A Mixed Heavier Si=Ge Analogue of a Vinyl Anion

The versatile reactivities of disilenides and digermenide, heavier analogues of vinyl anions, have significantly expanded the pool of silicon and germanium compounds with various unexpected structural motifs in the past two decades. We now report the synthesis and isolation of a cyclic heteronuclear vinyl anion analogue with a Si=Ge bond, potassium silagermenide as stable thf‐solvate and 18‐c‐6 solvate by the KC8 reduction of germylene or digermene precursors. Its suitability as synthon for the synthesis of functional silagermenes is proven by the reactions with chlorosilane and chlorophospane to yield the corresponding silyl‐ and phosphanyl‐silagermenes. X‐ray crystallographic analysis, UV/Vis spectroscopy and DFT calculations revealed a significant degree of π‐conjugation between N=C and Si=Ge double bonds in the title compound

Synthesis of a α-Chlorosilyl Functionalized Donor-Stabilized Chlorogermylene

Peripherally functionalized low-valent main group species allow for the introduction/interconversion of functional groups without increasing the formal oxidation state of the main group center. Herein, we report a straightforward method for the incorporation of a α-chlorosilyl moiety adjacent to the NHC-coordinated germanium(II) center

Chalcogen-Expanded Unsaturated Silicon Clusters: Thia-, Selena-, and Tellurasiliconoids

Reactions of silylenes with heavier chalcogens (E) typically result in Si=E double bonds or their π‐addition products. In contrast, the oxidation of a silylene‐functionalized unsaturated silicon cluster (siliconoid) with Group 16 elements selectively yields cluster expanded siliconoids Si7E (E=S, Se, Te) fully preserving the unsaturated nature of the cluster scaffold as evident from the NMR signatures of the products. Mechanistic considerations by DFT calculations suggest the intermediacy of a Si6 siliconoid with exohedral Si=E functionality. The reaction thus may serve as model system for the oxidation of surface‐bonded silylenes at Si(100) by chalcogens and their diffusion into the silicon bulk

Low-Valent Mx Al3 Cluster Salts with Tetrahedral [SiAl3 ]+ and Trigonal-Bipyramidal [M2 Al3 ]2+ Cores (M=Si/Ge)

Schnöckel's [(AlCp*)4] and Jutzi's [SiCp*][B(C6F5)4] (Cp*=C5Me5) are landmarks in modern main-group chemistry with diverse applications in synthesis and catalysis. Despite the isoelectronic relationship between the AlCp* and the [SiCp*]+ fragments, their mutual reactivity is hitherto unknown. Here, we report on their reaction giving the complex salts [Cp*Si(AlCp*)3][WCA] ([WCA]−=[Al(ORF)4]− and [F{Al(ORF)3}2]−; RF=C(CF3)3). The tetrahedral [SiAl3]+ core not only represents a rare example of a low-valent silicon-doped aluminium-cluster, but also—due to its facile accessibility and high stability—provides a convenient preparative entry towards low-valent Si−Al clusters in general. For example, an elusive binuclear [Si2(AlCp*)5]2+ with extremely short Al−Si bonds and a high negative partial charge at the Si atoms was structurally characterised and its bonding situation analysed by DFT. Crystals of the isostructural [Ge2(AlCp*)5]2+ dication were also obtained and represent the first mixed Al−Ge cluster

Exohedral functionalization vs. core expansion of siliconoids with Group 9 metals: catalytic activity in alkene isomerization

Taking advantage of pendant tetrylene side-arms, stable unsaturated Si6 silicon clusters (siliconoids) with the benzpolarene motif (the energetic counterpart of benzene in silicon chemistry) are successfully employed as ligands towards Group 9 metals. The pronounced σ-donating properties of the tetrylene moieties allow for sequential oxidative addition and reductive elimination events without complete dissociation of the ligand at any stage. In this manner, either covalently linked or core-expanded metallasiliconoids are obtained. [Rh(CO)2Cl]2 inserts into an endohedral Si–Si bond of the silylene-functionalized hexasilabenzpolarene leading to an unprecedented coordination sphere of the Rh centre with five silicon atoms in the initial product, which is subsequentially converted to a simpler derivative under reconstruction of the Si6 benzpolarene motif. In the case of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) a similar Si–Si insertion leads to the contraction of the Si6 cluster core with concomitant transfer of a chlorine atom to a silicon vertex generating an exohedral chlorosilyl group. Metallasiliconoids are employed in the isomerization of terminal alkenes to 2-alkenes as a catalytic benchmark reaction, which proceeds with competitive selectivities and reaction rates in the case of iridium complexes

Siliconoid Expansion by a Single Germanium Atom through Isolated Intermediates

The growth of (semi-)metal clusters is pivotal for nucleation processes in gaseous and condensed phases. We now report the isolation of intermediates during the expansion of a stable unsaturated silicon cluster (siliconoid) by a single germanium atom through a sequence of substitution, rearrangement and reduction. The reaction of ligato-lithiated hexasilabenzpolarene LiSi6Tip5 (1Li⋅(thf)2, Tip=2,4,6-triisopropylphenyl) with GeCl2⋅NHC (NHC=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) initially yields the product with exohedral germanium(II) functionality, which then inserts into an Si−Si bond of the Si6 scaffold. The concomitant transfer of the chloro functionality from germanium to an adjacent silicon preserves the electron-precise nature of the formed endohedral germylene. Full incorporation of the germanium heteroatom to the Si6Ge cluster core is finally achieved either by reduction under loss of the coordinating NHC or directly by reaction of 1Li⋅(thf)2 with GeCl2⋅1,4-dioxane

Persistent Digermenes with Acyl and α-Chlorosilyl Functionalities

We report the preparation of α-chlorosilyl- and acyl-substituted digermenes. Unlike the corresponding transient disilenes, these species with a Ge=Ge double bond show an unexpectedly low tendency for cyclization, but in turn are prone to thermal Ge=Ge bond cleavage. Triphenylsilyldigermene has been isolated as a crystalline model compound, and is the first fully characterized example of a neutral digermene with an A2 GeGeAB substitution pattern. Spectroscopic and computational evidence prove the constitution of 1-adamantoyldigermene as a first persistent species with a heavy double bond conjugated with a carbonyl moiety

Silicon‐carbon hybrid [2]‐ladderanes

The first silicon-carbon hybrid ladderanes consisting of trisila and tricarba ladder rails were obtained by the reactions of lithium disilenide R2Si=SiRLi (R=2,4,6-triisopropylphenyl) with allylchlorosilanes. The steric strain in the 1,2,6-trisilabicyclo[2.2.0]hexanes imposed by the bulky substituents leads to highly distorted ring systems with extreme puckering and long silicon-carbon bridgehead bonds. All 1,2,6-trisilabicyclo[2.2.0]hexanes show strong absorptions in the UV/vis and the rigidity of the [2]-ladderane framework gives rise to turquoise fluorescence

σ,π‐Conjugated Bis(germylene) Adducts with NHC and CAACs

Heavier tetrylenes attract attention for their potential in synthesis, catalysis and small molecule activation. The coordination by N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) results in substantial structural and electronic differences although typically only one of these yields stable derivatives for one and the same tetrylene. We now report both NHC- and CAAC-coordination to a bridged bis(germylene) motif. The NHC-coordinated bis(germylene) exhibits pyramidal germanium centers with lone pairs of electrons, while with CAAC an unprecedented stable bis(germene) with two Ge=C bonds is isolated. Spectroscopic and crystallographic evidence as well as DFT calculations confirm the effects of σ,π-conjugation between the two germanium centers in both cases. The coordination of NHC is reversible as the reaction with BPh3 liberates the transient bis(germylene) and thus provides an alternative low-temperature route towards polymers with Ge=Ge bonds

NHC-Coordinated Diphosphene-Stabilized Gold(I) Hydride and Its Reversible Conversion to Gold(I) Formate with CO2

An NHC-coordinated diphosphene is employed as ligand for the synthesis of a hydrocarbon-soluble monomeric AuI hydride, which readily adds CO2 at room temperature yielding the corresponding AuI formate. The reversible reaction can be expedited by the addition of NHC, which induces β-hydride shift and the removal of CO2 from equilibrium through the formation of an NHC-CO2 adduct. The AuI formate is alternatively formed by dehydrogenative coupling of the AuI hydride with formic acid (HCO2 H), thus in total establishing a reaction sequence for the AuI hydride mediated dehydrogenation of HCO2 H as chemical hydrogen storage material