With Aryl Mercury Chlorides

With Organometallic Compounds 1.2.1. With Aryl Mercury Chlorides 

Tellurium tetrachloride and tetrabromide react with equimolar quantities of aryl mercury chlorides to produce aryl tellurium trihalides in high yields. This reaction is useful when the trichlorotelluro group is required at a specific position in the aromatic molecule or when tellurium tetrachloride does not condense in an acceptable manner with the aromatic hydrocarbon. The solvent of choice is dioxane, because mercury dichloride precipitates as the dioxane adduct, facilitating the isolation and purification of the aryl tellurium trichlorides. 

4-Chlorophenyl Tellurium Trichloride A 100 one-necked flask is fitted with a reflux condenser carrying a calcium chloride drying tube and charged with 2.7 g (10 mmol) of tellurium tetrachloride, 3.5 g (10 mmol) of 4-chlorophenyl mercury chloride, and 30 m/ of dry dioxane. The mixture is heated under reflux for 4h, cooled to 20°, the mercury dichloride/dioxane complex is filtered off, and the filtrate is distilled under vacuum. The residue is recrystallized from glacial acetic acid yield 3.3 g (96%) m.p. 225° 

Equimolar quantities of tellurium tetrachloride and 3,3-bis[chloromercuro]-2,4-pentanedione in refluxing 1,4-dioxane produced 3-(chloromercuro)-2,4-dioxo-3-pentyl tellurium trichloride. The brown solid (recrystallized from diethyl ether) retained two molecules of dioxane that are slowly given off on storage . 

Al-Salim, A.A. West, W.R. MeWhinnie, T.A. Hamor, J. Chem. Soc., Dalton Trans. 1988, 2363. 

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The reaction between aryl (phenyl, substituted phenyl, naphthyl) tellurium trichlorides and aryl mercury chlorides or acetates are best carried out with dioxane as the solvent. The mercury(II) salts precipitate as their dioxane adducts. The symmetrical or unsymmetrical... 

Aryl tellurium halides react with aliphatic and aromatic Grignard reagents, with ethenyl magnesium halides , with ethynyl magnesium bromide with dimethyl and diethyl cadmium , with 2-(diphenylphosphino)-phenyl lithium, and with phenyl mercury chloride to produce aryl organo telluriums (p. 416). 

A convenient method for the preparation of unsymmetrical aryl organo tellurium dichlorides is the reaction of equimolar amounts of an aryl tellurium trichloride with an aromatic or aliphatic mercury chloride or acetate in refluxing dioxane. The yields vary... 

Although 1,2-dicarbonyl substrates (especially unsymmetrical benzils) are often difficult to make, there are a number of approaches which may be appropriate. Propane-1,3-dithiol reacts with aldehydes to give cyclic thioacetals (in 52-91% yields) which form stable dithiane anions when treated with butyllithium. Subsequent quenching with an acid chloride followed by mercury(ll) chloride treatment gives a 1,2-dicarbonyl species. Alternatively, substitution of an aldehyde for the acid chloride gives rise eventually to an a-hydroxycarbonyl derivative (Scheme 5.1.2) [16j. An alternative approach to a-ketoaldehydes (82-86% yields) reacts an a-ketonitrate ester with sodium acetate in DMSO [17]. Aryl a-diketones can be made from a-ketoanils, which are in turn made by cyanide ion-catalysed transformation of aromatic aldimines [18], and the range of unsymmetrical benzils has been increased by... 

Scheme 5. Reaction of iV-dialkyl-C-aryl chloroiminium chloride with bis(trimethylsilyl)mercury.

Cyclization to the desired head-to-taU-linked bis-benzimidazoles can also be performed by reaction of aryl or alkyl isothiocyanates with N,N -dicyclohexylcarbodi-imide (DCC) [83]. In a closely related and more recent study by the same group, mercury chloride was used as a catalyst to perform cyclization to the benzimidazoles [84]. Another application of the bis-hydroxylated polymer support PEG 6000, microwave-accelerated liquid-phase synthesis of thiohydantoins, has been reported [85, 86]. 

Mechanistic studies performed with Freeh s pincer catalyst in the Heck reaction excluded catalytic cycles with the involvement of homogeneous palladium(O) species, as indicated by the results obtained from the (recently developed) dibenzyl-test, which is directly applicable under the reactions conditions applied [24aj. Dibenzyl formation was - in contrast to Heck reactions catalyzed by palladium(O) complexes of type [Pd(PR3)2, where Pd /Pd" cycles are operative - not detectable by gas chromatography-mass spectrometry (GC/MS) when reaction mixtures of aryl bromide, olefin, benzyl chloride ( 10 mol% relative to aryl bromide), catalyst, and base were thermally treated. On the other hand, experimental observations, such as quantitative poisoning experiments with metallic mercury and CS2, which were shown to eflfidently inhibit catalysis, as well as analysis of the reaction profiles showed sigmoidal-shaped kinetics with induction periods and hence indicated that palladium nanoparticles are the catalytically active form... 

Silver imidazolate together with mercury(II) chloride or zinc(II) chloride has proved to an efficient promoting system for glycosidations. For example, l,2-(ra/w-linked aryl glucosides have been prepared from fully acetylated glycopyranosyl bromides in almost quantitative yield (equation 6).7(5... 

A common synthetic method is that of equation (9), where X = MeC02,168 PhS03,169 NO3170 or C104,171 and relies on the precipitation of silver chloride. A variation of this method is the synthesis of the ring complex (5), by the reaction (10).172 In other cases, the synthesis may involve mercury(II) salts or sodium salts (equations 11 and 12).173,174 Another useful synthetic method involves reaction of alkyl- or aryl-gold(I) complexes with carboxylic acids or acid anhydrides (equations 13-15).176,177... 

The monoaryl boric acids, RB(OH)2, arc usually isolated, as stated al >o x, l)y the action of water on the type RBXg, aitliough in certain cases this leads to the formation of the oxide RBO. The phenyl eom >ound has l)ecn obtained b " boiling with water the product of reaction from magnesium phenyl bromide and boron trifluoride. The most remarkable feature of the type RE(OH)2 is that the action of iiiercuric chloride upon them leads to the production of mercury aryl halides (RHgX). The anisyl and phenetyl compounds do not yield oxides when heated, or form salts, and tlie jS-naphthyl acid exists in two modifications. Dehydration of the acids in maw gives the oxides, RBO. 

Thiol esters of aromatic acids, ArC(0)SR, are cathodically reduced, with fission of the S-CO bond generating the arylcarbonyl radical and thiolate as in Eq. (25) [101]. The thiol may be obtained in good yield [102]—for example, L-cysteine in 83% yield from S-benzoyl-L-cysteine at a mercury cathode in DMF-water-tetramethylammonium chloride. The electroreduction of aryl thioesters [containing -C(0)SR, -C(S)OR, and -C(S)SR functions] has been studied, and some interesting products have been formed [103-105], as in Eqs. (26) through (29). Trithiocarbonates are reduced to the tetraalkyltetrathioethylenes [106]. 

Summary Bis(trimethylsilyl)mercury cleanly reacts at low temperature with chloroiminium chlorides to form stable metal-free cyclic and acyclic diaminocarbenes as well as aryl-, oxy-, chloro-, hydrogeno- and alkyl-amino carbenes. The aryl-, chloro-and hydrogeno-amino carbenes were formed as transient intermediates that undergo dimeri2ation into the corresponding alkenes, which were isolated in good yields. Alkyl-and oxy-amino carbenes were observed at low temperature by C NMR spectroscopy. 

In our quest to prepare new aryl amino carbenes, we reacted A-diisopropyl-C-phenyl chloroiminium chloride with bis(trimethylsilyl)mercury in THF. The reaction was monitored by C NMR spectroscopy at -78 °C, but the carbene was not observed. Instead, the dimer was formed as a 90/10 mixture of E and Z isomers. 

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