Pnictogen-based vanadacyclobutadiene complexes.

The reactivity of the V[triple bond, length as m-dash]C Bu multiple bonds in the complex (dBDI)V[triple bond, length as m-dash]C Bu(OEt) (C) (dBDI = ArNC(CH)CHC(CH)NAr, Ar = 2,6- PrCH) with unsaturated substrates such as N[triple bond, length as m-dash]CR (R = Ad or Ph) and P[triple bond, length as m-dash]CAd leads to the formation of rare 3d transition metal compounds featuring α-aza-vanadacyclobutadiene, (dBDI)V(κ- , - BuC(R)N) (R = Ad, 1; R = Ph, 2) and β-phospha-vanadacyclobutadiene moieties, (dBDI)V(κ- , - BuPAd) (3). Complexes 1-3 are characterized using multinuclear and multidimensional NMR spectroscopy, including the preparation of the 50% N-enriched isotopologue (dBDI)V(κ- , - BuCC(Ad)N) (1-N). Solid-state structural analysis is used to determine the dominant resonance structures of these unique pnictogen-based vanadacyclobutadienes.

Cationic Bis(hydrosilane)-Coinage-Metal Complexes: Synthesis, Characterization, and Use as Catalysts for Outer-Sphere C=O Hydrosilylation Not Involving Metal Hydrides.

The preparation of cationic bis(hydrosilane)-coinage-metal complexes by chloride abstraction from the neutral metal chloride precursors with Na[BAr ] is described. Unlike previously reported hydrosilane-stabilized copper and silver complexes, the presented complexes are cationic and feature two bidentate (ortho-silylphenyl)phosphine ligands. These complexes were fully characterized by NMR spectroscopy and X-ray diffraction analysis, revealing that both Si-H bonds are activated by the Lewis acidic cationic metal center.

Identification, Characterization, and Electronic Structures of Interconvertible Cobalt-Oxygen TAML Intermediates.

The reaction of Li[(TAML)Co]·3HO (TAML = tetraamido macrocyclic tetraanionic ligand) with iodosylbenzene at 253 K in acetone in the presence of redox-innocent metal ions (Sc(OTf) and Y(OTf)) or triflic acid affords a blue species , which is converted reversibly to a green species upon cooling to 193 K. The electronic structures of and have been determined by combining advanced spectroscopic techniques (X-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), X-ray absorption spectroscopy/extended X-ray absorption fine structure (XAS/EXAFS), and magnetic circular dichroism (MCD)) with theoretical studies. Complex is best represented as an = 1/2 [(Sol)(TAML)Co---OH(LA)] species (LA = Lewis/Brønsted acid and Sol = solvent), where an = 1 Co(III) center is antiferromagnetically coupled to = 1/2 TAML, which represents a one-electron oxidized TAML ligand.

Ynamide and Azaalleneyl. Acid-Base Promoted Chelotropic and Spin-State Rearrangements in a Versatile Heterocumulene [(Ad)NCC(Bu)].

We introduce the heterocumulene ligand [(Ad)NCC(Bu)] (Ad=1-adamantyl (CH), Bu=tert-butyl, (CH)), which can adopt two forms, the azaalleneyl and ynamide. This ligand platform can undergo a reversible chelotropic shift using Brønsted acid-base chemistry, which promotes an unprecedented spin-state change of the [V] ion. These unique scaffolds are prepared via addition of 1-adamantyl isonitrile (C≡NAd) across the alkylidyne in complexes [(BDI)V≡CBu(OTf)] (A) (BDI=ArNC(CH)CHC(CH)NAr), Ar=2,6-PrCH) and [(dBDI)V≡CBu(OEt)] (B) (dBDI=ArNC(CH)CHC(CH)NAr).

Stabilization of Naphthalene Diimide Anions by Ion Pair Formation in Nonaqueous Organic Redox Flow Batteries.

In redox flow batteries, a compelling strategy for enhancing the charge capacity of redox-active organic molecules involves storing multiple electrons within a single molecule. However, this approach poses unique challenges such as chemical instability by forming radicals, elevated energy requirements, and unsustainable charge concentration. Ion pairing is a possible solution to achieve charge neutrality and engineer redox potential shifts but has received limited attention.

Vanadium Alkylidyne Initiated Cyclic Polymer Synthesis: The Importance of a Deprotiovanadacyclobutadiene Moiety.

Reported is the catalytic cyclic polymer synthesis by a 3d transition metal complex: a V(V) alkylidyne, [(dBDI)V≡CBu(OEt)] (), supported by the deprotonated β-diketiminate dBDI (dBDI = ArNC(CH)CHC(CH)NAr, Ar = 2,6-PrCH). Complex is a precatalyst for the polymerization of phenylacetylene (PhCCH) to give cyclic poly(phenylacetylene) (-PPA), whereas its precursor, complex [(BDI)V≡CBu(OTf)] (; BDI = [ArNC(CH)]CH, Ar = 2,6-PrCH, OTf = OSOCF), and the zwitterion [((CF)B-dBDI)V≡CBu(OEt)] () exhibit low catalytic activity despite having a neopentylidyne ligand. Cyclic polymer topologies were verified by size-exclusion chromatography (SEC) and intrinsic viscosity studies.

Enantioselective Aziridination of Unactivated Terminal Alkenes Using a Planar Chiral Rh(III) Indenyl Catalyst.

Chiral aziridines are important structural motifs found in natural products and various target molecules. They serve as versatile building blocks for the synthesis of chiral amines. While advances in catalyst design have enabled robust methods for enantioselective aziridination of activated olefins, simple and abundant alkyl-substituted olefins pose a significant challenge.

Highly Enantioselective 6π Photoelectrocyclizations Engineered by Hydrogen Bonding.

Photochemical electrocyclization reactions are valued for both their ability to produce structurally complex molecules and their central role in elucidating fundamental mechanistic principles of photochemistry. We present herein a highly enantioselective 6π photoelectrocyclization catalyzed by a chiral Ir(III) photosensitizer. This transformation was successfully realized by engineering a strong hydrogen-bonding interaction between a pyrazole moiety on the catalyst and a basic imidazolyl ketone on the substrate.

Selective ring expansion and C-H functionalization of azulenes.

We report a transition metal-catalyzed ring expansion of azulene that can be contrasted with C-H functionalization. This study represents the first example of the successful ring expansion of azulene using Cu(hfacac) (hfacac: hexafluoroacetylacetonate) with a diazo reagent. This result is notable for extending the Buchner reaction, previously limited to benzenoid aromatics, to nonbenzenoid compounds.

Tellurolate: an effective Te-atom transfer reagent to prepare the triad of group 5 metal bis(tellurides).

We show in this work how lithium tellurolate Li(X)TeCHSiMe (X = THF, = 1, 1; X = 12--4, = 2, 2), can serve as an effective Te-atom transfer reagent to all group 5 transition metal halide precursors irrespective of the oxidation state. Mononuclear and bis(telluride) complexes, namely (PNP)M(Te) (M = V; Nb, 3; Ta, 4; PNP = N[2-PPr-4-methylphenyl]), are reported herein including structural and spectroscopic data. Whereas the known complex (PNP)V(Te) can be readily prepared from the trivalent precursor (PNP)VCl, two equiv.

APP-C31: An Intracellular Promoter of Both Metal-Free and Metal-Bound Amyloid-β Aggregation and Toxicity in Alzheimer's Disease.

Intracellular C-terminal cleavage of the amyloid precursor protein (APP) is elevated in the brains of Alzheimer's disease (AD) patients and produces a peptide labeled APP-C31 that is suspected to be involved in the pathology of AD. But details about the role of APP-C31 in the development of the disease are not known. Here, this work reports that APP-C31 directly interacts with the N-terminal and self-recognition regions of amyloid-β (Aβ ) to form transient adducts, which facilitates the aggregation of both metal-free and metal-bound Aβ peptides and aggravates their toxicity.

Copper-Catalyzed Regiodivergent Internal Allylic Alkylations.

We report a copper-catalyzed, regioselective, and stereospecific alkylation of unbiased internal allylic carbonates with functionalized alkyl and aryl Grignard reagents. The reactions exhibit high stereospecificity and regioselectivity for either S 2 or S 2' products under two sets of copper-catalyzed conditions, which enables the preparation of a broad range of products with E-alkene selectivity. Density functional theory calculations reveal the origins of the regioselectivity based on the different behaviors of homo- and heterocuprates.

Unveiling the impact of oxidation-driven endogenous protein interactions on the dynamics of amyloid-β aggregation and toxicity.

Cytochrome (Cyt ), a multifunctional protein with a crucial role in controlling cell fate, has been implicated in the amyloid pathology associated with Alzheimer's disease (AD); however, the interaction between Cyt and amyloid-β (Aβ) with the consequent impact on the aggregation and toxicity of Aβ is not known. Here we report that Cyt can directly bind to Aβ and alter the aggregation and toxicity profiles of Aβ in a manner that is dependent on the presence of a peroxide. When combined with hydrogen peroxide (HO), Cyt redirects Aβ peptides into less toxic, off-pathway amorphous aggregates, whereas without HO, it promotes Aβ fibrillization.

Nickel-Carbon Bond Oxygenation with Green Oxidants via High-Valent Nickel Species.

Described herein is the synthesis of the Ni complex (BuMetacn)Ni(cycloneophyl) (BuMetacn = 1--butyl-4,7-dimethyl-1,4,7-triazacyclononane, cycloneophyl = -CHCMe--CH-) and its reactivity with dioxygen and peroxides. The new BuMetacn ligand is designed to enhance the oxidatively induced bond-forming reactivity of high-valent Ni intermediates. Tunable chemoselectivity for Csp-O vs Csp-Csp bond formation was achieved by selecting the appropriate solvent and reaction conditions.

Photo- and Metal-Mediated Deconstructive Approaches to Cyclic Aliphatic Amine Diversification.

Described herein are studies toward the core modification of cyclic aliphatic amines using either a riboflavin/photo-irradiation approach or Cu(I) and Ag(I) to mediate the process. Structural remodeling of cyclic amines is explored through oxidative C-N and C-C bond cleavage using peroxydisulfate (persulfate) as an oxidant. Ring-opening reactions to access linear aldehydes or carboxylic acids with flavin-derived photocatalysis or Cu salts, respectively, are demonstrated.

Fractional Charge Density Functional Theory and Its Application to the Electro-inductive Effect.

We employed the chemical potential equalization principle to demonstrate that fractional electrons are involved in the electro-inductive effect as well as the vibrational Stark effect. By the chemical potential model, we were able to deduce that the frontier molecular orbitals of immobilized molecules can provide valuable insight into these effects. To further understand and quantify these findings, we introduced fractional charge density functional theory (FC-DFT), a canonical ensemble approach for open systems.

Enantioselective Rhodium-Catalyzed Pauson-Khand Reactions of 1,6-Chloroenynes with 1,1-Disubstituted Olefins.

An enantioselective rhodium(I)-catalyzed Pauson-Khand reaction (PKR) using 1,6-chloroenynes that contain challenging 1,1-disubstituted olefins is described. In contrast to the previous studies with these types of substrates, which are only suitable for a single type of tether and alkyne substituent, the new approach results in a more expansive substrate scope, including carbon and heteroatom tethers with polar and non-polar substituents on the alkene. DFT calculations provide critical insight into the role of the halide, which pre-polarizes the alkyne to lower the barrier for metallacycle formation and provides the proper steric profile to promote a favorable enantiodetermining interaction between substrate and chiral diphosphine ligand.

Studying Regioisomer Formation in the Pd-Catalyzed Fluorination of Cyclic Vinyl Triflates: Evidence for in situ Ligand Modification.

Pd-catalyzed nucleophilic fluorination reactions are important methods for the synthesis of fluoroarenes and fluoroalkenes. However, these reactions can generate a mixture of regioisomeric products that are often difficult to separate. While investigating the Pd-catalyzed fluorination of cyclic vinyl triflates, we observed that the addition of a substoichiometric quantity of TESCF significantly improved the regioselectivity of the reaction.

Controlling π-π Interactions of Highly Soluble Naphthalene Diimide Derivatives for Neutral pH Aqueous Redox Flow Batteries.

Organic redox-active molecules are a promising platform for designing sustainable, cheap, and safe charge carriers for redox flow batteries. However, radical formation during the electron-transfer process causes severe side reactions and reduces cyclability. This problem is mitigated by using naphthalene diimide (NDI) molecules and regulating their π-π interactions.

How To Enhance the Efficiency of Breslow Intermediates for SET Catalysis.

Oxidative carbene organocatalysis, which proceeds via single electron transfer (SET) pathways, has been limited by the moderately reducing properties of deprotonated Breslow intermediates s derived from thiazol-2-ylidene and 1,2,4-triazolylidene . Using computational methods, we assess the redox potentials of s based on ten different types of known stable carbenes and report our findings concerning the key parameters influencing the steps of the catalytic cycle. From the calculated values of the first oxidation potential of s derived from carbenes to , it appears that, apart from the diamidocarbene , all the others are more reducing than thiazol-2-ylidene and the 1,2,4-triazolylidene .

The Role of the Redox Non-Innocent Hydroxyl Ligand in the Activation of O Performed by [Ni(H)(OH)].

The cationic complex [Ni(H)(OH)] was previously found to activate dioxygen and methane in gas phase under single collision conditions. These remarkable reactivities were thought to originate from a non-classical electronic structure, where the Ni-center adopts a Ni(II), instead of the classically expected Ni(III) oxidation state by formally accepting an electron from the hydroxo ligand, which formally becomes a hydroxyl radical in the process. Such radicaloid oxygen moieties are envisioned to easily react with otherwise inert substrates, mimicking familiar reactivities of free radicals.

Spin-state crossover in photo-catalyzed nitrile dihydroboration Mn-thiolate cooperation.

The role of S-donors in ligand-assisted catalysis using first-row metals has not been broadly investigated. Herein is described a combined experimental and computational mechanistic study of the dihydroboration of nitriles with pinacolborane (HBpin) catalyzed by the Mn(i) complex, Mn(κ-SNS)(CO), that features thioether, imine, and thiolate donors. Mechanistic studies revealed that catalysis requires the presence of UV light to enter and remain in the catalytic cycle and evidence is presented for loss of two CO ligands.

Oxidatively induced reactivity in Rh(iii)-catalyzed 7-azaindole synthesis: insights into the role of the silver additive.

A typical synthetic protocol for preparing 7-azaindoles involves the coupling of 2-aminopyridine and alkyne substrates using a Rh(iii)-catalyst. The catalysis requires the assistance of an external Ag oxidant that is thought to regenerate the catalyst and increase the turnover efficiency. Density functional theory (DFT) simulations confirm that Ag can oxidize various neutral Rh(iii) intermediates encountered at different stages of the catalysis.

Metal-Ligand Cooperativity to Assemble a Neutral and Terminal Niobium Phosphorus Triple Bond (Nb≡P).

Decarbonylation along with P-atom transfer from the phosphaethynolate anion, PCO , to the Nb complex [(PNP)NbCl (N BuAr)] (1) (PNP=N[2-P Pr -4-methylphenyl] ; Ar=3,5-Me C H ) results in its coupling with one of the phosphine arms of the pincer ligand to produce a phosphanylidene phosphorane complex [(PNPP)NbCl(N BuAr)] (2). Reduction of 2 with CoCp* cleaves the P-P bond to form the first neutral and terminal phosphido complex of a group 5 transition metal, namely, [(PNP)Nb≡P(N BuAr)] (3). Theoretical studies have been used to understand both the coupling of the P-atom and the reductive cleavage of the P-P bond.