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D5h[PhSiO1.5]10 synthesis via F– catalyzed rearrangement of [PhSiO1.5]n. An experimental/computational analysis of likely reaction pathways

Journal Article · · Dalton Transactions
DOI:https://doi.org/10.1039/c5dt04182a· OSTI ID:1370072
 [1];  [1];  [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
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We describe here in this paper 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.
Research Organization:
Energy Frontier Research Centers (EFRC) (United States). Center for Solar and Thermal Energy Conversion (CSTEC)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0000957
OSTI ID:
1370072
Journal Information:
Dalton Transactions, Journal Name: Dalton Transactions Journal Issue: 3 Vol. 45; ISSN 1477-9226
Publisher:
Royal Society of ChemistryCopyright Statement
Country of Publication:
United States
Language:
English

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Synthetic application of silicates/silanolates and their hydrolyzed polysilanol siloxanes for polyhedral oligomeric silsesquioxanes (POSSs) journal May 2017
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Multifunctional imine-POSS as uncommon 3D nanobuilding blocks for supramolecular hybrid materials: synthesis, structural characterization, and properties journal January 2016
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Figures / Tables (21)

Scheme 1(p. 4)figure Scheme 1
Scheme 2(p. 8)figure Scheme 2
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Table 1(p. 12)table Table 1
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