The Role of Fluorine Substituents in the Regioselectivity of Intramolecular C–H Bond Functionalization of Benzylamines at Palladium(II)

The effect of fluorine substituents on the regio­selectivity of intramolecular reactions of mono- and difluorinated N,N-dimethylbenzylamines (1a–f) at palladium, to form palladacycles di-μ-acetato­bis­[o-dimethylaminomethyl-n-fluorophenyl-C,N)­dipalladium­(II) (2a–f) and di-μ-chloro­bis­[o-dimethylaminomethyl-n-fluorophenyl-C,N)­dipalladium­(II) (3a–e), has been investigated. When fluorinated substrates with two sites available for the C–H functionalization (1c and 1e) undergo cyclopalladation via a CMD mechanism (acetate-bridged palladacycles), they do not exhibit regioselectivity. In contrast, the same substrates exhibit complete regioselectivity for the C–H functionalization para to fluorine in cyclopalladation reactions that proceed via an SEAr mechanism (involving chloride-bridged palladacycles). X-ray crystal structures were obtained for all the palladacycles synthesized, and a structural analysis showed that the number and the position of the fluorine atoms on the aromatic ring have a marked effect on the “clamshell” structure of the acetate-bridged palladacycles. By contrast, there is no great variation in the structures of the planar chloride-bridged palladacycles.