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      Rhodium hydride enabled enantioselective intermolecular C–H silylation to access acyclic stereogenic Si–H

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          Abstract

          The tremendous success of stereogenic carbon compounds has never ceased to inspire researchers to explore the potentials of stereogenic silicon compounds. Intermolecular C–H silylation thus represents the most versatile and straightforward strategy to construct C–Si bonds, however, its enantioselective variant has been scarcely reported to date. Herein we report a protocol that allows for the enantioselective intermolecular C–H bond silylation, leading to the construction of a wide array of acyclic stereogenic Si–H compounds under simple and mild reaction conditions. Key to the success is (1) a substrate design that prevents the self-reaction of prochiral silane and (2) the employment of a more reactive rhodium hydride ([Rh]-H) catalyst as opposed to the commonly used rhodium chloride ([Rh]-Cl) catalyst. This work unveils opportunities in converting simple arenes into value-added stereogenic silicon compounds.

          Abstract

          Construction of chiral organosilicon compounds could have implications in photophysical, biological, and chemical fields, as silicon is isoelectronic with carbon, and can mimic carbon atoms while providing slightly different properties. Here the authors present an intermolecular, enantioselective C–H silylation of heterocycles via rhodium catalysis.

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          Catalytic Enantioselective Transformations Involving C-H Bond Cleavage by Transition-Metal Complexes.

          The development of new methods for the direct functionalization of unactivated C-H bonds is ushering in a paradigm shift in the field of retrosynthetic analysis. In particular, the catalytic enantioselective functionalization of C-H bonds represents a highly atom- and step-economic approach toward the generation of structural complexity. However, as a result of their ubiquity and low reactivity, controlling both the chemo- and stereoselectivity of such processes constitutes a significant challenge. Herein we comprehensively review all asymmetric transition-metal-catalyzed methodologies that are believed to proceed via an inner-sphere-type mechanism, with an emphasis on the nature of stereochemistry generation. Our analysis serves to document the considerable and rapid progress within in the field, while also highlighting limitations of current methods.
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            Borylation and silylation of C-H bonds: a platform for diverse C-H bond functionalizations.

            Methods that functionalize C-H bonds can lead to new approaches for the synthesis of organic molecules, but to achieve this goal, researchers must develop site-selective reactions that override the inherent reactivity of the substrates. Moreover, reactions are needed that occur with high turnover numbers and with high tolerance for functional groups if the C-H bond functionalization is to be applied to the synthesis of medicines or materials. This Account describes the discovery and development of the C-H bond functionalization of aliphatic and aromatic C-H bonds with borane and silane reagents. The fundamental principles that govern the reactivity of intermediates containing metal-boron bonds are emphasized and how an understanding of the effects of the ligands on this reactivity led us to broaden the scope of main group reagents that react under mild conditions to generate synthetically useful organosilanes is described. Complexes containing a covalent bond between a transition metal and a three-coordinate boron atom (boryl complexes) are unusually reactive toward the cleavage of typically unreactive C-H bonds. Moreover, this C-H bond cleavage leads to the formation of free, functionalized product by rapid coupling of the hydrocarbyl and boryl ligands. The initial observation of the borylation of arenes and alkanes in stoichiometric processes led to catalytic systems for the borylation of arenes and alkanes with diboron compounds (diborane(4) reagents) and boranes. In particular, complexes based on the Cp*Rh (in which Cp is the cyclopentadienyl anion) fragment catalyze the borylation of alkanes, arenes, amines, ethers, ketals, and haloalkanes. Although less reactive toward alkyl C-H bonds than the Cp*Rh systems, catalysts generated from the combination of bipyridines and iridium(I)-olefin complexes have proven to be the most reactive catalysts for the borylation of arenes. The reactions catalyzed by these complexes form arylboronates from arenes with site-selectivity for C-H bond cleavage that depends on the steric accessibility of the C-H bonds. These complexes also catalyze the borylation of heteroarenes, and the selectivity for these substrates is more dependent on electronic effects than the borylation of arenes. The products from the borylation of arenes and heteroarenes are suitable for a wide range of subsequent conversions to phenols, arylamines, aryl ethers, aryl nitriles, aryl halides, arylboronic acids, and aryl trifluoroborates. Studies of the electronic properties of the ancillary ligand on the rate of the reaction show that the flat structure and the strong electron-donating property of the bipyridine ligands, along with the strong electron-donating property of the boryl group and the presence of a p-orbital on the metal-bound atom, lead to the increased reactivity of the iridium catalysts. Based on this hypothesis, we studied catalysts containing substituted phenanthroline ligands for a series of additional transformations, including the silylation of C-H bonds. A sequence involving the silylation of benzylic alcohols, followed by the dehydrogenative silylation of aromatic C-H bonds, leads to an overall directed silylation of the C-H bond ortho to hydroxyl functionality.
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              Undirected, Homogeneous C–H Bond Functionalization: Challenges and Opportunities

              The functionalization of C–H bonds has created new approaches to preparing organic molecules by enabling new strategic “disconnections” during the planning of a synthetic route. Such functionalizations also have created the ability to derivatize complex molecules by modifying one or more of the many C–H bonds. For these reasons, researchers are developing new types of functionalization reactions of C–H bonds and new applications of these processes. These C–H bond functionalization reactions can be divided into two general classes: those directed by coordination to an existing functional group prior to the cleavage of the C–H bond (directed) and those occurring without coordination prior to cleavage of the C–H bond (undirected). The undirected functionalizations of C–H bonds are much less common and more challenging to develop than the directed reactions. This outlook will focus on undirected C–H bond functionalization, as well as related reactions that occur by a noncovalent association of the catalyst prior to C–H bond cleavage. The inherent challenges of conducting undirected functionalizations of C–H bonds and the methods for undirected functionalization that are being developed will be presented, along with the factors that govern selectivity in these reactions. Finally, this outlook discusses future directions for research on undirected C–H functionalization, with an emphasis on the limitations that must be overcome if this type of methodology is to become widely used in academia and in industry.
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                Author and article information

                Contributors
                qingweiz@ustc.edu.cn
                whe@mail.tsinghua.edu.cn
                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group UK (London )
                2041-1723
                14 February 2022
                14 February 2022
                2022
                : 13
                : 847
                Affiliations
                [1 ]GRID grid.12527.33, ISNI 0000 0001 0662 3178, MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology and School of Pharmaceutical Sciences, , Tsinghua University, ; Beijing, PR China
                [2 ]GRID grid.59053.3a, ISNI 0000000121679639, Department of Chemistry, , University of Science and Technology of China, ; Hefei, PR China
                Author information
                http://orcid.org/0000-0002-8577-6304
                http://orcid.org/0000-0001-8167-9155
                Article
                28439
                10.1038/s41467-022-28439-w
                8844420
                35165278
                b79db4ae-9c4f-4fb4-842d-3eb6db9824d2
                © The Author(s) 2022

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 25 June 2021
                : 11 January 2022
                Funding
                Funded by: FundRef https://doi.org/10.13039/501100001809, National Natural Science Foundation of China (National Science Foundation of China);
                Award ID: 21625104
                Award ID: 21901235
                Award ID: 21971133
                Award Recipient :
                Funded by: National Key Research and Development Program of China (No. 2017YFA0505203)
                Categories
                Article
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                © The Author(s) 2022

                Uncategorized
                synthetic chemistry methodology,asymmetric catalysis
                Uncategorized
                synthetic chemistry methodology, asymmetric catalysis

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