Metallocene Coordination to Neutral Alkaline Earth Metal Complexes

The geometrically constrained, Lewis acidic magnesium diamide complex, [Mg(EtNONTCHP)] (EtNONTCHP = 4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene), forms complexes with a series of metallocenes, [Mg(EtNONTCHP)(2-Cp2M)] (M = Mn, Fe, Co or Ni), in which one cyclopentadienyl ring of the metallocene is 2-coordinated to the magnesium center. Treating the heavier group 2 metal amide complexes, [M(EtNONTCHP){N(H)(SiMe3)2}] (M = Ca, Sr or Ba) with ferrocene yields complexes [M(EtNONTCHP)(5-Cp2Fe)] in which one cyclopentadienyl ring of ferrocene is 5-coordinated to the group 2 metal center. Computational studies on the metallocene complexes reveal that the metallocene-group 2 metal interactions are largely electrostatic in nature, but do possess some covalent character.