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, Cα,N-bridging dinuclear and Cα,N,Cα′-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.