Mechanistic and Computational Studies of Oxidatively-Induced Aryl−CF₃ Bond-Formation at Pd: Rational Design of Room Temperature Aryl Trifluoromethylation

Abstract

This article describes the rational design of 1st generation systems for oxidatively-induced Aryl–CF3 bond-forming reductive elimination from PdII. Treatment of (dtbpy)PdII(Aryl)(CF3) (dtbpy = di-tert-butylbipyridine) with NFTPT (N-fluoro-1,3,5-trimethylpyridium triflate) afforded the isolable PdIV intermediate (dtbpy)PdIV(Aryl)(CF3)(F)(OTf). Thermolysis of this complex at 80 °C resulted in Aryl–CF3 bond-formation. Detailed experimental and computational mechanistic studies have been conducted to gain insights into the key reductive elimination step. Reductive elimination from this PdIV species proceeds via pre-equilibrium dissociation of TfO− followed by Aryl–CF3 coupling. DFT calculations reveal that the transition state for Aryl–CF3 bond formation involves the CF3 acting as an electrophile with the Aryl ligand acting as a nucleophilic coupling partner. These mechanistic considerations along with DFT calculations have facilitated the design of a 2nd generation system utilizing the tmeda (N,N,N’,N’-tetramethylethylenediamine) ligand in place of dtbpy. The tmeda complexes undergo oxidative trifluoromethylation at room temperature.

Photocatalytic fluoroalkylation reactions of organic compounds

“…Trifluoromethylation has, in the past, relied on the use of transition metal catalysts, such as those containing Pd [22][23][24][25][26][27][28][29][30][31][32] and Cu [33][34][35][36][37][38][39][40][41][42][43][44][45][46] . Photoredox catalytic trifluoromethylation, fluoroalkylation and fluorination reactions provide a promising alternative to these existing methods, as it utilizes the environmentally benign protocols that rely on visible light or even sunlight irradiation.…”

Palladium-Mediated Organofluorine Chemistry

“…201 First they demonstrated that, as expected, the reductive elimination of Ar-CF 3 does not take place from the Pd(II) complex [PdAr(CF 3 )(LL)].…”

CH Bond Arylation of Diamondoids Catalyzed by Palladium(II) Acetate

“…Based on the obtained results three transition states may be proposed for the arylation event (Figure 7). TS1: direct insertion of palladium (C3 complex) into the C À I bond (leading to Pd IV complex [40] C4 IV ); TS2: ipso oxidative substitution (leading to Pd IV complex C4 IV ) or TS3: ipso substitution, which would lead to Pd II complex C4 II and upon reductive elimination, formation of aryl À carbon bond, to Pd 0 complex, that would be internally re-oxidized by formed N À I species. A detailed look at the MS spectra for intermediates or side products did not allow us to distinguish between these proposals.…”