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1. Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel‐Boron Cooperativity in a PBP‐Ni Complex

   https://doi.org/10.1002/ange.202306315  

   Álvarez‐Rodríguez, Lucía ; Ríos, Pablo ; Laglera‐Gándara, Carlos J. ; Jurado, Andrea ; Fernández‐de‐Córdova, Francisco José ; Gunnoe, T. Brent ; Rodríguez, Amor ( July 2023 , Angewandte Chemie)

   The synthesis and characterization of (^tBuPBP)Ni(OAc) (5) by insertion of carbon dioxide into the Ni−C bond of (^tBuPBP)NiMe (1) is presented. An unexpected CO₂cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (^tBuPBOP)₂Ni₄(μ‐CO)₂(6). Mechanistic investigation of this reaction indicates a reductive scission of CO₂by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO₂activation reaction produces a three‐coordinate (^tBuP₂BO)Ni‐acyl intermediate (A) that leads to a (^tBuP₂BO)−Ni^Icomplex (B) via a likely radical pathway. The Ni^Ispecies is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (^tBuP₂BO)Ni^II(η²‐TEMPO) (7). Additionally,¹³C and¹H NMR spectroscopy analysis using¹³C‐enriched CO₂provides information about the species involved in the CO₂activation process.

    

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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. Approaching Dianionic Tetraoxadiborecine Macrocycles: 10‐Membered Bora‐Crown Ethers Incorporating Borafluorenate Units

   https://doi.org/10.1002/anie.202215772  

   Wentz, Kelsie E. ; Molino, Andrew ; Freeman, Lucas A. ; Dickie, Diane A. ; Wilson, David J. D. ; Gilliard, Jr., Robert J. ( December 2022 , Angewandte Chemie International Edition)

   The addition of non‐benzenoid quinones, acenapthenequinone or aceanthrenequinone, to the 9‐carbene‐9‐borafluorene monoanion (1) affords the first examples of dianionic 10‐membered bora‐crown ethers (2–5), which are characterized by multi‐nuclear NMR spectroscopy (¹H,¹³C,¹¹B), X‐ray crystallography, elemental analysis, and UV/Vis spectroscopy. These tetraoxadiborecines have distinct absorption profiles based on the positioning of the alkali metal cations. When compound4, which has a vacant C₄B₂O₄cavity, is reacted with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate, a color change from purple to orange serves as a visual indicator of metal binding to the central ring, whereby the Na⁺ion coordinates to four oxygen atoms. A detailed theoretical analysis of the calculated reaction energetics is provided to gain insight into the reaction mechanism for the formation of2–5. These data, and the electronic structures of proposed intermediates, indicate that the reaction proceeds via a boron enolate intermediate.

    

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5. Approaching Dianionic Tetraoxadiborecine Macrocycles: 10‐Membered Bora‐Crown Ethers Incorporating Borafluorenate Units

   https://doi.org/10.1002/ange.202215772  

   Wentz, Kelsie E. ; Molino, Andrew ; Freeman, Lucas A. ; Dickie, Diane A. ; Wilson, David J. D. ; Gilliard, Jr., Robert J. ( December 2022 , Angewandte Chemie)

   The addition of non‐benzenoid quinones, acenapthenequinone or aceanthrenequinone, to the 9‐carbene‐9‐borafluorene monoanion (1) affords the first examples of dianionic 10‐membered bora‐crown ethers (2–5), which are characterized by multi‐nuclear NMR spectroscopy (¹H,¹³C,¹¹B), X‐ray crystallography, elemental analysis, and UV/Vis spectroscopy. These tetraoxadiborecines have distinct absorption profiles based on the positioning of the alkali metal cations. When compound4, which has a vacant C₄B₂O₄cavity, is reacted with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate, a color change from purple to orange serves as a visual indicator of metal binding to the central ring, whereby the Na⁺ion coordinates to four oxygen atoms. A detailed theoretical analysis of the calculated reaction energetics is provided to gain insight into the reaction mechanism for the formation of2–5. These data, and the electronic structures of proposed intermediates, indicate that the reaction proceeds via a boron enolate intermediate.

    

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