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  • Author: Heinrich Nöth x
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Bor-Stickstoff-Verbindungen sind in einfacher Weise durch Umamidierung zugänglich. Das Reaktionsprinzip wird durch die Gleichung

wiedergegeben. Da es sich um eine Gleichgewichtsreaktion handelt, müssen bestimmte Reaktionsbedingungen eingehalten werden, damit die Umsetzung quantitativ verläuft.

Hydrazino-N,N′-bis (dialkylborane) R2B—NH—NH—BR2 sind durch Umsetzung von Hydrazin mit Tetraalkyldiboranen (R2BH)2, durch Einwirkung von Hydrazin auf Trialkylborane BR bei 150—200°, und durch Umamidierung von Aminodialkylboranen R2B—NR2′ mit Hydrazin darstellbar. Hydrazino-dialkylborane R2B—NH—NH2 spalten leicht Hydrazin bei erhöhter Temperatur ab und gehen in Hydrazino-N,N′-bis(dialkylborane) über.

Die Umsetzung von Aminoboranen kann statt mit Hydrazin auch mit dessen Mono- und Dialkyl- oder arylderivaten durchgeführt werden.

Die Spaltung der Si—N-Bindung in Aminosilanen durch Borverbindungen RnBX3-n (X = H, F, Cl, Br, J) nach

führt, unter Eliminierung von Silan , zu Bor-Stickstoff-Verbindungen. /Durch Einwirkung von BX3 auf Dialkylaminotrimethylsilane Me3SiNR2 entstehen Dialkylaminoborane R2N—BX2. Bei der Umsetzung von Hexamethyldisilazan mit BX3 oder RBX2 erhält man Borazolderivate, während Dialkylborchloride R2BCI mit Hexamethyldisilazan im Molverhältnis 1 : 1 zu Verbindungen Me3Si—NH—BR2, im Molverhältnis 2 : 1 zu R2B—NH—BR2 und Trimethylchlorsilan reagieren.

Abstract

Ether solutions of LiAlH4 have been investigated by 27Al and 7Li magnetic resonance in the concentration range 3.75-0.0075 M. The Al-signal shows a fine structure due to Al-H coupling only at concentrations below 0.15 M. The observed chemical shift 27Al is only slightly concentration dependent. The line width of the 27Al signal, which is inversely proportional to T2*, reaches a minimum value at a concentration where the best resolution of the 27Al quintet is observed. This, however, is not matched by the 7Li line width whose minimum value was found at a somewhat higher concentration. The results are consistent with multiple ion formation at the higher concentrations and with an ion pair at low concentrations.

Mg(BH4)2 • 3 THF was prepared from MgHo and B2H6 in tetrahydrofuran. It crystallizes monoclinically, space group C2/c, Z = 4. The crystal structure reveals that the molecule contains a seven-coordinate Mg center. Its BH4 groups form double hydrogen bridges to magnesium. The geometry at Mg corresponds to a slightly distorted trigonal bipyramid for the O 3 B 2 (Mg)-coordination polyhedron, with two THF molecules in apical and one in equatorial position. A two-fold crystallographic axis passes through Mg and the equatorial oxygen atom thus posing C2 symmetry on the molecule

The crystal structures of the title compounds have been investigated in order to gain information on the problem of tautomerism associated with these and related compounds. [Ph2P(S)]2NH crystallizes in the triclinic space group P 1̄. Its structure is represented by the above formula, e.g. as a disubstituted amine with its nitrogen atom being sp2-hybridized. In contrast, ,,[Ph2P(O)]2NH" in the solid state is present as its tautomer Ph2P(O)-N = PPh2OH. It is an imidodiphosphinic acid as previously suggested. The crystals are monoclinic, space group P 21/n, Z - 2. Crystallographic inversion centers are occupied by the N- and the unique H-atom. Therefore a linear PNP arrangement as well as a symmetric OH-O-hydrogen bridge are characteristic for the structure of this molecule. The short PN bonds suggest a high bond order approaching 2. A consequence of the hydrogen bonded oxygen atoms are fairly long PO distances. The crystal structure of is made up of infinite zig-zag chains of Ph2P(0)NPPh2ÖH molecules along the crystals b-axis

Abstract

The title compound crystallizes in the rhombohedral space group R3, Z = 1. The boron atom occupies a special position on the threefold axis therefore imposing C3 symmetry to the molecule. The C2BN plane is twisted relative to the BN3 plane by 37.1°, and the BN bond length of 144.8(3) pm is on the upper limit of BN bond lengths found for other triaminoborane systems.

Irrespective of the ratio of the reactands AsBr3 and mesMgBr (mes = mesityl), two products are formed in THF solution: dimesitylarsenic bromide and a magnesium bromoarsenate of composition MgAs5Br17 · n THF. The latter, on crystallization from acetonitrile, yields [Mg(NCMe)4(THF)2][As3Br11 ]. The anion of this salt can be described as derived from three face sharing AsBr6 octahedra. The lone pair of electrons at the As atoms is stereochemically not active.

Monomeric and trimeric arsinoboranes have been obtained by three different methods. Bis(amino)arsinoboranes are monomeric, (C6H5)2BAs(CH3)2 is partially associated and decomposes readily, while (CH3)2BAs(CH3)2 proved to be trimeric as well as (CH3)2AsBBrCH3. Trimeric and tetrameric (CH3)2AsBH2 were isolated as the products of thermolysis of (CH3)4As2 · BH3. IR, MS and NMR data of the compounds are discussed.