Indirect Nuclear Spin-Spin Coupling Constants ¹J(¹⁷O,¹¹B). First Observation And Calculation Using Density Functional Theory (Dft)

Abstract

Coupling constants 1 J( 17 O, 11 B) of borates, borane adducts and boranes with boron-oxygen bonds have been calculated on the basis of optimised molecular structures using the B3LYP/6-311+G(d,p) level of theory. This indicates that such coupling constants can be of either sign and that their magnitudes can be rather small. Since both 11 B and 17 O are quadrupole nuclei, it is therefore difficult to measure representative data. In the cases of trimethoxyborane and tetraethyldiboroxanes, it proved possible to obtain experimental data 1 J( 17 O, 11 B) (22 and 18 Hz) by measurement of 17 O NMR spectra at high temperature (120 • C and 160 • C) respectively. The magnitude of these coupling constants is in reasonable agreement with calculated data. In the case of the diboroxane, this points towards a bond angle B-O-B more close to 180 • than to 140 • .

Dipolar Heteronuclear Correlation Solid-State NMR Experiments between Half-Integer Quadrupolar Nuclei: The Case of 11B–17O

“…Analytical fits that take into account the statistical probability of having an attached 17 O atom residing in the CT spin state suggest that the 17 O isotopic abundance of boric acid and BDBA is 30 and 10%, respectively, in excellent agreement with solution NMR and the 11 B­{ 17 O} RESPDOR results (see the Supporting Information for the J -resolved fitting procedure). The one-bond 11 B– 17 O J -coupling constants ( 1 J BO ) were determined to be 35 Hz, similar to those of B–O containing small molecules previously observed via solution NMR spectroscopy . Euler angles used in the numerically simulated RESPDOR curves were obtained from periodic plane-wave DFT calculations of BDBA or boric acid (Figure S1); however, the Euler angles had a minimal effect on the simulated RESPDOR curves (Figure S4A).…”

“…The one-bond 11 B− 17 O J-coupling constants ( 1 J BO ) were determined to be 35 Hz, similar to those of B−O containing small molecules previously observed via solution NMR spectroscopy. 108 Euler angles used in the numerically simulated RESPDOR curves were obtained from periodic plane-wave DFT calculations of BDBA or boric acid (Figure S1); however, the Euler angles had a minimal effect on the simulated RESPDOR curves (Figure S4A). Numerical simulations also suggest that the rate and extent of signal dephasing in a 11 B{ 17 O} RESPDOR experiment performed with 11 B recoupling are nearly identical to those of a 13 C{ 17 O} RESPDOR experiment with REDOR recoupling applied to the 13 C spins, suggesting that both experiments exhibit similar mechanisms for dipolar recoupling, that is, recoupling is driven by rotor-synchronized inversion or refocusing of the CT of the coupled or observed spin, respectively (Figure S4B).…”

Influence of fluorine substituents on the NMR properties of phenylboronic acids

“…These calculations were also performed using DFT, at the same level of theory, which provided a good correlation with experimental results. The calculated oxygen‐17 chemical shieldings ( σ ( 17 O)) were converted to chemical shifts scale ( δ ( 17 O)) by δ ( 17 O) X = σ ( 17 O) CO − σ ( 17 O) X + 350.1, where σ ( 17 O) CO is the shielding of the oxygen atom in carbon monoxide molecule, calculated in the same base as the other molecules ( σ ( 17 O) CO = −69.7 ppm), 350.1 ppm is the experimental chemical shift of CO in gas phase measured versus liquid H 2 O (0.0 ppm) . The calculations of geometry‐optimized TMS, CFCl 3 , and BF 3 gave the shielding values σ ( 1 H) TMS = 31.81 ppm, σ ( 13 C) TMS = 183.77 ppm, σ ( 19 F) CFCl3 = 156.59 ppm, and σ ( 11 B) BF3 = 89.19 ppm; thus, the calculated values of the chemical shifts of studied arylboronic acids are expressed as δ ( 1 H) X = 31.81− σ ( 1 H) X ; δ ( 13 C) X = 183.77− σ ( 13 C) X ; δ ( 19 F) X = 156.59− σ ( 19 F) X ; and δ ( 11 B) X = 89.19− σ ( 11 B) X , respectively.…”

Oxidative coupling of silylated nonagermanide clusters

“…48 Furthermore, the observed 11 B NMR shift matches with the shift of the closely related boryl ether Me 2 B-O-BMe 2 (52 ppm). 49 Additionally, the mass peak of the ionization product [Cy 2 B-O-BCy] + was detected in LIFDI-MS measurements (Fig. S12, ESI †).…”