Imidazole-containing (N3S)-Ni(II) complexes relating to nickel containing biomolecules.

Dimeric (N(2)S)Ni complexes and the monomeric N(2)S(2) bismercaptodiazacycloheptane nickel complex, (bme-dach)Ni, serve as precursors to two N(2)-, N'-/ S- complexes where N(2) = diazacycloheptane, N' = imidazole and S = thiolate. As rare examples of nickel complexes containing a mixed thiolate/imidazole ligand set, these complexes are characterized by X-ray diffraction, UV/vis, and variable temperature (1)H NMR spectroscopies, and electrochemistry. Density functional theory computations relate the orientation of the imidazole with respect to the N(2)N'SNi square plane to the VT NMR observed fluxionality and activation parameters. The superoxide dismutase activity of the imidazole complexes was investigated by the nitroblue tetrazolium assay.

Development of five-coordinate zinc mono- and dithiolates as S-donor metalloligands: formation of a Zn-W coordination polymer.

The synthesis and isolation of mono- and dithiolate-bridged Zn(mu-SR)(n)W(CO)(m) (where n = 1, m = 5; n = 2, m = 4) species from the dimeric N,N'-bis(2-mercaptoethyl)-1,4-diazacycloheptanezinc(II), [Zn-1'](2), and the monomeric [N-(3-thiabutyl)-N'-(3-thiapentaneoate)-1,5-diazacycloheptane]zinc(II), Zn-1'-Ac, are described. Upon cleavage of the dimeric [Zn-1'](2) with Na(+)[ICH(2)CO(2)](-), the resulting Zn-1'-Ac product is isolated as a monomeric, five-coordinate Zn(N(2)SS'O) complex equipped with one available Zn-bound thiolate for further reactivity. Cleavage of [Zn-1'](2) with [Et(4)N](+)Cl(-) afforded a monomeric intermediate, [Zn-1'-Cl](-), containing two Zn-bound thiolates. The zinc mono- and dithiolato complexes demonstrated reactivity toward labile-ligand tungsten carbonyl species, (THF)W(CO)(5) and (pip)(2)W(CO)(4), to yield respectively [(Zn-1'-Ac)W(CO)(5)](x) and [(Zn-1'-Cl)W(CO)(4)](-) complexes that were isolated and characterized spectroscopically and via X-ray diffraction. Upon binding to W(CO)(5), the five-coordinate Zn(N(2)SS'O) complex becomes six-coordinate within the coordination polymer [(Zn-1'-Ac)W(CO)(5)](x), in which the acetate tether of each molecule provides an O donor to occupy the octahedral axial position of a neighboring moiety. The [(Zn-1'-Cl)W(CO)(4)](-) dithiolate-bridged complex maintains a five-coordinate, square-pyramidal [Zn(N(2)S(2)Cl)](-) center, utilizing a chloride as the apical donor and resulting in an overall anionic complex. The addition of CO(g) to the [(Zn-1'-Cl)W(CO)(4)](-) complex was monitored by IR spectroscopy, which showed the emergence of [(Zn-1'-Cl)W(CO)(5)](-).

Thiolate bridging and metal exchange in adducts of a zinc finger model and Pt(II) complexes: biomimetic studies of protein/Pt/DNA interactions.

To provide precedents for the possible interactions of platinum DNA adducts with zinc finger proteins, the complexes [Pt(dien)Cl]Cl (dien = diethylenetriamine) and [Pt(terpy)Cl]Cl (terpy = 2,2':6',2''-terpyridine) were exposed to the N,N'-bis(2-mercaptoethyl)-1,4-diazacycloheptanezinc(II) dimer, [Zn(bme-dach)]2, and the products defined by electrospray ionization mass spectrometry (ESI-MS), X-ray crystallography and (195)Pt NMR spectroscopy. The presence of a leaving chloride in both platinum(II) complexes facilitates electrophilic substitution involving sulfur-containing zinc finger synthetic models or, as in previous studies, zinc finger peptidic sequences. Monitored via ESI-MS, both reactants yielded evidence for Zn-(mu-SR)-Pt bridges followed by zinc ejection from the N2S2 coordination sphere and subsequent formation of a trimetallic Zn-(mu-SR)2-Pt-(mu-SR)2-Zn-bridged species. The isolation of Zn-(mu-SR)-Pt-bridged species [(Zn(bme-dach)Cl)(Pt(dien))]Cl is, to our knowledge, the first Zn-Pt bimetallic thiolate-bridged model demonstrating the interaction between Zn-bound thiolates and Pt(2+). In the case of the [Pt(terpy)Cl]Cl reaction with the [Zn(bme-dach)]2, ESI-MS analysis further suggests metal exchange by formation of [Zn(terpy)Cl](+), whereas the [Pt(dien)Cl]Cl reaction does not yield the corresponding [Zn(dien)Cl](+) ion. Direct synthesis of the Zn-Pt thiolate-bridged species and the Pt(N2S2) chelate, where Pt has displaced the Zn from the chelate core, permitted the isolation of X-ray-quality crystals to confirm the bridging and metal-exchanged structures. The ESI-MS, (195)Pt NMR spectroscopy, and molecular structures of the di- and trinuclear complexes will be discussed, as they provide insight into the metal-exchange mechanism.

Comparisons of zinc with cadmium in N2S2 coordination and as S-bonded adducts to tungsten carbonyls.

The synthesis and characterization of bis-mercaptoethanediazaheptane cadmium(II) is reported and compared to the analogous zinc complex. Of significance is the dimeric form of the [Zn(N(2)S(2))](2) complex achieves penta-coordination about zinc through a bridging thiolate whereas cadmium engages two thiolate as S-bridges resulting in hexa-coordination about cadmium within a coordination polymer whose X-ray crystal structure is reported here. In the presence of W(CO)(5), this polymer breaks up, generating dimeric [Cd(N(2)S(2))](2) with two W(CO)(5) units appended to the terminal thiolates, a feat that is not observed for the zinc dimer analogue. The greater thiophilicity of cadmium over zinc is noted in several features of these complexes.

Zinc/nickel exchange and ligand cannibalism in N2S2O(1,2) donor ligand sets.

To explore the displacement of Zn(2+) by Ni(2+) from within N-, S-, and O-chelate ligands, (N-(3-thiabutyl)-N'-(3-thiapentaneoate)-1,4-diazacycloheptane)zinc(II), Zn-1'-Ac, and 1,4-diazacycloheptane-1,4-diylbis(3-thiapentanoato) zinc(II), Zn-1'-Ac(2), were reacted with Ni(BF(4))(2) in a methanol solution and were found to yield, in both cases, the bright blue, hexa-coordinate Ni-1'-Ac(2) metal-exchanged product. The latter conditions imply an intact-ligand unwrapping process as the hexadentate N(2)S(2)O(2) ligand is transferred from zinc to nickel. The former involves transfer of the pentadentate N(2)S(2)O ligand generating a green, penta-coordinate nickel intermediate which engages in CH(2)CO(2) fragment scavenging from a second zinc unit. This conclusion is supported by the observed analogous reformulation of the stable Zn-1'-Ac complex into Zn-1'-Ac(2) and the dithiolato [Zn-1'](2) dimer. To our knowledge, this is a rare (possibly the first) example of cannibalism reported in such ligand systems. The M-1'-Ac(2) complexes were characterized by X-ray diffraction and compared to the directly synthesized products.

Reactions of palladium and gold complexes with zinc-thiolate chelates using electrospray mass spectrometry and X-ray diffraction: molecular identification of [Pd(bme-dach)], [Au(bme-dach]+ and [ZnCl(bme-dach)]2Pd.

The reaction between the complexes [MCl(L)]Cl(x) (L = 2,2',2''-terpyridine, terpy and dien, diethylenetriamine; M = Pd, x = 1; M = Au, x = 2) and [Zn(bme-dach)](2), an N(2)S(2)-Zn-thiolate bridged dimer used to mimic zinc finger protein sites, was studied by Electrospray Ionisation Mass Spectrometry and the structures of some of the products confirmed by X-ray crystallography. All reactions investigated in this work gave heteronuclear (Zn-thiolate)-metal products, the predominant species being the trinuclear dithiolate-bridged aggregate {[Zn(bme-dach)](2)M}(n+) (M = Pd, Au). X-Ray diffraction studies verified the molecular structure of [{ZnCl(bme-dach)}(2)Pd], and further confirmed that the zinc within the [Zn(bme-dach)](2) unit was retained within the N(2)S(2) binding site. The Zn-bound thiolates form stable thiolate bridges to Pd(2+) in a stair-step shape, held together by a planar PdS(4) center. In addition, both zinc atoms maintained penta-coordinate coordination with apical chloride ligands rather than the more commonly observed tetrahedral geometry. Further, [Pd(bme-dach)] was directly synthesized for X-ray structural characterization of the metal exchanged product observed in mass spectrometry experiments. In the case of Au compounds, the reactions were very fast and the products were similar for both [AuCl(L)]Cl(2) (L = terpy and dien) starting materials. In addition to the multimetallic Zn,Au,Zn aggregate formation, the predominant species from the reaction between [Zn(bme-dach)](2) and both Au compounds was the [Au(bme-dach](+) cation observable via ESI-MS, suggesting Zn/Au metal exchange immediately after mixing the compounds. The direct synthesis of [Au(bme-dach)]BPh(4) confirmed the molecular structure of this species through X-ray crystallography. The reactivity profile of Pd(2+) and Au(3+) species is compared with previous studies using the isostructural Pt compounds and the biological relevance of the results discussed.