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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. Probing the Effects of Electron Deficient Aryl Substituents and a π‐System Extended NHC Ring on the Photocatalytic CO ₂ Reduction Reaction with Re‐pyNHC‐Aryl Complexes**

   https://doi.org/10.1002/cptc.202000296  

   Shirley, Hunter; Sexton, Thomas_More; Liyanage, Nalaka_P; Perkins, Morgan_A; Autry, Shane_A; McNamara, Louis_E; Hammer, Nathan_I; Parkin, Sean_R; Tschumper, Gregory_S; Delcamp, Jared_H (January 2021, ChemPhotoChem)

   Abstract The ever‐expanding need for renewable energy can be addressed in part by photocatalytic CO₂reduction to give fuels via an artificial photosynthetic process driven by sunlight. A series of rhenium photocatalysts are evaluated in the photocatalytic CO₂reduction reaction and via photophysical, electrochemical, and computational studies. The impact of various electron withdrawing substituents on the aryl group of the pyNHC‐aryl ligand along with the impact of extending conjugation along the backbone of the ligand is analyzed. A strong correlation between excited‐state lifetimes, photocatalytic rates, and computationally determined dissociation energy of the labile ligand of these complexes is observed. Additionally, computed orbital analysis provides an added understanding, which allows for prediction of the potential impact of an electron withdrawing substituent on photocatalysis. 

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3. Enhanced activity of bulky N-heterocyclic carbenes in nickel–NHC catalyzed Kumada–Corriu cross-coupling of aryl tosylates

   https://doi.org/10.1039/D2CY01805E  

   Kardela, Marlena; Halikowska-Tarasek, Katarzyna; Szostak, Michal; Bisz, Elwira (December 2022, Catalysis Science & Technology)

   Over the last decades, advances in Ni catalysis have expanded the chemical reactivity of cross-coupling reactions and led to the discovery of catalytic systems that are now widely applied in industrial and academic research. Herein, we report the cross-coupling of aryl tosylates by Ni–NHC catalysis using bulky N-heterocyclic carbene ligands. A notable feature of this operationally-simple method is the combination of ‘fluoride effect’ to minimize homocoupling and bulky NHC ligands, such as IPr* and IPr* MeO , that enhance the activity of Ni in cross-coupling and prevent hydrolysis of sensitive oxygen electrophiles. A broad range of aryl and heteroaryl tosylates underwent cross-coupling with high efficiency. The finding that easily accessible, bulky NHCs with flexible CHPh 2 wingtips enhance the reactivity in Ni–NHC cross-coupling represents a powerful approach for catalysis. 

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4. Synergistic N‐Heterocyclic Carbene/Palladium‐Catalyzed Umpolung 1,4‐Addition of Aryl Iodides to Enals

   https://doi.org/10.1002/anie.201912584  

   Yang, Wenjun; Ling, Bo; Hu, Bowen; Yin, Haolin; Mao, Jianyou; Walsh, Patrick J. (November 2019, Angewandte Chemie International Edition)

   Abstract An umpolung 1,4‐addition of aryl iodides to enals promoted by cooperative (terpy)Pd/NHC catalysis was developed that generates various bioactive β,β‐diaryl propanoate derivatives. This system is not only the first reported palladium‐catalyzed arylation of NHC‐bound homoenolates but also expands the scope of NHC‐induced umpolung transformations. A diverse array of functional groups such as esters, nitriles, alcohols, and heterocycles are tolerated under the mild conditions. This method also circumvents the use of moisture‐sensitive organometallic reagents. 

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5. gem-Difluoroallylation of Aryl Halides and Pseudo Halides with Difluoroallylboron Reagents in High Regioselectivity

   https://doi.org/10.1002/anie.202111476  

   Sakamoto, Shu; Butcher, Trevor W.; Yang, Jonathan L.; Hartwig, John F. (October 2021, Angewandte Chemie)

   We report the palladium-catalyzed gem-difluoroallylation of aryl halides and pseudo halides with 3,3-difluoroallyl boronates in high yield with high regioselectivity, and we report the preparation of the 3,3-difluoroallyl boronate reactants by a copper-catalyzed defluorinative borylation of inexpensive gaseous 3,3,3-trifluoropropene with bis(pinacola-to) diboron. The gem-difluoroallylation of aryl and heteroaryl bromides proceeds with low catalyst loading (0.1 mol% [Pd]) and tolerates a wide range of functional groups, including primary alcohols, secondary amines, ethers, ketones, esters, amides, aldehydes, nitriles, halides, and nitro groups. This protocol extends to aryl iodides, chlorides, and triflates, as well as substituted difluoroallyl boronates, providing a versatile synthesis of gem-difluoroallyl arenes that we show to be valuable intermediates to a series of fluorinated building blocks 

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