Formation of Difluoromethylene−Arenium Complexes by Consecutive Aryl−CF3C−C Bond Activation and C−F Bond Cleavage

Abstract

Oxidative addition of one of the strongest C−C bonds, Aryl−CF3, to Rh(I) takes place upon treating 1-CF3-2,6-(CH2PtBu2)2-C6H3 (1, PCP) with [RhClL2]2 (L = C2H4 or C8H14) in dioxane or toluene at elevated temperatures leading to quantitative formation of Rh(CF3)(2,6-(CH2PtBu2)2-C6H3)Cl (2-Cl). The iodide analogue 2-I was prepared by reacting Rh(η1-N2)(2,6-(CH2PtBu2)2-C6H3) (3) with CF3I at room temperature. ArCF2−F bond cleavage was not observed in parallel to the C−C bond activation. Treating a dioxane solution of the thermally stable RhIII−CF3 complexes 2-Cl,I with excess trifluoromethanesulfonic acid (HOTf) at room temperature resulted in CF bond cleavage and selective formation of the unique difluoromethylene−arenium complexes [Rh(1-CF2-2,6-(CH2PtBu2)2-C6H3)X][OTf] (4; X = Cl, I) which were characterized spectroscopically by NMR, UV/vis, and FD-MS. No reaction was observed with HCl. Reaction of 2-Cl with BF3 or Ph3CBF4 (trityl cation) also resulted in C−F bond cleavage to give [Rh(1-CF2-2,6-(CH2PtBu2)2-C6H3)Cl]BF4 (10).