Kernresonanzspektroskopische Untersuchungen an Borverbindungen, XIX. ¹³ C‐NMR‐Studien an Monoaminoboranen und Borazinen

Abstract

Chemische Verschiebungen δ13C von Aminoboranen R2BNR′2 1 und X2BNR2′ 2 sowie von Borazinen (RBNR′)3 3 und (XBNR′)3 4 (X = F, Cl, Br, I, OR, SR, NR2) könen mit der Wirkung eines γ‐Effektes von R und X auf δ13C(BC) und γ13C(NC) erklärt werden. Es bestehen Analogien zu Alkenen, Imoniumsalzen und Benzolderivaten. ‐ Heteronucleare 13C{1H, 11B} Tripelresonanz‐experimente erlauben die Betrachtung scharfer 13C(BC)‐Resonanzsignale.

Reactivity of a Sterically Unencumbered α‐Borylated Phosphorus Ylide towards Small Molecules

“…The 31 P{ 1 H} NMR chemical shifts clearly indicate the formation of the ylides. The 11 B NMR resonances are shifted upfield from δ =56.5 to 48.7 ppm for 2 and from δ =54.7 ppm to 47.6 ppm for 1 , respectively; these values perfectly match those reported in the literature for R 2 B−NH 2 …”

“…The 11 BNMR resonances are shiftedu pfield from d = 56.5 to 48.7 ppm for 2 and from d = 54.7 ppm to 47.6 ppm for 1,r espectively;t hesev alues perfectly match those reported in the literature forR 2 BÀNH 2 . [17] It should be notedt hat precedents for such reactivity have been published previously for dialkyl boron compounds. The splitting of NH 3 with the formation of R 2 BÀNH 2 takes place in boron compounds featuring Lewis basic substituents, such as R 2 BÀSEt, or with tBuC(O)OÀBEt 2 .…”

Dative σ- and π-bonding in boron–nitrogen compounds: molecular structures of (CH3)2NB(CH3)N(CH3)B(CH3)2 and [(CH3)2B]2NN(CH3)2 determined by gas electron diffraction and quantum chemical calculations

“…Both the 1 H and the 13 C spectra recorded at ambient temperatures indicated that the two methyl groups attached to the terminal N atom are nonequivalent, as are the two methyl groups attached to the terminal B atom: Internal rotation about the N1-B2 and N3-B4 bonds is presumably restricted by dative p-bonding. 3,4 A possible alternative structure, 1-c (c for closed) consists of a four-membered ring in which the terminal N atom has formed a dative r-bond to the terminal B atom. Indeed, an X-ray investigation of 2,2,6,6-tetramethylpiperidino[(dibromoboryl)tert-butylamino]bromoborane (3) shows that this compound adopts such a structure in the solid phase, and NMR spectra indicate that the structure is retained in solution.…”

“…Fig 4. The mechanism of the intramolecular rearrangement of Me 2 NN(BMe 2 ) 2 (2) that renders the two dimethylboryl groups NMR equivalent.…”