title: Theoretical studies of borazynes and azaborines.
abstract: Four isomers of didehydroborazine, B3N3H4, borazyne, and three isomers of azaborine, C4H4BN, are studied by DFT, CCSD, and CCSD(T) computational methods. The singlets of 1,2-borazyne (I) and 1,4-borazyne (IV) have angles about the boron of ca. 150 degrees . In 1,2-azaborine (V), the angles are ca. 140 degrees , while the N angles are ca. 112 degrees except in IV (127 degrees ) and 1,4- azaborine (VII, 120 degrees ). These geometries are almost reversed in the triplets. The 1,3-borazyne (III) shows more bicyclic character than the corresponding m-benzyne, with an N-N distance of 1.7 A. In all cases I was found to be lower in energy than the 2,4-borazyne (II), III, and IV. The order of stability of the azaborines is V > VII > 1,3- azaborine (VI). The nucleus-independent chemical shift (NICS) indicates that all isomers of borazyne are less aromatic than benzene and all isomers of azaborine are about as aromatic as benzene. Time-dependent DFT (TD-DFT) is used to study the excited states of the singlets. The significant structural differences between the singlet and triplet states suggest long phosphoresence lifetimes.
authors.affiliation: Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085, USA. paul.fazen@villanova.edu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Fazen
authors.forename: Luke A
authors.initials: LA
authors.lastname: Burke