sp-Hybridized Seesaw Ge⁰ Complexes via Germylone-to-Seesaw Isomerization in a Four-Electron Cyclic N₂Ge₂ Ligand

We report the first examples of two linear trigermanium complexes (μ-Ge)(κ²-N₂Ge₂^Ar) (Ar = 2,4,6-Me₃C₆H₂ (4), 2,6-Et₂C₆H₃ (5)), in which each central Ge⁰ atom displays a seesaw geometry enforced by a four-electron cyclic N₂Ge₂^Ar ligand. The pyridine-stabilized sp-hybridized Ge⁰ center is a four-electron donor and two terminal germylenes are electron-acceptors. Comparative studies show that the N₂Ge₂ scaffold uniquely stabilizes the Ge⁰ atom. This work not only introduces a new class of main-group seesaw complexes but also demonstrates ligand-driven control over hybridization and donor-acceptor dynamics. Compound 5 underwent one-electron reduction, followed by ligand rearrangement and dimerization, to afford a novel hexanuclear homounivalent germanium cluster, 10, featuring a snake-like Ge₆ core. In 10, each Ge atom in the central Ge^I-Ge^I unit is solely stabilized one amido ligand, while each of the remaining four Ge atoms is supported by one amido and one pyridyl donor. The isolation of a bulkier analogue (11) and a heteronuclear Ge₄Sn₂ cluster (16) further underscores the crucial role of ligand sterics in stabilizing these assemblies. These findings expand the structural diversity of low-valent group 14 compounds and establish a new paradigm for constructing multinuclear tetrel clusters.