Bromination of octaphenylsilsesquioxane

Abstract

The bromination and characterization of octaphenylsilsesquioxane is reported. The reaction is successful with a variety of methods, including microwave assisted synthesis. The analysis of the obtained product mix was carried out with a combination of high performance liquid chromatography and matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The analysis indicates that the bromination leads to multiple bromines per octaphenylsilsesquioxane molecule with a distribution dominated by statistical odds and the reaction conditions. The results showed that the bromination is not selective and does not lead to a single defined product.Abbreviations: MALDI-TOF-MS, matrix assisted laser desorption ionization time-of-flight mass spectra; POSS, polyhedral oligomeric silsesquioxane; OPS, octaphenylsilsesquioxane

Polyhedral Phenylsilsesquioxanes

“…Thus, LAs (e.g., iron or iron trichloride) will complex with Br 2 , generating cationic Br + equivalents that react readily with aromatic groups. , Iron-catalyzed bromination of [PhSiO 1.5 ] 8 or OPS was described by Laine et al (reaction ), by He et al, and by Brick et al The bromination of OPS by IBr was reported by Erben et al …”

“…The addition of the FeBr 3 catalyst after an initial stage of bromination without catalyst increases the degree of bromination beyond 16, reaction , providing highly insoluble white powders. Attempts to increase the degree of bromination to 24 led to significant Si−C cleavage as a side reaction, leaving a silanol functionalized corner, as detected in the crude reaction products by MALDI-TOF . It appears that the tribrominated corners are readily cleavedunder the highly acidic (due to HBr produced), oxidizing (due to excess Br 2 ) conditions.…”

[PhSiO1.5]8 promotes self-bromination to produce [o-BrPhSiO1.5]8: further bromination gives crystalline [2,5-Br2PhSiO1.5]8 with a density of 2.32 g cm−3 and a calculated refractive index of 1.7 or the tetraicosa bromo compound [Br3PhSiO1.5]8

“…The general mechanism involves Br 2 coordination with the Lewis acid to generate species that behave like Br + that serve as the electrophilic intermediate that attacks aromatic groups. 38,39 Iron and iron trichloride catalyzed bromination of OPS was explored by Brick et al 23 and He et al 34 The bromination of OPS by IBr was reported by Erben et al 40 These studies gave products that were relatively disordered with respect to substitution patterns and number, in part because of the insolubility of OPS, which leads to extended bromination of the first brominated species as they become more soluble with increasing bromination. However, following our success with iodination, 36,37 we concluded it might be possible to more selectively brominate OPS.…”

Polyphenylsilsesquioxanes. New structures–new properties

“…The most common of these reactions are nitration 76,77 followed by reduction to an amino group, as well as halogenation. [78][79][80][81] The feasibility of performing this reaction is rather unusual. This is due to the fact that reactions of this kind usually result in the electrophilic substitution of silicon at the ipso position of the phenyl ring.…”