Ruthenium-Promoted Acceptor-less Dehydrogenation of a Germane.

Abstract

The transition metal-mediated activation of element-hydrogen bonds is an important goal for the preparation of commodity chemical compounds and novel materials. Here a facile route to the activation of germanium-hydrogen bonds, based on the spontaneous elimination of dihydrogen, is reported. This represents a mechanistic divergence from the established methods for Ge─H bond cleavage. The novel complexes [Ru(η⁵-C₅H₅)(OTf)(PPh₃)₂] and [{Ru(η⁵-C₅H₅)(dppe)}₂(μ-N₂)]OTf₂ are central to the success of this route. These crystalline species may be prepared in high yield and are highly effective sources of the 16-electron [Ru(η⁵-C₅H₅)(P)₂]⁺ fragment. Both complexes react with GeH₂Ph₂ to eliminate H₂ and afford [Ru(η⁵-C₅H₅)(GePh₂OTf)(P)₂] [(P)₂ = 2 PPh₃, dppe], which is best described as a triflate-stabilized metallogermylenium complex. Different species are observed on initial treatment of [Ru(η⁵-C₅H₅)(OTf)(PPh₃)₂] or [{Ru(η⁵-C₅H₅)(dppe)}₂(μ-N₂)]OTf₂ with GeH₂Ph₂. In the dppe case, a σ-germane complex is identified, which is proposed to undergo spontaneous elimination of H₂: a key step in the double Ge─H bond activation, promoted by the sterically demanding half-sandwich ruthenium complexes. This represents a distinct pathway for Ge─H bond activation when compared to the established routes, such as deprotonation by a basic hydrocarbyl ligand or oxidative addition, leading the way to new pathways to functionalize organogermanium compounds.