Phenylselenolate Mercury Alkyl Compounds, PhSeHgMe and PhSeHgEt: Molecular Structures, Protolytic Hg-C Bond Cleavage and Phenylselenolate Exchange.

The phenylselenolate mercury alkyl compounds, PhSeHgMe and PhSeHgEt, have been structurally characterized by X-ray diffraction, thereby demonstrating that both compounds are monomeric with approximately linear coordination geometries; the mercury centers do, nevertheless, exhibit secondary Hg•••Se intermolecular interactions that serve to increase the coordination number in the solid state. The ethyl derivative, PhSeHgEt, undergoes facile protolytic cleavage of the Hg-C bond to release ethane at room temperature, whereas PhSeHgMe exhibits little reactivity under similar conditions. Interestingly, the cleavage of the Hg-C bond of PhSeHgEt is also more facile than that of the thiolate analogue, PhSHgEt, which demonstrates that coordination by selenium promotes protolytic cleavage of the mercury-carbon bond. The phenylselenolate compounds PhSeHgR (R = Me, Et) also undergo degenerate exchange reactions with, for example, PhSHgR and RHgCl. In each case, the alkyl groups preserve coupling to the 199Hg nuclei, thereby indicating that the exchange process involves metathesis of the Hg-SePh/Hg-X groups rather than metathesis of the Hg-R/Hg-R groups.

Gallium hydride and monovalent indium compounds that feature tris(pyrazolyl)hydroborate ligands.

The tris(pyrazolyl)hydroborate compounds [tris(3,5-dimethyl-1H-pyrazol-1-yl-κN(2))hydroborato]indium(I), [In(C15H22BN6)], abbreviated as [Tp(Me2)]In, and [tris(3-tert-butyl-5-methyl-1H-pyrazol-1-yl-κN(2))hydroborato]indium(I), [In(C24H40BN6)], abbreviated as [Tp(Bu(t),Me)]In, represent well defined examples of three-coordinate monovalent indium. In both compounds, the geometry at indium is pyramidal and natural bond orbital (NBO) calculations indicate that the indium lone pair occupies an orbital that is primarily 5s in character. The trivalent gallium hydride compound hydrido[tris(3-tert-butyl-5-methyl-1H-pyrazol-1-yl-κN(2))hydroborato]gallium(III) tetrachloridogallium(III), [Ga(C24H40BN6)H][GaCl4], abbreviated as {[Tp(Bu(t),Me)]GaH}[GaCl4], is obtained via reaction of [Tp(Bu(t),Me)]Tl with [HGaCl2]2, and the Ga-H bond length of 1.49 (6) Šcompares favorably with the mean value of 1.50 Šfor structurally characterized gallium hydride compounds that are listed in the Cambridge Structural Database.

Synthesis and structural characterization of tris(2-mercapto-1-adamantylimidazolyl)hydroborato complexes: a sterically demanding tripodal [S3] donor ligand.

The tris(2-mercapto-1-adamantylimidazolyl)hydroborato ligand, [Tm(Ad)], has been synthesized via the reaction of 1-adamantyl-2-mercaptoimidazole with MBH(4) (M = Li, K). [Tm(Ad)]M has been used to synthesize a variety of compounds of the main-group and transition elements, including [Tm(Ad)]ZnI, {[Tm(Ad)]GaI}[GaI(4)], {[Tm(Ad)]GaCl}[GaCl(4)], {[Tm(Ad)]GaGa[Tm(Ad)]}[GaCl(4)](2), {[Tm(Ad)](2)In}[InI(4)], [Tm(Ad)]In(κ(2)-mim(Ad))Cl, [Tm(Ad)]Ga→B(C(6)F(5))(3), [Tm(Ad)]In→B(C(6)F(5))(3), and [Tm(Ad)]Re(CO)(3). Structural characterization of [Tm(Ad)]Re(CO)(3) demonstrates that the [Tm(Ad)] ligand is more encapsulating than other [Tm(R)] ligands, including [Tm(Bu(t))], while IR spectroscopic studies indicate that the [Tm(Ad)] and [Tm(Bu(t))] ligands have very similar electron-donating properties.

Bis(2-mercapto-1-R-imidazolyl)hydroborato complexes of aluminium, gallium, indium and thallium: compounds possessing gallium-gallium bonds and a trivalent thallium alkyl.

The reactions of bis(mercaptoimidazolyl)hydroborato derivatives [Bm(R)]M' (R = Me, Bu(t); M' = Li, Na, Tl) with MX(3) trihalides of aluminium, gallium and indium yield both 1:1 and 2:1 complexes of the types [Bm(R)]MX(2) and [Bm(R)](2)MX, respectively. Structurally characterized examples of the [Bm(R)]MX(2) series include [Bm(Me)]AlCl(2), [Bm(Me)]GaI(2), [Bm(Me)]InI(2), [Bm(Bu(t))]AlCl(2) and [Bm(Bu(t))]GaX(2) (X = Cl, Br, I), while structurally characterized examples of the [Bm(R)](2)MX series include [Bm(Bu(t))](2)InX (X = Cl, Br, I). In addition to the halide complexes, the trivalent dimethyl thallium complex [Bm(Bu(t))]TlMe(2) has been synthesized via the reaction of [Bm(Bu(t))]Tl with Me(2)TlCl. The reactions of [Bm(R)]M' with the monovalent halides, "GaI", InCl and InI, result in disproportionation. In the case of indium, the mononuclear complexes [Bm(Bu(t))](2)InI and [Bm(Bu(t))]InCl(kappa(2)-mim(Bu(t))) are obtained, whereas for gallium, dinuclear compounds that feature Ga-Ga bonds, namely [Bm(R)](GaI)(GaI)[Bm(R)] (R = Me, Bu(t)) have been isolated.

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 [Tm(Bu(t))]HgEPh (E = S, Se, Te). In particular, X-ray diffraction studies on [Tm(Bu(t))]HgEPh demonstrate that although the Hg-S bonds involving the [Tm(Bu(t))] ligand are longer than the corresponding Cd-S bonds of [Tm(Bu(t))]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 A) < Se (0.035 A) < Te (0.057 A). This trend indicates that the chalcogenophilicity of mercury increases in the sequence S < Se < Te. Thus, while mercury is often described as being thiophilic, it is evident that it actually has a greater selenophilicity, a notion that is supported by the observation of facile selenolate transfer from zinc to mercury upon treatment of [Tm(Bu(t))]HgSCH(2)C(O)N(H)Ph with [Tm(Bu(t))]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.

Molecular structures of protonated and mercurated derivatives of thimerosal.

The carboxylate oxygen of thimerosal, [(Ar(CO(2)))SHgEt]Na, is subject to facile electrophilic attack by H(+) and [HgEt](+) to give (Ar(CO(2)H))SHgEt and [(Ar(CO(2)HgEt))SHgEt](2), respectively. X-Ray diffraction demonstrates that (Ar(CO(2)H))SHgEt exists as a hydrogen bonded dimer in the solid state whereas [(Ar(CO(2)HgEt))SHgEt](2) is tetranuclear, with the mercury centers being connected by bridging carboxylate groups. (1)H NMR spectroscopic studies indicate that the form of the (199)Hg satellites of the ethyl group of (Ar(CO(2)H))SHgEt are dependent on the magnetic field, such that the inner pair of CH(2) and CH(3) satellites appear as a singlet at 400 MHz, as a consequence of (2)J(Hg-H) and (3)J(Hg-H) having opposite signs and the difference in chemical shifts of the central CH(2) and CH(3) groups being equal to (1/2)[/(2)J(Hg-H)-(3)J(Hg-H)/].

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 degrees 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 degrees 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.

Monovalent indium in a sulfur-rich coordination environment: synthesis, structure and reactivity of tris(2-mercapto-1-tert-butylimidazolyl)hydroborato indium, [TmBut]In.

[Tm(Bu(t))]In, the first structurally-characterized monovalent indium compound that features a sulfur-rich coordination environment, has been synthesized via treatment of InCl with [Tm(Bu(t))]K; in contrast to the thallium counterpart, the lone pair of [Tm(Bu(t))]In is a site of reactivity, thereby allowing formation of [Tm(Bu(t))]In-->B(C(6)F(5))(3) and [Tm(Bu(t))]In(kappa(2)-S(4)) upon treatment with B(C(6)F(5))(3) and S(8), respectively.

Molecular structures of thimerosal (Merthiolate) and other arylthiolate mercury alkyl compounds.

The molecular structure of sodium ethylmercury thiosalicylate (also known as thimerosal and Merthiolate) and related arylthiolate mercury alkyl compounds, namely PhSHgMe and PhSHgEt, have been determined by single crystal X-ray diffraction. (1)H NMR spectroscopic studies indicate that the appearance of the (199)Hg mercury satellites of the ethyl group of thimerosal is highly dependent on the magnetic field and the viscosity of the solvent as a consequence of relaxation due to chemical shift anisotropy.

Applications of bis(1-R-imidazol-2-yl)disulfides and diselenides as ligands for main-group and transition metals: kappa2-(N,N) coordination, S-S bond cleavage, and S-S/E-E (E = S, Se) bond metathesis reactions.

Bis(1-R-imidazol-2-yl)disulfides, (mim(R))2 (R = Ph, Bu(t)), and diselenides, (seim(Mes))2, serve as bidentate N,N-donor ligands for main-group and transition metals. For example, [kappa2-(mim(Bu)(t))2]MCl2 (M = Fe, Co, Ni, Zn), [kappa2-(mim(Ph))2]MCl2 (M = Co, Zn), [kappa2-(mim(Bu)(t))2]CuX (X = Cl, I), and [kappa2-(seim(Mes))2]MCl2 (M = Fe, Co, Ni) are obtained by treatment of (mim(Bu)(t))2 or (seim(Mes))2 with the respective metal halide and have been structurally characterized by X-ray diffraction. On the other hand, the zerovalent nickel complex Ni(PMe3)4 effects cleavage of the disulfide bond of (mim(Bu)(t))2 to give square-planar trans-Ni(PMe3)2(mim(Bu)(t))2 in which the (mim(Bu)(t)) ligands coordinate via nitrogen rather than sulfur, a most uncommon coordination mode for this class of ligands. Although [kappa2-(mim(R))2]MCl2 (M = Fe, Co, Ni, Zn) are not subject to homolytic cleavage of the S-S bond because the tetravalent state is not readily accessible, the observation that [kappa2-(mimPh)2]CoCl2 and [kappa2-(mim(Bu)(t))2]CoCl2 form an equilibrium mixture with the asymmetric disulfide [kappa2-(mim(Ph))(mim(Bu)(t))]CoCl2 indicates that S-S bond cleavage via another mechanism is possible. Likewise, metathesis between disulfide and diselenide ligands is observed in the formation of [kappa2-(mim(Bu)(t))(seim(Mes))]CoCl2 upon treatment of [kappa2-(mim(Bu)(t))2]CoCl2 with [kappa2-(seim(Mes))2]CoCl2.