13C NMR studies on tricarbonylchromium complexes of dimethylaminofulvene and diphenylfulvene

The ¹³C NMR spectra of tricarbonylchromium complexes of dimethylaminofulvene diphenylfulvene have been studied. Comparison of the ¹³C NMR spectra of these complexes with those of the corresponding non-coordinated fulvenes shows that the contribution from the ylidic structure of the π-ligand in the first complex increases when the Cr atom becomes coordinated, while in the second complex this coordination does not favour a formation of the ylidic structure of the π-ligand.     

Pishchimuka's Intramolecular Rearrangement. The General Method for the Synthesis of 2-Oxo-1,2λ5-thiaphoapholanes and Thiaphosphorinanes

A new method is developed for the synthesis of 2-substituted 2-oxo-1,2⁵-thiaphospholanes and thiaphosphorinanes (thiolphostones) on the basis of intramolecular Pishchimuka rearrangement of thiophosphonic and thiophosphinic esters with -chloroalkyl substituents at the phosphorus atom. Intermediate compound in the Pishchimuka rearrangement, 2-ethyl-2-ethoxy-1,2⁴-thiaphospholanium perchlorate, was isolated.     

Synthesis and characterization of fluorophenylpalladium pincer complexes: electronic properties of some pincer ligands evaluated by multinuclear NMR spectroscopy and electrochemical studies

Palladium fluorophenyl complexes with different pincer ligands Pd(Ar)[2,6-(tBu(2)PCH(2))(2)C(6)H(3)] (13), Pd(Ar)[2,6-(tBu(2)PO)(2)C(6)H(3)] (14), Pd(Ar)[{2,5-(tBu(2)PCH(2))(2)C(5)H(2)}Fe(C(5)H(5))] (15), and Pd(Ar)[{2,5-(tBu(2)PCH(2))(2)C(5)H(2)}Ru(C(5)H(5))] (16) were synthesized by the reaction of LiAr (Ar = C(6)H(4)F-4) with the respective trifluoroacetate palladium pincer complexes 9-12. The molecular structures of 14 and 16 were determined by an X-ray crystallographic method. Complexes 13-16 and {Pd(Ar)[{2,5-(tBu(2)PCH(2))(2)C(5)H(2)}Fe(C(5)H(5))]}PF(6) (17) were studied by multinuclear NMR spectroscopy and cyclic voltammetry. On the basis of (19)F NMR chemical shifts and (1)J((13)C-(19)F) coupling constants, as well as Pd(II)/Pd(IV) oxidation potentials, electronic characteristics of the corresponding pincer ligands were elucidated.     

Cyclotrimerization of alkynes catalyzed by the naphthalene ruthenium complex [CpRu(C10H8)]+

The naphthalene ruthenium complex [CpRu(C₁₀H₈)]⁺ (in the presence of Cl^? ions) catalyzes the cyclotrimerization of 2,2-dimethyl-5,5-dipropargyl-1,3-dioxane-4,6-dione with alkynes (acetylene, hex-1-yne, hex-3-yne, oct-1-yne, phenylacetylene, trimetylsilylacetylene, octa-1,7-diyne, pent-1-yn-5-ol, methyl propargyl ether, and propargyl acetate) giving tricyclic aromatic compounds in 55–85% yields.     

Rh-Catalyzed asymmetric hydrogenation of (Z)-ethyl 3-acetamido-2-butenoate in supercritical carbon dioxide: the effect of cosolvents

Rh-Catalyzed asymmetric hydrogenation (up to 85% ee) of (Z)-ethyl 3-acetamido-2-butenoate was carried out for the first time in supercritical CO₂ using protic cosolvents. The activity of the Rh catalyst bearing the amidophosphite ligand increases with an increase in acidity of the protic cosolvents and with hydrogen pressure.     

Synthesis and Intramolecular Cyclization of ω-Haloalkyl Dithiophosporus Acid Esters

y -Haloalkyl dithiophosphorus acid esters undergo the thermal rearrangement resulting in the corresponding 2-oxo-1,3,2-dithiaphosphacyclanes.     

Investigation of Bis(α-Phenylethylamido)Methylphosphonates by NMR Spectroscopy

Abstract

The influence of the relative location of chiral carbon and phosphorus atoms and the position of the aryl-group on diastereomeric anisochronity in non-racemic mixtures of enantiomers has been examined. The optical isomers of methanephosphonic acid bis(α-phenylethylamide) (I), which contain pro-chiral phosphorus atom, were synthesized by the reaction of methanephosphonic acid dichloride(II) with (+)- or (-) -α-phenylethylamine (III). The extent of chemical shift nonequivalence in ³¹P and ¹H NMR spectra of non-racemic mixtures of RR- and SS-I was negligible. It can be explained by the absence of aryl-amino group, favouring intermolecular association, effect of SCADA¹, and the long distance between the chiral center and pro-chiral phosphorus. Phosphonylation of non-racemic mixtures of (+)- and (-)-III by II proceeds stereospecifically giving mixture of RR-, SS-I, and two meso-compounds analyzed by ³¹P ¹H NMR.     

Noise can prevent onset of chaos in spatiotemporal population dynamics

Many theoretical approaches predict the dynamics of interacting populations to be chaotic but that has very rarely been observed in ecological data. It has therefore risen a question about factors that can prevent the onset of chaos by, for instance, making the population fluctuations synchronized over the whole habitat. One such factor is stochasticity. The so-called Moran effect predicts that a spatially correlated noise can synchronize the local population dynamics in a spatially discrete system, thus preventing the onset of spatiotemporal chaos. On the whole, however, the issue of noise has remained controversial and insufficiently understood. In particular, a well-built nonspatial theory infers that noise enhances chaos by making the system more sensitive to the initial conditions. In this paper, we address the problem of the interplay between deterministic dynamics and noise by considering a spatially explicit predator-prey system where some parameters are affected by noise. Our findings are rather counter-intuitive. We show that a small noise (i.e. preserving the deterministic skeleton) can indeed synchronize the population oscillations throughout space and hence keep the dynamics regular, but the dependence of the chaos prevention probability on the noise intensity is of resonance type. Once chaos has developed, it appears to be stable with respect to a small noise but it can be suppressed by a large noise. Finally, we show that our results are in a good qualitative agreement with some available field data.     

A convenient one‐pot synthesis of 1,2‐azaphospholanium salts

A novel facile one‐pot synthesis of the 1,2‐azaphospholanes by intramolecular alkylation of 3‐halopropyl amides of tricoordinate phosphorus has been suggested. Using this method, a series of the differently N‐substituted 1,2‐azaphospholanium salts were synthesized. 3‐Aminopropylphosphine oxides were obtained by hydrolysis of the salts. A probable mechanism of the 1,2‐azaphospholanium salts formation is discussed. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:596–602, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10209