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1. Atmospheric ¹⁴ C/ ¹² C changes during the last glacial period from Hulu Cave

   https://doi.org/10.1126/science.aau0747  

   Cheng, Hai; Edwards, R. Lawrence; Southon, John; Matsumoto, Katsumi; Feinberg, Joshua M.; Sinha, Ashish; Zhou, Weijian; Li, Hanying; Li, Xianglei; Xu, Yao; et al (December 2018, Science)

   Paired measurements of¹⁴C/¹²C and²³⁰Th ages from two Hulu Cave stalagmites complete a precise record of atmospheric¹⁴C covering the full range of the¹⁴C dating method (~54,000 years). Over the last glacial period, atmospheric¹⁴C/¹²C ranges from values similar to modern values to values 1.70 times higher (42,000 to 39,000 years ago). The latter correspond to¹⁴C ages 5200 years less than calibrated ages and correlate with the Laschamp geomagnetic excursion followed by Heinrich Stadial 4. Millennial-scale variations are largely attributable to Earth’s magnetic field changes and in part to climate-related changes in the oceanic carbon cycle. A progressive shift to lower¹⁴C/¹²C values between 25,000 and 11,000 years ago is likely related, in part, to progressively increasing ocean ventilation rates. 

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2. Cobalt−NHC Catalyzed C(sp ² )−C(sp ³ ) and C(sp ² )−C(sp ² ) Kumada Cross‐Coupling of Aryl Tosylates with Alkyl and Aryl Grignard Reagents

   https://doi.org/10.1002/cctc.202001347  

   Piontek, Aleksandra; Ochędzan‐Siodłak, Wioletta; Bisz, Elwira; Szostak, Michal (November 2020, ChemCatChem)

   Abstract The first cobalt‐catalyzed cross‐coupling of aryl tosylates with alkyl and aryl Grignard reagents is reported. The catalytic system uses CoF₃and NHCs (NHC=N‐heterocyclic carbene) as ancillary ligands. The reaction proceeds via highly selective C−O bond functionalization, leading to the corresponding products in up to 98 % yield. The employment of alkyl Grignard reagents allows to achieve a rare C(sp²)−C(sp³) cross‐coupling of C−O electrophiles, circumventing isomerization and β‐hydride elimination problems. The use of aryl Grignards leads to the formation of biaryls. The C−O cross‐coupling sets the stage for a sequential cross‐coupling by exploiting the orthogonal selectivity of the catalytic system. 

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3. “Direct” ¹³ C Hyperpolarization of ¹³ C‐Acetate by MicroTesla NMR Signal Amplification by Reversible Exchange (SABRE)

   https://doi.org/10.1002/anie.201910506  

   Gemeinhardt, Max E.; Limbach, Miranda N.; Gebhardt, Thomas R.; Eriksson, Clark W.; Eriksson, Shannon L.; Lindale, Jacob R.; Goodson, Elysia A.; Warren, Warren S.; Chekmenev, Eduard Y.; Goodson, Boyd M. (November 2019, Angewandte Chemie International Edition)

   Abstract Herein, we demonstrate “direct”¹³C hyperpolarization of¹³C‐acetate via signal amplification by reversible exchange (SABRE). The standard SABRE homogeneous catalyst [Ir‐IMes; [IrCl(COD)(IMes)], (IMes=1,3‐bis(2,4,6‐trimethylphenyl), imidazole‐2‐ylidene; COD=cyclooctadiene)] was first activated in the presence of an auxiliary substrate (pyridine) in alcohol. Following addition of sodium 1‐¹³C‐acetate, parahydrogen bubbling within a microtesla magnetic field (i.e. under conditions of SABRE in shield enables alignment transfer to heteronuclei, SABRE‐SHEATH) resulted in positive enhancements of up to ≈100‐fold in the¹³C NMR signal compared to thermal equilibrium at 9.4 T. The present results are consistent with a mechanism of “direct” transfer of spin order from parahydrogen to¹³C spins of acetate weakly bound to the catalyst, under conditions of fast exchange with respect to the¹³C acetate resonance, but we find that relaxation dynamics at microtesla fields alter the optimal matching from the traditional SABRE‐SHEATH picture. Further development of this approach could lead to new ways to rapidly, cheaply, and simply hyperpolarize a broad range of substrates (e.g. metabolites with carboxyl groups) for various applications, including biomedical NMR and MRI of cellular and in vivo metabolism. 

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4. Probing Redox Non‐Innocence in Iron–Carbene Complexes {Fe=C(H)Ar} ^10–11 by ^1,2 H and ¹³ C Pulse Electron Paramagnetic Resonance

   https://doi.org/10.1002/anie.202110704  

   Arnett, Charles H.; Oyala, Paul H.; Agapie, Theodor (November 2021, Angewandte Chemie International Edition)

   Abstract We report the synthesis and spectroscopic characterization of a series of iron‐carbene complexes in redox states {Fe=C(H)Ar}^10–11. Pulse EPR studies of the^1,2H and¹³C isotopologues of {Fe=C(H)Ar}¹¹reveal the high covalency of the Fe–carbene bonding, leading to a more even spin distribution than commonly observed for reduced Fischer carbenes. 

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5. Substrate‐Mediator Duality of 1,4‐Dicyanobenzene in Electrochemical C(sp ² )−C(sp ³ ) Bond Formation with Alkyl Bromides

   https://doi.org/10.1002/anie.202312128  

   Johnston, Brandon; Loh, Daniel M.; Nocera, Daniel G. (November 2023, Angewandte Chemie International Edition)

   Abstract Electrochemical approaches to form C(sp²)−C(sp³) bonds have focused on coupling C(sp³) electrophiles that form stabilized carbon‐centered radicals upon reduction or oxidation. Whereas alkyl bromides are desirable C(sp³) coupling partners owing to their availability and cost‐effectiveness, their tendency to undergo radical‐radical homocoupling makes them challenging substrates for electroreductive cross‐coupling. Herein, we disclose a metal‐free regioselective cross‐coupling of 1,4‐dicyanobenzene, a useful precursor to aromatic nitriles, and alkyl bromides. Alkyl bromide reduction is mediated directly by 1,4‐dicyanobenzene radical anions, leading to negligible homocoupling and high cross‐selectivity to form 1,4‐alkyl cyanobenzenes. The cross‐coupling scheme is compatible with oxidatively sensitive and acidic functional groups such as amines and alcohols, which have proven difficult to incorporate in alternative electrochemical approaches using carboxylic acids as C(sp³) precursors. 

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