Mercury -, dihalides

The reaction of tetraethynylplatinum derivatives with mercury dihalide in acetone affords complexes 156 and 157 in which the mercury centers are coordinated to two neighboring mercury alkynyl functionalities.194 195 In turn, each alkynyl functionality interacts with the mercury center in an 7]Z-fashion. For complexes 156 and 157, the resulting Hg-Cjp bonds, which range from 2.41 to 2.77 A, are longer than typical Hg-C cr-bonds but shorter that those observed in 154. In 156, the greater flexibility of the structure allows for the formation of shorter Hg-C(.r/>) bonds than in 157 (av. Hg-C(.r/>) = 2.52 A for 156 and 2.64A for 157). The formation of such complexes is not limited to the case of... 

The cyclopropylmercury derivatives which have been isolated, have been synthesized by treating the corresponding cyclopropyllithium or cyclopropylmagnesium halide with a mercury dihalide the yields vary considerably. treatment of A.A-dlisopropyl-l-methylcyclopro-... 

While the 20 Group 1 metal halides all adopt either a face-centered or a body-centered crystal structure, crystals of the 32 dihalides of the Group 2 and 12 metals form a bewildering array of at least 15 different structure types. Both the crystal and the gas-phase structures have recently been described and correlated in comprehensive reviews by Hoffman and coworkers [16, 17]. In this section we shall be particularly concerned with the crystal stractures of the eight metal difluorides and the four mercury dihalides. 

In the following, we shall denote the number of electron pairs in the valence shell of the central atom by a digit in italics behind the formula. The mercury dihalides HgX2 (2) (X=C1, Br or I) and the Hg-Hg-bonded dimeric monohalides Hg2X2 (2) all have two bonding electrons pairs (and no nrmbonding electrons) in the valence shell of the merciuy atoms and all adopt linear structures. The structure of the ion [T1(CH3)2]" (2) is also linear. 

The chemistry of alkynes is dominated by electrophilic addition reactions, similar to those of alkenes. Alkynes react with HBr and HC1 to yield vinylic halides and with Br2 and Cl2 to yield 1,2-dihalides (vicinal dihalides). Alkynes can be hydrated by reaction with aqueous sulfuric acid in the presence of mercury(ll) catalyst. The reaction leads to an intermediate enol that immediately isomerizes to yield a ketone tautomer. Since the addition reaction occurs with Markovnikov regiochemistry, a methyl ketone is produced from a terminal alkyne. Alternatively, hydroboration/oxidation of a terminal alkyne yields an aldehyde. 

Trigeminal trihalides are completely reduced by catalytic hydrogenation over palladium [62] and Raney nickel [63], and partially reduced to dihalides or monohalides by electrolysis using mercury cathode [57 ], by aluminum... 

Arsolanes (4) have the properties of normal tertiary arsines. They react with halogens to form dihalides, form mercury(II) chloride adducts, are oxidized to arsine oxides and... 

Raman spectral studies of the species [MX ]("-2)- (n = 2-4 M = Zn, Cd or Hg X = Cl, Br or I) in anhydrous tributyl phosphate have been reported.1001 For the MX2 molecules, sufficient metal dihalide-solvent interaction exists to suggest bent X—M—X species with Cjv rather than D< h symmetry. The effect appears most marked for zinc(II) and least marked for mercury(II)... 

There is little evidence for the formation of soluble complexes in aqueous solutions of Hg1 halide and pseudohalide systems,12,32 but the mercury(I) halides themselves are well-known substances. X-ray studies on the dimercury(I) dihalides show that all these compounds possess... 

The wealth of information that has accumulated regarding the UPS of the main group halides is not considered here, since it falls outside the purview of this Chapter. Of the transition metal halides the largest amount of work has been done with the halides of the Group 2B metals and their monomethyl derivatives (28, 33, 63, 108, 112, 129, 233). In these studies it was found that the zinc and cadmium dihalides require significantly higher vaporization temperatures than the mercury compounds hence specialized high-temperature techniques were necessary. A summary of these and related methods may be found in a recent review article by Schweitzer (255). 

Suitable candidates for a-elimination reactions are silylmethyl halides (— base-induced elimination of H-Hal), silylmethyl dihalides (— halide/metal exchange followed by elimination of a metal halide) and stable carbenoid-type compounds such as (a-halo-a-silylalkyl)mercury compounds (— thermal elimination of mercury(II) halide). Bis(phenylthio)(trimethylsilyl)methyl lithium (— elimination of LiSPh) represents a borderline case (see Section III.E.8). 

Organic compounds of mercury, tin, and lead do not suffer from these shortcomings and convert tellurium tetrachloride and tetrabromide to diorgano tellurium dihalides in excellent yields. 

Diaryl tellurium compounds are converted to diaryl tellurium dihalides through reactions with sulfur tetrafluoride1, triaryl bismuth difluorides2-3, copper(II) halides4,5, iron(III) chloride, and mercury(II) chloride4. 

Diorgano tellurium dihalides form complexes with iodine and interhalogen compounds organic compounds with N, P, O, S, and Se donor atoms boron, aluminum, and gallium trihalides antimony pentachloride and mercury(II) halides. 

Depending on the mode of generation, a carbene may be initially formed in either the singlet or triplet state, irrespective of its stability. Common methods used for the generation of carbenes include photolytic, thermal, or metal catalyzed decomposition of diazocompounds, elimination of halogenfrom gem-dihalides, elimination of Hx from CHX3, decomposition of ketenes, thermolysis of a-halo-mercury compounds and cycloelimination of shelf stable substrates such as cyclopropanes, epoxides, aziridines and diazirines. 

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