Scandium SALEN Complexes Bearing Chloro, Aryloxo, and Hydroxo Ligands

Heteroleptic amide complexes (SALEN)Sc[N(SiHMe2)2] (SALEN = SalentBu,tBu, SalcyctBu,tBu, or SalprentBu,tBu if not stated differently) were examined as synthesis precursors according to silylamine elimination reactions. Treatment of (SALEN)Sc[N(SiHMe2)2] with H2O or phenols (HOArR,R; R = tBu, iPr) afforded complexes [(SALEN)Sc(μ-OH)]2 and (SALEN)Sc(OArR,R), while chloro exchange products were formed from the respective reactions with NH4Cl or AlMe2Cl. Such complexes [(SALEN)Sc(μ-Cl)]2 and (SALEN)ScCl(thf) were also obtained by utilizing alternative synthesis protocols, allowing for controlled donor absence and presence. Heteroleptic amide precursors [Sc(NiPr2)2(μ-Cl)(thf)]2 and [Sc[N(SiHMe2)2]2(μ-Cl)(thf)]2 readily undergo amine elimination reactions with H2SALEN derivatives to form the corresponding chloride complexes. Spectroscopic and X-ray structural data of the heteroleptic scandium complexes revealed an exclusive intramolecular tetradentate coordination mode of the SALEN ligands independent of the SALEN ligand bite angle and the nature of the “second” ligand (chloro, amido, aryloxo, hydroxo). The coordination of the SALEN ligands is rationalized on the basis of (a) the displacement d of the metal center from the [N2O2] least-squares plane, (b) the dihedral angle α between the phenyl rings of the salicylidene moieties, and (c) the angle β = Ct−Ln−Ct (Ct = centroid of the phenyl rings) in the case of strongly twisted ligands.