[2097-71-4] · C6H10Hg · Dipropenylmercury · (MW 282.75)
Physical Data: liquid; bp 90-92 °C/6.5 mmHg, 58-58.5 °C/1.5 mmHg; n
Solubility: sol diethyl ether.
Preparative Methods: there have been several reports of the synthesis of dipropenylmercury.7 The most straightforward synthesis is probably that reported by Borisov and co-workers.1 Allylmagnesium Bromide, prepared in ether, is reacted with mercury(II) bromide in THF at 5 °C. After 1 h, the reaction is quenched with saturated ammonium chloride. Evaporation and then distillation affords dipropenylmercury.
Handling, Storage, and Precautions: reported to be an unstable material, and is best used immediately after preparation. Despite the lack of specific toxicity data, it is reasonable to assume that as with all mercury compounds, care should be taken in handling these toxic reagents. Use in a fume hood.
The use of dipropenylmercury as a reagent in organic synthesis is not extensive, although this compound has been studied by IR8 and NMR spectroscopy9 and polarography10 in some depth.
The use of dipropenylmercury, as well as other mercury-containing reagents, has been explored in the reaction with Trimethylstannane.2 Trimethylpropenylstannane is formed as the product (eq 1).
The use of dipropenylmercury as a precursor to a trianion has been described.3 Thus treatment of dipropenylmercury with aniline and Mercury(II) Acetate, followed by acetate/bromide exchange with potassium bromide, affords an aminomercurial. Treatment of this aminomercurial with Phenyllithium and then Lithium powder affords the trianion derivative, which was characterized by quenching with D2O and then aqueous hydrochloric acid to afford the corresponding dideuterio compound (eq 2). A variety of other electrophiles were also employed.
The Hg-C bonds in dipropenylmercury are sensitive to homolysis.10 Thus in the reaction between dipropenylmercury and oxygen in the presence of tetraphenylporphyrin (TPP), the expected ene product is observed as a minor product, whereas acrolein is formed as the major product (eq 3), which, it was suggested, arises from oxidation of the propenyl radical formed upon homolysis of the Hg-C bond. However, other allylmercury reagents successfully undergo ene reactions with alternative ene coupling partners (which do not require photosensitization), and so there appears to be further scope for metallo-ene reactions of allylmercury reagents.
Treatment of dipropenylmercury with Thiophenol gives an exothermic reaction which results in the formation of mercury bis(thiophenolate), phenyl(propenyl)sulfide, and mercury metal.5 The reaction of dipropenylmercury with the sulfur-containing thianthrene cation radical has also been reported.6
I. Craig Baldwin & Jonathan M. J. Williams
Loughborough University of Technology, UK