RESUMEN
The reactivity of pyridine is a complex topic due to its unique electronic structure. The reactions of atomic boron with pyridine molecules in solid neon have been investigated using matrix isolation infrared absorption spectroscopy. Three products (marked as A, B, and C) were observed and characterized through 10B, D and 15N isotopic substitution pyridine regents as well as quantum chemical calculations. In the reaction, the ground-state boron atom can attack the lone pair electrons of the nitrogen atom in the pyridine molecule, resulting in the formation of a 1-boropyridinyl radical (A). Alternatively, addition to the aromatic π-system of pyridine can occur in a [1,4] type, leading to the formation of a B[η2(1,4)-C5H5N] complex (B). Under UV-visible light (280 < λ < 580 nm) irradiation, these two compounds can further undergo photo-isomerization to form BN-embedded seven-membered azaborepin compounds (C). The observation of species A, B, and the subsequent photo-isomerization to species C is consistent with theoretical predictions, indicating that these reactions are kinetically favorable. This research provides valuable insights into the future design and synthesis of corresponding BN heterocyclic derivatives.
RESUMEN
The boron atom is a highly electrophilic reagent due to the presence of its empty p orbital, making it prone to undergo electrophilic addition reactions with the carbon-carbon double bonds of olefins. In this study, the classical C=C reaction pathway occurs when a boron atom attacks the C=C bond of cyclohexene, resulting in the formation of the η2 (1,2)-BC6H10 complex (A) that contains a borirane radical subunit. This complex can further undergo photoisomerization, leading to the formation of a 3,4,5,6-tetrahydroborepine radical (C) through the cleavage of C-C bonds. In addition, two 1-boratricyclo[4.1.0.02,7]heptane radicals with chair (B) and boat (B') conformations were observed through α C-H cleavage reactions. Bonding analysis indicates that these radicals involve a four-center-one-electron (4c-1e) bond. Under UV light irradiation, these two radicals undergo ring-opening and rearrangement reactions, resulting in the formation of a 1-cyclohexen-1-yl-borane radical (D), which is a sp2 C-H activation product. These findings delineate a potential pathway for the synthesis of organoboron radicals through boron-mediated C-H and C-C bond cleavage reactions in cycloolefins.