Silver alkynes

Silver belongs to the late transition metals and, like gold, favors coordination to C=C triple bonds. A lot of silver-containing organometallic complexes, where silver-alkyne interactions assist the assembly of the complexes, are known. None of these complexes, however, was applied to efficient carbon-carbon bond formation in organic synthesis. 

The alkynes are bonded in essentially the same way as, but less firmly than, the olefins (see Section III,R). In the hex-3-yne series, substitution of an a-hydrogen atom by a methyl group reduces the argentation constant (a measure of the silver-alkyne bond strength) by a factor of roughly 1 /3 this influence of methyl substitution on complex formation is opposite to that observed in the platinum(II) complexes (see Section IV,J). 

Padwa et al.67 have used 3-oxo-lV-propargylamides and esters to build furopyrro-lidinones and furodihydrofuranones via a silver alkyne activation (Schemes 5.16 and 5.17). 

AgN02, MeOH, H2O, 24°, cool to 0°, add KCN, then HCl, 96% yield." The reduced electron density of the propargylic alkyne directs the electrophilic silver to the other alkyne and activates it for cleavage. 

The acidic hydrogen in terminal alkynes can readily be replaced by silver, in a diagnostic test. [(Me3P)Ag(C=CPh)] has a polymeric structure while [(Ph3P)Ag(C=CPh)]4 is made of [Ag(PPh3)2]+ and [Ag(C=CPh)2] fragments linked so that the silver atoms form a square [147]. 

Terminal alkynes can be converted readily into alkynylsilanes by reaction of the corresponding alkyne anion or its metalloid equivalent with a suitable chlorosilane (/). The reverse reaction, that of liberation of the alkyne, is quite facile, being effected by several reagent combinations, including hydroxide ion, methanolysis, fluoride anion, silver(i) followed by cyanide anion, and methyl lithium-lithium bromide (2). 

SN displacement reactions, 27-9 a-Selenocyclohexanones, 77 Senecioyl chloride, 33 Silmagnesiation, platinum-catalysed, 8 Silametallation of terminal alkynes, 7-9 Silver acetylide, 49 Silver trifluoroacctate, 42,127 Silyl cuprates, 7... 

The fact that pentacarbonyl carbene complexes react with enynes in a chemo-selective and regiospecific way at the alkyne functionality was successfully applied in the total synthesis of vitamins of the Kj and K2 series [58]. Oxidation of the intermediate tricarbonyl(dihydrovitamin K) chromium complexes with silver oxide afforded the desired naphthoquinone-based vitamin K compounds 65. Compared to customary strategies, the benzannulation reaction proved to be superior as it avoids conditions favouring (E)/(Z)-isomerisation within the allylic side chain. The basic representative vitamin K3 (menadione) 66 was synthesised in a straightforward manner from pentacarbonyl carbene complex 1 and propyne (Scheme 38). 

Fig. 2.12 Silver, gold and platinum complexes with monodentate NHC ligands as catalysts for the diboration of alkenes and alkynes...

Fedchenfeld, H. and Weaver, M.J. (1989) Binding of alkynes to silver, gold, and underpotential deposited silver electrodes as deduced by surface-enhanced Raman spectroscopy. The Journal of Physical Chemistry, 93, 4276—4282. 

When acetylene and real alkynes are in contact with copper, silver and transition metals, they form acetylides and analogues that are explosive, from ambient temperature upwards for acetylides. For instance, acetylene that was accidentally in the presence of electrical wires whose copper was bare led to a detonation. 

Recently, the three-component couplings of a-oxyaldehydes, alkynes, and amines in water were investigated by using gold, silver, and copper... 

Mercury, Silver perchlorate See Silver perchlorate Alkynes, etc. 

The bicyclo[6.1.0]nonatriene 46 is transformed to the 8,8-dihydroindene on treatment with a catalytic amount of [Rh(CO)2Cl]2 [24], The stereoselectivity depends on the reaction temperature. [5 + 2]cycloaddition of vinylcyclo-propanes 47 with alkynes is catalyzed by RhCl(PPh3)3 in the presence of silver triflate to give seven-membered rings 48 [25]. (Scheme 17 and 18)... 

Similar intramolecular hydroarylations of alkynes and alkenes, which obviate the need for a halide or triflate group on the aryl ring, are now well established. Sames group screened over 60 potential catalysts and over 200 reaction conditions, and found that Ru(m) complexes and a silver salt were optimal. This process appears to tolerate steric hindrance and halogen substrates on the arene (Equations (175)—(177)). The reaction is thought to involve alkene-Ru coordination and an electrophilic pathway rather than a formal C-H activation of the arene followed by alkene hydrometallation, and advocates the necessary cautious approach to labeling this reaction as a C-H functionalization... 

This system also worked well in ionic liquids.518 Li etal. found silver-phosphine complexes to promote aldehyde-alkyne coupling in water. When triphenylphosphinesilver chloride was used as a catalyst in water, the only detected product was the aldehyde addition product instead of the adduct derived from imine (Scheme 111).519... 

Grigg extended this alkyne cyclization to trapping with stannanes to give 3-exo-dienes [347], alkynes to afford tetracycles [338, 348], and alkenes leading to cyclopropanes [349], an example of which is illustrated. In his studies Grigg and co-workers have found that thallium and silver salts suppress direct capture of these palladium intermediates prior to capture [350]. 

Investigations by Vermeer and co-workers have shown that 3-substituted allenyl methyl thioethers 309 can be prepared by regioselective addition of an alkyl silver species to the terminal C=C bond of enyne sulfides 308 (Scheme 8.83) [172], Remarkably, this method can also be applied to the preparation of several allenyl-phosphines starting from the corresponding phosphorus-substituted alkynes. 

A Ag/Pd-cathode hydrogenates 2-butyne-1,4-diol and acetylene dicarboxylic acid exclusively to the cis-olefin [323]. Similar results were obtained at a Cu net covered with spongy silver [324]. With dimethyl butynedioate the cis/trans ratio of the product dimethyl butenedioate on a Pd black cathode decreased with increasing pH both in electrolytic and catalytic hydrogenation [325]. On the other side at a Hg cathode a trans addition to alkynes occurs [326]. In methy-lamine/liCl, dialkylacetylenes are reduced to trans-olefins. Nonconjugated aromatic internal acetylenes are selectively reduced to aromatic trans-olefins [327]. 

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