Characterization of mononuclear and dinuclear germylplatinum complexes and Ge-Ge bond formation at the platinum center

The reaction of the zerovalent platinum complex [Pt(PPh3)(2)(eta(2)-C2H4)] (1) with the germanium trihydride GeH(3)Mes (Mes = 2,4,6-trimethylphenyl) produced various germylplatinum complexes by control of the molar ratio. When complex 1 reacted with GeH(3)Mes in a molar ratio of 1:1, dimerization of the platinum unit occurred at -30 degrees C to afford the unsymmetrical diplatinum complex [Pt-2(PPh3)(3)(mu-GeH2MeS)(2)] (2) and the symmetrical diplatinum complex [Pt(PPh3)(mu-GeH(2)Mes)](2) (3) for which the H-1 NMR spectrum indicated a mixture of cis/trans-isomers in a ratio of 2:3. When a toluene solution of 2 increased in temperature from -20 degrees C to room temperature, liberation of a PPh3 group occurred at the Pt(PPh3)(2) site, followed by rotation of the bridging germyl group to form a mixture of cis/trans-3. Otherwise, treatment of 1 with GeH(3)Mes at a molar ratio of 1:2 afforded the bis(germyl)platinum complex [Pt(PPh3)(2)(GeH2MeS)(2)] (4) at -30 degrees C, and then 4 converted to the digermanylplatinum hydride [Pt(PPh3)(2)(H)(GeHMesGeH(2)Mes)] (5) at room tern. toluene. The conversion rate obeyed a first-order rate law, and the activation parameters Delta H-double dagger and Delta S-double dagger were calculated at 20(2) kcal mol(-1) and -7(8) cal K-1 mol(-1), respectively. These results suggest that in later transition metal platinum complexes, Ge-Ge bond formation is carried out by intramolecular germyl migration.