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1. Ni‐Catalyzed Linearizable Cyclization/Coupling with Detachable Silicon‐Oxygen Linker: Access to 1,2‐Oxasilolanes, 3‐Hydroxysilanes and 4‐Arylalkanols

   https://doi.org/10.1002/anie.202404679  

   Lakomy, Margaret_G; Shankar, Majji; Del_Rio, Ava_C; Giri, Ramesh (May 2024, Angewandte Chemie International Edition)

   Abstract We disclose a Ni‐catalyzed cyclization/alkylmetal interception reaction in which products are readily linearized to permit regiodefined alkene dicarbofunctionalization. This method offers a convenient route to access 1,2‐oxasilolane heterocycles, 3‐hydroxysilanes and 4‐arylalkanols with the formation of C(sp³)−C(sp³) bonds at primary and secondary alkyl carbon centers. In this reaction, a silicon‐oxygen (Si−O) bond functions as a detachable linker that can be delinked with several hydride, alkyl, aryl and vinyl nucleophiles to create profusely functionalized 3‐hydroxysilanes. A silicon motif in the cyclic C(sp³)−Si−O construct in 1,2‐oxasilolane heterocycles can also be selectively deleted by Pd‐catalyzed hydrodesilylation affording Si‐ablated linear alcohol products reminiscent of vicinal ethylene dicarbofunctionalization with C(sp³) and C(sp²) carbon sources. 

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2. Compressed glassy carbon maintaining graphite-like structure with linkage formation between graphene layers

   https://doi.org/10.1038/s41598-019-43954-5  

   Shibazaki, Yuki; Kono, Yoshio; Shen, Guoyin (May 2019, Scientific Reports)

   Abstract Amorphous diamond, formed by high-pressure compression of glassy carbon, is of interests for new carbon materials with unique properties such as high compressive strength. Previous studies attributed the ultrahigh strength of the compressed glassy carbon to structural transformation from graphite-likesp²-bonded structure to diamond-likesp³-bonded structure. However, there is no direct experimental determination of the bond structure of the compressed glassy carbon, because of experimental challenges. Here we succeeded to experimentally determine pair distribution functions of a glassy carbon at ultrahigh pressures up to 49.0 GPa by utilizing our recently developed double-stage large volume cell. Our results show that the C-C-C bond angle in the glassy carbon remains close to 120°, which is the ideal angle for thesp²-bonded honey-comb structure, up to 49.0 GPa. Our data clearly indicate that the glassy carbon maintains graphite-like structure up to 49.0 GPa. In contrast, graphene interlayer distance decreases sharply with increasing pressure, approaching values of the second neighbor C-C distance above 31.4 GPa. Linkages between the graphene layers may be formed with such a short distance, but not in the form of tetrahedralsp³bond. The unique structure of the compressed glassy carbon may be the key to the ultrahigh strength. 

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3. 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)

   Abstract 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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4. Iron‐Catalyzed Tertiary Alkylation of Terminal Alkynes with 1,3‐Diesters via a Functionalized Alkyl Radical

   https://doi.org/10.1002/anie.202100641  

   Tian, Ming‐Qing; Shen, Zhen‐Yao; Zhao, Xuefei; Walsh, Patrick J.; Hu, Xu‐Hong (March 2021, Angewandte Chemie International Edition)

   Abstract Direct oxidative C(sp)−H/C(sp³)−H cross‐coupling offers an ideal and environmentally benign protocol for C(sp)−C(sp³) bond formations. As such, reactivity and site‐selectivity with respect to C(sp³)−H bond cleavage have remained a persistent challenge. Herein is reported a simple method for iron‐catalyzed/silver‐mediated tertiary alkylation of terminal alkynes with readily available and versatile 1,3‐dicarbonyl compounds. The reaction is suitable for an array of substrates and proceeds in a highly selective manner even employing alkanes containing other tertiary, benzylic, and C(sp³)−H bonds alpha to heteroatoms. Elaboration of the products enables the synthesis of a series of versatile building blocks. Control experiments implicate the in situ generation of a tertiary carbon‐centered radical species. 

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5. Observation of Transition‐Metal–Boron Triple Bonds in IrB ₂ O ⁻ and ReB ₂ O ⁻

   https://doi.org/10.1002/anie.202006652  

   Chen, Teng‐Teng; Cheung, Ling Fung; Chen, Wei‐Jia; Cavanagh, Joseph; Wang, Lai‐Sheng (June 2020, Angewandte Chemie International Edition)

   Abstract Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d_π→BR back‐donation, despite the electron deficiency of boron. An electron‐precise metal–boron triple bond was first observed in BiB₂O⁻[Bi≡B−B≡O]⁻in which both boron atoms can be viewed as sp‐hybridized and the [B−BO]⁻fragment is isoelectronic to a carbyne (CR). To search for the first electron‐precise transition‐metal‐boron triple‐bond species, we have produced IrB₂O⁻and ReB₂O⁻and investigated them by photoelectron spectroscopy and quantum‐chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB₂O⁻has a closed‐shell bent structure (C_s,¹A′) with BO⁻coordinated to an Ir≡B unit, (⁻OB)Ir≡B, whereas ReB₂O⁻is linear (C_∞v,³Σ⁻) with an electron‐precise Re≡B triple bond, [Re≡B−B≡O]⁻. The results suggest the intriguing possibility of synthesizing compounds with electron‐precise M≡B triple bonds analogous to classical carbyne systems. 

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