Showing papers on "Carborane published in 1976"

Cobalt-hydrogen metallocarboranes. Synthesis of closo-[(CH3)2C2B4H4]2CoH and nido,closo-[(CH3)2C2B3H5]CoH[(CH3)2C2B4H4] and their conversion to new cobalt-cobalt bonded metallocarboranes

Abstract: : The reaction of Na(+)((CH3)2C2B4H5)(-) with CoCl2 at 25C yields the red neutral commo-metallocarborane (C,C'-(CH3)2C2B4H4)2Co(III)H. From NMR evidence the hydrogen atom associated with the metal is proposed to be face-bonded to a triangular face on the polyhedral surface. The compound is converted in aqueous acid to a nido-closo species, (C,C'-(CH3)2C2B3H5)CoH(C,C'-(CH3)2C2B4H4), which in turn can be metal-deprotonated by NaH to give the ((CH3)2C2B3H5)Co((CH3)2C2B4H4)(-) ion; reaction of the latter species with aqueous HCl regenerates the neutral metal-protonated compound. The reaction of the ion with CoCl2 and NaC5H5 produces nido-closo ((CH3)2C2B3H5)CoH((CH3)2C2B3H3)Co(eta to the 5th power-C5H5) in which a Co-Co bond is postulated. Treatment of (C,C'-(CH3)2C2B4H4)2Co(III)H with (eta to the 5th power-C5H5)Co(CO)2 yields 4,5 - (CH3)2-1,2,4,5-(eta to the 5th power-C5H5)2Co2C2B3H3 and (eta to the 5th power-C5H5)Co((CH3)2C2B3H3)CoH((CH3)2C2B3H3)Co(eta to the 5th power-C5H5), the latter species having a proposed Co-Co link. Air-oxidation of (C,C'-(CH3)2C2B4H4)2Co(III)H produces the tetracarbon carborane (CH3)4C4B8H8.

The separation of amino acid enatiomers on optically active dipeptide carborane stationary phases

Abstract: N-Trifluoroacetyl (TFA) dipeptide-o-carboranyl propyl esters of L-valyl-L-valine and L-α-amino-n-butyryl-L-α-amino-n-butyric acid have been prepared and the properties of these two new stationary phases for the gas-liquid chromatographic sepaation of amino acid enantiomers have been examined. It was found that the amino acid derivatives have shorter retention times, while maintaining good separation factors, on these carborane phases as compared to other dipeptide stationary phases. Both high and low boiling derivatives have been resolved on a 165 m×0.5 mm capillary column. The new phases have greater thermal stability and can be utilized over a wide temperature range.

The crystal and molecular structure of tribromo-m-carborane

Abstract: The sequence of electrophilic substitution for o- and m-carborane has been the subject of much experimental and theoretical work. The molecular structure of tribromo-m-carborane (m-B10Br3H7C2H2) shows that the third bromine atom to be substituted is found bonded to boron atom 12 (or 5). The crystal data are: space group, Pbcm; a = 8.47(4), b = 12.19(8), and c = 12.25(8) A; ρo = 1.98(2) and ρc = 2.00 g/cm3 for Z = 4. Data were collected using Weissenberg geometry and Ni-filtered CuK, radiation. The visually estimated intensities of 920 reflections were used in the anisotropic block-diagonalized least-squares refinement of the 76 structural parameters. The final value of the conventional residual index was 0.087.

Thermo-oxidative degradation of carborane containing polyamides

Abstract: A study has been made of the thermo-oxidative degradation of carborane containing polyamides of varying structure in the temperature range 200–500°. It is shown that the first stage of the degradative process is direct oxidation of the carborane ring, which leads to enhancement of the overall thermo-oxidative stability of these polymers compared with ordinary aromatic polyamides.

Study of the mono- and dianions of isomeric diphenylcarboranes by the method of C13 NMR spectroscopy

Abstract: 1. The C13 NMR spectra were obtained for the isomeric diphenylcarboranes, the dianions of these carboranes, 1,2-dimethyl-o-carborane, its dianion, and also the monoanions. The dianions from the o- and m-carborane are identical but the dianion from the p-carborane differs from them. The carbon nuclei of the carborane polyhedron occupy equivalent positions. 2. The C13 NMR spectra were obtained for the dianion from 1,2-diphenyl-o-carborane in THF at 0, −30, and −50°. There are no changes in the dianion's structure in this temperature rangs. 3. The monoanions, obtained from the isomeric diphenylcarboranes, are identical. The carbon nuclei of the carborane fragment and the phenyl rings in them have a nonequivalent position.

Method for preparing carborane

Abstract: Improved yields of n-hexyl carborane are obtained by slowly adding an ether solution of decaborane and dialkylsulfide to 1-octyne at a temperature between about 110° and 140° C.

Polyimides based on m- and p-carboranylenediamines☆

Abstract: m - and p -carborane-containing poly (acid) amides have been produced by reacting m - and p -carboranylenediamines with tetracarboxylic acid dianhydrides; their chemical and thermal cyclodehydrations have been investigated. The formation of m -carborane containing polyimides was found to be accompanied by conversion of the m -carborane ring to the dicarbaundecarborate anion. The chemical and thermal cyclization of the poly (acid)amides containing the p -carborane group was found to give rise to polyimides without the carborane ring being fractured.

On the relative heat stability of polyamides containing m- and p-carborane fragments

Abstract: A study has been made of the heat stability of polyamides containing m- and p-carborane fragments in the acidic as well as in the amino components. It is shown that at elevated temperatures the behaviour of the polymers is greatly influenced not only by the isomery of the carborane nucleus, but also by mutual positioning of the latter and of the NH group of the amide bond.

Synthesis of decaborane-14 and alkyl-substituted decaborane-14

Abstract: A method for preparing a mixture of decaborane-14 and an alkyl-substitutedecaborane-14 which comprises admixing an ethereal solution of nonaborane-14 ions with an alkaliboron halide at a temperature from 20° C to 30° C and at pressure from atmospheric pressure to 400 psig and a method of preparing decaborane-14 which comprises preparing an ethereal solution of nonaborane-14 by a reaction in an ethereal solution of an alkali metal borohydride with an excess of pentaborane-9 at temperature from 20° C to 30° C and admixing this ethereal solution of nonaborane-14 ions with diborane-6 at a temperature from 20° C to 30° C and at a pressure of at least 50 psig. Such compounds are useful as precursor compounds for the synthesis of important carborane derivatives, such as n-hexylcarborane (a catalyst for rocket propellants) and high-temperature-resistant carborane/siloxane polymers.

1H and 11B NMR study of molecular reorientation in crystalline 9‐bromo‐meta‐carborane

Abstract: 1H and 11B NMR have been used to characterize molecular reorientation in crystalline 9‐bromo‐meta‐carborane. A structural phase transition has been found at 344±2 K. In the high temperature (α) phase, reorientation is rapid and apparently isotropic, with activation energy EA=22.4±1.3 kJ/mol. In the low temperature (β) phase, reorientation is anisotropic, with an apparent activation energy of 47.0±6.3 kJ/mol for temperatures above the proton T1 minimum (∼300–344 K), and 14.7±1.3 kJ/mol for temperatures below the T1 minimum (∼230–290 K). Temperature dependences of the linewidths and shapes in the β phase are tentatively interpreted to indicate a more complicated reorientation than was observed in ortho‐carborane.

Synthesis and study of polybenzimidazoles containing p-carborane☆

Abstract: Polybenzimidazoles containing p-carborane were obtained by a single stage method in melt formed of diphenyl ester of p-carborane dicarboxylic acid and aromatic tetramines and a two stage method from p-carborane dicarboxylic acid dichloride and aromatic tetramines in THF solution in the presence of trioctylamine with the separation of linear polyaminoamides and subsequent cyclodehydration to polybenzimidazoles. The properties of both polyaminoamides and polybenzimidazoles were examined and it was shown that these properties are not only influenced by the isomerism of the carborane nucleus, but also conditions of synthesis.