Salts of 2-amino-5-iodo-pyridinium.

Reaction of 2-amino-5-iodo-pyridine (5IAP) with concentrated HBr at room temperature yielded 2-amino-5-iodo-pyridinium bromide, CHIN ·Br or (5IAPH)Br. The complex formed pale-yellow crystals, which exhibit significant hydrogen bonding between the amino and pyridinium N-H donors and bromide ion acceptors. Halogen bonding is also observed.

Designing chemical systems for precision deuteration of medicinal building blocks.

Methods are lacking that can prepare deuterium-enriched building blocks, in the full range of deuterium substitution patterns at the isotopic purity levels demanded by pharmaceutical use. To that end, this work explores the regio- and stereoselective deuteration of tetrahydropyridine (THP), which is an attractive target for study due to the wide prevalence of piperidines in drugs. A series of d-d tetrahydropyridine isotopomers were synthesized by the stepwise treatment of a tungsten-complexed pyridinium salt with H/D and H/D.

Synthesis of Quinoline-Based Pt-Sb Complexes with L- or Z-Type Interaction: Ligand-Controlled Redox via Anion Transfer.

A series of Pt-Sb complexes with two or three L-type quinoline side arms were prepared and studied. Two ligands, tri(8-quinolinyl)stibane (SbQ, Q = 8-quinolinyl, ) and 8,8'-(phenylstibanediyl)diquinoline (SbQPh, ), were used to synthesize the Pt-Sb complexes (SbQ)PtCl () and (SbQPh)PtCl (). Chloride abstraction with AgOAc provided the bis-acetate complexes (SbQ)Pt(OAc) () and (SbQPh)Pt(OAc) ().

Di-chloridotetra-kis-(3-meth-oxy-aniline)nickel(II).

The reaction of nickel(II) chloride with 3-meth-oxy-aniline yielded di-chlorido-tetra-kis-(3-meth-oxy-aniline)nickel(II), [NiCl(CHNO)], as yellow crystals. The Ni ion is pseudo-octa-hedral with the chloride ions to each other. The four 3-meth-oxy-aniline ligands differ primarily due to different conformations about the Ni-N bond, which also affect the hydrogen bonding.

Carbodicarbene-Stibenium Ion-Mediated Functionalization of C(sp)-H and C(sp)-H Bonds.

Main-group element-mediated C-H activation remains experimentally challenging and the development of clear concepts and design principles has been limited by the increased reactivity of relevant complexes, especially for the heavier elements. Herein, we report that the stibenium ion [(CDC)Sb][NTf] (1) (CDC=bis-pyridyl carbodicarbene; NTf=bis(trifluoromethanesulfonyl)imide) reacts with acetonitrile in the presence of the base 2,6-di-tert-butylpyridine to enable C(sp)-H bond breaking to generate the stiba-methylene nitrile complex [(CDC)Sb(CHCN)][NTf] (2). Kinetic analyses were performed to elucidate the rate dependence for all the substrates involved in the reaction.

Borafluorene-Mediated Sulfur Activation: Isolation of Boryl-Linked S and S Catenates and Related Chalcogenide Molecules.

Although the activation of elemental sulfur by main group compounds is well-documented in the literature, the products of such reactions are often heterocyclic in nature. However, the isolation and characterization of sulfur catenates (i.e.

Acid Strength Effects on Dimerization during Metal-Free Catalytic Dioxygen Reduction.

Development of earth-abundant catalysts for the reduction of dioxygen (ORR) is essential for the development of alternative industrial processes and energy sources. Here, we report a transition metal-free dicationic organocatalyst () for the ORR. The ORR performance of this compound was studied in acetonitrile solution under both electrochemical conditions and spectrochemical conditions, using halogenated acetic acid derivatives spanning a p range of 12.

Pre-equilibrium reactions involving pendent relays improve CO reduction mediated by molecular Cr-based electrocatalysts.

Homogeneous earth abundant transition-metal electrocatalysts capable of carbon dioxide (CO) reduction to generate value-added chemical products are a possible strategy to minimize rising anthropogenic CO emissions. Previously, it was determined that Cr-centered bipyridine-based NO complexes for CO reduction are kinetically limited by a proton-transfer step during C-OH bond cleavage. Therefore, it was hypothesized that the inclusion of pendent relay groups in the secondary coordination sphere of these molecular catalysts could increase their catalytic activity.

Pentacyclic fused diborepinium ions with carbene- and carbone-mediated deep-blue to red emission.

Designing molecules that can undergo late-stage modifications resulting in specific optical properties is useful for developing structure-function trends in materials, which ultimately advance optoelectronic applications. Herein, we report a series of fused diborepinium ions stabilized by carbene and carbone ligands (diamino-N-heterocyclic carbenes, cyclic(alkyl)(amino) carbenes, carbodicarbenes, and carbodiphosphoranes), including a detailed bonding analysis. These are the first structurally confirmed examples of diborepin dications and we detail how distortions in the core of the pentacyclic fused system impact aromaticity, stability, and their light-emitting properties.

Improving co-electrocatalytic carbon dioxide reduction by optimizing the relative potentials of the redox mediator and catalyst.

The effects of fixing the redox mediator (RM) reduction potential relative to a series of Cr-centered complexes capable of the reduction of CO to CO are disclosed. The greatest co-electrocatalytic activity enhancement is observed when the reduction potentials of the catalyst and RM are identical, implying that controlling the speciation of the Cr complex relative to RM activation is essential for improving catalytic performance. In all cases, the potential where co-catalytic activity is observed matches the reduction potential of the RM, regardless of the relative reduction potential of the Cr complex.

Hexa-Fe(III) Carboxylate Complexes Facilitate Aerobic Hydrocarbon Oxidative Functionalization: Rh Catalyzed Oxidative Coupling of Benzene and Ethylene to Form Styrene.

Fe(II) carboxylates react with dioxygen and carboxylic acid to form Fe(μ-OH)(μ-O)(μ-X)(HX) (X = acetate or pivalate), which is an active oxidant for Rh-catalyzed arene alkenylation. Heating (150-200 °C) the catalyst precursor [(η-CH)Rh(μ-OAc)] with ethylene, benzene, Fe(II) carboxylate, and dioxygen yields styrene >30-fold faster than the reaction with dioxygen in the absence of the Fe(II) carboxylate additive. It is also demonstrated that Fe(μ-OH)(μ-O)(μ-X)(HX) is an active oxidant under anaerobic conditions, and the reduced material can be reoxidized to Fe(μ-OH)(μ-O)(μ-X)(HX) by dioxygen.

Mono- and Bis-Phosphine Promoted Incorporation of Boron, Nitrogen, and Phosphorus into Heterocycles via Staudinger Reactions of Borafluorene Azides.

We report the synthesis and characterization of a series of BNP-incorporated borafluorenate heterocycles formed via thermolysis reactions of pyridylphosphine and bis(phosphine)-coordinated borafluorene azides. The use of diphenyl-2-pyridylphosphine (PyPhP), trans-1,2-bis(diphenylphosphino)ethylene (PhP(H)C═C(H)PPh), and bis(diphenylphosphino)methane (PhPC(H)PPh) as stabilizing ligands resulted in Staudinger reactions to form complex heterocycles with four- (BNP, BNPC, PN) and five-membered (BNPC and BNPC) rings, which were successfully isolated and fully characterized by multinuclear NMR and X-ray crystallography. However, when bis(diphenylphosphino)benzene (PhP-Ph-PPh) was used as the ligand in a reaction with 9-bromo-9-borafluorene (BF-Br), due to the close proximity of the donor P atoms, the diphosphine-stabilized borafluoronium ion with an unusual borafluorene dibromide anion was formed.

Synthesis of 1-Azatriene Complexes of Tungsten: Metal-Promoted Ring-Opening of Dihydropyridine.

For nearly a century, chemists have explored how transition-metal complexes can affect the physical and chemical properties of linear conjugated polyenes and heteropolyenes. While much has been written about higher hapticity complexes (η-η), less is known about the chemistry of their η analogues. Herein, we describe a general method for synthesizing 5,6-η-(1-azatriene) tungsten complexes via a 6π-azaelectrocyclic dihydropyridine ring-opening that is promoted by the π-basic nature of {WTp(NO)(PMe)}.

Controlling product selectivity during dioxygen reduction with Mn complexes using pendent proton donor relays and added base.

The catalytic reduction of dioxygen (O) is important in biological energy conversion and alternative energy applications. In comparison to Fe- and Co-based systems, examples of catalytic O reduction by homogeneous Mn-based systems is relatively sparse. Motivated by this lack of knowledge, two Mn-based catalysts for the oxygen reduction reaction (ORR) containing a bipyridine-based non-porphyrinic ligand framework have been developed to evaluate how pendent proton donor relays alter activity and selectivity for the ORR, where Mn(dhbpy)Cl (1) was used as a control complex and Mn(dhbpy)Cl (2) contains a pendent -OMe group in the secondary coordination sphere.

Unlocking Biradical Character in Diborepins.

Systems that possess open- and closed-shell behavior attract significant attention from researchers due to their inherent redox and charge transport properties. Herein, we report the synthesis of the first diborepin biradicals. They display tunable biradical character based on the steric and electronic profile of the stabilizing ligand and the resulting geometric deviation of the diborepin core from planarity.

Unveiling Three Interconvertible Redox States of Boraphenalene.

Neutral 1-boraphenalene displays the isoelectronic structure of the phenalenyl carbocation and is expected to behave as an attractive organoboron multi-redox system. However, the isolation of new redox states have remained elusive even though the preparation of neutral boron(III)-containing phenalene compounds have been extensively studied. Herein, we have adopted an N-heterocyclic carbene ligand stabilization approach to achieve the first isolation of the stable and ambipolar 1-boraphenalenyl radical .

Tungsten-anisole complex provides 3,6-substituted cyclohexenes for highly diversified chemical libraries.

Medicinal chemists use vast combinatorial molecular libraries to develop leads for new pharmaceuticals. The syntheses of these compounds typically rely on coupling molecular fragments through atoms with planar (sp) geometry. These so-called flat molecules often lack the protein binding site specificity needed to be an effective drug.

Geminal bimetallic coordination of a carbone to main-group and transition metals.

The non-bonding carbone lone pair in geometrically-constrained antimony and bismuth carbodiphosphorane complexes readily complexed AuCl to afford rare examples of geminal bimetallic carbone coordination featuring a main-group metal.

Air- and photo-stable luminescent carbodicarbene-azaboraacenium ions.

Substitution of a C=C bond by an isoelectronic B-N bond is a well-established strategy to alter the electronic structure and stability of acenes. BN-substituted acenes that possess narrow energy gaps have attractive optoelectronic properties. However, they are susceptible to air and/or light.

The Tungsten-Promoted Synthesis of Piperidyl-Modified -Methylphenidate Derivatives.

Due to its efficacy as a dopamine receptor agonist, methylphenidate (MPH) is of interest as a potential therapeutic for cocaine addiction. While numerous derivatives of MPH have been investigated for their potential medicinal value, functionalization of the piperidine ring has not been explored. The pyridine borane ligand in WTp(NO)(PMe)(η-pyBH) is dearomatized by the metal and can be elaborated to the analogous η-mesylpyridinium complex.

Bis(9-Boraphenanthrene) and Its Stable Biradical.

Selective and site-specific boron-doping of polycyclic aromatic hydrocarbon frameworks often give rise to redox and/or photophysical properties that are not easily accessible with the analogous all-carbon systems. Herein, we report ligand-mediated control of boraphenanthrene closed- and open-shell electronic states, which has led to the first structurally characterized examples of neutral bis(9-boraphenanthrene) (-) and its corresponding biradical (). Notably, compounds and show intramolecular charge transfer absorption from the 9-boraphenanthrene units to -quinodimethane, exhibiting dual (red-shifted) emission in solution due to excited state conjugation enhancement (ESCE).

Photochemically and Thermally Generated BN-Doped Borafluorenate Heterocycles via Intramolecular Staudinger-Type Reactions.

A series of BN-incorporated borafluorenate heterocycles, bis(borafluorene-phosphinimine)s (-), have been formed via molecular Staudinger-type reactions. The reactions were promoted by light or heat using monodentate phosphine-stabilized 9-azido-9-borafluorenes (RP-BF-N; -) and involve the release of dinitrogen (N), migration of phosphine from boron to nitrogen, and oxidation of the phosphorus center (P to P). Density functional theory (DFT) calculations provide mechanistic insight into the formation of these compounds.

The double protonation of dihapto-coordinated benzene complexes enables dearomatization using aromatic nucleophiles.

Friedel-Crafts Arylation (the Scholl reaction) is the coupling of two aromatic rings with the aid of a strong Lewis or Brønsted acid. This historically significant C-C bond forming reaction normally leads to aromatic products, often as oligomeric mixtures, dictated by the large stabilization gained upon their rearomatization. The coordination of benzene by a tungsten complex disrupts the natural course of this reaction sequence, allowing for Friedel-Crafts Arylation without rearomatization or oligomerization.

An Inorganic Fluorescent Chemosensor: Rational Design and Selective Mg Detection.

A Zn based complex, , displays greatly increased fluorescence emission in the presence of Mg. Fluorescent and computational studies suggest that selectively interacts with Mg due to optimal cavity size formation between two uncoordinated pyrazole side arms. This work thus represents a new approach to the development of fluorescent chemosensors.