[587-85-9] · C12H10Hg · Diphenylmercury · (MW 354.81)
Physical Data: mp 128-129 °C; d420 2.30 g cm-3.
Solubility: sol diethyl ether, dichloromethane.
Form Supplied in: commercially available as a white solid; widely available.
Handling, Storage, and Precautions: harmful if swallowed, inhaled, or absorbed through the skin. Inhalation may be fatal as a result of spasm, inflammation and edema of the larynx and bronchi, chemical pneumonitis, and pulmonary edema. Use in a fume hood.
In general, the reaction of diphenylmercury with haloalkanes is unsuccessful. However, it has been reported that diphenylbromomethane reacts with diphenylmercury to afford triphenylmethane (eq 1).3
Heck has demonstrated the use of diphenylmercury as a coupling partner in palladium-promoted and -catalyzed phenylation of alkenes.1 Thus treatment of an alkene with diphenylmercury in the presence of a stoichiometric amount of a palladium salt affords the phenyl-substituted alkene (eq 2). The results of this reaction are summarized in Table 1.1
To some extent, this reaction has been superseded by the more conventional Heck reaction using aryl iodides as the coupling partner.4 However, a palladium-catalyzed procedure has also been reported, where a reoxidant is added to regenerate the palladium catalyst.1 Diphenylmercury reacts with acid chlorides in the presence of sodium iodide and a palladium catalyst. For example, under these conditions, cinnamoyl chloride can be converted into chalcone (eq 3).5
The palladium- and rhodium-catalyzed carbonylation of diphenylmercury is also possible. The reaction of diphenylmercury with Carbon Monoxide in the presence of a rhodium catalyst affords benzophenone (eq 4).6 The carbonylation of diphenylmercury and related compounds by Octacarbonyldicobalt has also been reported.7
Diphenylmercury undergoes radical reactions. Treatment of a tetrachloromethane solution of diphenylmercury in the presence of Dibenzoyl Peroxide catalyst affords the products of radical reaction (eq 5).8 The reaction of diphenylmercury with a fluoroxy compound affords the product of electrophilic fluorination, fluorobenzene (eq 6).9 Treatment of diphenylmercury with Thiocyanogen affords phenyl thiocyanate and phenylmercury thiocyanate (eq 7).10
Diphenylmercury has been widely exploited for the preparation of other organometallic reagents by transmetalation processes.2 While a simple method for the preparation of diphenylmercury is from the Grignard reagent phenylmagnesium bromide,11 there has nevertheless been an interest in the preparation of diphenylmagnesium from diphenylmercury. Thus treatment of diphenylmercury in THF with Magnesium metal affords a solution of diphenylmagnesium (eq 8).12
Diphenylzinc has been prepared by treatment of diphenylmercury with Zinc metal (eq 9) which afforded the product with sufficient quality that, after crystallization, an X-ray crystal structure determination could be carried out. The fact that the diphenylzinc can be obtained under salt-free conditions is useful.13
The reaction between a trichlorotin complex and diphenylmercury results in ligand exchange of one of the chlorides for a phenyl group (eq 10).14 Reaction of an osmium hydrido complex with diphenylmercury results in the formation of a coordinatively unsaturated s-aryl osmium complex (eq 11).15 Similar reactions have also been reported for ruthenium complexes and, independently, rhodium complexes.16
The transmetalation of diphenylmercury can lead to other phenylmetal species which can be used synthetically in situ. For example, the reaction between diphenylmercury and Lead(IV) Acetate affords phenyllead triacetate,17 which reacts with nucleophiles. In the presence of 2-Nitropropane, 2-phenyl-2-nitropropane is produced in 63% yield (eq 12).18
Diphenylmercury has been converted into the corresponding bis(chromium tricarbonyl) adduct. The reaction with 2 equiv of n-Butyllithium affords the aryllithium, which can be trapped with a variety of electrophiles including Carbon Dioxide (eq 13).19
The reaction of diphenylmercury with excess Borane-Tetrahydrofuran affords an intermediate arylboron species, which upon oxidative workup affords a good yield of phenol (eq 14).20
Other metals (or their complexes) which have been phenylated by diphenylmercury include cadmium,2 antimony,2 silicon,2 arsenic,2 ytterbium,21 palladium,22 and tellurium.23
I. Craig Baldwin & Jonathan M. J. Williams
Loughborough University of Technology, UK