Chemistry of B1- and B10- boranes containing halogen or pseudohalogen groups

The research described in this thesis involved the chemistry of borane-species which contain one or more halide or pseudohalide groups. Both monoboron species e.g. [BH3X]- and "cluster" borane species e.g. [B10H9X]2- and I-Se B11H10 were studied. The first chapter is a review of the syntheses, properties and reactions of halide and pseudohalide species containing from one to ten boron atoms. Chapter Two is a theoretical investigation of' the electronic and molecular structures of two series of boranes i. e. [BH3X]- and [B10H9X]2- where X = H, CI, CN, NCS, SCN and N3. The calculational method used was the Modified Neglect of Differential Overlap (MNDO) method of Dewar et al. The results were compared where possible with experimental results such as the X-ray crystallographically determined structures of [BH3CI]- and [B10H10]2-. Chapter Three concerns halogenated selenaborane clusters and reports an improved synthesis of 12-Br-SeB11H10 and the first structural data for a simple non-metal containing selenaborane cage with the X-ray crystallographically determined structure of 12-1-SeB11H10. Finally, an indepth n.m.r. study of Se2B9H9 is also reported together with attempts to halogenate this compound. The last two chapters are based on single boron systems. Chapter Four concerns the synthetic routes to amine-boranes and -cyanoboranes from [BH4]- and [BH3CN]- substrates. This chapter discusses some difficulties encountered when polyamines were used in these reactions. The characterisation of an unusual ketone isolated from some of these reactions, the X-ray crystallographically determined structure of 4-dimethylamino-pyridine-cyanoborane and a new route to pyrazabole dimeric species are also discussed. The final chapter reports on work carried out at producing BH2X (X = H, CN) adducts of aminophosphines. Three routes were attempted to generate P-B and N-B bonded species with varying degrees of success. Some unusual products of these reactions are discussed including [Ph2(O) PPPh2 ] [Ph2NH]2, the structure of which was determined by X-ray crystallography.

Reactions of simple and peptidic alpha-carboxylate radical anions with dioxygen in the gas phase

alpha-Carboxylate radical anions are potential reactive intermediates in the free radical oxidation of biological molecules (e. g., fatty acids, peptides and proteins). We have synthesised well-defined alpha-carboxylate radical anions in the gas phase by UV laser photolysis of halogenated precursors in an ion-trap mass spectrometer. Reactions of isolated acetate ((center dot)CH(2)CO(2)) and 1-carboxylatobutyl (CH(3)CH(2)CH(2)(center dot)CHCO(2)(-)) radical anions with dioxygen yield carbonate (CO(3)(center dot-)) radical anions and this chemistry is shown to be a hallmark of oxidation in simple and alkyl-substituted cross-conjugated species. Previous solution phase studies have shown that C(alpha)-radicals in peptides, formed from free radical damage, combine with dioxygen to form peroxyl radicals that subsequently decompose into imine and keto acid products. Here, we demonstrate that a novel alternative pathway exists for two alpha-carboxylate C(alpha)-radical anions: the acetylglycinate radical anion (CH(3)C(O)NH(center dot)CHCO(2)(-)) and the model peptide radical anion, YGGFG(center dot-). Reaction of these radical anions with dioxygen results in concerted loss of carbon dioxide and hydroxyl radical. The reaction of the acetylglycinate radical anion with dioxygen reveals a two-stage process involving a slow, followed by a fast kinetic regime. Computational modelling suggests the reversible formation of the C(alpha) peroxyl radical facilitates proton transfer from the amide to the carboxylate group, a process reminiscent of, but distinctive from, classical proton-transfer catalysis. Interestingly, inclusion of this isomerization step in the RRKM/ME modelling of a G3SX level potential energy surface enables recapitulation of the experimentally observed two-stage kinetics.

Preparation of Hexafluorodisilane and Reactions of Hexafluorodisilane and Hexachlorodisilane with Sulfur Trioxide

Hexafluorodisilane has been prepared by the fluorination of hexachlorodisilane or hexabromodisilane by potassium fluoride in boiling acetonitrile, in yields approximating 45 and 60% respectively. Hexafluorodisilane has been characterised by infrared spectral data, vapour density measurements and analytical data. Both hexafluorodisilane and hexachlorodisilane are found to react with sulfur trioxide when heated to 400°C for 12 h. The products of reaction are silicon tetrafluoride, silica and sulfur dioxide with hexafluorodisilane while hexachlorodisilane in addition gives rise to hexachlorodisiloxane.

Studies of phosphazenes. 28. Reactions of pentachloro- and pentafluoro(triphenylphosphazenyl)cyclotriphosphazenes with sodium methoxide. Mechanistic aspects and their implications for nucleophilic displacement at a tetrahedral phosphorus(V) center

Abstract is not available.

Kinetic studies of the reactions of hexachlorocyclotriphosphazene and octachlorocyclotetraphosphazene with t-butylamine

The rates of the reactions of hexachlorocyclotriphosphazene (N3P3Cl6) and octachlorocyclotetraphosphazene (N4P4Cl8) with t-butylamine in methyl cyanide were determined at three temperatures in the range 273–308 K. The reaction of N3P3Cl6 was also studied in tetrahydrofuran. Rigorous purification of the chlorophosphazenes and the solvents was essential to obtain reproducible results. An SN2(P) mechanism involving the formation of a five-co-ordinate phosphorus intermediate is in accord with the kinetic data. The greater reactivity of N4P4Cl8 compared to that of N3P3Cl6 arises entirely from the lowering of the enthalpy of activation. The effects of ring size and the solvent on the rates are discussed in terms of the activation parameters.

Reactions of copper(I) aryloxides with phenyl isothiocyanate: steric and ligand control in the oligomerization of [N-phenylimino(aryloxy)methanethiolato]copper(I) complexes

The preparation of five different copper(I) complexes [CuSC(=NPh)(OAr)}L(n)]m (1-5) formed by the insertion of PhNCS into the Cu-OAr bond and the crystal structure analyses of three of them have been carried out. A monomeric species 1 (OAr = 2,6-dimethylphenoxide) is formed in the presence of excess PPh3 (n = 2, m = 1) and crystallizes as triclinic crystals with a = 12.419(4) angstrom, b = 13.298(7) angstrom, c = 15.936(3) angstrom, alpha = 67.09(3)-degrees, beta = 81.63(2)-degrees, gamma = 66.54(3)-degrees, V = 2224(2) angstrom3, and Z = 2. The structure was refined by the least-squares method to final R and R(w) values of 0.038 and 0.044, respectively, for 7186 unique reflections. Copper(I) 2,5-di-tert-butyl-4-methylphenoxide results in the formation of a dimeric species 2 in the presence of P(OMe)3 (n = 1, m = 2), where the coordination around Cu is trigonal. Crystals of 2 were found to be orthorhombic with a = 15.691(2) angstrom, b = 18.216(3) angstrom, c = 39.198(5) angstrom, v = 11204(3) angstrom3, and Z = 8. Least-squares refinement gave final residuals of R = 0.05 and R(w) = 0.057 with 6866 unique reflections. A tetrameric species 3 results when PPh3 is replaced by P(OMe)3 in the coordination sphere of copper(I) 2,6-dimethylphenoxide. It crystallizes in the space group P1BAR with a = 11.681 (1) angstrom, b = 13.373(2) angstrom, c = 20.127(1) angstrom, a = 88.55(l)-degrees, beta = 89.65(l)-degrees, gamma = 69.28(1)-degrees, V = 2940(l) angstrom3, and Z = 2. Least-squares refinement of the structure gave final values of 0.043 and 0.05 for R and R(w) respectively using 12214 unique reflections. In addition, a dimeric species 4 is formed when 1 equiv of PPh3 is added to the copper(I) 4-methylphenoxide, while with an excess of PPh3 a monomeric species 5 is isolated. Some interconversions among these complexes are also reported.

High-temperature reactions of alkali and plagioclase feldspars with alkali and alkaline-earth chlorides-formation of celsian

High-temperature reactions (Ca 900-degrees-C) involving albite, K-feldspar or plagioclase and K, Ba-or K, Sr chlorides were experimentally studied. These experiments reveal that the reaction between K-exchanged albite, potash feldspar, or plagioclase and Ba-chloride/Ba-K chloride results in the formation of celsian by the breakdown of the starting feldspar structure above 800-degrees-C. Sr-feldspar does not form under similar conditions. A size-effect of the large M-site cation appears to be responsible for the formation of celsian. The reaction between K-feldspar and barium chloride may be used as a method for synthesizing celsian.

Hydrogen-deuterium exchange reactions of cis- and trans-cyclopropane derivatives with D2O and CD3OD in the gas phase

Gas-phase hydrogen-deuterium (H/D) exchange reactions involving four isomeric cyclopropane derivatives were investigated under chemical ionization (CI) conditions, using D2O and CD3OD as reagent gases. There are abundant ions at [M + 1](+), [M + 2](+) and [M + 3](+) in the D2O and CD3OD positive-ion CI mass spectra of the two isomer pairs 1, 2 and 3, 4, Their CI mass spectra are identical with each pair, and so are the collision-induced dissociation (CID) spectra of ions [M + 1](+), [M + 2](+) and [M + 3](+) of each of the two isomer pairs. The CID spectra of [M + 1](+) ions indicate that they have common D/H exchange reactions within each pair, which take place between molecular ions and deuterium-labeling reagents to form the [M - H + D](+) ions. Those of their [M + 2](+) ions show that they have common D/H exchange reactions within each pair, which form the [M-d1 + H](+) ions. Those of their [M + 3](+) ions show that they have common D/H exchange reactions within each pair, which take place between the [M-d1] and deuterium-labeling reagents to produce [Md-2 + H](+) for the isomer pair 1, 2 and [M-d1 + D](+) for the Isomer pair 3, 4. The number and position, and active order of the active hydrogen atoms of the isomer pairs 1, 2 and 3, 4 were determined. Copyright (C) 2000 John Wiley & Sons, Ltd.

Gas-phase ion - Molecule reactions of neutral C-60 with the plasmas of alkyl methyl ethers and primary alcohols

The gas-phase ion-molecule reactions of C-60 with the methoxymethyl ion [CH3O=CH2](+) and the 1-hydroxyethyl ion [CH3CH=OH](+) generated under the self-chemical-ionization (self-CI) conditions of alkyl methyl ethers and primary alcohols were studied in the ion source of a mass spectrometer. The adduct ions [C60C2H5O](+) and protonated molecules [C60H](+) were observed as the major products of C-60 with the plasma of alkyl methyl ethers. On the contrary, the reactions of C-60 With the plasmas of primary alcohols produced few corresponding adduct ions. The AM1 semiempirical molecular orbital calculations were carried out on 14 possible structures. The calculated results showed that the most stable structure among the possible isomers of [C60C2H5O](+) is the [3+2] cycloadduct. According to experimental and theoretical results, the pathway for the formation of the adduct was presented.

Ion-molecule reactions of cis- and trans-cyclopropane derivatives with methane, acetone and vinyl acetate under chemical ionization conditions

Ion-molecule reactions of four isomeric cyclopropane derivatives were investigated under chemical ionization(CI) conditions, using methane, acetone and vinyl acetate as reagent gases, The methane positive-ion CI mass spectra of each of two isomer pairs 1,2 and 3,4 are identical, and so are the collision-induced dissociation (CTD) spectra of the protonated molecules of each of the two isomer pairs, The protonation reactions for the isomer pairs 1,2 and 3,4 occurred on the sites of the carboxyl groups and the R groups, respectively, Differences between isomers 1 and 2 are observed in their acetone (A) positive-ion CI mass spectra and in the CID spectra of their adduct ions ([M+H+A](+)), The adduct ions of compounds 2, 3 and 4 with protonated acetone and with protonated acetone dimer are observed in their CI mass spectra, However, only the adduct ions of compound 1 with protonated acetone appear in its CI mass spectrum, The protonated dimers of each of the four compounds are found in their vinyl acetate positive-ion CI mass spectra, and the CID spectra of these dimers for isomers 1 and 2 can also reflect their stereostructural difference. (C) 1998 John Wiley & Sons, Ltd.

STUDIES ON THE REACTIONS OF TRANSITION-METAL HYDRIDES WITH HETEROCUMULENES .6. REACTION OF CP2ZR(H)CL WITH RNCS (R=C6H5, 2-C10H7, C-C6H11 AND N-C4H9)

The novel NS-containing zirconacycle complexes Cp2ZrCl[SC(H)NR] (1a, R = C6H5; 1b, R = 2-C10H7; 1c, R= C-C6H11; 1d; R = n-C4H9) were obtained by insertion reactions of Cp2Zr(H)Cl with RNCS. 1(a-d) could react further with Cp2Zr(H)Cl to yield a sulphur-bridging compleX (Cp2ZrCl)2S (2) and a Schiff base RN=CH2. The crystal structure of la has been determined by X-ray analysis.

[1H,15N] N.M.R. Kinetic Studies of Reactions of cis- and trans-[PtCl2(15NH3)(c-C6H1115NH2)] with Guanosine 5'-Monophosphate

cis-[PtCl2(15NH3)(c-C6H11NH2)] is an active metabolite of the oral platinum(IV) anticancer drug cis,trans,cis-[PtCl2(CH3CO2)2(NH2)(c-C6H11NH2)]. Since it is likely that guanine bases on DNA are targets for this drug, we have analysed the kinetics of reaction of this platinum(II) metabolite with guanosine 5′-monophosphate (5′-GMP) at 310 K, pH 7, using [1H, 15N] n.m.r. methods. Reactions of the trans isomer are reported for comparison. The reactions proceed via aquated intermediates, and, for the cis isomer, the rates of aquation and substitution of H2O by 5′-GMP are 2-5 times faster trans to the amine ligand (c-C6H11NH2) compared to trans to NH3 for both the first and second steps. For the trans complex, the first aquation step is c. 3 times faster than for the cis complex, as expected from the higher trans influence of Cl¯, whereas the rate of the second aquation step (trans to N7 of 5′-GMP) is comparable to that trans to NH3. These findings have implications for the courses of reactions with DNA.

Reactions of artemisinin and arteether with acid: Implications for stability and mode of antimalarial action

The currently accepted mechanism of trioxane antimalarial action involves generation of free radicals within or near susceptible sites probably arising from the production of distonic radical anions. An alternative mechanistic proposal involving the ionic scission of the peroxide group and consequent generation of a carbocation at C-4 has been suggested to account for antimalarial activity. We have investigated this latter mechanism using DFT (B3LYP/6-31+G* level) and established the preferred Lewis acid protonation sites (artemisinin O5a >> O4a approximate to O3a > O2a > O1a; arteether O4a >= O3a > O5b >> O2a > O1a; Figure 3) and the consequent decomposition pathways and hydrolysis sites. In neither molecule is protonation likely to occur on the peroxide bond O1-O2 and therefore lead to scission. Therefore, the alternative radical pathway remains the likeliest explanation for antimalarial action.

The gas-phase reactions Of SiCl4 and Si2Cl6 with CH3OH and C2H5OH: an investigation by mass spectrometry and matrix-isolation infrared spectroscopy

The gas phase reactions Of SiCl4 and Si2Cl6 With CH3OH and C2H5OH have been investigated using both mass spectrometry and matrix isolation techniques. SiCl4 reacts with both CH3OH and C2H5OH upon mixing of the vapours for times in excess of 3 h to generate the HCl-elimination products SiCl3OR (R = CH3 or C2H5). The identity of these products is confirmed by deuteration experiments and by ab initio calculations at the HF/6-31G(d) level. Further products are generated when the mixture is passed through a tube heated to 750degreesC. Si2Cl6 reacts with CH3OH and C2H5OH via a different mechanism in which the Si-Si bond is cleaved to yield SiCl3OR and HCl. Other products of the type SiCl4-n(OCH3)(n) are tentatively identified by a combination of mass spectrometric and matrix isolation measurements. These latter products indicate further replacement of Cl atoms by OR groups as a result of reaction of CH3OH or C2H5OH with the initial product.

Gas-solid reactions of single crystals: a study of reactions of NH3 and NO2 with single crystalline organic substrates by infrared microspectroscopy

Reaction of single crystals of benzoic and trans-cinnamic acids with 200 Torr pressure of ammonia gas in a sealed glass bulb at 20 degrees C generates the corresponding ammonium salts; there is no sign of any 1:2 adduct as has been reported previously for related systems. Isotopic substitution using ND3 has been used to aid identification of the products. Adipic acid likewise reacts with NH3 gas to form a product in which ammonium salts are formed at both carboxylic acid groups. Reaction of 0.5 Torr pressure of NO2 gas with single crystals of 9-methylanthracene and 9-anthracenemethanol in a flow system generates nitrated products where the nitro group appears to be attached at the 10-position, i.e. the position trans to the methyl or methoxy substituent on the central ring. Isotopic substitution using (NO2)-N-15 has been used to confirm the identity of the bands arising from the coordinated NO2 group. The products formed when single crystals of hydantoin are reacted with NO2 gas under similar conditions depend on the temperature of the reaction. At 20 degrees C, a nitrated product is formed, but at 65 degrees C this gives way to a product containing no nitro groups. The findings show the general applicability of infrared microspectroscopy to a study of gas-solid reactions of organic single crystals. (c) 2005 Elsevier B.V. All rights reserved.