Acyclic boron-containing π-ligand complexes: η2- and η3-coordination modes

Cyclic boron-containing pi-ligands such as boratabenzenes and borollides are well established, in particular as supporting ligands. By contrast, the chemistry of acyclic boron-containing pi-ligands has remained relatively unexplored, presumably in part due to the higher reactivity of acyclic pi-ligands relative to cyclic analogues. This perspective is focused on the synthesis, structures and reactivity of isolated transition metal complexes bearing eta(n)-coordinated (n = 2 or 3) acyclic boron-containing ligands. Both monometallic and multimetallic compounds are included, and are discussed with an emphasis on metal-ligand and intraligand bonding and parallels with hydrocarbon pi-ligand complexes.