Mono- and Dinuclear Germapalladacycles Obtained via the Ge−Ge Bond Forming Reactions Promoted by Palladium Complexes

Heating a toluene solution of bis(germyl)palladium complex [Pd(GeHPh2)2(dmpe)] (2) (dmpe = 1,2-bis(dimethylphosphino)ethane) at 70 °C produced a mixture of dipalladium complexes, one with bridging digermene and germylene ligands, [{Pd(dmpe)}2(μ-GePh2)(μ-Ge2Ph4)] (3), and also a mononuclear tetragermapalladacyclopentane, [Pd(GePh2GePh2GePh2GePh2)(dmpe)] (4), in 92:8 molar ratio, respectively. The reaction of H2GePh2 with 2 in 10:1 molar ratio formed complex 4 as the main product (3:4 = 4:96). Complexes 3 and 4 were isolated from the above reactions and characterized by X-ray crystallography and NMR spectroscopy. Complex 3 reacted with H2GePh2 (Pd:Ge = 1:10) at 80 °C to yield 4 quantitatively, whereas simple heating of 3 at the same temperature did not form 4 at all. Reaction pathways for the Ge−Ge bond formation are discussed.