On the bonding in π-complexes of borazine

The electronic structure of [Cr(eta(6)-B3N3H6))(CO)(3)] has been investigated.in detail using high quality density functional calculations. The bonding is found to be similar to the well established scheme in the arene analogue with the usual ring --> metal donation and metal -->, ring backdonation utilizing the pi bonding and anti-bonding orbitals respectively of the ring. The interactions are not localized Cr-N bonds and the ring does not bind as a triamine ligand. The polarization of the pi bonding and anti-bonding functions of the free and complexed ligand is however key in determining the adoption of a structure with the CO ligands located trans to the nitrogen atoms of the ring in contrast to the structure found for the arene analogue. Puckering of the borazine ring is due to the repulsive interactions between high lying, boron dominated, ring cr-bonding orbitals and the metal's 'lone pairs'. The electronic structure of the unknown diborazine chromium complex is also investigated. Its likely conformation and possible reasons for its instability are suggested. (C) 1998 Elsevier Science Ltd. Ah rights reserved.