C,N-Palladacycle based on <em>N,N</em>-dimethyl-<em>N</em>-(diphenylmethyl)amine as an effective phosphine-free (pre)catalyst for the Suzuki-Miyaura cross-coupling

Over the last 50 years, palladium-catalyzed cross-coupling has become ubiquitous in chemical synthesis from laboratory to commercial scale. Due to the great importance of these reactions, extensive research efforts have been devoted to improving the sustainability, cost, and diversity of the catalysts and coupling partners. Herein, we report the rational design and experimental validation of a metal-free catalyst for the cross-coupling of formate esters with organoboranes, forming aldehydes under mild, additive-free conditions. The novel mechanism establishes a model for direct C(acyl)-C(sp2) bond formation, a motif previously inaccessible via metal-free or radical-free cross-coupling pathways. Overall, this boron-/nitrogen-based system is found to even outperform the efficacy of state-of-the-art nickel catalysts for ester cross-coupling, demonstrating the utility of main-group catalysts in efficiently activating challenging bonds.

The synthesis of cost-effective, noble metal and copper-free NiZn alloy, CdS quantum dots (QDs), and their hybrid NiZn-CdS nanocomposite is reported and their efficiency as heterogeneous catalysts for visible light-mediated Suzuki-Miyaura cross-coupling (SMCC) and regioselective azide-alkyne cycloaddition (AAC) reactions is compared. A key breakthrough of this study is the catalytic inefficiency of hierarchically arranged NiZn alloy alone for SMCC reaction, under visible light illumination. However, upon integrating CdS QDs onto NiZn alloy nanoparticles via nanoscale interfacial engineering, a remarkable catalytic enhancement is observed. The newly developed NiZn-CdS composite exhibits unprecedented photocatalytic efficiency for SMCC reaction. In contrast, for AAC reaction, the composite demonstrates no catalytic activity under visible light. Interestingly, when CdS QDs are decoupled, the NiZn alloy alone shows outstanding catalytic performance for the regioselective formation of 1,4-disubstituted 1,2,3-triazoles at room temperature. This represents the first report of a room temperature, copper-free catalytic system without the use of any noble metal, that outperforms many previously reported copper-free catalysts for AAC, both in terms of activity and selectivity. Further, the sustainability matrices of the developed catalytic protocols are determined through comprehensive green chemistry assessments which demonstrate the protocol's environmental friendliness and adherence to green chemistry principles.

While earth-abundant metals are green and sustainable alternatives to precious metals for catalytic chemical conversions, the fast ligand exchange involving most of the base metals renders their development into robust, reusable catalysts very challenging. Described in this work is a new type of heterogeneous catalyst derived from a 2D metal-organic layer (MOL) grafted with catenane-coordinated Cu(I) complexes. In addition to the good substrate accessibility, easy functionalization, and other favorable features due to the MOL support, the mechanical bond in the anchored catenane ligands also represents a new mechanism to dynamically confine the coordination environment and kinetically stabilize the coordinated Cu(I) to give a well-defined, active yet stable heterogeneous catalyst. Pilot catalytic studies using a model dehydrogenative C─O cross-coupling reaction showed that the Cu(I) catenane-grafted MOL led to exclusive formation of the C─O coupled product, whereas control catalysis using a similar Cu(I) catalyst supported by non-interlocked macrocyclic ligands was found to also give a C─C coupled by-product, whose formation was found to be mediated by the uncontrolled oxidation of the Cu(I) to Cu(II), highlighting the distinctive roles and untapped potential of the catenane coordination in developing base metal-derived catalysts for challenging catalytic conditions.

This study presents a new, highly effective, and reusable catalyst: UiO-66-NH2@Epichlorohydrin@Cyclodextrin@Au-NPs. This innovative catalyst starts with the Zr-based UiO-66 material, which is functionalized with amino groups (–NH2). We enhanced its surface compatibility by modifying it with epichlorohydrin and cyclodextrin via a post-synthesis modification method. Gold nanoparticles were then stabilized on this modified composite, resulting in the UiO-66-NH2@Epichlorohydrin@Cyclodextrin@Au-NPs complex. We used this catalyst for C–C coupling and Carbonylative Sonogashira reactions in mild conditions. Its effectiveness was underscored by various analytical techniques, including XRD, EDS, SEM, FT-IR, TEM, BET, ICP, TGA, and elemental mapping. The catalyst exhibited exceptional performance in Sonogashira, Heck, Suzuki coupling, and Carbonylative reactions, achieving good to excellent yields. It proved to be highly recyclable, maintaining its catalytic activity for up to nine cycles with minimal loss.

A general and efficient method for the direct alkynylation and oxidation of remote C(sp3)-H bonds under photoirradiation is described. In this reaction, the Pd catalyst acts as both a photocatalyst to generate the nitrogen radical and a cross-coupling catalyst with a terminal alkyne. Attractive features of this system include good functional group tolerance, scalability, convenient reagents, and an operating system. The utility of this protocol is highlighted by its application for derivatization of several valuable aza-heterocycles such as caspase-3 inhibitor and azepinone derivatives.

In recent years, progress in synthetic organic chemistry has been propelled by light-induced reactions, especially by combining photoredox catalysis with nickel catalysis to facilitate cross-coupling reactions that were previously unattainable. Our group embarked on exploring the activation of nickel catalysts through light over the past 5 years, aiming to develop gentle and selective C(sp3)−H cross-coupling reactions by light exposure, eliminating a Ni−Cl bond. Inspired by Nocera laboratory findings, we envisioned using light-induced chlorine atoms to facilitate hydrogen atom transfer (HAT), enabling redox-neutral processes. A Ni/photoredox-catalyzed α-oxy C(sp3)−H arylation was developed and extended it to selectively functionalize aryl chlorides, even those in complex substrates. Exploring various oxidation states, Trimethyl orthoformate was utilized as a methyl radical source for methylation reactions and cross-coupling with feedstock chemicals and late-stage intermediates. Mechanistic investigations, including computational simulations and spectroscopic analyses, revealed the crucial role of chlorine radical generation in these methods, emphasizing the importance of understanding the photochemical behavior of cross-coupling catalysts in metallaphotoredox processes. Deeper insights gained from these studies are expected to facilitate the design of new catalysts and the development of innovative synthetic methods.

A heterogeneous and recyclable bis-oxime palladacycle-derived silica immobilized palladium catalyst for decarbonylative cross-coupling reactions of esters with arylboronic acid in the presence of 2-MeTHF.

NiII 2,2'-bipyridine complexes are commonly invoked intermediates in metallaphotoredox cross-coupling reactions. Despite their ubiquity, design principles targeting improved catalytic performance remain underdetermined. A series of Ni(Rbpy)(R'Ar)Cl (R = MeOOC, t-Bu, R' = CH3, CF3) complexes were proposed to have multiconfigurational electronic structures on the basis of multiconfigurational/multireference calculations, with significant mixing of Ni → bpy metal-to-ligand charge transfer (MLCT) configurations into the ground-state wave function. Here, Ni K-edge and L2,3-edge X-ray absorption spectroscopies provide experimental support for the highly covalent and multiconfigurational electronic structures of these complexes. The pre-edge intensity in the K-edge spectrum reflects highly covalent Ni-aryl bonding. The L3-edge spectral shape is dependent on ligand functionalization, and a feature reflecting the MLCT character is assigned using prior ab initio and new semiempirical calculations. The results suggest the push/pull effects of the aryl/bpy ligands moderate the changes in electron density on Ni during the multiredox cross-coupling reaction cycle.

In this study chitin derived from shrimp shells was used in the design of heterogeneous Pd-based catalysts for Heck and Suzuki-Miyaura cross-coupling reactions. The synthesis of Pd nanoparticles supported on N-doped carbons was performed through different approaches, including a sustainable mechanochemical approach, by using a twin-screw extruder. All catalytic systems were characterized by a multitechnique approach and the effect of nanoparticles size, N-doping on the support, and their synergistic interactions were elucidated. Specifically, Kelvin Probe Atomic Force Microscopy provided valuable insights on charge transfer and metal-support interactions. The catalytic behaviour of the samples was investigated in cross-coupling reactions under batch conditions and under semi-continuous flow solvent-free conditions, respectively obtaining a quantitative yield and a noteworthy productivity of 8.7 mol/(gPdh).

RhRu Bimetallic Cluster Catalysts for Dehydrogenative Cross-Coupling of Arenes and Carboxylic Acids

A convenient bottom up route to covalently anchor Pd(II)-PEPPSI on layered zirconium(IV) phosphonate: Efficient catalyst for Suzuki-Miyaura cross coupling of aryl chlorides

Laccases act as green catalysts for oxidative cross-coupling of phenolic antioxidnt compounds, but low stability and non-recyclability limit its application. To address that, metal-organic frameworks Cu-BTC and Cr-MOF were synthesized as supports to immobilize the efficient laccase from Cerrena sp. HYB07. The Brunauer-Emmett-Teller surface area of Cu-BTC and Cr-MOF were 1213.2 and 907.1m2/g, respectively. The two carriers respectively presented pore diameters of 1.2-10nm and 1.4-12nm as octahedron, indicating nano-scale mesoporosity. These Cu-BTC and Cr-MOF carriers could adsorb laccase with enzyme loading of 1933.2 and 1564.4U/g carrier, respectively. The stability and organic solvent tolerance of Cu-BTC-laccase and Cr-MOF-laccase were both obviously improved compared to free laccase. Thermal inactivation kinetics showed that both the two immobilized laccases displayed lower thermal inactivation rate constants. Importantly, the Cu-BTC-laccase and Cr-MOF-laccase both showed much higher activity for cross-coupling of ethyl ferulate than free laccase, which had 2.5-fold higher cross-coupling efficiency than that by free laccase. The ethyl ferulate coupling product was also analyzed by mass spectroscopy and the synthesis pathway of ethyl ferulate dimer was proposed. The cross coupling of ethyl ferulate required the formation of radical intermediates of ethyl ferulate generated by laccase mediated oxidation. This work paved the way for MOFs immobilized laccase for cross coupling of antioxidant phenols.

The use of redox-active ligands with the f-block elements has been employed to promote unique chemical transformations and explore their unique emergent electronic properties for a myriad of applications. In this study, we report eight new tris(amido) metal complexes: 1-Ln (Ln = Tb3+, Dy3+, Ho3+, Er3+, Tm3+, and Yb3+), 1-La, and 1-Ti (an early transition metal analogue). The one-electron oxidation of the tris(amido) ligand was conducted to generate semi-iminato complexes 2-Ln, 2-La, and 2-Ti, and these complexes were studied using EPR. Tris(amido) complexes 1-Ln, 1-La, and 1-Ti were fully characterized using a range of spectroscopic (NMR and UV-vis/NIR) and physical techniques (X-ray diffraction and cyclic voltammetry, with the exception of 1-La). Computational methods were employed to further elucidate the electronic structures of these complexes. Lastly, complexes 1-Ln, 1-La, and 1-Ti were probed as catalysts for alkyl-alkyl cross-coupling, and the initial rate of the reaction was measured to explore the influence of the metal ion.

Palladium-catalyzed cross-couplings of aryl chlorides usually call for bulky, electron-rich ligands such as phosphines or heterocyclic carbenes. We have now found that similarly powerful cross-coupling catalysts are obtained by the reaction of palladium salts with alkynyllithium reagents. The species initially formed in this process was characterized as a dilithium tetraalkinyl palladate complex. It catalyzes the coupling of aryl chlorides with the lithium salts of various terminal alkynes to give alkynyl arenes. The isolated Li-alkynyl-Pd complex also efficiently promotes the reaction of aryl, and allyl chlorides with (hetero)aryl-, alkyl-, and allyllithium compounds as well as lithium amides. None of these reactions proceeded in the presence of palladium salts alone. The preparative utility of this approach was demonstrated by the synthesis of 49 molecules, including pharmaceutically relevant compounds.

The design of metal-organic frameworks (MOFs) allows the definition of properties for their final application in small-scale heterogeneous catalysis. Incorporating various catalytic centers within a single structure can produce a synergistic effect, which is particularly intriguing for cross-coupling reactions. The URJC-1 material exhibits catalytic duality: the metal centers act as Lewis acid centers, while the nitrogen atoms of the organic ligand must behave as basic centers. The impact of reaction temperature, catalyst concentration, and basic agent concentration was evaluated. Several copper-based catalysts, including homogeneous and heterogeneous MOF catalysts with and without the presence of nitrogen atoms in the organic ligand, were assessed for their catalytic effect under optimal conditions. Among the catalysts tested, URJC-1 exhibited the highest catalytic activity, achieving complete conversion of 4-nitrobenzaldehyde with only 3% mol copper concentration in one hour. Furthermore, URJC-1 maintained its crystalline structure even after five reaction cycles, demonstrating remarkable stability in the reaction medium. The study also examined the impact of various substituents of the substrate alcohol on the reaction using URJC-1. The results showed that the reaction had high activity when activating substituents were present and for most cyclic alcohols rather than linear ones.

Two new palladium(II) catalysts, each containing a phenylthiazole ligand (2-methyl- (1a) and 2-amino-4-phenyl-1,3-thiazole (1b)), are prepared and characterized. The crystal structure of one, 2-methyl-4-phenyl)palladium(II) acetate (3a), is presented; it crystallizes as a dimer, with the ligand attached through the nitrogen on the thiazole and the ortho-carbon on the phenyl ring. The organometallic compounds can be used as catalysts in Suzuki–Miyaura aryl cross-coupling reactions. They are compatible with a wide range of functional groups, including carbonyls, amines, and phenols.

Gold(I) Complex with a Photoactive Ligand Behaves as a Two-in-One Dual Metallaphotoredox Cross-Coupling Catalyst

Transition-metal photoredox catalysis has transformed organic synthesis by harnessing light to construct complex molecules. Nickel(II)-bipyridine (bpy) aryl halide complexes are a significant class of cross-coupling catalysts that can be activated via direct light excitation. This study investigates the effects of molecular structure on the photophysics of these catalysts by considering an underexplored, structurally constrained Ni(II)-bpy aryl halide complex in which the aryl and bpy ligands are covalently tethered alongside traditional unconstrained complexes. Intriguingly, the tethered complex is photochemically stable but features a reversible Ni(II)-C(aryl) ⇄ [Ni(I)···C(aryl)•] equilibrium upon direct photoexcitation. When an electrophile is introduced during photoirradiation, we demonstrate a preference for photodissociation over recombination, rendering the parent Ni(II) complex a stable source of a reactive Ni(I) intermediate. Here, we characterize the reversible photochemical behavior of the tethered complex by kinetic analyses, quantum chemical calculations, and ultrafast transient absorption spectroscopy. Comparison to the previously characterized Ni(II)-bpy aryl halide complex indicates that the structural constraints considered here dramatically influence the excited state relaxation pathway and provide insight into the characteristics of excited-state Ni(II)-C bond homolysis and aryl radical reassociation dynamics. This study enriches the understanding of molecular structure effects in photoredox catalysis and offers new possibilities for designing customized photoactive catalysts for precise organic synthesis.

Cu-SSZ-39 zeolite nanosheets-heterogeneous catalyst for the decarboxylative cross-coupling of cinnamic acids with ethers