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1. Palladium‐Catalyzed Aryldifluoromethylation of Aryl Halides with Aryldifluoromethyl Trimethylsilanes

   https://doi.org/10.1002/anie.202208204  

   Choi, Kyoungmin; Mormino, Michael G.; Kalkman, Eric D.; Park, John; Hartwig, John F. (September 2022, Angewandte Chemie International Edition)

   Abstract Diaryl difluoromethanes are valuable targets for medicinal chemistry because they are bioisosteres of diaryl ethers and can function as replacements for diaryl methane, ketone, and sulfone groups. However, methods to prepare diaryl difluoromethanes are scarce, especially methods starting from abundant aryl halides. We report the Pd‐catalyzed aryldifluoromethylation of aryl halides with aryldifluoromethyl trimethylsilanes (TMSCF₂Ar). The reaction occurs when the catalyst contains a simple, but unusual, dialkylaryl phosphine ligand that promotes transmetallation of the silane. Computational studies show that reductive elimination following transmetallation occurs with a low barrier, despite the fluorine atoms on the α‐carbon, due to coordination of the difluorobenzyl π‐system to palladium. The co‐development of a cobalt‐catalyzed synthesis of the silanes broadened the scope of the process including several applications to the synthesis biologically relevant diaryl difluoromethanes. 

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2. Cooperative Bond Activation and Facile Intramolecular Aryl Transfer of Nickel–Aluminum Pincer‐type Complexes

   https://doi.org/10.1002/anie.202104050  

   Graziano, Brendan J.; Vollmer, Matthew V.; Lu, Connie C. (June 2021, Angewandte Chemie International Edition)

   Abstract Pincer‐type nickel–aluminum complexes were synthesized using two equivalents of the phosphinoamide, [PhNCH₂PⁱPr₂]⁻. The Ni⁰–Al^IIIcomplexes, {(^MesPAlP)Ni}₂(μ‐N₂) and {(^MesPAlP)Ni}₂(μ‐COD), where^MesPAlP is (Mes)Al(NPhCH₂PⁱPr₂)₂, were structurally characterized. The (PAlP)Ni system exhibited cooperative bond cleavage mediated by the two‐site Ni–Al unit, including oxidative addition of aryl halides, H₂activation, and ortho‐directed C−H bond activation of pyridine N‐oxide. One intriguing reaction is the reversible intramolecular transfer of the mesityl ring from the Al to the Ni site, which is evocative of the transmetalation step during cross‐coupling catalysis. The aryl‐transfer product,(THF)Al(NPhCH₂PⁱPr₂)₂Ni(Mes), is the first example of a first‐row transition metal–aluminyl pincer complex. The addition of a judicious donor enables the Al metalloligand to convert reversibly between the alane and aluminyl forms via aryl group transfer to and from Ni, respectively. Theoretical calculations support a zwitterionic Ni^δ−–Al^δ+electronic structure in the nickel–aluminyl complex. 

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

   https://doi.org/10.1002/anie.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 International Edition)

   Abstract 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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4. Insertion of CO ₂ Mediated by a (Xantphos)Ni ^I –Alkyl Species

   https://doi.org/10.1002/anie.201906005  

   Diccianni, Justin B.; Hu, Chunhua T.; Diao, Tianning (August 2019, Angewandte Chemie International Edition)

   Abstract The incorporation of CO₂into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of Ni^IIto Ni^Iby either Zn or Mn, followed by CO₂insertion into Ni^I‐alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu‐Xantphos)Ni^IIBr₂by Zn affords Ni^Ispecies. (tBu‐Xantphos)Ni^I‐Me and (tBu‐Xantphos)Ni^I‐Et complexes undergo fast insertion of CO₂at 22 °C. The substantially faster rate, relative to that of Ni^IIcomplexes, serves as the long‐sought‐after experimental support for the proposed mechanisms of Ni‐catalyzed carboxylation reactions. 

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5. Vapor-phase grafting of functional silanes on atomic layer deposited Al2O3

   https://doi.org/10.1116/6.0002364  

   Rozyyev, Vepa; Shevate, Rahul; Pathak, Rajesh; Murphy, Julia G.; Mane, Anil U.; Sibener, S. J.; Elam, Jeffrey W. (May 2023, Journal of Vacuum Science & Technology A)

   Fundamental studies are needed to advance our understanding of selective adsorption in aqueous environments and develop more effective sorbents and filters for water treatment. Vapor-phase grafting of functional silanes is an effective method to prepare well-defined surfaces to study selective adsorption. In this investigation, we perform vapor phase grafting of five different silane compounds on aluminum oxide (Al2O3) surfaces prepared by atomic layer deposition. These silane compounds have the general formula L3Si–C3H6–X where the ligand, L, controls the reactivity with the hydroxylated Al2O3 surface and the functional moiety, X, dictates the surface properties of the grafted layer. We study the grafting process using in situ Fourier transform infrared spectroscopy and ex situ x-ray photoelectron spectroscopy measurements, and we characterize the surfaces using scanning electron microscopy, atomic force microscopy, and water contact angle measurements. We found that the structure and density of grafted aminosilanes are influenced by their chemical reactivity and steric constraints around the silicon atom as well as by the nature of the anchoring functional groups. Methyl substituted aminosilanes yielded more hydrophobic surfaces with a higher surface density at higher grafting temperatures. Thiol and nitrile terminated silanes were also studied and compared to the aminosilane terminated surfaces. Uniform monolayer coatings were observed for ethoxy-based silanes, but chlorosilanes exhibited nonuniform coatings as verified by atomic force microscopy measurements. 

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