The Effect of a Single Trifluoromethyl Substituent on the Reactivity of Chelating <i>C</i> ₂ and <i>C</i> _s -Symmetric Bis(alkoxide) Ligands on a Terphenyl Platform

Herein we describe the synthesis and preliminary reactivity studies of new racemic <i>C</i>₂-symmetric and meso <i>C</i>_s-symmetric bis(alkoxide) ligands on a <i>para</i>-terphenyl platform. The ligands were synthesized by reaction of 2,2'-dilithium-<i>p</i>-terphenyl with trifluoroacetophenone, separated by column chromatography, and obtained in 36% (racemic, <i>rac</i>-Lig²H₂) and 26% (meso, <i>meso</i>-Lig²H₂) isolated yields. The reaction with <i>n</i>-butyl-<i>sec</i>-butylmagnesium led to formation of the expected <i>C</i>₂-symmetric and <i>C</i>_s-symmetric mononuclear magnesium complexes. In contrast, the reaction with Cr(N(SiMe₃)₂)₂(THF)₂ exhibited a profoundly different coordination chemistry from that of all-phenyl chelating bis(alkoxide) or monodentate alkoxides. While the latter generally form Cr₂(OR)₄ dimers in which the geometry at Cr(II) is Y-shaped, these new ligands lead to square-planar Cr(II) complexes. DFT calculations help rationalize the distinct dimeric species Cr₂(<i>rac</i>-Lig²)₂(THF)₄ and Cr₂(<i>meso</i>-Lig²)₂ observed for these new ligands.