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A method is proposed that can efficiently identify the material of a single-organic particle; the identification is realized by improving an apparatus formerly used to observe the field-induced translations of particles. Using this new setup, the material of an unidentified organic particle can be determined without consuming the sample. Specifically, the diamagnetic susceptibility χDIA of the particle was obtained from its translating velocity induced in a field-gradient produced by an Nd magnetic circuit, and its material was identified by comparing the experimental χDIA value with a list of published values. In principle, the proposed method of identification based on the χDIA value is effective even for micrometersized particles because the mass measurement of the sample is unnecessary. Hence, the method can be used to thoroughly extract and identify a rare material from a mixture of heterogeneous particles without consuming the sample, before performing a refined analysis. [ABSTRACT FROM AUTHOR]

An ensemble of graphite and magnesia particles was successfully separated into different groups of materials by translating them in an area of magnetic field produced by a NdFeB magnetic-circuit. The absolute value of diamagnetic susceptibility χdia| was 2:6 × 10-7 emu/g in magnesia; previously the separation of diamagnetic grains was possible in materials with |χdia| values above 5 × 10-7 emu/g. Terminal velocity observed in a area outside the magnetic field in the magnesia particles having different mass between 0.12 to 0.35 mg, converged to a constant value 1:27 ± 0:05 cm/s; the value was consistent with a theoretical value based on a simple conversion rule between magnetic potential and kinetic energy assumed in the particles. Similar result was obtained for the graphite particles. The technical improvements introduced in the present study to translate the MgO particles can be applied to realize magnetic separation of diamagnetic materials in general. [ABSTRACT FROM AUTHOR]

A Gram-negative bacillus that defies identification was isolated from blood cultures of 17 patients with fever. Fifteen patients were male adults, and 14 patients had underlying diseases, including previous splenectomy in five, which impair host defenses against infection. Illnesses occurred in the summer and autumn in 14 cases and had been recently preceded by dog bites in 10 cases. Clincal syndromes included cellulitis in seven cases, primary bacteremia without localization in four, purulent meningitis in four, and endocarditis in three. Three patients died. The organism grows slowly on blood or chocolate agar in 10% CO, is oxidase- and catalase-positive, and is negative for nitrate reduction, indole production, and urease. It produces acid from glucose, lactose, and maltose. These features distinguish it from all previously described and classified bacteria. Furthermore, the epidemiologic features of the patients suggest that this organism is an opportunistic invader and may have an animal reservoir in nature. [ABSTRACT FROM AUTHOR]

Most existing solids are categorised as diamagnetic or weak paramagnetic materials. The possibility of magnetic motion has not been intensively considered for these materials. Here, we demonstrate for the first time that ensembles of heterogeneous particles (diamagnetic bismuth, diamond and graphite particles, as well as two paramagnetic olivines) can be dynamically separated into five fractions by the low field produced by neodymium (NdFeB) magnets during short-duration microgravity (μg). This result is in contrast to the generally accepted notion that ordinary solid materials are magnetically inert. The materials of the separated particles are identified by their magnetic susceptibility (χ), which is determined from the translating velocity. The potential of this approach as an analytical technique is comparable to that of chromatography separation because the extraction of new solid phases from a heterogeneous grain ensemble will lead to important discoveries about inorganic materials. The method is applicable for the separation of the precious samples such as lunar soils and/or the Hayabusa particles recovered from the asteroids, because even micron-order grains can be thoroughly separated without sample-loss. [ABSTRACT FROM AUTHOR]

The ensemble of nano-sized crystals is expected to attain additional physical properties when preferential alignments of certain crystal-axes are achieved by a magnetic field. The reduction of temperature T may realize alignment even if the mole number of the particle N and the diamagnetic anisotropy per mole (Δχ)DIA are considerably small for the nano-sized diamagnetic oxides, since alignment proceeds by the balance between the energy of rotational Brownian motion and field-induced anisotropy energy. Alignment of various basic inorganic oxides such as gypsum, quartz, forsterite, KDP or calcite, having a size of 20 nm diameter, is expected to occur by a field intensity of ∼50 T at T = 10 K; this intensity is presently available at a high magnetic-field laboratory. It is expected that the magnetic alignment of nano-sized particles can be observed by dispersing the particles in He gas, as achieved recently for micron-sized graphite crystals; a cryogenic liquid cannot be used as a dispersing medium. Measured (Δχ)DIA values accumulated for basic inorganic-oxides are explained quantitatively by assuming that individual bonding-orbital composing the material possesses a constant amount of diamagnetic anisotropy; hence the majority of diamagnetic nano-sized insulators are expected to show magnetic alignment at finite field intensity. [ABSTRACT FROM PUBLISHER]

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.

Transition metal-catalyzed carbene transfer reactions have a century-old history in organic chemistry and are a primary method for the synthesis of cyclopropanes. Much of the work in this field has focused on the use of diazo compounds and related precursors, which can transfer a carbene fragment to a catalyst with concomitant loss of a stable byproduct. Despite the utility of this approach, there are persistent limitations in the scope of viable carbenes, most notably those lacking stabilizing substituents. By coupling carbene transfer chemistry with two-electron redox cycles, it is possible to expand the available starting materials that can be used as carbene precursors. In this Minireview, we discuss emerging catalytic reductive cyclopropanation reactions using either gem-dihaloalkanes or carbonyl compounds. This strategy is inspired by classic stoichiometric transformations, such as the Simmons-Smith cyclopropanation and the Clemmensen reduction, but instead entails the formation of a catalytically generated transition metal carbene or carbenoid. We also present recent efforts to generate carbenes directly from methylene (CR 2 H 2 ) groups via a formal 1,1-dehydrogenation. These reactions are currently restricted to substrates containing electron-withdrawing substituents, which serve to facilitate deprotonation and subsequent oxidation of the anion., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Targeting antigens with antibodies exhibiting pH/Ca 2+ -dependent binding against an antigen is an attractive strategy to mitigate target-mediated disposition and antigen buffering. Studies have reported improved serum exposure of antibodies exhibiting pH/Ca 2+ -binding against membrane-bound receptors. Asialoglycoprotein receptor 1 (ASGR1) is a membrane-bound receptor primarily localized in hepatocytes. With a high expression level of approximately one million receptors per cell, high turnover, and rapid recycling, targeting this receptor with a conventional antibody is a challenge. In this study, we identified an antibody exhibiting pH/Ca 2+ -dependent binding to ASGR1 and generated antibody variants with increased binding to neonatal crystallizable fragment receptor (FcRn). Serum exposures of the generated anti-ASGR1 antibodies were analyzed in transgenic mice expressing human FcRn. Contrary to published reports of increased serum exposure of pH/Ca 2+ -dependent antibodies, the pH/Ca 2+ -dependent anti-ASGR1 antibody had rapid serum clearance in comparison to a conventional anti-ASGR1 antibody. We conducted sub-cellular trafficking studies of the anti-ASGR1 antibodies along with receptor quantification analysis for mechanistic understanding of the rapid serum clearance of pH/Ca 2+ -dependent anti-ASGR1 antibody. The findings from our study provide valuable insights in identifying the antigens, especially membrane bound, that may benefit from targeting with pH/Ca 2+ -dependent antibodies to obtain increased serum exposure.

Cobalt catalysts promote highly enantioselective ring-opening reactions of 2,5-dihydrofurans using vinylidenes. The products are acyclic organozinc compounds that can be functionalized with an electrophile. The proposed mechanism involves the generation of a cobalt vinylidene species that adds to the alkene by a [2+2]-cycloaddition pathway. Ring-opening then occurs via outer-sphere β-O elimination assisted by coordination of a ZnX 2 Lewis acid to the alkoxide leaving group. DFT models reveal that competing inner-sphere syn β-H and β-O elimination pathways are suppressed by the geometric constraints of the metallacycle intermediate. These models rationalize the observed stereochemical outcome of the reaction., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Nickel PyBox catalysts promote nucleophilic cyclopropanation reactions using CH 2 Cl 2 as a methylene source and Mn as a stoichiometric reductant. The substrate scope includes a broad range of alkenes bearing electron-withdrawing substituents, including esters, amides, ketones, nitriles, sulfones, phosphonate esters, trifluoromethyl groups, and electron-deficient arenes. Enantioselective cyclopropanations of α,β-unsaturated esters have been developed using chiral PyBox ligands. Mechanistic studies suggest the intermediacy of a (PyBox)Ni=CH 2 species, which adds to the alkene by a stepwise [2+2]-cycloaddition/C-C reductive elimination mechanism. DFT models provide a rationale for the nucleophilic character of the nickel carbene and the sense of enantioinduction., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Transition-metal-catalyzed reductive coupling reactions of alkynes and imines are attractive methods for the synthesis of chiral allylic amines. Mechanistically, these reactions involve oxidative cyclization of the alkyne and the imine to generate a metallacyclic intermediate, which then reacts with H 2 or a H 2 surrogate to form the product. As an alternative to this hydrogenolysis pathway, here we show that transmetalation to zinc can occur, forming a zinc metallacycle product. This organozinc product serves as a versatile nucleophile for carbon-carbon and carbon-heteroatom coupling reactions. Mechanistic studies based on isotopic labeling experiments and DFT calculations suggest that the key transmetalation step occurs between a Co(II) species and ZnCl 2 .

Cyclopropanes are common building blocks in pharmaceuticals, agrochemicals, and organic materials. The most general methods for the synthesis of chiral cyclopropanes are catalytic additions of diazoalkanes to alkenes. However, a limitation of this approach is that diazoalkanes can only be safely handled on preparative scales if they possess stabilizing substituents. Here we show that gem -dichloroalkanes can serve as precursors to nonstabilized carbenes for asymmetric cyclopropanation reactions of alkenes. The process uses a cobalt catalyst and is proposed to involve the formation of a cationic carbenoid species bearing structural resemblance to the Simmons-Smith reagent. High levels of enantioselectivity are observed for monosubstituted, 1,1-disubstituted, and internal alkenes. The reaction is compatible with alkyl-substituted carbenes, which are susceptible to undergoing competing 1,2-hydride shifts.

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.

A dinickel catalyst promotes the [2 + 2 + 1]-cycloaddition of two aldehyde equivalents and a vinylidene. The resulting methylenedioxolane products can be deprotected in one pot under acidic conditions to reveal α-hydroxy ketones. This method provides convenient access to unsymmetrical alkyl-substituted α-hydroxy ketones, which are challenging to synthesize selectively using cross-benzoin reactions. Mechanistic studies are consistent with an initial migratory insertion of the aldehyde into a dinickel bridging vinylidene. Insertion of the second aldehyde followed by C-O reductive elimination furnishes the cycloadduct. Under dilute conditions, an enone side product is generated due to a competing β-hydride elimination from the proposed metallacyclic intermediate. A DFT model consistent with the concentration-dependent formation of the methylenedioxolane and enone is presented., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Efforts to develop catalytic carbene transfer reactions have largely relied on the use of diazo precursors. However, diazoalkanes are susceptible to undergoing violent exothermic decomposition unless they contain stabilizing substituents. Consequently, most synthetic methods are restricted to diazoacetates or related derivatives. In this Perspective, we describe an alternative approach to carbene transfer catalysis based on the generation of metal carbenoids from gem -dihaloalkanes and gem -dihaloalkenes. These precursors are readily available and stable in unsubstituted form or with a variety of donor and acceptor substituents. Using this approach, it is possible to design cyclopropanation reactions with non-stabilized carbenes, such as methylene, isopropylidene, and vinylidene. Furthermore, due to the distinct mechanistic pathways of these reactions, novel modes of cycloaddition can be carried out, including [4 + 1]-cycloadditions., Competing Interests: DECLARATION OF INTERESTS The authors declare no competing interests.

A dinickel catalyst promotes reductive cyclization reactions of 1,1-dichloroalkenes containing pendant olefins. The reactions can be conducted with a Zn reductant or electrocatalytically using a carbon working electrode. Mechanistic studies are consistent with the intermediacy of a Ni 2 (vinylidene) species, which adds to the alkene and generates a metallacyclic intermediate. β-Hydride elimination followed by C-H reductive elimination forms the cyclization product. The proposed dinickel metallacycle is structurally characterized and its stoichiometric conversion to product is demonstrated. Spin polarized, unrestricted DFT calculations are used to further examine the cyclization mechanism. These computational models reveal that both nickel centers function cooperatively to mediate the key oxidative addition, migratory insertion, β-hydride elimination, and reductive elimination steps.

Redox reactions that take place in enzymes and on the surfaces of heterogeneous catalysts often require active sites that contain multiple metals. By contrast, there are very few homogeneous catalysts with multinuclear active sites, and the field of organometallic chemistry continues to be dominated by the study of single metal systems. Multinuclear catalysts have the potential to display unique properties owing to their ability to cooperatively engage substrates. Furthermore, direct metal-to-metal covalent bonding can give rise to new electronic configurations that dramatically impact substrate binding and reactivity. In order to effectively capitalize on these features, it is necessary to consider strategies to avoid the dissociation of fragile metal-metal bonds in the course of a catalytic cycle. This Account describes one approach to accomplishing this goal using binucleating redox-active ligands.In 2006, Chirik showed that pyridine-diimines (PDI) have sufficiently low-lying π* levels that they can be redox-noninnocent in low-valent iron complexes. Extending this concept, we investigated a series of dinickel complexes supported by naphthyridine-diimine (NDI) ligands. These complexes can promote a broad range of two-electron redox processes in which the NDI ligand manages electron equivalents while the metals remain in a Ni(I)-Ni(I) state.Using (NDI)Ni 2 catalysts, we have uncovered cases where having two metals in the active site addresses a problem in catalysis that had not been adequately solved using single-metal systems. For example, mononickel complexes are capable of stoichiometrically dimerizing aryl azides to form azoarenes but do not turn over due to strong product inhibition. By contrast, dinickel complexes are effective catalysts for this reaction and avoid this thermodynamic sink by binding to azoarenes in their higher-energy cis form.Dinickel complexes can also activate strong bonds through the cooperative action of both metals. Norbornadiene has a ring-strain energy that is similar to that of cyclopropane but is not prone to undergoing C-C oxidative addition with monometallic complexes. Using an (NDI)Ni 2 complex, norbornadiene undergoes rapid ring opening by the oxidative addition of the vinyl and bridgehead carbons. An inspection of the resulting metallacycle reveals that it is stabilized through a network of secondary Ni-π interactions. This reactivity enabled the development of a catalytic carbonylative rearrangement to form fused bicyclic dienones.These vignettes and others described in this Account highlight some of the implications of metal-metal bonding in promoting a challenging step in a catalytic cycle or adjusting the thermodynamic landscape of key intermediates. Given that our studies have focused nearly exclusively on the (NDI)Ni 2 system, we anticipate that many more such cases are left to be discovered as other transition-metal combinations and ligand classes are explored.

Conjugated polymers containing main chain azoarene repeat units are synthesized by a dinickel catalyzed N=N coupling reaction of aromatic diazides. The polymerization exhibits broad substrate scope and is compatible with heterocycles commonly featured in high performance organic materials, including carbazole, thiophene, propylenedioxythiophene (ProDOT), diketopyrrolopyrrole (DPP), and isoindigo. Copolymerizations can be carried out using monomer mixtures, and monoazide chain stoppers can be used to install well-defined end groups. Azopolymers possess unique properties owing to the functionality of the azo linkages. For example, protonation at nitrogen results in LUMO lowering and red-shifted absorption bands. Additionally, N=N bonds possess low-lying π* levels, allowing azopolymers to be reversibly reduced under mild conditions.

(NDI)Ni 2 catalysts (NDI=naphthyridine-diimine) promote cyclopropanation reactions of 1,3-dienes using (Me 3 Si)CHN 2 . Mechanistic studies reveal that a metal carbene intermediate is not part of the catalytic cycle. The (NDI)Ni 2 (CHSiMe 3 ) complex was independently synthesized and found to be unreactive toward dienes. Based on DFT models, we propose an alternative mechanism that begins with a Ni 2 -mediated coupling of (Me 3 Si)CHN 2 and the diene. N 2 extrusion followed by radical C-C bond formation generates the cyclopropane product. This model reproduces the experimentally observed regioselectivity and diastereoselectivity of the reaction., (© 2020 Wiley-VCH GmbH.)

A (pybox)Ni catalyst (pybox = pyridine-bis(oxazoline)) promotes the reductive cyclization of β-hydroxy 1,1-dichloroalkenes to form 2,3-dihydrofurans. The substrates for this reaction are conveniently prepared by an aldol addition followed by one-carbon homologation. Chiral substrates are accessible in highly enantioenriched form, allowing for the synthesis of stereochemically complex 2,3,4-trisubstituted products. Mechanistic studies support a vinylidene O-H insertion pathway rather than C-O cross-coupling followed by reductive dechlorination., Competing Interests: The authors declare no competing financial interest

A nickel-catalyzed reductive cyclization of 1,1-dichloroalkenyl silanes is reported. The products of this reaction are unsaturated five- or six-membered silacycles. Intermolecular variants are also described, providing access to trisubstituted vinyl silanes that are not accessible by alkyne hydrosilylation or sila-Heck-type processes. A variety of silanes can be utilized, including those that serve as nucleophilic partners in Hiyama cross-coupling reactions. Mechanistic studies using deuterium-labelled silanes are described.

Dinickel naphthyridine-bis(oxazoline) catalysts promote enantioselective intermolecular [4 + 1]-cycloadditions of vinylidene equivalents and 1,3-dienes. The products of this reaction are methylenecyclopentenes, and the exocyclic alkene is generally obtained with high Z selectivity. E - and Z -dienes react in a stereoconvergent fashion, providing cycloadducts with the same sense of absolute stereochemistry and nearly identical ee values. This feature allows dienes that are commercially available as E / Z mixtures to be used as substrates for the cycloaddition. A DFT model for the origin of asymmetric induction is provided.

Polysubstituted cyclohexenes bearing 1,3 ( meta ) substitution patterns are challenging to access using the Diels-Alder reaction (the ortho - para rule). Here, we report a cobalt-catalyzed reductive [5 + 1]-cycloaddition between a vinylcyclopropane and a vinylidene to provide methylenecyclohexenes bearing all- meta relationships. Vinylidene equivalents are generated from 1,1-dichloroalkenes using Zn as a stoichiometric reductant. Experimental observations are consistent with a mechanism involving a cobaltacyclobutane formed from a [2 + 2]-cycloaddition between a cobalt vinylidene and a vinylcyclopropane.

Cobalt pyridine-diimine (PDI) complexes catalyze the reductive spirocyclopropanation of terminal 1,3-dienes. gem -Dichlorocycloalkanes serve as carbene precursors and Zn is used as a terminal electron source. The reaction is effective for a range of gem -dichloro partners including those containing sulfur and nitrogen heterocycles. An example of an intramolecular Rh-catalyzed [5 + 2]-cycloaddition of a vinyl spirocyclopropane is demonstrated, providing rapid access to a complex tricyclic framework. Overall, this catalyst system is capable of suppressing the kinetically facile 1,2-hydride shift, which has hampered the development of Simmons-Smith reactions using Zn carbenoids possessing β-hydrogen atoms.

Most solid particles, composed of diamagnetic or weak paramagnetic materials, cannot be extracted by a conventional magnetic separator. Here we report that an ensemble of heterogeneous particles, composed of bismuth, gold, graphite and rock forming minerals are separated into fractions of different materials by small NdFeB magnetic plates. It is based on a recent finding that acceleration of a translating particle, induced by magnetic volume force in an area of field gradient, is uniquely determined by intrinsic susceptibility of material; the acceleration is independent to particle mass. The setup will serve as an effective technique of pre-treatment in analysing mixture of heterogeneous particles; such a technique is desired in various research fields of science, and the magnetic separation may play a role of a "chromatography technique" conventionally used in the analysis of organic molecules. The portable and low-cost system could provide a breakthrough for on-site research in industrial and medical fields as well as in resource explorations in nature. Extraction of rare materials such as gold or platinum becomes possible in a hazardless manner.

Cycloaddition reactions provide direct and convergent routes to cycloalkanes, making them valuable targets for the development of synthetic methods. Whereas six-membered rings are readily accessible from Diels-Alder reactions, cycloadditions that generate five-membered rings are comparatively limited in scope. Here, we report that dinickel complexes catalyze [4 + 1]-cycloaddition reactions of 1,3-dienes. The C 1 partner is a vinylidene equivalent generated from the reductive activation of a 1,1-dichloroalkene in the presence of stoichiometric zinc. Intermolecular and intramolecular variants of the reaction are described, and high levels of asymmetric induction are achieved in the intramolecular cycloadditions using a C 2 -symmetric chiral ligand that stabilizes a metal-metal bond., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Dimethylcyclopropanes are valuable synthetic targets that are challenging to access in high yield using Zn carbenoid reagents. Herein, we describe a cobalt-catalyzed variant of the Simmons-Smith reaction that enables the efficient dimethylcyclopropanation of 1,3-dienes using a Me 2 CCl 2 /Zn reagent mixture. The reactions proceed with high regioselectivity based on the substitution pattern of the 1,3-diene. The products are vinylcyclopropanes, which serve as substrates for transition-metal-catalyzed ring-opening reactions, including 1,3-rearrangement and [5+2] cycloaddition. Preliminary studies indicate that moderately activated monoalkenes are also amenable to dimethylcyclopropanation under the conditions of cobalt catalysis., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cyclic structures are highly represented in organic molecules, motivating a wealth of catalytic methods targeting their synthesis. Among the various ring-forming processes, cyclooligomerization reactions possess several attractive features but require addressing a unique challenge associated with controlling ring-size selectivity. Here we describe the catalytic reductive cocyclooligomerization of an enone and three carbene equivalents to generate a cyclopentane, a process that constitutes a formal [2 + 1 + 1 + 1]-cycloaddition. The reaction is promoted by a (quinox)Ni catalyst and uses CH 2 Cl 2 /Zn as the C 1 component. Mechanistic studies are consistent with a metallacycle-based pathway, featuring sequential migratory insertions of multiple carbene equivalents to yield cycloalkanes larger than cyclopropanes.

The synthesis and reactivity of a dinickel bridging carbene is described. The previously reported [ i- Pr NDI]Ni 2 (C 6 H 6 ) complex (NDI = naphthyridine-diimine) reacts with Ph 2 CN 2 to generate a metastable diazoalkane adduct, which eliminates N 2 at 60 °C to yield a paramagnetic Ni 2 (μ-CPh 2 ) complex. The Ni 2 (μ-CPh 2 ) complex undergoes carbene transfer to t -BuNC via an initial isonitrile adduct, which, upon heating, releases free t -BuNCCPh 2 . Based on this sequence of stoichiometric reactions, a catalytic carbene transfer reaction is demonstrated., Competing Interests: The authors declare no competing financial interest.

Azoarenes are valuable chromophores that have been extensively incorporated as photoswitchable elements in molecular machines and biologically active compounds. Here, we report a catalytic nitrene dimerization reaction that provides access to structurally and electronically diverse azoarenes. The reaction utilizes aryl azides as nitrene precursors and generates only gaseous N 2 as a byproduct. By circumventing the use of a stoichiometric redox reagent, a broad range of organic functional groups are tolerated, and common byproducts of current methods are avoided. A catalyst featuring a Ni-Ni bond is found to be uniquely effective relative to those containing only a single Ni center. The mechanistic origins of this nuclearity effect are described.