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1. Enantioselective and Regiodivergent Synthesis of Propargyl‐ and Allenylsilanes through Catalytic Propargylic C−H Deprotonation

   https://doi.org/10.1002/ange.202318040  

   Zhu, Jin ; Xiang, Hengye ; Chang, Hai ; Corcoran, James C. ; Ding, Ruiqi ; Xia, Yue ; Liu, Peng ; Wang, Yi‐Ming ( March 2024 , Angewandte Chemie)

   We report a highly enantioselective intermolecular C−H bond silylation catalyzed by a phosphoramidite‐ligated iridium catalyst. Under reagent‐controlled protocols, propargylsilanes resulting from C(sp³)−H functionalization, as well the regioisomeric and synthetically versatile allenylsilanes, could be obtained with excellent levels of enantioselectivity and good to excellent control of propargyl/allenyl selectivity. In the case of unsymmetrical dialkyl acetylenes, good to excellent selectivity for functionalization at the less‐hindered site was also observed. A variety of electrophilic silyl sources (R₃SiOTf and R₃SiNTf₂), either commercial or in situ‐generated, were used as the silylation reagents, and a broad range of simple and functionalized alkynes, including aryl alkyl acetylenes, dialkyl acetylenes, 1,3‐enynes, and drug derivatives were successfully employed as substrates. Detailed mechanistic experiments and DFT calculations suggest that an η³‐propargyl/allenyl Ir intermediate is generated upon π‐complexation‐assisted deprotonation and undergoes outer‐sphere attack by the electrophilic silylating reagent to give propargylic silanes, with the latter step identified as the enantiodetermining step.

    

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2. A general strategy for C(sp3)–H functionalization with nucleophiles using methyl radical as a hydrogen atom abstractor

   https://doi.org/10.1038/s41467-021-27165-z  

   Leibler, Isabelle Nathalie-Marie ; Tekle-Smith, Makeda A. ; Doyle, Abigail G. ( November 2021 , Nature Communications)

   Photoredox catalysis has provided many approaches to C(sp³)–H functionalization that enable selective oxidation and C(sp³)–C bond formation via the intermediacy of a carbon-centered radical. While highly enabling, functionalization of the carbon-centered radical is largely mediated by electrophilic reagents. Notably, nucleophilic reagents represent an abundant and practical reagent class, motivating the interest in developing a general C(sp³)–H functionalization strategy with nucleophiles. Here we describe a strategy that transforms C(sp³)–H bonds into carbocations via sequential hydrogen atom transfer (HAT) and oxidative radical-polar crossover. The resulting carbocation is functionalized by a variety of nucleophiles—including halides, water, alcohols, thiols, an electron-rich arene, and an azide—to effect diverse bond formations. Mechanistic studies indicate that HAT is mediated by methyl radical—a previously unexplored HAT agent with differing polarity to many of those used in photoredox catalysis—enabling new site-selectivity for late-stage C(sp³)–H functionalization.

    

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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/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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4. 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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5. Further Studies of Co III (TIM) Mono‐Alkynyl and Bis‐Alkynyl Complexes

   https://doi.org/10.1002/ejic.202200641  

   Rodriguez Segura, Leobardo ; Cox, Kenneth E. ; Samayoa‐Oviedo, Hugo Y. ; Ren, Tong ( December 2022 , European Journal of Inorganic Chemistry)

   A new series of mono‐ and bis‐alkynyl Co^III(TIM) complexes (TIM=2,3,9,10‐tetramethyl‐1,4,8,11‐tetraazacyclotetradeca‐1,3,8,10‐tetraene) is reported herein. Thetrans‐[Co(TIM)(C₂R)Cl]⁺complexes were prepared from the reaction betweentrans‐[Co(TIM)Cl₂]PF₆and HC₂R (R=tri(isopropyl)silyl or TIPS (1), ‐C₆H₄‐4‐^tBu (2), ‐C₆H₄‐4‐NO₂(3 a), andN‐mesityl‐1,8‐naphthalimide or NAP^Mes(4 a)) in the presence of Et₃N. The intermediate complexes of the typetrans‐[Co(TIM)(C₂R)(NCMe)](PF₆)(OTf),3 band4 b, were obtained by treating3 aand4 a, respectively, with AgOTf in CH₃CN. Furthermore, bis‐alkynyltrans‐[Co(TIM)(C₂R)₂]PF₆complexes,3 cand4 c, were generated following a second dehydrohalogenation reaction between3 band4 b, respectively, and the appropriate HC₂R in the presence of Et₃N. These new complexes have been characterized using X‐ray diffraction (2,3 a,4 a, and4 c), IR,¹H NMR, UV/Vis spectroscopy, fluorescent spectroscopy (4 c), and cyclic voltammetry.

    

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