The σ–π transmitted coupling over five and six bonds in pyridine–borane complexes. MO calculations on structure and spin–spin couplings

Abstract

Can J Chern 59, 3026 (1981) The spin-spin coupling over six bonds between borane and ring protons in the borane complexes of pyridine and 2,6-lutidine has the same magnitude as in toluene. This D-7i transmitted coupling suggests that the hyperfine parameters QCCH and QUBH have the same magnitude. Comparison of INDO MO F P T calculations of hJ for these compounds and the methyl borazines with experiment indicates the relative degree of electron delocalization in these systems. An STO-3G structure is calculated for pyridine-borane. Almost free rotation about the B-N bond is predicted (sixfold barrier). The calculated 6JH.BH3 depends exponentially on the B-N bond length. Solvent effects on the proton chemical shift are in qualitative agreement uith the reaction field model.Can. J . Chem. 59. 3026 (1981). La constante de couplage spin-spin a travers six liaisons entre le borane et les protons du cycle dans les complexes du borane avec la pyridine s t la lutidine-2.6 est du mkme ordre de grandeur que dans le toluene. Ce couplage D-7i suggere que les parametres hyperfins Q,,, et C) , , , , ont le mkme ordre de grandeur. La comparaison des calculs INDO MO FPT des 6J de ces composes et des mithylborazines avec les resultats experimentaux indiquent le degrl de dllocatisation relative des electrons dans ces systkmes. En utilisant les calculs STO-3G on a calculi. une structure pour la pyridine-borane. On a prldit une rotation presque libre autour de la liaison B-N (barrikre du sixieme ordre). Les constantes 6JH.Bt'i calculees varient d'une f a~o n exponentielle avec la longueur de la liaison B-N. Les effets de solvant sur le deplacement chimique du proton sont qualitativement en accord avec le modkle de champ reactionnel.[Traduit par le journal] Introductionfor N-methyl and B-methyl borazines (4), giving an Theory and experiment agree that the spin-spin average of 7J of 0.06Hz in P-dimethylborazine.

Deformative Transition of the Menschutkin Reaction and Helical Atropisomers in a Congested Polyheterocyclic System

“…The flat boron species should be more easily inserted into the gap between the nitrogen lone pair and the phenyl group, and the initial complex is structurally akin to the transition state of the S N 2(C) reaction, just before configurational inversion of the electrophilic center. The complexation of 1A with borane failed to give any product; however, the complexation of 9 with borane did give a 1:2-adduct 10 quantitatively (Scheme ) which displays distinct NMR characteristics.…”

Synthesis, characterization, and spectrophotometric studies of novel fluorescent arachno decaborane and nonaborane clusters containing aza-distyrylbenzene derivatives

“…It has been shown previously that the colors of the 6,9-bis-pyridine-arachno-decaborane {6,9-(C 5 H 5 N) 2 -arachno-B 10 H 12 } and its ring substituted derivatives vary from a very pale yellow to a deep red, depending on the substituent group on the pyridine ligand [5,19]. In the case of {6,9-(C 5 H 5 N) 2 -arachno-B 10 H 12 }and its ring-substituted derivatives, electron-withdrawing substituents also shifted the absorption band at the longest wavelength to the red, whereas a p-donor substitutent led to a blue shift.…”

“…In the case of {6,9-(C 5 H 5 N) 2 -arachno-B 10 H 12 }and its ring-substituted derivatives, electron-withdrawing substituents also shifted the absorption band at the longest wavelength to the red, whereas a p-donor substitutent led to a blue shift. The differences of the number of boron atoms of the cluster between 10-vertex arachno {B 10 } and 9-vertex arachno {B 9 } would, therefore, appear to have no significant influence on the color of their pyridine complexes, because the {B 9 } series shows very similar colorations to the {B 10 } series [5,19]. The results of our calculations suggest a strong dependence of the absorption maxima in UV-Vis spectra on the LUMO energy of the substituted pyridines.…”