Erhard Uhlemann

Rotational barriers in metal chelates. Hindered rotation about the terminal NC(X)-bond in Ni-coordinated isomeric unsaturated 1,3-(S,O)-ligands

The barrier of hindered rotation about the terminal NC(X)-bond has been measured in the ligands as well as in the nickel(II) chelates using 1H NMR. The free energy of activation for hindered rotation is lower in the cases where charge delocalization occurs in the chelate ring (chelates with methine groups) and higher in the cases where it takes place in a smaller degree (aza-analogous chelates). Thus the bonding situation investigated by 1H NMR corresponds fairly well with that determined by other methods.

Voltammetric and Potentiometric Studies on the Stability of Vanadium(IV) Complexes. A Comparison of Solution Phase Voltammetry with the Voltammetry of Microcrystalline Solid Compounds

Formal potentials of non-oxo vanadium complexes obtained by the cyclic voltammetry of solutions and of solid microcrystalline compounds are compared with potentiometrically determined stability constants of the corresponding oxovanadium(IV) complexes. The stability constants show a qualitative correlation with the formal potentials. The non-oxo complexes exhibit a reversible one-electron system VIV/VIII as well as VIV/VV in dichloromethane solution whereas the oxo complexes only show the transition between VIV and VV. Generally, the oxidation of non-oxo vanadium(IV) complexes proceeds at higher potentials than that of the corresponding oxovanadium(IV) species. The shift of the formal potentials is clearly correlated with the structure of the compounds.

SALICYLALDEHYDE-2-MERCAPTOANILATO (2-)-2-HYDROXYPHENYL-BENZTHIAZOLATO-NITROSYL-MOLYBDENUM(II) - A CHELATE WHICH SIMULTANEOUSLY CONTAINS AN AZOMETHINE LIGAND AND ITS CYCLIC OXIDATION PRODUCT

Salicylaldehyde-2-mercaptoanilato(2−)-2-hydroxyphenylbenzthiazolato-nitrosyl-molybdenum(II) was synthesized by ligand exchange reaction of Mo(NO) 2 acac 2 with salicylaldehyde-2-mercaptoanil. Besides the starting ligand the complex likewise contains the cyclic oxidation product. The compound crystallizes in the monoclinic space group P 2 1 / n (No. 14) with a = 11.026(9), b = 9.228(3), c = 23.883(10)A, β = 102.23(5)°, V = 2375A 3 .

Ligand exchange reactions of ReCl4(PPh3)2, ReOCl3(PPh3)2 and NiCl2(PPh3)2 with acetylacetone thiobenzoylhydrazone. An unexpected template reaction at the ReO3+ core. Molecular structures of the resulting oxorhenium(V) and nickel complexes

Abstract The ligand exchange reactions of ReCl4(PPh3)2, ReOCl3(PPh3)2 and NiCl2(PPh3)2 with acetylacetone thiobenzoylhydrazone have been studied. An unexpected template reaction at the ReO3+ core forming the new tetradentate triacidic ligand triacetylmethane bis(thiobenzoylhydrazone) will be described and discussed. The final products were characterized by elemental analysis, mass spectroscopy, 1H NMR, IR, UV-VIS spectroscopy and X-ray structural analysis. [Acetylacetone thiobenzoylhydrazonato(2-)]chloro-oxorthenium(V) was isolated as an intermediate. The crystal structures have been determined of [triacetylmethane bis(thiobenzoylhydrazonato) (3-)- S,S′,N,N′]oxorhenium(V) C21H19N4O2S2Re, monoclinic P2 1 /m, a = 7.451(1), B = 11.262(3), c = 12.639(4) A , β = 90.66(2)°, Z = 2, R 1 = 0.0445 , and [acetylacetone thiobenzoylhydrazonato(2-)]-triphenylphosphane-nickel(II) C30H27N2OSPNi, orthombic Pbca, a = 16.658(2), b = 14.725(2), c = 21.950(2) A , Z = 8, R 1 = 0.0283 .

Ligand exchange reactions of ReCl4(PPh3)2 with tridentate diacidic ligands with the donor set ONO(S). Molecular structures of the resulting oxo-rhenium(V) complexes

Abstract Ligand exchange reactions of ReCl4(PPh3)2 with tridentate diacidic ligands with the donor set ONO(S) were studied. The reaction course was cleared up by mass spectrometric and X-ray structural analysis of intermediate and final products. The rhenium (IV chelates formed first react further to give oxo-rhenium(V) chelates via aerial oxidation. To clarify the structural properties of these rhenium(V) chelates, X-ray analyses were carried out. The crystal structures were determined for salicylaldehyde thiobenzoylhydrazonato (2−) salicylaldehyde thiobenzoylhydrazonato oxo-rhenium(V) (1) C28H21N4O3Re: monoclinic P2 1 /c, a=9.9183(13), b=12.721(2), c=20.802(3) A , β = 96.416(13)°, Z = 4, R1 = 0.0513; benzoylacetone thiobenzoylhydrazonato (2−) benzoylacetone thiobenzoylhydrazonato oxo-rhenium(V) (2) C34H29N4S2Re: triclinic P 1 , a = 10.811(4), b = 11.364(9), c = 14.878(16) A , α = 67.56(4), β = 71.54(3) , γ = 79.50(3)°, Z = 2, R1 = 0.0354. Benzoylacetonato-dichloro-triphenylphosphane-oxo-rhenium(V) (3b) is characterized as a decomposition product resulting from oxidation of rhenium(IV) to oxo-rhenium(V) and hydrolysis of the ligand benzoylacetone benzoylhydrazone. Crystal data for 3b. C28H24O3PCl2Re: monoclinic P2 1 /c, a = 15.904(2), b = 11.021(5), c = 17.227(2) A , β = 115.476(11)°, Z=4, R 1 = 0.0394 .

Nuclear magnetic resonance studies and molecular modelling of the solution structure of some dibenzo crown ethers and their complexes

Abstract The 1 H and 13 C NMR spectra of the structurally related crown ethers 1 – 7 with further potential coordination groups (OH, COOH) and the alkali metal complexes of the latter were recorded. Structural information was deduced especially from 13 C NMR chemical shifts, the salt-induced 13 C chemical shifts (as a measure of both the in-plane interactions HC 2 C 1 OC 8 H 2 and HC 5 C 6 OC 7 H 2 ), vicinal H,H coupling constants and spin-lattice relaxation times, T 1 , of protonated 13 C nuclei. The complex stability constants ( K A ) for the complexes of 1 – 7 with LiI were determined by 7 Li NMR spectroscopy. Accompanying quantum-mechanical calculations corroborate the spectroscopical conclusions about the preferred conformers of the studied crown ethers both in the free and in the complexed state. New insights into the complexation behaviour of the crown ether carboxylic acids 3 – 5 were obtained which are in contrast to the generally discussed “cavity effects”. The results of NMR spectroscopy and molecular modelling prove the complexation of the crown ether carboxylic acid to take place first at the carboxyl group. In a second step, the bound cation is folded over the cavity of the same crown ether or over one of another crown ether ring system.

Voltammetric studies of non-oxo vanadium(IV) chelates

A series of non-oxo vanadium(IV) chelates with tridentate diacidic ligands was studied by cyclovoltammetry using a platinum electrode and by differential pulse polarography using a hanging mercury drop electrode. The reversibility of the electrode processes was observed for the electrochemical redox reaction. A diffusion-controlled one-electron transfer was mostly found. The influence of structural parameters on the stability of the compounds was discussed considering the shift of the reduction potential of the complexes.

Strukturelle Unterschiede von Ruthenium(III)-Chelaten mit SN- und SO -Liganden. Strukturen von Tris(1-phenyl-3-methyl-4-phenylhydrazono-5-thionato)ruthenium (III) und Tris(thiodibenzovlm ethanato)ruthenium( III) / Structural Differences of Ruthenium (III) Chelates with SN- and SO-Ligands. Crystal Structures of Tris(1-phenyl-3-methyl-4-phenyl-hydrazono-5-thionato)- ruthenium (III) and Tris(thiodibenzoylmethanato)ruthenium (III)

Both complexes were synthesized and characterized by X-ray analysis.They have a distorted octahedral structure. In the first case a meridional arrangement of ligands was found whereas the compound with thiodibenzoylmethane has a facial structure. Crystal data: C48H39N12RuS3: a = 1400,9(3)pm , b = 1839,3(4) pm , c = 1969,9(4) pm, β = 109,65(3°); space group: P2(1)/c , Z = 4, C45H33O3RuS3: a = 1013,2(2) pm, b = 1762,7(4) pm, c = 2151,5(4) pm; β = 100,11(3°), space group: P2(1)/n, Z = 4.

Redoxreaktionen von Molybdänverbindungen mit Bis(2-salicyliden- aniinophenvl Klisulfid. Kristallstruktur von Salicylaldehyd-2-mercapto- anilato(2-)-triphenylphosphanoxid-dioxomolybdän(VI) Redox / Reactions of Molybdenum Compounds with Bis(2-salicylidene-aminophenyl)disulfide. Crystal Structure of Salicylaldehyde-2-mercaptoanilato(2-)– triphenylphosphaneoxide-dioxo- molybdenum(VI)

Abstract The reactions of Mo(CO)6, Mo(acac)2(NO)2, and MoO2(acac)2 with bis(2-salicylideneaminophenyl) disulfide in the presence of triphenylphosphane have been studied. The crystal structure of salicylaldehyde-2-mercaptoanilato(2-)-triphenylphosphaneoxidedioxomolybdenum (VI) was determined by X-ray analysis.

Synthese dreizähniger Liganden durch Spaltung von 3,5-Diphenyl-1,2-dithioliumsalzen mit (Thio)benzoylhydrazin oder 2-Hydroxy-5-methyl-anilin. Strukturen der gebildeten Nickelchelate / Synthesis of Tridentate Ligands by Cleavage of 3.5-Diphenyl-1.2-dithiolium Salts with (Thio)benzoylhydrazine or 2-Hydroxy-5-methyl-aniline. Structures of the Corresponding Nickel Chelates

Tridentate ligands having the donor set S⌒ N⌒ O(S ) were synthesized by cleavage of 3.5-diphenyl-1.2-dithiolium salts with (thio)benzoylhydrazine or 2-hydroxy-5-methyl-aniline. The ligands were characterized as their nickel chelates formed in the presence of triphenylphosphane. The same nickel compounds result by template reactions of dithiolium salt, nickel acetate and the corresponding amine component. Crystal structures were determined for thiodibenzoylmethane benzoylhydrazone 1a, [thiodibenzoylmethane benzoylhydrazonato(2-)]-triphenylphosphane-nickel(II) 1b, [thiodibenzoylmethane thiobenzoylhydrazonato(2-)]-triphenylphosphane-nickel(II) 2b and [thiodibenzoylm ethane 2- hydroxy-5-methyl-anilato(2-)] triphenylphosphane-nickel(II)ethanol 3.