Mechanistic and Computational Studies of Oxidatively-lnduced Aryl-CF_3 Bond-Formation at Pd: Rational Design of Room Temperature Aryl Trifluoromethylation

摘要

This article describes the rational design of first generation systems for oxidatively induced Aryl-CF_3 bond-forming reductive elimination from Pd . Treatment of (dtbpy)Pd~Ⅱ(Aryl)(CF_3) (dtbpy = di-tert-butylbipyridine) with NFTPT (N-fluoro-l,3,5-trimethylpyridinium triflate) afforded the isolable Pd~Ⅳ intermediate (dtbpy)Pd~Ⅳ(Aryl)(CF_3)(F)-(OTf). Thermolysis of this complex at 80 ℃ resulted in Aryl-CF_3 bond-formation. Detailed experimental and computational mechanistic studies have been conducted to gain insights into the key reductive elimination step. Reductive elimination from this Vd~Ⅳ species proceeds via pre-equilibrium dissociation of TfO~- followed by Aryl-CF_3 coupling. DFT calculations reveal that the transition state for Aryl-CF_3 bond formation involves the CF_3 acting as an electrophile with the Aryl ligand serving as a nucleophilic coupling partner. These mechanistic considerations along with DFT calculations have facilitated the design of a second generation system utilizing the tmeda (N,N,N',N'-tetramethylethylenediamine) ligand in place of dtbpy. The tmeda complexes undergo oxidative trifluoromethylation at room temperature.