Cobalt-Catalyzed (E)-β-Selective Hydrogermylation of Terminal Alkynes

Nucleophilic Germylation of Stable π Bonds via Ge─Ge Bond Heterolysis

Organogermanes have recently attracted a great deal of attention as building blocks for the synthesis of bioactive products, drugs, and functional materials. Metallo-germyls were classically synthesized and employed for nucleophilic germylation to form C─Ge bonds. However, their syntheses require highly reactive organometal reagents, and the scope of germylations involving metallo-germyls is limited due to competition with kinetically favored side reactions. Here, we present a regio/stereo-convergent nucleophilic germylation of stable π bonds by germyl anion generated in situ via heterolytic cleavage of the Ge─Ge bond of digermane (Ge─Ge) in the presence of KOtBu. This methodology affords unprecedented reactivity, enabling multiple germylation of alkynes and internally selective germylation of alkenes. These reactions are operationally simple, have broad functional group tolerance, and afford densely functionalized aliphatic organogermanes, such as 1-alkyl-1-germylalkanes, 1,1-digermylalkanes, and 1,1,1-trigermylalkanes, without any catalyst.

Hydrogermylation of alkynes via metal-ligand cooperative catalysis

E-H bond activation (E = B, Ge, Sn) with a (PNS)Pd complex has been investigated theoretically and experimentally. Et3GeH readily adds across the Pd/S bond. Subsequent transfer to CC bonds enables catalytic hydrogermylation. The reaction is most regio and stereoselective with terminal alkynes. Downstream derivatization of silyl-functionalized vinyl germanes is exemplified.

Photoinduced decarboxylative germylation of α-fluoroacrylic acids: access to germylated monofluoroalkenes

Herein, a novel strategy is presented for the photoinduced decarboxylative and dehydrogenative cross-coupling of a wide range of α-fluoroacrylic acids with hydrogermanes. This methodology provides an efficient and robust approach for producing various germylated monofluoroalkenes with excellent stereoselectivity within a brief photoirradiation period. The feasibility of this reaction has been demonstrated through gram-scale reaction, conversion of germylated monofluoroalkenes, and modification of complex organic molecules.

Recent Developments with Organogermanes: their Preparation and Application in Synthesis and Catalysis

Within the sphere of traditional Pd0 /PdII cross coupling reactions, organogermanes have been historically outperformed both in terms of scope and reactivity by more conventional transmetalating reagents. Subsequently, this class of compounds has been largely underutilized as a coupling partner in bond-forming strategies. Most recent studies, however, have shown that alternative modes of activation of these notoriously robust building blocks transform organogermanes into the most reactive site of the molecule-capable of outcompeting other functional groups (such as boronic acids, esters and silanes) for both C-C and C-heteroatom bond formation. As a result, over the past few years, the literature has increasingly featured methodologies that explore the potential of organogermanes as chemoselective and orthogonal coupling partners. Herein we highlight some of these recent advances in the field of organogermane chemistry both with respect to their synthesis and applications in synthetic and catalytic transformations.

B(C6F5)3-catalyzed hydrogermylation of enones: a facile route to germacycles

Organogermacycles are important skeletons for medicinal chemistry and materials. Herein, we reported a B(C6F5)3 mediated domino hydrogermylation reaction of enones with dihydrogermanes, affording 21 variants of organogermacycle compounds. These germacyclic compounds were obtained in good to excellent yields (up to 99% yield) under mild reaction conditions.

Activation of robust bonds by carbonyl complexes of Mn, Fe and Co

Metal carbonyl complexes possess among the most storied histories of any compound class in organometallic chemistry. Nonetheless, these old dogs continue to be taught new tricks. In this Feature, we review the historic discoveries and recent advances in cleaving robust bonds (e.g., C-H, C-O, C-F) using carbonyl complexes of three metals: Mn, Fe, and Co. The use of Mn, Fe, and Co carbonyl catalysts in controlling selectivity during hydrofunctionalization reactions is also discussed. The chemistry of these earth-abundant metals in the field of robust bond functionalization is particularly relevant in the context of sustainability. We expect that an up-to-date perspective on these seemingly simple organometallic species will emphasize the wellspring of reactivity that continues to be available for discovery.

Highly selective α-hydrogermylation of alkynes catalyzed by an in situ generated bulky NHC-cobalt complex

A new catalytic system, based on an octacarbonyl dicobalt(0) complex and bulky ligand, providing a route to α-vinylgermanes is described. The proposed method can be effectively used for Markovnikov-selective hydrogermylation of a number of terminal and internal alkynes. It has been proved that analogous catalytic systems containing less sterically demanding ligands cannot serve as selective catalysts in this transformation.

Access to Unsaturated Organogermanes via (De)Hydrosilylation Mediated by Cobalt Complexes

The functionalization of alkynylgermanes using hydrosilanes was accomplished by employing cobalt catalysis. Depending on the reactants used, the reaction can proceed via dehydrogenative coupling or hydrosilylation. Importantly, the presented method is characterized by mild reaction conditions, allowing rapid access to a wide range of organogermanes.

Direct C-H Dehydrogenative Germylation of Terminal Alkynes with Hydrogermanes

A direct C(sp)-H germylation of terminal alkynes with triethyl germanium hydride is reported. The method is operationally simple and makes use of B(C₆F₅)₃ catalysis in combination with 2,6-lutidine as an organic base. Exclusive selectivity for dehydrogenative germylation of the alkyne over the competing hydrogermylation is observed.

Copper-Catalyzed Three-Component Germyl Peroxidation of Alkenes

The concurrent incorporation of a germyl fragment and another functional group (beyond the hydrogen atom) across the C═C double bond is a highly appealing yet challenging task. Herein we demonstrate the efficient germyl peroxidation of alkenes with germanium hydrides and tert-butyl hydroperoxide via a copper-catalyzed three-component radical relay strategy. This protocol exhibits excellent functional group tolerance and exquisite chemo- and regioselectivity under mild conditions and represents a rare example of constructing synthetically challenging metal-embedded organic peroxides.

Hydrogermylation initiated by trialkylborohydrides: a living anionic mechanism

A trialkylborohydide-initiated hydrogermylation of aromatic alkenes is reported along with a DFT-supported mechanism following the course of a ‘living’ process.

Hydrogermylation of Alkenes via Organophotoredox-Initiated HAT Catalysis

This Letter discloses the straightforward hydrogermylation of olefins under visible-light organophotoredox-initiated HAT catalysis conditions to yield primary and secondary alkyl germanes at room temperature. The protocol is operationally simple, metal-free, and tolerant of various functional groups. The synthesized alkyl germanes proved to be highly robust toward acidic, basic, or oxidizing conditions and chemical transformations of C_sp²-GeEt₃ or C_sp²-BPin functionalities in their presence.

Nickel-Catalyzed Reductive C-Ge Coupling of Aryl/Alkenyl Electrophiles with Chlorogermanes

Cross-electrophile coupling has emerged as a promising tool for molecular synthesis; however, current studies have focused mainly on forging C-C bonds. We report a cross-electrophile C-Ge coupling reaction and thereby demonstrate the possibility of constructing organogermanes from carbon electrophiles and chlorogermanes. The reaction proceeds under mild conditions and offers access to both aryl and alkenyl germanes. Electron-rich, electron-poor, and ortho-/meta-/para-substituted (hetero)aryl electrophiles, as well as cyclic and acyclic alkenyl electrophiles, were coupled. Gram-scale reaction, incorporation of the -GeR₃ moiety into complex biologically active molecules, and derivatization of formed organogermanes are demonstrated.

Iron-catalysed radical cyclization to synthesize germanium-substituted indolo[2,1-a]isoquinolin-6(5H)-ones and indolin-2-ones

A simple and efficient strategy for iron-catalysed cascade radical cyclization was developed, by which an array of germanium-substituted indolo[2,1-a]isoquinolin-6(5H)-ones and indolin-2-ones were obtained in one pot with germanium hydrides as radical precursors. A rapid intramolecular radical trapping mode enabled the selective arylgermylation of alkenes over the prevalent hydrogermylation reaction.

Radical Germylzincation of Aryl- and Alkyl-Substituted Internal Alkynes

The stereoselective germylzincation of internal alkynes delivering trisubstituted vinylgermanes is achieved via a radical chain process involving Ph₃GeH and Et₂Zn with AIBN as the initiator. Excellent levels of regiocontrol are observed for nonsymmetric (aryl, alkyl)-substituted alkynes and for propargylic alcohols with aryl-, alkyl-, or silyl-substituted alkynes. The germylzincation reaction can be combined in one pot with the Cu(I)-mediated electrophilic substitution of the C(sp²)-Zn bond to obtain synthetically challenging tetrasubstituted vinylgermanes.