Organogermanes as Orthogonal Coupling Partners in Synthesis and Catalysis

Base-Catalyzed Remote Hydrogermylation of Olefins

Although remote functionalization has emerged as a powerful strategy for modifying unactivated sites that are traditionally challenging to functionalize, there has been no remote hydrogermylation known to date. This work reports the first remote hydrogermylation of alkenes, achieved through a rare base-catalyzed approach-completely free of added transition metal catalysts. The methodology is operationally simple, versatile, and capable of achieving up to 8-carbon chain walks, overcoming the previous two-carbon limit of base-mediated processes.

Asymmetric Synthesis of Propargylic and Allenic Silanes, Germanes, and Stannanes

Enantioenriched propargylic and allenic derivatives of silicon, germanium, and tin are versatile building blocks for stereoselective synthesis. Consequently, considerable efforts toward their efficient and selective synthesis have been made, both through classical approaches for chirality transfer and catalytic enantioselective strategies that employ the latest developments in transition metal catalysis, organocatalysis, and photoredox catalysis. In this review, we survey broadly applicable synthetic strategies and discuss the scope and mechanistic details for specific protocols that afford these compounds in a regio- and stereoselective manner.

Cu-Catalyzed Enantioselective Carbene Insertion into Ge-H and Si-H Bonds Enabled by SPSiBox with a Tunable Chiral Pocket

Here, we report the Cu-catalyzed asymmetric carbene insertion into both Ge-H and Si-H bonds with α-trifluoromethyl diazo compounds, enabled by a class of newly developed C2-symmetrical bisoxazoline ligands. This protocol provides an efficient method for the preparation of enantioenriched α-trifluoromethyl ogranogermanes and organosilanes, featuring a broad substrate scope, mild reaction conditions, excellent enantioselectivity, and low catalyst loading. The key to the tolerance of both Si-H and Ge-H bonds is the use of SPSiBox ligands bearing a flexible and tunable chiral pocket. Preliminary mechanistic studies and computational studies unveiled the origin of chiral induction with SPSiBox ligands, the mechanism of Cu-catalyzed Ge-H insertion. This method not only provides a new method for the construction of trifluoromethyl-containing chiral molecules but also opens a new avenue for the preparation of chiral Si- and Ge-containing functional molecules.

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.

Precision installation of silyl synthetic handles within arenes by regiocontrolled ruthenium C(sp 2)-H functionalization

The site-selective functionalization of C(sp 2)-H bonds represents a powerful strategy for the synthesis of structurally diverse compounds with broad applicability. Here we report efficient regioselective catalytic methods for the formation of benzyltrimethylsilanes through ruthenium-catalysed C(sp 2)-H silylmethylation. The developed protocols enable selective functionalization at both ortho and meta positions within arenes bearing N-based directing groups. The resulting silylmethyl compounds can undergo diverse transformations, including nucleophilic aromatic substitution, carbonyl addition, olefination and desilylation. Significantly, the regiodivergent installation of silylmethyl synthetic handles allows for the synthesis of the pharmaceutical losmapimod and could further be applied in direct late-stage functionalizations. Mechanistically, an essential role for biscyclometallated ruthenium(II) species has been found, with the formation of intermediate ruthenium(III) species indicated by paramagnetic NMR experiments. These synthetic inventions and mechanistic elucidations signify a transformative step within ruthenium-catalysed C(sp 2)-H functionalization, enabling diverse syntheses and providing a framework for future development.

Elemental Germanium Activation and Catalysis Enabled by Mechanical Force

In the realm of materials science and chemical industry, germanium emerges as a strategic resource with distinctive properties that extend its applicability beyond traditional electronics and optics into the promising field of chemical catalysis. Despite its significant role in advanced technological applications, the potential of elemental germanium as a catalyst remains unexplored. Leveraging recent developments in mechanochemistry, this study introduces a groundbreaking approach to activate elemental germanium via mechanical force, facilitating the Reformatsky reaction without the reliance on external reducing agents. Meanwhile, we have also demonstrated, for the first time, the catalytic activity of elemental germanium, successfully achieving this through the bromoalkylation of alkenes. These achievements mark a significant advancement in the field of catalysis and open up a new promising avenue for both academic research and industrial applications.

C-H functionalization through benzylic deprotonation with π-coordination or cation-π-interactions

Benzylic C-H functionalization is a valuable tool to make complex aromatic molecules from simple, readily available alkylbenzenes. While methods that involve benzylic radicals or cations generated by hydrogen atom transfer or oxidation have been well demonstrated, they often require oxidative conditions. In contrast, deprotonation methods offer a complementary approach to transform benzylic C-H bonds through a benzylic carbanion generated by deprotonation. Electrophilic transition metal complexes acidify benzylic protons upon π-coordination to the phenyl ring of substrates, facilitating deprotonation by stabilizing the corresponding benzylic carbanion. Cation-complexes with group(I) metals also acidify benzylic C-H bonds. These approaches enable a significant expansion of the scope and diversity of alkylarenes with various electrophilic reagents. In this review, we discuss the development of benzylic functionalization through deprotonation of η6-arene complexes of transition-metals and cation-π interactions with group(I) metals, as well as progress made in catalysis through reversible arene-metal interactions.

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.

Nucleophilic Triphenylgermanides of Magnesium and Calcium

The dimeric calcium and magnesium hydrides, [(BDI)AeH]2 [BDI=HC{(Me)CNDipp}2, Dipp=2,6-i-Pr2C6H3; Ae=Mg or Ca] do not react with Ph3GeH in non-coordinating solvent. Addition of THF, however, induces deprotonation and access to monomeric Ae-germanide complexes, [(BDI)Ae{GePh3}(THF)], both of which have been structurally characterized. Although this process is facile when Ae=Ca, the analogous magnesium-based reaction requires heating to temperatures >100 °C, under which conditions germanide formation is complicated by THF ring opening and the generation of an alkaline earth germyl-C-terminated n-butoxide, [(BDI)Mg{μ2-O(CH2)4GePh3}]. Reactions of [(BDI)Ca{GePh3}(THF)] with N,N'-di-isopropylcarbodiimide and benzophenone provide the respective germylamidinate and germylalkoxide derivatives, [(BDI)Ca{(i-PrN)2CGePh3}(THF)] and [(BDI)Ca{OC(GePh3)Ph2}(THF)], demonstrating its potential as a well-defined and soluble source of the [Ph3Ge]- anion in nucleophilic addition reactions.

Germanyl triazoles as a platform for CuAAC diversification and chemoselective orthogonal cross-coupling

We report the synthesis of germanyl triazoles formed via a copper-catalysed azide-alkyne cycloaddition (CuAAC) of germanyl alkynes. The reaction is often high yielding, functional group tolerant, and compatible with complex molecules. The installation of the Ge moiety enables further diversification of the triazole products, including chemoselective transition metal-catalysed cross-coupling reactions using bifunctional boryl/germyl species.

Synthesis, Structures, and Reactivity of Organostannanides and Organogermanides of Copper(I)

Organogermane and organostannane compounds are valuable reagents in cross coupling reactions, and copper(I) germanide and stannanide complexes can provide convenient access to these compounds. This review presents the chemistry of copper(I) germanide and stannanide complexes, with a particular focus on systems at the frontier of organic and inorganic chemistry where structural characterisation of coordination complexes facilitates rationalisation of organic mechanisms. These species show both similarities to, and significant divergences from their lighter silanide congeners. For example, they are all viable sources of the relevant organotetranide anion, but in the cases of both germanium and tin, the tetranides can be accessed via direct deprotonation of the corresponding tetranes, a reaction unknown for silicon. Further divergences between copper(I) germanides and stannanides are highlighted; whilst both can be used in productive organic transformations to access organotetranes, catalytic reactions are only reported for germanium. The rather striking ability of triphenylstannanides to acts as sources of the phenyl anion are discussed; the mechanism of this reaction is still subject to discussion, but its absence in the chemistry of germanium and silicon is now well-rationalised. We conclude this review by considering potential research directions in the synthesis and exploitation of copper(I) germanides and stannanides.

Direct synthesis of α-functionalized amides via heteroatom-hydrogen insertion reactions using amide-sulfoxonium ylides

α-Functionalized Si-, Ge-, B-, Se-, and S-amide moieties are present in many medicinally active molecules, but their synthesis remains challenging. Here, we demonstrate a high-throughput synthesis using amide-sulfoxonium ylides as carbene precursors in a Si-H, Ge-H, B-H, Se-H, and S-H insertion reactions to target a wide range of α-silyl, α-geryl, α-boryl, α-selenyl, and α-sulfur (hetero)amides. The process is featured as simple operation, mild conditions, broad substrate scope, high functional group compatibility, and excellent chemoselectivity. Both experimental and computational studies are conducted to explore the mechanisms underlying the formation of C-Si/Ge/B/Se/S bond. This research highlights the use of highly selective X-H insertion reactions with amide-sulfoxonium ylide-derived carbenes, paving the way for the preparation of diverse functional organosilane, organogermane, organoboron, organoselenium, and organosulfur compounds from accessible and bench-stable precursors.

Photocatalytic Generation of Germyl Radicals from Digermanes Enabling the Hydro/Deuteriogermylation of Alkenes

We have developed a visible-light-induced method to photolyze digermanes through single-electron oxidation using a photocatalyst, in contrast to direct excitation, to generate germyl radicals and achieve the hydro/deuteriogermylation of alkenes. This protocol allows the previously elusive incorporation of the small trimethylgermyl group and deuterium, metabolically stable bioisosteres of tert-butyl and hydrogen, respectively, making this approach attractive in not only organic synthesis but also medicinal chemistry.

Cobalt-catalyzed reductive cross-coupling: a review

Transition-metal-catalyzed reductive cross-coupling is highly efficient for forming C-C bonds. It earns its limelight from its application by coupling unreactive electrophilic substrates to synthesize a variety of carbon-carbon bonds with various hybridizations (sp, sp2, and sp3), late-stage functionalization, and bioactive molecules' synthesis. Reductive cross-coupling is challenging to bring selectivity but promising approach. Cobalt is comparatively more affordable than other highly efficient metals e.g., palladium and nickel but cobalt catalysis is still facing efficacy challenges. Researchers are trying to harness the maximum out of cobalt's catalytic properties. Shortly, with efficiency achieved combined with the affordability of cobalt, it will revolutionize industrial applications. This review gives insight into the core of cobalt-catalyzed reductive cross-coupling reactions with a variety of substrates forming a range of differently hybridized coupled products.

Palladium-Catalyzed Suzuki-Miyaura Reactions with Triazenyl-Tethered Aryl Bromides: Exploiting the Orthogonal Coupling Sites under Different Conditions

Transition-metal-catalyzed cross-coupling of arenes bearing two or more potential coupling sites is often challenging because of the chemoselectivity issue. If orthogonal cross-couplings were applicable, one can develop a synthetically useful approach for consecutive functionalization of the starting arenes compounds. We herein reported a Suzuki-Miyaura coupling of triazenyl-substituted aryl bromides catalyzed by PdCl2(PCy3)2/PPh3 under basic conditions. The resultant polyfunctionalized aryl triazenes could undergo Suzuki-Miyaura couplings under acidic conditions or be converted to many other functionalized arenes. This orthogonal coupling strategy allows for a sequential functionalization of arenes with same type of nucleophilic reagents toward the synthesis of diverse biaryls and teraryls.

Photoinduced Palladium-Catalyzed Radical Germylative Arylation of Alkenes with Chlorogermanes

We describe a visible light-induced palladium-catalyzed radical germylative arylation of alkenes with easily accessible chlorogermanes. This protocol provides expedient access to germanium-substituted indolin-2-ones in good to excellent yields under mild reaction conditions. The key step for this strategy lies in the reductive activation of germanium-chloride bonds with an excited palladium complex under visible light irradiation. The involvement of germanium radicals was evidenced by electron paramagnetic resonance spectroscopy experiments.

Electrochemistry-Enabled C-Heteroatom Bond Formation of Alkyl Germanes

Because of their robustness and orthogonal reactivity features, alkyl germanes bear significant potential as functional handles for the construction of C(sp3)-rich scaffolds, especially in the context of modular synthetic approaches. However, to date, only radical-based reactivity has been accessible from these functional handles, which limits the types of possible decorations. Here, we describe the first general C(sp3)-heteroatom bond formation of alkyl germanes (-GeEt3) by leveraging electrochemistry to unlock polar reactivity. This approach allowed us to couple C(sp3)-GeEt3 with a variety of nucleophiles to construct ethers, esters, amines, amides, sulfonamides, sulfides, as well as C-P, C-F, and C-C bonds. The compatibility of the electrochemical approach with a modular synthetic strategy of a C1 motif was also showcased, involving the sequential functionalization of Cl, Bpin, and ultimately GeEt3 via electrochemistry.

Visible-Light-Driven Germyl Radical Generation via EDA-Catalyzed ET-HAT Process

We have established a facile and efficient protocol for the generation of germyl radicals by employing photo-excited electron transfer (ET) in an electron donor-acceptor (EDA) complex to drive hydrogen-atom transfer (HAT) from germyl hydride (R3GeH). Using a catalytic amount of EDA complex of commercially available thiol and benzophenone derivatives, the ET-HAT cycle smoothly proceeds simply upon blue-light irradiation without any transition metal or photocatalyst. This protocol also affords silyl radical from silyl hydride.

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.

Photogeneration of α-Bimetalloid Radicals via Selective Activation of Multifunctional C1 Units

Light-driven strategies that enable the chemoselective activation of a specific bond in multifunctional systems are comparatively underexplored in comparison to transition-metal-based technologies, yet desirable when considering the controlled exploration of chemical space. With the current drive to discover next-generation therapeutics, reaction design that enables the strategic incorporation of an sp3 carbon center, containing multiple synthetic handles for the subsequent exploration of chemical space would be highly enabling. Here, we describe the photoactivation of ambiphilic C1 units to generate α-bimetalloid radicals using only a Lewis base and light source to directly activate the C-I bond. Interception of these transient radicals with various SOMOphiles enables the rapid synthesis of organic scaffolds containing synthetic handles (B, Si, and Ge) for subsequent orthogonal activation. In-depth theoretical and mechanistic studies reveal the prominent role of 2,6-lutidine in forming a photoactive charge transfer complex and in stabilizing in situ generated iodine radicals, as well as the influential role of the boron p-orbital in the activation/weakening of the C-I bond. This simple and efficient methodology enabled expedient access to functionalized 3D frameworks that can be further derivatized using available technologies for C-B and C-Si bond activation.

When transition-metal catalysis meets electrosynthesis: a recent update

While aiming at sustainable synthesis, organic electrosynthesis has attracted increasing attention in the past few years. In parallel, with a deeper understanding of catalyst and ligand design, 3d transition-metal catalysis allows the conception of more straightforward synthetic routes in a cost-effective fashion. Owing to their intrinsic advantages, the merger of organic electrosynthesis with 3d transition-metal catalysis has offered huge opportunities for conceptually novel transformations while limiting ecological footprint. This review summarizes the key advancements in this direction published in the recent two years, with specific focus placed on strategy design and mechanistic aspects.

Accessing elusive σ-type cyclopropenium cation equivalents through redox gold catalysis

Cyclopropenes are the smallest unsaturated carbocycles. Removing one substituent from cyclopropenes leads to cyclopropenium cations (C3+ systems, CPCs). Stable aromatic π-type CPCs were discovered by Breslow in 1957 by removing a substituent on the aliphatic position. In contrast, σ-type CPCs-formally accessed by removing one substituent on the alkene-are unstable and relatively unexplored. Here we introduce electrophilic cyclopropenyl-gold(III) species as equivalents of σ-type CPCs, which can then react with terminal alkynes and vinylboronic acids. With catalyst loadings as low as 2 mol%, the synthesis of highly functionalized alkynyl- or alkenyl-cyclopropenes proceeded under mild conditions. A class of hypervalent iodine reagents-the cyclopropenyl benziodoxoles (CpBXs)-enabled the direct oxidation of gold(I) to gold(III) with concomitant transfer of a cyclopropenyl group. This protocol was general, tolerant to numerous functional groups and could be used for the late-stage modification of complex natural products, bioactive molecules and pharmaceuticals.

From Quaternary Carbon to Tertiary C(sp3)-Si and C(sp3)-Ge Bonds: Decyanative Coupling of Malononitriles with Chlorosilanes and Chlorogermanes Enabled by Ni/Ti Dual Catalysis

Transition-metal-catalyzed C-Si/Ge cross-coupling offers promising avenues for the synthesis of organosilanes/organogermanes, yet it is fraught with long-standing challenges. A Ni/Ti-catalyzed strategy is reported here, allowing the use of disubstituted malononitriles as tertiary C(sp3) coupling partners to couple with chlorosilanes and chlorogermanes, respectively. This method enables the catalytic cleavage of the C(sp3)-CN bond of the quaternary carbon followed by the formation of C(sp3)-Si/C(sp3)-Ge bonds from ubiquitously available starting materials. The efficiency and generality are showcased by a broad scope for both of the coupling partners, therefore holding the potential to synthesize structurally diverse quaternary organosilanes and organogermanes that were difficult to access previously.

Orthogonal sp3-Ge/B Bimetallic Modules: Enantioselective Construction and Enantiospecific Cross-Coupling

In this study, a series of enantioenriched sp3-Ge/B bimetallic modules were successfully synthesized via an enantioselective copper-catalyzed hydroboration of carbagermatrane (Ge)-containing alkenes. Orthogonal cross-coupling selectivity under different Pd-catalyzed conditions was achieved in an enantiospecific manner. Notably, the chiral secondary Ge exhibited a remarkable transmetallation ability prior to primary or secondary Bpin. The effectiveness of this Ge/B bimetallic strategy was further demonstrated through the development of new functional small molecules with Aggregation-Induced Emission (AIE) and Circularly Polarized Luminescence (CPL) performance. This represents the first successful example of synthesis of enantioenriched alkylgermanium reagents that permit enantiospecific cross-coupling reactions.

Triply Selective & Sequential Diversification at Csp 3: Expansion of Alkyl Germane Reactivity for C-C & C-Heteroatom Bond Formation

We report the triply selective and sequential diversification of a single Csp 3 carbon carrying Cl, Bpin and GeEt3 for the modular and programmable construction of sp3-rich molecules. Various functionalizations of Csp 3-Cl and Csp 3-BPin (e.g. alkylation, arylation, homologation, amination, hydroxylation) were tolerated by the Csp 3-GeEt3 group. Moreover, the methodological repertoire of alkyl germane functionalization was significantly expanded beyond the hitherto known Giese addition and arylation to alkynylation, alkenylation, cyanation, halogenation, azidation, C-S bond formation as well as the first demonstration of stereo-selective functionalization of a Csp 3-[Ge] bond.

Construction of Ge-Stereogenic Center by Desymmetric Carbene Insertion of Dihydrogermanes

We developed a method for the enantioselective synthesis of germanium-stereogenic compounds by the desymmetric carbene insertion of dihydrogermanes. A chiral rhodium phosphate catalyst decomposes diaryldiazo-methanes to generate rhodium carbenes that insert enantioselectively into one of the two Ge-H bonds of dihydrogermanes to form germanium-stereogenic compounds under mild reaction conditions. By this method, a variety of chiral germanes with germanium-stereogenic centers were synthesized in high yields and excellent enantioselectivities. Kinetic studies of the reaction showed that the diazo decomposition process was the rate-determining step. The remaining Ge-H bond of the chiral germane products provides a possibility for preparing chiral tetra-substituted germanium-stereogenic compounds.

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.

The structures and reactivity of NHC-supported copper(i) triphenylgermyls

Deprotonation of triphenyl germane with NHC-supported copper alkoxides afforded four novel (NHC)CuGePh3 complexes. Of these, (IPr)CuGePh3 (IPr = :C{N(2,6-iPr2C6H3)CH}2) was selected for further investigation. Analysis by EDA-NOCV indicates it to be a germyl nucleophile and its σ-bond metathesis reaction with a range of p-block halides confirmed it to be a convenient source of [Ph3Ge]-. The Cu-Ge bond of (IPr)CuGePh3 underwent π-bond insertions with tBuNCS, CS2, and PhNCO to furnish a series of germyl substituted carboxylate derivatives, (IPr)CuXC(Y)GePh3 (X = S, NPh; Y = S, NtBu, O), which were structurally characterised. (IPr)CuGePh3 inserted phenyl acetylene, providing both the Markovnikov and anti-Markovnikov products. The (NHC)CuGePh3 compounds were validated as catalytic intermediates; addition of 10 mol% of NHC-copper(i) alkoxide to a mixture of triphenyl germane and a tin(iv) alkoxide resulted in a tin/germanium cross coupling with concomitant formation of alcohol. Moreover, a catalytic hydrogermylation of Michael acceptors was developed with Ph3GeH adding to 7 activated alkenes in good conversions and yields in the presence of 10 mol% of NHC-copper(i) alkoxide. In all cases, this reaction provided the β-germylated substrate implicating nucleophilicity at germanium.

Modular access to alkylgermanes via reductive germylative alkylation of activated olefins under nickel catalysis

Carbon-introducing difunctionalization of C-C double bonds enabled by transition-metal catalysis is one of most straightforward and efficient strategies to construct C-C and C-X bonds concurrently from readily available feedstocks towards structurally diverse molecules in one step; however, analogous difunctionalization for introducing germanium group and other functionalities remains elusive. Herein, we describe a nickel-catalyzed germylative alkylation of activated olefins with easily accessible primary, secondary and tertiary alkyl bromides and chlorogermanes as the electrophiles to form C-Ge and C-Calkyl bonds simultaneously. This method provides a modular and facile approach for the synthesis of a broad range of alkylgermanes with good functional group compatibility, and can be further applied to the late-stage modification of natural products and pharmaceuticals, as well as ligation of drug fragments. More importantly, this platform enables the expedient synthesis of germanium substituted ospemifene-Ge-OH, which shows improved properties compared to ospemifene in the treatment of breast cancer cells, demonstrating high potential of our protocol in drug development.

Orthogonal Olefination with Organogermanes

Reported herein is a fully orthogonal olefination, which involves the site- and E-selective coupling of aryl germanes with alkenes, tolerating otherwise widely employed coupling handles such as aromatic (pseudo)halogens (C-I, C-Br, C-Cl, C-F, C-OTf, C-OSO2 F), silanes and boronic acid derivatives as well as alternative functionalities. This unprecedented [Ge]-based oxidative Heck coupling proceeds at room temperature with high speed (10 min to 2 hours) and operational simplicity owing to its base-free and air-tolerant features.

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.

Catalytic ipso-Nitration of Organosilanes Enabled by Electrophilic N-Nitrosaccharin Reagent

Nitroaromatic compounds represent one of the essential classes of molecules that are widely used as feedstock for the synthesis of intermediates, the preparation of nitro-derived pharmaceuticals, agrochemicals, and materials on both laboratory and industrial scales. We herein disclose the efficient, mild, and catalytic ipso-nitration of organotrimethylsilanes, enabled by an electrophilic N-nitrosaccharin reagent and allows chemoselective nitration under mild reaction conditions, while exhibiting remarkable substrate generality and functional group compatibility. Additionally, the reaction conditions proved to be orthogonal to other common functionalities, allowing programming of molecular complexity via successive transformations or late-stage nitration. Detailed mechanistic investigation by experimental and computational approaches strongly supported a classical electrophilic aromatic substitution (SE Ar) mechanism, which was found to proceed through a highly ordered transition state.

Site-Selective Nitration of Aryl Germanes at Room Temperature

We report a site-selective ipso-nitration of aryl germanes in the presence of boronic esters, silanes, halogens, and additional functionalities. The protocol is characterized by operational simplicity, proceeds at room temperature, and is enabled by [Ru(bpy)3](PF6)2/blue light photocatalysis. Owing to the exquisite robustness of the [Ge] functionality, nitrations of alternative functional handles in the presence of the germane are also feasible, as showcased herein.

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.

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.

Recent Advances in C-H Functionalisation through Indirect Hydrogen Atom Transfer

The functionalisation of C-H bonds has been an enormous achievement in synthetic methodology, enabling new retrosynthetic disconnections and affording simple synthetic equivalents for synthons. Hydrogen atom transfer (HAT) is a key method for forming alkyl radicals from C-H substrates. Classic reactions, including the Barton nitrite ester reaction and Hofmann-Löffler-Freytag reaction, among others, provided early examples of HAT. However, recent developments in photoredox catalysis and electrochemistry have made HAT a powerful synthetic tool capable of introducing a wide range of functional groups into C-H bonds. Moreover, greater mechanistic insights into HAT have stimulated the development of increasingly site-selective protocols. Site-selectivity can be achieved through the tuning of electron density at certain C-H bonds using additives, a judicious choice of HAT reagent, and a solvent system. Herein, we describe the latest methods for functionalizing C-H/Si-H/Ge-H bonds using indirect HAT between 2018-2023, as well as a critical discussion of new HAT reagents, mechanistic aspects, substrate scopes, and background contexts of the protocols.

Visible-Light-Driven Silyl or Germyl Radical Generation via Si-C or Ge-C Bond Homolysis

We report a simple, rapid, and selective protocol for visible-light-driven generation of silyl radicals through photoredox-induced Si-C bond homolysis. Irradiating 3-silyl-1,4-cyclohexadienes with blue light in the presence of a commercially available photocatalyst smoothly generated silyl radicals bearing various substituents within 1 h, and these radicals were trapped by a broad range of alkenes to afford products in good yields. This process is also available for efficient generation of germyl radicals.

cis-Selective Hydrogenation of Aryl Germanes: A Direct Approach to Access Saturated Carbo- and Heterocyclic Germanes

A catalytic approach of synthesizing the cis-selective saturated carbo- and heterocyclic germanium compounds (3D framework) is reported via the hydrogenation of readily accessible aromatic germanes (2D framework). Among the numerous catalysts tested, Nishimura's catalyst (Rh2O3/PtO2·H2O) exhibited the best hydrogenation reactivity with an isolated yield of up to 96%. A broad range of substrates including the synthesis of unprecedented saturated heterocyclic germanes was explored. This selective hydrogenation strategy could tolerate several functional groups such as -CF3, -OR, -F, -Bpin, and -SiR3 groups. The synthesized products demonstrated the applications in coupling reactions including the newly developed strategy of aza-Giese-type addition reaction (C-N bond formation) from the saturated cyclic germane product. These versatile motifs can have a substantial value in organic synthesis and medicinal chemistry as they show orthogonal reactivity in coupling reactions while competing with other coupling partners such as boranes or silanes, acquiring a three-dimensional structure with high stability and robustness.

Diphenylsilylsilanolates Enable the Transfer of a Wide Range of Silyl Groups

Development of silylating reagents that can transfer a wide range of silyl groups has been a long-standing challenge. Herein we report sodium diphenylsilylsilanolates as new stable and handy silylating reagents that could be synthesized from chlorosilanes. The new reagents retain the ability of dimethylsilylsilanolates for the delivery of a variety of silyl groups in palladium-catalyzed silylation of aryl bromides irrespective of the steric and electronic properties of silyl groups to be transferred.

σ-GeH and Germyl Cationic Pt(II) Complexes

The low electron count Pt(II) complexes [Pt(NHC')(NHC)][BAr^F] (where NHC is a N-heterocyclic carbene ligand and NHC' its metalated form) react with tertiary hydrogermanes HGeR₃ at room temperature to generate the 14-electron platinum(II) germyl derivatives [Pt(GeR₃)(NHC)₂][BAr^F]. Low-temperature NMR studies allowed us to detect and characterize spectroscopically some of the σ-GeH intermediates [Pt(η²-HGeR₃)(NHC')(NHC)][BAr^F] that evolve into the platinum-germyl species. One of these compounds has been characterized by X-ray diffraction studies, and the interaction of the H-Ge bond with the platinum center has been analyzed in detail by computational methods, which suggest that the main contribution is the donation of the H-Ge to a σ*(Pt-C) orbital, but backdonation from the platinum to the σ*(Ge-H) orbital is significant. Primary and secondary hydrogermanes also produce the corresponding platinum-germyl complexes, a result that contrasts with the reactivity observed with primary silanes, in which carbon-silicon bond-forming reactions have been reported. According to density functional theory calculations, the formation of Pt-Ge/C-H bonds is both kinetically and thermodynamically preferred over the competitive reaction pathway leading to Pt-H/C-Ge bonds.

Reductive Cross-Coupling of Unreactive Electrophiles

Transition-metal-catalyzed reductive coupling of electrophiles has emerged as a powerful tool for the construction of molecules. While major achievements have been made in the field of cross-couplings between organic halides and pseudohalides, an increasing number of reports demonstrates reactions involving more readily available, low-cost, and stable, but unreactive electrophiles. This account summarizes the recent results in our laboratory focusing on this topic. These findings typically include deoxygenative C-C coupling of alcohols, reductive alkylation of alkenyl acetates, reductive C-Si coupling of chlorosilanes, and reductive C-Ge coupling of chlorogermanes.The reductive deoxygenative coupling of alcohols with electrophiles is synthetically appealing, but the potential of this chemistry remains to be disclosed. Our initial study focused on the reaction of allylic alcohols and aryl bromides by the combination of nickel and Lewis acid catalysis. This method offers a selectivity that is opposite to that of the classic Tsuji-Trost reactions. Further investigation on the reaction of benzylic alcohols led to the foundation of a dynamic kinetic cross-coupling strategy with applications in the nickel-catalyzed reductive arylation of benzylic alcohols and cobalt-catalyzed enantiospecific reductive alkenylation of allylic alcohols. The titanium catalysis was later established to produce carbon radicals directly from unactivated tertiary alcohols via C-OH cleavage. The development of their coupling reactions with carbon fragments delivers new methods for the construction of all-carbon quaternary centers. These reactions have shown high selectivity for the functionalization of tertiary alcohols, leaving primary and secondary alcohols intact. Alkenyl acetates are inexpensive, stable, and environmentally friendly and are considered the most attractive alkenyl reagents. The development of reductive alkylation of alkenyl acetates with benzyl ammoniums and alkyl bromides offers mild approaches for the conversion of ketones into aliphatic alkenes.Extensive studies in this field have enabled us to extend the cross-electrophile coupling from carbon to silicon and germanium chemistry. These reactions harness the ready availability of chlorosilanes and chlorogermanes but suffer from the challenge of their low reactivity toward transition metals. Under reductive nickel catalysis, a broad range of alkenyl and aryl electrophiles couple well with vinyl- and hydrochlorosilanes. The use of alkyl halides as coupling partners led to the formation of functionalized alkylsilanes. The C-Ge coupling seems less substrate-dependent, and various common chlorogermanes couple well with aryl, alkenyl, and alkyl electrophiles. In general, functionalities such as Grignard-sensitive groups (e.g., acid, amide, alcohol, ketone, and ester), acid-sensitive groups (e.g., ketal and THP protection), alkyl fluoride and chloride, aryl bromide, alkyl tosylate and mesylate, silyl ether, and amine are tolerated. These methods provide new access to organosilicon and organogermanium compounds, some of which are challenging to obtain otherwise.

Catalytic cyclopropanation reactions with α-silyl-, germanyl- and stannyl carbenes generated from cyclopropenes

Silylcyclopropenes are employed as precursors of α-silyl vinyl carbenes and trapped with alkenes. Cyclopropylsilanes were obtained in good yields with ample scope and complete regio- and diastereoselectivity. Stereoretentive protodesilylations enabled access to cis-1,2-disubstituted cyclopropanes. Cyclopropylstannanes and -germanes can also be prepared from the corresponding cyclopropenes.

Pd-Catalyzed Hydroxyl-Directed Cascade Hydroarylation/C-H Germylation of Nonterminal Alkenes and Aryl Iodides

Pd-catalyzed cascade hydroarylation and C-H germylation of nonterminal alkenes and aryl iodides enabled by hydroxyl assistance have been developed. The key step in this C-H germylation cascade is the formation of a highly reactive oxo-palladacycle intermediate, which markedly restrained the β-H elimination process. Mechanistically, control experiments indicated that the hydroxyl group played an important role in this process. This transformation shows excellent reactivity and selectivity for most substrates investigated.

Modular Generation of (Iodinated) Polyarenes Using Triethylgermane as Orthogonal Masking Group

While the modular construction of molecules from suitable building blocks is a powerful means to more rapidly generate a diversity of molecules than through customized syntheses, the further evolution of the underlying coupling methodology is key to realize widespread applications. We herein disclose a complementary modular coupling approach to the widely employed Suzuki coupling strategy of boron containing precursors, which relies on organogermane containing building blocks as key orthogonal functionality and an electrophilic (rather than nucleophilic) unmasking event paired with air-stable PdI dimer based bond construction. This allows to significantly shorten the reaction times for the iterative coupling steps and/or to close gaps in the accessible compound space, enabling straightforward access also to iodinated compounds.

Dual-photofunctional organogermanium compound based on donor-acceptor-donor architecture

A dual-photofunctional organogermanium compound based on a donor-acceptor-donor architecture that exhibits thermally activated delayed fluorescence and mechano-responsive luminochromism has been developed. The developed compound was successfully applied as an emitter for efficient organic light-emitting diodes.

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.