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Die Hybridliganden β-(Diphenylphosphino)-athylpyridin-(2)(DPPAP) und β-(Diphenylarsino)-athylpyridin-(2) (DPAsAP) bilden mit Palladium(II) 1,1- und 1,2-Komplexe. Dabei fungieren sie in den 1,1-Komplexen Pd(DPPAAP)Cl2 und Pd(DPAsAP)Cl2 und in den Perchloraten [Pd(DPPAP)2](ClO4)2 und [Pd(DPAsAP)2]((ClO4)2 zweizahlig. In den Verbindungen Pd(DPPAP)2Cl2 und Pd(DPAsAP)2Cl2 dagegen besetzen sie nur eine Koordinationsstelle und zwar durch die Diphenylphosphino- bzw. die Diphenylarsinogruppe, die die weichen Donoratome Phosphor bzw. Arsen enthalten. Es werden die IR-Spektren und die elektrische Leitfahigkeit der neuen Verbindungen diskutiert. Palladium(II) Complexes of 2-(β-Diphenylphosphinoethyl)-pyridine and 2-(β-(Diphenylarsinoethyl)-pyridine The hybrid ligands 2-(β-diphenylphosphinoethyl)-pyridine (DPPAP) and 2-(β-diphenylarsinoethyl)-pyridine (DPAsAP) form 1,1- and 1,2-complexes with palladium(II). In the 1,1-complexes Pd(DPPAP)Cl2 and Pd(DPAsAP)Cl2, and in the perchlorates [Pd(DPPAP)2](ClO4)2 and [Pd(DPAsAP)2](ClO4)2 they function as bidentates. In the compounds Pd(DPPAP)2Cl2 and Pd(DPAsAP)2Cl2, however, they occupy only one coordination site via the diphenylphosphino or the diphenylarsino group, containing the soft donor atoms phosphorus or arsenic. The ir-spectra and the electric conductivity of the new compounds are discussed.

Eine Reihe von Metallchelaten N-substituierter bzw. N, N-disubstituierter 2-Acylthioacetamide wurde in Substanz isoliert und die Koordinationsverhaltnisse untersucht. Zur Charakterisierung der Komplexbildung dienten weiterhin die in Dioxan-Wasser-Mischung ermittelten Saure- und Komplexstabilitatskonstanten. Bemerkenswert ist die gegenuber Nickel hohere Stabilitat der Zinkchelate. Das Adduktbildungsvermogen der Nickelchelate mit Pyridin wurde in Relation zur Komplexstabilitat und zum Einflus von Substituenten im Liganden betrachtet. Chelates of s-Dicarbonyl Compounds and their Derivatives. 60. Coordination Ability of 2-Acylthioacetamides A series of metal chelates with N-substituted and N, N-disubstituted 2-acylthioacetamides was synthesized in the solid state, and the coordination site was studied. Acid constants and complex stability constants determined in dioxane-water mixture were used to characterize the coordination ability of the ligands. In comparison with nickel the zinc chelates show a higher stability. The formation of pyridine adducts of the nickel chelates was discussed in their relation to complex stability and the influence of substituents in the ligands.

The four methyl and acetyl complexes In(CO)(L)FeR (L = CO, PPH3; R = CH3, COCH3) have been synthesized and characterized as η5-indenyl (In) complexes. These were prepared in an attempt at using the indenyl ligand to generate a vacant coordination site, through its η5/η3 tautomerization, and hence promote hydrogenation of the methyl or acetyl ligand. These complexes, however, remain inert towards H2 under generally mild conditions: to 50 °C/1200 psig H2 in 1,2-dichloroethane solution. When the temperature is raised to 100 °C these complexes degrade, with no evidence for acetaldehyde/ethanol production.

A study of the stereochemistry of the ‘carbonyl insertion’ reactions: [IrCl 2 Et(CO) 2 L]+L′[IrCl 2 (COEt)(CO)LL′] shows that the rate-determining step involves the combination of ethyl and carbonyl ligands to give a five-coordinate intermediate, probably of square-pyramidal geometry, with the propionyl group in the apical position. The combination is a symmetrical process for which the two terms ‘carbonyl insertion’ and ‘alkyl migration’ are equally misleading. Subsequent attack by the incoming ligand L′ occurs at the vacant octahedral coordination site trans to the propionyl group. That the stereochemistry of the products is a direct result of the mechanism of the reactions is shown by the subsequent rearrangement of the products to a more thermodynamically stable isomer.

The use of Yb(DPM)3 as an aid in assigning the 13C chemical shifts of steroids is described. The 13C spectra of cholesterol, i-cholesterol, and epi-i-cholesterol have been determined in the presence and absence of the reagent. A computer program was used to position the lanthanide using five or six readily assigned lines. All other carbon resonances were then calculated and assignments made. Application of the technique with Eu(DPM)3 was less satisfactory especially for those carbons near the coordination site. Cholesterol served as the model compound, and the technique then applied to the i-steroids.

Metal complexes of acetylhydrazide and benzoylhydrazide are reported. I.R. spectra of the normal and deuterated complexes, visible spectra of both solids and solutions, u.v. spectra, magnetic data and conductance data are discussed. Monodentate character and “imidol” structure of the ligands, in the complexes are suggested. The NH nitrogen atom is proved to be the coordination site.

The ligand 7-nitroso-8-hydroxyquinoline-5-sulphonic acid (H2L) is prepared by the nitrosation of 8-hydroxyquinoline-5-sulphonic acid. This ligand possess the coordination sites of 2-nitroso-1-naphthol and of 8-hydroxyquinoline where the hydroxyl group is functional at either site. The Fe(II) and Co(II) complexes were prepared by the reaction of the metal ion with the acid ligand, while the Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Sr(II), Cd(II), Th(IV) and UO2(II) were prepared from the reaction of the metal ion with the disodium salt of the ligand (Na2L). Charge transfer bands were only observed in the electronic spectra of the Fe(II), and Co(II) complexes. Chemical analysis, and physico-chemical evidence are compatible with formulating the Fe(II), and Co(II) complexes as H[M(HL)3] the UO2(II) complex as (LNa)2 UO2. 2H2O, the Th(IV) complex as L2M. 4H2O, and the Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Sr(II), and Cd(II) as LM. 2H2O, where the 2-nitroso-1-naphthol site is involved in metal chelation.

The rate constant for dissociation of [Ca(AA − )] + , where (AA − ) is the radical anion of ascorbic acid, has been measured by observation of specific line broadening in the ESR spectrum. Its value in DMSO at 298 K is 4.68 × 10 5 s −1 . The mechanism for the line broadening is a combination of a g and a hyperfine shift upon coordination of the metal ion.

In the reaction with phenylacetylene leading to [(PPh 3 ) 2 (CO)IrCl (HNNC 6 H 4 R- p )(CCPh)] (BF 4 ) (R  NO 2 , CN, COCH 3 ), the vacant coordination site in [(PPh 3 ) 2 (CO)IrCl(N 2 C 6 H 4 R- p )] (BF 4 ) plays a key role in the activation of the acetylenic CH bond. ca]To whom correspondence should be addressed.

Integrins use divalent cations, held within a novel ‘MIDAS' motif, for ligand binding. It is proposed that a missing coordination site for the cation is provided by a critical acidic residue in the ligand.

Circular dichroism studies on the methylcobalamin-intrinsic factor complex, together with studies on the carbethoxylation of histidine residues in this complex, indicate that 5,6 dimethylbenzimidazole is probably displaced by a histidine residue of intrinsic factor which coordinates to the cobalt atom at the sixth coordination site. In addition, the stability of the CoC σ bond for methylcobalamin bound to intrinsic factor is identical to that stability measured for the free methyl-cobinamide-histidine complex, but considerably different from the stability of this σ bond in free methylcobalamin.

Zinc(II) promotes the reduction of unactivated ketones and aldehydes by (methyl-substituted) 1-methyl-1,4-dihydropyridines. Coordination of the dihydropyridines to the metal, which occurs via their annular nitrogen atoms, is essential for hydrogen-transfer. The reductions proceed best in apolar non-aromatic solvents, which are unable to compete with the carbonyl group of the substrate for a coordination site at the metal. Virtually no hydrogen-transfer takes place in the absence of Zn(II) salts or when zinc coordination complexes are used in which the metal is coordinatively saturated. The results of this study are discussed in terms of a possible relationship with the role of zinc in alcohol dehydrogenases and metal-catalyzed reductions in biomimetic systems.

Assignment of the ESR spectra was made for a low-spin pentacoordinated Co(II) complex, CoII(phenylisocyanide)5(C1O4)2, and its hydrated form, in which the sixth coordination site is occupied by a water molecule. It was shown that the occurrence in the frozen state of each form, anhydrous or hydrated, is determined by the solvent, i.e., by whether a hydrophobic or hydrophilic solvent is used. Based upon the assignment, the effect of attaching the sixth ligand on the ESR parameters was examined. It was pointed out that the effect is to shift one of the g components toward a higher value and the 59Co isotropic contact term toward a more negative value. This conclusion was corroborated by examining the ESR parameters of the tetrakis and hexakis (phenylisocyanide) complexes. A brief explanation was given in terms of vibronic mixing of \({{d}_{{{x}^{2}}-{{y}^{2}}}}\) into \({{d}_{{{z}^{2}}}}\).

Significance of the phase transfer catalysis for the synthesis of less accessible aromatic and heterocyclic compounds is emphasized. A series of novel azo compounds containing pyrazole and quinoline fragments has been prepared and employed in the synthesis of 3d-metal coordination compounds with desired types of the coordination site.

The crystal and molecular structure of the title complex has been determined by X-ray diffraction. It is a distorted trigonal-bipyramidal complex: each dithiophosphato ligand spanns an oblique edge of the coordination polyhedron, and triphenylphosphine occupies the fifth coordination site with unusually long Co–P bond length of 2.551 A.

Chemical shift reagents (csr) markedly expand the nuclear magnetic resonance spectra of lipid derivatives thus providing considerably more structural information than it has hitherto been possible to obtain. Preferred csr are rare earth complexes of europium (III) and praseodymium (III) with certain anionic ligands. The use of csr with methyl oleate is described here.