Metals alkali, acetylides

The last isomerization is remarkable in that the triple bond can shift through a long carbon chain to the terminus, where it is fixed as the (kinetically) stable acetylide. The reagent is a solution of potassium diami no-propyl amide in 1,3-di-aminopropane. In some cases alkali metal amides in liquid ammonia car also bring about "contra-thermodynamic" isomerizations the reactions are successful only if the triple bond is in the 2-position. 

Ethynylation of the totally synthetic racemic 18-methyl-17-ketone (63) with acetylene and potassium t-butoxide in t-butanol-toluene or with alkali metal acetylide in liquid ammonia gives a low yield of rac-18-methyl-17a-ethynyl-3-methoxyestra-l,3,5(10)-trien-17/ -ol (64). 

The largest industrial use of LiC2H is in the production of vitamin A, where it effects ethynyl-ation of methyl vinyl ketone to produce a key tertiary carbinol intermediate. The acetylides and dicarbides of the other alkali metals are prepared similarly. It is not always necessary to prepare this type of compound in liquid ammonia and, indeed, further substitution to give the bright red perlithiopropyne Li4C3 can be effected in hexane under reflux ... 

Alkali metal acetylides M2C2, MCCH and MCCR can readily be prepared by passing C2H2 or C2HR into solutions of the alkali metal in liquid NH3, and these can be used to synthesize a wide range of transition-element... 

Acetylenes are sufficiently acidic to react with sodium metal to generate acetylides, useful nucleophiles in the formation of carbon-carbon bonds. The reaction is classically carried out in liquid ammonia, which is a good solvent for alkali metals but which is troublesome to handle. Two convenient modifications of the acetylide generation reaction overcome this difficulty and are discussed below along with the classical method. 

Triple bonds can also be selectively reduced to double bonds with DIBAL-H, " with activated zinc (see 12-36), with hydrogen and Bi2B-borohydride exchange resin, ° or (internal triple bonds only) with alkali metals (Na, Li) in liquid ammonia or a low-molecular-weight amine.Terminal alkynes are not reduced by the Na—NH3 procedure because they are converted to acetylide ions under these conditions. However, terminal triple bonds can be reduced to double bonds by the... 

Because of the slightly acidic nature of the sp C-H bonds, the reaction of metal acetylides with various electrophiles is one of the most general strategies in organic transformations.1 Traditionally, such reactions are carried out by using alkali metal acetylides which are air and water sensitive. On the other hand, there is much interest in developing transition-metal catalyzed terminal alkyne reactions involving soft and more stable C-M bonds as reaction intermediates, because many such reactions can tolerate water. 

See ALKALI-METAL DERIVATIVES OF HYDROCARBONS See Other METAL ACETYLIDES... 

The mono- and di-alkali metal acetylides, copper acetylides, iron, uranium and zirconium carbides all ignite in chlorine, the former often at ambient temperature. See Caesium acetylide Halogens Dicopper(I) acetylide Halogens Iron carbide Halogens... 

Ternary acetylides of the composition M[M (C2)J, M = alkali metal, M = transition metal, are solid-state compounds, which depending upon their composition may exhibit either insulator or semi-conductor behavior. 

Arbuzova, S.N., Brandsma, L., Gusarova, N.K., Nikitin, M.V., and Trofimov, B.A., Reaction of alkali metal acetylides with red phosphorus, Mendeleev Commun., 66, 2000. 

Alkali metal alkyls, particularly n-butyl lithium, are the most frequently used reagents to form metallated intermediates.246 247 In certain cases (di- and triphenyl-methane, acetylene and 1-alkynes, cyclopentadiene) alkali metals can be directly applied. Grignard reagents are used to form magnesium acetylides and cyclopenta-dienyl complexes.248 Organolithium compounds with a bulky alkoxide, most notably M-BuLi-ferf-BuOK in THF/hexane mixture, known as the Lochmann-Schlosser reagent or LICKOR superbase, are more active and versatile reagents.249-252... 

Nonempirical quantum-chemical calculations of acetylide molecules support the ready displacement of alkali metal cations to the bridge position (87IZV2777 88IZV1335, 88IZV1339). This naturally leads to the conclusion that the polarization and deformation of the ir-electronic shell of acetylene must depend on the atomic number of the cation attached to the acetylene anion. However, the acetylene activation in the reaction with ketoximes via acetylides suggests nucleophile attack at a carbanionlike complex, which is of course a week point of the hypothesis. Nevertheless, the electrophilic assistance from the alkali metal cation (Na+) to the... 

Several of the mono- and di-alkali metal acetylides and copper acetylides ignite at ambient temperature or on slight warming, with either liquid or vapour. The alkaline earth, iron, uranium and zirconium carbides ignite in the vapour on heating. 

Acetylene is a Brpnsted acid (pA), 25). Its chemistry is associated with its triple-bond character and the labile hydrogen atoms. It can easily lose one proton to form the acetylide monoanion HC=C-(IUPAC name acetylenide) or release two to give the acetylide dianion C=C (C22-, IUPAC name acetylenedi-ide). The acetylenide H-C=C and substituted derivatives R-C=C- form organometallic compounds with the alkali metals. In these compounds, the interactions of the n orbitals of the C=C fragment with metal orbitals may lead to many structural types, e.g.,... 

Alkali metal acetylides obtained from acetylenes and sodium in liquid ammonia1 react with tellurium powder to yield sodium ethynetellurolates that are easily alkylated with alkyl halides. 

Palladium and platinum. Reactions of alkali metal acetylides, M2C2 (M = Na, K) with Pd or Pt (550 °C, in argon) gave black M2(Pd/Pt)C2,... 

More recently, reactions of alkali metal acetylides, HC2M (M = Li-Cs), with Aul in liquid NH3 and subsequent heating of the solid product in pyridine (Li-K) or in vacuum (Rb, Cs) gave pale yellow M2AuC2.184,185 They contain [Au C C chains, which interact with the alkali metal cations via the C2 units, and are generally similar to the analogous silver compounds.204... 

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