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

The coordination of [(eta-Cp)(2)Pb] and [(eta-Cp)(2)Sn] by bidentate Lewis-base ligands gives the first examples of adducts of neutral p-block metallocenes. Ab initio MO calculations of [(eta-Cp)(2)Pb . TMEDA] (1) (TMEDA = (Me2NCH2)(2)), [Cp2Pb . 4,4'-Me(2)bipy] (2) (4,4'-Me(2)bipy = 4,4'-dimethylbipyridine), and the new complex [(eta-Cp)(2)Sn . 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'-Me(2)bipy. This finding is a consequence of the greater reorganization energy of 4,4'-Me(2)bipy compared to TMEDA. The low association energies of these species can be rationalized in terms of metal lone pair/ligand lone pair repulsion.