Novel types of hydrogen bonding with transition metal π-complexes and hydrides

This review deals with the results of investigations of novel types of hydrogen bond involving transition metal complexes, namely H-bonds with a metal atom (XH ⋯ M) and those with the hydride hydrogen atom (XH ⋯ HM) as a base, as well as those with cationic hydrides as proton donors with organic bases ([MH] + ⋯ B). Spectral, thermodynamic and structural characteristics of intra- and intermolecular hydrogen bonds are described. The influence of the nature of the metal atom, and of electronic and steric properties of ligands on the proton donor ability of the metal atom and hydride hydrogen are discussed. Studies of proton transfers occurring through intermediate hydrogen bonds are also analysed.