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While smaller polyhedral oligomeric silsesquioxanes T n R n (POSS) are readily accessible or even commercially available, unambiguously authenticated larger systems (n>12) have barely been reported. Synthesis and isolation procedures are lengthy, and yields are often very low. Herein, we present the surprisingly straightforward and high-yielding access to the phenyl-substituted derivative of a so far only postulated second D 3h -symmetric T 14 isomer and with that the largest crystallographically characterized POSS cage with organic substituents. Treatment of the commercially available incompletely condensed T 7 Ph 7 (OH) 3 silsesquioxane with catalytic amounts of trifluoromethanesulfonic acid results in high yields of the T 14 Ph 14 framework, which is isolated in crystalline form by a simple work-up. D 3h -T 14 Ph 14 was analyzed by single crystal X-ray diffraction, multinuclear NMR spectroscopy and thermal analysis. The relative energies of all four theoretically possible T 14 Ph 14 isomers were determined by optimization of the corresponding structure using DFT methods., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

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 BPh 3 liberates the transient bis(germylene) and thus provides an alternative low-temperature route towards polymers with Ge=Ge bonds., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

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 Si 7 E (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 Si 6 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., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

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 A 2 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., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Permethylated disila[2]metallocenophanes of silicon, germanium, tin, lead, 2 a-d, (tetrelocenophanes) and antimony, 3 a,b, (pnictogenocenophanes) are described. In the case of antimony, a chloro-substituted stibonocenophane, 3 a, as well as cationic stibonocenophanium tetrachloroaluminate and tetraphenylborate salts, 3 b[X] (X=[AlCl 4 ], [BPh 4 ]), were synthesized. These represent the first examples of metallocenophanes of any Group 15 element. All compounds were studied in solution and in the solid state. Without exception the ansa-bridge exerts a strong influence on the bending angle of the two Cp-ligands. For disila[2]plumbocenophane, 2 d, its reactivity towards Group 15 halides was probed. Treatment of disila[2]plumbocenophane, 2 d, with two equivalents of phosphorus(III) chloride or arsenic(III) chloride, results in a ring-opening reaction and gives the bis(dihalopnictogenyl)-substituted products, 4 a,b., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Functionalized disilenes are valuable auxiliary tools in preparative chemistry. In the following review the various synthetic potential of disilenes as precursors is presented. Upon consumption of the Si=Si unit in disilenes, cyclic, polycyclic and cluster-like arrangements are obtainable., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report the synthesis and isolation of molecular iron germanide motifs in the stoichiometry of Fe 3 Ge and Fe 2 Ge, which are stabilized by the coordination of N-heterocyclic carbene (NHC) and carbon monoxide (CO) ligands. NHCiPr2Me2 ⋅Ge[Fe(CO) 4 ][Fe 2 (CO) 8 ] (NHCiPr2Me2 =1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene), a germanium(0) ligand with just one NHC as an auxiliary ligand, assumes a bridging coordination mode between a mononuclear [Fe(CO) 4 ] and a dinuclear [(CO) 4 FeFe(CO) 4 ] unit with rapid exchange between the two binding modes in solution. The electronic structure of this species is analysed by NBO and ELF calculations with DFT methods, as well as the mechanistic details of its fluxional coordination behaviour. Treatment of NHCiPr2Me2 ⋅Ge[Fe(CO) 4 ] [Fe 2 (CO) 8 ] with the sterically less demanding NHCMe4 (NHCMe4 =1,3,4,5-tetramethylimidazol-2-ylidene) leads to a dinuclear iron complex (NHCMe4 ) 2 Ge[Fe(CO) 4 ] 2 that contains a bridging germylone ligand with two stabilizing NHC equivalents., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the presence of a Lewis acid or base, cyclotrisilene cSi3Tip4 (Tip = 2,4,6-triisopropylphenyl) reacts with CO to form stable adducts of a 1,3-disila-2-oxyallyl zwitterion. Coordination of an N-heterocyclic carbene (NHC) to one silicon center results in a localized Si=C bond, whereas B(C6F5)3 bonds to the carbonyl moiety leading to the delocalization of the positive charge over the oxyallyl moiety. Computational analysis of the electronic structure of the Lewis acid adduct reveals a considerable interaction between the two silicon atoms in 1,3-position and thus aromaticity akin to the homocyclopropenium cation., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A catalyst- and by-product-free protocol for the synthesis of σ-π conjugated organosilicon polymers is reported. The regiospecific [2+2] cycloaddition of C≡C triple bonds to Si=Si double bonds allowed the preparation of air-stable ethynyl-terminated extended monomers from 1,4-bis(ethynyl)benzene and the para-phenylene bridged tetrasiladiene, Tip2 Si=SiTip-pC6H4-SiTip=SiTip2 (Tip = 2,4,6-iPr3C6H2). The polymer obtained from the extended monomer and further tetrasiladiene exhibits pronounced σ-π conjugation, as was evident from the red-shift in the absorption spectrum compared to model systems. We show that the thermal stability of the employed bis(alkyne) co-monomer is translated into this polymer., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

E=Si transfer: Anionic compounds capable of transferring a silicon-containing double bond are reviewed (see figure), particularly reagents with Si=Si moieties (Tip=2,4,6-iPr(3)C(6)H(2), M=Li, Na, K) and their applications towards main-group and transition-metal electrophiles, as well as their reactivity towards organic compounds. A few recently reported derivatives with Si=C (Ad=1-adamantyl) and Si=P moieties are included for completeness.Anionic compounds capable of transferring a silicon double bond are summarized following an introduction to the differences between alkenes and their heavier homologues. The main focus is on reagents with Si=Si moieties and their applications towards main-group and transition-metal electrophiles, as well as their reactivity towards organic compounds, but a few recently reported derivatives with Si=C and Si=P bonds are also included.