boron and benzyne

Ortho-benzyne and 1,2-azaborinine are related by the formal exchange of the CC triple bond by the isoelectronic BN unit. The (2 + 2) and (2 + 4) cycloaddition reactions of 1,2-azaborinine with the different organic π systems (ethene, ethyne, 1,3-butadiene, 1,3-cyclopentadiene, furan, benzene) were examined computationally using density functional, second-order perturbation, and coupled-cluster methods. All reactions of 1,2-azaborinine with the studied substrates are highly exothermic and involve the formation of Lewis acid-base complexes of 1,2-azaborinine and respective π systems. The interaction between the π bond of the substrates and the empty p orbital of the boron atom in these complexes is remarkably strong, resulting in two-step mechanisms for the (2 + 2) and (2 + 4) cycloaddition reactions. Cycloaddition reactions have lower barriers than CH insertion reactions, and (2 + 4) reactions are favored over (2 + 2) cycloadditions.

Topics: Acetylene; Benzene Derivatives; Boron

The BN analogue of ortho-benzyne, 1,2-azaborine, is generated by flash vacuum pyrolysis, trapped under cryogenic conditions, and studied by direct spectroscopic techniques. The parent BN aryne spontaneously binds N2 and CO2, thus demonstrating its highly reactive nature. The interaction with N2 is photochemically reversible. The CO2 adduct of 1,2-azaborine is a cyclic carbamate which undergoes photocleavage, thus resulting in overall CO2 splitting.

Topics: Benzene Derivatives; Boron; Boron Compounds; Carbamates; Carbon Dioxide; Models, Molecular; Nitrogen