Alkynyl silvers

Rueping has recently reported an interesting alknylation reaction of a-imino esters employing both phosphoric acid Ip and AgOAc as orthogonal cocatalysts [35]. As seen in the catalytic cycle in Scheme 5.21, generation of chiral iminium ion pair I nucleophilic and alkynyl-silver species II proceeds simultaneously. Subsequent nucelophilic addition completes both parallel cycles [36]. 

The zinc-cyanide complexes are on the interface of organic and inorganic chemistry. We include them here because of their Zn—C bond. (Perhaps this will encourage thermo-chemical investigations on the isoelectronic alkynylzinc species, much as there has been interest in both cyano and alkynyl silver-containing species. ) The species Zn(CN)2, Zn(CN)3 and Zn(CN)4 have all been thermochemically characterized in aqneons soln-tion by thermometric titration. The enthalpy of reaction values kJmoL are shown for reactions 9-11. 

It has been demonstrated by 1H, 13C, and 109Ag NMR that a 7r-alkyne-Ag complex and then an alkynyl silver are formed in situ from alkyne and silver salt under conditions related to those used for Ag-catalysed alkynylation or for Ag/Pd-catalysed sp-sp2 cross-coupling reactions.142 These observations have prompted a rationale of the mechanisms of these reactions. 

The title reactions refer to alkylation reactions using alkynyl silvers as reagents. It seems that no catalytic version has so far been reported, and only a few examples of stoichiometric reactions are known.8... 

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. 

Further investigations including 109Ag NMR confirmed the in situ formation of alkynyl silver through jt complexation and proton abstraction.117 They also revealed that the best palladium catalyst, namely, palladium tetrakis(triphenylphosphine), played a key role, in that a phosphine liberated by decoordination ended up on the alkynyl silver, stabilizing it and rendering it more soluble.118 The resulting alkynyl silver then entered the palladium catalytic cycle at the transmetallation step (See section 10.6.2).105... 

Silver(I) Inflate and copper(I) triflate can be applied as catalysts A representative example is the preparation of alkynyl tosylates by the catalytic decomposition of alkynyl lodonium salts in the presence of these salts [727] (equation 67)... 

Syntheses and luminescence studies of mixed-metal gold(I)-copper(l) and -silver (I) alkynyl complexes. The tuming-on of emission upon d metal ion encapsulation. Dalton Transactions, 1830-1835. 

Synthesis and Properties of Alkynyl and Related Complexes of Silver 226... 

Silver(m) Complexes with Alkyl, Alkynyl, and Cyano Ligands 241... 

Although reports on silver(i) cr-alkynyl complexes have appeared for more than a century, the number of examples was still very limited prior to the past decade, and many of them were referred to as insoluble homoleptic polymeric [Ag(C=CR)]oo. Molecular alkynylsilver(i) complexes were often heteroleptic in nature and were achieved commonly through the stabilization by an extra coordination with strong cr-donor ligands such as amines, phosphines, and arsines. 

In addition to the well-known luminescent Re(NAN)(GO)3 moieties, the electrochemically active ferrocenyl groups were employed as building blocks for the construction of polynuclear silver(i) alkynyl complexes. Yip reported the synthesis, structural characterization, and electrochemistry of a tetranuclear complex, [Ag3(dppm)3(C=CFc)(OTf)]OTf 96 (Figure 43), with the Ag3(dppm)3 skeletal unit being capped by a ferrocenylethynyl ligand on one side and an OTP anion on the other, all in a /Z3-771-bonding mode.170... 

Figure 42 Decanuclear silver(i)—rhenium(i) alkynyl complexes 95a-d.

A wide variety of organoalkynyl derivatives of cotarnine hydrochloride, a cyclic iminium salt with rich biological activity, were prepared from the direct alkynylation of cotarnine hydrochloride using silver(l) alkynyls.180 Substituted enynes were prepared from the coupling reactions of silver alkynyls with the palladium allyl intermediates, which was... 

Stable organosilver(m) complexes having a general formula [Ag(GF3) X(4 )] with organic groups such as cyano, halo, methyl, alkynyl, difluoromethyl, and perfluoroethyl, replacing the trifluoromethyl groups in the [Ag(CF3)4] anion, as well as [Ag(CF3)3(NCMe)], were prepared. For instance, the air and moisture sensitive silver(i)... 

Alkynyl halides are possible monomers for the cross-coupling polymerization, in which boronic acids are used as the organometallic counterparts. For example, bifunctional boronic acid 46 is allowed to react with l,4-di(bromoethy-nyl)benzene 138 to afford the corresponding PAE 139 as shown in Equation (64). Polymerization proceeds at room temperature in toluene in the presence of silver(i) oxide as an activator of the boron reagent. The polymer 139 is obtained in 30-50% yield showing color of red-brown to deep red-brown and slight solubility in toluene (<0.1 wt.%). The molecular weight (Mr of 139 was 1700-4300 (PDI = 1.3-3.6). 

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