Bis-(benzothiazol-2-yl)-amines and their metal amides: a structural comparison in the solid state

Abstract

Within this work, the field of amide ligand platforms for group 13 metal complexation, especially for Al(III) is investigated in a synthetic as well as in a structural comparative approach. Starting from bis-heterocyclo methanides, which mimic the omnipresent nacnac ligand, the next enhancement in this class of ligands includes the exchange of the central methylene bridge by an amine nitrogen atom. With this modification three different sec. amines, each symmetrically substituted, could be synthesised as parent neutral benzothiazole containing ligand systems: (NCSC₆H₄)₂NH (1), (4-MeNCSC₆H₃)₂NH (2) and (4-OMeNCSC₆H₃)₂NH (3). Apart from these compounds also a lithiated species and a row of group 13 metal complexes of the deprotonated ligands could be examined by applying single crystal X-ray diffraction analyses. In this course three new dimethyl aluminium containing complexes [Me₂Al{(NCSC₆H₄)₂N}] (4), [Me₂Al{(4-MeNCSC₆H₃)₂N}] (5) and [Me₂Al{(4-OMeNCSC₆H₃)₂N}·AlMe₃] (6) as well as two lithiated compounds [Li{(NCSC₆H₄)₂N}]₄ (7), [Li{(4-MeNCSC₆H₃)₂N}]₄ (8) were structurally and spectroscopically characterised. A subsequent structural comparison of 1–6 and 8 in the solid state shows that the parent ligand systems prefer a planar cis-trans alignment due to hydrogen bond formation. In contrast to that, the metallated species favour a planar but trans–trans or cis–cis alignment depending on the metal cation.