Dimerization of diboradiazacyclobutadienes to form tetraboratetraazacyclooctatetraenes: Computational study of boron-nitrogen ring formation and ringopening

Computational studies of the dimerization of the diboradiazacyclobutadienes (HBNH)(2) and (MeBNMe)(2) to form the tetraboratetraazacyclooetatetraenes (RBNR)(4) suggest that the preferred pathway involves "face-to-face" dimeri zation of the four-membered ring, followed by asynchronous, one-step scissi on of the two transannular BN bonds to form the eight-membered monocyclic p roduct. Detection of the proposed intermediates in either system is unlikel y, as they he in shallow potential energy wells. That in certain situations the four- and eight-membered rings establish equilibria is consistent with the comparatively small energy difference between (MeBNMe)(2) and (MeBNMe) (4).