C2-symmetric ansa-lanthanidocene complexes.: Theoretical evidence for a symmetric Ln•••(Si--H) β-diagostic interaction

Density functional calculations on ansa-bridged rare earth disilylamide complexes confirm the presence of a new type of symmetric Ln . . . (Si-H) beta -diagostic interaction, the origin and electronic structure of which are delineated in terms of structural criteria, vibrational spectra, natural population analyses, natural bond orbitals, and canonical molecular orbitals. The interaction turns out to be dominated by electrostatic effects, and the presence of vacant f orbitals appears to be of minor importance for the bonding in this case. It is shown that only central metals of sufficient size allow for a diagostic coordination mode due to steric hindrance.