K. Niedenzu

A 13C NMR study on some phenylborane derivatives

Abstract The intensity of 13 NMR signals of carbon atoms bonded to boron can frequently be increased by recording the spectra at low temperatures. Though this procedure results in a loss of fine structure, it enables the determination of chemical shift data for NMR signals that are either broad or unobservable at ambient temperature. On the other hand, high temperature recording of spectra seems to be a useful technique for resolving multiples resonance signals that are collapsed in ambient temperature spectra. 13 C NMR data are reported for a variety of phenylborane derivatives; no simple correlation seems to exist between σ 13 C of the phenyl carbon atom bonded to boron and σ 11 B of the phenylborane species.

Synthesis and characterization of 1,3-dimethyl-2-phenyldiazaborolin

Abstract The preparation and characterization of the first diazaborolin, a system which is isoelectronic with the cyclopentadienide anion, is described.

Boronnitrogen compounds : LXI. Studies on (2-pyridylamino)diphenylborane and some related species☆☆☆

Abstract (2-Aminopyridine)-triphenylborane, (2-H 2 NC 5 H 4 N)B(C 6 H 5 ) 3 , has been prepared from its acidbase pair constituents; pyrolysis of the compound yields B -triphenyl- N -tris(2-pyridyl)borazine, [BC 6 H 5 N(2-C 5 H 4 N)] 3 . An intermediate in the transamination of (dimethylamino)diphenylborane with 2-aminopyridine to yield (2-pyridylamino)diphenylborane, (2-C 5 H 4 N)NHB(C 6 H 5 ) 2 , has been isolated and was identified to be a 1 : 1 molar adduct of (dimethylamino)diphenylborane with 2-aminopyridine. Somewhat related to this 1 : 1 adduct is a material that is obtained as initial product of the interaction of (2-pyridylamino)diphenylborane with water, which can be formulated as a 1 : 1 : 1 adduct of (2-pyridylamino)diphenylborane, (hydroxy)diphenylborane and 2-aminopyridine; pyrolysis of this species yields (diphenylboryl)(2-pyridylamino-phenylboryl) oxide, (C 6 H 5 ) 2 BOBC 6 H 5 NH(2-C 5 H 4 N), for which a coordinated cyclic structure is suggested. This same diboryl oxide is obtained from the interaction of (2-pyridylamino)dipheynylborane with molecular oxygen and also by the reaction of the cited aminoborane with acetophenone via oxygen abstraction from the latter. (2-Pyridylamino)diphenylborane 1,2-aminoboronates one CO double bond of carbon dioxide; this reaction is analogous to the reaction of (2-pyridylamino)diphenylborane with aldehydes or ketones as described previously.

Photoelektronenspektroskopische untersuchungen an bor-verbindungen : III. π-Elektronendelokalisation in 1,3,2-diazaborolinen

Abstract Comparison of the He(I) photoelectron (PE) spectra of derivatives of 1,3,2-diazaborolin(I) and 1,3,2-diazaborolidin(II) demonstrates a considerable delocalization of the six π electrons within the unsaturated five-membered heterocycle. This result agrees with 11B NMR chemical shift and UV data and CNDO/S calculations.

Boron—nitrogen compounds : LX. The reaction of (2-pyridylamino)diphenylborane with aldehydes and ketones

Abstract (2-Pyridylamino)diphenylborane reacts cleanly with aldehydes or ketones in a 1,2-addition of the 2-pyridylamino and diphenylboryl fragments of the aminoborane across a carbonyl group. The 1 : 1 molar reaction proceeds smoothly and with good yields; the resultant products are stable in air indicating fourfold coordination at the boron, This assumption is also borne out by spectroscopic data.

Boron-Nitrogen Compounds. XLII The Preparation of 1,3-Dimethyl-2-Trimethylstannyl-Diazaboracyclopentane

Abstract 1,3-Dimethyl-2-chloro-diazaboracyclopentane reacts with trimethylstannyl lithium to yield 1,3-dimethyl-2-trimethylstannyl-diazaboracyclopentane. The compound is not oxygen-sensitive and a boron-tin vibrational mode is tentatively assigned at 760 cm−1.

A spectroscopic study of 1,3-dimethyl-2-(trimethylstannyl)-1,3-diaza-2-boracycloakanes

The vibrational spectra of 1,3-dimethyl-2-(trimethylstannyl)-1,3-diaza-2-boracyclopentane and the corresponding diazacyclohexane derivatives as well as those of some other 1,3-diaza-2-boracycloalkanes have been recorded. Boron-nitrogen valence vibrations are observed in the 1500±10 cm−1 frequency region and boron-tin stretching is assigned near 760 cm−1. These data are discussed in conjunction with the 11B and 1H NMR spectra of the various heterocycles and the tin Mossbauer spectra of the two boron-tin species.

Boron-nitrogen compounds: XCVI. Studies of the chemical behavior of monomeric pyrazol-1-ylboranes☆

Abstract Two 1,3-dimethyl-2-(methylpyrazol-1′-yl)-1,3,2-diazaboracyclopentanes have been prepared. The interaction of such monomeric pyrazol-1-ylboranes containing trigonal boron with pyrazoles has been examined and 1 1 molar addition compounds have been identified and isolated. Labelling experiments support spectroscopic evidence to suggest a mobile bridging hydrogen in the cited adducts at ambient temperature and above. Monomeric 1,3-dimethyl-2-(pyrazol-1′-yl)-1,3,2-diazaboracyclopentane reacts with (dimethylamino)dialkylboranes by an exchange of the pyrazolyl with the dimethylamino group. A cyclic transition state involving a B 2 N 3 ring system is suggested for this process in which the corresponding 2-dimethylamino-1,3,2-diazaboracyclopentane and B -tetraalkylpyrazaboles are the final products. The latter are also found among the reaction products of pyrazole adducts of monomeric pyrazol-1-ylboranes with (dimethylamino)dialkylboranes. The interaction of (dimethylamino)dialkylboranes with pyrazole gives B -tetraalkylpyrazaboles in essentially quantitative yield.

Boron—nitrogen compounds : LXX. Boron derivatives of 3,3′-diaminodipropylamine☆

The reaction of borane(3) with 3,3′-diaminodipropylamine yields BH2B-bridge associated [3,3′-bis(dihydroborylamino)dipropylamino]dihydroborane, 1-aminopropyl-1,3,2-diazaboracyclohexane, or 1,8,10,9-triazaboradecalin (I), depending on the reaction conditions and the stoichiometry of the reactants. If tris(dimethylamino)borane is treated with 3,3′-diaminodipropylamine, only I or 1-bis-(dimethylamino)boryl-1,8,10,9-triazaboradecalin are obtained.

Boron-nitrogen compounds: CXX. Complexes of B-triethylboroxin with ethylenediamine and derivatives thereof☆

Abstract B-Triethylboroxin forms colorless 1 1 molar complexes of the type (C2H5BO)3·L with L = ethylenediamine (1) and various derivatives of the latter, i.e., N,N-dimethylethylenediamine (2), N,N,N′,N′-tetramethylethylenediamine (3, piperazine (4), 1,4-diazabicyclo[2.2.2]octane (5), diethylenetriamine (6), and tris(2-aminoethyl)amine (7). The cited boroxin also forms 2 1 molar complexes, 2(C2H5BO)3·L, with L = ethylenediamine (8) and those derivatives of the latter which may be considered as symmetrical species, i.e., N,N,N′,N′-tetramethylethylenediamine (9), piperazine (10), 1,4-diazabicyclo[2.2.2]octane (11), and diethylenetriamine (12). NMR spectroscopic data suggest that the complexes are fluxional in solution at room temperature with a single nitrogen coordinating to the three boron atoms of a given boroxin ring and where, in solution, the 1 1 molar complexes of symmetrical amines appear to exchange their donor sites. There seem to be no principal differences in the complexing of (RBO)3 with R = C2H5 or C6H5. Two species of the unusual composition 3(RBO)3·2H2NCH2NH2 were also identified.