N-aryloxide-amidinate group 4 metal complexes

Abstract

A N-aryloxide-amidine ligand (H₃L), integrating phenoxide (PhO⁻) and amidine ligands through methylene linkers, has been synthesized from 2-(aminomethyl)-6-(tert-butyl)phenol in two steps. Upon reacting the deprotonated H₃L ligand with group 4 metal chloride M^IVCl₄, a corresponding (LM^IV–Cl)₂ dimer could be obtained. The coordination modes exhibit variation depending on the radius of the metal ions. In the case of (LTi^IV–Cl)₂, the two ArO⁻ arms from the same ligand bond to two different Ti(IV) centers, while in the case of (LZr^IV/Hf^IV–Cl)₂, both ArO⁻ arms coordinate with the same metal center. Moreover, the two C–N bonds in the amidinate moiety are localized in (LTi^IV–Cl)₂, whereas they delocalize in (LZr^IV–Cl)₂. Notably, (LHf^IV–Cl)₂ could further react with one equivalent of HfCl₄, yielding the binuclear metal azide in the presence of KN₃ and LiCl, where the coordination mode of the amidinate moiety changed from the bidentate chelating type to the bimetallic bridging coordination.