Azanonaborane-pyridine derivatives [(R′C5H4N)B8H11NHR″]: synthesis, structure and some molecular-orbital calculations

The molecular structure of hypho-type [(RNH2)B8H11NHR] is based on a {B8} cluster with one nitrogen bridge and one exo amine ligand. In general these azanonaboranes are synthesized by the reaction of [B9H13(SMe2)] with primary amines. Modifications of these azanonaboranes are possible by ligand-exchange reactions. Necessary conditions for ligand-exchange reactions of the azanonaboranes [(RNH2)B8H11NHR], in which the exo-{NH2R} group is replaced by other nitrogen-donor ligands, are reported. The nitrogen-donor ligands that have been examined include primary, secondary and tertiary amines as well as a series of substituted pyridines. The structures of the pyridine-containing azanonaboranes [(C5H5N)B8H11NHR] where R=methyl, ethyl, isopropyl or tertiary butyl, have been determined crystallographically, and are compared with the aliphatic azanonaboranes [(RNH2)B8H11NHR]. The reactions of the various [(RNH2)B8H11NHR] species with pyridine or the substituted pyridines give coloured products, contrasting with the colourless nature of the starting alkylamine species. The electronic interaction between the {B8} hypho-type unit and the bonded pyridine units has been investigated by UV–vis spectroscopy and by AM-1 molecular-orbital calculations.