Computational studies of dative bond containing heterocyclic ring structures

Ab initio calculations are reported for several related heterocyclic compounds, each of which contains two dative bonds when they self-dimerize. Thus, these molecules are nominally dimers that contain either a boron–carbon–nitrogen (BCN) or boron–carbon–phosphorous (BCP) segment. Molecules with this motiff have been found experimentally to have several unusual properties that may be related to a “multi-polar framework’’ that results from charge separation associated with the two dative bonds. Structures obtained from full geometry optimizations without symmetry constraints, dative bond energies and charge distributions for four multipolar molecules are reported, the BCN–BCN dimer and the BCN–BCP dimer with and without carboxylation of one boron atom. Comparisons to single dative bond, self-cyclized monomers and the role of ring strain in molecular stabilities are also discussed.