Synthetic application of silicates/silanolates and their hydrolyzed polysilanol siloxanes for polyhedral oligomeric silsesquioxanes (POSSs)

Abstract

Several types of silicate and their hydrolyzed polysilanols were applied to the synthesis of polyhedral oligomeric silsesquioxanes (POSSs). Silicate cubic octasilicate [Si 8 O 20 ] 8− 5 was silylated with trimethylchlorosilane to yield the incompletely trimethylsilylated cubic octasilicate [Si 8 O 20 ](SiMe 3 ) 7 H 1b bearing one silanol in addition to the totally trimethylsilylated derivative [Si 8 O 20 ](SiMe 3 ) 8 1a. Further silylation of the monosilanol 1b with dimethylchlorosilane and α,ω-hydridochlorooctamethylt etrasiloxane resulted in the formation of POSSs 1c,d, which have hydrosilyl groups as elongated siloxane side chain. Attempts to generate an amino-substituted POSS via chloromethyldimethylsilylation of silicate 5 followed by reaction with amine as well as lithium amide failed. Amino-substitution was accomplished via the use of amine as a catalyst for the capping reaction of incompletely condensed trisilanol 10b with γ-aminopropyltrimethoxysilane affording mono amino-functionalized POSSs 2b,c in moderate yields. Another group of silanolates 7-9 was hydrolyzed with AcOH or HCl to give the corresponding cyclic polysilanol siloxanes 11a-c, respectively.Amine-catalyzed condensation of several of these polysilanol siloxanes 11a-c resulted in the formation of POSSs in high yields depending on the structure of substrates.

Silsesquioxane Cages under Solvent Regimen: The Influence of the Solvent on the Hydrolysis and Condensation of Alkoxysilane

“…This maneuver could heighten their reactivity in corner-capping reactions involving trialkoxysilanes. In line with Kawakami’s observations, the phenyl cage of POSS(OH) 3 does not undergo corner-capping with 3-aminopropyltriethoxysilane within an acetone medium in the presence of triethylamine (contrary to the less sterically demanding isobutyl cage). Should the root of this scenario lie in a pronounced inclination toward dimerization, employing a separating solvent might potentially elevate the reaction yields.…”

“…Nonetheless, the crystal structure of the monomeric form of POSS(OH) 3 ( mono-POSS(OH) 3 ) is unveiled here for the first time (Figure B). This derivative was acquired utilizing the methodology previously reported by Kawakami …”

“…This particular silanol group's distinctive behavior could likely be attributed to robust intramolecular hydrogen bonding, which in turn lowers the pK a of the silanol group's hydrogen, enhancing its acidity. The crystal structure depicted in Figure 1B can also provide insight into the rationale behind performing the synthesis of POSS(OH) 3 in THF 47 and not, like DDSQ(OH) 4 , in isopropanol. 32 Evidence from prior research 41,55 has substantiated that the structure of POSS(OH) 3 is bolstered by the potential for dimerization (as supported by density functional theory (DFT) calculations).…”

“…The DDSQ(OH) 4 and POSS(OH) 3 were prepared as reported previously with yields of 58 and 80%, respectively. 32,47 Single crystals of DDSQ(OH) 4 and POSS(OH) 3 solvates were obtained by the slow evaporation of toluene (for DDSQ(OH) 4 •toluene) and isopropanol (for DDSQ(OH) 4 •2(isopropanol) and mono-POSS(OH) 3 ).…”

Copper‐Promoted Formation of Vinylsiloxanes

“…In the last decades, non‐hydrolytic processes, including sol‐gel reactions, were found to be very efficient for precise design of siloxane‐based materials. Several types of cross‐coupling reactions of halosilanes with silanols, silanolates, or alkoxysilanes have been reported, but special emphasis must be placed on processes using an extraneous source of oxygen, such as ethers, air or dimethyl sulfoxide . In summary, the development of one‐pot efficient synthesis of siloxanes has continued to intensify in the last decade and will continue to expand in the future.…”