Enhancing CO Capture via Metal-Ligand Cooperativity: Tuning Ligand Basicity and Zn(II) Lewis Acidity.

A series of thiosemicarbazonato-hydrazinatopyridine zinc(II) complexes were evaluated as direct air CO capture agents. The complexes sequester CO in a methanol solution as a metal-coordinated methylcarbonate. The reaction is reversible upon sparging of solutions with an inert gas (N or Ar).

Ligand and Linkage Isomers of Bis(ethylthiocarbamato) Copper Complexes with Cyclic CH Backbone Substituents: Synthesis, Characterization, and Antiproliferation Activity.

A series of isomeric bis(alkylthiocarbamate) copper complexes have been synthesized, characterized, and evaluated for antiproliferation activity. The complexes were derived from ligand isomers with 3-methylpentyl (HL) and cyclohexyl (HL) backbone substituents, which each yield a pair of linkage isomers. The thermodynamic products CuL have two imino N and two S donors resulting in three five-member chelate rings (555 isomers).

Physical structure of constitutional isomers influences antiproliferation activity of thiosemicarbazone-alkylthiocarbamate copper complexes.

A series of hybrid thiosemicarbazone-alkylthiocarbamate copper complexes with similar electronic environments but distinct physical structures have been prepared, characterized, and evaluated for antiproliferation activity. The complexes include the constitutional isomers (1-phenylpropane-1-imine-(O-ethylthiocarbamato)-2-one-(N-methylthiosemicarbazonato))copper(II) (CuL) and (1-phenylpropane-1-one-(N-methylthiosemicarbazonato)-2-imine-(O-ethylthiocarbamato))copper(II) (CuL) along with (1-propane-1-imine-(O-ethylthiocarbamato)-2-one-(N-methylthiosemicarbazonato))copper(II) (CuL). Complexes CuL and CuL differ in the positions of the pendent thiosemicarbazone (TSC) and alkylthiocarbamate (ATC) moieties on the 1-phenylpropane backbone.

Metal-Ligand Cooperativity Promotes Reversible Capture of Dilute CO as a Zn(II)-Methylcarbonate.

In this study, a series of thiosemicarbazonato-hydrazinatopyridine metal complexes were evaluated as CO capture agents. The complexes incorporate a non-coordinating, basic hydrazinatopyridine nitrogen in close proximity to a Lewis acidic metal ion allowing for metal-ligand cooperativity. The coordination of various metal ions with (diacetyl-2-(4-methyl-thiosemicarbazone)-3-(2-hydrazinopyridine) (HL) yielded ML (M = Ni(II), Pd(II)), ML(CHOH) (M = Cu(II), Zn(II)), and [ML(PPh)]BF (M = Co(III)) complexes.

Investigations of Bis(alkylthiocarbamato)copper Linkage Isomers.

Linkage isomers are coordination compounds with the same composition but different donor atoms, resulting in distinct physical and electronic structures. A pair of linkage isomers, and , derived from phenylglyoxal bis(ethylthiocarbamate) were synthesized, isolated, and characterized by structural, electrochemical, and spectroscopic methods. The isomers are stable in solution under ambient conditions, but converts to in acid, consistent with quantum-chemical calculations.

Exploiting Metal-Ligand Cooperativity to Sequester, Activate, and Reduce Atmospheric Carbon Dioxide with a Neutral Zinc Complex.

As atmospheric levels of carbon dioxide (CO) continue to increase, there is an immediate need to balance the carbon cycle. Current approaches require multiple processes to fix CO from the atmosphere or flue gas and then reduce it to value-added products. The zinc(II) catalyst Zn(DMTH) (DMTH = diacetyl-2-(4-methyl-3-thiosemicarbazonate)-3-(2-pyridinehydrazonato)) reduces CO from air to formate with a faradaic efficiency of 15.

Synthesis, Characterization, and Biological Activity of Hybrid Thiosemicarbazone-Alkylthiocarbamate Metal Complexes.

A series of hybrid ligands (-) derived from 4-methyl-3-thiosemicarbazide and hydrazinecarbothioic acid -alkyl esters were synthesized and characterized by NMR. The ligands were chelated with copper (-), nickel (-), and zinc (-) and characterized by spectroscopy, electrochemistry, and single crystal X-ray crystallography. The chelated metals displayed substantial anodic shifts in the Cu reduction potential of ∼160 mV relative to their bis(thiosemicarbazone) analogues.

Utilizing Charge Effects and Minimizing Intramolecular Proton Rearrangement to Improve the Overpotential of a Thiosemicarbazonato Zinc HER Catalyst.

The zinc(II) complex of diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-hydrazonepyridine), ZnL (), was prepared and evaluated as a precatalyst for the hydrogen evolution reaction (HER) under homogeneous conditions in acetonitrile. Complex is protonated on the noncoordinating nitrogen of the hydrazonepyridine moiety to yield the active catalyst Zn(HL)OAc () upon addition of acetic acid. Addition of methyl iodide to yields the corresponding methylated derivative ZnLI ().

Effect of Stacking Interactions on the Translation of Structurally Related Bis(thiosemicarbazonato)nickel(II) HER Catalysts to Modified Electrode Surfaces.

A series of crystalline nickel(II) complexes (-) based on inexpensive bis(thiosemicarbazone) ligands diacetylbis(4-methyl-3-thiosemicarbazone) (HATSM), diacetylbis(4,4-dimethyl-3-thiosemicarbazone) (HATSDM), and diacetylbis[4-(2,2,2-trifluoroethyl)-3-thiosemicarbazone] (HATSM-F) were synthesized and characterized by single-crystal X-ray diffraction and NMR, UV-visible, and Fourier transform infrared spectroscopies. Modified electrodes - were prepared with films of - deposited on glassy carbon and evaluated as potential hydrogen evolution reaction (HER) catalysts. HER studies in 0.

A 5 + 1 Protic Acid Assisted Aza-Pummerer Approach for Synthesis of 4-Chloropiperidines from Homoallylic Amines.

We report that HCl·DMPU induces the formation of (thiomethyl)methyl carbenium ion from DMSO under mild conditions. Homoallylic amines react with this electrophile to generate 4-chloropiperidines in good yields. The method applies to both aromatic and aliphatic amines.

Metal-Assisted Ligand-Centered Electrocatalytic Hydrogen Evolution upon Reduction of a Bis(thiosemicarbazonato)Cu(II) Complex.

In this study, we report the electrocatalytic behavior of the neutral, monomeric Cu(II) complex of diacetyl-bis(N-4-methyl-3-thiosemicarbazonato), CuL, for metal-assisted ligand-centered hydrogen evolution in acetonitrile and dimethylformamide. CuL displays a maximum turnover frequency (TOF) of 10 000 s in acetonitrile and 5100 s in dimethylformamide at an overpotential of 0.80 and 0.

Copper catalysed aerobic oxidation of benzylic alcohols in an imidazole containing N ligand framework.

The catalytic aerobic oxidation of benzylic alcohols to corresponding aldehydes has been investigated employing a tetradentate copper(ii) complex that incorporates N-methyl imidazole (NMI) as an integral part of an N-ligand framework. The complex [L-Cu] [(L = 1-methyl-4,5-dihydro-1H-imidazol-2-yl)methyl(2-ethyl)amine] has been synthesized, characterized by spectroscopic and structural techniques, and its catalytic activity towards the aerobic oxidation of benzylic alcohols studied under ambient conditions. Catalytic turnover required addition of the nitroxyl radical initiator TEMPO.

Achieving regio- and stereo-control in the fluorination of aziridines under acidic conditions.

We developed an efficient fluorination protocol that converts easily accessible aziridines into β-fluoroamines, which are important motifs in biologically active molecules. In contrast with traditional fluorination approaches, DMPU-HF has shown both higher reactivity and regioselectivity and good functional group tolerance; thus, a wide scope of β-fluoroamines can now be accessed conveniently. The stereochemical behavior of the ring opening depends on the substitution pattern of the aziridine substrate.

Reversible methanol addition to copper Schiff base complexes: a kinetic, structural and spectroscopic study of reactions at azomethine C[double bond, length as m-dash]N bonds.

The reversible methanolysis of an azomethine C[double bond, length as m-dash]N in a series of copper(ii) Schiff base complexes has been investigated through combined spectroscopic, structural, and kinetic studies. Pentadentate copper(ii) complexes [L-Cu(X)]Y (L = 1,2-bis[(1-methyl-2-imidazolyl)methyleneamino]ethane; X = Y = ClO (1); X = Y = TfO (2); X = Y = BF (3); X = HO, Y = (ClO) (4) spontaneously add methanol in a ligand centered reaction to yield stable, isolable hemiaminal ether product complexes 5-8. In methanol free solution, 5-8 spontaneously release alcohol to regenerate 1-4.

Proposed Ligand-Centered Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation at a Noninnocent Mononuclear Metal-Thiolate.

The noninnocent coordinatively saturated mononuclear metal-thiolate complex ReL3 (L = diphenylphosphinobenzenethiolate) serves as an electrocatalyst for hydrogen evolution or hydrogen oxidation dependent on the presence of acid or base and the applied potential. ReL3 reduces acids to H2 in dichloromethane with an overpotential of 380 mV and a turnover frequency of 32 ± 3 s(-1). The rate law displays a second-order dependence on acid concentration and a first-order dependence on catalyst concentration with an overall third-order rate constant (k) of 184 ± 2 M(-2) s(-1).

A highly efficient and broadly applicable cationic gold catalyst.

Gold catalysts capable of promoting reactions at low-level loadings under mild conditions are the exception rather than the norm. We examined reactions where the regeneration of cationic gold catalyst (e.g.

2-[(Di-methyl-phenyl-phosphanyl-idene)aza-nium-yl]-5-methyl-benzene-sulfonate benzene monosolvate.

The title compound, C15H18NO3PS·C6H6, is a rare example of a crystallographically characterized exocyclic phosphiniminium-arene-sulfonate zwitterion, which crystallises as its benzene solvate. The crystal structure shows that the N atom is protonated and that the iminium H atom forms both intra- and inter-molecular hydrogen bonds to the single-bonded sulfonate O atom in an R 2 (2)(4) graph-set motif. The dihedral angle between the aromatic rings in the main molecule is 89.

Gold-catalyzed addition of N-hydroxy heterocycles to alkynes and subsequent 3,3-sigmatropic rearrangement.

Gold-catalyzed intermolecular addition of hydroxybenzotriazole derivatives to alkynes at room temperature, gives vinyl ethers 3 in high yields and with excellent regioselectivity. Unlike many other vinyl ethers, 3 can easily be purified by regular silica-gel chromatography. On heating, 3,3-sigmatropic rearrangement of 3 gives access to highly functionalized benzotriazoles.

Gold-catalyzed annulations of 2-alkynyl benzaldehydes with vinyl ethers: synthesis of dihydronaphthalene, isochromene, and bicyclo[2.2.2]octane derivatives.

With the suitable selection of a gold catalyst as well as the appropriate control of the reaction conditions, various new gold-catalyzed cyclizations of 2-alkynyl benzaldehyde with acyclic or cyclic vinyl ethers have been developed. Acetal-tethered dihydronaphthalene and isochromenes were obtained from the reactions of 2-alkynyl benzaldehydes with acyclic vinyl ethers under mild conditions. And, more interestingly, the gold-catalyzed reactions of 2-alkynyl benzaldehyde with a cyclic vinyl ether afforded the bicyclo[2.

Selective and reversible base-induced elimination of a ruthenium dithioether yields a vinyl metallosulfonium complex.

Chemical oxidation of tris(2-diphenylphosphinebenzenethiolato)ruthenate(II) [Ru-1](-) with ferrocenium hexafluorophosphate in the presence of ethylene yields [(2-diphenylphosphinebenzenethiolato)(ethane-1,2-diylbis(thio-2,1-phenylene)diphenylphosphine)ruthenium(II)] hexafluorophosphate, [Ru-1·C(2)H(4)]PF(6), from addition of the alkene across cis sulfur sites. The [Ru-1·C(2)H(4)](+) complex displays a single redox couple at +794 mV versus ferrocenium/ferrocene. (1)H NMR of [Ru-1·C(2)H(4)](+) displays ethylene resonances at δ = 1.

Physangulidines A, B, and C: three new antiproliferative withanolides from Physalis angulata L.

Bioassay-directed fractionation of the whole plant of Physalis angulata L. afforded three new antiproliferative withanolides with an unusual carbon framework: physangulidines A (1), B (2), and C (3). Structures of the three isomeric withanolides were determined by a combination of HRMS, NMR spectroscopic, and X-ray crystallographic methods.

Tetra-μ-acetato-κO:O'-bis-{[2,2-dimeth-yl-N-(pyridin-2-yl)propanamide-κN]copper(II)}(Cu-Cu).

The crystal structure of the title compound, [Cu(2)(C(2)H(3)O(2))(4)(C(10)H(14)N(2)O)(2)], reveals a dinuclear Cu(II) complex located about a center of inversion. The coordination environment of each Cu(II) cation is distorted octa-hedral, composed of four bridging acetate ligands, an apical pyridine donor and is completed by a Cu-Cu bond. The amide H atom forms intra-molecular hydrogen bonds to two carboxyl O atoms.

Metal-stabilized thiyl radicals as scaffolds for reversible alkene addition via C-S bond formation/cleavage.

The one-electron oxidation of metal thiolates results in an increased oxidation state of the metal ion or the formation of a sulfur-based, thiyl radical in limiting extremes. For complexes with highly covalent M-S bonds, the unpaired electron may be delocalized over the metal and the sulfur, yielding a metal-stabilized thiyl radical. Oxidation of the metal thiolate precursors [Ru(DPPBT)(3)](-), [Ru-1](-), and Re(DPPBT)(3), Re-1 (DPPBT = diphenylphosphinobenzenethiolate), generates metal-stabilized thiyl radicals that react with alkenes to yield dithioether-metal products.

Racemic (1,4-dioxan-2-yl)diphenylmethanol.

The title compound, C(17)H(18)O(3), prepared by microwave irradiation of benzophenone and dioxane, crystallizes in a racemic mixture that forms one-dimensional chains via strong hydrogen bonding of the hydroxy group to the adjacent symmetry-generated 1,4-dioxan-2-yl group; the O-H···O distance is 1.99 (3) Å and the O-H···O angle is 160 (2)°.

Controlled sulfur oxygenation of the ruthenium dithiolate (4,7-bis-(2'-methyl-2'-mercaptopropyl)-1-thia-4,7-diazacyclononane)RuPPh(3) under limiting O(2) conditions yields thiolato/sulfinato, sulfenato/sulfinato, and bis-sulfinato derivatives.

The ruthenium(II) dithiolate complex (bmmp-TASN)RuPPh(3) (1) reacts with O(2) under limiting conditions to yield isolable sulfur oxygenated derivatives as a function of reaction time. With this approach, a family of sulfur-oxygenates has been prepared and isolated without the need for O-atom transfer agents or column chromatography. Addition of 5 equiv of O(2) to 1 yields the thiolato/sulfinato complex (bmmp-O(2)-TASN)RuPPh(3) (2) in 70% yield within 5 min.