Nickel Catalysis Research Articles

Reductive Alkylation of Alkenyl Acetates with Alkyl Bromides by Nickel Catalysis

AbstractCatalytic alkylation of stable alkenyl C−O electrophiles is synthetically appealing, but studies to date have typically focused on the reactions with alkyl Grignard reagents. We report herein a cross‐electrophile reaction of alkenyl acetates with alkyl bromides. This work has enabled a new method for the synthesis of aliphatic alkenes from alkenyl acetates to be established that can be used to add more structural complexity and molecular diversity with enhanced functionality tolerance. The method allows for a gram‐scale reaction and modification of biologically active molecules, and it affords access to useful building blocks. Preliminary mechanistic studies reveal that the NiI species plays an essential role for the success of the coupling of these two reactivity‐mismatched electrophiles.

Nickel‐Catalyzed Allylic Substitution Reactions: An Evolving Alternative

AbstractTransition metal‐catalyzed allylic substitution reactions represent versatile transformations in organic synthesis forging C−C and C‐heteroatom bonds. Despite major contributions realized with precious transition metals, earth‐abundant nickel catalysis over the years has emerged as a relative sustainable and efficient alternative in the area of allylic substitution reactions. During the last two decades, the field has witnessed successful accomplishments of chemo‐, regio‐ and enantioselective conversions affording a plethora of products through the employment of Ni‐based methodologies. In this Minireview, the most imperative contributions will be discussed with special attention for the more sustainable character and unique reactivity of Ni, the overall process selectivity features and the functional group tolerance and product scope.

Ni/Chiral Sodium Carboxylate Dual Catalyzed Asymmetric O-Propargylation.

A highly enantioselective O-propargylation catalyzed by combining a phosphine-nickel complex and an axially chiral sodium dicarboxylate has been developed. The transformation features mild reaction conditions, a broad substrate scope, and excellent functional group tolerance, offering an efficient approach to an array of enantioenriched O-propargyl hydroxylamines. Mechanistic studies support the presumed role of the chiral carboxylate as a counterion for nickel catalysis enabling the discovery of highly stereoselective transformations. The power of this reaction is illustrated by its application in the asymmetric total synthesis of potent firefly luciferase inhibitors and (S)-dihydroyashabushiketol.

Origin and Regioselectivity of Direct Hydrogen Atom Transfer Mechanism of C(sp3)-H Arylation by [W10O32]4-/Ni Metallaphotoredox Catalysis.

Polyoxometalates (POMs) have a broad array of applied platforms with well-characterized catalysis including photocatalysis to achieve aliphatic C(sp3)-H bond functionalization. However, the reaction mechanism of POMs in organic transformation remains unknown due to the complexity of POM structures. Here, a challenging [W10O32]4-/Ni metallaphotoredox-catalyzed C(sp3)-H arylation of alkane has been investigated by density functional theory (DFT) calculations. The calculation revealed that the superficial active center located in bridged oxygen of *[W10O32]4- is responsible for the abstraction of a foreign hydrogen atom and the activation of a C(sp3)-H bond. Furthermore, we discussed this activated process using the direct activation model of the C(sp3)-H σ-bond to deepen our mechanistic understanding of POM mediated C-H bond activation via the hydrogen atom transfer (HAT) pathway. Specifically, comparing three common mechanisms for nickel catalysis inducing by Ni0, NiI, and NiII to construct a C-C bond, the nickel catalytic cycle induced by the NiI active catalyst is profitable in kinetics and thermodynamics. Finally, a radical mechanism merging the ([W10O32]4--*[W10O32]4--[HW10O32]4--[W10O32]4-) decatungstate reductive quenching cycle, ([HW10O32]4--[H2W10O32]4--[HW10O32]4-) electron relay, and (NiI-NiII-NiI-NiIII-NiI) nickel catalytic cycle is proposed to be favorable. We hope that this work would provide a better understanding of the unique catalytic activity of decatungstate anions for the direct functionalization of the C(sp3)-H bond.

Nickel-Catalyzed Regiodivergent Asymmetric Cycloadditions of α,β-Unsaturated Carbonyl Compounds

Nickel-Catalyzed Regiodivergent Asymmetric Cycloadditions of α,β-Unsaturated Carbonyl Compounds

Nickel-Catalyzed Ipso/Ortho Difunctionalization of Aryl Bromides with Alkynes and Alkyl Bromides via a Vinyl-to-Aryl 1,4-Hydride Shift.

Polysubstituted arenes are ubiquitous structures in a myriad of medicinal agents and complex molecules. Herein, we report a new catalytic blueprint that merges the modularity of nickel catalysis for bond formation with the ability to enable a rather elusive 1,4-hydride shift at arene sp2 C-H sites, thus allowing access to ipso/ortho-difunctionalized arenes from readily available aryl halides under mild conditions and exquisite selectivity profile.

The Journey of Ni(I) Chemistry

AbstractIn the last twenty years, nickel has successfully imprinted its role in the field of homogeneous catalysis as a valid and complementary alternative to palladium and platinum catalysts. However, compared to those, there are often many different available pathways in nickel catalysis due to the facile access of intermediate oxidation states. Among them, Ni(I) has been increasingly proposed as a key oxidation state in multiple transformations. This oxidation state had already been suggested a long time ago but has only recently undergone a renaissance with extensive ligand design which has led to over 100 isolated Ni(I) complexes. In addition, the analysis of many catalytic cycles has revealed that the Ni(I) species can not only occur as a decomposition product perturbing a Ni(0)–Ni(II) pathway but can also play a key role in alternative Ni(I)–Ni(III) cycles. This behavior is highly dependent on the class of transformation and ligand employed in catalysis. Herein, we concisely describe the journey of this oxidation state, combining the information gathered from inorganic synthesis and mechanistic investigations, from its synthesis to its postulated role in different catalytic cycles.

Regio- and Stereoselective Alkylboration of Endocyclic Olefins Enabled by Nickel Catalysis.

Whereas there is a significant interest in the rapid construction of diversely substituted saturated heterocycles, direct and modular access is currently limited to the mono-, 2,3-, or 3,4-substitution pattern. This Communication describes the straightforward and modular construction of 2,4-substituted saturated heterocycles from readily available materials in a highly stereo- and regioselective manner, which sets the stage for numerous readily accessible drug motifs. The strategy relies on chain walking catalysis.

Mechanistic Understanding of Arylation vs Alkylation of Aliphatic Csp3–H Bonds by Decatungstate–Nickel Catalysis

Computational analysis of the arylation of aliphatic Csp3–H bonds catalyzed by decatungstate–nickel validates the reaction mechanism and provides valuable insights into how to accomplish the corres...

Nickel-Catalyzed Regiodivergent Cyanation of Allylic Alcohols: Scope, Mechanism, and Application to the Synthesis of 1,n-Dinitriles

Here, we report a regiodivergent cyanation of allylic alcohols under nickel catalysis. With a delicate control over the regioselectivity of allylic cyanation, more challenging branched products were successfully obtained. A variety of alkenyl nitriles and branched allylic nitriles can be synthesized. In addition, dinitriles can also be achieved from the corresponding allylic alcohols in good yields with high selectivity by a subsequent hydrocyanation process. The obtained dinitriles can easily undergo amidation or reduction or can be converted to heterocycles, piperidines, and multisubstituted pyridines. Density functional theory (DFT) calculations offered more information on the crucial role of ligands in tuning the regioselectivity and reactivity.

Palladium and Nickel Catalyzed Suzuki Cross-Coupling with Alkyl Fluorides.

Suzuki cross-coupling of benzylic and unactivated aliphatic fluorides with aryl- and alkenylboronic acids has been achieved via mechanistically distinct Pd and Ni catalyzed pathways that outperform competing protodeboronation, β-hydride elimination, and homocoupling processes. The utility is demonstrated with more than 20 examples including heterocyclic structures, 1,1-disubstituted and trans-1,2-disubstituted alkenes, and by the incorporation of acetonitrile into functionalized (hetero)arenes.

Nickel-Catalyzed Enantioselective Arylative Activation of Aromatic C-O Bond.

The pioneering nickel-catalyzed cross-coupling of C-O electrophiles was unlocked by Wenkert in the 1970s; however, the transition-metal-catalyzed asymmetric activation of aromatic C-O bonds has never been reported. Herein the first enantioselective activation of an aromatic C-O bond is demonstrated via the catalytic arylative ring-opening cross-coupling of diarylfurans. This transformation is facilitated via nickel catalysis in the presence of chiral N-heterocyclic carbene ligands, and chiral 2-aryl-2'-hydroxy-1,1'-binaphthyl (ArOBIN) skeletons are delivered axially in high yields with high ee. Moreover, this versatile skeleton can be transformed into various synthetic useful intermediates, chiral catalysts, and ligands by using the CH- and OH-based modifiable sites. This chemistry features mild conditions and good atom economy.

Hierarchical Porous Ni/NiO Nanoflowers with Adjustable Ni As Anode for Lithium-Ion Batteries

The construction of advanced nanostructures as well as the hybridization of different active materials are highly desirable for achieving lithium-ion batteries (LIBs) anode with superior electrochemical performance. In this work, flower-like Ni/NiO nanoflowers was prepared through a facile solvothermal route. Firstly, α-Ni(OH)2 was synthesized by heating Ni(NO3)2·6H2O precursor in methanol/water in the presence of PVP. After that, a two-step thermal annealing process was carried out. First, Ni-NiO was formed by annealing the α-Ni(OH)2 precursor under inert Ar environment. Subsequently, the Ni was annealed in air and partially oxidized to form NiO. The Ni/NiO ratio could be tuned by simply adjusting the annealing time in air. Alternatively, raw NiO could be obtained by directly annealing in air without the step annealing in Ar. It is found that amount of metallic Ni phase determined the lithium storage performance. When applied as the anode for LIBs, Ni/NiO nanoflowers exhibited an enhanced capacity of 994.6 mAh g-1 at 0.1 A g-1 after 70 cycles than the raw NiO (194.3 mAh g-1). As the integrated amount of Ni increased, the discharge capacity decreased to 828.4 mAh g-1. Thus, benefitting from the advantages of the intrinsic nanoarchitecture and the electrochemical catalysis of metallic nickel, NiO with appropriate Ni content is demonstrated to be well-suited for LIB anode with high capacity, remarkable rate capability and superior cycling stability. This work brings a novel direction to design metal/metal oxide hybrid nanostructured anode materials with excellent lithium storage performance.

Photoredox-Enabled Deoxygenative Cross-Coupling of Alcohols Activated by NHCs

Key words nickel catalysis - iridium catalysis - deoxygenative cross-coupling - photochemistry

Transition-Metal-Catalyzed Hydroxylation Reaction of Aryl Halide for the Synthesis of Phenols

AbstractPhenols are important components of pharmaceuticals, biologically active natural products, and materials. Here, we briefly discuss recent advances in catalytic hydroxylation reactions for the synthesis of phenols, with particular attention to our recent work. H2O is proved to be an efficient hydroxide reagent in converting (hetero)aryl halides into the corresponding phenols under synergistic organophotoredox and nickel catalysis. Aryl bromides as well as less reactive aryl chlorides show high reactivity in this catalytic system. This methodology can be applied to the efficient synthesis of diverse phenols and allows the hydroxylation of multifunctional pharmaceutically relevant aryl halides.1 Introduction2 Representative Methods for Transition-Metal-Catalyzed Hydroxylation of (Hetero)Aryl Halides3 Organophotoredox/Ni Dual Catalytic Hydroxylation of Aryl Halides with Water4 Summary and Outlook

Mechanisms, Challenges, and Opportunities of Dual Ni/Photoredox-Catalyzed C(sp2)-C(sp3) Cross-Couplings.

The merging of photoredox and nickel catalysis has revolutionized the field of C-C cross-coupling. However, in comparison to the development of synthetic methods, detailed mechanistic investigations of these catalytic systems are lagging. To improve the mechanistic understanding, computational tools have emerged as powerful tools to elucidate the factors controlling reactivity and selectivity in these complex catalytic transformations. Based on the reported computational studies, it appears that the mechanistic picture of catalytic systems is not generally applicable, but is rather dependent on the specific choice of substrate, ligands, photocatalysts, etc. Given the complexity of these systems, the need for more accurate computational methods, readily available and user-friendly dynamics simulation tools, and data-driven approaches is clear in order to understand at the molecular level the mechanisms of these transformations. In particular, we anticipate that such improvement of theoretical methods will become crucial to advance the understanding of excited-state properties and dynamics of key species, as well as to enable faster and unbiased exploration of reaction pathways. Further, with greater collaboration between computational, experimental, and spectroscopic communities, the mechanistic investigation of photoredox/Ni dual-catalytic reactions is expected to thrive quickly, facilitating the design of novel catalytic systems and promoting our understanding of the reaction selectivity.

Nickel/Enamine Cooperative Catalysis Enables Highly Enantioselective Allylic Alkylation of α-Branched Aldehydes

All-carbon quaternary stereocenters constitute a significant portion of natural products and bioactive compounds. Here we disclose a nickel and chiral amine cooperative catalysis to enable a highly...

Dual Photoredox/Nickel-Promoted Alkylation of Heteroaryl Halides with Redox-Active Esters.

Herein a method for the radical alkylation of heteroaryl halides that relies upon the combination of photoredox and nickel catalysis is described. The use of aliphatic N-(acyloxy)phthalimides as redox-active esters affords primary and secondary radicals for the decarboxylative dual cross-coupling with pyrimidine and pyridine heteroaryl chlorides, bromides, and iodides. The method provides an additional synthetic tool for the incorporation of medicinally relevant heterocyclic motifs.

Chiral Arylated Amines via C−N Coupling of Chiral Amines with Aryl Bromides Promoted by Light

The Buchwald-Hartwig C-N coupling reaction has found widespread applications in organic synthesis. Over the past two decades or so, many improved catalysts have been introduced, allowing various amines and aryl electrophiles to be readily used nowadays. However, there lacks a protocol that could be used to couple a wide range of chiral amines and aryl halides, without erosion of the enantiomeric excess (ee). Reported in this article is a method based on molecular Ni catalysis driven by light, which enables stereoretentive C-N coupling of optically active amines, amino alcohols, and amino acid esters with aryl bromides, with no need for any external photosensitizer. The method is effective for a wide variety of coupling partners, including those bearing functional groups sensitive to bases and nucleophiles, thus providing a viable alternative to accessing synthetically important chiral N-aryl amines, amino alcohols, and amino acids esters. Its viability is demonstrated by 92 examples with up to 99 % ee.

Nickel-Catalyzed Enantioselective Synthesis of Pre-Differentiated Homoallylic syn- or anti-1,2-Diols from Aldehydes and Dienol Ethers.

Nickel catalysis allied with cyclodiphosphazane or VAPOL-derived phosphoramidite ligands provides selective access to monoprotected vicinal diols by reductive coupling of dienol ethers and aldehydes. The observed regioselectivity is unprecedented, in that the diene reacts at the least nucleophilic and most hindered C atom that is attached to the oxygen substituent rather than at the terminal position. Notably, both syn and anti diastereomers of the products can be accessed depending on the configuration of the diene partner with usually excellent diastereo- and enantioselectivity.