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1. Dehydrocoupling: A General Route to Bonds Between P-Block Elements

   Waterman, Rory (December 2024, The Chemical educator)

   Dehydrocoupling is a unique reaction to p-block elements that allows for the formation of bonds between these main group elements with loss of hydrogen. The transformation is highly atom economical, and hydrogen is a relatively benign byproduct that also provides the thermodynamic driving force for the reaction. For these reactions, couplings between most of the p-block elements are known. In the instance when bonds between the same elements are formed, then this reaction primarily applies to elements in the third period (3p) and heavier. For reactions between different elements, most any combination of p-block elements is possible. These reactions are known to make small molecules and polymers. Catalysts for this reaction include metal compounds (i.e., organometallic catalysts), Lewis acids, and frustrated Lewis pairs, and the mechanisms of dehydrocoupling are highly varied, representing much of the spectrum of catalysis. 

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2. Recent advances in oxidative allylic C–H functionalization via group IX-metal catalysis

   https://doi.org/10.1039/D0CC05554A  

   Kazerouni, Amaan M.; McKoy, Quincy A.; Blakey, Simon B. (November 2020, Chemical Communications)

   null (Ed.)

   Allylic substitution, pioneered by the work of Tsuji and Trost, has been an invaluable tool in the synthesis of complex molecules for decades. An attractive alternative to allylic substitution is the direct functionalization of allylic C–H bonds of unactivated alkenes, thereby avoiding the need for prefunctionalization. Significant early advances in allylic C–H functionalization were made using palladium catalysis. However, Pd-catalyzed reactions are generally limited to the functionalization of terminal olefins with stabilized nucleophiles. Insights from Li, Cossy, and Tanaka demonstrated the utility of RhCp x catalysts for allylic functionalization. Since these initial reports, a number of key intermolecular Co-, Rh-, and Ir-catalyzed allylic C–H functionalization reactions have been reported, offering significant complementarity to the Pd-catalyzed reactions. Herein, we report a summary of recent advances in intermolecular allylic C–H functionalization via group IX-metal π-allyl complexes. Mechanism-driven development of new catalysts is highlighted, and the potential for future developments is discussed. 

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3. Metalloradical Catalysis: General Approach for Controlling Reactivity and Selectivity of Homolytic Radical Reactions

   https://doi.org/10.1002/anie.202320243  

   Lee, Wan‐Chen Cindy; Zhang, X. Peter (April 2024, Angewandte Chemie International Edition)

   Abstract Since Friedrich Wöhler's groundbreaking synthesis of urea in 1828, organic synthesis over the past two centuries has predominantly relied on the exploration and utilization of chemical reactions rooted in two‐electron heterolytic ionic chemistry. While one‐electron homolytic radical chemistry is both rich in fundamental reactivities and attractive with practical advantages, the synthetic application of radical reactions has been long hampered by the formidable challenges associated with the control over reactivity and selectivity of high‐energy radical intermediates. To fully harness the untapped potential of radical chemistry for organic synthesis, there is a pressing need to formulate radically different concepts and broadly applicable strategies to address these outstanding issues. In pursuit of this objective, researchers have been actively developing metalloradical catalysis (MRC) as a comprehensive framework to guide the design of general approaches for controlling over reactivity and stereoselectivity of homolytic radical reactions. Essentially, MRC exploits the metal‐centered radicals present in open‐shell metal complexes as one‐electron catalysts for homolytic activation of substrates to generate metal‐entangled organic radicals as the key intermediates to govern the reaction pathway and stereochemical course of subsequent catalytic radical processes. Different from the conventional two‐electron catalysis by transition metal complexes, MRC operates through one‐electron chemistry utilizing stepwise radical mechanisms. 

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4. Transamidation of N-acyl-glutarimides with amines

   Liu, Yongmei; Achtenhagen, Marcel; Liu, Ruzhang; Szostak, Michal (February 2018, Organic & biomolecular chemistry)

   The development of new transamidation reactions for the synthesis of amides is an important and active area of research due to the central role of amide linkage in various fields of chemistry. Herein, we report a new method for transamidation of N-acyl-glutarimides with amines under mild, metal-free conditions that relies on amide bond twist to weaken amidic resonance. A wide range of amines and functional groups, including electrophilic substituents that would be problematic in metal-catalyzed protocols, are tolerated under the reaction conditions. Mechanistic experiments implicate the amide bond twist, thermodynamic stability of the tetrahedral intermediate and leaving group ability of glutarimide as factors controlling the reactivity of this process. The method further establishes the synthetic utility of N-acyl-glutarimides as bench-stable, twist-perpendicular, amide-based reagents in acyl-transfer reactions by a metal-free pathway. The origin of reactivity of N-acyl-glutarimides in metal-free and metal-catalyzed processes is discussed and compared. 

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5. Activator-free single-component Co( i )-catalysts for regio- and enantioselective heterodimerization and hydroacylation reactions of 1,3-dienes. New reduction procedures for synthesis of [L]Co( i )-complexes and comparison to in situ generated catalysts

   https://doi.org/10.1039/d2dt01484j  

   Parsutkar, Mahesh M.; Moore, Curtis E.; RajanBabu, T. V. (June 2022, Dalton Transactions)

   Warren Piers (Ed.)

   Although cobalt( i ) bis-phosphine complexes have been implicated in many selective C–C bond-forming reactions, until recently relatively few of these compounds have been fully characterized or have been shown to be intermediates in catalytic reactions. In this paper we present a new practical method for the synthesis and isolation of several cobalt( i )-bis-phosphine complexes and their use in Co( i )-catalyzed reactions. We find that easily prepared ( in situ generated or isolated) bis-phosphine and (2,6- N -aryliminoethyl)pyridine (PDI) cobalt( ii ) halide complexes are readily reduced by 1,4-bis-trimethylsilyl-1,4-dihydropyrazine or commercially available lithium nitride (Li 3 N), leaving behind only innocuous volatile byproducts. Depending on the structures of the bis-phosphines, the cobalt( i ) complex crystallizes as a phosphine-bridged species [(P∼P)(X)Co I [μ-(P∼P)]Co I (X)(P∼P)] or a halide-bridged species [(P∼P)Co I [μ-(X)] 2 Co I (P∼P)]. Because the side-products are innocuous, these methods can be used for the in situ generation of catalytically competent Co( i ) complexes for a variety of low-valent cobalt-catalyzed reactions of even sensitive substrates. These complexes are also useful for the synthesis of rare cationic [(P∼P)Co I -η 4 -diene] + X − or [(P∼P)Co I -η 6 -arene] + X − complexes, which are shown to be excellent single-component catalysts for the following regioselective reactions of dienes: heterodimerizations with ethylene or methyl acrylate, hydroacylation and hydroboration. The reactivity of the single-component catalysts with the in situ generated species are also documented. 

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