The reaction of hexaalkyldisilazanes with aluminum and boron halides

Summary When hexamethyldisilazane reacts with aluminum and boron halides under mild conditions, aluminum and boron trimethylsilylamine dihalides are obtained.     

Sodium fluoroaluminates formed in the reaction between aluminum fluoride solution and crystalline sodium fluoride

The reaction of aluminum fluoride solution with crystalline sodium fluoride was investigated. Conditions for the formation of Na₃AlF₆ (cryolite), Na₅Al₃F₁₄ (chiolite) and NaAlF₄.H₂O were established. The hitherto presumed to be unstable NaAlF₄.H₂O was isolated and its X-ray diffraction data as well as thermal behavior were determined. The possibility to convert these compounds one into the other was outlined.     

Synthesis and structure of complexes formed in the reaction between dicobalt octacarbonyl and tetramethyl-biphosphine disulfide

Co₂(CO)₈ and Me₂P(S)P(S)Me₂ react to form the two cluster complexes: Co₄(CO)₉S(PMe₂)₂) (1) and Co₃(CO)₇S(SPMe₂) (2). The strucure of1 and of the disubstituted triphenyl phosphine derivative of2. Co₃(CO)₅(PPh₃)₂S (SPMe₃) (2a) were determined. Compound1 contains a quasi-planar rhomboidal Co₄ cluster formed by two Co₃ isosceles triangles sharing a Co-Co edge. One triangle is capped by a sulfur atom, the other triangle has two edge-bridging PMe₂ moieties. Electron counting gives 64 electrons corresponding to a planar system; the distribution of long Co-Co distances, in particular in the triangle bearing PMe₂ bridges, suggests that the excess electrons are located on Co-Co antibonding ortibals. Compound2a contains a Co₃S cluster with one side bridged by a SPMe₂ unit forming a four-membered Co₂SP ring. The substitution of two CO groups with two PPh₃ causes a large deformation of the cluster Co-Co bondscis to these two phosphorus atoms. Crystal data for1, space group P1,a = 9.728(2) Å,b = 10.288(2) Å,c = 11.860(3) Å, = 86.41(2)°, = 76.20(2)°, = 80.37(5)°,Z = 2, 5300 reflections,R = 0.0398; for2a, space group P1,a = 9.78(3) Å,b = 13.05(4) Å,c = 18.28(6) Å, = 93.23(3)°, = 99.17(2)°, = 97.26(6)°,Z = 2, 2976 reflections,R = 0.0579.     

EPR Spectra of complexes of 3,5-di-tert-butyl-o-benzoquinone with lead diethyldithiocarbamate,ethylxanthate, and o,o-diethyldithiophosphate and reaction with bases

We have observed the solvent dependence of the hyperfine coupling constant for hyperfine coupling with the metal nucleus in ortho-semiquinone complexes of lead(II) diethyldithiocarbamate, ethylxanthate, and O,O-diethyldithiophosphate. This is connected with the process of solvation of the metal cation with the solvent molecules. We observe a correlation between the hyperfine coupling constant (due to the²⁰⁷Pb isotope) and the basicity factor of the solvent. Using the EPR method, we have studied the dynamics of solvation of the 3,5-di-tert-butyl-o-semiquinone complex of lead diethyldithiocarbamate by amines. We have obtained the thermodynamic and kinetic parameters of the solvation process. We observe a compensation effect for the kinetics of the forward and backward solvation reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 52–58, January, 1990.     

Structure and properties of dibutylamine complexes with aluminum and gallium halides: The role of hydrogen bonds

Reactions of aluminum and gallium halides MX₃ (M = Al, Ga; X = Cl, Br) with dibutylamine in benzene solutions were studied by calorimetry, dielectrometry, and cryoscopy. The formation of molecular complexes Bu₂NH·MX₃ (1:1), 2Bu₂NH·MX₃ (2:1) and 6Bu₂NH·MX₃ (6:1) was established. In the 1:1 complexes, the donor-acceptor bond is formed by the lone electron pair of the nitrogen atom and a vacant orbital of the metal. Hydrogen bonds strongly affect the structure and properties of the 2:1 and 6:1 complexes. Complexes of the composition 2Bu₂NH·MX₃ are present in solution as six-membered metallacycle with a four-coordinate metal atom, and the second amine molecule linked with the complex Bu₂NH·MX₃ with N-H···N and N-H···X hydrogen bonds.     

3]Pseudorotaxane-like complexes formed between bipyridinium dications and bis-p-xylyl[26]crown-6

[structure: see text]. The crown ether BPX26C6 forms a [3]pseudorotaxane-like complex with the N,N'-dimethyl-4,4'-bipyridinium dication both in solution and in the solid state. The facile one-pot synthesis of a [2]rotaxane from neutral precursors-BPX26C6, 4,4'-dipyridyl, and 3,5-di-tert-butylbenzyl bromide-suggests that BPX26C6 may bind to (mono)pyridinium cations in a [2]pseudorotaxane-like manner.     

Nature of the complexes formed by alkali metal halides with phosphine oxides

Reaction of alkali metal halides (MX) with methylenediphosphine oxides and various related compounds in nonaqueous solutions leads to the formation of complex compounds. The compositions, properties, and stabilities of these compounds, which have been studied in detail in acetonitrile, are determined by the nature of the cations and anions of the alkali metal halides. Formation of neutral complexes with the composition [MX · L] and cationic complexes with the composition [ML]⁺ has been established. The most characteristic representative of complexes of the first type is [NaI · L]; in the complexes studied, L=R₂P(O)CH₂P(O)R₂ (R=Bu, BuO, or Ph), Ph₂P(O)CH₂P(O) (OC₂H₅)CH₂P(O)Ph₂ and (p-OCH₃C₆H₄)₂P(O)CH₂P(O)(C₆H₄CF₃-p)₂. Compound [LiL]⁺ is characteristic of complexes of the second type; the compounds containing Ph₃P(O), Ph₂P(O)CH₂P(O)Ph₂, and Ph₂P(O)CH₂P(O)(OC₂H₅)CH₂P(O)Ph₂ as ligands have been studied. Stability constants of the complexes [NaI · L] and [LiL]⁺ have been determined by measuring the dependence of the electrical conductivity of solutions of the alkali metal halides in acetonitrile on the concentration of the ligands. The complex-forming power of phosphine oxides increases with increase in the number of P=O groups. Stabilities of the complexes [NaI · L] with ligands with identical structure decrease with increase in the electronegativity of the substituents on the phosphorus atoms.     

A new paramagnetic intermediate formed during the reaction of nitrite with deoxyhemoglobin

The reduction of nitrite by deoxygenated hemoglobin chains has been implicated in red cell-induced vasodilation, although the mechanism for this process has not been established. We have previously demonstrated that the reaction of nitrite with deoxyhemoglobin produces a hybrid intermediate with properties of Hb(II)NO(+) and Hb(III)NO that builds up during the reaction retaining potential NO bioactivity. To explain the unexpected stability of this intermediate, which prevents NO release from the Hb(III)NO component, we had implicated the transfer of an electron from the β-93 thiol to NO(+) producing ·SHb(II)NO. To determine if this species is formed and to characterize its properties, we have investigated the electron paramagnetic resonance (EPR) changes taking place during the nitrite reaction. The EPR effects of blocking the thiol group with N-ethyl-maleimide and using carboxypeptidase-A to stabilize the R-quaternary conformation have demonstrated that ·SHb(II)NO is formed and that it has the EPR spectrum expected for NO bound to the heme in the β-chain plus that of a thiyl radical. This new NO-related paramagnetic species is in equilibrium with the hybrid intermediate "Hb(II)NO(+) ? Hb(III)NO", thereby further inhibiting the release of NO from Hb(III)NO. The formation of an NO-related paramagnetic species other than the tightly bound NO in Hb(II)NO was also confirmed by a decrease in the EPR signal by -20 °C incubation, which shifts the equilibrium back to the "Hb(II)NO(+) ? Hb(III)NO" intermediate. This previously unrecognized NO hemoglobin species explains the stability of the intermediates and the buildup of a pool of potentially bioactive NO during nitrite reduction. It also provides a pathway for the formation of β-93 cysteine S-nitrosylated hemoglobin [SNOHb:S-nitrosohemoglobin], which has been shown to induce vasodilation, by a rapid radical-radical reaction of any free NO with the thiyl radical of this new paramagnetic intermediate.     

Studies of reaction heats and structure of complexes formed between strong N-bases and phenols

The heats of reactions between various phenols and two strong N-bases of guanidine-like character in acetonitrile, are determined. The values can be used as a measure of self-assembly abilities of the phenol molecules in the interactions with strong N-bases, playing a very important role in biological systems. In the case of TBD complexes with corresponding nitrophenols, the protonated N-base is hydrogen-bonded to the nitro group excluding the self-assembly process of the phenols. In the case of other phenols, the self-assembly abilities are dependent on pK_a values of phenols. With increasing acidity of phenols their ability to form the hydrogen-bonded chains decreases. The maximum of length of the chains is observed for 4-methylphenol, which has a similar pK_a value to that in the tyrosine residue in biological systems.     

Cascade reaction of 2,3-naphthalenediol with benzene in the presence of aluminum halides

2,3-Naphthalenediol on superelectrophilic activation with aluminium halides smoothly reacts with benzene to give 4-((3-phenyl-1H-inden-1-yl)methyl)benzene-1,2-diol, which in turn undergoes intramolecular cyclization to form 5,10-methano-5-phenyldibenzo[a,d]cycloheptane-2,3-diol. The mechanistic aspects of these unusual transformations are discussed.     

Dimer formation in the reaction of aryl halides catalyzed by nickel complexes

The synthesis of diaryls catalyzed by electrochemically generated zero-valent nickel with 2,2-diapyridyl as the ligand was carried out from aryl halides in high yield. Feasibility was demonstrated for synthesizing the catalyst itself by the anodic dissolution of nickel in the presence of 2-bromopyridine in a diaphragmless cell.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Science Center, Russian Academy of Sciences, 420083 Kazan. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1674–1676, July, 1992.     

Separation parameters in the reaction between volatile halides and hydrogen

Equations for calculating the separation coefficient and factor in reactions of volatile halides with hydrogen from the equilibrium constants of the corresponding reactions and initial reactant concentrations were obtained. The concept of the limiting impurity concentration was introduced. The values specified were calculated for the reduction of volatile chlorides with hydrogen.     

Nature of paramagnetic centers in anodic aluminum oxide formed in a solution of tartaric acid

Films of anodic aluminum oxide, prepared in an aqueous solution of 0.4 M tartaric acid, are studied by means of electron paramagnetic resonance (EPR) before and after heating at 200–700°C. The presence of a carbon radical is established in the films (g factor, 2.0027 ± 0.0002). The nature and conditions of its formation during the electrochemical oxidation of aluminum and the heat-treating of anodic aluminum oxide films are discussed.