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

We prepared the bimetallic hafnium complex <b>1</b> by reaction of Hf­(CH₂Ph)₄ with the alcohol-imine proligand <b>L</b> via deprotonation and subsequent benzyl migration from the hafnium atom to the imine moiety of <b>L</b>. The complex <b>1</b> was obtained as a diastereomeric mixture of <b>1a</b> (<i>SR</i>, heterochiral) and <b>1b</b> (<i>RR</i> and <i>SS</i>, homochiral); the <i>SR</i> isomer <b>1a</b> was readily isolated by simply washing with toluene. Treatment of <b>1a</b> with [Ph₃C]­[B­(C₆F₅)₄] in C₆H₅Cl afforded the dicationic complex <b>2a</b>, 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 <b>2a</b> 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 <b>2a</b> to quantitatively afford alkene <b>3</b> at room temperature after hydrolysis. The addition of PMe₂Ph and pyridine to <b>2a</b> dissociated the η⁶-arene coordination of the ligand to give the corresponding adducts <b>5a</b> and <b>6a</b>, whose structures were fully characterized by X-ray diffraction analysis.