B(C6F5)3-Catalyzed Dehydrocoupling of POSS Silanols with Hydrosilanes: A Metal-Free Strategy for Effecting Functionalization of Silsesquioxanes

What do we know about bifunctional cage-like T8 silsesquioxanes? Theory versus lab routine

In this article, we explore theoretical validations of experimental findings pertaining to the classical corner-capping reactions of a commercially available heptaisobutyltrisilanol cage to mono-substituted phenylhepta(isobutyl)-POSS cages. Additionally, the process of opening a fully condensed cage is tracked to assess the possibility of isolating and separating the resulting isomers. The corner-capping reactions of potential silanotriols, both as monomers and dimers, and the impact of these structural motifs on their closing to bifunctional POSS cages are also investigated. Our studies highlight that analyzing experimental results alone, without incorporating complex theoretical investigations, does not offer a clear understanding of the reactions involving multiple simultaneously reacting substrates, which may also undergo further transformations, potentially complicating the conventional pathways of classic corner-opening/capping reactions.

Tris(pentafluorophenyl)borane-catalyzed Hydride Transfer Reactions in Polysiloxane Chemistry-Piers-Rubinsztajn Reaction and Related Processes

Tris(pentafluorophenyl)borane (TPFPB) is a unique Lewis acid that catalyzes the condensation between hydrosilanes (Si-H) and alkoxysilanes (Si-OR), leading to the formation of siloxane bonds (Si-OSi) with the release of hydrocarbon (R-H) as a byproduct-the so-called Piers-Rubinsztajn reaction. The analogous reactions of hydrosilanes with silanols (Si-OH), alcohols (R-OH), ethers (R-OR') or water in the presence of TPFPB leads to the formation of a siloxane bond, alkoxysilane (Si-OR or Si-OR') or silanol (Si-OH), respectively. The above processes, often referred to as Piers-Rubinsztajn reactions, provide new synthetic tools for the controlled synthesis of siloxane materials under mild conditions with high yields. The common feature of these reactions is the TPFPB-mediated hydride transfer from silicon to carbon or hydrogen. This review presents a summary of 20 years of research efforts related to this field, with a focus on new synthetic methodologies leading to numerous previously difficult to synthesize well-defined siloxane oligomers, polymers and copolymers of a complex structure and potential applications of these new materials. In addition, the mechanistic aspects of the recently discovered reactions involving hydride transfer from silicon to silicon are discussed in more detail.

Cobalt-Catalyzed Dehydrogenative C-H Silylation of Alkynylsilanes

Herein, we report that a cobalt catalyst permits the general synthesis of substituted alkynylsilanes through dehydrogenative coupling of alkynylsilanes and hydrosilanes. Several silylated alkynes, including di‐ and trisubstituted ones, were prepared in a one‐step procedure. Thirty‐seven compounds were synthesized for the first time by applying our catalyst system. The alkynylsilanes bearing hydrosilyl moieties provide an opportunity for further functionalization (e. g., hydrosilylation). The use of primary silanes as substrates and precatalyst activators permits the use of inexpensive and easily accessible 3d metal precatalysts, and avoids the presence of additional activators.

Alkenyl-Functionalized Open-Cage Silsesquioxanes (RSiMe2O)3R'7Si7O9: A Novel Class of Building Nanoblocks

Trifunctional incompletely condensed polyhedral oligomeric silsesquioxanes (RSiMe₂O)₃R′₇Si₇O₉ (IC-POSSs) are considered as intriguing building nanoblocks dedicated to constructing highly advanced organic–inorganic molecules and polymers. Up to now, they have been mainly obtained via hydrosilylation of olefins, while the hydrosilylation of the C≡C bonds has not been studied at all, despite the enormous potential of this approach resulting from the possibility of introducing 3, 6, or even more functional groups into the IC-POSS structure. Therefore, in this work, we present a highly selective and efficient synthesis of the first example of tripodal alkenyl-functionalized IC-POSSs, obtained via platinum-catalyzed hydrosilylation of the terminal and internal alkynes, as well as symmetrically and nonsymmetrically 1,4-disubstituted buta-1,3-diynes with silsesquioxanes (HSiMe₂O)₃R′₇Si₇O₉ (R′ = i-C₄H₉ (1a), (H₃C)₃CH₂C(H₃C)HCH₂C (1b)). The resulting products are synthetic intermediates that contain C=C bonds and functional groups (e.g., OSiMe₃, SiR₃, Br, F, B(O(C(CH₃)₂)₂ (Bpin)), thienyl), which make them suitable for application in the synthesis of novel, complex, hybrid materials with unique properties.

The first example of the synthesis of alkenyl-functionalized open-cage silsesquioxanes (IC-POSS) via platinum-catalyzed hydrosilylation of C−C triple bonds in alkynes and buta-1,3-diynes is presented. The optimized synthetic procedure allowed for the selective and efficient synthesis of 20 new functional molecules capable of further modification by hydrosilylation, hydroboration, or other chemical processes.

Vinyl-Functionalized Janus Ring Siloxane: Potential Precursors to Hybrid Functional Materials

A vinyl-functionalized all-cis-tetrasiloxycyclotetrasiloxane [ViSi(OSiMe2H)O]4 (Vi = vinyl group) Janus precursor was prepared from potassium cyclotetrasiloxane silanolate. The Janus precursor was selectively modified at its dimethylhydrosilyl groups [-SiMe2H] via the Piers-Rubinsztajn reaction to obtain a family of new tetravinyl-substituted Janus rings [ViSi(OR')O]4 containing various functional groups in moderate yields. Remarkably, the tetravinyl groups on the structure remained intact after modification by the Piers-Rubinsztajn reaction. Since these synthesized compounds possess multiple functional groups (up to eight per molecule), they are potential precursors for advanced hybrid organic-inorganic functional materials.

Tris(pentafluorophenyl)borane catalyzed C-C and C-heteroatom bond formation

A series of boron based Lewis acids have been reported to date, but among them, tris(pentafluorophenyl)borane (BCF) has gained the most significant attention in the synthetic chemistry community. The viability of BCF as a potential Lewis acid catalyst has been vastly explored in organic and materials chemistry due to its thermal stability and commercial availability. Most explorations of BCF chemistry in organic synthesis has occurred in the last two decades and many new catalytic reactivities are currently under investigation. This review mainly focuses on recent reports from 2018 onwards and provides a concise knowledge to the readers about the role of BCF in metal-free catalysis. The review has mainly been categorized by different types of organic transformation mediated through BCF catalysis for the C-C and C-heteroatom bond formation.

Janus ring siloxane: a versatile precursor of the extended Janus ring and tricyclic laddersiloxanes

All-cis-tetrasiloxycyclotetrasiloxanes (Janus ring siloxanes) were facilely prepared from all-cis-cyclotetrasiloxanetetraol or sodium cyclotetrasiloxane silanolates. Moreover, we demonstrated the synthesis of extended Janus rings, [RSi(OR')O]4, containing various functional groups, via the Piers-Rubinsztajn reaction using a Janus ring siloxane as a precursor. Remarkably, we discovered the formation of an unexpected all-cis tricyclic laddersiloxane as a by-product. These synthesized compounds can be potential monomers of well-defined cage silsesquioxanes, Janus-type nanomaterials, and porous materials.

Silylation of silanols with hydrosilanes via main-group catalysis: the synthesis of unsymmetrical siloxanes and hydrosiloxanes

Apart from some specific synthetic solutions, a dehydrogenative coupling of silanols with hydrosilanes seems to be the most atom-economical and practical method for the formation of unsymmetrical siloxanes.