A series of Pd complexes bearing modified tetradentate pyridinophane ligands RN3CH, containing a C-donor phenyl group, were isolated and characterized. The (RN3CH)PdII(OAc)2 complexes contain a Cipso-H bond that remains unactivated at the PdII stage, even upon heating or addition of excess acetate. These PdII(OAc)2 complexes exhibit catalytic reactivity in the Kharasch radical addition of bromotrichloromethane to methyl methacrylate. Interestingly, novel PdIII complexes (RN3C)PdIIIBr2 were isolated from the Kharasch reaction mixture and have been characterized by EPR, UV-vis spectroscopy, and X-ray crystallography, suggesting that activation of the Cipso-H bond has occurred during the oxidative conditions of the Kharasch radical addition. Inspired by this observation, several (pMeN3C)PdIII complexes were synthesized upon oxidation of the PdII precursors with PhICl2 and subsequent halide abstraction with thallium salts. Furthermore, additional one-electron oxidation generates detectable PdIV species, including an uncommon tricationic [(pMeN3C)PdIV(MeCN)3]3+ complex. Overall, these initial results show that the RN3C(H) ligand system is capable of stabilizing high-valent Pd species that can undergo uncommon oxidative and catalytic reactivity, including C-H bond activation.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry