Reactivity toward Neutral N- and P‑Donor Ligands of Eight-Membered Palladacycles Arising from Monoinsertion of Alkynes into the Pd–C Bond of Orthopalladated Homoveratrylamine and Phentermine. A New Example of the Transphobia Effect

Eight-membered
palladacycles arising from the insertion of one
molecule of alkyne into the Pd–C bond of the palladacycles
derived from homoveratrylamine and phentermine react with neutral
N- and P-donor ligands to give mononuclear or unusual dinuclear complexes,
containing a vinylarylethylamino bridge, depending on the size of
the ligand and the substituents of the palladacycle. Diffusion-ordered
nuclear magnetic resonance spectroscopy experiments are used to measure
the diffusion coefficients and propose the nuclearity of these complexes
in solution. Density functional theory calculations show that steric
and electronic (transphobia) effects are responsible for the unprecedented
observed reactivity differences. A mechanism for the formation of
the unusual dinuclear complexes is proposed.