Synthesis and Structural Characterization of Tris(2-mercapto-1-adamantylimidazolyl)hydroborato Complexes: A Sterically Demanding Tripodal [<i>S</i>₃] Donor Ligand

The tris(2-mercapto-1-adamantylimidazolyl)hydroborato ligand, [TmAd], has been synthesized via the reaction of 1-adamantyl-2-mercaptoimidazole with MBH4 (M = Li, K). [TmAd]M has been used to synthesize a variety of compounds of the main-group and transition elements, including [TmAd]ZnI, {[TmAd]GaI}[GaI4], {[TmAd]GaCl}[GaCl4], {[TmAd]GaGa[TmAd]}[GaCl4]2, {[TmAd]2In}[InI4], [TmAd]In(κ2-mimAd)Cl, [TmAd]Ga→B(C6F5)3, [TmAd]In→B(C6F5)3, and [TmAd]Re(CO)3. Structural characterization of [TmAd]Re(CO)3 demonstrates that the [TmAd] ligand is more encapsulating than other [TmR] ligands, including [TmBut], while IR spectroscopic studies indicate that the [TmAd] and [TmBut] ligands have very similar electron-donating properties

Synthesis and Structural Characterization of Tris(2-mercapto-1-adamantylimidazolyl)hydroborato Complexes: A Sterically Demanding Tripodal [<i>S</i>₃] Donor Ligand

The tris(2-mercapto-1-adamantylimidazolyl)hydroborato ligand, [TmAd], has been synthesized via the reaction of 1-adamantyl-2-mercaptoimidazole with MBH4 (M = Li, K). [TmAd]M has been used to synthesize a variety of compounds of the main-group and transition elements, including [TmAd]ZnI, {[TmAd]GaI}[GaI4], {[TmAd]GaCl}[GaCl4], {[TmAd]GaGa[TmAd]}[GaCl4]2, {[TmAd]2In}[InI4], [TmAd]In(κ2-mimAd)Cl, [TmAd]Ga→B(C6F5)3, [TmAd]In→B(C6F5)3, and [TmAd]Re(CO)3. Structural characterization of [TmAd]Re(CO)3 demonstrates that the [TmAd] ligand is more encapsulating than other [TmR] ligands, including [TmBut], while IR spectroscopic studies indicate that the [TmAd] and [TmBut] ligands have very similar electron-donating properties

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, [mim(Bu(t))]HgR and {[Hmim(Bu(t))]HgR}(+) (Hmim(Bu(t)) = 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 CH(4), the analogous reaction of PhSHgEt with PhSH leads to evolution of C(2)H(6) over the course of 2 days at 100 °C. Furthermore, protolytic cleavage of the Hg–C bond by PhSH is promoted by Hmim(Bu(t)). For example, whereas the reaction of {[Hmim(Bu(t))]HgEt}(+) with PhSH eliminates C(2)H(6) at elevated temperatures, the protolytic cleavage occurs over a period of 2 days at room temperature in the presence of Hmim(Bu(t)). The ability of Hmim(Bu(t)) to promote the protolytic cleavage is interpreted in terms of the formation of a higher coordinate species {[Hmim(Bu(t))](n)HgR}(+) that is more susceptible to Hg–C bond cleavage than is two-coordinate {[Hmim(Bu(t))]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

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

On the Chalcogenophilicity of Mercury: Evidence for a Strong Hg−Se Bond in [Tm^{Bu^t}]HgSePh and Its Relevance to the Toxicity of Mercury

One of the reasons for the toxic effects of mercury has been attributed to its influence on the biochemical roles of selenium. For this reason, it is important to understand details pertaining to the nature of Hg−Se interactions and this has been achieved by comparison of a series of mercury chalcogenolate complexes that are supported by tris(2-mercapto-1-t-butyl-imidazolyl)hydroborato ligation, namely [TmBut]HgEPh (E = S, Se, Te). In particular, X-ray diffraction studies on [TmBut]HgEPh demonstrate that although the Hg−S bonds involving the [TmBut] ligand are longer than the corresponding Cd−S bonds of [TmBut]CdEPh, the Hg−EPh bonds are actually shorter than the corresponding Cd−EPh bonds, an observation which indicates that the apparent covalent radii of the metals in these compounds are dependent on the nature of the bonds. Furthermore, the difference in Hg−EPh and Cd−EPh bond lengths is a function of the chalcogen and increases in the sequence S (0.010 Å) But]HgSCH2C(O)N(H)Ph with [TmBut]ZnSePh. The significant selenophilicity of mercury is in accord with the aforementioned proposal that one reason for the toxicity of mercury is associated with it reducing the bioavailability of selenium