Synthesis, Characterization, and Reactivity of an N-Heterocyclic Germanium(II) Hydride: Reversible Hydrogermylation of a Phosphaalkyne

The β-diketiminato germanium(II) chloride complex [(ButMesNacnac)GeCl] (ButMesNacnac = [{N(Mes)C(But)}2CH]−, Mes = mesityl) has been prepared and spectroscopically characterized. Treating this compound and a less bulky system, [(MeMesNacnac)GeCl] (MeMesNacnac = [{N(Mes)C(Me)}2CH]−), with K[HBEt3] led to differing outcomes, namely, the formation of the novel diamido germylene [(ButMesNacnacH)Ge:] (ButMesNacnacH = [N(Mes)C(H)(But)C(H)C(But)N(Mes)]2‑) and the germanium(II) hydride [(MeMesNacnac)GeH], both of which were crystallographically characterized. The former product forms via a 1,3-hydrogen migration reaction involving [(ButMesNacnac)GeH] as an unstable reaction intermediate. Reactions of [(MeMesNacnac)GeH] with CO2 and PCBut proceed at or below ambient temperature, in the absence of a catalyst, to give the crystallographically characterized hydrogermylation products [(MeMesNacnac)GeOC(O)H] and [(MeMesNacnac)GeC(But)PH], with complete regioselectivity. When a solution of the latter was gently heated, the hydrogermylation reaction was partially reversed, regenerating [(MeMesNacnac)GeH] and PCBut. Heating to higher temperatures led to the irreversible isomerization of [(MeMesNacnac)GeC(But)PH] to (E)-[(MeMesNacnac)GePC(H)(But)], theoretical studies of which indicate is the thermodynamic product of the original hydrogermylation reaction.