Mercury triflate formation

Periana et al. have reported a mercury system that catalyzes the partial oxidation of methane to methanol.81 Hg(II) is typically considered to be a soft electrophile and is known to initiate electrophilic substitution of protons from aromatic substrates. The catalytic reaction employs mercuric triflate in sulfuric acid, and a key step in the catalytic cycle is Hg(II)-mediated methane C—H activation. For methane C—H activation by Hg(II), an oxidative addition reaction pathway via the formation of Hg(IV) is unlikely. Thus, an electrophilic substitution pathway has been proposed, although differentiation between proton transfer to an uncoordinated anion versus intramolecular proton transfer to a coordinated anion (i.e., o-bond metathesis) has not been established. Hg(II)-based methane C H activation was confirmed by the observation of H/D exchange between CH4 and D2S04 (Equation 11.9). 

Intramolecnlar alkenylation at a furan a- or P-position by an alkyne occurs, with the formation of bicycUc derivatives, when promoted by mercury(II) acetate (or Hg(OAc)(OTf), generated in situ from mercuric acetate and scandinm triflate). In the case of closure onto a p-position, a spirocyclic intermediate from preferred attack at the a-position, may be involved, as shown. 

Portella also reported the formation of non-hydroxy-containing 1,4- and l,5-bis(acylsilanes). For example, treatment of 2-TMS-1,3-dithiane with n-butyllithium followed by exposure to a variety of l,2-bis(triflates) provided symmetric and unsymmet-ric 1,4-bisdithianes in modest to good yield. Treatment with mercury salts or Mel revealed the bis(acylsilane), which upon exposure to PTSA cyclized to afford the corresponding 2,5-bis-trimethylsilylfuran (eq 32). 

Arylyne cyclization is an important reaction affording the formation of carbocycles in the synthesis of complex molecules. CT-Bonded metal salt polymer or organic moiety linked to the inorganic support, silaphenylmercuiic triflate, showed efficient catalytic activity for a variety of mercury(ll) trifluoromethanesulfonate [Hg(OTf)J-catalyzed reactions [104,132-134]. Examples described by Equations (8.36)-(8.43) present cyclo- and cycloisometization reactions leading to the synthesis of both carbocycles and heterocycles. 

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