The Effect of a Single Trifluoromethyl Substituent on the Reactivity of Chelating C 2 and C s -Symmetric Bis(alkoxide) Ligands on a Terphenyl Platform

High Resolution Image Download MS PowerPoint Slide Herein we describe the synthesis and preliminary reactivity studies of new racemic C 2 -symmetric and meso C s -symmetric bis(alkoxide) ligands on a para -terphenyl platform. The ligands were synthesized by reaction of 2,2′-dilithium- p -terphenyl with trifluoroacetophenone, separated by column chromatography, and obtained in 36% (racemic, rac -Lig 2 H 2 ) and 26% (meso, meso -Lig 2 H 2 ) isolated yields. The reaction with n -butyl- sec -butylmagnesium led to formation of the expected C 2 -symmetric and C s -symmetric mononuclear magnesium complexes. In contrast, the reaction with Cr(N(SiMe 3 ) 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 Cr 2 (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 Cr 2 ( rac -Lig 2 ) 2 (THF) 4 and Cr 2 ( meso -Lig 2 ) 2 observed for these new ligands.