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Al(OR^F)₃ (R^F = C(CF₃)₃) activated silica: a well-defined weakly coordinating surface anion.

ABSTRACT: Weakly Coordinating Anions (WCAs) containing electron deficient delocalized anionic fragments that are reasonably inert allow for the isolation of strong electrophiles. Perfluorinated borates, perfluorinated aluminum alkoxides, and halogenated carborane anions are a few families of WCAs that are commonly used in synthesis. Application of similar design strategies to oxide surfaces is challenging. This paper describes the reaction of Al(OR^F)₃*PhF (R^F = C(CF₃)₃) with silica partially dehydroxylated at 700 °C (SiO_2-700) to form the bridging silanol [triple bond, length as m-dash]Si-OH⋯Al(OR^F)₃ (1). DFT calculations using small clusters to model 1 show that the gas phase acidity (GPA) of the bridging silanol is 43.2 kcal mol^-1 lower than the GPA of H₂SO₄, but higher than the strongest carborane acids, suggesting that deprotonated 1 would be a WCA. Reactions of 1 with NOct₃ show that 1 forms weaker ion-pairs than classical WCAs, but stronger ion-pairs than carborane or borate anions. Though 1 forms stronger ion-pairs than these state-of-the-art WCAs, 1 reacts with alkylsilanes to form silylium type surface species. To the best of our knowledge, this is the first example of a silylium supported on derivatized silica.

SUBMITTER: Culver DB

PROVIDER: S-EPMC8148071 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Al(ORF)3 (RF = C(CF3)3) activated silica: a well-defined weakly coordinating surface anion.

Culver Damien B DB Venkatesh Amrit A Huynh Winn W Rossini Aaron J AJ Conley Matthew P MP

Chemical science 20191219 6

Weakly Coordinating Anions (WCAs) containing electron deficient delocalized anionic fragments that are reasonably inert allow for the isolation of strong electrophiles. Perfluorinated borates, perfluorinated aluminum alkoxides, and halogenated carborane anions are a few families of WCAs that are commonly used in synthesis. Application of similar design strategies to oxide surfaces is challenging. This paper describes the reaction of Al(ORF)3*PhF (RF = C(CF3< ...[more]

PMID: 34084380

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Project description:ConspectusResearch at historically black colleges and universities (HBCUs) started with humble beginnings by G. W. Carver at Tuskegee Institute AL, the nation's first HBCU. He is now remembered as the man who transformed one crop, peanuts to more than 300 useful products such as food, beverages, medicines, cosmetics, and chemicals. However, research was not the focus of most of the newly founded HBCUs to provide, primarily, liberal arts education and training in agriculture for the black minority. HBCUs remained segregated, lacking facilities such as libraries and scientific/research equipment comparable to those at traditionally white institutions. While the Civil Rights Act of 1964 heralded the dawn of "equal opportunity" and progressive desegregation in the South, many public HBCUs had to close or merge with white institutions due to loss of funding and/or students. In order to remain competitive in enrollment and financial support of the best talents, HBCUs have been expanding their research and federal contracts by working in collaboration with research-intensive institutions and/or minority-serving institutions (MSIs). Albany State University (ASU), an HBCU with a great tradition of in-house and extramural undergraduate research, has partnered with the laboratory of Dr. John Miller at Brookhaven National Laboratory (BNL) to offer the best training and mentorship to our undergraduates. Students synthesized and performed conductivity measurements on a new generation of ion-pair salts. One of these constitutes, potentially, a nonaqueous electrolyte for the next generation of high-energy-density batteries owing to its electrochemical properties.The quest for rechargeable batteries with greater energy density and capable of shorter recharge time at the "pump" for electrical vehicles (EVs) is leading the development of electrolytes with higher ionic mobility and greater limiting conductivity. In order to achieve high energy density, it is vital for an electrolyte to be electrochemically stable while operating at high voltages.The development of a weakly coordinating anion/cation electrolyte for energy storage applications offers a challenge of technological significance. This class of electrolytes is advantageous for the investigation of electrode processes in low-polarity solvents. The improvement arises from the optimization of both ionic conductivity and solubility of the ion pair formed between a substituted tetra-arylphosphonium (TAPR) cation and tetrakis-fluoroarylborate (TFAB), a weakly coordinating anion. The chemical "push-pull" between cation and anion affords a highly conducting ion pair in low-polarity solvents such as tetrahydrofuran (THF) and tert-butyl methyl ether (TBME). The limiting conductivity value of the salt, namely, tetra-p-methoxy-phenylphosphonium-tetrakis(pentafluorophenyl)borate or TAPR/TFAB (R = p-OCH3), is in the range of lithium hexafluorophosphate (LiPF6) used in lithium-ion batteries (LIBs). This TAPR/TFAB salt can improve the efficiency and stability of batteries over those of existing and commonly used electrolytes by optimizing the conductivity tailored to the redox-active molecules. LiPF6 dissolved in carbonate solvents is unstable with high-voltage electrodes that are required to achieve greater energy density. In contrast, the TAPOMe/TFAB salt is stable and has a good solubility profile in low-polarity solvents given its relatively great size. And it constitutes a low-cost supporting electrolyte capable of bringing nonaqueous energy storage devices to compete with existing technologies.

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Al(OR^F)₃ (R^F = C(CF₃)₃) activated silica: a well-defined weakly coordinating surface anion.

Publications

Al(OR<sup>F</sup>)<sub>3</sub> (R<sup>F</sup> = C(CF<sub>3</sub>)<sub>3</sub>) activated silica: a well-defined weakly coordinating surface anion.

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