Half-Sandwich Rare-Earth-Metal Alkylaluminate Complexes Bearing Peripheral Boryl Ligands

[(C5Me5)­LnMe2]3 (Ln = Y, Lu) dissolve readily in a n-hexane/toluene mixture upon addition of 3 equiv of the organoaluminum boryl compound [Me2Al­{B­(NDippCH)2}]2 (Dipp = C6H3iPr2-2,6). The half-sandwich complexes (C5Me5)­Ln­[(AlMe3)­{B­(NDippCH)2}]2 thus formed display unsymmetrical heteroaluminate coordination not only in the solid state but also at lower temperatures in solution, which is distinct from the behavior of the homoaluminate congeners (C5Me5)­Ln­(AlMe4)2. The effect of homo- versus heteroaluminate coordination is assessed in the coordinative polymerization of isoprene.