Copper complexes for the chemoselective N-arylation of arylamines and sulfanilamides via Chan-Evans-Lam cross-coupling

Copper(II) complexes with tridentate NNN-ligands were utilized for Chan-Evans-Lam (CEL) cross-coupling reactions to enable the N-arylation of multifarious N-nucleophiles through the activation of aryl boronic acids. A condition-specific methodology was developed to chemoselectively target the amine versus sulfonamide N-arylation of 4-aminobenzenesulfonamide using new catalysts. Two different pyridine-based ligands and corresponding copper(II) complexes were characterized using 1H and 13C-NMR, FTIR, and UV-vis spectroscopy, HRMS, single-crystal X-ray diffraction, and cyclic voltammetry. Solvent and base-controlled cross-coupling reactions were observed, which led to the optimization of selective conditions for targeted C-N bond formation of sulfanilamides. Beyond the chemoselective processes reported here, a breadth of N-nucleophiles including sulfanilamides and arylamines were screened for arylation by this CEL catalyst.

Anion influences on the structures of pyridyl-iminosulfonate copper(II) complexes and their reactivity in Chan–Lam couplings

Reaction of pyridylcarbaldehyde with taurine or orthanilic acid in the presence of copper salts provided copper complexes (PyC(H)N-CxHy-SO3)CuX with X = chloride, nitrate, acetate, or triflate and CxHy = o-C6H4 or C2H4. All complexes were characterized by single crystal X-ray diffraction and formed either mononuclear water adducts, dimeric complexes, or one-dimensional coordination polymers. Activities in the Chan–Lam coupling of aniline with phenylboronic acid varied by less than a factor of two between catalysts with various anions, supporting previous mechanistic claims that the anion does not participate in the formation of copper–boron intermediates. There is no difference in the performance of a catalyst with an alkyl backbone, indicating that sulfonate dissociation is not part of the catalytic cycle.

Copper complexes for the promotion of iminopyridine ligands derived from β-alanine and self-aldol additions: relaxivity and cytotoxic properties

In the study presented herein, we explore the ability of copper complexes with coordinated pyridine-2-carboxaldehyde (pyca) or 2-acetylpyridine (acepy) ligands to promote the addition of amines (Schiff condensation) and other nucleophiles such as alcohols (hemiacetal formation). Distinct reactivity patterns are observed: unlike pyca complexes, acepy copper complexes can promote self-aldol addition. The introduction of a flexible chain via Schiff condensation with β-alanine allows the possibility of chelate ring ring-opening processes mediated by pH. Further derivatization of the complex [CuCl(py-2-C(H)[double bond, length as m-dash]NCH2CH2COO)] is possible by replacing its chloride ligand with different pseudohalogens (N3-, NCO- and NCS-). In addition to the change in their magnetism, which correlates with their solid-state structures, more unexpected effects in their cytotoxicity and relaxitivities are observed, which determines their possibility to be used as MRI contrast agents. The replacement of a chloride by another pseudohalogen, although a simple strategy, can be used to critically change the cytotoxicity of the Schiff base copper(ii) complex and its selectivity towards specific cell lines.

Syntheses, Structures, and Catalytic Hydrocarbon Oxidation Properties of N-Heterocycle-Sulfonated Schiff Base Copper(II) Complexes

Reaction of the o-[(o-hydroxyphenyl)methylideneamino]benzenesulfonic acid (H2L) (1) with CuCl2·2H2O in the presence of pyridine (py) leads to [Cu(L)(py)(EtOH)] (2) which, upon further reaction with 2,2’-bipyridine (bipy), pyrazine (pyr), or piperazine (pip), forms [Cu(L)(bipy)]·MeOH (3), [Cu2(L)2(μ-pyr)(MeOH)2] (4), or [Cu2(L)2(μ-pip)(MeOH)2] (5), respectively. The Schiff base (1) and the metal complexes (2–5) are stabilized by a number of non-covalent interactions to form interesting H-bonded multidimensional polymeric networks (except 3), such as zigzag 1D chain (in 1), linear 1D chain (in 2), hacksaw double chain 1D (in 4) and 2D motifs (in 5). These copper(II) complexes (2–5) catalyze the peroxidative oxidation of cyclic hydrocarbons (cyclooctane, cyclohexane, and cyclohexene) to the corresponding products (alcohol and ketone from alkane; alcohols, ketone, and epoxide from alkene), under mild conditions. For the oxidation of cyclooctane with hydrogen peroxide as oxidant, used as a model reaction, the best yields were generally achieved for complex 3 in the absence of any promoter (20%) or in the presence of py or HNO3 (26% or 30%, respectively), whereas 2 displayed the highest catalytic activity in the presence of HNO3 (35%). While the catalytic reactions were significantly faster with py, the best product yields were achieved with the acidic additive.

Copper(II) Complexes of Arylhydrazone of 1H-Indene-1,3(2H)-dione as Catalysts for the Oxidation of Cyclohexane in Ionic Liquids

The copper(II) complexes [CuL(H2O)2]∙H2O (1) and [CuL(dea)] (2) [L = 2-(2-(1,3-dioxo-1H-inden-2(3H)-ylidene)hydrazinyl)benzenesulfonate, dea = diethanolamine] were applied as catalysts in the peroxidative (with tert-butyl-hydroperoxide or hydrogen peroxide) conversion of cyclohexane to cyclohexanol and cyclohexanone, either in acetonitrile or in any of the ionic liquids [bmim][NTf2] and [hmim][NTf2] [bmim = 1-butyl-3-methylimidazolium, hmim = 1-hexyl-3-methylimidazolium, NTf2 = bis(trifluoromethanesulfonyl) imide]. Tert-butyl-hydroperoxide led to better product yields, as compared to H2O2, with a selectivity directed towards cyclohexanone. The ILs showed a better performance than the conventional solvent for the copper complex 1. No catalytic activity was observed for 2 in the presence of an IL.

Novel Cu(ii) complexes with NNO-Schiff base-like ligands – structures and magnetic properties

The X-ray structures and magnetic properties of 22 copper(ii) complexes, derived from six new tridentate Schiff base-like ligands and various conterions, are discussed.

Preparation and characterization of two new CuII supramolecular coordination polymers incorporating sulfobenzoate and flexible heterocyclic ligands

The assembly of Cu^II with the multifunctional ligand 2-amino-4-sulfobenzoic acid (H₂asba) in the presence of the auxiliary flexible ligands 1,4-bis(triazol-1-ylmethyl)benzene (bbtz) and 1,4-bis(imidazol-1-ylmethyl)benzene (bix) under ambient conditions resulted in two new supramolecular coordination polymers, namely poly[[(3-amino-4-carboxybenzenesulfonato-κO)aquabis[μ₂-1,4-bis(triazol-1-ylmethyl)benzene-κ²N⁴:N^4']copper(II)] 3-amino-4-carboxybenzenesulfonate tetrahydrate], {[Cu(C₇H₆NO₅S)(C₁₂H₁₂N₆)₂(H₂O)](C₇H₆NO₅S)·4H₂O}_n, (1), and poly[[bis(μ₂-2-amino-4-sulfonatobenzoato-κ³O¹:N,O^1')tetraaqua[μ₂-1,4-bis(triazol-1-ylmethyl)benzene-κ²N⁴:N^4']dicopper(II)] tetrahydrate], {[Cu₂(C₇H₅NO₅S)₂(C₁₄H₁₄N₄)(H₂O)₄]·4H₂O}_n, (2). Single-crystal X-ray structure diffraction analysis of (1) reveals that the bbtz ligand acts as a bridge, linking adjacent Cu^II ions into a two-dimensional cationic (4,4) topological network, in which the coordinated 3-amino-4-carboxybenzenesulfonate (Hasba^-) anion uses its sulfonate group to bind with the Cu^II ion in a monodentate fashion and the carboxylate group remains protonated. The lattice Hasba^- anion resides in the two-dimensional layer and balances the charge. The carboxylate group of the 2-amino-4-sulfonatobenzoate (asba^2-) ligand in (2) is involved in bidentate coordination, connecting adjacent Cu^II ions into carboxylate-bridged chains which are further bridged by the auxiliary flexible bix ligand in a trans-gauche (TG) mode, resulting in the formation of a two-dimensional network architecture. The amino group of the asba^2- ligand in (2) also takes part in the coordination with the central Cu^II ion. The six-coordinated Cu^II centres in (1) and (2) exhibit distorted octahedral coordination geometries. Extensive hydrogen bonding exists in both (1) and (2). The interlayer hydrogen bonds in both compounds further extend adjacent two-dimensional layers into three-dimensional supramolecular network architectures. Furthermore, a detailed analysis of the solid-state UV-Vis-NIR (NIR is near IR) diffuse reflectance data indicates that (1) and (2) may have potential as wide band gap indirect semiconductor materials. Compounds (1) and (2) show reversible and irreversible dehydration-rehydration behaviours, respectively.

Unfolding biological properties of a versatile dicopper(II) precursor and its two mononuclear copper(II) derivatives

Synthesis, inter-conversions and biological study of the dichloro bridged dicopper(II) compound [CuLCl]₂ (1) and its two mononuclear derivatives [CuLCl(H₂O)]·H₂O (2) and [CuLCl(py)] (3) (HL=2-(2-pyridylmethyleneamino)benzenesulfonic acid) are described. The dimeric compound 1 collapses into monomers 2 and 3 in the presence of coordinating solvents, water and pyridine, respectively, and 1 is regenerated upon simple stirring of 2 or 3 in methanol. The reactions of 1 with neutral (present study) and charged (earlier studies) ligands result in monomeric and multimeric compounds, respectively, attesting that it is a versatile dicopper(II) precursor. The anticancer activity of these copper complexes (1-3) was screened against lung (A-549) and breast (MDA-MB-231) human cancer cell lines. The IC₅₀ (half maximal inhibitory concentration) value for one (3) of the compounds suggests preferential cytotoxicity against breast cancer MDA-MB-231 cell line. Furthermore, the IC₅₀ value obtained for complex 3 is found to be almost two-fold times cytotoxic than the standard drug cisplatin. In addition, the underlying possible mechanism of its apoptosis-inducing efficacy in MDA-MB-231 cells has been rationalized by using flow cytometry (FACS) and Hoechst 33342/propidium iodide (PI) fluorescence staining. The stimulation of apoptotic induction for complex 3 has further been affirmed by reactive oxygen species (ROS) generation and mitochondrial aggregations studies.

Sulfonato-imino copper(ii) complexes: fast and general Chan–Evans–Lam coupling of amines and anilines

A simple coordination complex allows Chans–Evans–Lam arylations of a wide variety of amines and anilines without optimization of reaction conditions.

Stereoselective Alkane Oxidation with meta-Chloroperoxybenzoic Acid (MCPBA) Catalyzed by Organometallic Cobalt Complexes

Cobalt pi-complexes, previously described in the literature and specially synthesized and characterized in this work, were used as catalysts in homogeneous oxidation of organic compounds with peroxides. These complexes contain pi-butadienyl and pi-cyclopentadienyl ligands: [(tetramethylcyclobutadiene)(benzene)cobalt] hexafluorophosphate, [(C₄Me₄)Co(C₆H₆)]PF₆ (1); diiodo(carbonyl)(pentamethylcyclopentadienyl)cobalt, Cp*Co(CO)I₂ (2); diiodo(carbonyl)(cyclopentadienyl)cobalt, CpCo(CO)I₂ (3); (tetramethylcyclobutadiene)(dicarbonyl)(iodo)cobalt, (C₄Me₄)Co(CO)₂I (4); [(tetramethylcyclobutadiene)(acetonitrile)(2,2′-bipyridyl)cobalt] hexafluorophosphate, [(C₄Me₄)Co(bipy)(MeCN)]PF₆ (5); bis[dicarbonyl(B-cyclohexylborole)]cobalt, [(C₄H₄BCy)Co(CO)₂]₂ (6); [(pentamethylcyclopentadienyl)(iodo)(1,10-phenanthroline)cobalt] hexafluorophosphate, [Cp*Co(phen)I]PF₆ (7); diiodo(cyclopentadienyl)cobalt, [CpCoI₂]₂ (8); [(cyclopentadienyl)(iodo)(2,2′-bipyridyl)cobalt] hexafluorophosphate, [CpCo(bipy)I]PF₆ (9); and [(pentamethylcyclopentadienyl)(iodo)(2,2′-bipyridyl)cobalt] hexafluorophosphate, [Cp*Co(bipy)I]PF₆ (10). Complexes 1 and 2 catalyze very efficient and stereoselective oxygenation of tertiary C–H bonds in isomeric dimethylcyclohexanes with MCBA: cyclohexanols are produced in 39 and 53% yields and with the trans/cis ratio (of isomers with mutual trans- or cis-configuration of two methyl groups) 0.05 and 0.06, respectively. Addition of nitric acid as co-catalyst dramatically enhances both the yield of oxygenates and stereoselectivity parameter. In contrast to compounds 1 and 2, complexes 9 and 10 turned out to be very poor catalysts (the yields of oxygenates in the reaction with cis-1,2-dimethylcyclohexane were only 5%–7% and trans/cis ratio 0.8 indicated that the oxidation is not stereoselective). The chromatograms of the reaction mixture obtained before and after reduction with PPh₃ are very similar, which testifies that alkyl hydroperoxides are not formed in this oxidation. It can be thus concluded that the interaction of the alkanes with MCPBA occurs without the formation of free radicals. The complexes catalyze oxidation of alcohols with tert-butylhydroperoxide (TBHP). For example, tert-BuOOH efficiently oxidizes 1-phenylethanol to acetophenone in 98% yield if compound 1 is used as a catalyst.

Highly efficient extraction of actinides with pillar[5]arene-derived diglycolamides in ionic liquids via a unique mechanism involving competitive host–guest interactions

A novel extraction mechanism is described.

A sulfonated Schiff base dimethyltin(iv) coordination polymer: synthesis, characterization and application as a catalyst for ultrasound- or microwave-assisted Baeyer–Villiger oxidation under solvent-free conditions

The sulfonated Schiff base dimethyltin(iv) coordination polymer is an efficient heterogeneous catalyst for the peroxidative Baeyer–Villiger oxidation of ketones, under ultrasound or microwave irradiation and solvent- and additive-free conditions.