Metal ions in biological systems, vol. 2, metal ligand complexes : ed. by H. Sigel, Dekker, New York, 1973, xiv + 294 pages, $25.25

The kinetic isotope effect for β-hydride elimination from alkyliridium(I) complexes has bee found to be k_H/k_D = 2.28 ± 0.20.     

Reactions of dimethyl acetylenedicarboxylate—X: Reaction with salicylaldehyde,ortho hydroxyacetophenone, 2-hydroxychalcones and 2,2′-dihydroxychalcones

Salicylaldehyde reacts with dimethyl acetylenedicarboxylate in benzene solution to give a mixture of dimethyl o-formylphenoxymaleate, dimethyl o-formylphenoxyfumarate, 2,3-dicarbomethoxychrom - 2 - en - 4 - ol, 2,3 - dicarbomethoxychrom - 3 - en - 2 - ol, dimethyl (2,3 - dicarbomethoxychrom - 2 - en - 4 - yl) - oxalacetate and dimethyl fumarate. 2,3 - Dicarbomethoxychrom - 3 - en - 2 - ol in this reaction is formed from 2,3 - dicarbomethoxychrom - 2 - en - 4 - ol through a benzopyrylium intermediate. The reaction of salicylaldehyde with excess of dimethyl acetylenedicarboxylate, however, gives a mixture of 2,3 - dicarbomethoxychrom - 3 - en - 2 - ol and dimethyl (2,3 - dicarbomethoxychrom - 3 - en) - 2 - oxyfumarate. 2,3 - Dicarbomethoxychrom - 3 - en - 2 - ol itself reacts further with dimethyl acetylenedicarboxylate to give 2,3,12 - tricarbomethoxychrom - 3,4 - eno[2,3 - b] pyrone. Similarly, the reaction of o-hydroxyacetophenone with dimethyl acetylendicarboxylate gives a mixture of dimethyl o-acetylphenoxymaleate, dimethyl o-acetylphenoxyfumarate, 2,3 - dicarbomethoxy - 4 - methylchrom - 2 - en - 4 - ol and 2,3 - dicarbomethoxy - 4 - methylchrom - 3 - en - 2 - ol. Both 2-hydroxychalcone and 2 - hydroxy - 4′ - methoxychalcone give mixtures of chalcone - 2 - oxymaleate and chalcone - 2 - oxyfumarate. The reaction of 2,2t?-dihydroxychalcone, however, gives 2′-hydroxyflavone, in addition to the expected maleate and fumarate. Similar reactions of 5 - chloro - 2,2′ - dihydroxychalcone and of 3,5 - dibromo - 2,2′ - dihydroxychalcone, on the other hand, give 2,3 - dicarbomethoxy - 4 - (o - hydroxyphenacyl) - 6 - chlorochrom - 2 - ene and 2,3 - dicarbomethoxy - 4 - (o - hydroxyphenacyl) 6,8 - dibromochrom - 2 - ene, respectively, together with the corresponding maleates and fumarates.     

Isocyanide addition to MN2(CO)5(Ph2PCH2PPh2)2 and the formation of a four-electron doubly-bridging isocyanide

The reactions of Fe(CO)₅, Fe(CO)₄P(C₆H₅)₃, M(CO)₆ (M  W, Mo, Cr), and (CH₃C₅H₄Mn(CO)₃ with KH and several boron and aluminium hydrides were investigated. Iron pentacarbonyl was converted quantitatively to K⁺Fe(CO)₄-(CHO) by hydride transfer from KBH(OCH₃)₃ allowing isolation of [P(C₆H₅)₃]₂-Nⁿ⁺Fe(CO)₄(CHO)^? in 50% yield. Lower yields were obtained with LiBH(C₂H₅)₃, and other hydride sources gave little or no formyl product. The stability of Fe(CO)₄(CHO)^? in THP was found to depend on the cation, decreasing in the order [P(C₆H₅)₃]₂N⁺ > K⁺ > Na⁺ > Li⁺. No formyl complexes were isolated and no spectroscopic evidence for formyl formation was observed in the reactions of the other transition metal carbonyls with several hydride sources. Fe(CO)₄-P(C₆H₅)₃ gave K₂Fe(CO)₄ when treated with KHB(OCH₃)₃. When treated with LiBH(C₂H₅)₃, W(CO)₆ gave a mixture of HW₂(CO)₁₀^?and (OC)₅W(COC₂H₅)^?; the latter was methylated to give the carbene complex (OC)₅WC(OCH₃)C₂H₅.     

Mössbauer and infrared spectroscopic studies of some organotin(IV) schiff base complexes

Several organotin(IV) complexes with quadri- and terdentate anionic Schiff base ligands have been investigated in the solid state using ¹¹⁹Sn Mössbauer and IR spectroscopies, Mössbauer parameters derived from both zero-field and magnetically perturbed spectra suggest that the R₂Sn(Salen)(R = Me, Et, Ph) and Me₂Sn(Saldap-2OH) complexes have similarly distorted trans-octahedral structures. However, in Ph₂Sn(HSaldap-2-O) the ligand appears to be only terdentate, leading to a penta-coordinate structure similar to those of the R₂Sn(Sal-N-2-OC₆H₄) derivatives (R = Me, Ph). For Ph₃Sn(Sal-N-2-OC₆H₄) the asymmetry parameter of the electric field gradient is close to unity, confirming a mer-octahedral configuration for this complex.     

Reagents for Organic Synthesis : Vol. 5; by M. Fieser and L.F. Fieser,Wiley-Interscience,New York/London/Sydney/Toronto, 1975, 864 pages, $32.15, £16.15.

Phosphorus-31 NMR and X-ray crystallography show that the two similar chelating triphosphine ligands PhP(CH₂CH₂PPh₂)₂(2,2-P₃) and PhP(CH₂CH₂CH₂ PPh₂)₂(33-P₃) form cobalt(I) complexes having trigonal-bipyramidal and square-pyramidal structures, respectively. The structures and PP coupling constants of [Co(33-P₃)(P(OMe)₃)CO]BF₄·1THF and [Co(22-P₃)(P(OMe)₃)₂]BF₄ are given, and the change from square-pyramidal geometry in [Co(33-P₃)P(OMe)₃)CO]⁺ to trigonal-bipyramidal in [Co(22-P₃)(P(OMe)₃)₂]⁺ may be rationalized in terms of a decreased “chelate bite angle” for the PhP(CH₂CH₂PPh₂)₂ ligand.     

Effect of pH on the electrochemical reduction of some heterocyclic quinones

The reduction of 1,10-phenanthroline-5,6-quinone(I), 5,8-quinolinequinone(II) and 6,7-dichloro-5,8-quinolinequinone(III) was investigated using cyclic voltammetry and coulometry at mercury electrodes and 50% dimethylsulfoxide+water solvent. Each compound is reduced to the corresponding hydroquinone in a diffusion-controlled, reversible two-electron process. The pH-dependence of the reversible potential indicated that the quinone forms were unprotonated, but the hydroquinones could be protonated at the heterocyclic nitrogen atom with pK_a = 5.3 for I and 3.5 for III. Careful analysis of the cyclic voltammetric peak shape revealed that the difference between the standard potentials for the introduction of successive electrons, E₂⁰ ? E₁⁰, was 70 ±20, >100 and 80 ± 20 mV for I–III. Investigation of the pH-dependence of E₁⁰ and E₂⁰ showed that the pK_a of the semiquinone of I was about 8.     

The electrochemical behavior of Os(II) complexes with α,α′-bipyridine and o-phenanthroline in non-aqueous solvents

The electrode reactions of Os(II) complexes with α,α′-bipyridine and o-phenanthroline have been studied in non aqueous solvents. Tris bipyridine and tris phenanthroline complexes of Os(II) give one-step oxidation waves and three-step reduction waves, while bis bipyridine complexes of Os(II) containing py₂, en, CN₂, Cl₂ and Br₂ as mixed ligands give one-step oxidation waves and two-step reduction waves. Most of these waves correspond to reversible single electron transfers. It is noticed that the half-wave potentials or the peak potentials of bis bipyridine complexes are shifted to more negative direction than those of the tris complex in both oxidation and reduction processes. This is attributable to less electron with drawing nature of substituted ligands than bipyridine. These potential data, the shifts of E_1/2 or E_p from those of tris complexes, and δE*, the potential difference between two consecutive single electron waves, are discussed in terms of molecular orbital scheme.     

13 C 183W-Kopplungen als sonde für metall—carbin-, —carbenund—alkyl-bindungen

Carbon-13 NMR data are reported for trimethyltin derivatives containing ER_n groups where E  C, Si, Ge, Sn, N, O and S including a series of cyclic amines with ring sizes from three to seven. Coupling constant values for the homologous series of fourth group derivatives give goood correlations with the electronegativity of E. The observation of the two-bond, ¦ ²J(¹¹⁹SnE¹³C) ¦ couplings only in the derivatives containing bulky R groups is rationalized by a bimolecular exchange of ER_n groups in the concentrated solutions studied.     

Stability and thermodynamics of La(III)-, Pr(III)-, Nd(III)-, Gd(III)- and Eu(III)-p-nitrobenzaldehyde thiosemicarbazone systems

Three complexes containing bidentate N-2,3-dimethylphenylglycine, (2,3-HDPG), N-2,4-dimethylphenylglycine, (2,4-HDPG) and N-2-ethylphenylglycine, (2-HEPG) acids have been prepared and characterized. These compounds have the general formula Zn(2,3-DPG)₂·2 H₂O, Zn(2,4-DPG)₂ and Zn(2-EPG)₂·2 H₂O, respectively. The structure of the complexes as inferred from their chemistries have been found to be compatible with the infrared spectral data. The thermal behaviour of these complexes has been studied from their TG, DTG and DSC diagrams obtained in a dynamic atmosphere of pure air. Heats of dehydration have been calculated from DSC curves.     

The reduction of oxygen in molten lithium carbonate

Oxygen reduction on immersed gold electrodes has been studied in Li₂CO₃ melt under steady-state conditions and by the potential-sweep method. Reaction order measurements have established that the species being reduced is not molecular oxygen, but the peroxide ion. The latter is in chemical equilibrium with molecular oxygen and oxide ions. The rate-determining step is the primary charge transfer

where (O^?) is a transient species. The exchange current densities and activation energies have been determined. Under conditions where O₂^2? diffusion is not limiting (e.g. meniscus electrodes) the rate of neutralization of oxide by CO₂ at the electrode surface is probably rate-determining.