Structure of bis-, tris- and tetrakispyrazolylborates in the solid state (sodium and potassium salts of tetrakispyrazolylborate by X-ray crystallography) and in solution (1H, 11B, 13C and 15N NMR)

Notizen: The Bishydridobis(tetrazol-1-yl)borate Anion, [H2B(CHN4)2]-: Synthesis and Structure of the First Tetrazolylborate

“…The equivalency of both rings in their bond ing to boron is verified, and an N -l connectivity is established. The B -N , C -N, and N -N bond lengths, as well as most bond angles are not much different from those of the bis-or tris-(pyrazolyl)borate ligands [10] or tetrazolate com plexes [11]. We only note that the "inner" N -N bonds N 2 -N 3, and N 6 -N 7 are shorter by about 4 pm than the neighboring N -N bonds.…”

Addition of 3(5)-methylpyrazole to p-benzoquinone

“…As we have discussed elsewhere, the formation of bispyrazolyl hydroquinones implies the oxidation of the mono adducts by p-benzoquinone. 1 H and 13 C NMR spectroscopies…”

“…In the case of the pyrazole signals of compound 3, it is based on the fact that J 45 > J 34 (J 4'5' > J 3"4" ). 13 To distinguish between 2,3-and 2,5-disubstituted derivatives, we have used the criteria, previously established, that the pyrazole protons are shielded in the 2,3-bis derivative and slightly deshielded in the 2,5-one. 2 The chemical shifts of the OH groups deserve some attention.…”

“…Assignments are based on previous studies on pyrazoles [14][15][16] and azolylhydroquinones. [1][2][3] In the solid state, using the CPMAS technique, we have recorded the 13 C NMR spectra of these compounds (Tables 2 and 3), all of them being very well resolved. Compound 1 does not present any anomaly; the splitting of C-5' should correspond to some amount of disorder in the conformation of the pyrazole ring.…”

“…Table 2. 13 C NMR spectra (δ, ppm, J, Hz) of compounds (1) and (4). In solution, the rotational barrier being low, 2 both conformations are in rapid equilibrium at room temperature and only average signals are observed.…”