Silver acetylides reactivity

On the basis of the above-mentioned calculations it seems that coordination chemistry is a viable alternative to stabilize this heterocumulene. However, the experimental access to metal complexes containing the tricarbon monoxide ligand remains a challenge. Thus, to date, the coordination chemistry of C3O is confined to [Cr(=C=C=C=0)(C0)s] (89), obtained by treatment of [n-Bu4N] [CrI(CO)5] with the silver acetylide derived of sodium propiolate in the presence of Ag" (Scheme 28) [105]. Reaction of the presumed Tt-alkyne intermediate complex 88 with thiophosgene generates the heterocumulene 89. Neither structural nor reactivity studies were undertaken with this complex. 

The use of silver acetylides to effect useful synthetic transformations has been perhaps more widely reported than the use of any other organosilver compound, as previously reviewed by Pale et al.81 and Sladkov et al.82 Their use, however, in comparison to that of other metal acetylides (Na, Cu, Li), has perhaps been limited by their relatively low reactivity and/or solubility. The silver acetylides are, however, generally comparatively more stable than the more commonly used metal acetylides, as they can be... 

Most silver acetylides are highly insoluble in standard organic solvents because of the formation of coordination polymers, and this characteristic can cause difficulties with characterization and limit reactivity. This can be overcome by the addition of coordinating donor molecules such as triphenylphosphine that perturb the formation of the polymeric structure.91 In the experience of the authors, however, the addition of such ligands can decrease reactivity. 

The poorly nucleophilic silver acetylides are generally not considered reactive enough to add directly to unactivated carbonyl groups, although a number of... 

Silver acetylides participate in the zirconium-catalyzed nucleophilic addition to carbonyls in the absence of base to produce functionalized y - h yd ro x y - a, [3 - ac e t y I e n i c esters.106 Although this reaction involves a transmetallation rather than a direct addition of a silver acetylide to an unactivated aldehyde, its particular attraction of is the avoidance of strong bases to produce the reactive zirconium species (Scheme 1.43). 

Although catalytic amounts of Ag20 have been found to promote the palladium-catalyzed coupling of aryl boronic acids and terminal alkynes, the authors in this case do not attribute the desired reactivity to the formation, and subsequent transmetalla-tion, of a silver acetylide. Rather, it is proposed that the Ag20 activates the alkynylpalladium complex to allow transmetallation from the boronic acid, and that any competing formation of the silver acetylide results in a homocoupling of the alkynes (Scheme 1.55).123... 

Since such reactivity has recently been reviewed,8 only a few examples are reported here. Acyl halides or epoxides can be alkynylated with preformed silver acetylides. Such processes have been applied to the total synthesis of the antibiotic macrolide (+ )-methynolide,96 and in the total synthesis of the antitumor agent FR901464 isolated from a Pseudomonas species (Scheme 10.62).97... 

Interestingly, the first catalytic version of such nucleophilic additions of alkynyl silvers to aldehydes has been described." Indeed, silver chloride in the presence of tricyclohexylphosphine and mild bases such as ethyldiisopropylamine catalyzed the addition of terminal alkynes to aldehydes in good to high yields (Table 10.5). The reaction proved to be almost insensitive to electronic effects however, alkyla-cetylenes were less reactive than arylacetylenes. The solvent had a dramatic effect on the reaction course. Control experiments with preformed phenylethynylsilver showed that both phosphine and water activated the silver acetylide. 

Vinyliodonium ions, 35 and 36, are hypervalent iodine species in which one or two alkenyl ligands are bound to a positively charged iodine(III) atom. Although they are reactive with nucleophilic reagents, they are less labile than alkynyliodonium ions, and stable halide salts of vinyliodonium ions can be prepared. The first vinyliodonium compounds [i.e. (a, / -dichlorovinyl)iodonium salts] were synthesized by the treatment of silver acetylide-silver chloride complexes with (dichloroiodo)arenes or l-(dichloroiodo)-2-chloroethene in the presence of water (equation 152). The early work was summarized by Willgerodt in 1914115. This is, of course, a limited and rather impractical synthetic method, and some time elapsed before the chemistry of vinyliodonium salts was developed. Contemporary synthetic approaches to vinyliodonium compounds include the treatment of (1) vinylsilanes and vinylstannanes with 23-iodanes, (2) terminal alkynes with x3-iodanes, (3) alkynyliodonium salts with nucleophilic reagents and (4) alkynyliodonium salts with dienes. 

Reactivity and Incompatibility Contact of metallic silver and silver compounds with acetylene may cause formation of silver acetylide, which is a shock-sensitive explosive. Contact with ammonia may cause formation of compounds that are explosive when dry. Contact with strong hydrogen peroxide solutions causes violent decomposition with the formation of... 

Taki, K. Reactive species in the explosion of silver acetylide I. Reaction with saturated hydrocarbons. Bull. (5hem. Soc. Jpn. 42, 2906-2911 (1969)... 

Copper(II), iron(III), and other silver(I) salts displayed no reactivity, apart from AgqO, which produced inferior yields (63%). The reaction was unaffected by acidic or basic additives, and moiecuiar oxygen was inoperabie as a terminal oxidant consequentiy, 2.0 equiv of Ag2C03 was required for optimal yields. Various 2-aminopyridines were viabie, exhibiting minimal substituent effects. Additionaiiy, 1-aminoisoquinoiine and 2-aminoquinoline couid be cyciized however, imidazoie dispiayed diminished reactivity (40% yieid). A diversity of terminai aryi alkynes could also be employed. A silver acetylide species was postulated to serve as a key intermediate. Notably, zolimidine, a marketed antiulcer drug, could be efficiently obtained via this process (eq 36). 

Acetylene is a reactive material that poses a fire and explosion hazard. Its lower and upper explosive limits in air are 2.5% and 93%, respectively. Acetylene reacts with active metals (e.g., copper, silver, and mercury) to form explosive acetylide compounds. Acetylene manufactured from calcium carbide can contain impurities such as phosphine and arsine that are responsible for the ethereal to garlic-like odor of commercial acetylene and pose a greater human... 

Incompatibilities and Reactivities Zinc oxygen other oxidizing agents such as halogens [Note Forms explosive acetylide compounds with copper, mercury, silver brasses (containing more than 66% copper).] ... 

Reactivity and Incompatibility Acetylene forms highly unstable acetyUdes with many metals, including copper, brass, mercury, potassium, silver, and gold. The dry acetylides are sensitive, powerful explosives. Acetylene may react violently with fluorine and other halogens (chlorine, bromine, iodine) and forms explosive compounds on contact with nitric acid. 

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