Perfluoroalkyl derivatives mercury

Perfluoroalkyl derivatives of mercury were the first fluorocarbon-organometallic compounds to be reported. Alkylmercurials are valuable in that they are able to alkylate other metals, but the toxicity of mercurials greatly inhibits the use of these systems. Perfluoroalkyl iodides react with mercury on heating or irradiation with ultraviolet light to give perfluoroalkylmercury(ll) iodides [58-60] (Figure 10.17). 

The stereochemistry of the reaction of mercuric trifluoroacetate with cyclopro panes has been determined formation in the rate-determining step of corner-mercurated cyclopropanes, e.g. (34) from cM.-l,2,3-trimethylcyclopropane, is proposed. For other uses of mercuric trifluoroacetate and related compounds see discussion on formation of perfluoroalkyl derivatives of mercury and carbenes (see p. 193), and on preparation of polyfluoroarylmercuric trifluoroacetates (see p. 437). An X-ray determination of the crystal structure of mercuric trifluoroacetate has been carried out and a further report has appeared on the formation of the cyclohexyl-mercurinium ion [from addition of cyclohexene-SOs to (CF3 C02)2Hg-FS03H-SbFs-S02 at -60°C via mercuric ion attack on the w-system of the alkene] (see Vol. 2, p. 128). 

Mercury.—A new convenient method of synthesis of perfluoroalkyl derivatives of mercury has been developed, viz. reaction of mercuric chloride with perfluoroalkylpotassium compounds prepared in situ from potassium fluoride and perfluoro-olefins, e.g. 

The carbon-iodine bond in perfluoroalkyl iodides is usually susceptible to homolytic fission this was exploited in early work on the synthesis of mercurials and in later work relating to group IVB and transition-metal derivatives (Figure 10.2). 

The organometallic compounds prepared from alkali metal derivatives of metal carbonyls include compounds in which a transition metal of a metal carbonyl residue is cr-bonded to another atom such as a carbon atom in an alkyl, acyl, aryl, or perfluoroalkyl group, to the heavier congeners of carbon —silicon, germanium, tin, and lead—to mercury and gold which form unusually stable compounds, and even to other transition metals. The preparation and properties of all of these classes of compounds will be considered and, for the sake of completeness, a few related compounds prepared by routes other than those involving anionic metal carbonyl derivatives will be discussed. 

As seen above, compounds of the type R2Fe(CO)4 with iron-carbon a bonds are known only when R is a perfluoroalkyl radical or a maleoyl radical. However, compounds of this type where the iron atom is a-bonded to an element other than carbon, are somewhat more common. Derivatives are known in which the iron atom is cr-bonded to gold, mercury, tin, and lead. 

There are several other methods for generation of (per)fluoroalkyl radicals in reactions with diazines. In particular, photochemical decomposition of perfluoroalkyl mercury derivatives was used for perfluoroalkylation of uracils 568 (Scheme 120) [297]. Whereas for the parent uracil the method gave satisfactory results (30-54 % yields), the procedure was unfruitful for the sugar-modified derivatives (6-11 % yields). 

Several attempts were made to prepare compounds havii a perfluoro-alkyl group bonded to boron before success was achieved. In the case of tricoordinate boron compounds, Ry—B linkages were expected to be unstable because of the inability of Rp groups to relieve the electrophilic character of the boron atom by tt bonding (44). In confirmation of this idea, bis(perfluoroalkyl)mercury compounds [e.g., (C2Fs)2Hg] afibrd boron trifluoride when heated with boron trichloride (45, 46). Boron trifluoride formation presumably occurs via a transitory Rp—B derivative ... 

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