Chemistry - A European Journal
Chemistry - A European Journal
5 years ago

Synthesis and Reduction of Sterically Encumbered Mesoionic Carbene-Stabilized Aryldihaloboranes

Synthesis and Reduction of Sterically Encumbered Mesoionic Carbene-Stabilized Aryldihaloboranes
Haopeng Gao, Holger Braunschweig, Merle Arrowsmith, Jens Seufert, Marc-André Légaré, Valerie Paprocki, Julian Böhnke
Sterically hindered, in situ generated 1,3,4-substituted 1,2,3-triazol-5-ylidene mesoionic carbenes (MICs) were employed to stabilize a number of aryl- and heteroaryldihaloboranes, as well as the first MIC-supported diborane. Reduction of borane adducts of the 1-(2,6-diisopropylphenyl)-3-methyl-4-tert-butyl-1,2,3-triazol-5-ylidene ligand with KC8 in non-coordinating solvents led to intramolecular C−H- and, C−C-activation at an isopropyl residue of the supporting ligand. DFT calculations showed that each of these activation reactions proceeds via a different isomer of a borylene intermediate. Sterically encumbered mesoionic carbene adducts of (hetero)aryldihaloboranes and a diaryldihalodiborane were obtained by borane addition to in situ deprotonated 1,3,4-substituted 1,2,3-triazoles. Reduction with KC8 in toluene led to competitive intramolecular C−H and C−C activation at a ligand isopropyl group via two distinct borylene pathways, as determined by computational modelling.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201700500

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