Acetylide dianion

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.,... 

G.-C. Guo, G-D. Zhou and T. C. W. Mak, Structural variation in novel double salts of silver acetylide with silver nitrate fully encapsulated acetylide dianion in different polyhedral silver cages. J. Am. Chem. Soc. 121, 3136—4-1 (1999). 

By analogy to aurophilicity, argentophilicity has been demonstrated to exist in silver cluster complexes. In the crystal structures of a variety of silver double and multiple salts containing a fully encapsulated acetylide dianion C (IUPAC name acetylenediide) in different polyhedral silver cages (see Fig. 14.3.11), there exist many Ag- -Ag contacts shorter than twice the van der Waals radius of silver (2 x 170 = 340 pm). Further details are given in Chapter 20. 

Similar reaction in an acetylene atmosphere gives the neutral dimers [(oepg)Ln]2 [(/c-C2)(/x-Na)4]. X-ray crystal structure analysis of the neodymium derivative (Figure 19b) shows the acetylide dianion end on bonded to the two metal centers. 

Wang Q-M, Mak TCW (2003) Assembly of discrete, one-, two-, and three-dimensional silver(I) supramo-leculttf complexes containing encapsulated acetylide dianion with nitrogen-donor spacers. Inorg Chem 42 1637-1643... 

The addition of acetylides to oxiranes yields 3-alkyn-l-ols (F. Sondheimer, 1950 M.A. Adams, 1979 R.M. Carlson, 1974, 1975 K. Mori, 1976). The acetylene dianion and two a -synthons can also be used. 1,4-Diols with a carbon triple bond in between are formed from two carbonyl compounds (V. Jager, 1977, see p. 52). The triple bond can be either converted to a CIS- or frans-configurated double bond (M.A. Adams, 1979) or be hydrated to give a ketone (see pp. 52, 57, 131). 

Propargyl dianion (QF I ). This anion can be prepared by dilithiation of allene with BuLi in 1 1 ether/hexane. Use of THF (- 50°) or BuLi/TMEDA results in a mixture of propargylide and allenyl anions. The anion couples readily with alkyl and allyl halides to give terminal alkynes. The intermediate lithium acetylide can also react with various electrophiles.3 Example ... 

Two major developments in the preparation of bimetallic allenylidene complexes involve (i) metal fragment condensation of a monomeric allenylidene complex with a lightly stabilized metal fragment and (ii) deoxygenation of the dianionic acetylide intermediates, [M2(CO)9 C=C-C( Bu2)0 ]2-, with COCI2. 

An addition which completely destroys the triple bond — but at the same time illustrates the synthetic usefulness of 100 - is demonstrated by the trapping of its etherate complex (see above) with dimethylamine under in-situ conditions the glycinamide 147 is isolated in 50% yield [92] according to Eq. (28). Formally, 100 has behaved in this transformation as an equivalent of the synthon 148 in the same sense as disodium acetylide (149) is synthetically equivalent to the dianion ISO. 

In addition, the linear approach was represented by sequential dithiane coupling [21] of the epoxides for the necessary fragments to either side of the ketone function at C21. Another approach uses microbial reduction (baker s yeast) to set the stereocenter at C25 before elaboration of that fragment into a methyl acetylenic ketone [89]. This acetylenic ketone was condensed with the aldehyde partner representing Cl5-19 to give the aldol adduct which was cyclized in acid to afford a precursor similar to those obtained from acetylide addition to lactone B 3. Yet another linear assembly pathway involves the alkylation of the portion containing C23-27 of 22,23-dihydroavermectin B to the dianion of 2,4-pentanedione followed by another condensation to 3-be-nzyloxypropanal [108]. Subsequent acidic cyclization and standard chemistry provided the thermodynamic spiroketal. 

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