Application of the semilocalized approach to chemical reactivity of butadiene

The semilocalized approach to chemical reactivity (J. Mol. Struct. (Theochem) 588 (2002) 99; Int. J. Quant. Chem. 94 (2003) 302) is applied to study the addition reaction of an electrophile or nucleophile to the butadiene molecule. In accordance with the classical concept of the reaction center and its neighborhood (substituent), only one of the two H₂C=CH-fragments of butadiene is supposed to be under a direct attack of the reagent, whereas the remaining H₂C=CH-group is assumed to play the role of the substituent and thereby to participate in the process indirectly by exerting certain electron-donating or accepting effect upon the former group and/or the reagent. The main aim of the study consists in revealing the role of the H₂C=CH-substituent in the formation of the known higher reactivity of the terminal carbon atom of the attacked C=C-bond (as compared to the internal atom) irrespective of the nature of the reagent. To this end, we seek to obtain an explicit algebraic representation of the interdependence between the direction and the extent of the total influence of the H₂C=CH-substituent, on the one hand, and the nature of the reagent, on the other hand. The expressions for electron density and bond order redistributions among separate fragments of contacting molecules derived previously in the form of power series are shown to yield the above-anticipated representation. On this basis, it is demonstrated that the electron-donating effect of the initially occupied (bonding) orbital of the substituent and the electron-accepting effect of its initially vacant (antibonding) orbital upon the remaining fragments of the whole reacting system may be considered independently whatever the nature of the reagent. However, a strong interdependence is established between the actual relative extents of these two components of the total effect of the H₂C=CH-group and the electron-donating (accepting) properties of the reagent. Moreover, this group of atoms is shown to manifest itself as an electron-donating (accepting) substituent under influence of an electrophilic (nucleophilic) attack. Using this principal result of the paper, the actual reactivity of butadiene with respect to electrophile (nucleophile) is interpreted by invoking a model system of a substituted ethene containing a simple (one-orbital) electron-donating (accepting) substituent, and a terminal addition easily follows for both types of the reagent.     

Three-component catalytic method for synthesis of α-amino phosphonates with the use of α-amino acids as amine component

Interaction of aliphatic and aromatic aldehydes and ketones with optically active L-α-amino acids or their esters in the three-component catalytic one-pot synthesis of α-aminophosphonates was studied. The corresponding α-amino phosphonates are formed in high yields as mixtures of diastereomers. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 768–774, April, 2007.     

Synthesis and electrochemistry of Group 6 tetracarbonyl (N,N′-bis(ferrocenylmethylene)ethylenediamine)metal(0) complexes

Thermal substitution reaction of Cr(CO)₄(η^2:2-1,5-cyclooctadiene), Mo(CO)₄(η^2:2-norbornadiene), and W(CO)₅(η²-bis(trimethylsilyl)ethyne) with N,N′-bis(ferrocenylmethylene)ethylenediamine (bfeda) yields M(CO)₄(bfeda) complexes which could be isolated from the reaction solution and characterized by elemental analysis, MS, IR, and NMR spectroscopy. In the case of tungsten, W(CO)₅(bfeda) is formed as intermediate and then undergoes the ring closure reaction yielding the ultimate product W(CO)₄(bfeda). The electrochemical behavior of the M(CO)₄(bfeda) complexes was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in dichloromethane with tetrabutylammonium tetrafluoroborate as electrolyte. Constant potential electrolysis of the complexes was performed successively at their peak potentials at 0 °C in their CH₂Cl₂ solution and the electrolysis was followed by in situ recording the electronic absorption spectra in every 5 mC. In the electrolysis of Cr(CO)₄(bfeda), the central Cr(0) is oxidized first and electrolysis continues with oxidations of two ferrocenyl groups until the end of totally three moles of electron passage per mole of complex. In the electrolysis of Mo(CO)₄(bfeda) and W(CO)₄(bfeda) the first oxidation occurs on the central atom forming a short-lived species which undergoes an intramolecular one-electron transfer and is reduced back to M(0) while one of the ferrocene units is oxidized to the ferrocenium cation at the same time. This indicates that the electron is transferred from iron to the central metal atom.     

异亚硝基乙酰乙酸乙酯亚胺Pd(Ⅱ)配合物的合成、表征和tran Pd(p-CH3C6H4-IEAI)2的晶体结构

Six palladium(Ⅱ) complexes with isonitrosoethylacetoacetate imine Schiff base ligands, Pd(R-IEAI)₂, were prepared and characterized by IR, Raman and electronic spectra. Complex tran Pd(p-CH₃C₆H₄-IEAI)₂ (2) cry- stallizes in the monoclinic system, space group P2₁/c,with a=1.2002(2),b=0.9972(2),c=1.1121(2)nm,β=90.43(3)°,Z=2,F(000)=616,μ=7.44cm^-1. The final R and wR are 0.0244 and 0.0625 for 2620 ob-served reflections with I≥2σ(I), respectively. The geometry around the Pd(Ⅱ) ions in those complexes has a distorted PdN₄ square plane, the Schiff base ligands R-IEAI^- being coordinated through their oximino-nitrogen atoms and imino-nitrogen atoms.     

Cu2(μ-dppb)2(μ-Cl)2的合成、晶体结构及非线性光学性质

The complex Cu₂(μ-dppb)₂(μ-Cl)₂ has been synthesized from the reaction of CuCl， dppb and (n-Bu)₄NCl. The crystal belongs to the triclinic with space group P1. The unit cell parameters are: a=9.939(4)?， b=10.083(6)?， c=14.104(5)?， α=76.46(3)°， β=71.02(2)°， γ=70.87(5)°. The single crystal X-ray diffraction analysis reveals that it has a bi-ring structure with a symmetry center at the middle of two Copper atoms. The outer ring is a 14-membered ring of Cu-dppb-Cu-dppb， and the inner ring is a 4-membered ring composed of two Cl^- and two Cu(Ⅰ). Investigation of third-order optical nonlinearity shows that it exhibits considerable nonlinear absorptive and self-defocusing effect with α₂=1.75×10^-13m·W^-1 and n₂=3.19×10^-18m²·W^-1. CCDC: 193113.     

Calculating the knowledge-based similarity of functional groups using crystallographic data

A knowledge-based method for calculating the similarity of functional groups is described and validated. The method is based on experimental information derived from small molecule crystal structures. These data are used in the form of scatterplots that show the likelihood of a non-bonded interaction being formed between functional group A (the `central group') and functional group B (the `contact group' or `probe'). The scatterplots are converted into three-dimensional maps that show the propensity of the probe at different positions around the central group. Here we describe how to calculate the similarity of a pair of central groups based on these maps. The similarity method is validated using bioisosteric functional group pairs identified in the Bioster database and Relibase. The Bioster database is a critical compilation of thousands of bioisosteric molecule pairs, including drugs, enzyme inhibitors and agrochemicals. Relibase is an object-oriented database containing structural data about protein-ligand interactions. The distributions of the similarities of the bioisosteric functional group pairs are compared with similarities for all the possible pairs in IsoStar, and are found to be significantly different. Enrichment factors are also calculated showing the similarity method is statistically significantly better than random in predicting bioisosteric functional group pairs.     

The modulation of face-face π-π interactions in Lewis acid catalysis

The enantiomeric excess observed for the exo-adduct from the Lewis acid catalysed Diels-Alder reaction between cyclopentadiene and methacrolein can be increased up to 21% by simple modification of the electronics of the aromatic ring in a series of stilbene-derived diol ligands, suggesting that the proposed face-face π-π interaction between the catalyst and the dienophile can be modulated by altering the electron density on the aromatic ring.     

Interference of Copper(II) ions with Non-covalent Interactions in Uridine or Uridine 5′-Monophosphate Systems with Adenosine,Cytidine, Thymidine and their Monophosphates in Aqueous Solution

Coordination reactions of copper(II) ions and their effect on non-covalent interactions in uridine (Urd) or uridine 5′-monophosphate (UMP) systems with nucleosides (Ado, Cyd, Thd) and nucleotides (AMP and CMP) in aqueous solutions have been studied. At high pH the effective coordination centers are deprotonated N(3) atoms from Urd and Thd, whereas at low pH, the N(3) atoms of pyrimidine nucleosides are blocked for coordination and the metallation sites are endocyclic nitrogen atoms from Ado, Cyd, AMP and CMP. Moreover, at low pH, the main reaction center in nucleotide solutions is the phosphate group. The NMR study has proven the occurrence of non-covalent ion-dipole interactions and stacking interactions in the systems considered. Introduction of a copper ion in the majority of systems causes the disappearance of weak interactions between ligands. The structures of the complexes in solution have been inferred from the equilibrium study: an analysis of the pH range of their occurrence with respect to the pH range of deprotonation of particular groups in the compounds studied, using Vis, EPR and ¹³C as well as ³¹P NMR spectral analysis.     

Organoelement Compounds with Al?Al,Ga?Ga,and In?In Bonds

In the attempt to synthesize compounds with aluminum in a low oxidation state and an Al Al bond, by the reduction of alkylaluminum halides with alkali metals, analogous to a Wurtz coupling, in general the deposition of elemental aluminum and the formation of the corresponding trialkylaluminum compounds is observed. Thus, tetrasubstituted dialuminum compounds R₂Al AlR₂, apart from a few poorly characterized examples, were for a long time considered part of an unverified class of substances. Only with the sterically very highly shielded tetrakis[bis(trimethylsilyl)methyl]dialuminum did we achieve the synthesis of the first completely characterized organoelement compound with unlimited stability, which shows aluminum in the oxidation state + II and has an Al Al bond. In the meantime, corresponding compounds for the elements gallium and indium have been obtained. With the simple access to tetrasubstituted dimetal compounds, a fascinating new research area has opened for preparative chemistry, in which the particular interest will naturally lie in the reactive properties of the metal-metal bond.     

Critical micelle concentrations for alkyltrimethylammonium bromides in water from 25 to 160°C

Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol^–1.