Arene C−H Bond Activation and Arene Oxidative Coupling by Cationic Palladium(II) Complexes

N, N ‘ - Diaryl-α-diimine-ligated Pd(II) dimethyl complexes ( tBu 2 Ar DAB Me )PdMe 2 and { (CF 3 ) 2 Ar DAB Me }PdMe 2 { tBu 2 Ar DAB Me: ArN C(CH 3 )−C(CH 3 ) NAr, Ar = 3,5-di- tert- butylphenyl; (CF 3 ) 2 Ar DAB Me: Ar = 3,5-bis(trifluoromethyl)phenyl} undergo protonolysis with HBF 4 (aq) in trifluoroethanol (TFE) to form cationic complexes [(α-diimine)Pd(CH 3 )(H 2 O)][BF 4 ]. The cations activate benzene C−H bonds at room temperature. Kinetic analyses reveal trends similar to those observed for the analogous platinum complexes: the C−H activation step is rate-determining (KIE = 4.1 ± 0.5) and is inhibited by H 2 O. The kinetic data are consistent with a mechanism in which benzene substitution proceeds by a solvent- (TFE-) assisted associative pathway. Following benzene C−H activation under 1 atm O 2, the products of the reaction are biphenyl and a dimeric μ-hydroxide complex, [(α-diimine)Pd(OH)] 2 [BF 4 ] 2 . The Pd(0) formed in the reaction is reoxidized by O 2 to the dimeric μ-hydroxide complex after the oxidative C−C bond formation. The regioselectivity of arene coupling was investigated with toluene and α,α,α-trifluorotoluene as substrates.