Dinuclear and tandem tetranuclear palladium(II) complexes formed by oxidative addition of 2,6-bis(chloromethyl)-pyridine to [Pd(PPh3)4]

Abstract

2,6-Bis(chloromethyl)pyridine reacts with [Pd(PPh₃)₄] in toluene at 100 °C to afford two types of oxidative-addition products, C^α,N-bridging dinuclear and C^α,N,C^α′-bridging tandem tetranuclear palladium(II) complexes [{PdCl[C₅H₃(6-CH₂Cl)N-2-CH₂](PPh₃)}₂]1 and [{Pd₂Cl₂[C₅H₃N-2,6-(CH₂)₂]-(PPh₃)₂}₂]2. When the reactant molar ratio was 1.3:1 the best yield (56%) of complex 1 was obtained, while that (39%) of complex 2 was also obtained using a 1:2 molar ratio. Complex 2 was also obtained in 48% yield by the reaction (1:2 molar ratio) between complex 1 and [Pd(PPh₃)₄]. With [Pt(PPh₃)₄], an analogous heteronuclear tetrametral complex was isolated. These were characterized by IR and NMR (¹H, ¹³C and ³¹P) spectroscopy and mass spectrometry as well as elemental analysis and molecular weight determinations. Complex 2 reacts with excess NaBr and Ag(O₂CR)(R = CH₃ or CF₃) to give the corresponding metathesis and substitution products respectively; diphosphines Ph₂PCH₂CH₂PPh₂ or cis-Ph₂PCHCHPPh₂ partially displace the triphenylphosphine ligands. On the other hand, Tl(acac)(acac = pentane-2,4-dionate) cleaves the tandem tetranuclear structure to afford a dinuclear palladium(II) complex.