Cyclopalladation of (S)-4-tert-butyl-2-methyl-2-oxazoline:: An unprecedented case of (sp3)C-H bond activation resulting in exo-palladacycle formation

Direct cyclopalladation of (S)-4-tert-butyl-2-methyl-2-oxazoline at the nonactivated tertbutyl group using palladium(ii) acetate in acetic acid afforded the first example of an oxazoline-derived exo-palladacycle with an (Sp(3))C-Pd bond. The structure of the new palladacycle was established using spectroscopic and X-ray studies of the mu-chloro-dimeric complex 2 and two mononuclear triphenylphosphane derivatives: neutral adduct 4 and its cationic benzonitrile-phosphane analogue 5. Analysis of NMR data for compounds 4 and 5 suggests a highly puckered A(S) conformation of the palladacycle in solution. The X-ray crystal structure of cationic complex 5 confirmed the same highly puckered (S) conformation of the palladacycle in the solid state; in addition, it revealed unusual pi(-)pi-interactions between the phenyl rings of the benzonitrile and PPh3 ligands and a distorted M-propeller configuration of the PPh3 fragment.