Tailoring the Synthesis and Stability of Germylenes via Electron-Rich P═C-P and P═C-P(=S) Derivatives

The formation of stable germylene species through the attachment of a >Ge(II) center to electron-rich P═C-P and P═C-P(=S) backbones is supported by both experimental and theoretical means. The reaction between the phosphavinylphosphorane Mes*P═C(Cl)-P(i-Pr)₂ (1) and GeCl₂·dioxane affords the novel germylene Mes*P═C(GeCl₂)-P(H) (i-Pr)₂, which is unexpectedly achieved via a C→Ge donation rather than through a conventional σ(C-Ge) bond. The solid-state structure is confirmed by X-ray analysis, while DFT mechanistic studies explain its formation based on a fast ligand exchange between the dioxane group and the carbanionic P═C^(-)-P moiety. On the contrary, the reaction of the phosphavinyl(thioxo)phosphorane Mes*P═C(Cl)-P(=S) (i-Pr)₂ (2) with GeCl₂·dioxane yields a chelate-stabilized germylene, Mes*P═C(GeCl)-P(=S) (i-Pr)₂. This species features a σ(C-Ge) covalent bond and an intramolecular S→Ge coordination, which combined contribute to its stabilization. The chemical behavior of compounds 1 and 2 toward NHC^i-Pr·GeCl₂ is also investigated. The current work highlights that the lone pair of electrons on the P(sp³) atom dictates the reactivity of P═C-P and P═C-P(=S) units with Ge(II)Cl₂ fragments and impacts the stability of the resulting germylene species.