Hydrogen atom storage upon Z-class borane ligand functions: an alternative approach to ligand cooperation

Ligand cooperation has become an important strategy in the development of new transition metal based transformations. By using this approach some remarkable new catalytic transformations have been achieved, all in the space of only a few years. The purpose of this tutorial review is to explore the potential utilisation of ligands containing borohydride and borane functionalities as reversible hydrogen atom stores. At the heart of this review will be a discussion on hydrogen transfer reactions and the transformation between borohydride and borane moieties. An outline of the various synthetic routes to metal–borane (metallaboratrane) complexes will be provided together with a discussion of their further reactivity including key transformations such as 1,2 additions across the metal–boron bond and ‘recharging’ the borane functional group back to borohydride. Finally, an evaluation of the potential future applications of such reactivity will be provided.