5256-79-1Relevant academic research and scientific papers
Higher polyhedral silsesquioxane (POSS) cage by amine-catalyzed condensation of silanols and related siloxanes
Kawakami, Yoshiteru,Yamaguchi, Kazuo,Yokozawa, Tsutomu,Serizawa, Takanori,Hasegawa, Minoru,Kabe, Yoshio
, p. 792 - 793 (2007)
Amine-catalyzed condensation of silanols (1a and 1b) and related siloxanes (1c-1f) provided polyhedral oligomeric silsesquioxane (POSS) (2a, 2e, 3f, 4a, 4f, and 5f) in moderate yields. Although phenyl, o-methylphenyl (o-MePh) and vinyl (Vi) substituted silanols (1a and 1b) and siloxanes (1c-1f) gave a separable mixture of cage compounds, amine catalyst showed the selectivity of higher cage formation. Copyright
Modified procedure for improved synthesis of some octameric silsesquioxanes via hydrolytic polycondenzation in the presence of Amberlite ion-exchange resins
Dare, Enock O.,Liu, Ling-Kang,Peng, James
, p. 3668 - 3671 (2006)
Practical alternative procedures are described for the syntheses of octavinylsilsesquioxane 1, octaphenylsilesquioxane and octabenzylsilsesquioxane. The hydrolytic polycondensation of RSiX3 (R = CH2CH-, C6H5- or C6H5CH2-; X = Cl, OCH3, or OC2H5) in the presence of solid acid or base Amberlite ion-exchange resin gave improved yields of the corresponding octameric oligosilsesquioxanes. Repetitive usage of the Amberlite resin as the hydrolysis reagent was tested during synthesis of 1. The results indicate that it could be used many times in the same solvent making the procedure a more economically viable technique. The Royal Society of Chemistry 2006.
Mechanistic Insights into the Synthesis of Fully Condensed Polyhedral Octaphenylsilsesquioxane
Qin, Zhao-Lu,Yang, Rong-Jie,Zhang, Wen-Chao,Jiao, Qing-Jie
, p. 1051 - 1056 (2019)
A comprehensive study on the efficient one-pot synthesis of polyhedral octaphenylsilsesquioxane (OPS) is reported via the hydrolytic condensation of phenyltrimethoxysilane (PTMS) in the presence of basic catalyst to investigate the specific synthesis mechanism. The synthetic reactions are monitored with real time infrared (RTIR) spectroscopy. Then RTIR coupled with 29Si nuclear magnetic resonance spectroscopy (NMR) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) are used to monitor the reactions and identify the intermediary species during the reaction. The rapid hydrolysis of PTMS is detected by RTIR. Contrary to previous reports, the ladder-like structured species are identified as intermediates during the reaction process. It is suggested that formation of caged T8 OPS is realized through the chain break and rearrangement of the ladder-like phenyltrimethoxysilanes. Accordingly, a scheme from hydrolysis of the PTMS to formation of the OPS is provided.
Cesium Carbonate-Catalyzed Oxidation of Substituted Phenylsilanes for the Efficient Synthesis of Polyhedral Oligomeric Silsesquioxanes
Li, Yuefeng,Cui, Chunming
, p. 13477 - 13485 (2018/10/24)
Cesium carbonate-catalyzed oxidation of substituted phenylsilanes (ArSiH3) in N,N-dimethylformamide (DMF) at room temperature for the efficient synthesis of polyhedral oligomeric silsesquioxanes (POSS) was described. This protocol allowed the rapid and selective access to several types of new POSS cages in modest to good yields under nonaqueous conditions. Depending on the bulkiness of the substituents on the phenyl rings, hexa- (T6), octa- (T8), and dodecaphenylsilsesquioxanes (T12) can be selectively obtained. With the more bulky 2-(2′,4′,6′-trimethylphenyl)phenyl group, the cyclic tetrasiloxane (D4) bearing four hydroxyl groups was isolated. Mechanism studies disclosed that the initial step involved the Cs2CO3-catalyzed hydrosilylation of DMF with a hydrosilane to generate a siloxymethylamine intermediate followed by the dehydrocarbonative cross-coupling of the hydrosilane with the siloxymethylamine.
Synthetic application of silicates/silanolates and their hydrolyzed polysilanol siloxanes for polyhedral oligomeric silsesquioxanes (POSSs)
Kawakami, Yoshiteru,Seino, Hirofumi,Ohtaki, Kazushi,Kabe, Yoshio
, (2017/06/27)
Several types of silicate and their hydrolyzed polysilanols were applied to the synthesis of polyhedral oligomeric silsesquioxanes (POSSs). Silicate cubic octasilicate [Si8O20]8? 5 was silylated with trimethylchlorosilane to yield the incompletely trimethylsilylated cubic octasilicate [Si8O20](SiMe3)7H 1b bearing one silanol in addition to the totally trimethylsilylated derivative [Si8O20](SiMe3)8 1a. Further silylation of the monosilanol 1b with dimethylchlorosilane and α,ω-hydridochlorooctamethyltetrasiloxane 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.
Nucleophilic attack of R-lithium at tetrahedral silicon in alkoxysilanes. An alternate mechanism
Furgal, Joseph C.,Laine, Richard M.
, p. 705 - 725 (2016/07/14)
The currently accepted mechanism for nucleophilic attack at silicon in tetraalkoxysilanes, e.g. Si(OEt)4 is suggested to involve formation of penta- and then hexacoordinated intermediates as supported by the apparent exclusive formation of R3SiOR′ and R4Si from nucleophilic attack by RLi and RMgX. Our recent discovery of a direct route from biogenic silica to tetraalkoxyspirosiloxanes prompted us to revisit this reaction as a potential route to diverse silicon-containing species with single SiC bonds as early studies demonstrate that spirosiloxanes form quite stable pentacoordinated alkoxysilane compounds. As anticipated, Si(2-methyl-2,4-pentanediolato)2 (SP) reacts with RLi (R = Ph, anthracene, phenylacetylene, etc.) at -78 °C to form pentacoordinated Si, e.g. LiPhSP equilibrates with the starting reagents even at 3:1 ratios of PhLi:SP with no evidence for formation of hexacoordinated species by mass spectral, NMR and quenching studies. Thus, quenching with MeI or Me3SiCl allows isolation of monosubstituted products from RLi:SP; RSi(OR′)3 including some ring-opened oligomers. Comparative studies of reactions of PhLi with Si(OEt)4 allows isolation of mono- and disubstituted products again even at 1:1 ratios of PhLi:Si(OEt)4. However, on standing at -78 °C for long periods of time or on warming to 0 °C, the primary product for both reactions is Ph4Si even with 0.5 equivalents of PhLi. At reaction temperatures ≥0 °C the primary product is again Ph4Si. These results suggest that hexacoordinated intermediates are not part of the substitution mechanism and may suggest that the higher-substituted compounds arise from disproportionation processes. We also briefly describe the conversion of anthracenylSP and 9,9-dimethylfluoreneSP to silsesquioxanes.
D5h [PhSiO1.5]10 synthesis via F- catalyzed rearrangement of [PhSiO1.5]n. An experimental/computational analysis of likely reaction pathways
Furgal, Joseph C.,Goodson, Theodore,Laine, Richard M.
supporting information, p. 1025 - 1039 (2016/01/15)
We describe here the synthesis and analysis of the reaction pathways leading to formation of the rare D5h decaphenylsilsesquioxane (SQ) [PhSiO1.5]10via F- catalyzed rearrangement of [PhSiO1.5]nn = 8, 12, and oligomers initially synthesized from PhSi(OEt)3. Isolated yields of ～50% [PhSiO1.5]10 are obtained via rearrangement of all starting materials. The recovered starting materials can be re-equilibrated using catalytic F- to generate similar yields in second batches. These yields arise because [PhSiO1.5]10 exhibits higher solubility and better energy stabilization (10 kcal mol-1 theory) in CH2Cl2 compared to [PhSiO1.5]8 or [PhSiO1.5]12. Reaction intermediates were identified using time dependent 19F NMR and MALDI-ToF mass spectrometry eventually equilibrating to form the 8 : 10 : 12 cages in a 1 : 3 : 1.3 equilibrium in CH2Cl2. Experimental results coupled with modeling using the Gamess computational package provide multiple reasonable pathways for SQ rearrangements to [RSiO1.5]10, starting from [RSiO1.5]8. Heats of reaction for interconversion of the model intermediates [HSiO1.5]x determined computationally, were used to select the most reasonable reaction pathways. The findings support a mechanism involving activation and cleavage of a T8 cage corner by F- attachment, followed by the corners stepwise removal as [i.e. RSi(OH)3], followed thereafter by reinsertion forming [RSiO1.5]9-OH followed by, insertion of another corner to form [RSiO1.5]10-(OH)2 and finally condensation to give [RSiO1.5]10. The most enthalpically favorable path (-24 kcal mol-1) involves a hybrid mechanism.
Influences of polyhedral oligomeric silsesquioxanes (POSSs) containing different functional groups on crystallization and melting behaviors of POSS/polydimethylsiloxane rubber composites
Zhang, Dian,Shi, Yunhui,Liu, Yufeng,Huang, Guangsu
, p. 41364 - 41370 (2015/01/08)
In this article, three kinds of polyhedral oligomeric silsesquioxanes (POSSs) - octamethylsilsesquioxane (OMS), octaphenylsilsesquioxane (OPS) and heptaphenylhydrogensilsesquioxane (H-POSS) - were successfully synthesized. Then, POSSs were incorporated into polydimethylsiloxane (PDMS) rubber through solution blending followed by open two-roll mill blending with curing agent. Finally, the blends were cured with a plate vulcanizing press and the effects of POSSs on crystallization and melting behaviors of PDMS were investigated. DSC tests indicated that crystallinity (Xc) of the OMS/PDMS composite was lowered, while Xcand the melting temperature (Tm) of the OPS/PDMS composite could be significantly enhanced when 20 wt% OPS was incorporated. OPS was proved to play a role as a nucleating agent in the crystallization of PDMS, but its nucleation mechanism was different from H-POSS which was previously studied by us. The crystals of OPS were flake-like with huge surfaces which provide templates for PDMS crystals to grow. However, due to the grafting of H-POSS onto PDMS chains, H-POSS played a role as physical crosslinking points to reduce the mobility of the PDMS chain segments. This journal is
Influences of polyhedral oligomeric silsesquioxanes (POSSs) containing different functional groups on crystallization and melting behaviors of POSS/polydimethylsiloxane rubber composites
Zhang, Dian,Shi, Yunhui,Liu, Yufeng,Huang, Guangsu
, p. 41364 - 41370 (2015/05/20)
In this article, three kinds of polyhedral oligomeric silsesquioxanes (POSSs) - octamethylsilsesquioxane (OMS), octaphenylsilsesquioxane (OPS) and heptaphenylhydrogensilsesquioxane (H-POSS) - were successfully synthesized. Then, POSSs were incorporated into polydimethylsiloxane (PDMS) rubber through solution blending followed by open two-roll mill blending with curing agent. Finally, the blends were cured with a plate vulcanizing press and the effects of POSSs on crystallization and melting behaviors of PDMS were investigated. DSC tests indicated that crystallinity (Xc) of the OMS/PDMS composite was lowered, while Xc and the melting temperature (Tm) of the OPS/PDMS composite could be significantly enhanced when 20 wt% OPS was incorporated. OPS was proved to play a role as a nucleating agent in the crystallization of PDMS, but its nucleation mechanism was different from H-POSS which was previously studied by us. The crystals of OPS were flake-like with huge surfaces which provide templates for PDMS crystals to grow. However, due to the grafting of H-POSS onto PDMS chains, H-POSS played a role as physical crosslinking points to reduce the mobility of the PDMS chain segments. This journal is
Further studies of fluoride ion entrapment in octasilsesquioxane cages; X-ray crystal structure studies and factors that affect their formation
Taylor, Peter G.,Bassindale, Alan R.,El Aziz, Youssef,Pourny, Manuel,Stevenson, Richard,Hursthouse, Michael B.,Coles, Simon J.
body text, p. 2048 - 2059 (2012/04/17)
A range of fluoride-encapsulated octasilsesquioxane cage compounds have been prepared using the TBAF route. Our studies suggest that whilst it is relatively straightforward to prepare fluoride-encapsulated octasilsesquioxane cage compounds with adjacent sp2 carbons, leading to a range of aryl and vinyl substituted compounds, the corresponding sp3 carbon derivatives are more capricious, requiring an electron withdrawing group that can stabilize the cage whilst not acting as a leaving group. Analysis by X-ray crystallography and solution 19F/29Si NMR spectroscopy of R8T8@F- reveal very similar environments for the encapsulated fluoride octasilsesquioxane cages. Migration of a fluoride ion from inside the cage to outside the cage without breaking the T8 framework and the possibility of encapsulating other anions within silsesquioxane cages have been also investigated.
