Organic Substituents Research Articles

Ligand Substituent Effects on the Electronic Properties of Lindqvist‐Type Polyoxometalate Multi‐Level‐Switches in the Gas Phase, Solution and on Surfaces

AbstractAlthough the intrinsic electronic properties of polyoxometalates (POMs) can be greatly influenced by modifying them with organic substituents, their resistive switching behavior on surfaces dependent on the organic substituents remains largely unexplored. In this work, we assessed the importance of electron‐withdrawing and electron‐donating ligand substituents on the material properties of a series of hybrid Lindqvist‐type hexavanadates TBA2[V6O13((OCH2)3CCH2OH)2] (TBA2V6‐OH), TBA2[V6O13((OCH2)3CMe)2] (TBA2V6‐Me), TBA2[V6O13((OCH2)3CNHCOCH2Cl)2] (TBA2V6‐Cl), and TBA2[V6O13((OCH2)3CNHCOCH2‐OOCC10H15)2] (TBA2V6‐Ad) as potential resistive random‐access memory (ReRAM) components. Compared to their redox behavior in solution, changing the ligand substituents on surfaces results in no significant effect on the potential and, thus, no effect on the resistance steps in the current‐voltage profiles. However, while the current‐voltage characteristics do not change, the peripheral metal‐free substituents in the trisalkoxide framework of Lindqvist‐type hexavanadate molecules influence the adsorption and switching stability of these POMs on gold. This work highlights the noticeable differences between hexavanadate's redox properties in solution (which follow the trend observed in the gas phase) and hexavanadate's resistive switching properties on conducting surfaces. Importantly, their multi‐state switching behavior is not significantly altered by the different type of substituent at the periphery of the trisalkoxo ligands.

Origin of the Nonlinear Optical Response in Organotetrel Molecules, (Hetero)adamantane-Type Clusters with Organic Substituents, and Related Species.

The nonlinear optical response of (hetero)adamantane-type clusters and organotetrel molecules with the general formula [(RT)4E6] and [TR4] (T = group 14, R = organic substituents, E = S, CH2) is investigated from first principles. These clusters have been reported to efficiently convert infrared radiation into white light and are therefore extremely attractive functional materials for a multitude of applications. We demonstrate that the optical nonlinearities of the clusters in the range from 0 to 3 eV have their origin in electronic transitions within the substituents. The cluster core does not directly take part to the generation process; however, it strongly affects the intensity of the linear and nonlinear response. The relationships between optical properties and cluster symmetry, stoichiometry, substituent field, core composition, and further structural characteristics are investigated by systematical variation of R and T. This also demonstrates the possibility to finely tune the intensity as well as the frequency dependence of the optical response. Upon formation of cluster dimers, the intensity of the nonlinearities depends on the overall dimer geometry. In the case of heterogeneous dimers, the optical response strongly resembles that of a dominant cluster. Similarly, upon formation of cluster crystals, the compound inherits the optical characteristics of the parent molecules.

Theoretical Investigations and Comparisons of the Amorphous Structures of Adamantane-like Cluster Materials Utilizing Molecular Dynamics Simulations.

Cluster materials of the composition AdR4 (Ad = adamantane, R = organic substituent) and [(RT)4E6] (R = organic substituent; T = Si, Ge, Sn; and E = S, Se, Te) exhibit directional white light emission or produce second harmonics when irradiated with a continuous wave infrared laser source. The nature of the nonlinear optical properties correlates with the macroscopic structures of the cluster materials. The desired white light emission predominantly occurs in amorphous materials. It is therefore crucial to understand the geometric structures of the materials and the order within the materials. Here, we investigate the geometric structures of 12 different adamantane-like cluster materials by molecular dynamics simulations using a nonperiodic particle approach. The comparison of the calculated structure factors for two cluster materials with the corresponding experimental data obtained from diffraction and EXAFS measurements shows very good agreement. Our computations revealed that, on the one hand, larger, more flexible core structures (Ad < {Si4S6} < {Ge4S6} < {Sn4S6}) tend to lead to amorphous solids. On the other hand, larger substituents (methyl < phenyl < naphthyl) lead to more defined nearest neighbor interactions, with a tendency toward crystalline solids. Overall, our results show that a beginning order in the material results from a combination of the degree of flexibility of the core structure and the variation of the nearest neighbor interaction determined by the substituents.

Dimers and 2D Networks of Adamantane-Related Ternary Organosilicon Coinage Metal Sulfide Clusters.

Adamantane-type organotin sulfide clusters were recently shown to react with coinage metal phosphine complexes under replacement of an organic substituent by a metal-phosphine unit. An extension of such studies involving the silicon-based congener [(PhSi)4S6] (A) revealed that the cluster core will be partly disassembled and a {PhSi} moiety is replaced by a coinage metal phosphine complex to form [(Et3PAg)3(PhSi)3S6] (B) and [Na2(thf)2.33][(Me3PCu)(PhSi)3S6] (C). Herein, we present an extension of this work upon variation of the reactants and reaction conditions. Besides the isolation of crystalline precursor complexes [CuCl(PMe2Ph)3] (1) and [AgCl(PMe2Ph)2]2 (2), the study addresses reactions of A with AgCl and a phosphine ligand in CH2Cl2, upon which A is completely disassembled to form [(Ph3P)3Ag(μ-S)SiCl2Ph] (3). In another case a CH2 group, most likely stemming from CH2Cl2, was attached to the ligand, thus generating [{PhCl(S)SiSCH2P(Ph2)CH2CH2}2] (4). Upon using CuCl and 1,4-bis(diphenylphosphino)butane (dppb) we isolated the phosphine-bridged analog of B, [{(dppbCu2)CuP(Ph2)(CH2CH2)(PhSi)3S6}2] (5). In order to receive the yet elusive silver homolog of C, we used PMe2Ph as a bulkier ligand. This way we generated a 2D coordination polymer of the desired composition, [Na2(thf)1.5][(Me2PhPAg)(PhSi)3S6] (6). UV-visible spectra of 6 indicated a bandgap of 3.89 eV, thus blue-shifted in regards to B and C.

Aromaticity of tropylium derivatives: When and why might captodative structures be preferred over the isomeric push‐pull structures?

AbstractAn intriguing question in the general problem of aromaticity is whether captodative aromatic systems with the donor and acceptor substituents at the same carbon of the CC bond can be more stable than the π‐conjugated push‐pull counterparts? The analysis of electronic, magnetic, and structural criteria of aromaticity showed that for conventional organic substituents XO, TfN, (NC)2C, (NO2)2C, Tf2C, the push‐pull tropylidene derivatives [tropylium]+CHCHX− are expectedly more stable than their captodative isomers [tropylium]+C(X−)CH2, with the lowest ΔE for the most strong acceptor Tf2C. A different behavior is observed for XMHlg3 (MB, Al; HlgF, Cl). They are not only structurally and magnetically most aromatic in both series but show the inverse stability of the push‐pull and captodative isomers, the latter being more stable by up to 10 kcal/mol (in gas).The difference between the MHlg3 groups and conventional organic groups is that in the latter the electron density is transferred to the π‐system of the substituent, while the former can accept it only to the σ*(CM) orbital. Thus, when the electron donor and acceptor effects are separated between the σ and π systems, captodative isomers can be more stable than their push‐pull isomers with more extended conjugation.

Characterization of Germanium Nanoparticles from Arylgermanium Trihydrides.

Germanium is a promising basis for nanomaterials due to its low toxicity and valuable optical and electronic properties. However, germanium nanomaterials have seen little research compared to other group 14 elements due to unpredictable chemical behavior and high costs. Here, we report the dehydrocoupling of o-tolylgermanium trihydride to amorphous nanoparticles. The reaction is facilitated through reflux at 162 °C and can be accelerated with an amine base catalyst. Through cleavage of both H2 and toluene, new Ge-Ge bonds form. This results in nanoparticles consisting of crosslinked germanium with o-tolyl termination. The particles are 2-6 nm in size and have masses above approximately 3500 Da. The organic substituents are promising for further functionalization. Combined with strong absorption up to 600 nm and moderate solubility and air stability, there are numerous possibilities for future applications.

Hyperbranched, Functional Polyethoxysiloxanes: Tunable Molecular Building Blocks.

Functional silanes are multifaceted cross-linkers, compatibilizers, coupling agents, and surface modifiers. Herein, we present organofunctional polysiloxane building blocks that offer great versatility in terms of molecular weight, degree of condensation, and the choice and loading of organic substituent groups. The organofunctional polyethoxysilanes (funPEOS) are prepared in a one-pot, two-step process: synthesis of the PEOS carrier/substrate, followed by grafting a functional silane "shell", both based on condensation with acetic anhydride. The reaction was optimized at the lab scale and scaled up to a 7 L reactor. The acetylation, condensation, and hyperbranched structure of the carrier were confirmed by 29Si NMR, while 29Si-29Si 2D INADEQUATE NMR provides strong evidence for the grafting of functional silanes onto the carrier (Q-T coupling). IR, 1H, and 13C NMR spectroscopy demonstrate that the functional groups remain intact. The molar mass can be tailored by stoichiometric control of the acetic anhydride to silane monomer ratio (M n 3500-20,000 g/mol). The compounds are stable organic liquids with a long shelf life. Selected applications are presented: scratch-resistant coatings with water contact angles of ∼90°, stable water emulsions, and surfactant-free, mesoporous silica foams.

Exploring the Effects of Se Basicity on a Te···Se Interaction Supported by a Rigid Indazolium Backbone.

With an interest in chalcogen bonding, we use a rigid indazolium backbone to install a formally zero-valent Se center next to a divalent Te center, allowing us to investigate the effects of oxidation of the Se center on the observed Te···Se interaction. Through spectroscopic and computational comparison of the Se(0) species with its Se(II) counterpart and their monochalcogen analogues, we experimentally and computationally investigate the effect of modulating Se basicity on the resulting Te···Se interaction. Comparison with well-studied naphthalene and acenaphthene variants indicates that the increased basicity of the Se(0) center allows for a comparably strong Te···Se interaction despite longer peri distances and a larger splay angle. Finally, our study illuminates the potential non-innocence of cationic organic substituents in chalcogen-bonding catalysis of the transfer hydrogenation of quinolines.

Phenyl-Substituted Cage Silsesquioxane-Based Star-Shaped Giant Molecular Clusters: Synthesis, Properties, and Surface Segregation Behavior.

The crystallinity, solubility, and physical properties of polyhedral oligomeric silsesquioxane (POSS) compounds are highly dependent on their organic substituents. We previously synthesized a series of isobutyl-substituted star-shaped POSS derivatives with aliphatic chain linkers of different length. In this study, we prepared C3- and C6-linked phenyl-substituted star-shaped POSS derivatives (3Ph-C3 and 3Ph-C6) by the hydrosilylation of heptaphenylallyl- and hexenyl-POSS (1a and 1b) and octadimethylsiloxy-Q8-silsesquioxane (Q8M8H) (2), respectively, and their properties were compared with those of the corresponding isobutyl-substituted derivatives (5iBu-C3 and 5iBu-C6). Although 3Ph-C6 was only soluble in chloroform and insoluble in tetrahydrofuran (THF) and toluene, 3Ph-C3 was soluble even in THF and toluene, suggesting that the shorter linkers of the derivative afford a wider range of solvents for dissolution. Differential scanning calorimetry analysis showed that 3Ph-C3 exhibited a baseline shift at 190 °C and an endothermic peak at 316 °C. However, no clear baseline shift was observed for 3Ph-C6. Thermogravimetric analysis showed that the shorter linker in the phenyl-substituted star-shaped POSS derivative significantly increased the decomposition temperature compared with the longer linker. The annealed cast film of 3Ph-C3 at 340 °C above its melting temperature formed a transparent film even after cooling to room temperature. However, an opaque whitish film was formed in the case of 3Ph-C6. Poly(methyl methacrylate) (PMMA) films containing 2 wt % 3Ph-C3 and 3Ph-C6 were prepared by casting their chloroform solutions onto glass substrates overnight at room temperature. The static water contact angle measurements and XPS analysis for the castings film containing 3Ph-C3 and 3Ph-C6 suggested that degree of the segregation amount of 3Ph-C3 was larger than that of 3Ph-C6. The shorter linker length in the phenyl-substituted star-shaped POSS derivative, 3Ph-C3, with its greater predicted solubility in PMMA, exhibited entropy-driven surface segregation.

Functionalization and Structural Evolution of Conducting Quasi-One-Dimensional Chevrel-Type Telluride Nanocrystals.

Interfacing organic molecular groups with well-defined inorganic lattices, especially in low dimensions, enables synthetic routes for the rational manipulation of both their local or extended lattice structures and physical properties. While appreciably studied in two-dimensional systems, the influence of surface organic substituents on many known and emergent one-dimensional (1D) and quasi-1D (q-1D) crystals has remained underexplored. Herein, we demonstrate the surface functionalization of bulk and nanoscale Chevrel-like q-1D ionic crystals using In2Mo6Te6, a predicted q-1D Dirac semimetal, as the model phase. Using a series of alkyl ammonium (-NR4+; R = H, methyl, ethyl, butyl, and octyl) substituents with varying chain lengths, we demonstrate the systematic expansion of the intrachain c-axis direction and the contraction of the interchain a/b-axis direction with longer chain substituents. Additionally, we demonstrate the systematic expansion of the intrachain c-axis direction and the contraction of the interchain a/b-axis direction as the alkyl chain substituents become longer using a combination of powder X-ray diffraction and Raman experiments. Beyond the structural modulation that the substituted groups can impose on the lattice, we also found that the substitution of ammonium-based groups on the surface of the nanocrystals resulted in selective suspension in aqueous (NH4+-functionalized) or organic solvents (NOc4+-functionalized), imparted fluorescent character (Rhodamine B-functionalized), and modulated the electrical conductivity of the nanocrystal ensemble. Altogether, our results underscore the potential of organic-inorganic interfacing strategies to tune the structural and physical properties of rediscovered Chevrel-type q-1D ionic solids and open opportunities for the development of surface-addressable building blocks for hybrid electronic and optoelectronic devices at the nanoscale.

Oligo-Condensation Reactions of Silanediols with Conservation of Solid-State-Structural Features.

Oligo- and polysiloxanes are usually prepared by condensation reactions in solvents without control of stereochemistry. Here we present a solventless thermal condensation of stable organosilanols. We investigated the condensation reactions of organosilanediols with different organic substituents, having in common at least one aromatic group. The condensation kinetics of the precursors observed by NMR spectroscopy revealed a strong dependence on temperature, time, and substitution pattern at the silicon atom. SEC measurements showed that chain length increases with increasing condensation temperature and time and lower steric demand of the substituents, which also influences the glass transition temperatures (Tg) of the resulting oligo- or polymers. X-ray diffraction studies of the crystalline silanediols and their condensation products revealed a structural correlation between the substituent location in the crystalline precursors and the formed macromolecules induced by the hydrogen bonding pattern. In certain cases, it is possible to carry out topotactic polymerization in the solid-state, which has its origin in the crystal structure.

Polyhedral Oligomeric Silsesquioxane D3h-(RSiO1.5)14.

While smaller polyhedral oligomeric silsesquioxanes TnRn (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 D3h-symmetric T14 isomer and with that the largest crystallographically characterized POSS cage with organic substituents. Treatment of the commercially available incompletely condensed T7Ph7(OH)3 silsesquioxane with catalytic amounts of trifluoromethanesulfonic acid results in high yields of the T14Ph14 framework, which is isolated in crystalline form by a simple work-up. D3h-T14Ph14 was analyzed by single crystal X-ray diffraction, multinuclear NMR spectroscopy and thermal analysis. The relative energies of all four theoretically possible T14Ph14 isomers were determined by optimization of the corresponding structure using DFT methods.

Design and Synthesis of New Fullerene Derivatives for Organic Solar Cells

Bulk heterojunction (BHJ) organic solar cells based on p-type polymers and n-type fullerene derivatives have attracted increasing attention due to their promising potential for providing low–cost solar electricity. In this paper, we will introduce our recent work on the development of new fullerene derivatives. Through Rh complex catalyzed coupling reactions and cycloaddition reactions, we attached several organic functional groups to the fullerene skeleton. It was found that the organic substituents had little impact on the fullerene energy levels. Instead, the organic substituents have huge impact on the other physical properties of the resulting fullerene derivatives, such as solubility, crystallinity, and electron mobility. We designed and synthesized a novel series of alkoxy substituted indene derivatives as solubilizing groups for fullerenes. Preliminary experimental results demonstrated that these 5 alkoxyindene modified C70 derivatives are superior to widely used PC71BM when blended with poly[N-heptadecanyl-2,7 carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'- benzothiadiazole)] (PCDTBT) in BHJ solar cells. The device series resistance decreased from 10 cm2 for the PC71BM based device to 4 cm2 for the 5-methoxyindene-C70 monoadduct based device. As a result, the device fill factor increased from 0.60 to 0.69, and the overall EQE-calibrated power conversion efficiency was enhanced from 5.6% to 6.2%.

Control of thermal and mechanical properties by double-cyclopolymerization and copolymerization of trifunctional POSS with varying organic substituents

Abstract Phenyl- and trifluoropropyl-substituted corner-opening type cage silsesquioxane (CO-POSS) monomers capped with methacrylethoxypropyldimethylsiloxy groups at the three silanol moieties were prepared by the hydrosilylation of trisdimethylsilyl-capped heptaphenyl- and heptatrifluoropropyl-substituted trisilanols with ethylene glycol monoallyl ether and subsequent reaction with methacryloyl chloride. Reversible addition-fragmentation chain transferpolymerization was performed on these monomers, and their structures and properties were compared to those of their previously-reported isobutyl-substituted counterparts. The polymer with a phenyl group exhibited enhanced thermal and mechanical properties, whereas the polymer with a trifluoropropyl group exhibited not only water repellency but also oil repellency. In addition, trifunctional CO-POSS monomers with different organic substituents could be used for double-cyclocopolymerization, and tuning of their properties was achieved. Furthermore, the trifunctional CO-POSS monomer could be used for double-cyclocopolymerization with methyl methacrylate without cross-linking.

A Computational Chemistry Investigation of the Influence of Steric Bulk of Dithiocarbamato-Bound Organic Substituents upon Spodium Bonding in Three Homoleptic Mercury(II) Bis(N,N-dialkyldithiocarbamato) Compounds for Alkyl = Ethyl, Isobutyl, and Cyclohexyl

Three homoleptic Hg(S2CNR2)2, for R = ethyl (1), isobutyl (2), and cyclohexyl (3), compounds apparently exhibit a steric-dependent supramolecular association in their crystals. The small group in 1 allows for dimer formation via covalent Hg–S interactions through an eight-membered {–HgSCS}2 ring as the dithiocarbamato ligands bridge centrosymmetrically related Hg atoms; intradimer Hg···S interactions are noted. By contrast, centrosymmetrically related molecules in 2 are aligned to enable intermolecular Hg···S interactions, but the separations greatly exceed the van der Waals radii. The large group in 3 precludes both dimerization and intermolecular Hg···S interactions. Computational chemistry indicates that the potential region at the Hg atom is highly dependent on the coordination geometry about the Hg atom. Intramolecular (1) and intermolecular (2) spodium bonding (SpB) is demonstrated. Even at separations approaching 0.4 Å beyond the sum of the assumed van der Waals radii, the energy of the stabilization afforded by the structure directs SpB in 2 amounts to approximately 2.5 kcal/mol. A natural bond orbital (NBO) analysis points to the importance of the LP(S) → σ*(Hg–S) charge transfer and to the dominance of the dispersion forces and electron correlation to the SpB in 2.

Steric congestion in heavy pnictines alters oxidative halogenation pathways

Dihalotriorganopnictoranes serve as important synthetic precursors in Group 15 chemistry, but the influence of the organic substituents on the synthesis and reactivity of these compounds remains underexplored for the heavy pnictogens. We recently reported the isolation of Dipp3Sb (Dipp = 2,6-diisopropylphenyl). The bulky Dipp substituents permit the isolation of monomeric tetrahedral stibine oxide Dipp3SbO, yet also allow for the formation of the trigonal bipyramidal Dipp3SbF2. We now report the isolation of a sterically crowded bismuthine, Dipp3Bi. Reaction between Dipp3Bi and XeF2 afforded Dipp3BiF2, which features a distorted trigonal bipyramidal geometry in the solid state. Reaction between Dipp3Bi and PhICl2 resulted in the generation of 1-chloro-2,6-diisopropylbenzene. Reaction between Dipp3Sb and PhICl2 resulted in the formation of Dipp3SbCl2, which features a square pyramidal geometry in the solid state. Mes3SbCl2, Mes3SbBr2, Mes3BiCl2, and Mes3BiBr2 (Mes = mesityl) were structurally characterized and all exhibit trigonal bipyramidal geometries in the solid state. Solution-phase spectroscopic measurements reflect the fluxionality of all of these molecules, but theoretical analyses in the gas phase suggest that the square pyramidal geometry of Dipp3SbCl2 is more thermodynamically favorable than the trigonal bipyramidal geometry, possibly due to the presence of intramolecular secondary interactions between the Dipp and Cl substituents. These results highlight the ability of Dipp substituents to alter reactivity pathways of heavy pnictines.

Polymers with double‐decker and side‐opened cage silsesquioxanes: Effects of cage structures on materials properties

AbstractCage silsesquioxanes, also known as polyhedral oligomeric silsesquioxanes (POSS), serve as crucial building blocks in crafting precisely designed organic–inorganic hybrid materials, given that their well‐defined silsesquioxane clusters can be adorned with organic substituents. While polymers with POSS in their main chains have been thoroughly examined, analyzing the correlation between cage structure and material properties in main‐chain‐type polymers remains challenging. This difficulty stems from the limited range of organic substituents on traditional POSS monomers, thereby precluding comparisons between polymers with unified substituents and different cage structures. In this study, we synthesized double‐decker silsesquioxane (DDSQ) and side‐opened POSS (SO‐POSS) monomers, both featuring phenyl groups. Subsequent platinum‐catalyzed hydrosilylation polymerization yielded main‐chain‐polymers. Both the cage and linker structures influence thermal stability and the glass transition temperature, while the hardness was primarily determined by the linker structure. This research is the first to elucidate the impact of cage structure on the material properties of main‐chain‐type POSS polymers.

Polyurethanes with open‐ and closed‐cage silsesquioxanes: Effects of organic substituents on materials properties

AbstractThe physical properties of silsesquioxane materials are commonly controlled by varying the proportion of silane coupling agents with different substituents. In contrast, with cage silsesquioxanes (polyhedral oligomeric silsesquioxane, POSS) that allow for precise molecular design, the material properties can be controlled by isomers, similar to organic materials. In this study, we synthesized polyurethanes with corner‐opened POSS (CO‐POSS) and completely condensed POSS (CC‐POSS) in the main and side chains, respectively. For the substituents on POSS, we used a combination of phenyl and isobutyl groups and investigated their effects on the physical properties by changing this combination. Notably, the thermal and mechanical properties changed in polymers where the substituents of CO‐POSS (main chain) and CC‐POSS (side chain) were interchanged. This demonstrates that the isomeric structure significantly affects the properties of silsesquioxane‐based materials and provides important design guidelines for these materials.

Effect of Linker Substituent Nature on Performance of Active Sites in UiO-66: Combined FT-IR and DFT Study.

The nature of organic linker substituents plays an important role in gas sorption and separation as well as in catalytic applications of metal-organic frameworks. Zirconium-based UiO-66 is one of the most tunable members of this class of materials. However, the prediction of its properties is still not a fully solved problem. Here, the infrared spectroscopic measurements using highly sensitive CO probe molecules, combined with DFT calculations, are used in order to characterize the performance of different acidic sites caused by the presence of different organic linker substituents. The proposed model allowed differentiation between various active sites over the UiO-66 and clarification of their behavior. The experimental IR bands related to CO adsorption can be unambiguously assigned to one type of site or another. The previously undescribed highly red-shifted band is attributed to CO adsorbed on coordinatively unsaturated zirconium sites through an O atom. The results confirm the lower and higher Lewis's acidity of coordinatively unsaturated Zr sites on linker defects in the UiO-66 structure when electron-withdrawing and electron-donating groups are, respectively, included in a terephthalate moiety, whilst the Brønsted acidity of zirconium oxo-cluster remains almost unchanged.

Silicon analogues of unsaturated hydrocarbons

The proposed communication demonstrates the efforts of researchers undertaken to prove the existence of fundamental analogies in the chemistry of structurally related compounds of carbon and silicon. Stable silicon analogues of ethylene - silenes or silaethylenes R2C=SiR2 - were obtained in 1979, disilynes R2Si=SiR2 - in 1981, and analogues of ethine or acetylene - disilins RSi≡SiR - only in 2004. Moving towards the intended goals, scientists synthesized a number of unique branched (bulky) organic and organosilicon substituents, attached them to silicon atoms, closed them from the action of oxygen and air moisture, and prevented secondary dimerization (oligomerization) reactions. The created steric protection led to the preparation of kinetically stable unsaturated silicon compounds and made it possible to characterize them by IR, NMR, UV-visible spectroscopy, and X-ray diffraction analysis.