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1. Thermochemistry and mechanisms of the Pt + + SO 2 reaction from guided ion beam tandem mass spectrometry and theory

   https://doi.org/10.1063/5.0091510  

   Armentrout, P. B. ( May 2022 , The Journal of Chemical Physics)

   The kinetic energy dependences of the reactions of Pt + ( 2 D 5/2 ) with SO 2 were studied using a guided ion beam tandem mass spectrometer and theory. The observed cationic products are PtO + and PtSO + , with small amounts of PtS + , all formed in endothermic reactions. Modeling the kinetic energy dependent product cross sections allows determination of the product bond dissociation energies (BDEs): D 0 (Pt + –O) = 3.14 ± 0.11 eV, D 0 (Pt + –S) = 3.68 ± 0.31 eV, and D 0 (Pt + –SO) = 3.03 ± 0.12 eV. The oxide BDE agrees well with more precise literature values, whereas the latter two results are the first such measurements. Quantum mechanical calculations were performed for PtO + , PtS + , PtO 2 + , and PtSO + at the B3LYP and coupled-cluster with single, double, and perturbative triple [CCSD(T)] levels of theory using the def2-XZVPPD (X = T, Q) and aug-cc-pVXZ (X = T, Q, 5) basis sets and complete basis set extrapolations. These theoretical BDEs agree well with the experimental values. After including empirical spin–orbit corrections, the product ground states are determined as PtO + ( 4 Σ 3/2 ), PtS + ( 4 Σ 3/2 ), PtO 2 + ( 2 Σ g + ), and PtSO + ( 2 A′). Potential energy profiles including intermediates and transition states for each reaction were also calculated at the B3LYP/def2-TZVPPD level. Periodic trends in the thermochemistry of the group 9 metal chalcogenide cations are compared, and the formation of PtO + from the Pt + + SO 2 reaction is compared with those from the Pt + + O 2 , CO 2 , CO, and NO reactions. 

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2. IR spectroscopic characterization of products of methane and cyclopropane activation by Ru cations

   https://doi.org/10.1016/j.ijms.2023.117165  

   Wensink, Frank J. ; Pradeep, Deepak ; Armentrout, P.B. ; Bakker, Joost M. ( January 2024 , International Journal of Mass Spectrometry)

   Methane and cyclopropane (c-C3H6) were reacted with Ru+ ions in a room temperature ion trap and the resulting products were identified using a combination of mass spectrometry, IR action spectroscopy, and density functional theory calculations. In the reaction with methane, no products with odd numbers of carbon atoms were located, whereas significant amounts of products with even numbers of carbon atoms were observed. We identified [Ru,2C,4H]+ as the Ru+ ion with an ethene ligand attached, and [Ru,4C,6H]+ as a Ru(η4-cis-1,3-butadiene)+ complex. The barrier toward formation of Ru(C2H4)+ + 2 H2 was calculated at the B3LYP/def2-TZVPPD level to be 0.80 eV above the energy of the ground state Ru+ (4F) + 2 CH4 reactants. In the reaction of c-C3H6 with Ru+, we identified the dehydrogenation product [Ru,3C,4H]+ as Ru(η2-propyne)+, [Ru,2C,2H]+ as Ru+ with an ethyne ligand, and [Ru,5C,5H]+ as Ru(η5-c-C5H5)+ having a cyclopentadienyl ligand. 

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3. Copper‐Catalyzed C(sp 3 )−H Amidation: Sterically Driven Primary and Secondary C−H Site‐Selectivity

   https://doi.org/10.1002/anie.201810556  

   Bakhoda, Abolghasem ; Jiang, Quan ; Badiei, Yosra M. ; Bertke, Jeffery A. ; Cundari, Thomas R. ; Warren, Timothy H. ( February 2019 , Angewandte Chemie International Edition)

   Undirected C(sp³)−H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C−H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C−H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C−H bonds over tertiary and benzylic C−H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C−H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N₃. Mechanistic and DFT studies indicate that C−H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ²‐N,O‐NC(O)Ar) to provide carbon‐based radicals R^.and copper(II)amide intermediates [Cu^II]‐NHC(O)Ar that subsequently capture radicals R^.to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C−H amidation selectivity in the absence of directing groups.

    

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4. Copper‐Catalyzed C(sp 3 )−H Amidation: Sterically Driven Primary and Secondary C−H Site‐Selectivity

   https://doi.org/10.1002/ange.201810556  

   Bakhoda, Abolghasem ; Jiang, Quan ; Badiei, Yosra M. ; Bertke, Jeffery A. ; Cundari, Thomas R. ; Warren, Timothy H. ( February 2019 , Angewandte Chemie)

   Undirected C(sp³)−H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C−H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C−H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C−H bonds over tertiary and benzylic C−H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C−H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N₃. Mechanistic and DFT studies indicate that C−H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ²‐N,O‐NC(O)Ar) to provide carbon‐based radicals R^.and copper(II)amide intermediates [Cu^II]‐NHC(O)Ar that subsequently capture radicals R^.to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C−H amidation selectivity in the absence of directing groups.

    

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5. Atomic Transition Probabilities for Transitions of Si i and Si ii and the Silicon Abundances of Several Very Metal-poor Stars ∗  

   https://doi.org/10.3847/1538-4365/acb642  

   Den Hartog, E. A. ; Lawler, J. E. ; Sneden, C. ; Roederer, I. U. ; Cowan, J. J. ( March 2023 , The Astrophysical Journal Supplement Series)

   We report new measurements of branching fractions for 20 UV and blue lines in the spectrum of neutral silicon (Sii) originating in the 3s²3p4s³P^o_1,2,¹P^o₁, and 3s3p³¹D^o_1,2upper levels. Transitions studied include both strong, nearly pure LS multiplets as well as very weak spin-forbidden transitions connected to these upper levels. We also report a new branching fraction measurement of the⁴P_1/2–²P^o_1/2,3/2intercombination lines in the spectrum of singly ionized silicon (Siii). The weak spin-forbidden lines of Siiand Siiiprovide a stringent test on recent theoretical calculations, to which we make comparison. The branching fractions from this study are combined with previously reported radiative lifetimes to yield transition probabilities and log(gf) values for these lines. We apply these new measurements to abundance determinations in five metal-poor stars.

    

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