Synthesis, Structure, and Reactivity of Dicationic Bimetallic Tetrabenzyldihafnium Complexes Bearing a Chelating (2-Hydroxyethyl)amido Ligand

We prepared the bimetallic hafnium complex 1 by reaction of Hf­(CH₂Ph)₄ with the alcohol-imine proligand L via deprotonation and subsequent benzyl migration from the hafnium atom to the imine moiety of L. The complex 1 was obtained as a diastereomeric mixture of 1a (SR, heterochiral) and 1b (RR and SS, homochiral); the SR isomer 1a was readily isolated by simply washing with toluene. Treatment of 1a with [Ph₃C]­[B­(C₆F₅)₄] in C₆H₅Cl afforded the dicationic complex 2a, which was characterized by spectroscopic data and an X-ray diffraction study, revealing the η⁶ coordination of the phenyl group bound to the chelating ligand to the cationic hafnium center. Complex 2a showed catalytic activity for 1-hexene oligomerization at 100 °C in combination with 2 equiv of [Ph₃C]­[B­(C₆F₅)₄], while 4,4′-dimethoxydiphenylacetylene reacted with 2a to quantitatively afford alkene 3 at room temperature after hydrolysis. The addition of PMe₂Ph and pyridine to 2a dissociated the η⁶-arene coordination of the ligand to give the corresponding adducts 5a and 6a, whose structures were fully characterized by X-ray diffraction analysis.