A theoretical multinuclear NMR study of pyrazolylborates

Abstract

The experimental chemical shifts and coupling constants of fi ve borates of general formula BH n Pz 4 -n [from the borohydride to tetrakis(pyrazol-1-yl)borate] anions were compared with calculations carried out at the B3LYP/6-311 + + G(d,p) level (GIAO for absolute shieldings), in general with satisfying results. The most stable conformations of pyrazolylborate anions are similar to those of neutral pyrazolylmethanes.

Three centered hydrogen bonds of the type CO⋯H(N)⋯X–C in diphenyloxamide derivatives involving halogens and a rotating CF3group: NMR, QTAIM, NCI and NBO studies

“…There are many reports on the signs and magnitudes of couplings involving hydrogen bonds. 19,[27][28][29][30][31] As reported earlier, 12,18,19 J HF is negative, and hence its contribution is À2.9 Hz (in CDCl 3 ) and +0.85 Hz (in DMSO). Then the contribution from the H-bond alone turns out to be À3.75 Hz.…”

The structures of two scorpionates: thallium tetrakis(3-phenyl-1H-pyrazol-1-yl)borate and potassium tetrakis(3-cyclopropyl-1H-pyrazol-1-yl)borate

“…Unsubstituted tetrakis(1H-pyrazol-1-yl)borate, when isolated, has two minimum energy conformations, of D 2 and S 4 symmetries, the latter being the most stable by 34.8 kJ mol À1 (Alkorta et al, 2010). The same happens with the title compounds: 31.9 kJ mol À1 for (1) and 35.3 kJ mol À1 for (2).…”

“…Our past contribution to this field has been centred mainly on the study of structural properties, using as cations 'innocent' ones such as K + or Tl + , via negative-ion fast-atom bombardment mass spectra of pyrazolylborates (Aubagnac et al, 1991); the structures of bis-, tris-and tetrakispyrazolyl-borates in the solid state by X-ray crystallography, and in solution by NMR (Ló pez et al, 1990); determination of the protonation site of tetrakis(pyrazol-1-yl)borate in the solid state and in solution (Ló pez et al, 1994); structural characterization of paramagnetic octahedral homoscorpionate cobalt complexes by 1 H and 13 C NMR spectroscopy and by FAB-mass spectrometry (Aubagnac et al, 1995); the fluxional behaviour of molybdenum pyrazolylborates (Santa María et al, 2007); several multinuclear magnetic resonance studies both in solution and in the solid state (Ló pez et al, 1995;Sanz et al, 1996;Claramunt et al, 2004a,b), where, amongst other things, some 13 C-11 B and 13 C- 205 Tl residual coupling constants were measured. We also published a theoretical study of all possible pyrazolylborates derived from the parent pyrazole (Alkorta et al, 2010).…”

The organic chemistry of poly(1H-pyrazol-1-yl)methanes

“…Comparative papers include a 13 C NMR study of polyphenyl-, poly-N-azolyl-and poly-Nbenzazolylmethanes [32]; a review on substituent effects on the 15 N NMR parameters of azoles [263]; a theoretical multinuclear NMR study of pyrazolylborates that includes for comparative purposes the parent pyrazolylmethanes 2, 1 and 15 [264]; and an experimental and theoretical (GIAO/DFT) study of the pyrenyl derivative 213 [265].…”

“…DFT calculations on the different conformations of compound 1 and their interconversion pathways have been carried out and related to the binding abilities toward Ag(I) and Cu(I) [266]. Although the paper is mainly devoted to pyrazolylborates, a conformational analysis was carried out on 2, 1 and 15 for comparative purposes: for 15 two minima were found, the most stable of which has S 4 symmetry and the least stable a D 2 symmetry [264]. The di(1H-pyrazol-1-yl)methane (2) has been studied theoretically [PBE0/6-31+G(d,p)] and its IR spectrum measured and compared with the calculated one [267].…”