Coordination of vanadyl acetylacetonate with nitrogen-containing donor bases

Conclusions From results obtained in an investigation of modulation effects in the electron spin echo of adducts of VO²⁺acac₂ with nitrogen-containing donor bases, we have been able to determine the constants of HFI of the unpaired electron of the vanadium with the nitrogen nucleus, for a large class of these bases. The values of the HFI constant are in the range 3.6–6 MHz.The sensitivity of modulation effects in ESE to the selection of the base offers a means for determining the relative stability of these adducts.Translated from Zhurnal Strukturnoi Khimii, Vol. 26, No. 3, pp. 53–58, May–June, 1985.Translated from Zhurnal Strukturnoi Khimii, Vol. 26, No. 3, pp. 53–58, May–June, 1985.     

Structure and reactivity of vanadium(V) complexes formed in the reaction between vanadyl acetylacetonate and alkyl hydroperoxides. To the mechanism of selective epoxidation of olefins

Vanadium(V) complexes formed in the reaction between vanadyl acetylacetonate and alkylhydroperoxides are characterized according to their¹H and⁵¹V NMR spectra and the reactivity of these complexes towards cyclohexene is studied.

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¹H ⁵¹V , .

     

Metal complexes with ligands–organic phosphites as polyolefin antioxidants. I. Kinetics and mechanism of polyolefin and model hydrocarbon stabilization by organic phosphites

The most effective mechanism of protective action of organic phosphites–linear termination of kinetic chains on the inhibitor—has been established and the relative contribution of the other phosphite reactions (with hydroperoxides, their chain “self-oxidation”) to the summary mechanism has been determined. The quantitative kinetic characteristics of efficiency and length of inhibitive action of different structure phosphites in the wide range of the phase state of the oxidized substrate (solid polymer, its melt, liquid phase) have been given. On this basis the regularities which allow the prediction of the structures of phosphites scavenging peroxy substrate radicals more effectively (effective inhibitors) have been formulated.     

Proton spin relaxation in some paramagnetic transition-metal acetylacetonate complexes. Comparison between theory and experiment

Proton spin-lattice (T₁) and spin-spin (T₂) relaxation times have been measured for CH₃ protons in a series of paramagnetic transition-metal acetylacetonate complexes and the results interpreted in terms of current relaxation theory, τ_r, the correlation time for molecular reorientation, was estimated from the ¹³C T₁ in the analogous diamagnetic Co(III) and Pd(II) complexes. Using this approach and treating in detail the effects of fast CH₃ group internal motion good agreement is obtained between theory and experiment. In all cases electron-nuclear dipolar coupling dominates T₁ whereas the hyperfine contribution can be important for T₂.     

A carbon-13 n.m.r. study of sulfur-donor ligand ortho-metalated iron carbonyl complexes

Carbon-13 n.m.r. data are reported for a series of sulfur-donor ligand ortho-metalated iron carbonyl complexes derived from thiobenzophenones. The chemical shift δ153·5–161·4 for the aromatic carbon σ-bonded to iron is readily identified, and occurs in the same region as the signal for the corresponding carbon in a related nitrogen-donor ligand complex. The benzylic carbon gives a signal at δ62·8–63·3, subject to the nature of the complex.     

Carbonyl complexes of manganese(I) with pyridazine: Synthesis and1H n.m.r. study

Summary Three new pyridazine complexes of manganese(I): [MnBr(pyr)₂(CO)₃] (1), [Mn(pyr)(CO)₅][ClO₄] (2) and [Mn(pyr)₃(CO)₃][ClO₄] (3) (pyr=pyridazine) have been prepared and their i.r. and variable-temperature¹H n.m.r. spectra investigated.     

Metal complexes with ligand-organic phosphites as polyolefin antioxidants. II. Kinetics and mechanism of synergism at oxidation inhibition by metal acetylacetonates and organic phosphites

The widely known synergism of oxidation inhibitors with metals of transient valency is shown in the new process with organic phosphite participation. The effects of inadditive strengthening phosphite action by acetylacetonates of transient metals (Me) have been investigated in different oxidation systems (solid polymer, melt, and liquid phase). The kinetic interpretation of effects, their quantitative analysis, and mathematical modeling are given, and the general regularities governing the efficiency of Me + organic phosphite compositions in any oxidation mode in the presence of initiator and at polymer autoxidation are revealed.     

Isotropic paramagnetic shifts of the phosphorus and proton magnetic resonance and the spin density distribution in paramagnetic complexes of triphenylphosphine with nickel acetylacetonate

The Isotropic paramagnetic shifts in the H¹ and P³¹ NMR spectra of triphenylphosphine, forming labile complexes in chloroform with the acetylacetonato compound of nickel(II), have been measured. The concentration dependence of the shifts has been used to calculate the hyperfine interaction constants and the spin densities in an individual complex, on the assumption that the complex has the composition [Ni(AA)₂] (PPh₃)₂. It has been found that the spin density in the sp³ hybrid orbital of the phosphorus atom is positive and amounts to not less than 10%, indicating a -mechanism of transfer of spin density from the nickel to the phosphorus. The spin densities on the carbon atoms of the phenyl rings are smaller fay about two orders of magnitude than those on the phosphorus atom, and this is attributed to the orientation of these rings, which is unsuitable for conjugation with the unshared pair. The contributions of the different mechanisms to the delocalization of the spin density from the phosphorus atom to the -system of the rings have been estimated.The authors wish to express their gratitude to the late Academician V. V. Voevodskii, whose initiative and constant support made this joint work possible. The authors thank A. Nesmei, for assistance in the construction of the phosphorus resonance measurement apparatus, and G. M. Zhidomirov, for discussion of the results.     

An n.m.r. study on displacements from platinum(II) complexes by dimethylsulphoxide

Summary Substitutions of platinum(II) complexes with nitrogen donors by the soft sulphur donor dimethylsulphoxide (DMSO) were studied by n.m.r. spectroscopy and quantum-mechanical calculations.The results indicate that the softness of halide as well as the affinities of the displaced ligands influence the substitution processes.     

1H n.m.r. conformational studies of glycyl-L-phenylalanine and L-phenylalanyl-glycine dipeptides and their complexes with palladium (II)

The conformations of Gly-Phe and Phe-Gly dipeptides and those of their complexes with the Pd(II) ion has been established by means of ¹H n.m.r. spectra over various pH ranges. In the most stable rotamer of both dipeptides the bulkiest groups, i.e. carboxylate (or carbonyl) and the aromatic ring, are in trans position to each other. In the 1:1 molar ratio complexes, the dipeptides are the tridentate ligands within the 3–10 pH region. In the predominant conformer the aromatic ring lies over the complex plane, which suggests its interaction with the metal ion. At pH above 13, the carboxyl group becomes non-coordinated. The dipeptides are then bidentate and the most stable rotamers are the same as those found for the metal-free ligands, i.e. the carboxyl or carbonyl group is in the trans position to the aromatic ring. The glycine chelate ring in the Pd(II) Gly-Phe complex is planar up to pH 10 and its distortion from planarity follows when the ligand becomes bidentate.     

13C n.m.r. spectra of cyclopropenes

¹³C n.m.r. chemical shifts and one bond ¹³C, ¹H coupling constants for cyclopropene and its 1- and 3-methyl derivatives as well as for methyl cyclopropane have been measured. The data for cyclopropene are 108·9 ppm and 228·2 Hz, 2·3 ppm and 167·0 Hz in the olefinic and allylic position, respectively. Substituent effects for the methyl group are discussed.     

A 13C n.m.r. study of the charge-transfer complexes between o-chloranil and some aromatic electron donors

The ¹³C n.m.r. spectra of complexes between o-chloranil and aromatic electron donors were studied. Complexation leads to a general diamagnetic shift of the ¹³C n.m.r. signals for the acceptor (o-chloranil), but for signals from the ¹³C nuclei in the donors both diamagnetic and paramagnetic shifts are found. These phenomena are thought to be the result of competing anisotropy and charge-migration effects. Charge migration in o-chloranil complexes appears to be more important than in corresponding 1,3,5-trinitrobenzene complexes.     

Carbon-13 n.m.r. studies of methylquinolines and methylisoquinolines

Spectra are reported for all seven methylquinolines, nine dimethylquinolines, six methylisoquinolines and one dimethylisoquinoline. Substituent effects for the α, ortho, meta, para, vinylogous para and peri positions are reported for the monomethylcompounds. Additivity of these substituent effects is demonstrated for the dimethyl compounds which also exhibit a vicinal dimethyl steric effect.     

13C n.m.r. spectra of quercetin and rutin

The noise-decoupled and gated-decoupled ¹³C n.m.r. spectra of quercetin and rutin are studied and assignments are proposed. The previous assignments of carbons 2 and 4′, carbons 5 and 9, carbons 6 and 8 have been reversed.