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1. Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica

   https://doi.org/10.1002/ange.202205745  

   Samudrala, Kavyasripriya K. ; Huynh, Winn ; Dorn, Rick W. ; Rossini, Aaron J. ; Conley, Matthew P. ( August 2022 , Angewandte Chemie)

   Al(OC(CF₃)₃)(PhF) reacts with silanols present on partially dehydroxylated silica to form well‐defined ≡SiOAl(OC(CF₃)₃)₂(O(Si≡)₂) (1).²⁷Al NMR and DFT calculations with a small cluster model to approximate the silica surface show that the aluminum in1adopts a distorted trigonal bipyramidal coordination geometry by coordinating to a nearby siloxane bridge and a fluorine from the alkoxide. Fluoride ion affinity (FIA) calculations follow experimental trends and show that1is a stronger Lewis acid than B(C₆F₅)₃and Al(OC(CF₃)₃)(PhF) but is weaker than Al(OC(CF₃)₃) andⁱPr₃Si⁺. Cp₂Zr(CH₃)₂reacts with1to form [Cp₂ZrCH₃][≡SiOAl(OC(CF₃)₃)₂(CH₃)] (3) by methide abstraction. This reactivity pattern is similar to reactions of organometallics with the proposed strong Lewis acid sites present on Al₂O₃.

    

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2. Synthesis of a “Masked” Terminal Zinc Sulfide and Its Reactivity with Brønsted and Lewis Acids

   https://doi.org/10.1002/ange.202002364  

   Baeza Cinco, Miguel Á. ; Wu, Guang ; Kaltsoyannis, Nikolas ; Hayton, Trevor W. ( April 2020 , Angewandte Chemie)

   The “masked” terminal Zn sulfide, [K(2.2.2‐cryptand)][^MeLZn(S)] (2) (^MeL={(2,6‐ⁱPr₂C₆H₃)NC(Me)}₂CH), was isolated via reaction of [^MeLZnSCPh₃] (1) with 2.3 equivalents of KC₈in THF, in the presence of 2.2.2‐cryptand, at −78 °C. Complex2reacts readily with PhCCH and N₂O to form [K(2.2.2‐cryptand)][^MeLZn(SH)(CCPh)] (4) and [K(2.2.2‐cryptand)][^MeLZn(SNNO)] (5), respectively, displaying both Brønsted and Lewis basicity. In addition, the electronic structure of2was examined computationally and compared with the previously reported Ni congener, [K(2.2.2‐cryptand)][^tBuLNi(S)] (^tBuL={(2,6‐ⁱPr₂C₆H₃)NC(^tBu)}₂CH).

    

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3. Synthesis of a “Masked” Terminal Zinc Sulfide and Its Reactivity with Brønsted and Lewis Acids

   https://doi.org/10.1002/anie.202002364  

   Baeza Cinco, Miguel Á. ; Wu, Guang ; Kaltsoyannis, Nikolas ; Hayton, Trevor W. ( April 2020 , Angewandte Chemie International Edition)

   The “masked” terminal Zn sulfide, [K(2.2.2‐cryptand)][^MeLZn(S)] (2) (^MeL={(2,6‐ⁱPr₂C₆H₃)NC(Me)}₂CH), was isolated via reaction of [^MeLZnSCPh₃] (1) with 2.3 equivalents of KC₈in THF, in the presence of 2.2.2‐cryptand, at −78 °C. Complex2reacts readily with PhCCH and N₂O to form [K(2.2.2‐cryptand)][^MeLZn(SH)(CCPh)] (4) and [K(2.2.2‐cryptand)][^MeLZn(SNNO)] (5), respectively, displaying both Brønsted and Lewis basicity. In addition, the electronic structure of2was examined computationally and compared with the previously reported Ni congener, [K(2.2.2‐cryptand)][^tBuLNi(S)] (^tBuL={(2,6‐ⁱPr₂C₆H₃)NC(^tBu)}₂CH).

    

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

   https://doi.org/10.1039/C9SC05904K  

   Culver, Damien B. ; Venkatesh, Amrit ; Huynh, Winn ; Rossini, Aaron J. ; Conley, Matthew P. ( February 2020 , Chemical Science)

   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(CF 3 ) 3 ) with silica partially dehydroxylated at 700 °C (SiO 2-700 ) to form the bridging silanol 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 H 2 SO 4 , but higher than the strongest carborane acids, suggesting that deprotonated 1 would be a WCA. Reactions of 1 with NOct 3 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. 

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5. A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R 3 Si + Species

   https://doi.org/10.1002/ange.202117279  

   Gao, Jiaxin ; Dorn, Rick W. ; Laurent, Guillaume P. ; Perras, Frédéric A. ; Rossini, Aaron J. ; Conley, Matthew P. ( March 2022 , Angewandte Chemie)

   The silylium‐like surface species [ⁱPr₃Si][(R^FO)₃Al−OSi≡)] activates (N^N)Pd(CH₃)Cl (N^N=Ar−N=CMeMeC=N−Ar, Ar=2,6‐bis(diphenylmethyl)‐4‐methylbenzene) by chloride ion abstraction to form [(N^N)Pd−CH₃][(R^FO)₃Al−OSi≡)] (1). A combination of FTIR, solid‐state NMR spectroscopy, and reactions with CO or vinyl chloride establish that1shows similar reactivity patterns as (N^N)Pd(CH₃)Cl activated with Na[B(Ar^F)₄]. Multinuclear¹³C{²⁷Al} RESPDOR and¹H{¹⁹F} S‐REDOR experiments are consistent with a weakly coordinated ion‐pair between (N^N)Pd−CH₃⁺and [(R^FO)₃Al−OSi≡)].1catalyzes the polymerization of ethylene with similar activities as [(N^N)Pd−CH₃]⁺in solution and incorporates up to 0.4 % methyl acrylate in copolymerization reactions.1produces polymers with significantly higher molecular weight than the solution catalyst, and generates the highest molecular weight polymers currently reported in copolymerization reactions of ethylene and methylacrylate.

    

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