Bonding of H2, N2, ethylene, and acetylene to bivalent lanthanide metallocenes:: Trends from DFT calculations on CP2M and Cp*2M (M = Sm, Eu, Yb) and experiments with Cp*2Yb

The results of DFT calculations have been used to define the trends in the interactions of H-2, N-2, C2H4, C2H2, and C2Me2 with the bivalent lanthanide metallocenes CP2M (CP = eta(5)- C5H5) and CP*M-2 (Cp* = eta(5)-C5Me5), where M = Sm, Eu, Yb. These results, together with those previously published for the bonding of CO to Cp2M (M = Ca, Eu, Yb), suggest that the interaction of these ligands with the lanthanide metallocenes results from a subtle balance between attractive (dipole-dipole or dipole-induced dipole) and repulsive (electron-electron repulsion within the f shell) forces. The balance between the attractive and repulsive forces, and therefore the net bond energy, depends on the f-electron count in these bivalent lanthanide metallocenes. The computational results are compared with experimental observations on paramagnetic CP*Eu-2 and diamagnetic ytterbocene, CP*Yb-2.