Weakly Bonded Lewis Base Adducts of Plumbocene and Stannocene:  A Synthetic and Calculational Study

Abstract

The coordination of [(η-Cp) 2 Pb] and [(η-Cp) 2 Sn] by bidentate Lewis-base ligands gives the first examples of adducts of neutral p-block metallocenes. Ab initio MO calculations of [(η-Cp) 2 Pb·TMEDA] ( 1 ) (TMEDA = (Me 2 NCH 2 ) 2 ), [Cp 2 Pb·4,4‘-Me 2 bipy] ( 2 ) (4,4‘-Me 2 bipy = 4,4‘-dimethylbipyridine), and the new complex [(η-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.