A N , N′ ‐ p ‐Tolyl Substituted Diazadiene Ligand with a Dithienylethane Backbone in Hexacoordinated Group IV Tetrachlorido Complexes—Steric Repulsions Govern the Axial Chirality Mode

The reaction of 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)‐ N , N ‐di‐ p ‐tolylethane‐1,2‐diimine ( DAD DTEthane 2 ) with MCl 4 metal precursors furnishes the monomeric complexes [MCl 4 ( DAD DTEthane )] with M = Ti, Zr, Hf ( 3a–c ). Upon coordination of 2 the respective metal center is chelated via both imino‐groups, giving rise to a planar five‐membered metalla‐cycle, rendering the two adjacent thiophene rings of the ligand backbone in a noncoplanar arrangement with respect to the metallacycle, resulting in two chiral C–C axes in the ligand backbone. This finding is in sharp contrast to the previously reported similar complexes bearing the closely related 1,2‐diketon ligand 1,2‐bis(2,5‐dimethylthiophen‐3‐yl)ethane‐1,2‐dione ( 1 , DTEthane ), exhibiting coplanar dithenyl rings, which gives rise to only one C–C chiral axis. The observed structural features for 3a–c are rather similar to the related 2e − reduced en‐diolato ligand featuring a ‐O‐ C ( R ) =C ( R )‐O‐ (R= (2,5‐dimethylthiophen‐3‐yl)) double bond. Our single crystal X‐ray diffraction study in combination with our computations on density functional theory level suggests the steric repulsion between the thiophen entities and the N ‐aryl substituents as decisive for the axial chirality mode in complexes 3a–c .