Molecular transition-metal boron compounds. Any interest?

Abstract

Molecular metallaboranes, which feature complexes with M–B rather than M–C bonds, constitute a class of compounds which has revealed new possibilities for the way metal and borane fragments interact to generate novel structures, demonstrating an important role for the transition metal in the structural arrangement. Early transition-metal dimetallaboranes in particular adopt deltahedra with the same total connectivities as the borane anions or late transition-metal metallaboranes but with flattened geometries rather than spherical shapes. They are characterised by high metal coordination numbers, M–M cross-cluster distances within the single bond range, and formal (apparent) cluster electron counts three skeletal electron pairs short of that required for a canonical structure of the same nuclearity. A selection of these boron-rich dimetallaboranes is theoretically investigated and compared to illustrate the role of the transition metal in their cluster bonding.