Unsaturated main-group compounds containing heteroleptic double bonds of bismuth remain exceedingly rare due to inherent pπ-pπ bond weakness. Here we report the synthesis and characterization of the first isolable silylidenebismuthane complexes, L(Me3Si)Si═Bi(SiMe3) and L(Me3Si)Si═Bi(SiiPr3) ((E)-1a,b) (L = PhC(NtBu)2), containing a neutral but strongly polarized silicon-bismuth double bond. The complexes were obtained as the E isomers in 55% and 60% yield through the salt metathesis reaction of LSiIICl with the corresponding potassium bis(silyl)bismuthanide complexes. Remarkably, LSiII-Bi(SiMe3)2 and LSiII-Bi(SiMe3)(SiiPr3) could not be observed but undergo a trimethylsilyl group migration from the BiIII atom to the SiII atom to form a Si═Bi moiety containing σ3λ4-coordinate SiII and σ2λ2-coordinate BiI atoms. The reactions of (E)-1a,b with [W(CO)5(thf)] cause the (E) → (Z) isomerization with respect to the silyl groups attached to furnish the corresponding terminal Bi→W(CO)5 complexes (Z)-2a,b, in which the Si═Bi π bonding interaction is significantly weakened. This and the nature of the Si═Bi bonds are corroborated by DFT calculations.

ABSTRACT Diazo compounds, >C═N═N, typically undergo C═N bond cleavage to form carbenes and N 2 , whereas direct N═N bond breaking remains exceedingly rare in main‐group chemistry. We report the N═N bond scission of diazodiarylmethanes, Ar 2 C═N═N (Ar = phenyl, Ar 2 C = 9,9‐fluorendiyl), mediated by a chelating bis‐NHSi (NHSi = N‐heterocyclic silylene). Three bis‐NHSi scaffolds with tunable Si···Si distances were examined: While XT(LSi:) 2 (XT = 9,9‐dimethyl‐9H‐xanthene‐4,5‐diyl, L = PhC(tBuN) 2 ) and PhN(LSi:) 2 lead to end‐on addition products with partial N═N bond activation, the carborane‐based CB(LSi:) 2 (CB = 1,2‐C 2 B 10 H 10 ) engenders complete N═N bond cleavage to afford isolable disilicon nitrido imino species containing a Si═N─Si─N═CAr 2 unit that hydrolyzes to Ar 2 C═NH, NH 3 , SiO 2 , C 2 B 10 H 12 , and LH. According to density functional theory (DFT) calculations, the N═N cleavage stems from a unique cooperative interaction of the two divalent silicon centers.

Lignin is the largest resource of biobased renewable aromatic feedstock for chemicals and fuels. For profitable biorefineries, lignin valorization is essential, as it enhances the overall efficiency of biomass conversion and improves process economics. In recent decades, lignin valorization and depolymerization processes have attracted significant scientific interest. Many approaches have been explored, including thermochemical methods, such as pyrolysis, oxidative depolymerization, and reductive catalytic fractionation; biological methods, like enzymatic depolymerization and microbial degradation; and electrochemical techniques, such as electrocatalytic oxidation and electrocatalytic hydrogenation. Among them, electrochemical processes play a significant role in lignin valorization by employing green electricity sources with in situ hydrogen generation, being environmentally friendly, and contributing to the economic feasibility of lignin conversion. In this review, the electrochemical conversion of lignin from lignocellulosic biomass, including lignin fractionation or depolymerization to lignin derived compounds (such as vanillin, benzoic acid and quinones) through electrocatalytic oxidation, and its upgrading through electrocatalytic hydrogenation or hydrogenolysis to produce industrially valuable lignin-based chemicals, are discussed in detail. Finally, a summary of current challenges, limitations and emerging opportunities in electrochemical valorization of lignin is provided to frame this technology for sustainable and biobased development.

Herein, we report isolable donor-acceptor-stabilized SiII-EII-SiII trimetallylenes (E = Ge (2), Sn (3), Pb (4); SiII = Mes(cAAC)Si; Mes = 2,4,6-Me3C6H2; cAAC = C(CH2)(CMe2)2N-2,6-iPr2C6H3), stabilized by a cyclic alkylaminocarbene attached to the divalent Si atoms. They were synthesized through salt-metathesis reactions of the dimeric silanylidene anion (SiIIK)2 1a and EX2 precursors (X = Cl, N(SiMe3)2). Computational analyses reveal that 2-4 adopt bent donor-acceptor-stabilized SiII-EII-SiII frameworks featuring polarized Si-C(cAAC) π interactions together with delocalized Si-E π interactions involving the Lewis-acidic EII center. This donor-acceptor electronic structure results in small HOMO-LUMO gaps, giving rise to pronounced near-infrared (NIR) absorption. Remarkably, the one-electron reduction of 2 and 3 leads to the GeI- and SnI- radical anions 2•- and 3•-, respectively, thereby highlighting that this donor-acceptor motif can even stabilize heavy Group 14 elements in lower oxidation states.

Organic oxidation reactions (OORs) are emerging as attractive alternatives to the oxygen evolution reaction (OER) for renewable energy conversion. Effective OOR demands catalysts that function across diverse organic substrates and a broad chemical phase space. Here, we report a well-defined Ni12P5 nanostructure as an efficient alkaline OOR catalyst for 5-hydroxymethylfurfural (HMF) and 5-amino-1H-tetrazole (AmTET), yielding carboxylated and dehydrogenative N=N-coupled products, respectively. Dynamic redox behavior and self-reconstruction were investigated to identify the active phase. At OER potentials, Ni12P5 converts into NiIII/IV oxyhydroxides typical of OER catalysts. However, upon introducing organic substrates at catalytic potentials, the in situ formed NiIII/IVOOH is rapidly reduced, generating an OOR-active material dominated by NiII sites, as evidenced by quasi in situ X-ray absorption and in situ Raman spectroscopy. This work demonstrates the versatility and robustness of Ni-based electrocatalysts formed via potential-driven material transformations.

The development of efficient electrocatalysts for value-added organic oxidation reactions (OORs) is essential for sustainable chemical production and achieving carbon neutrality. In this work, we report a helical cobalt borophosphate...

ABSTRACT Herein, we report isolable donor–acceptor‐stabilized Si II –E II –Si II trimetallylenes (E = Ge ( 2 ), Sn ( 3 ), Pb ( 4 ); Si II = Mes(cAAC)Si; Mes = 2,4,6‐Me 3 C 6 H 2 ; cAAC = C(CH 2 )(CMe 2 ) 2 N‐2,6‐ i Pr 2 C 6 H 3 ), stabilized by a cyclic alkylaminocarbene attached to the divalent Si atoms. They were synthesized through salt‐metathesis reactions of the dimeric silanylidene anion (Si II K) 2 1a and EX 2 precursors (X = Cl, N(SiMe 3 ) 2 ). Computational analyses reveal that 2–4 adopt bent donor–acceptor‐stabilized Si II –E II –Si II frameworks featuring polarized Si–C(cAAC) π interactions together with delocalized Si–E π interactions involving the Lewis‐acidic E II center. This donor–acceptor electronic structure results in small HOMO–LUMO gaps, giving rise to pronounced near‐infrared (NIR) absorption. Remarkably, the one‐electron reduction of 2 and 3 leads to the Ge I ‐ and Sn I ‐ radical anions 2 •− and 3 •− , respectively, thereby highlighting that this donor–acceptor motif can even stabilize heavy Group 14 elements in lower oxidation states.

Transition metal chalcogenides (TMCs) are among the most investigated precatalysts for alkaline oxygen evolution reaction (OER). However, the origins of their activity and the role of the nature of chalcogen atoms remain unclear. To address these questions, we developed analogous single-source precursors to synthesize structurally and morphologically alike CoS, CoSe, and CoTe phases, serving as ideal starting materials to isolate the chalcogens' role for the OER. We uncover the importance of reliable active site quantification, intrinsic activity evaluation, and monitoring in situ structural changes during OER. In our electrochemical analyses, special emphasis is placed on accurate redox activity evaluation. Our results show that the in situ-formed layered oxyhydroxide phases have similar intrinsic activities. The nature of the chalcogen atom influences the number of active sites, leading to the geometric activity trend: CoSe > CoS > CoTe. These insights are crucial for the understanding and development of future electrocatalysts and application-oriented devices.

The very different features of cooperative disilicon(II)‐mediated N═N bond activation of trans ‐ vs. cis ‐azobenzene are reported, employing two bis‐silylenes with distinct intramolecular Si···Si distances, PhN(LSi:)₂ 1 (L = PhC( t BuN)₂, Si···Si: 2.9 Å) and XT(LSi:)₂ 2 (XT = 9,9‐dimethyl‐xanthene‐4,5‐diyl, Si···Si: 4.3 Å). While trans ‐azobenzene reacts with both bis‐silylenes to form C─H and N═N π bond activation products, the cis ‐isomer undergoes only N═N bond scission. Thus, the reaction of 1 with cis ‐azobenzene at room temperature affords the unprecedented N═N bond cleavage product 4 , featuring a bis‐silaimine with terminal and bridging Si═N moieties. In contrast, the reaction of 2 with cis ‐azobenzene at –30 °C in THF allows for the isolation of the [1+2] cycloaddition intermediate 6 , containing a three‐membered SiN₂ ring (siladiazirane), which rearranges to the N═N bond cleavage product 8 at room temperature. Compound 6 reacts with one additional equivalent of cis ‐azobenzene to form bis‐silaazirane 7 with two SiN₂ rings. Density functional theory (DFT) calculations support stepwise Si(II)···Si(II) cooperative activation mechanisms and provide insights into the role of bis‐silylenes for selective N═N cleavage reactions.

[AlI 2 + ] complexes of a bis-silylenyl carborane have been synthesised with three interconvertible ligand oxidation states. Further reduction using K(C 10 H 8 ) furnishes 1,4-naphthalene derivatives, indicative of low oxidation state Al intermediates.

Herein, the first report on the isolated and unambiguously proven benzene radical trianion is presented. This unprecedented radical oxidation state of benzene is stabilized through two trivalent rare earth (RE) metal cations each supported by a bis(guanidinate) scaffold. Specifically, the one‐electron chemical reduction of the neutral inverse‐sandwich yttrium complex [[{(Me 3 Si) 2 NC(N i Pr) 2 } 2 Y] 2 ( μ – ƞ 6 : ƞ 6 –C 6 H 6 )] 1 , containing a benzene dianion, with potassium graphite (KC 8 ) in the presence of [2.2.2]‐cryptand yielded the title complex [K([2.2.2]‐cryptand)][[{(Me 3 Si) 2 NC(N i Pr) 2 } 2 Y] 2 ( μ – ƞ 6 : ƞ 6 –C 6 H 6 • )] 2 , featuring a benzene radical trianion. Analyses through single‐crystal X‐ray diffraction, EPR and UV–vis spectroscopy, elucidated its molecular structure and revealed strong [Y III –(C 6 H 6 ) 3–• –Y III ] metal–radical interactions. Although the Y centers remain in the +3 oxidation state, the spin density of the unpaired electron resides primarily on the benzene trianion moiety and extends toward the Y III ions. Density functional theory (DFT) calculations on 2 corroborate this assignment and further suggest weak aromaticity for the benzene radical trianion.

The first silylone-3d-metal complexes, LSiCu(NacNacM) (2) [L = 1,2-(RSi)2-1,2-C2B10H10, R = PhC(NtBu)2; NacNacM = HC(CMeNMes)2, Mes = 2,4,6-Me3-C6H2] and LSiNi(NacNacD) (3) [NacNacD = HC(CMeNDipp)2, Dipp = 2,6-iPr2-C6H3], are reported, resulting from the reaction of the strongly σ-donating and chelating bis(silylenyl)-ortho-carborane silylone LSi0 with [(NacNacMCu)2benzene] and [(NacNacDNi)2toluene], respectively. Density Functional Theory (DFT) analyses reveal that complex 2 features a Si0→CuI dative bond, while 3 exhibits a Si0→NiI bond. Oxidation of the Si0-NiI species 3 with [Cp2Fe]+ occurs at the Ni site to form the [3]+ cation with a Si0→NiII coordination.

As a by‐product of biofuel production, glycerol needs to find its use in various applications, for example, as a substrate for electrosynthesis of more valuable chemicals. The glycerol oxidation reaction (GOR) in aqueous media is technologically feasible but produces various products with hard‐to‐control selectivity. Less explored is the electrooxidation of anhydrous glycerol, which theoretically limits possible products to aldehydes/ketones, including high‐cost glyceraldehyde. Herein, the GOR with gold electrodes is investigated using glycerol and acetonitrile as solvents without and with base, TEMPO (2,2,6,6‐tetramethylpiperidine 1‐oxyl) redox mediator, and a copper(I)‐bipyridyl catalyst added into the lithium bis(trifluoromethanesulfonyl)imide electrolyte solutions. Both redox‐mediated and heterogeneous oxidation are slow when glycerol is used as a solvent even at 90 °C, as in particular probed by Fourier‐transformed alternating current voltammetry. Redox‐mediated glycerol oxidation to glyceraldehyde is achieved in acetonitrile at a yield rate of 6 ± 3 nmol s −1 cm −2 , but the reaction essentially stops after ≈1 h of electrolysis. Heterogeneous catalytic GOR in acetonitrile is more stable but requires significantly more positive potentials and produces a mix of products. While demonstrating the possibility of selective anhydrous glycerol electrooxidation, our results highlight the need for improvements in the mediator and catalyst designs.

The first N-heterocyclic carbene (NHC)-stabilized diboraoxirane complex 4 [NHC = IPr = C{N(iPr)CMe}2] was synthesized through the reduction of the corresponding bis(dichloroboryl-IPr)xanthene 3 with potassium graphite. Intriguingly, its formation stems from a diboron(I)-mediated C-O-C deoxygenation of the xanthene spacer via a bis(borylene)xanthene as a reactive intermediate. Consistent with the proposed pathway, bis(borylene)xanthene 6 with three-coordinate B(I) atoms could be isolated when the sterically less demanding NHC ligand IMe [IMe = C{N(Me)CMe}2] was employed. Due to its ring strain, the B-B bond of the B2O ring in 4 undergoes versatile ring-expansion reactions with small molecules to engender new boron-containing heterocycles. In fact, oxidation of 4 with trimethylamine N-oxide, O2, and elemental sulfur afforded the unprecedented 1,3-dioxa-2,4-diboretane 7, 1,3,4-trioxa-2,5-diborolane 8, and 1-oxa-3,4-dithio-2,5-diborolane 9, respectively. Moreover, 4 activates isocyanide to produce 1-oxa-2,4-diborete 10 and readily reacts with the C=O groups of benzophenone and CO2 to generate the ring-expansion products 11 and 12, respectively.