Theoretical investigation on multinuclear NMR chemical shifts of some tris(trifluoromethyl)boron complexes

Abstract

Tris(trifluoromethyl)boron complexes have unusual properties and may find applications in many fields of chemistry, biology, and physics. To gain insight into their NMR properties, the isotropic 11B, 13C, and 19F NMR chemical shifts of a series of tris(trifluoromethyl)boron complexes were systematically studied using the gauge-included atomic orbitals (GIAO) method at the levels of B3LYP/6-31 + G(d,p)//B3LYP/6-31G* and B3LYP/6-311 + G(d,p)//B3LYP/6-311 + G(d,p). Solvent effects were taken into account by polarizable continuum models (PCM). The calculated results were compared with the experimental values. The reason that the structurally inequivalent fluorine atoms in a specific species give a same chemical shift in experimental measurements is attributed to the fast rotation of CF3 group around the B-C(F3) bond because of the low energy barrier. The calculated 11B, 13C(F3), and 19F chemical shifts are in good agreement with the experimental measurements, while the deviations of calculated 13C(X, X = O, N) chemical shifts are slightly large. For the latter, the average absolute deviations of the results from B3LYP/6-311 + G(d,p)//B3LYP/6-311 + G(d,p) are smaller than those from B3LYP/6-31 + G(d,p)//B3LYP/6-31G*, and the inclusion of PCM reduces the deviation values. The calculated 19F and 11B chemical shieldings of (CF3)3BCO are greatly dependent on the optimized structures, while the influence of structural parameters on the calculated 13C chemical shieldings is minor.

A Solid-State 11B NMR and Computational Study of Boron Electric Field Gradient and Chemical Shift Tensors in Boronic Acids and Boronic Esters

“…An examination of the correlation between experimental and calculated spans (Figure ) suggested a potential relationship between ϕ CCBO and both the experimental and calculated Ω values. Previous work by Zhang et al reported a dependence of the computed energy of boronic acids on this dihedral angle . A plot of the value of Ω as a function of the calculated value of ϕ CCBO for each compound reveals no clear and direct correlation, which is not surprising, as there are several variables changing simultaneously.…”

“…Previous work by Zhang et al reported a dependence of the computed energy of boronic acids on this dihedral angle. 54 A plot of the value of Ω as a function of the calculated value of φ CCBO for each compound reveals no clear and direct correlation, which is not surprising, as there are several variables changing simultaneously. For example, boronic acids have hydrogen bonding interactions taking place whereas the esters do not; the aromatic substituents are different on the various compounds, and the dihedral angle changes primarily due to sterics.…”

Applications of nuclear shielding

“…The calculated 19 F and 11 B chemical shieldings of (CF 3 ) 3 BCO are greatly dependent on the optimised structures, while the influence of structural parameters on the calculated 13 C chemical shieldings is minor. 168 Novel fluorinated boroxines, tris(2,6-difluorophenyl)boroxin (DF), tris(2,4,6-trifluorophenyl)boroxin (TF) and tris(pentafluorophenyl)boroxin (PF), were investigated for potential applications in lithium-ion batteries through fluoride anion binding, ab initio calculations and ionic cond. measurements.…”