Weakly bonded Lewis base adducts of plumbocene and stannocene: A synthetic and calculational study

The coordination of [(η-Cp)₂Pb] and [(η-Cp)₂Sn] by bidentate Lewis-base ligands gives the first examples of adducts of neutral p-block metallocenes. Ab initio MO calculations of [(η-Cp)₂Pb·TMEDA] (1) (TMEDA = (Me₂NCH₂)₂), [Cp₂Pb·4,4′-Me₂bipy] (2) (4,4′-Me₂bipy = 4,4′-dimethylbipyridine), and the new complex [(η-Cp)₂Sn·TMEDA] (3) confirm that despite the presence of longer Pb-N and Sn-N bonds in the solid-state structures of the TMEDA adducts, the association of TMEDA with the metallocenes is more favorable than with 4,4′-Me₂bipy. This finding is a consequence of the greater reorganization energy of 4,4′-Me₂bipy compared to TMEDA. The low association energies of these species can be rationalized in terms of metal lone pair/ligand lone pair repulsion.