Transition metal–σ-borane complexes

Synthesis, structure and bonding in transition metal complexes with borane ligands HBcat’ (catecholborane or substituted catecholborane), HBpin (pinacolborane), HBCy2 (dicyclohexylborane), HBEt2 (diethylborane) and HBMe2 (dimethylborane) have been discussed. The review summarizes the results and progress in the understanding of the nature of the metal–borane bonds, which has been gained in recent theoretical studies. Geometrical data (both experimental and theoretically calculated) show M–B, M–H and B–H bond distances longer than the sum of covalent radii. These results are consistent with the interaction of both boron and hydrogen with metal central, while preserving B–H bond character. The nature of the metal–borane interactions is quantitatively analyzed with an energy decomposition analysis. The [LnM]-[η2-BHR2] bonding in metal–borane complexes is more than half electrostatic.