Synthesis, Reactions, and Structures of Heterocycle-Tethered Boranes and Their Precursors

Abstract

Heterocycle-tethered organoboranes generally dimerize by using the heteroatom present in them. When this does not take place, some interesting molecules or properties are bound to be observed. This is demonstrated in this work, as well. The lithium salt of 1,2-dimethylimidazole reacts with Et2B­(OMe) or 9-BBN-OMe to give the air-stable intermolecular adduct of 2-(dialkylborylmethyl)-1-methylimidazole (alkyl = Et (1) and 9-BBN (2)) after treatment with BF3·OEt2. These two dimers exist in two stereoisomers: clockwise and counterclockwise, as shown by their X-ray structures. On the contrary, in the analogous reaction between the lithium salt of 1,3,5-trimethylpyrazole and Et2B­(OMe) in the presence of BF3·OEt2, an air- and moisture-sensitive adduct, 1-(diethylborylmethyl)-3,5-dimethylpyrazole·BF2(OMe) (3), was isolated as a liquid in an excellent yield, instead of its dimer. Its structure is based on 1H, 19F, 11B, and HRMS methods and supported by anion binding studies. Consequently, the reactive neat liquid 3 decomposes in air to give the bicyclo[3.3.1]­nonane-like neutral bicycle 4. Notably, a CH2Cl2 solution of 3 decomposes differently to give the OH-bridged cationic analogous bicycle 5. In addition, their precursors, [2-(diethylborylmethyl)-1-methylimidazole·LiOMe­(1,2-dimethylimidazole)]2 6, [(1-(diethylborylmethyl)-3,5-dimethylpyrazole·LiOMe)2THF] 7, and [(1-(diethylborylmethyl)-3,5-dimethylpyrazole·LiOMe­(DMAP)2] 8, were also isolated and structurally characterized. In the crystal lattices of structures of 4, 5, and 7, both enantiomers RR and SS are present.

Iridium Diphosphine Complexes Featuring Pendant Lewis Acids: Efforts toward Selective Heteroarene Borylation

“…This reaction suggests a boron SCS effect that provides an alternative to the β‐H elimination pathway. Trisubstituted boranes have been shown to coordinate oxygen‐based nucleophiles including hydroxide and methoxide, manifesting in exergonic B‐O interactions having κ 1 ‐O and μ 2 ‐B−O‐B inter‐ and intramolecular bonding motifs [30–32] . In this instance, we suggest that intramolecular stabilization is conferred to the bound [Ir]‐OCH 3 group ( II , Scheme 5), resulting in a stabilized moiety that is subsequently removed from the iridium(I) primary coordination sphere to give a four‐coordinate 16‐electron compound with a peripheral borate in its SCS.…”

“…boranes have been shown to coordinate oxygen-based nucleophiles including hydroxide and methoxide, manifesting in exergonic B-O interactions having k 1 -O and μ 2 -BÀ O-B inter-and intramolecular bonding motifs. [30][31][32] In this instance, we suggest that intramolecular stabilization is conferred to the bound [Ir]-OCH 3 group (II, Scheme 5), resulting in a stabilized moiety that is subsequently removed from the iridium(I) primary coordination sphere to give a four-coordinate 16-electron compound with a peripheral borate in its SCS. Despite the asymmetry observed by 31 P{ 1 H} NMR spectroscopy, a single -OCH 3 resonance was observed at δ H = 3.39 ppm by 1 H NMR spectroscopy, suggesting it to be non-affiliated with iridium.…”