Synthesis, Structure, and Reactivity of Two-Coordinate Mercury Alkyl Compounds with Sulfur Ligands: Relevance to Mercury Detoxification

The susceptibility of two-coordinate mercury alkyl compounds of the type X−Hg−R (where X is a monodentate sulfur donor) towards protolytic cleavage has been investigated as part of ongoing efforts to obtain information relevant to understanding the mechanism of action of the organomercurial lyase, MerB. Specifically, the reactivity of the two-coordinate mercury alkyl compounds PhSHgR, [mimBut]HgR and {[HmimBut]HgR}+ (HmimBut = 2-mercapto-1-t-butylimidazole; R = Me, Et) towards PhSH was investigated, thereby demonstrating that the ability to cleave the Hg−C bond is very dependent on the nature of the system. For example, whereas the reaction of PhSHgMe with PhSH requires heating at 145 °C for several weeks to liberate CH4, the analogous reaction of PhSHgEt with PhSH leads to evolution of C2H6 over the course of 2 days at 100 °C. Furthermore, protolytic cleavage of the Hg−C bond by PhSH is promoted by HmimBut. For example, whereas the reaction of {[HmimBut]HgEt}+ with PhSH eliminates C2H6 at elevated temperatures, the protolytic cleavage occurs over a period of 2 days at room temperature in the presence of HmimBut. The ability of HmimBut to promote the protolytic cleavage is interpreted in terms of the formation of a higher coordinate species {[HmimBut]nHgR}+ that is more susceptible to Hg−C bond cleavage than is two-coordinate {[HmimBut]HgR}+. These observations support the notion that access to a species with a coordination number greater than two is essential for efficient activity of MerB.