Oxidative Addition and Reductive Elimination at Main-Group Element Centers

Transition Metal Parent Alumylene Complexes: Synthesis, Structures, and XPS Characterization of Aluminum Oxidation State

The first isolation and characterization of transition metal complexes with the parent Al(I)-H unit were achieved in base-stabilized forms. W and Fe complexes, Cp*(CO)n(H)M←:AlH(NHC)2 (NHC = N-heterocyclic carbene, n = 1 or 2), were synthesized in 43-63% yields by the one-step reaction of Cp*M(CO)n(py)Me with H3Al·NHC. The characterization included 1H and 27Al nuclear magnetic resonance (NMR), and infrared (IR) spectroscopic analysis, as well as DFT calculations, which revealed the extremely strong σ-donating ability of the :AlH(NHC)2 ligand, and the highly polarized M(δ-)←:Al(δ+) coordination bonds. The monovalent oxidation state of the Al center of these complexes was confirmed by X-ray photoelectron spectroscopy (XPS). The hydroalumination of carbodiimide and the reduction of CO2 to CO were also demonstrated.

Diverse Functionality of Molecular Germanium: Emerging Opportunities as Catalysts

Fundamental research on germanium as the central element in compounds for bond activation chemistry and catalysis has achieved significant feats over the last two decades. Designing strategies for small molecule activations and the ultimate catalysts established capitalize on the orbital modalities of germanium, apparently imitating the transition-metal frontier orbitals. There is a growing body of examples in contemporary research implicating the tunability of the frontier orbitals through avant-garde approaches such as geometric constrained empowered reactivity, bimetallic orbital complementarity, cooperative reactivity, etc. The goal of this Perspective is to provide readers with an overview of the emerging opportunities in the field of germanium-based catalysis by perceiving the underlying key principles. This will help to convert the discrete set of findings into a more systematic vision for catalyst designs. Critical exposition on the germanium's frontier orbitals participations evokes the key challenges involved in innovative catalyst designs, wherein viewpoints are provided. We close by addressing the forward-looking directions for germanium-based catalytic manifold development. We hope that this Perspective will be motivational for applied research on germanium as a constituent of pragmatic catalysts.

Dialumene as a Dimeric or Monomeric Al Synthon for C-F Activation in Monofluorobenzene

The activation of C-F bonds has long been regarded as the subject of research in organometallic chemistry, given their synthetic relevance and the fact that fluorine is the most abundant halogen in the Earth's crust. However, C-F bond activation remains a largely unsolved challenge due to the high bond dissociation energies, which was historically dominated by transition metal complexes. Main group elements that can cleave unactivated monofluorobenzene are still quite rare and restricted to s-block complexes with a biphilic nature. Herein, we demonstrate an Al-mediated activation of monofluorobenzene using a neutral dialumene, allowing for the synthesis of the formal oxidative addition products at either double or single aluminum centers. This neutral dialumene system introduces a novel methodology for C-F bond activation based on formal oxidative addition and reductive elimination processes around the two aluminum centers, as demonstrated by combined experimental and computational studies. A "masked" alumylene was unprecedentedly synthesized to prove the proposed reductive elimination pathway. Furthermore, the synthetic utility is highlighted by the functionalization of the resulting aryl-aluminum compounds.

Mechanochemical Synthesis of a Sodium Anion Complex [Na+(2,2,2-cryptand)Na-] and Studies of Its Reactivity: Two-Electron and One-Electron Reductions

Group 1 metal molecular chemistry is dominated by a +1 oxidation state, while a 0 oxidation state is widespread in the metals. A more exotic, yet still available, oxidation state of group 1 metal is -1, i.e., alkalide. Reported as early as the 1970s, the alkalides appear in every modern inorganic chemistry textbook as an iconic chemical curiosity, yet their reactivity remains unexplored. This is due to their synthetic hurdles. In this work, we report the first facile synthesis of the archetypical alkalide complex, [Na+(2,2,2-cryptand)Na-], which allows us to unveil a versatile reactivity profile of this once exotic species.

Carbene-Decorated Geometrically Constrained Borylenes for Bond Activations

While metal-ligand cooperativity is well-known, studies on element-ligand cooperativity involving main group species are comparatively much less explored. In this study, we computationally designed a few geometrically constrained borylenes supported by different carbenes. Our density functional theory studies indicate that they possess enhanced nucleophilicity as well as electrophilicity, thus rendering them promising candidates for exhibiting borylene-ligand cooperativity. The cooperation between the boron and adjacent carbene centers facilitates different bond activation processes, including the cycloaddition of acetylene across the boron-carbene bond as well as B-H/Si-H bond activation reactions, which have been analyzed in detail. To the best of our knowledge, the borylenes proposed in this study represent the first examples of theoretically proposed geometrically constrained bis(carbene)-stabilized borylenes capable of cooperative activation of enthalpically strong bonds.

Synthesis, Isolation, and Reactivity Studies of 'Naked' Acyclic Gallyl and Indyl Anions

By exploiting the electronic capabilities of the N-heterocyclic boryloxy (NHBO) ligand, we have synthesized "naked" acyclic gallyl [Ga{OB(NDippCH)2}2]- and indyl [In{OB(NDippCH)2}2]- anions (as their [K(2.2.2-crypt)]+ salts) through K+ abstraction from [KGa{OB(NDippCH)2}2] and [KIn{OB(NDippCH)2}2] using 2.2.2-crypt. These systems represent the first O-ligated gallyl/indyl systems, are ultimately accessed from cyclopentadienyl GaI/InI precursors by substitution chemistry, and display nucleophilic reactivity which is strongly influenced by the presence (or otherwise) of the K+ counterion.

Synthesis and Characterization of Bulky 1,3-Diamidopropane Complexes of Group 2 Metals (Be-Sr)

Reaction of lithium 1,3-diamidopropane Li2(TripNCN) (TripNCN=[{(Trip)NCH2}2CH2]2-, Trip=2,4,6-triisopropylphenyl) with BeBr2(OEt2)2 gave the diamido beryllium complex, [(TripNCN)Be(OEt2)]. Deprotonation reactions between the bulkier 1,3-diaminopropane (TCHPNCN)H2 (TCHPNCN=[{(TCHP)NCH2}2CH2]2-, TCHP=2,4,6-tricyclohexylphenyl) and magnesium alkyls afforded the adduct complexes [(TCHPNCN)Mg(OEt2)] and [(TCHPNCN)Mg(THF)2], depending on the reaction conditions employed. Treating [(TCHPNCN)Mg(THF)2] with the N-heterocyclic carbene :C{(MeNCMe)2} (TMC) gave [(TCHPNCN)Mg(TMC)2] via substitution of the THF ligands. Reactions of (ArNCN)H2 (Ar=Trip or TCHP) with Mg{CH2(SiMe3)}2, in the absence of Lewis bases, yielded the N-bridged dimers [{(ArNCN)Mg}2]. Salt metathesis reactions between alkali metal salts M2(TCHPNCN) (M=Li or K) and CaI2 or SrI2 led to the THF adduct compounds [(TCHPNCN)Ca(THF)3] and [(TCHPNCN)Sr(THF)4], the differing number of THF ligands in which is a result of the different sizes of the metals involved. The described complexes hold potential as precursors to kinetically protected, low oxidation state group 2 metal species.

Hydrogen splitting at a single phosphorus centre and its use for hydrogenation

Catalytic processes are largely dominated by transition-metal complexes. Main-group compounds that can mimic the behaviour of the transition-metal complexes are of great interest due to their potential to substitute or complement transition metals in catalysis. While a few main-group molecular centres were shown to activate dihydrogen via the oxidative addition process, catalytic hydrogenation using these species has remained challenging. Here we report the synthesis, isolation and full characterization of the geometrically constrained phosphenium cation with the 2,6-bis(o-carborano)pyridine pincer-type ligand. Notably, this cation can activate the H-H bond by oxidative addition to a single PIII cationic centre, producing a dihydrophosphonium cation. This phosphenium cation is also capable of catalysing hydrogenation reactions of C=C double bonds and fused aromatic systems, making it a main-group compound that can both activate H2 at a single molecular main-group centre and be used for catalytic hydrogenation. This finding shows the potential of main-group compounds, in particular phosphorus-based compounds, to serve as metallomimetic hydrogenation catalysts.

Redox-Active Carboranyl Diphosphine as an Electron and Proton Transfer Agent

In this work, we report the first example of the PCET reactivity for a boron cluster compound, the zwitterionic nido-carboranyl diphosphonium derivative 7-P(H)tBu2-10-P(H)iPr2-nido-C2B10H10. This main-group reagent efficiently transfers two electrons and two protons to quinones to yield hydroquinones and regenerate a neutral closo-carboranyl diphosphine, 1-PtBu2-2-PiPr2-closo-C2B10H10. As we have previously reported the conversion of this closo-carboranyl diphosphine into the zwitterionic nido- derivative upon reaction with main group hydrides, the transformation reported herein represents a complete synthetic cycle for the metal-free reduction of quinones, with the redox-active carboranyl diphosphine scaffold acting as a mediator. The proposed mechanism of this reduction, based on pKa determination, electrochemical studies, and kinetic isotope effect determination, involves the electron transfer from the nido- cluster to the quinone coupled with the delivery of protons.

Antimony Redox Catalysis: Hydroboration of Disulfides through Unique Sb(I)/Sb(III) Redox Cycling

The stibinidene ArSbI (Ar = [2,6-(tBuN═CH)2-C6H3], 1) reacts with S2Tol2 (Tol = p-tolyl) to form ArSbIII(STol)2 (2), which upon treatment with pinacolborane, regenerates 1. These processes unveil an unprecedented antimony redox catalysis involving Sb(I)/Sb(III) cycling for the hydroboration of organic disulfides. Elementary reaction studies and density functional theory calculations support that the catalysis mimics transition metal processes, proceeding through oxidative addition, ligand metathesis, and reductive elimination. The thiophenols and sulfidoborates generated from the hydroboration of disulfides react in situ with α,β-unsaturated carbonyl compounds with the assistance of 1 as a base catalyst. These tandem reactions establish a one-pot synthetic method for β-sulfido carbonyl compounds, in which a stibinidene functions as a redox catalyst and a base catalyst successively, illustrating the versatility and efficiency of antimony catalysis in organic synthesis.

ZnCl2-catalysed transfer hydrogenation of carbonyls and chemoselective reduction of the CC bond in α,β-unsaturated ketones

This manuscript describes chemoselective reduction of CC in α,β-unsaturated ketones and the transfer hydrogenation of aldehydes and ketones catalysed by ZnCl2-phosphinamino-triazolyl-pyridine (0.5 mol%) using KOH/iPrOH as a H2 source. A detailed mechanistic study using DFT calculations (B3LYP-D3/def2-TZVP) revealed the key role of metal-ligand cooperation (MLC) in the catalytic reaction demonstrating the non-innocent behaviour of the phosphine ligand.

Bisgermylene-Stabilized Stannylone: Catalytic Reduction of Nitrous Oxide and Nitro Compounds via Element-Ligand Cooperativity

This study describes the synthesis, structural characterization, and catalytic application of a bis(germylene)-stabilized stannylone (2). The reduction of digermylated stannylene (1) with 2.2 equiv of potassium graphite (KC8) leads to the formation of stannylone 2 as a green solid in 78% yield. Computational studies showed that stannylone 2 possesses a formal Sn(0) center and a delocalized 3-c-2-e π-bond in the Ge2Sn core, which arises from back-donation of the p-type lone pair electrons on the Sn atom to the vacant orbitals of the Ge atoms. Stannylone 2 can serve as an efficient precatalyst for the selective reduction of nitrous oxide (N2O) and nitroarenes (ArNO2) with the formation of dinitrogen (N2) and hydrazines (ArNH-NHAr), respectively. Exposure of 2 with N2O (1 atm) resulted in the insertion of two oxygen atoms into the Ge-Ge and Ge-Sn bonds, yielding the germyl(oxyl)stannylene (3). Moreover, the stoichiometric reaction of 2 with 1-chloro-4-nitrobenzene afforded an amido(oxyl)stannylene (4) through the complete scission of the N-O bonds of the nitroarene. Stannylenes 3 and 4 serve as catalytically active species for the catalytic reduction of nitrous oxide and nitroarenes, respectively. Mechanistic studies reveal that the cooperation of the low-valent Ge and Sn centers allows for multiple electron transfers to cleave the N-O bonds of N2O and ArNO2. This approach presents a new strategy for catalyzing the deoxygenation of N2O and ArNO2 using a zerovalent tin compound.

Understanding the Impact of Group 14 Elements on the Reactivity of [1 + 2] Cycloaddition Reaction between a Cyclic (Alkyl)(amino)carbene Analogue with a Group 14 Element and a Heavy Acetylene Molecule

Computational exploration using the density functional theory framework (M06-2X-D3/def2-TZVP) was undertaken to investigate the [1 + 2] cycloaddition reaction between a five-membered-ring heterocyclic carbene analogue (G14-Rea; G14 = group 14 element) and a heavy acetylene molecule (G14G14-Rea). It was theoretically observed that exclusively Si-Rea, Ge-Rea, and Sn-Rea demonstrate the capacity to participate in the [1 + 2] cycloaddition reaction with the triply bonded SiSi-Rea. In addition, only three heavy acetylenes (SiSi-Rea, GeGe-Rea, and SnSn-Rea) can catalyze the [1 + 2] cycloaddition reaction with Si-Rea. Our theoretical findings elucidated that the reactivity trend observed in these [1 + 2] cycloaddition reactions primarily arise from the deformation energies of the distorted G14G14-Rea. Also, our study reveals that the bonding characteristics of their respective transition states are controlled by the singlet-singlet interaction (donor-acceptor interaction), rather than the triplet-triplet interaction (electron-sharing interaction). Additionally, our work demonstrates that the bonding behavior between G14-Rea and G14G14-Rea is predominantly determined by the filled p-π orbital of G14G14-Rea (HOMO) → the empty perpendicular p-π orbital of G14-Rea (LUMO), rather than the vacant p-π* orbital of G14G14-Rea (LUMO) ← the filled sp2 orbital of G14-Rea (HOMO).

Applications of low-valent compounds with heavy group-14 elements

Over the last two decades, the low-valent compounds of group-14 elements have received significant attention in several fields of chemistry owing to their unique electronic properties. The low-valent group-14 species include tetrylenes, tetryliumylidene, tetrylones, dimetallenes and dimetallynes. These low-valent group-14 species have shown applications in various areas such as organic transformations (hydroboration, cyanosilylation, N-functionalisation of amines, and hydroamination), small molecule activation (e.g. P4, As4, CO2, CO, H2, alkene, and alkyne) and materials. This review presents an in-depth discussion on low-valent group-14 species-catalyzed reactions, including polymerization of rac-lactide, L-lactide, DL-lactide, and caprolactone, followed by their photophysical properties (phosphorescence and fluorescence), thin film deposition (atomic layer deposition and vapor phase deposition), and medicinal applications. This review concisely summarizes current developments of low-valent heavier group-14 compounds, covering synthetic methodologies, structural aspects, and their applications in various fields of chemistry. Finally, their opportunities and challenges are examined and emphasized.

Synthesis, Reactivity, and Complexation with Fe(0) of a Tight-bite Bis(N-heterocyclic silylene)

The synthesis, reactivity, and complexation with Fe(0) precursor of a tight-bite bis(N-heterocyclic silylene) (bis(NHSi)) ligand 1 are reported. The reaction of 1 with p-toluidine led to the activation of both N-H bonds across Si(II) atoms to afford a four-membered heterocyclic cyclodisilazane 2, with hydride substituents attached to five-coordinate Si atoms. A 1 : 2 reaction of 1 with Fe(CO)5 led to an intriguing dinuclear complex 3 featuring a five-membered (N-Si-Fe-Fe-Si) ring with a Fe-Fe bond distance of 2.6892(13) Å. All compounds (1-3) were thoroughly characterized by various spectroscopic methods and X-ray diffraction studies conclusively established their molecular structures. DFT calculations were carried out to shed light on bonding and energetic aspects in 1-3.

Synthetic, structural and reactivity studies of a boryl-ethynyl Silylene

The salt metathesis of a boryl-ethynyl lithium salt {[(HCDipN)2]B-CC-Li} with a monochlorosilylene [LSi(:)Cl; L = PhC(NtBu)2] produced an isolable boryl-ethynyl silylene {1; [(HCDipN)2]B-CC-Si(L)}. The Si(II) center in 1 possesses a nonbonding lone pair and forms a covalent bond with the ethynyl group. The characterization of 1 was carried out by multinuclear NMR spectroscopy, single-crystal X-ray structure analysis and DFT calculations. Additionally, a reactivity study of 1 was conducted towards oxygen-containing and aryl C-F substrates.

Boron bis-(4-methylbenzoxazol-2-yl)-methanide complexes

Boron compounds have attracted the attention of chemists because of their unique catalytic properties and potential wider material applications. Although group 13 metal compounds, which are based on the bis-(benzoxazol-2-yl)-methane system (Box, ({NCOC6H4}2CH2)), have been reported in the last several years, boron containing Box compounds were still missing. Now we report their successful syntheses and spectroscopic characterisation in this work. The borane compound [({NCOC6H3}2CH)BH2] (1) and haloboranes [({NCOC6H3}2CH)BF2] (2), [({NCOC6H3}2CH)BCl2] (3) and [({NCOC6H3}2CH)BBr2] (4) were characterised in the solid state by single crystal X-ray diffraction and in solution by NMR techniques. In addition, the fluorescence properties of compounds 1-4 are communicated.

Diverse Reactivity of Amidinate-Supported Boron Centers with the Hypersilyl Anion and Access to a Monomeric Secondary Boron Hydride

Diverse reactivity of the bulky tris(trimethylsilyl)silyl substituent [Si(SiMe3)3], also known as the hypersilyl group, was observed for amidinate-supported dichloro- and phenylchloroborane complexes. Treatment of the dichloroborane with potassium tris(trimethylsilyl)silyl led to the activation of the backbone β-carbon center and formation of saturated four-membered heterocyclic chloroboranes R'{Si(SiMe3)3}C(NR)2BCl [R' = Ph, R = Cy (3); R' = Ph, R = iPr (6); R' = tBu, R = Cy (8)], whereas the four-membered amidinate hypersilyl-substituted phenyl borane 4 {PhC(NCy)2B(Ph)[Si(SiMe3)3]} was observed for the case of an amidinate-supported phenylchloroborane. The highly deshielded 11B NMR spectroscopic resonance and the distinct difference in the 29Si NMR spectrum confirmed the presence of a σ-donating hypersilyl effect on compounds 3, 6, and 8. Reaction of 3 with the Lewis acid AlCl3 led to the formation of complex 11 in which an unusual cleavage of one of the C-N bonds of the amidinate backbone is observed. Nucleophilic substitution at the boron center of saturated chloroborane 3 with phenyllithium generated the phenylborane derivative 12, whereas the secondary monomeric boron hydride 13 was observed after treatment with alane (AlH3). All compounds (2-13) have been fully characterized by NMR spectroscopy and single-crystal X-ray structure determination studies.

Visible-Light Activation of Diorganyl Bis(pyridylimino) Isoindolide Aluminum(III) Complexes and Their Organometallic Radical Reactivity

We report on the synthesis and characterization of a series of (mostly) air-stable diorganyl bis(pyridylimino) isoindolide (BPI) aluminum complexes and their chemistry upon visible-light excitation. The redox non-innocent BPI pincer ligand allows for efficient charge transfer homolytic processes of the title compounds. This makes them a universal platform for the generation of carbon-centered radicals. The photo-induced homolytic cleavage of the Al-C bonds was investigated by means of stationary and transient UV/Vis spectroscopy, spin trapping experiments, as well as EPR and NMR spectroscopy. The experimental findings were supported by quantum chemical calculations. Reactivity studies enabled the utilization of the aluminum complexes as reactants in tin-free Giese-type reactions and carbonyl alkylations under ambient conditions, which both indicated radical-polar crossover behavior. A deeper understanding of the physical fundamentals and photochemical process was provided, furnishing in turn a new strategy to control the reactivity of bench-stable aluminum organometallics.

Reversible [4 + 1] Cycloaddition of Arenes by a "Naked" Acyclic Aluminyl Compound

The large steric profile of the N-heterocyclic boryloxy ligand, -OB(NDippCH)2, and its ability to stabilize the metal-centered HOMO, are exploited in the synthesis of the first example of a "naked" acyclic aluminyl complex, [K(2.2.2-crypt)][Al{OB(NDippCH)2}2]. This system, which is formed by substitution at AlI (rather than reduction of AlIII), represents the first O-ligated aluminyl compound and is shown to be capable of hitherto unprecedented reversible single-site [4 + 1] cycloaddition of benzene. This chemistry and the unusual regioselectivity of the related cycloaddition of anthracene are shown to be highly dependent on the availability (or otherwise) of the K+ countercation.

Highly selective, reversible water activation by P,N-cooperativity in pyridyl-functionalized phosphinines

Tetrapyridyl-functionalized phosphinines were prepared and structurally characterized. The donor-functionalized aromatic phosphorus heterocycles react highly selectively and even reversibly with water. Calculations reveal P,N-cooperativity for this process, with the flanking pyridyl groups serving to kinetically enhance the formal oxidative addition process of H2O to the low-coordinate phosphorus atom via H-bonding. Subsequent tautomerization forms 1,2-dihydrophosphinine derivatives, which can be quantitatively converted back to the phosphinine by applying vacuum, even at room temperature. This process can be repeated numerous times, without any sign of decomposition of the phosphinine. In the presence of CuI·SMe2, dimeric species of the type ([Cu2I2(phosphinine)]2) are formed, in which each phosphorus atom shows the less common μ2-bridging 2e--lone-pair-donation to two Cu(i)-centres. Our results demonstrate that fully unsaturated phosphorus heterocycles, containing reactive P[double bond, length as m-dash]C double bonds, are interesting candidates for the activation of E-H bonds, while the aromaticity of such compounds plays an appreciable role in the reversibility of the reaction, supported by NICS calculations.

Electrocatalytic Reduction of CO2 and H2O with Zn(II) Complexes Through Metal-Ligand Cooperation

Air and water-stable zinc (II) complexes of neutral pincer bis(diphenylphosphino)-2,6-di(amino)pyridine ("PN3P") ligands are reported. These compounds, [Zn(κ2-2,6-{Ph2PNR}2(NC5H3))Br2] (R=Me, 1; R=H, 2), were shown to be capable of electrocatalytic reduction of CO2 at -2.3 V vs. Fc+/0 to selectively yield CO in mixed water/acetonitrile solutions. These complexes also electrocatalytically generate H2 from water in acetonitrile solutions, at the same potential, with Faradaic efficiencies of up to 90 %. DFT computations support a proposed mechanism involving the first reduction of 1 or 2 occurring at the PN3P ligand. Furthermore, computational analysis suggested a mechanism involving metal-ligand cooperation of a Lewis acidic Zn(II) and a basic ligand.

Approach to the "Missing" Diarylsilylene: Formation, Characterization, and Intramolecular C-H Bond Activation of Blue Diarylsilylenes with Bulky Rind Groups

The treatment of the bulky Rind-based dibromosilanes, (Rind)2SiBr2 (2) [Rind = 1,1,7,7-tetra-R1-3,3,5,5-tetra-R2-s-hydrindacen-4-yl: EMind (a: R1 = Et, R2 = Me) and Eind (b: R1 = R2 = Et)], with two equivalents of tBuLi in Et2O at low temperatures resulted in the formation of blue solutions derived from the diarylsilylenes, (Rind)2Si: (3). Upon warming the solutions above -20 °C, the blue color gradually faded, accompanying the decomposition of 3 and yielding cyclic hydrosilanes (4) via intramolecular C-H bond insertion at the Si(II) center. The molecular structures of the bulky Eind-based 3b and 4b were confirmed by X-ray crystallography. Thus, at -20 °C, blue crystals were formed (Crystal-A), which were identified as mixed crystals of 3b and 4b. Additionally, colorless crystals of 4b as a singular component were isolated (Crystal-B), whose structure was also determined by an X-ray diffraction analysis. Although the isolation of 3 was difficult due to their thermally labile nature, their structural characteristics and electronic properties were discussed based on the experimental findings complemented by computational results. We also examined the hydrolysis of 3b to afford the silanol, (Eind)2SiH(OH) (5b).

Metal-metal cooperativity boosts Lewis basicity and reduction properties of the bis(gallanediyl) CyL2Ga2

The interplay of two proximate gallium centres equips the bimetallic complex CyL2Ga2 (1, CyL2 = 1,2-trans-Cy[NC(Me)C(H)C(Me)N(Dip)]2, Dip = 2,6-i-Pr2C6H3) with increased Lewis basicity and higher reducing power compared to the monometallic gallanediyl LGa (2, L = HC[MeCN(Dip)]2) as evidenced by cross-over experiments. Quantum chemical calculations were employed to support the experimental findings.

Polar X-H Bond (X=O, S, N) Activation at a Cage Silanide

Low-valent silicon compounds such as neutral silylenes display versatile reactivity for the activation of small molecules. In contrast, their anionic congeners silanides ([R3 Si- ]) have primarily been investigated for their nucleophilic reactivity. Here we show that incorporating a silanide center in a bicyclic cage structure allows for formal oxidative addition of polar element-hydrogen bonds (RX-H, R=aromatic residue, X=O, S, NH). The resulting hydrosilicates were isolated and characterized structurally and spectroscopically. Density Functional Theory (DFT) calculations and experimental observations support an ionic mechanism for RX-H bond activation. Finally, the reactivity of the RS-H bond adduct was further investigated, revealing that it behaves as a Lewis pair upon facile heterolytic cleavage of the Si-S bond.

Activation of non-polar bonds by an electron-rich gallagermylene

The electron-rich germylene LGa(μ-Cl)GeArMes (1) (L = CH[C(Me)N(Dipp)]2, Dipp = 2,6-iPr2C6H3, ArMes = 2,6-Mes2C6H3, Mes = 2,4,6-Me3C6H2) shows promising potential in the σ-bond activation of unpolar molecules as is shown in oxidative addition reactions with H2 and P4, yielding L(Cl)GaGe(H)2ArMes (2) and L(Cl)Ga(P4)GeArMes (3). Compounds 2 and 3 were characterised spectroscopically (1H, 13C{1H}, (31P{1H}), IR) and by single-crystal X-ray diffraction (sc-XRD).

Ambiphilicity of ring-expanded N-heterocyclic carbenes

N-heterocyclic carbenes, such as imidazole-2-ylidenes and imidazolin-2-ylidenes, the popular class of singlet carbenes introduced by Arduengo in 1991 have not been shown to be ambiphilic owing to the two σ-withdrawing, π-donating amino groups flanking the carbene centre. However, our experimental data suggest that ring-expanded N-heterocyclic carbenes (RE-NHCs), especially the seven and eight membered rings, are significantly ambiphilic. Our results also show that the steric environment in RE-NHCs can become a determining factor for controlling the E-H bond activation.

Diversity of transformation of heteroallenes on acenaphthene-1,2-diimine aluminum oxide

The reactions of oxide [(dpp-bian)Al(μ2-O)2Al(dpp-bian)] (1) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with phenyl- or cyclohexylisocyanates result in the formation of carbonimidate derivatives [(dpp-bian)Al(μ-O)(μ-RNCO2)Al(dpp-bian)] (R = Ph, 2; Cy, 3). Addition of N,N'-dicyclohexylcarbodiimide to compound 1 leads to the formation of ureate complex [(dpp-bian)Al(μ-O)(μ-(CyN)2CO)Al(dpp-bian)] (4). The reactions of the oxide 1 with pinacolborane and catecholborane afford oxo-bridged hydride [{(dpp-bian)Al(H)}(μ-O){Al(OBpin)(dpp-bian)}] (5) and compound [{(dpp-bian)Al(OBCat)}2(μ-O)] (7), respectively. Insertion of cyclohexylisocyanate into the Al-H bond of compound 5 gives CO insertion product [{(dpp-bian)Al(OC(H)NCy)}(μ-O){Al(OBpin)(dpp-bian)}] (6). New compounds have been characterized by ESR and IR spectroscopy; their molecular structures have been established by single-crystal X-ray analysis. The oxide 1 serves as a catalyst for the hydroboration of heteroallenes (isocyanates, carbodiimides) with pinacolborane.

Bismuth in Radical Chemistry and Catalysis

Whereas indications of radical reactivity in bismuth compounds can be traced back to the 19th century, the preparation and characterization of both transient and persistent bismuth-radical species has only been established in recent decades. These advancements led to the emergence of the field of bismuth radical chemistry, mirroring the progress seen for other main-group elements. The seminal and fundamental studies in this area have ultimately paved the way for the development of catalytic methodologies involving bismuth-radical intermediates, a promising approach that remains largely untapped in the broad landscape of synthetic organic chemistry. In this review, we delve into the milestones that eventually led to the present state-of-the-art in the field of radical bismuth chemistry. Our focus aims at outlining the intrinsic discoveries in fundamental inorganic/organometallic chemistry and contextualizing their practical applications in organic synthesis and catalysis.

Metallomimetic C-F Activation Catalysis by Simple Phosphines

Delivering metallomimetic reactivity from simple p-block compounds is highly desirable in the search to replace expensive, scarce precious metals by cheap and abundant elements in catalysis. This contribution demonstrates that metallomimetic catalysis, involving facile redox cycling between the P(III) and P(V) oxidation states, is possible using only simple, cheap, and readily available trialkylphosphines without the need to enforce unusual geometries at phosphorus or use external oxidizing/reducing agents. Hydrodefluorination and aminodefluorination of a range of fluoroarenes was realized with good to very good yields under mild conditions. Experimental and computational mechanistic studies show that the phosphines undergo oxidative addition of the fluoroaromatic substrate via a Meisenheimer-like transition state to form a fluorophosphorane. This undergoes a pseudotransmetalation step with a silane, via initial fluoride transfer from P to Si, to give experimentally observed phosphonium ions. Hydride transfer from a hydridosilicate counterion then leads to a hydridophosphorane, which undergoes reductive elimination of the product to reform the phosphine catalyst. This behavior is analogous to many classical transition-metal-catalyzed reactions and so is a rare example of both functional and mechanistically metallomimetic behavior in catalysis by a main-group element system. Crucially, the reagents used are cheap, readily available commercially, and easy to handle, making these reactions a realistic prospect in a wide range of academic and industrial settings.

Selective and efficient H2 evolution upon NH3BH3 hydrolysis at subzero temperatures

In the winter months, the temperature in most of the Earth stays below 0°C; the average temperature in winter at the South Pole is about -60°C. Therefore, it is urgent to develop efficient catalytic systems for selective and efficient H2 evolution upon NH3BH3 hydrolysis at subzero temperatures. For solving the freezing issue of water at below 0°C, herein, we have employed a facile and surfactant-free approach to synthesize M-Pt/C nanocomposites (M = Pd, Rh, Ru, Ni, Cu, or Fe), by the alloying of commercial Pt/C with Pd, Rh, Ru, Cu, Ni, or Fe for selective and efficient H2 evolution upon NH3BH3 hydrolysis in saline solution at below 0°C, even at -15°C. In addition, NH3BH3 hydrolysis over Pd-Pt/C in the saturated NaCl solution is utilized not only for safe hydrogen production but also for its in situ hydrogenation reduction in organic chemistry, which could avoid using dangerous hydrogen cylinders.

Gallaphosphene L(Cl)GaPGaL: A novel phosphinidene transfer reagent

Gallaphosphene L(Cl)GaPGaL 1 (L=HC[C(Me)N(Ar)]2 ; Ar=2,6-iPr2 C6 H3 ) reacts with N-heterocyclic carbenes R NHC (R NHC=[CMeN(R)]2 C; R=Me, iPr) to R NHC-coordinated phosphinidenes R NHC→PGa(Cl)L (R=Me 2 a, iPr 2 b) and with isonitriles RNC (R=iPr, Cy) to 1,3-phosphaazaallenes L(Cl)GaP=C=N-R (R=iPr 3 a, Cy 3 b), respectively. Quantum chemical calculations reveal that 2 a/2 b possess two localized lone pair of electrons, whereas 3 a/3 b only show one localized lone pair as was reported for gallaphosphene 1. 2 b reacts with 2.5 equivalents of a borane (THF ⋅ BH3 ) to the NHC-stabilized phosphinidene-borane complex [iPr NHC→P(BH2 )]2 (BH3 )3 4 with concomitant formation of LGa(H)Cl 5. 2-5 are characterized by heteronuclear (1 H, 13 C{1 H}, 31 P{1 H}) NMR and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction (sc-XRD).

(3+2) Annulation of 4-Acetoxy Allenoate with Aldimine Enabled by AgF-Assisted P(III)/P(V) Catalysis

A phosphine-catalyzed (3+2) annulation of 4-acetoxy allenoate and aldimine with the assistance of AgF is described. The success of this reaction hinges on the metathesis between the enolate-phosphonium zwitterion and AgF, leading to a key intermediate comprising of silver enolate and a fluorophosphorane P(V)-moiety. The former is able to undergo a Mannich reaction with aldimine, whereas the latter initiates a cascade sequence of AcO-elimination/aza-addition, thus furnishing the P(III)/P(V) catalysis. By taking advantage of the silver enolate, a preliminary attempt at an asymmetric variant was conducted with the combination of an achiral phosphine catalyst and a chiral bis(oxazolinyl)pyridine ligand (PyBox), giving moderate enantioselectivity.

Mono(Lewis Base)-Stabilized Gallium Iodide: An Unexplored Class of Promising Ligands

Quantum-chemical (DFT) calculations on hitherto unknown base(carbene)-stabilized gallium monoiodides (LB→GaI) suggest that these systems feature one lone pair of electrons and a formally vacant p-orbital - both centered at the central gallium atom - and exhibit metallomimetic behavior. The calculated reaction free energies as well as bond dissociation energies suggest that these LB→GaI systems are capable of forming stable donor-acceptor complexes with group 13 trichlorides. Examination of the ligand exchange reactions with iron and nickel complexes indicates their potential use as ligands in transition metal chemistry. In addition, it is found that the title compounds are also able to activate various enthalpically robust bonds. Further, a detailed mechanistic investigation of these small molecule activation processes reveals the non-innocent behavior of the carbene (base) moiety attached to the GaI fragment, thereby indicating the cooperative nature of these bond activation processes. The energy decomposition analysis (EDA) and activation strain model (ASM) of reactivity were also employed to quantitatively understand and rationalize the different activation processes.

Redox-active ligands - a viable route to reactive main group metal compounds

Anionic redox-active ligands such as o-amidophenolates, catecholates, dithiolenes, 1,2-benzendithiolates, 2-amidobenzenethiolates, reduced α-diimines, ferrocenyl and porphyrinates are capable of reversible oxidation and thus have the ability to act as sources of electrons for metal centres. These and other non-innocent ligands have been employed in coordination complexes of base transition metals to influence their redox chemistry and afford compounds with useful catalytic, optical, magnetic and conducting properties. Despite the focus in contemporary main group chemistry on designing reactive compounds with potential catalytic activity, comparatively few studies exploring the chemistry of main group metal complexes incorporating redox-active ligands have been reported. This article highlights relevant chemical reactivity and electrochemical studies that probe the oxidation/reduction of main group metal compounds possessing redox-active ligands and comments on the prospects for this relatively untapped avenue of research.

A planar per-borylated digermene

A tetraboryl digermene synthesized by the reaction between a dianionic digermanide nucleophile and a boron halide electrophile is dimeric both in the solid state and in hydrocarbon solution. It features both a planar 'alkene-like' geometry for the Ge2B4 core, and an exceptionally short GeGe double bond. These structural features are consistent with the known electronic properties of the boryl group, and with lowest energy (in silico) fragmentation into two triplet bis(boryl)germylene fragments.

Structures, Bonding Analyses and Reactivity of a Dicationic Digallene and Diindene Mimicking trans-bent Ditetrylenes

The reaction of bisdicyclohexylphosphinoethane (dcpe) and the subvalent MI sources [MI (PhF)2 ][pf] (M=Ga+ , In+ ; [pf]- =[Al(ORF )4 ]- ; RF =C(CF3 )3 ) yielded the salts [{M(dcpe)}2 ][pf]2 , containing the first dicationic, trans-bent digallene and diindene structures reported so far. The non-classical MI ⇆MI double bonds are surprisingly short and display a ditetrylene-like structure. The bonding situation was extensively analyzed by quantum chemical calculations, QTAIM (Quantum Theory of Atoms in Molecules) and EDA-NOCV (Energy Decomposition Analysis with the combination of Natural Orbitals for Chemical Valence) analyses and is compared to that in the isoelectronic and isostructural, but neutral digermenes and distannenes. The dissolved [{Ga(dcpe)}2 ]2+ ([pf]- )2 readily reacts with 1-hexene, cyclooctyne, diphenyldisulfide, diphenylphosphine and under mild conditions at room temperature. This reactivity is analyzed and rationalized.

π-Electron Fluctuation-Induced P+ /C- Ambiphilic Interaction for Intramolecular CAr -H Bond Activation

Herein, we describe how computational mechanistic understanding has led directly to the discovery of new 2H-phosphindole for C-CAr bond activation and dearomatization reaction. We uncover an unexpected intramolecular C-H bond activation with a 2H-phosphindole derivative. This new intriguing experimental observation and further theoretical studies led to an extension of the reaction mechanism with 2H-phosphindole. Through DFT calculations, we confirm that within a five-membered ring, the polarizable PC3 unit orchestrates the formation of an electrophilic phosphorus atom (P+ ) and a nucleophilic carbon atom (C- ). This kinetically accessible ambiphilic phosphorus/carbon couple is spatially separated by geometric constraints, and their reactivity is modulated through structural resonance.

Reversible Oxidative Addition of Nonactivated C-H Bonds to Structurally Constrained Phosphenium Ions

A series of structurally constrained phosphenium ions based on pyridinylmethylamidophenolate scaffolds are shown to undergo P(III)/P(V) oxidative addition with C-H bonds of alkynes, alkenes, and arenes. Nonactivated substrates such as benzene, toluene, and deactivated chlorobenzene are phosphorylated in quantitative yields. Computational and spectroscopic studies suggest a low-barrier isomerization from a bent to a T-shaped isomer that initiates a phosphorus-ligand-cooperative pathway and subsequent ring-chain tautomerism. Remarkably, C-H bond activations occur reversibly, allowing for reductive elimination back to P(III) at elevated temperatures or the exchange with other substrates.

Utilizing bis(imino)dihydroacridanide pincer ligands in p-block chemistry: synthesis and catalysis of an antimony monocation salt

We present the synthesis and characterization of an Sb(III) monocation salt stabilized by a bulky bis(imino)dihydroacridanide pincer ligand. The Lewis acidity of the Sb cation is quantified using the Guttmann-Beckett method and confirmed by its reaction with 4-dimethylaminopyridine, which forms a Lewis acid-base adduct. This Sb cation exhibits catalytic activity in the cyanosilylation of arylketones. The electronic structure of the Sb cation as well as the mechanism of the catalytic transformation are explored by density functional theory computations.

Diverse Reactions of Formazanate/Formazan with Tetrylenes: Reduction, C-H Bond Activation, Substitution and Addition

The reactivity of the formazanate potassium salt [LtBu K(thf)] (LtBu= PhNNC(4-t BuPh)NNPh) with the group 14 chlorotetrylenes [{PhC(t BuN)2 }ECl] (E=Si, Ge, Sn) was investigated. Three corresponding compounds with unique configurations were formed, demonstrating the diverse reactivity of the system. In addition to the anticipated salt metathesis reactions of the potassium salt with the chlorine function of tetrylenes, unexpected reduction/insertion steps into the N=N bond of the formazanate (Si, Ge) and subsequent C-H activation (Ge) were also observed. Furthermore, when the neutral formazan ligand [LtBu H] was exposed to silylenes [{PhC(t BuN)2 }SiCl] and [LPh SiNMePy], substitution and addition reactions occurred. These discoveries significantly enrich the diversity of formazanate/formazan redox chemistry, opening up new avenues for exploration in this field.

Uncovering Nitrosyl Reactivity at N-Heterocyclic Carbene Center

N-heterocyclic carbenes (NHCs) have garnered much attention due to their unique properties, such as strong σ-donating and π-accepting abilities, as well as their transition-metal-like reactivity toward small molecules. In 2015, we discovered that NHCs can react with nitric oxide (NO) gas to form radical adducts that resemble transition metal nitrosyl complexes. To elucidate the analogy between NHC and transition metal NO adducts, here we have undertaken a systematic investigation of the electron- and proton-transfer chemistry of [NHC-NO]⋅ (N-heterocyclic carbene nitric oxide radical) compounds. We have accessed a suite of compounds, comprised of [NHC-NO]+ , [NHC-NO]- , [NHC-NOH]0 , and [NHC-NHOH]+ species. In particular, [NHC-NO]- was isolated as potassium and lithium ion adducts. Most interestingly, a monomeric potassium [NHC-NO]- compound was isolated with the assistance of 18-crown-6, which is the first instance of a monomeric alkali N-oxyl compound to the best of our knowledge. Our results demonstrate that [NHC-NO]⋅ exhibits redox behavior broadly similar to metal nitrosyl complexes, which opens up more possibilities for utilizing NHCs to build on the known reactivity of metal complexes.

Main group metal-mediated strategies for C-H and C-F bond activation and functionalisation of fluoroarenes

With fluoroaromatic compounds increasingly employed as scaffolds in agrochemicals and active pharmaceutical ingredients, the development of methods which facilitate regioselective functionalisation of their C-H and C-F bonds is a frontier of modern synthesis. Along with classical lithiation and nucleophilic aromatic substitution protocols, the vast majority of research efforts have focused on transition metal-mediated transformations enabled by the redox versatilities of these systems. Breaking new ground in this area, recent advances in main group metal chemistry have delineated unique ways in which s-block, Al, Ga and Zn metal complexes can activate this important type of fluorinated molecule. Underpinned by chemical cooperativity, these advances include either the use of heterobimetallic complexes where the combined effect of two metals within a single ligand set enables regioselective low polarity C-H metalation; or the use of novel low valent main group metal complexes supported by special stabilising ligands to induce C-F bond activations. Merging these two different approaches, this Perspective provides an overview of the emerging concept of main-group metal mediated C-H/C-F functionalisation of fluoroarenes. Showcasing the untapped potential that these systems can offer in these processes; focus is placed on how special chemical cooperation is established and how the trapping of key reaction intermediates can inform mechanistic understanding.

Boosting the Catalytic Performance of NiMoO4 Nanorods in H2 Generation upon NH3BH3 Hydrolysis via a Reduction Process

Although a range of noble metal catalysts, including Ru, Rh, Pd, Pt, and Au, have been developed for efficient H2 generation upon NH3BH3 hydrolysis at room temperature, this is a highly urgent need for exploring earth-abundant metal nanocatalysts for H2 generation upon NH3BH3 hydrolysis. Herein, a NaBH4 reduction strategy was developed to boost the catalytic performance of NiMoO4 nanorods in H2 generation upon NH3BH3 hydrolysis. Indeed, the pristine NiMoO4 nanorods were catalytically inert in NH3BH3 hydrolysis. Significantly, the reduced NiMoO4 nanorods presented excellent catalytic activity in H2 generation upon NH3BH3 hydrolysis, with a turnover frequency (TOF) of 31.2 L(H2)·gcat-1·h-1. Interestingly, the TOF of NH3BH3 hydrolysis over reduced NiMoO4 nanorods significantly increased from 31.2 to 53.6 L(H2)·gcat-1·h-1 under 0.3 M NaOH. The boosting catalytic performance of NiMoO4 nanorods via NaBH4 reduction in H2 generation might be attributed to the higher content of Oads and the formation of nickel boride in the reduced NiMoO4 nanorods. In this work, NH3BH3 hydrolysis over reduced NiMoO4 nanorods was not only used for safe H2 generation but also for its in situ tandem hydrogenation in organic chemistry.

Dearomatization of C6 Aromatic Hydrocarbons by Main Group Complexes

The dearomatization reaction is a powerful method for transformation of simple aromatic compounds to unique chemical architectures rapidly in synthetic chemistry. Over the past decades, the chemistry in this field has evolved significantly and various important organic compounds such as crucial bioactive molecules have been synthesized through dearomatization. In general, photochemical conditions or assistance by transition metals are required for dearomatization of rigid arenes. Recently, main-group elements, especially naturally abundant elements in the Earth's crust, have attracted attention as they have low toxicity and are cost-effective compared to the late transition metals. In recent decades, a variety of low-valent main-group molecules, which enable the activation of stable aromatic compounds under mild conditions, have been developed. This minireview highlights the developments in the chemistry of dearomatization of C6 aromatic hydrocarbons by main-group compounds leading to the formation of seven-membered EC6 (E=main-group elements) ring or cycloaddition products.

Activation of the GaI Cation for Bond Activation: from Oxidative Additions into C-Cl and H-P Bonds to Reversible Insertion into P4

Although the discovery of the GaI complex salt [Ga(PhF)2-3 ][Al(ORF )4 ] (RF =C(CF3 )3 , PhF=C6 H5 F) invoked the preparation of a diverse library of cationic Ga(I) coordination complexes and clusters, studies on small molecule activation with low-valent GaI cations are scarce. Herein, a first experimental study on the reactivity of a monomeric Ga(I) cation activated with a pyridine-diimine pincer ligand (in [Ga(PDIdipp )][Al(ORF )4 ]) towards small-molecules is reported. First controlled oxidative additions of the GaI cation into C-Cl, H-P and P-P bonds are presented. Moreover, the [4+1]cycloaddition to butadienes was achieved. Intriguingly, the isolated, blue insertion product into the P-P bond of P4 allows for the quantitative release of the P4 molecule upon reaction with AlEt3 and butadienes. Reversible P4 insertion of main-group metals has previously been reported for Ge and Sn, respectively. The experimental study is supported by high-level computational analysis of the in-part reversible oxidative additions at the DLPNO-CCSD(T)/def2-TZVPP//PBEh-3c/def2-mSVP level of theory with COSMO-RS solvation in 1,2-difluorobenzene.

Seven-Membered Cyclic Diamidoalumanyls of Heavier Alkali Metals: Structures and C-H Activation of Arenes

Like the previously reported potassium-based system, rubidium and cesium reduction of [{SiNDipp}AlI] ({SiNDipp} = {CH2SiMe2NDipp}2) with the heavier alkali metals [M = Rb and Cs] provides dimeric group 1 alumanyl derivatives, [{SiNDipp}AlM]2. In contrast, similar treatment with sodium results in over-reduction and incorporation of a formal equivalent of [{SiNDipp}Na2] into the resultant sodium alumanyl species. The dimeric K, Rb, and Cs compounds display a variable efficacy toward the C-H oxidative addition of arene C-H bonds at elevated temperatures (Cs > Rb > K, 110 °C) to yield (hydrido)(organo)aluminate species. Consistent with the synthetic experimental observations, computational (DFT) assessment of the benzene C-H activation indicates that rate-determining attack of the Al(I) nucleophile within the dimeric species is facilitated by π-engagement of the arene with the electrophilic M+ cation, which becomes increasingly favorable as group 1 is descended.

Anions featuring an aluminium-silicon core with alumanyl silanide and aluminata-silene characteristics

Molecular species containing multiple bonds to aluminium have long been challenging synthetic targets. Despite recent landmark discoveries in this area, heterodinuclear Al-E multiple bonds (where E is a group-14 element) have remained rare and limited to highly polarized π-interactions (Al=E ↔ +Al-E-). Here we report the isolation of three alumanyl silanide anions that feature an Al-Si core stabilized by bulky substituents and a Si-Na interaction. Single-crystal X-ray diffraction studies, spectroscopic analysis and density functional theory calculations show that the Al-Si interaction possesses partial double bond character. Preliminary reactivity studies support this description of the compounds through two resonance structures: one that displays a predominant nucleophilic character of the sodium-coordinated silicon centre in the Al-Si core, as shown by silanide-like reactivity towards halosilane electrophiles and the CH-insertion of phenylacetylene. Moreover, we report an alumanyl silanide with a sequestered sodium cation. Cleavage of the Si-Na bond by [2.2.2]cryptand increases the double bond character of the Al-Si core to produce an anion with high aluminata-silene (-Al=Si) character.

Heterobimetallic Hydrides with a Germanium(II)-Zinc Bond

In the presence of TMEDA (TMEDA=N,N,N',N'-tetramethylethylenediamine), zinc dihydride reacted with germanium(II) compounds (BDI-H)Ge (1) and [(BDI)Ge][B(3,5-(CF3 )2 C6 H3 )4 ] (3) (BDI-H = HC{(C=CH2 )(CMe)(NAr)2 }, BDI = [HC(CMeNAr)2 ]; Ar = 2,6-i Pr2 C6 H3 ) by formal insertion of the germanium(II) center into the Zn-H bond of polymeric [ZnH2 ]n to give neutral and cationic zincagermane with a H-Ge-Zn-H core [(BDI-H)Ge(H)-(H)Zn(tmeda)] (2) and [(BDI)Ge(H)-(H)Zn(tmeda)][B(3,5-(CF3 )2 C6 H3 )4 ] (4), respectively. Compound 2 eliminated [ZnH2 ] giving diamido germylene 1 at 60 °C. Compound 2 and deuterated analogue 2-d2 exchanged with [ZnH2 ]n and [ZnD2 ]n in the presence of TMEDA to give a mixture of 2 and 2-d2 . Compounds 2 and 4 reacted with carbon dioxide (1 bar) at room temperature to form zincagermane diformate [(BDI-H)Ge(OCHO)-(OCHO)Zn(tmeda)] (5) and formate bridged digermylene [({BDI}Ge)2 (μ-OCHO)]+ [B(C6 H3 (CF3 )2 )4 ] (6) along with zinc formate [(tmeda)Zn(μ-OCHO)3 Zn(tmeda)][B(C6 H3 (CF3 )2 )4 ] (7), respectively. The hydridic nature of the Ge-H and Zn-H bonds in 2 and 4 was probed by reactions with Brönsted and Lewis acids.