Dinickel Active Sites Supported by Redox-Active Ligands

Synthesis and Characterization of Bimetallic Copper(I) Complexes Supported by a Hexadentate Naphthyridine-Based Macrocycle Ligand

Herein, we report the synthesis, characterization, and binding properties of a new ligand, N,N'-di-tert-butyl-3,7-diaza-1,5(2,7)-1,8-naphthyridinacyclooctaphane (tBuN6), with copper (I), CuI, centers. We demonstrate the flexibility and the ability of tBuN6 to adopt various conformations in solution and when coordinated to CuIcenters. NMR studies exhibit the labile coordination nature of CuI. However, the lability of the complexes is blocked by counterion exchange, which enables the use of less coordinating solvents such as tetrahydrofuran (THF) and avoids using acetonitrile. Thus, the exchange of [BF4]- with tetrakis 3,5-bis(trifluoromethyl)phenyl borate, [B(ArF)4]-, in 1·BF4, [Cu2(MeCN)2(tBuN6)][BF4], generates 1·B(ArF)4, which is stable in THF and reacts under a CO atmosphere to generate a syn,syn bis(carbonyl) complex. This complex is sufficiently stable in solution under CO and Ar atmosphere to be characterized by NMR and IR spectroscopy, the latter revealing two stretching bands for the CO bound to the CuI-centers at 2102 and 2088 cm-1.

Access to Heterobimetallic MII/CuI Complexes with a Multichelate Platform and Their Reactivity Studies in CO2RR

We describe the selective formation of heterobimetallic complexes, exploiting the coordination trends of the developed bis-terpyridyl trans-1,2-cyclohexadiamine platform (L). Following a stepwise addition, we first reacted ligand L toward tetrakisacetonitrile transition metal precursors, [M(MeCN)4][BF4]2 (where M = Fe or Ni), to generate the monometallic complexes 1 ([FeL][BF4]2) and 2 ([NiL][BF4]2). These species were later combined with the tetrakisacetonitrile precursor [Cu(MeCN)4][BF4], generating the corresponding heterobimetallic complexes 3 ([FeCuL(MeCN)2][BF4]3) and 4 ([NiCuL(MeCN)2][BF4]3). The four species obtained, in high yields, have been structurally characterized. Their cyclic voltammetry analysis revealed the impact of the CuI-atom presence on the heterobimetallic complexes under argon and carbon dioxide (CO2) atmospheres. Controlled potential electrolysis studies revealed the instability of complexes 1-4 toward CO2RR, generating the heterogeneous material in solution and on the electrode surface. In contrast, CO2 photoreduction studies revealed higher stability and photocatalytic activity for the FeII-based complexes (1 and 3), generating CO with 88% selectivity.

Dinickel-Catalyzed Asymmetric Allylic Alkylation of Cyclic Ketones with Allylic Amine Derivatives

A dinickel-catalyzed direct asymmetric allylic alkylation of benzocyclic ketones has been developed. This method enables the efficient transformation of various α-alkyl benzocyclohexanones and benzocyclopentanones with allylic sulfonamides, affording chiral ketones bearing α-quaternary carbon stereocenters in high yields and with excellent enantioselectivities.

Na Ions Doped Fe2VO4 Cathode for High Performance Aqueous Zinc-ion Batteries

Aqueous zinc ion batteries are thought to be a new generation of secondary batteries that will replace lithium-ion batteries due to their great safety and inexpensive cost. In the cathode materials of aqueous zinc ion batteries with long life and high capacity, abundant active sites and crystal structure stability play an important role. In the present work, the strategy of Na+ intercalation of Fe2VO4 (FVO) is proposed, aiming at the insertion of Na+, which not only enriches the active sites, but also sodium and iron ions act as guest species with the negatively charged VOx lattice to provide strong electrostatic attraction to stabilize the lamellar structure. In terms of electrochemical performance, the discharge specific capacity is 370 mAh g-1 at a current density of 0.1 A g-1, and when the current density is arising 5 A g-1, the specific capacity also reaches 200 mAh g-1 after cycling 2000 with a capacity retention of 99 %, which is better than the electrochemical performance of Fe2VO4 (FVO) alone at 50 mAh g-1. The superior electrochemical performance proves that FVO-Na is an ideal cathode material for zinc ion batteries.

Dinickel-Catalyzed N=N Coupling Reactions for the Synthesis of Hindered Azoarenes

Azoarenes are the largest class of photoswitching molecules, and they have a broad range of applications in photopharmacology and materials science. Azoarenes possessing ortho-substitution often display improved properties, including isomerization under visible light irradiation, near-quantitative switching, and long thermal half-lives in the cis form. The synthesis of hindered ortho-substituted azoarenes is often low-yielding using established oxidative or reductive coupling methods. Here, we describe the design and synthesis of a new dinickel complex that catalyzes the dimerization of ortho-substituted aryl azides in high yield. Applications of this method in the synthesis of high-performance photoswitches, photoactive peptide cross-linkers, hindered diazocines, and main-chain azoarene polymers are described.

Heteromultimetallic Platform for Enhanced C-H Bond Activation: Aluminum-Incorporated Dicopper Complex Mimicking Cu-ZSM-5 Structure and Oxidative Reactivity

Bimetallic complexes have sparked interest across various chemical disciplines, driving advancements in research. Recent advancements in this field have shed light on complex reactions in metalloenzymes and unveiled new chemical transformations. Two primary types of bimetallic platforms have emerged: (1) systems where both metals actively participate in reactivity, and (2) systems where one metal mediates the reaction while the other regulates reactivity. This study introduces a novel multinucleating ligand platform capable of integrating both types of bimetallic systems. To demonstrate the significance of this platform, we synthesized a unique dicopper complex incorporating aluminum in its coordination environment. This complex serves as the first structural model for the active site in copper-based zeolites, highlighting the role of aluminum in hydrogen atom abstraction reactivity. Comparative studies of oxidative C-H bond activation revealed that the inclusion of aluminum significantly alters the thermodynamic driving force (by -11 kcal mol-1) for bond activation and modifies the proton-coupled electron-transfer reaction mechanism, resulting in a 14-fold rate increase. Both computational and experimental data support the high modularity of this multinucleating ligand platform, offering a new approach to fine-tune the reactivity of bimetallic complexes.

Bis[μ-3-(pyridin-2-yl)pyrazolato]bis-[acetato-(3,5-dimethyl-1H-pyrazole)-nickel(II)]

The title compound, [Ni2(C8H6N3)2(C2H3O2)2(C5H8N2)2] or [Ni(μ-OOCCH3)(2-PyPz)(Me2PzH)]2 (1) [2-PyPz = 3-(pyridin-2-yl) pyrazole; Me2PzH = 3,5-dimethyl pyrazole] was synthesized from Ni(OOCCH3)2·4H2O, 2-PyPzH, Me2PzH and tri-ethyl-amine as a base. Compound 1 {[Ni2(C30H34N10Ni2O4)]} at 100 K has monoclinic (P21/n) symmetry and the mol-ecules have crystallographic inversion symmetry. Mol-ecules of 1 comprise an almost planar dinuclear NiII core with an N4O2 coordination environment. The equatorial plane consists of N3,O coordination derived from one of the bidentate acetate O atoms and three of the N atoms of the chelating 2-PyPz ligand while the axial positions are occupied by neutral Me2PzH and the second O atom of the acetate unit. The Ni atoms are bridged by the nitro-gen atom of a deprotonated 2-PyPz ligand. Compound 1 exhibits various inter- and intra-molecular C-H⋯O and N-H⋯O hydrogen bonds.

Studies on the Coordination Patterns of Diamine-Bridged Tetraphenoxy Ligands with Group 3 and 4 Metals

Alkane elimination reactions between the diamino- and dianilino-bridged tetrakis(phenolate) proligands 1a,b-H4 and precursors M(CH2SiMe3)3(THF)2, M(CH2C6H4-o-NMe2)3 (M = Sc and Y), and Hf(CH2Ph)4 were investigated. The diamino-bridged 1a-H4 afforded nonsymmetric complex 2a-Y2 incorporating two metal centers in different coordination environments. This one and other dinuclear compounds 2b-Sc2, 2a-Hf2, and 2b-Hf2 were characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction study (for 2a-Y2 and 2b-Sc2) and turned out to be symmetric in solution. Compound 2a-Y2, upon treatment with 2 equiv of 2-phenylpyridine, afforded symmetric bis(aryl) product 3a-Y2, which was authenticated by NMR spectroscopy and X-ray crystallography. The mechanism of its formation was studied by DFT computations and presumably involves a cooperative reorganization process within the nonsymmetric parent 2a-Y2 to afford a symmetric isomer prior to its reaction with 2-phenylpyridine.

Valence Tautomerism Induced Proton Coupled Electron Transfer:X-H Bond Oxidation with a Dinuclear Au(II) Hydroxide Complex

We report the preparation and characterization of the dinuclear AuII hydroxide complex AuII 2(L)2(OH)2 (L=N,N'-bis (2,6-dimethyl) phenylformamidinate) and study its reactivity towards weak X-H bonds. Through the interplay of kinetic analysis and computational studies, we demonstrate that the oxidation of cyclohexadiene follows a concerted proton-coupled electron transfer (cPCET) mechanism, a rare type of reactivity for Au complexes. We find that the Au-Au σ-bond undergoes polarization in the PCET event leading to an adjustment of oxidation levels for both Au centers prior to C(sp3)-H bond cleavage. We thus describe the oxidation event as a valence tautomerism-induced PCET where the basicity of one reduced Au-OH unit provides a proton acceptor and the second more oxidized Au center serves as an electron acceptor. The coordination of these events allows for unprecedented radical-type reactivity by a closed shell AuII complex.

Two active species from a single metal halide precursor: a case study of highly productive Mn-catalyzed dehydrogenation of amine-boranes via intermolecular bimetallic cooperation

Metal-metal cooperation for inert bond activation is a ubiquitous concept in coordination chemistry and catalysis. While the great majority of such transformations proceed via intramolecular mode in binuclear complexes, to date only a few examples of intermolecular small molecule activation using usually bimetallic frustrated Lewis pairs (Mδ+⋯M'δ-) have been reported. We introduce herein an alternative approach for the intermolecular bimetallic cooperativity observed in the catalytic dehydrogenation of amine-boranes, in which the concomitant activation of N-H and B-H bonds of the substrate via the synergetic action of Lewis acidic (M+) and basic hydride (M-H) metal species derived from the same mononuclear complex (M-Br). It was also demonstrated that this system generated in situ from the air-stable Mn(i) complex fac-[(CO)3(bis(NHC))MnBr] and NaBPh4 shows high activity for H2 production from several substrates (Me2NHBH3, tBuNH2BH3, MeNH2BH3, NH3BH3) at low catalyst loading (0.1% to 50 ppm), providing outstanding efficiency for Me2NHBH3 (TON up to 18 200) that is largely superior to all known 3d-, s-, p-, f-block metal derivatives and frustrated Lewis pairs (FLPs). These results represent a step forward towards more extensive use of intermolecular bimetallic cooperation concepts in modern homogeneous catalysis.

Unsymmetrical Imidazopyrimidine-Based Ligand and Bimetallic Complexes

With bimetallic catalysts becoming increasingly important, the development of electronically and structurally diverse binucleating ligands is desired. This work describes the synthesis of unsymmetric ligand 2,7-di(pyridin-2-yl)imidazo[1,2-a]pyrimidine (dpip) that is achieved in four steps on a multigram scale in an overall 54% yield. The ability of dpip to act as a scaffold for the formation of bimetallic complexes is demonstrated with the one-step syntheses of the dicopper complex [Cu2(dpip)(μ-OH)(CF3COO)3] (4), the dipalladium complex [Pd2(dpip)(μ-OH)(CF3COO)2](CF3COO)·CF3COOH (5), and the dimeric dinickel complex [Ni4(dpip)2(μ-Cl)4Cl2MeOH6][2Cl] (6) in good yields (79-92%). All bimetallic complexes were characterized by spectroscopic methods and X-ray crystallography, which revealed metal-metal distances between 3.4821(9) and 4.106(2) Å. Additionally, quantum chemical calculations were conducted on complex 4 and an analogous 1,8-naphthyridine-based dicopper complex to investigate the differences between the imidazopyrimidine motif reported here and the widely used 1,8-naphthyridine motif. Natural bonding orbital (NBO) and Mayer bond order (MBO) analyses validated the ability of dpip to coordinate metals more strongly. Finally, NBO calculations quantified the differences in the binding energy between the two pockets of the unsymmetrical dpip ligand.

Ring Walking Mediated by Ni-Ni Species as a Vehicle for Enabling Distal C(sp2)-H Functionalization of Aryl Pivalates

Herein, we report the utilization of Ni-Ni species as a manifold for enabling a "ring-walking" event by dynamic translocation of the metal center over the arene backbone. Experimental and computational studies support a translocation occurring via a 1,2-hydride shift. The synthetic applicability of the method is illustrated in a series of C-C bond formations that occur at distal C(sp2)-H sites of simple aryl pivalates.

Catalytic Asymmetric α-Alkylation of Ketones with Unactivated Alkyl Halides

A catalytic, enantioselective method for direct α-alkylation of ketones with unactivated alkyl halides is realized by employing an α-enolizable ketone in a nickel-catalyzed C(sp3)-C(sp3) cross-coupling reaction. The key to the success is attributed to a unique bimetallic ligand. A variety of acyclic ketones and unactivated alkyl iodides can serve as suitable substrates under mild conditions to generate chiral ketones with α-quaternary carbon stereocenters in high yields with good enantioselectivities. A range of transformations based on the ketone moiety are also demonstrated to show the potential application of this method. Preliminary mechanistic studies support a dinickel-catalyzed cross-coupling mechanism.

Binuclear Complexes Supported by a Tetrapyridyl Ligand with a Bending Anthraquinodimethane Linker

A tetrapyridyl ligand with a bending anthraquinodimethane linker has been synthesized, and its complexation with coinage metals has been examined. The treatment of the ligand with Ag(I) and Au(I) cations afforded binuclear complexes, wherein the two metal centers were in close proximity to the inside space of the ligand. X-ray analyses corroborated with theoretical calculations indicated that the ligand has reasonable flexibility toward a bending deformation of the linker moiety to provide a ligand pocket suitable for the proximal binuclear complexes, even though such deformations accompany a non-negligible amount of energetic cost. On the other hand, treatment with 2 equiv of Cu(I) salt afforded a binuclear complex, in which both copper atoms were coordinated at the periphery of the ligand.

New Insights into the Cooperativity and Dynamics of Dimeric Enzymes

A survey of protein databases indicates that the majority of enzymes exist in oligomeric forms, with about half of those found in the UniProt database being homodimeric. Understanding why many enzymes are in their dimeric form is imperative. Recent developments in experimental and computational techniques have allowed for a deeper comprehension of the cooperative interactions between the subunits of dimeric enzymes. This review aims to succinctly summarize these recent advancements by providing an overview of experimental and theoretical methods, as well as an understanding of cooperativity in substrate binding and the molecular mechanisms of cooperative catalysis within homodimeric enzymes. Focus is set upon the beneficial effects of dimerization and cooperative catalysis. These advancements not only provide essential case studies and theoretical support for comprehending dimeric enzyme catalysis but also serve as a foundation for designing highly efficient catalysts, such as dimeric organic catalysts. Moreover, these developments have significant implications for drug design, as exemplified by Paxlovid, which was designed for the homodimeric main protease of SARS-CoV-2.

Dinickel-Catalyzed N═N Bond Rotation

Azoarenes function as molecular switches that can be triggered by external stimuli, such as heat, light, and electrochemical potential. Here, we show that a dinickel catalyst can induce cis/trans isomerization in azoarenes through a N═N bond rotation mechanism. Catalytic intermediates containing azoarenes bound in both the cis and trans forms are characterized. Solid-state structures reveal the importance of π-back-bonding interactions from the dinickel active site in lowering the N═N bond order and accelerating bond rotation. The scope of the catalytic isomerization includes high-performance acyclic, cyclic, and polymeric azoarene switches.

Bimetallic Nickel Complexes Supported by a Planar Macrocyclic Diphosphoranide Ligand

Metal-metal cooperativity is emerging as an important strategy in catalysis. This requires appropriate ligand scaffolds that can support two metals in close proximity. Here we report nickel-promoted formation of a dinucleating planar macrocyclic ligand that can support bimetallic dinickel(II) and dinickel(I) complexes. Reaction outcomes can be tuned by variation of the substituents and reaction conditions to favour dinucleating macrocyclic, mononucleating macrocyclic or conventional pincer architectures.

One Bridge, Three Bonds: A Frontier in Multiple Bonding in Heterobimetallic Complexes

A single bridging phosphinoamide ligand was shown to support a metal-metal triple bond in a Zr/Co heterobimetallic complex. The similarity of the bonding in this compound to previously synthesized Zr/Co species, and therefore the assignment of the Zr/Co triple bond, is supported by the structural parameters of the complex, the electronic structure predicted by density functional theory, and complete-active-space self-consistent-field (CASSCF) calculations. This demonstrates that metal-metal multiple bonds can be realized in heterobimetallic complexes without multiple bridging ligands to enforce the proximity of the two metals.

Tunable Construction of Sandwich-Type Double-[1 + 1] and Half-Folded [2 + 2] Schiff-Base Complexes Controlled by the Combination of Primary and Secondary Template Effects

The first-row transition-metal ions Mn²⁺-Cu²⁺ could serve as effective templates to construct three types of double-[1 + 1], [2 + 2], and [1 + 1] Schiff-base dinuclear macrocyclic complexes in the presence of dialdehydes with different pendant arms and a common 1,8-diamine. The extremely flexible nature of macrocyclic ligands allows for the multiple template-directed syntheses, but the final products could be finely tuned by the subtle variations of Mn²⁺-Cu²⁺ ions in a 3d-electronic configuration, radius, and coordination number/geometry as well as the auxiliary (pendant-armed and anionic) template effect at the same time. Two borderlines are observed at the Co²⁺ ion for forming double-[1 + 1] and [2 + 2] metallacycles involving the H₂pdd precursor and the [1 + 1] Cu²⁺ complex for double-[1 + 1] and [2 + 2] macrocycles containing the H₂hpdd unit, respectively. The structural diversity is originated from the non-perfect match between [1 + 1]/[2 + 2] Schiff-base macrocycles and dinuclear metal centers; hence, a compromise between the metal coordination modes and alterations of the ligand conformation takes place.

Heteroligand Metal Complexes with Extended Redox Properties Based on Redox-Active Chelating Ligands of o-Quinone Type and Ferrocene

A combination of different types of redox-active systems in one molecule makes it possible to create coordination compounds with extended redox abilities, combining molecular and electronic structures determined by the features of intra- and intermolecular interactions between such redox-active centres. This review summarizes and analyses information from the literature, published mainly from 2000 to the present, on the methods of preparation, the molecular and electronic structure of mixed-ligand coordination compounds based on redox-active ligands of the o-benzoquinone type and ferrocenes, ferrocene-containing ligands, the features of their redox properties, and some chemical behaviour.

Where is the unpaired electron density? A combined experimental and theoretical finding on the geometric and electronic structures of the Co(iii) and Mn(iv) complexes of the unsymmetrical non-innocent pincer ONS ligand

The geometry and electronic structures of the Co and Mn complexes of the pincer H3LONS ligand composed of both hard and soft donor atoms at the coordinating sites are reported.

Catalytic synthesis of azoarenes via metal-mediated nitrene coupling

Various valuable properties of azoarenes (“azo dyes”), including their vivid colors and their facile cis-trans photoisomerization, lead to their wide use in the chemical industry. As a result, ~700,000 metric...