NNpyC- and ONpyC-Pincers as functional ligands for palladium(II) complexes and assemblies

The pyridyl-imine, -amine and -alcohol pro-ligands, 2-(2-MeC6H4)-6-{CMe=N(2,6-i-Pr2C6H3)}C5H3N (HL1), 2-(2-MeC6H4)-6-{CMe2NH(2,6-i-Pr2C6H3)}C5H3N (HL2) and 2-(2-MeC6H4)-6-(CMe2OH)C5H3N (HL3), each appended with an ortho-tolyl unit, have been synthesized by a combination of condensation and methylation approaches, all deriving from the common acetylpyridine precursor, 2-(2-MeC6H4)-6-(CMe=O)C5H3N. Treatment of HL1, HL2 and HL3 with Pd(OAc)2 results in cyclopalladation via sp2-CH activation of the tolyl unit to give the organometallic palladium(II) NNC- or ONC-pincer complexes (L1)Pd(OAc) (1a), (L2)Pd(OAc) (2a) and (L3)Pd(OAc) (3a). Quantitative conversion of 1a, 2a and 3a to their chloride derivatives, (L1)PdCl (1b), (L2)PdCl (2b) (L3)PdCl (3b), respectively, has been demonstrated. Intramolecular NH···Oacetate (2a) and intermolecular OH···Oacetate (3a) or OH⋯Cl (3b) hydrogen-bonding interactions are a feature of the crystal structures for 2a, 3a and 3b; notably in 3a and 3b this leads to self-assembly into dimers with differing metal···metal separations. The molecular structures for HL1, HL2, 1a, 1b and 2b are additionally reported as is full characterization data for both the pro-ligands and complexes.