DINUCLEAR AND TANDEM TETRANUCLEAR PALLADIUM(II) COMPLEXES FORMED BY OXIDATIVE ADDITION OF 2,6-BIS(CHLOROMETHYL)-PYRIDINE TO [PD(PPH3)4]

2,6-Bis(chloromethyl)pyridine reacts with [Pd(PPh3)4] in toluene at 100-degrees-C to afford two types of oxidative-addition products, C(alpha),N-bridging dinuclear and C(alpha),N,C(alpha')-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 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 tetrametal complex was isolated. These were characterized by IR and NMR (H-1, C-13 and P-31) 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-Ph2PCH=CHPPh2 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.