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Ulrich Abram

Publications and source records attributed to Ulrich Abram.

15 recordsLinked to original sources
PubMed2006

Technetium tetrachloride as a precursor for small technetium(IV) complexes.

Polymeric technetium tetrachloride reacts with monodentate donor ligands such as THF, acetonitrile, DMSO, thioxane (1-oxa-4-thiacyclohexane), PMe2Ph, PPh3, OPPh3, or OH2 via cleavage of the polymeric network and the formation of [TcCl4(L)2] complexes. The configuration of the products is dependent on the donor atoms such that trans coordination is established with "soft" donor atoms such as sulfur or phosphorus, while cis-[TcCl4(L)2] complexes are formed with the "harder" donors oxygen or nitrogen. The ambivalent thioxane binds to technetium via the sulfur atom. The trans products are air stable and resistant to hydrolysis. The cis complexes, however, undergo stepwise hydrolysis, during which complexes of the composition [Cl3(L)2TcOTc(L)2Cl3] (L = CH3CN, DMSO, or OH2) are formed. They are the first representatives of a new class of technetium(IV) complexes with a bridging oxo ligand. The Tc-O bond lengths in these bridges are between 1.803(1) and 1.823(2) A.

Journal Article↗
PubMed2006

Technetium complexes with triazacyclononane.

[NBu4][TcOCl4] reacts with ethylene glycol and 1,4,7-triazacyclononane (tacn) in MeOH under the formation of the deep-blue oxotechnetium(V) cation [TcO(OC2H4O)(tacn)]+, which can readily be oxidized by air to give the stable technetium(VII) compound [TcO3(tacn)]+. The reaction with aqueous HCl results in reduction and the formation of the cationic technetium(III) complex [TcCl2(OH2)(tacn)]Cl. The products were isolated in crystalline form and studied spectroscopically and by X-ray diffraction.

Journal Article↗
PubMed2005

Controlled ligand deprotonation in lanthanide chelates with asymmetric semicarbazone/benzoylhydrazone or semicarbazone/thiosemicarbazone coordination spheres.

Asymmetric, potentially pentadentate ligands (H(2)L(3)) are formed by subsequent condensation of a semicarbazide and benzoylhydrazine on 2,6-diacetylpyridine. Two equivalents of H(2)L(3) reacts with CeCl(3).7H(2)O, Ce(SO(4))(2).4H(2)O, or EuCl(3).6H(2)O under formation of [Ln(III)(HL(3))(2)](+) cations (Ln = Ce, Eu) with exclusive deprotonation of the benzoylhydrazone ligand arms. The Ce(4+) ion of the sulfate salt is reduced during the reaction and forms 10-coordinate singly charged complex cations, the structure of which is identical to the product of the reaction of cerium(III) chloride. The exact position of deprotonation in the ligands is resolved by infrared spectroscopy, bond lengths considerations, and the hydrogen bonding in the solid-state structures of the products. A similar approach allows the synthesis of mixed semicarbazone/thiosemicarbazone ligands (H(2)L(4)). The reaction of H(2)L(4) with Sm(NO(3))(3).6H(2)O leads to the first structurally characterized lanthanide complex with thiosemicarbazone coordination. The solid-state structure of the 10-coordinate complex [Sm(HL(4))(2)]NO(3).H(2)O shows exclusive deprotonation of the thiosemicarbazone arms of the ligands. All isolated complexes are air stable and do not undergo ligand exchange reactions or hydrolysis in the presence of water.

Journal Article↗
PubMed2005

Rhenium(V) and technetium(V) complexes with phosphoraneimine and phosphoraneiminato ligands.

Air-stable rhenium(V) nitrido complexes are formed when [ReOCl3(PPh3)2], [NBu4][ReOCl4], or [NBu4][ReNCl4] are treated with an excess of silylated phosphoraneiminates of the composition Me3SiNPPh3 or Ph2P(NSiMe3)CH2PPh2 in CH2Cl2. Complexes of the compositions [ReNCl(Ph2PCH2PPh2NH)2]Cl (1), [ReN(OSiMe3)(Ph2PCH2PPh2NH)2]Cl (2) or [ReNCl2(PPh3)2] (3) were isolated and structurally characterized. The latter compound was also produced during a reaction of the rhenium(III) precursor [ReCl3(PPh3)2(CH3CN)] and Me3SiNPPh3. Nitrogen transfer from the phosphorus to the rhenium atoms and the formation of nitrido ligands were observed in all examples. All products of reactions with an excess of the potentially chelating phosphoraneiminate Me3SiNP(Ph2)CH2PPh2 contain neutral Ph2PCH2PPh2NH ligands. The required protons are supplied by a metal-induced decomposition of the solvent dichloromethane. The Re-N(imine) bond lengths (2.055-2.110 A) indicate single bonds, whereas the N-P bond with lengths between 1.596 A and 1.611 A reflect considerable double bond character. An oxorhenium(V) phosphoraneiminato complex, the dimeric compound [ReOCl2(mu-N-Ph2PCH2PPh2N)]2 (4), is formed during the reaction of [NBu4][ReOCl4] with an equivalent amount of Ph2P(NSiMe3)CH2PPh in dry acetonitrile. The blue neutral complex with two bridging phosphoraneiminato units is stable as a solid and in dry solvents. It decomposes in solution, when traces of water are present. The rhenium-nitrogen distances of 2.028(3) and 2.082(3) A are in the typical range of bridging phosphoraneiminates and an almost symmetric bonding mode. Technetium complexes with phosphoraneimine ligands were isolated from reactions of [NBu4][TcOCl4] with Me3SiNPPh3, and [NBu4][TcNCl4] with Me3SiNP(Ph2)CH2PPh2. Nitrogen transfer and the formation of a five-coordinate nitrido species, [TcNCl2(HNPPh3)2] (5), was observed in the case of the oxo precursor, whereas reduction of the technetium(VI) starting material and the formation of the neutral technetium(V) complex [TcNCl2(Ph2PCH2PPh2NH)] (6) or [TcNCl(Ph2PCH2PPh2NH)2]Cl (7) was observed in the latter case. Both technetium complexes are air stable and X-ray structure determinations show bonding modes of the phosphoraneimines similar to those in the rhenium complexes.

Journal Article↗
PubMed2005

Mono- and dinuclear tricarbonyltechnetium(I) complexes with thiosemicarbazones.

[NEt4]2[Tc(CO)3Cl3] reacts with thiosemicarbazones derived from 2,2'-dipyridyl ketone (HL3) and 4-acetylpyridine (HL4) to form stable technetium(I) complexes of the compositions [Tc(CO)3Cl(HL3-Npy,Npy)] and [Tc2(CO)6Cl2(micro-HL4-Npy,S)]. Whereas exclusively the pyridine nitrogen atoms are involved in coordination in the monomeric complex, the binuclear compound represents the first technetium complex with a coordinated thiosemicarbazone functionality.

Journal Article↗
PubMed2005

Novel Cu(II) quinoxaline N1,N4-dioxide complexes as selective hypoxic cytotoxins.

As an effort to develop novel selective hypoxia-cytotoxins and to improve bioavailability and pharmacological and toxicological properties of quinoxaline N1,N4-dioxide derivatives (L1 = 3-amino-6(7)-chloroquinoxaline-2-carbonitrile N1,N4-dioxide, L2 = 3-amino-6(7)-bromoquinoxaline-2-carbonitrile N1,N4-dioxide and L3 = 3-amino-6(7)-methylquinoxaline-2-carbonitrile N1,N4-dioxide) and to get a synergism among metals and these type of bioreductive agents, L2 and three novel Cu(II) complexes of general formulae [Cu(II)(H2O)x(L - H)2], where L = L1 (x = 1), L2 (x = 0) or L3 (x = 2) were developed. L2 and complexes were synthesized and structurally characterized by elemental and thermal analyses, and FTIR, electronic, MS, NMR, and EPR spectroscopies. The new compounds were subjected to cytotoxic evaluation in V79 cells in hypoxic and aerobic conditions. The complexes showed excellent selective cytotoxicity in hypoxia, being their cytotoxicity similar to or higher than that of the ligands L1-L3. Besides, the copper complexes were so poorly cytotoxic in oxia as the free ligands. In addition, for the first time Cu(II)-quinoxaline complexes are reported as a family of hypoxic cytotoxins.

Animals↗
PubMed2004

Rhenium(V) oxo complexes with N-heterocyclic carbenes.

Air-stable rhenium(V) oxo complexes are formed when [ReOCl(3)(PPh(3))(2)] is treated with N-heterocyclic carbenes of the 1,3-dialkyl-4,5-dimethylimidazol-2-ylidene type, L(R) (R = Me, Et, i-Pr). Complexes of the compositions [ReO(2)(L(R))(4)](+), [ReOCl(L(R))(4)](2+), or [ReO(OMe)(L(R))(4)](2+) can be isolated depending on the alkyl substituents at the nitrogen atoms of the ligands and the reaction conditions applied. Despite the steric overcrowding of the equatorial coordination spheres of the metal atoms by each of the four carbene ligands, stable complexes with six-coordinate rhenium atoms are obtained. Steric demands of the alkyl groups allow control of the stability of the mono-oxo intermediates. Air-stable cationic complexes of the compositions [ReOCl(L(Me))(4)](2+), [ReOCl(L(Et))(4)](2+), and [ReO(OMe)(L(Me))(4)](2+) have been isolated, whereas reactions of [ReOCl(3)(PPh(3))(2)] or other rhenium(V) precursors with the more bulky 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (L(i)(-)(Pr)) directly yield the dioxo complex [ReO(2)(L(i)(-)(Pr))(4)](+). X-ray structures of [ReO(2)(L(i)(-)(Pr))(4)][ReO(4)], [ReO(2)(L(i)(-)(Pr))(4)][PF(6)], [ReO(2)(L(Me))(4)][ReO(4)](0.45)[PF(6)](0.55), [ReO(MeOH)(L(Me))(4)][PF(6)](2), and [ReOCl(L(Et))(4)][PF(6)](2) show that the equatorial coordination spheres of the rhenium atoms are essentially planar irrespective of the steric demands of the individual carbene ligands.

Journal Article↗
PubMed2004

Tricarbonylrhenium(I) complexes with thiosemicarbazone derivatives of 2-acetylpyridine and 2-pyridine formamide showing two unusual coordination modes of tridentate thiosemicarbazone ligands.

[NEt(4)](2)[Re(CO)(3)Br(3)] reacts with 2-acetylpyridine phenylthiosemicarbazone (HL(1)) and 2-pyridine formamide thiosemicarbazone (HL(2)) under formation of air-stable, neutral rhenium(I) complexes of the compositions [Re(CO)(3)(L(1)-N,N,S)] and [Re(CO)(3)Br(HL(2)-N,N)]. Spectroscopic studies and X-ray crystallography show that the potentially tridentate thiosemicarbazones adopt unusual coordination modes. Whereas HL(1) deprotonates and binds to the metal in a nonplanar fashion, HL(2) acts as neutral N,N donor ligand. The bond lengths inside the chelate rings are almost uninfluenced by the overall bonding situation.

Journal Article↗
PubMed2004

Stable gold(III) complexes with thiosemicarbazone derivatives.

Novel thiosemicarbazonato complexes of gold(III) have been prepared from reactions of [Au(damp-C1,N)Cl2(damp- = 2-(N,N-dimethylaminomethyl)phenyl) or [NBu4][AuCl4] with 2-pyridineformamide thiosemicarbazones (HL). The thiosemicarbazones deprotonate and coordinate as mononegative, tridentate NNS ligands to gold to give [Au(Hdamp-C1)(L)]Cl2 or [AuCl(L)]Cl complexes. The organometallic damp- ligand is protonated during the reactions and the Au-N bond is cleaved. The [AuCl(L)]+ cations represent the first gold(III) complexes with thiourea derivatives which are not stabilised by an additional organometallic ligand. Reactions of [NBu4][AuX4](X = Cl, Br) with diphenylthiocarbazone (dithizone) result in reduction of the metal and the formation of gold(I) complexes of the composition [AuX(SCN4-3,4-Ph2)] where SCN4-3,4-Ph2 is 3,4-diphenyltetrazole thione which is formed from cyclisation of dithizone.

Crystallography, X-Ray↗
PubMed2004

Complexes of dichloro[2-(dimethylaminomethyl)phenyl-C1,N]gold(III), [Au(damp-C1,N)Cl2], with formylferrocene thiosemicarbazones: synthesis, structure and cytotoxicity.

Dichloro[2-(dimethylaminomethyl)phenyl- phenyl-C1,N]gold(III), [Au(damp-C1,N)Cl2], reacts with the formylferrocene thiosemicarbazones derived from 4-methyl-, 4-phenyl-, 4-ethyl- and 4,4-dimethyl-3-thiosemicarbazides, HFcTSC, to give complexes of general formula [Au(Hdamp-1C)Cl(FcTSC)]Cl. These complexes were isolated and characterized by elemental analysis, mass spectrometry and IR, 1H NMR and (13)C NMR spectroscopy. In some cases, cyclic voltammetric studies were carried out and these showed that the complexation of gold affects the redox behaviour of the ferrocene unit. The in vitro antitumor activity against the HeLa cell line was also determined for the more soluble complexes. The IC(50) values were found to be higher than that of cisplatin but the maximum antiproliferative activity was similar.

Antineoplastic Agents↗
PubMed2003

Synthesis and structural characterization of cationic rhenium(V) and technetium(V) dioxo complexes containing four N-heterocyclic carbene ligands.

Cationic dioxorhenium and dioxotechnetium complexes of the composition [MO(2)(L(1))(4)](+) (L(1) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) have been prepared from various starting materials and studied spectroscopically and by X-ray crystallography. The metal-carbon distances range from 2.216(4) to 2.232(4) A indicating mainly sigma-bonding.

Journal Article↗
PubMed1998

Structural and (99)Tc NMR Investigations of Complexes with fac-[Tc(CO)(3)](+) Moieties and Macrocyclic Thioethers of Various Ring Sizes: Synthesis and X-ray Structure of the Complexes fac-[Tc(9-ane-S(3))(CO)(3)]Br, fac-[Tc(2)(tosylate)(2)(18-ane-S(6))(CO)(6)], and fac-[Tc(2)(20-ane-S(6)-OH)(CO)(6)][tosylate](2).

Starting originally from the organometallic precursor [NEt(4)](2)[TcBr(3)(CO)(3)] (1b), substitution reactions were performed with the macrocyclic thioethers 1,4,7-trithiacyclononane (9-ane-S(3)), 1,4,7,10,13,16-hexathiacyclooctadecane (18-ane-S(6)), and 3,6,9,13,16,19-hexathiacycloicosanol (20-ane-S(6)-OH). The corresponding complexes fac-[Tc(9-ane-S(3))(CO)(3)]Br (2), fac-[Tc(2)(tosylate)(2)(18-ane-S(6))(CO)(6)] (3), and fac-[Tc(2)(20-ane-S(6)-OH)(CO)(6)][tosylate](2) (5) were isolated in good yields and characterized spectroscopically by IR, (1)H, (99)Tc NMR, and X-ray diffraction methods. In the case of 18-ane-S(6) and 20-ane-S(6)-OH the formation of the 1:2 as well as the 1:1 complex could be observed in the (99)Tc NMR experiment, depending on the ligand to metal ratio. Complex 2crystallizes in the monoclinic space group P2(1)/c, a = 14.79(2) Å, b = 11.691(2) Å, c = 16.94(2) Å, beta = 94.88(6) degrees, Z = 8. The tripodal ligand is coordinated through the sulfur atoms to the metal center, forming three favorable five-membered chelate rings. Complex 3 crystallizes in the monoclinic space group C2/c, a = 26.073(4) Å, b = 9.288(1) Å, c = 17.898(3) Å, beta = 99.84(1) degrees, Z = 4. The binuclear unit is formed by two fac-[Tc(tosylate)(CO)(3)] moieties which are trans, bidentate coordinated to the macrocyclic ligand. Compound 5 crystallizes in the monoclinic space group Pc, a = 25.737(4) Å, b = 14.009(1) Å, c = 26.479(3) Å, beta = 149.56(2) degrees, Z = 4. In the case of the dicationic compound 5, the two Tc(I) centers are tripodal, cis coordinated toward the thia crown ether. A detailed analysis of the ring conformation in the solid state structure explained to a certain extent the formation of only one isomer (trans in the case of 3 and cis in the case of 5, respectively) during the substitution reaction.

Journal Article↗
PubMed1996

Silver(I) Complexes of the Derivatized Crown Thioether Ligands 3,6,9,12,15,18-Hexathianonadecanol and 3,6,9,13,16,19-Hexathiaicosanol. Determination of Stability Constants and the Crystal Structures of [Ag(19-aneS6-OH)][CF(3)SO(3)] and [Ag(20-aneS6-OH)][BF(4)].

The derivatized 19- and 20-membered macrocyclic thio crowns 3,6,9,12,15,18-hexathianonadecanol C(13)H(26)OS(6) (19-aneS6-OH) (1) and 3,6,9,13,16,19-hexathiacycloicosanol C(14)H(28)OS(6) (20-aneS6-OH) (2) have been synthesized by [1 + 1] cyclization in about 30% yield. The ligands 1 and 2 react readily at room temperature with different silver(I) salts in water and in organic solvents to form in quantitative yields the complexes [Ag(19-aneS6-OH)](+) (3) and [Ag(20-aneS6-OH)](+) (4) for which crystals of X-ray quality were grown by slow diffusion of diethylether into methanol. [Ag(19-aneS6-OH)][CF(3)SO(3)] crystallizes in the triclinic space group P&onemacr; with Z = 2, a = 10.760(1), b = 10.853(2) and c = 11.326(2)Å, and alpha = 78.73(1), beta = 73.47(1), and gamma = 74.99(1) degrees. [Ag(20-aneS6-OH)][BF(4)] also crystallizes in the triclinic space group P&onemacr; with Z = 4. The unit cell constants were determined with a = 10.076(4), b = 10.525(3), and c = 22.135(8)Å, alpha = 93.32(2), beta = 102.43(2), and gamma = 100.32(2) degrees. The complex cations [Ag(19-aneS6-OH)](+) and [Ag(20-aneS6-OH)](+) are coordinated through only four sulfur atoms; thus, a distorted tetrahedral coordination geometry is exhibited. In addition we found a highly asymmetric Ag-S bond lengths distribution throughout all complex cations. The stability constants of [Ag](+) with 1 and 2 and, for comparison with [18-aneS6] (5), have been determined in methanol by potentiometric [Ag](+) measurements. Log K values for the formation of 3, 4, and [Ag(18-aneS6](+) (6) are 12.04 +/- 0.19, 11.49 +/- 0.15, and 12.67 +/- 0.13 respectively. Owing to a comparable macrocyclic effect, the similar log K values are reasonable but, since 6 coordinates octahedrally, not expected. (1)H and (13)C NMR investigations at various temperatures give evidence for fluxional coordinative behavior between all six sulfur atoms in solution. Consequently [Ag(19-aneS6-OH)](+), [Ag(20-aneS6-OH)](+), and [Ag(18-aneS6](+) seem to exhibit principally the same solution structures although the solid structures are very different.

Journal Article↗