σ‑GeH and Germyl Cationic Pt(II) Complexes

The low electron count Pt­(II) complexes [Pt­(NHC′)­(NHC)]­[BArF] (where NHC is a N-heterocyclic carbene ligand and NHC′ its metalated form) react with tertiary hydrogermanes HGeR3 at room temperature to generate the 14-electron platinum­(II) germyl derivatives [Pt­(GeR3)­(NHC)2]­[BArF]. Low-temperature NMR studies allowed us to detect and characterize spectroscopically some of the σ-GeH intermediates [Pt­(η2-HGeR3)­(NHC′)­(NHC)]­[BArF] that evolve into the platinum-germyl species. One of these compounds has been characterized by X-ray diffraction studies, and the interaction of the H–Ge bond with the platinum center has been analyzed in detail by computational methods, which suggest that the main contribution is the donation of the H–Ge to a σ*­(Pt–C) orbital, but backdonation from the platinum to the σ*­(Ge–H) orbital is significant. Primary and secondary hydrogermanes also produce the corresponding platinum-germyl complexes, a result that contrasts with the reactivity observed with primary silanes, in which carbon–silicon bond-forming reactions have been reported. According to density functional theory calculations, the formation of Pt–Ge/C–H bonds is both kinetically and thermodynamically preferred over the competitive reaction pathway leading to Pt–H/C–Ge bonds.