Ligand versus Complex: C−F and C−H Bond Activation of Polyfluoroaromatics at a Cyclic (Alkyl)(Amino)Carbene

C−F and C−H bond activation reactions of polyfluoroaromatics at the cyclic (alkyl)(amino)carbene (cAAC) cAAC methyl ( 1 ) are reported. Studies on the C−F bond activation using the cAAC‐stabilized nickel(0) complex [Ni(cAAC methyl ) 2 ] ( 2 ) have shown that 2 does not react with fluorinated arenes. However, these investigations led to the observation of C−F bond cleavage of perfluorinated arenes by the carbene ligand cAAC methyl ( 1 ) itself. The reaction of 1 with C 6 F 6 , C 6 F 5 −C 6 F 5 , C 6 F 5 −CF 3 , and C 5 F 5 N afforded the insertion products of cAAC into one of the C−F bonds of the substrate, that is, the C−F bond activation products (cAAC methyl )F(Ar f ) (Ar f =C 6 F 5 4 a , C 6 F 4 −C 6 F 5 4 b , C 6 F 4 −CF 3 4 c , C 5 F 4 N 4 d ). These products decompose readily upon heating to 80 °C within a few hours in solution with formation of ionic iminium salts [(cAAC methyl )(Ar f )][X] 6 a – d or neutral alkenyl perfluoroaryl imine compounds 7 a – d . The compounds (cAAC methyl )F(Ar f ) 4 a – d readily transfer fluoride, which has been exemplified by the fluoride transfer of all compounds using BF 3 etherate as fluoride acceptor. Fluoride transfer has also been achieved starting from (cAAC methyl )F(C 6 F 4 ‐CF 3 ) ( 4 c ) or (cAAC methyl )F(C 5 F 4 N) ( 4 d ) to other selected substrates such as trimethylchlorosilane, benzoyl chloride and tosyl chloride. Instead of C−F bond activation, insertion of the cAAC into the C−H bond was observed if 1 was treated with the partially fluorinated arenes C 6 F 5 H, 1,2,4,5‐C 6 F 4 H 2 , 1,3,5‐C 6 F 3 H 3 , and 1,3‐C 6 F 2 H 4 . The compounds (cAAC methyl )H(Ar f ) (Ar f =C 6 F 5 12 e , 2,3,5,6‐C 6 F 4 H 12 f , 2,4,6‐C 6 F 3 H 2 12 g and 2,6‐C 6 F 2 H 3 12 h ) have been isolated in good yields and have been characterized including X‐ray analysis. Fluorobenzene C 6 FH 5 (p K a ≈37), the least C−H acidic fluoroarene used in this study, does not react. In order to investigate the scope and limitations of this type of cAAC C−H bond activation reaction, cAAC methyl ( 1 ) was treated with several other reagents of different C−H acidity such as imidazolium salts, imidazoles, esters, and trimethylphosphine. These investigations led to the isolation and characterization of the compounds [(cAAC methyl )H(R 2 Im Me2 )]X ( 13 a,b ), (cAAC methyl )H(Im R2 ) ( 14 a – c ), (cAAC methyl )H(CH(COOCH 3 ) 2 ) ( 15 b ) and (cAAC methyl )H(CH 2 ‐PMe 2 ) ( 16 ). Deprotonation of [(cAAC methyl )H(Me 2 Im Me2 )][BF 4 ] ( 13 a ) at the cAAC carbon atom using KHMDS as a base led to isolation and structural characterization of the cAAC methyl ‐NHC heterodimer ( 17 ).