone. Nitrile oxides condense directly with unsaturated compounds. 

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