Berkelium–Carbon Bonding in a Tetravalent Berkelocene

Interest in actinide–carbon bonds has persisted since actinide organometallics were first targeted for isotope separation during the Manhattan Project. Sandwich complexes with cyclooctatetraenide ligands have been used extensively to form tetravalent actinide compounds, “actinocenes,” from thorium through plutonium. These complexes have been pivotal in the development of electronic structure models used throughout inorganic chemistry. The isolation and structural characterization of transplutonium organometallics is extremely challenging due to limited isotope inventories, a scarcity of suitable laboratory infrastructure, and intrinsic difficulties with the anaerobic conditions required. Herein, we show that berkelium–carbon bonds can be stabilized in an organometallic “berkelocene” complex. Metal–ligand bonding involves the berkelium 5f orbitals in covalent overlap; however, charge transfer from the ligands is reduced to maximize contributions from the stable, half-filled 5f^7 configuration of tetravalent berkelium.