Silver complexes acetylene

Activation of the acetylene by coordination of the triple bond to the silver cation enables a 5-endo-dig cydization via nucleophilic attack of the amine [14]. Protonation of the resulting vinyl silver complex leads to an iminium ion. Subsequent p-hydride elimination affords metallic silver and a pyrrylium ion which aromatizes by proton loss to the pyrrole. For trimethylsilyl-substituted homopropargylamines (R = SiMes), the resulting pyrrole (R = SiMe3) undergoes protodesilylation to the 1,2-disubstituted pyrrole. 

Trani-allylstannylation is possible with ZrC as a Lewis acid catalyst, reported by Yamamoto and coworkers, also in 1996 (Scheme 5.7.4). Varions terminal alkynes such as aryl-, alkyl-, alkenyl-, or non-substituted acetylenes undergo the reaction with non- or methyl-substituted allylstannanes. Recently, silver complexes were also found to be effective as catalysts for the intra-molecular allylstannylation of alkynes (Scheme 5.7.5). The silver complex is considered to activate the triple bond, giving a cyclo-propylmethylidene or an alkenyl complex as an intermediate. Similar intra-molecular allylstannylations, but with yn-selectivity are known to proceed in the presence of a Pd(0) or an InCls catalyst. 

Acetylene-copper complexes are polymeric in nature, and little is known concerning acetylene-silver complexes. Some unstable solid complexes are known, and in solution they are less stable than olefin complexes 115). 

The K value for the silver complex of an acetylene, hex-3-yne, as determined by the distribution method 14>, was found to be 19.1, i.e. smaller than those of alkenes such as the pentenes and cyclohexene, but greater than those of aromatic hydrocarbons 1S). A later study of silver-acetylene complexes 16> using the more rapid solubility technique of Andrews and Keefer 1S> gave rise to quasi thermodynamic equilibrium constants , Ka (as opposed to K) for various methyl substituted hex-3-ynes and hept-2-yne. There was good agreement for the K values for hex-3-yne for the two different methods in each case, replacement of an a-hydrogen atom by a methyl group caused a decrease in the value of Ka, similar to that observed in alkenes. Values of AH approximated to 19-21 kJ mole-1. 

Temkin and co-workers have investigated the thermodynamic properties of the soluble complexes of unsaturated hydrocarbons with various metal salts with particular reference to their role in catalytic reactions. Using a potentio-metric technique, they were able to calculate the thermodynamic data shown in Table 6 for the silver(I)-acetylene complexes 30) and the silver(I)-ethylene complex 31). The results obtained for acetylene have been related to the low activity of silver salts as catalysts for the hydration of acetylene. For the sil-ver(I)-ethylene complex, the relationship between the ionic concentrations and... 

The silver salts of acetylene, which are suspected to be silver complexes (Fig. 6-11), are usually insoluble and are utilized in purification or separation. 

Silver fluoborate, reaction with ethyl bromide in ether, 46, 114 Silver nitrate, complexing with phenyl-acetylene, 46, 40 Silver oxide, 46, 83 Silver thiocyanate, 45, 71 Sodium amide, in alkylation of ethyl phenylacetate w ith (2-bromo-ethyl)benzene, 47, 72 in condensation of 2,4-pentanedione and 1 bromobutane to give 2,4-nonanedione, 47, 92 Sodium 2 ammobenzenesulfinate, from reduction of 2 mtrobenzenesul-finic acid, 47, 5... 

It is interesting to note that the C-C triple bond character for the acetylenediide inside the silver(l) cages is retained in most of the examples due to the close resemblance of their C=C bond lengths ( 1.09-1.28 A) with that observed in free acetylene (1.205 A).212 The Ag-C bond distances, on the other hand, span a fairly wide range ( 2.01-3.53 A) due to the presence of both a- and 7r-bonding interactions in these systems. The observation of short Ag-Ag contacts of 2.71-3.37A, compared to that in silver metal (2.89 A)213 and the sum of van der Waals radii for silver ( 3.4 A), 1 was suggestive of weak argentophilic interactions associated with these complexes. 

Silver fluoborate, reaction with ethyl bromide in ether, 46, 114 Silver nitrate, complexing with phenyl-acetylene, 46, 40 Silver oxide, 46, 83 Silver thiocyanate, 46, 71 Sodio-2-formyl-6-methylcyclohexanone, 48,41... 

Catalytic forms of copper, mercury and silver acetylides, supported on alumina, carbon or silica and used for polymerisation of alkanes, are relatively stable [3], In contact with acetylene, silver and mercury salts will also give explosive acetylides, the mercury derivatives being complex [4], Many of the metal acetylides react violently with oxidants. Impact sensitivities of the dry copper derivatives of acetylene, buten-3-yne and l,3-hexadien-5-yne were determined as 2.4, 2.4 and 4.0 kg m, respectively. The copper derivative of a polyacetylene mixture generated by low-temperature polymerisation of acetylene detonated under 1.2 kg m impact. Sensitivities were much lower for the moist compounds [5], Explosive copper and silver derivatives give non-explosive complexes with trimethyl-, tributyl- or triphenyl-phosphine [6], Formation of silver acetylide on silver-containing solders needs higher acetylene and ammonia concentrations than for formation of copper acetylide. Acetylides are always formed on brass and copper or on silver-containing solders in an atmosphere of acetylene derived from calcium carbide (and which contains traces of phosphine). Silver acetylide is a more efficient explosion initiator than copper acetylide [7],... 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

The ease with which olefins form complexes with metals naturally led to investigation of acetylenes as ligands but until recent years only a few ill-defined, unstable acetylene complexes of copper and silver were known. Now complexes of acetylenes with metals of the chromium, manganese, iron, cobalt, nickel, and copper subgroups are known. These complexes fall naturally into two classes—those in which the structure of the acetylene is essentially retained and those in which the acetylene is changed into another ligand during complex formation. Complexes of the first class are discussed here and the second class is discussed in Section VI. 

Di silver Oxide 4 Acetylene 4 Disllver Chromate (Complex), AgaO 4 CaHa 4 AgaCi04. Or-red crysts, expl ca 157°. Can be prepd from acetylene and a boiling soln of silver bichromate ... 

Acetylenic oxy-Cope rearrangement (12, 51). The oxy-Cope rearrangement of 5-hexen-l-yn-3-ols is accelerated in refluxing N-methyl-2-pyrrolidone (9, 316), but the required temperature (165°) can result in rearranged products. The rearrangement can proceed at 20-60° in the presence of silver trifiate (1 equiv.), which is known to complex with triple bonds.2. ... 

K bromide solns v si sol in w. It occurs in nature as the mineral born silver and is formed when a soln of a sol chloride is added to a soln of a Ag salt. Silver chloride in contact with metallic Na or K is exploded by percussion (Ref 3). Its ammoniacal soln absorbs acetylene, forming Silver Acetylide Chloride complexes which are expl (See Vol 1, p A80 l. Silver chloride is used in medicine as an antiseptic nerve sedative, in the manuf of pure Ag Ag salts, and in photography photometry(Refs... 

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