Germanium(II) hydrides

[2] Initial attempts to synthesize the compound involved treating a β-diketiminato germylene chloride precursor, [{HC-(CMeNAr)2}GeCl] (where Ar = 2,6-iPr2C6H), with LiAlH4, though this proved unsuccessful, with the formation of an aluminum dihydride species instead.

They found that the Ge-H bond was inert in this adduct, and so the borane adduct was able to be selectively removed at room temperature by a PMe3 scavenger, resulting in the desired terminal germylene hydride:[1] When the β-diketiminato germylene chloride was treated with the alane-amine adduct AlH3•NMe3 in toluene at -4 °C, the solution underwent a color change from yellow to orange-red as the volatile trimethylamine was removed from the solution, and the resulting power was identified as the stable terminal germylene hydride with 60% yield, thus affording the first direct synthetic route:[2] The synthesis and isolation of two digermanium germanium(II) hydrides have also been reported.

Although synthesized from multiple synthetic pathways, reaction of the germylene chloride with L-selectride in toluene at -80 °C most directly gives the orange crystalline hydrido-digermene with 52% yield.

This digermene is thought to be in equilibrium with a two-coordinate hydrido-germylene, which can be isolated upon addition of DMAP (dimethylaminopyridine) at 20 °C, giving pale yellow crystals of the three-coordinate germylene hydride in 27% yield.

[5] This compound can be formed from a two step process, starting with the reaction of potassium bis(NHC)-borate with GeCl2•dioxane to yield a zwitterionic germyliumylidene chloride.

[9] The stability of the germylene hydride to water also allows it to be recovered from the other reaction products via an extraction in benzene, an important property for any catalyst to be used to generate chemical feedstocks.

Two equivalents of elemental sulfur react with the β-diketiminato germylene hydride to give a germanium dithiocarboxylic acid analogue in moderate yield (60%).

The previously reported[4] acyclic amido germylene hydride was found to catalyze the hydroboration of a variety of aldehydes and ketones with the mild borane reagent HBpin (pin = pinacolato).

The mechanism for germanium(IV) diamide is less clear, though it is proposed that the pathway involves an oxidative addition-insertion of a nitrene (:NSiMe3), formed in situ via dinitrogen elimination from the azide, along with intramolecular hydride shifts.

The β-diketiminato germylene hydride has been reported to react with both ethyl diazoacetate and trimethylsilyldiazomethane, forming germanium(II)-substituted hydrazone derivatives.

The oxidative addition of the β-diketiminato germylene hydride with diethyl azodicarboxylate (DEAD) is also reported to proceed at room temperature in high yield.

Synthesis of stable monomeric germylene hydride from a borane adduct
Synthesis of stable monomeric germylene hydride from a borane adduct
Direct synthesis of a stable, monomeric terminal germylene hydride
Direct synthesis of a stable, monomeric terminal germylene hydride
Synthesis of first stable acyclic germylene hydride
Synthesis of first stable acyclic germylene hydride
Synthesis of first stable monomeric germanium(II) hydride cation (a germyliumylidene hydride)
Synthesis of first stable monomeric germanium(II) hydride cation (a germyliumylidene hydride)
Molecular graphs of GeH and Ge 2 H in the lowest lying electronic state. Bond critical points shownin orange with corresponding ellipticity values, ring critical points shown in yellow, and attractors shown in purple with atoms-in-molecules charges plus natural bond order charges shown in parentheses. [ 6 ]
Electron localization function isosurface (η=0.7) of neutral GeH molecule in the ground electronic state. The C(Ge) basin is shown in orange, the V(Ge) basin is in turquoise, and the V(H,Ge).
Reported reactions of β-diketiminato germylene hydride
Proposed mechanism for conversion of carbon dioxide to methanol with a germylene hydride catalyst [ 8 ]
Proposed catalytic cycle for hydroboration of carbonyl compounds, (R 1 )(R 2 )CO (R 1 /R 2 = Alkyl, Aryl, or H), catalyzed by amido germylene hydride [ 11 ]