Nuclear Quadrupole Double Resonance of Compounds with Transannular Boron—Nitrogen Bonds

Abstract

The boron and nitrogen nuclear quadrupole double resonance spectra of several ring com pounds with transannular b o ro n -n itro g e n bonds are reported. The electron donation from nitro gen to boron as seen by their quadrupole coupling parallels the b o ro n -nitrogen bond lengths. One of the compounds exhibits a transannular valence topom erisation between two identical boron-nitrog en pairs in solution which is frozen in the solid state but may possibly exist in a preformed state o f this equilibrium from its quadrupole coupling. The oxygen-boron 7t-bond in boroxines, whose extent is deduced from the quadrupole coupling in one of the compounds with a boroxine-like structure at boron and in (PhBO)3, is approximately half as strong as the nitrogen-boro n 7t-bond in borazine.

Reaction of N,N′-dihydroxy-.N,N′-dimethylmethanediamine with phenylboronic acid and the crystal and molecular structure of N,N′-dihydroxy-N,N′-dimethylmethanediamine

“…the "reverse anomeric effect". A decrease of electron density at the trivalent nitrogen in 2 has recently been indicated by nuclear quadrupole double resonance experiments (35 …”

A Solid-State Multinuclear Magnetic Resonance Investigation of Hexamethylborazine

“…The 11 B quadrupolar coupling constant may be compared to previously determined values for related compounds. For example, several solid-state 11 B NMR studies report values of C Q ( 11 B) ranging from 2.7 to 2.9 MHz for hexagonal boron nitride, 24,31 polyborazylene, 24 and B-trialcynylborazine, 24 whereas values of 3.2 and 3.6 MHz have been reported for the parent borazine by nuclear quadrupole resonance (NQR) 15 and solution 1 H NMR 13,14 studies, respectively. This range of 11 B quadrupolar coupling constants is characteristic of B 3 N 3 ring structures 24 and, in general, values of C Q ( 11 B) are less than 5 MHz.…”

“…This range of 11 B quadrupolar coupling constants is characteristic of B 3 N 3 ring structures 24 and, in general, values of C Q ( 11 B) are less than 5 MHz. 96 Boron and nitrogen NQR 11,12,15 studies of borazine at 77 K report values of η Q that are significantly nonzero at 77 K: η Q ( 11 B) ) 0.133, 12,15 η Q ( 14 N) ) 0.10, 15 and η Q ( 14 N) ) 0.097. 11 The nonzero asymmetry parameters indicate that the borazine ring is not jumping rapidly about its C 3 axis at 77 K. Ab initio and DFT calculations for a static molecule of I yield nonzero values of η Q (Table 2).…”

“…The parent, borazine (R, R′ ) H), which is isoelectronic and isostructural with benzene, was discovered in 1926 by Stock and Pohland 1 and has been the subject of considerable theoretical [2][3][4][5][6][7][8][9] and experimental [10][11][12][13][14][15][16][17][18][19] interest ever since. Although possessing similar structural and physical properties as the prototypal carbon-based aromatic systems, borazine and its derivatives are chemically much more reactive.…”

“…This work has been complemented by a characterization study of polyborazylene by Gervais et al using various 11 B and 15 N solid-state NMR experiments. 28 These NMR techniques proved to be very useful in identifying and differentiating the 15 NH x sites (x ) 0-3) and the two types of boron environments, BN 2 H and BN 3 , in polyborazylene.…”