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We describe the application of a mild, molecular-based, hydride metathesis protocol for the preparation of metastable germanium(II) dihydrides with compositions approaching [GeH2]n. The common starting material for this work [Ge(OtBu)2] was prepared in a high yield and shown to undergo OtBu/H exchange at Ge with the hydride sources pinacolborane (HBpin), catecholborane (HBcat), and diisobutylaluminum hydride (DIBAL-H) to give the [GeH2]n materials as yellow to orange solids. Heating one of these [GeH2]n materials to 200 °C affords a narrowing of the optical band gap (from 2.5 eV) and the generation of amorphous Ge. Reaction of [Ge(OtBu)2] with excess H3B·SMe2 in toluene at 70 °C provides a convenient route to thin films of amorphous Ge, including its deposition onto soft substrates, such as polyethyleneterephthalate (PET). Accompanying computations give insight into the energetics of OtBu/H exchange at Ge, and reveal a general thermodynamic preference for branched structures of [GeH2]n oligomers over linear forms as the Ge chain becomes longer. We also show that [Ge(OtBu)2] is a suitable pre-catalyst for the borylation of aldehydes. [ABSTRACT FROM AUTHOR]

Allylgermanes with a 4‐, 5‐, and 6‐coordinated germanium center were characterized by X‐ray crystallography. Cationic 6‐coordinated group 14 allylmetals, which were hitherto assumed to be a transition‐state structure of allylations, were successfully isolated. Forming high coordination states significantly enhanced the reactivity of the allylgermanes. In contrast to the 4‐coordinated allylgermanes with low reactivity, the highly coordinated species readily reacted with several aldehydes. Furthermore, the high coordination states exerted a significant effect on the E/Z selectivity of allylation depending on external additives. The coordination structure had a dramatic influence on the electronic and steric environments around the Ge center, enabling the geometrically controlled allylation of aldehydes. [ABSTRACT FROM AUTHOR]

We describe the application of a mild, molecular-based, hydride metathesis protocol for the preparation of metastable germanium(II) dihydrides with compositions approaching [GeH 2 ] n . The common starting material for this work [Ge(O t Bu) 2 ] was prepared in a high yield and shown to undergo O t Bu/H exchange at Ge with the hydride sources pinacolborane (HBpin), catecholborane (HBcat), and diisobutylaluminum hydride (DIBAL-H) to give the [GeH 2 ] n materials as yellow to orange solids. Heating one of these [GeH 2 ] n materials to 200 °C affords a narrowing of the optical band gap (from 2.5 eV) and the generation of amorphous Ge. Reaction of [Ge(O t Bu) 2 ] with excess H 3 B·SMe 2 in toluene at 70 °C provides a convenient route to thin films of amorphous Ge, including its deposition onto soft substrates, such as polyethyleneterephthalate (PET). Accompanying computations give insight into the energetics of O t Bu/H exchange at Ge, and reveal a general thermodynamic preference for branched structures of [GeH 2 ] n oligomers over linear forms as the Ge chain becomes longer. We also show that [Ge(O t Bu) 2 ] is a suitable pre-catalyst for the borylation of aldehydes.

The treatment of α,β-unsaturated ketones with divalent germanium salts cleanly generated C, O-chelated germyl enolates. The aldol reactions of the chelated enolates with the aldehydes achieved a high diastereoselectivity in the construction of the five-membered aldol adducts. Furthermore, the subsequent transformation of the Ge-C bond in the aldol adduct enabled the stereocontrolled synthesis of triols bearing four asymmetric centers.

The Group 14 enolates play an important part in many organic reactions. Herein, the reduction of an α-bromo ketone with germanium(II) salts cleanly afforded the corresponding germyl enolate as an isolatable species. This experimental reductive generation of a germyl enolate enabled us to characterize both C- and O-bound tautomers derived from an identical precursor and to unveil the tautomeric mechanisms, including the kinetic parameters and the relative stability of these tautomers, along with confirmation from DFT calculations. Moreover, the highly coordinated germyl enolates were isolated by a stabilization process induced by adding ligands. All products were characterized by NMR spectroscopy and X-ray crystallography., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)