Boron-nitrogen compounds. 100. Bromination of pyrazabole

Hanecker, E.; Hodgkins, T. G.; Niedenzu, K.; Noeth, H.

doi:10.1021/ic00198a005

Cited by 33 publications

(17 citation statements)

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“…Thus the B atoms in these three compounds should be ranked in order of increasing Lewis acidity as: N2BH2, N2BHBr, N2BBr2. Similar reasoning has been invoked to explain trends in BraN bond lengths in other Bhalopyrazaboles (Clarke, Das, Hanecker, Mariategui, Niedenzu, Niedenzu, Nrth & Warner, 1987;Hanecker, Hodgkins, Niedenzu & N6th, 1985). (09)is observed, which distorts the angles O9--C9--C9a [123.3 (1) °] and N1--C1--C9a [122.0 (1)°].…”

Section: -Bromopyrazabolesupporting

confidence: 52%

“…seen in a dibromoboryl-phenanthroline compound (Klebe & T ranqui, 1984). This lengthening may help to explain the thermal instability of 4-bromopyrazabole relative to the two symmetrical compounds pyrazabole and 4,8-dibromopyrazabole (Hanecker, Hodgkins, Niedenzu & N6th, 1985). Also, the two kinds of B--N bonds in 4-bromopyrazabole are of distinctly different lengths: N2BHBr 1.530 (6)/k average; N2BH2 1.562(7)A average.…”

Section: -Bromopyrazabolementioning

confidence: 92%

“…Since then, dozens of other pyrazaboles have been reported; this subject was recently reviewed by Niedenzu (1988). The compound 4-bromopyrazabole was found to be thermally unstable with respect to formation of 4,8-dibromopyrazabole and pyrazabole (Hanecker, Hodgkins, Niedenzu & N6th, 1985). A study of the crystal structure of 4-bromopyrazabole was undertaken to look for structural reasons for this instability.…”

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confidence: 99%

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Structure of 4-bromopyrazabole

Powell¹

1992

Acta Crystallogr C

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Section: -Bromopyrazabolesupporting

confidence: 52%

Section: -Bromopyrazabolementioning

confidence: 92%

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confidence: 99%

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Structure of 4-bromopyrazabole

Powell¹

1992

Acta Crystallogr C

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“…− 11.4, − 7.5) are rather close to the experimental data. This has been verified by calculating the optimized geometry and the 11 B chemical shift for pyrazabole 1a : folding angle along the B···B axis: calcd 132.3° (see also Alvarado et al 22), to be compared with 134.7°, determined for crystalline 1a ;23 and δ 11 B: calcd − 10.8 and exp. − 8.6 19…”

Section: Resultsmentioning

confidence: 68%

Indazaboles—synthesis and molecular structure

Wrackmeyer¹,

Shahid²,

Kempe³

et al. 2010

Applied Organom Chemis

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The reaction of 1-trimethylsilyl-indazole with boranes affords indazaboles accompanied by elimination of trimethysilane. Thus, the two isomers of parent indazabole are formed in a 1 : 1 ratio using borane in THF (BH 3 /THF), characterized by NMR spectroscopy in solution ( 1 H, 11 B and 13 C NMR). In contrast, the analogous reaction with 1,2-bis(tetramethylene)diborane(6) proceeds to give a single isomer of the B-alkylated indazabole via symmetric ring cleavage of the diborane(6), as shown by NMR in solution and X-ray structural analysis in the solid state. The molecular structure is fluxional in solution. In the solid state, the central B 2 N 4 ring adopts a distorted boat conformation. Calculated gas phase geometries of the parent indazaboles and of the B-alkylated indazabole were optimized by DFT methods at the B3LYP/6-311+G(d,p) level of theory.

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“…[10] Pyrazabole is the heterocycle that results from the dimerization of two pyrazole rings through a double BH 2 bridge connected to the nitrogen atoms, [11] a process that gives a stable six-membered central B 2 N 4 ring with a boat conformation. [12,13] We explored the reactivity of the pyrazabole ring and found that 2,6-bis(ethynyl)pyrazabole (1), or the deuterated analogue 4,4,8,8-tetradeutero-2,6-bis-(ethynyl)pyrazabole (2), can be converted into compounds 3 and 4 by a Sonogashira cross-coupling reaction with two equivalents of 4-iodophenyl 4-tetradecyloxybenzoate (Scheme 1) and thus show a similar reactivity to that of ethynylpyrazoles. [14] We confirmed the bent geometry of these pyrazabole cores by solving the structure of the diacetylenic compound 2 by single-crystal X-ray diffraction.…”

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confidence: 99%