1,2-Azaborolyl-Ligated Half-Sandwich Complexes of Scandium(III) and Lutetium(III): Synthesis, Structures, and Syndiotactic Polymerization of Styrene

Half-sandwich Sc(III) and Lu(III) complexes with ancillary trisubstituted 1,2-azaborolyl (Ab) ligands have been conveniently prepared via the reaction of the corresponding anionic Ab ligands with cationic Sc(III) and Lu(III) dialkyl species in good yields and characterized crystallographically. In the solid-state molecular structures of the half-sandwich mono-Ab Sc(III) complexes 5 and 6, the interaction between the Sc metal center and Ab ligand is strongly influenced by the exocyclic B substituent, whereas in the analogous Lu(III) system 8 this interaction becomes much less prominent, as indicated by a relatively shorter Lu-B bond distance along with an attenuated exocyclic B-N bond interaction. Upon activation, the Sc(III) complexes 5 and 7 were found to be highly active in the syndiospecific polymerization of styrene.