Mercury substitution reactions

Usually, C-mercury substituted phosphorus ylides are monomers and in order to stabilize these complexes the presence of a second substituent on the carbon is necessary to balance the electron-donating effect of the metal. However a dimeric complex 85 has been obtained by the reaction of mercuric halides HgX2... 

The specific rotation of the initial. y-butyl bromide used by Charman, Hughes, and Ingold was —15.2°. The specific rotation of the product of the mercury exchange reaction was exactly half that, — 7.6°. When mercuric acetate or mercuric nitrate was used as the cleaving salt, the products showed a specific rotation of —7.5° and —7.8°, respectively. Thus this electrophilic substitution clearly proceeds with retention of configuration. 

Aromatic ketones arylations, 10, 140 asymmetric hydrogenation, 10, 50 G—H bond alkylation, 10, 214 dialkylzinc additions, 9, 114-115 Aromatic ligands mercuration, 2, 430 in mercury 7t-complexes, 2, 449 /13-77-Aromatic nitriles, preparation, 6, 265 Aromatic nucleophilic substitution reactions, arene chromium tricarbonyls, 5, 234... 

Fig. 1.16. NaBH4-induced air oxidation of a (/3-alkoxy-alkyl)mercury (II) trifluoroac-etate (see Figure 3.39) to a glycol derivative. In terms of Figure 1.2 it is "substitution reaction including a fragmentation and an addition. ...

When (/3-hydroxyalkyl)mercury(II) acetates are treated with NaBH4 and no additional reagent, they first form (( - h y d roxy a Iky 1) me rcu ry (II) hydrides. These decompose via the chain reaction shown in Figure 1.12 to give a mercury-free alcohol. Overall, a substitution reaction R—Hg(OAc) — R—H takes place. The initiation step for the chain reaction participating in this transformation is a homolysis of the C—Hg bond. This takes place rapidly at room temperature and produces the radical Hg—H and a /3-hydroxylated alkyl radical. As the initiating radical, it starts the first of the two... 

A systematic study of substitution reactions of oxazole itself has not been reported. Bromination of 2-methyl-4-phenyloxazole or 4-methyl-2-phenyloxazole with either bromine or NBS gave in each case the 5-bromo derivative, while 2-methyl-5-phenyloxazole was brominated at C(4). Mercuration of oxazoles with mercury(II) acetate in acetic acid likewise occurs at C(4) or C(5), depending on which position is unsubstituted 4,5-di-phenyloxazole yields the 2-acetoxymercurio derivative. These mercury compounds react with bromine or iodine to afford the corresponding halogenooxazoles in an electrophilic replacement reaction (81JHC885). Vilsmeier-Haack formylation of 5-methyl-2-phenyloxazole with the DMF-phosphoryl chloride complex yields the 4-aldehyde. 

Thus, not only should alkylmercuric iodides and dialkylmercurials have a more nucleophilic carbon compared with the others, but their respective -Hg-X functions should also be better leaving groups in electrophilic substitution reactions. This latter prophesy is supported in part by the results of Hughes et al. from their kinetic studies of mercury exchange reactions (20). 

Mercury(II) is known to accelerate Ligand Substitution reactions of complexes of formnla ML5X (M = Rh, Cr, Co, Ru L = H2O or NH3 X = bridging halide or psendohalide), probably by forming an intermediate with a halide bridge between Hg and M. 

Mercury salts can react directly with hydrocarbons exchanging hydrogen for mercury. This reaction is an electrophilic substitution (equation 5) and hence can take place with arenes, cyclopentadienyls, terminal aUcynes, and also with aliphatic hydrocarbons that contain activated carbon-hydrogen bonds (e.g. carbonyl or nitrile compoimds). When the hydrocarbon contains several equivalent hydrogen atoms, polymercuration is often observed. 

Brominative cyclizatlon of dienes. Reaction of homogeranic acid (1) with this mercury salt in CH3NO2 results in a mercury-substituted lactone 2, which can be converted into either 4 or 5 via 3. Lower yields are obtained when the mercury salt is replaced by silver tetrafluoroborate (15%). ... 

Kinetic studies have proposed evidence for the formation of heterodinuclear intermediate. In order to study the structure of the intermediate in solution as related to the reaction mechanism, extended X-ray absorption fine structure (EXAFS) measurements have been undertaken for the metal-substitution reaction of mercury(ll) porphyrin complex with copper(II) in an acetate buffer (pH = 5.6). 

Scheme 2. Reaction scheme of the metal-substitution reaction of Hg2(lpps)2- with copperfll) in an acetate buffer. 1. free base porphyrin 2, mercury(II) acetato complex 3, homodinuclear mcrcury(ll) porphyrin 4, copperfll) acetato complex 5, heterodinuclear intermediate 6, mercuryfll) acetato complex 7, coppetflll porphyrin.

On the basis of theoretical and experimental results a symmetrical mercurinium ion, with most of the positive charge on mercury, has therefore been proposed in reactions of symmetrically substituted alkenes , while asymmetrical mercurinium ions or weakly bridged mercury-substituted carbocations have been proposed when there is a substituent, such as an aryl group, on the double bond -. Finally, with substituents highly capable of stabilizing carbocations, fully open intermediates have been proposed . ... 

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