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Cobalt-catalysed sp 2 C–H bond functionalization has attracted considerable attention in recent years because of the low cost of cobalt complexes and interesting modes of action in the process. In comparison, much less efforts have been devoted to the sp 3 carbons. Here we report the cobalt-catalysed site-selective dehydrogenative cyclization of aliphatic amides via a C–H bond functionalization process on unactivated sp 3 carbons with the assistance of a bidentate directing group. This method provides a straightforward synthesis of monocyclic and spiro β- or γ-lactams with good to excellent stereoselectivity and functional group tolerance. In addition, a new procedure has been developed to selectively remove the directing group, which enables the synthesis of free β- or γ-lactam compounds. Furthermore, the first cobalt-catalysed intermolecular dehydrogenative amination of unactivated sp 3 carbons is also realized. Functionalizing unactivated carbon–hydrogen bonds is challenging, especially when using non-precious metals and dealing with sp 3 hybridized carbons. Here, the authors report an intramolecular cobalt catalysed amination of C–H bonds of sp 3 carbons, giving access to β- and γ-lactams.

The past decade has witnessed significant advances in C–H bond functionalizations with the discovery of new mechanisms. Non-precious transition-metal-catalysed radical oxidative coupling for C( sp 3 )–H bond transformations is an appealing strategy for C–C bond formations. The radical oxidative C( sp 3 )–H/C( sp 3 )–H cross-coupling reactions of α-C( sp 3 )–H bonds of amines with free radicals represent a conceptual and practical challenge. We herein develop the coordinating activation strategy to illustrate the nickel-catalysed radical oxidative cross-coupling between C( sp 3 )–H bonds and (hetero)arylmethyl free radicals. The protocol can tolerate a rich variety of α-amino acids and (hetero)arylmethanes as well as arylmethylenes and arylmethines, affording a large library of α-tertiary and α-quaternary β-aromatic α-amino acids. This process also features low-cost metal catalyst, readily handled and easily removable coordinating group, synthetic simplicity and gram-scale production, which would enable the potential for economical production at commercial scale in the future. Oxidative coupling of two C(sp3)-H groups is an attractive approach for the formation of carbon-carbon bonds, building structural complexity while avoiding the formation of waste salts. Here, the authors report such a transformation, using a nickel catalyst to functionalise amino acids with benzylic radicals.

The Suzuki–Miyaura cross-coupling is a metal-catalysed reaction in which boron-based nucleophiles and halide-based electrophiles are reacted to form a single molecule. This is one of the most reliable tools in synthetic chemistry, and is extensively used in the synthesis of pharmaceuticals, agrochemicals and organic materials. Herein, we report a significant advance in the choice of electrophilic coupling partner in this reaction. With a user-friendly and inexpensive nickel catalyst, a range of phenyl esters of aromatic, heteroaromatic and aliphatic carboxylic acids react with boronic acids in a decarbonylative manner. Overall, phenyl ester moieties function as leaving groups. Theoretical calculations uncovered key mechanistic features of this unusual decarbonylative coupling. Since extraordinary numbers of ester-containing molecules are available both commercially and synthetically, this new ‘ester’ cross-coupling should find significant use in synthetic chemistry as an alternative to the standard halide-based Suzuki–Miyaura coupling. The Suzuki-Miyaura cross-coupling is a mainstay of organic synthesis, allowing carbon-carbon bond formation between a variety of coupling partners. Here, the authors report a decarbonylative process, whereby alkyl or aryl esters can be coupled with organoboron compounds using nickel catalysts.

Reductive elimination of carbon–carbon bonds occurs in numerous metal-catalysed reactions. This process is well documented for a variety of transition metal complexes. However, carbon–carbon bond reductive elimination from a limited number of Au( III ) complexes has been shown to be a slow and prohibitive process that generally requires elevated temperatures. Herein we show that oxidation of a series of mono- and bimetallic Au (I) aryl complexes at low temperature generates observable Au( III ) and Au (II) intermediates. We also show that aryl–aryl bond reductive elimination from these oxidized species is not only among the fastest observed for any transition metal, but is also mechanistically distinct from previously studied alkyl–alkyl and aryl–alkyl reductive eliminations from Au( III ). Mechanistic studies of reductive elimination that forms aryl–aryl bonds from simple mono- and dinuclear gold phosphine complexes are disclosed. The observed rates for reductive elimination are unusually fast, even at temperatures as low as –52 °C, providing insight into the fundamental reactivity of oxidized organogold complexes.

Classically, late transition-metal organometallic compounds promote multielectron processes solely through the change in oxidation state of the metal centre. In contrast, uranium typically undergoes single-electron chemistry. However, using redox-active ligands can engage multielectron reactivity at this metal in analogy to transition metals. Here we show that a redox-flexible pyridine(diimine) ligand can stabilize a series of highly reduced uranium coordination complexes by storing one, two or three electrons in the ligand. These species reduce organoazides easily to form uranium–nitrogen multiple bonds with the release of dinitrogen. The extent of ligand reduction dictates the formation of uranium mono-, bis- and tris(imido) products. Spectroscopic and structural characterization of these compounds supports the idea that electrons are stored in the ligand framework and used in subsequent reactivity. Computational analyses of the uranium imido products probed their molecular and electronic structures, which facilitated a comparison between the bonding in the tris(imido) structure and its tris(oxo) analogue. Multi-electron redox chemistry is important in transition-metal-mediated processes, but is rarely observed with uranium due to its propensity to undergo single-electron reactions. Now, uranium can use its electrons, coupled with those stored in redox-active ligands, to perform multi electron reduction of organoazides and form uranium tris(imido) derivatives.

In a remote functionalization, reaction occurs at a site distant from the site of initial activation. This Review discusses attempts to achieve this challenging goal with a particular focus on reactions that exploit alkene isomerizations to effect transit of the catalyst from a reactive alkene to a distant sp 3 centre. Exploiting the reactivity of one functional group within a molecule to generate a reaction at a different position is an ongoing challenge in organic synthesis. Effective remote functionalization protocols have the potential to provide access to almost any derivatives but are difficult to achieve. The difficulty is more pronounced for acyclic systems where flexible alkyl chains are present between the initiating functional group and the desired reactive centres. In this Review, we discuss the concept of remote functionalization of alkenes using metal complexes, leading to a selective reaction at a position distal to the initial double bond. We aim to show the vast opportunity provided by this growing field through selected and representative examples. Our aim is to demonstrate that using a double bond as a chemical handle, metal-assisted long-distance activation could be used as a powerful synthetic strategy.

The environmental and geopolitical problems associated with fossil fuels might be alleviated if it were possible to produce synthetic multicarbon fuels efficiently from single-carbon feedstocks; here, a molybdenum compound supported by a terphenyl–diphosphine ligand is used to convert carbon monoxide into a metal-free C 2 O 1 fragment, with the ligand both serving as an electron reservoir and stabilizing the different intermediate species. Design for carbon monoxide reduction Oxygenated carbon gases (CO 2 and CO) are products of fossil fuel combustion and gasification, and many of the problems caused by the use of fossil fuels could be alleviated if they could be efficiently converted into synthetic liquid fuels. Many catalysts can reduce CO 2 to CO, but further reduction to liquid fuel chemicals is difficult and hampered by lack of mechanistic understanding of the transformation. Joshua Buss and Theodor Agapie now describe a system utilizing molybdenum, an inexpensive and abundant transition metal, that is capable of enacting C–O bond cleavage, C–C bond formation, and release of the resulting C 2 O 1 fragment. This complex transformation is enabled by a terphenyl-diphosphine ligand that acts as an electron reservoir and stabilizes the reaction intermediates. Similar design elements might help develop catalysts for CO conversion to fuel chemicals. Carbon dioxide is the ultimate source of the fossil fuels that are both central to modern life and problematic: their use increases atmospheric levels of greenhouse gases, and their availability is geopolitically constrained 1 . Using carbon dioxide as a feedstock to produce synthetic fuels might, in principle, alleviate these concerns. Although many homogeneous and heterogeneous catalysts convert carbon dioxide to carbon monoxide 2 , further deoxygenative coupling of carbon monoxide to generate useful multicarbon products is challenging 3 . Molybdenum and vanadium nitrogenases are capable of converting carbon monoxide into hydrocarbons under mild conditions, using discrete electron and proton sources 4 . Electrocatalytic reduction of carbon monoxide on copper catalysts 5 also uses a combination of electrons and protons, while the industrial Fischer–Tropsch process uses dihydrogen as a combined source of electrons and electrophiles for carbon monoxide coupling at high temperatures and pressures 6 . However, these enzymatic and heterogeneous systems are difficult to probe mechanistically. Molecular catalysts have been studied extensively 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 to investigate the elementary steps by which carbon monoxide is deoxygenated and coupled, but a single metal site that can efficiently induce the required scission of carbon–oxygen bonds and generate carbon–carbon bonds has not yet been documented. Here we describe a molybdenum compound, supported by a terphenyl–diphosphine ligand, that activates and cleaves the strong carbon–oxygen bond of carbon monoxide, enacts carbon–carbon coupling, and spontaneously dissociates the resulting fragment. This complex four-electron transformation is enabled by the terphenyl–diphosphine ligand 24 , 25 , which acts as an electron reservoir and exhibits the coordinative flexibility needed to stabilize the different intermediates involved in the overall reaction sequence. We anticipate that these design elements might help in the development of efficient catalysts for converting carbon monoxide to chemical fuels, and should prove useful in the broader context of performing complex multi-electron transformations at a single metal site.

A long-standing challenge in synthetic chemistry is the development of the transamidation reaction. This process, which involves the conversion of one amide to another, is typically plagued by unfavourable kinetic and thermodynamic factors. Although some advances have been made with regard to the transamidation of primary amide substrates, secondary amide transamidation has remained elusive. Here we present a simple two-step approach that allows for the elusive overall transformation to take place using non-precious metal catalysis. The methodology proceeds under exceptionally mild reaction conditions and is tolerant of amino-acid-derived nucleophiles. In addition to overcoming the classic problem of secondary amide transamidation, our studies expand the growing repertoire of new transformations mediated by base metal catalysis. Transamidation reactions are kinetically and thermodynamically challenging because of the stability of the amide starting materials. Here, the authors show a two-step process—activation of a secondary amide, followed by nickel-catalysed C–N bond cleavage—that allows mild and high yielding transamidation.

Some of the most recent and significant developments in homogeneous nickel catalysis are reviewed, including nickel-mediated cross-coupling reactions and carbon–hydrogen bond activation reactions. Nickel shows its mettle in small-molecule synthesis Nickel is an important catalyst that has attracted particular interest from organic chemists since the 1970s, both for cross-coupling and for a range of reactions of alkenes and alkynes. This Review focuses on more recent advances in the use of homogeneous nickel catalysis in small-molecule synthesis, including nickel-mediated cross-coupling reactions and C–H activation reactions. Tremendous advances have been made in nickel catalysis over the past decade. Several key properties of nickel, such as facile oxidative addition and ready access to multiple oxidation states, have allowed the development of a broad range of innovative reactions. In recent years, these properties have been increasingly understood and used to perform transformations long considered exceptionally challenging. Here we discuss some of the most recent and significant developments in homogeneous nickel catalysis, with an emphasis on both synthetic outcome and mechanism.

New carbon–carbon bond formation reactions expand our horizon of retrosynthetic analysis for the synthesis of complex organic molecules. Although many methods are now available for the formation of C( sp 2 )–C( sp 3 ) and C( sp 3 )–C( sp 3 ) bonds via transition metal-catalyzed cross-coupling of alkyl organometallic reagents, direct use of readily available olefins in a formal fashion of hydrocarbonation to make C( sp 2 )–C( sp 3 ) and C( sp 3 )–C( sp 3 ) bonds remains to be developed. Here we report the discovery of a general process for the intermolecular reductive coupling of unactivated olefins with alkyl or aryl electrophiles under the promotion of a simple nickel catalyst system. This new reaction presents a conceptually unique and practical strategy for the construction of C( sp 2 )–C( sp 3 ) and C( sp 3 )–C( sp 3 ) bonds without using any organometallic reagent. The reductive olefin hydrocarbonation also exhibits excellent compatibility with varieties of synthetically important functional groups and therefore, provides a straightforward approach for modification of complex organic molecules containing olefin groups. Olefins are employed in many coupling procedures but direct hydrocarbonations of unactivated olefins remain to be developed. Here, the authors report the nickel-catalyzed reductive coupling of olefins with aryl and alky electrophiles under mild conditions and with a broad substrate scope.