Synthesis, Structure, and Reactivity of a Mononuclear η2-(Ge-H)palladium(0) Complex Bearing a PGeP-Pincer-Type Germyl Ligand: Reactivity Differences between Silicon and Germanium

Reactivity differences between silicon and germanium as supporting ligands in PEP-pincer type palladium complexes (E = Si, Ge) were clarified by experimental and theoretical studies. An eta(2)-(Ge-H)palladium(0) complex, which was synthesized and structurally characterized for the first time, exhibited higher reactivity for hydrometallation of ethylene than the silyl-analogue. The resulting PGeP-ethylpalladium(II) complex was more stable than the silyl-analogue, which allowed its isolation and structural analysis by X-ray crystallography. Formation of a Ge-bridged Pd dimer complex by thermal decomposition of the eta(2)-(Ge-H)palladium(0) complex was also demonstrated. Experimental and theoretical studies clarified that the germanium ligand stabilizes the Pd-II state with the Pd-E bond and destabilizes the eta(2)-(E-H)Pd-0 state compared to the case of the silicon ligand. This study provided useful insights for rational design of transition metal complexes bearing a heavier group 14 element as a supporting ligand in organometallic chemistry.