Metallation of aliphatic carbon atoms. Part 5. Synthesis and characterization of the cyclopalladated complexes of 2-(trimethylsilyl)pyridine and their dynamic behaviour observed by proton nuclear magnetic resonance spectroscopy

Abstract

2-(Trimethylsilyl)pyridine reacts with palladium(II) acetate in benzene at 47 °C to give an acetato-bridged binuclear cyclopalladated complex [{[graphic omitted])(O₂CMe)}₂](1). Complex (1) is converted to a chloro-bridged analogue, [{[graphic omitted])Cl}₂](2), by metathetical reaction with LiCl·H₂O. Each of complexes (1) and (2) is composed of cis and trans isomers, and shows dynamic behaviour in its ¹H n.m.r. spectrum. This phenomenon in (1) is ascribed to inversion of the acetato bridges, whereas that of (2) is associated with cis–trans isomerization. Complex (2) undergoes bridge-splitting reactions with triphenylphosphine and 3,5-dimethylpyridine to yield the corresponding mononuclear cyclopalladated complexes. All the cyclopalladated complexes are characterized by means of i.r. and n.m.r. spectroscopy.