Hypoxia-activated dissociation of heteroleptic cobalt(III) complexes with functionalized 2,2'-bipyridines and a model anticancer drug esculetin.

A low oxygen level in solid tumors is behind the modern concept of selective chemotherapy by hypoxia-activated prodrugs, such as heteroleptic complexes of transition metals (cobalt(III), iron(III) or platinum(IV)) with bi- or tetradentate ligands and an anticancer drug molecule as a co-ligand. A series of new cobalt(III) complexes [Co(LR)(esc)]ClO with esculetin (6,7-dihydroxycoumarin) and 2,2'-bipyridines (2,2'-bipy) functionalized by different substituents R were probed in the hypoxia-activated delivery of this model anticancer drug. Their combined study by cyclic voltammetry and NMR spectroscopy allowed identifying linear correlations of the electrochemical reduction potentials and the rate of the hypoxia-activated dissociation of [Co(LR)(esc)]ClO with the Hammett constants of the substituents in 2,2'-bipy ligands.

Multifunctional Dy Complexes with Triphenylmethanolates: Structural Diversity, Luminescence, and Magnetic Relaxation.

The coordination environment of magneto-luminescent Dy-based Single-Molecule Magnets (SMM) is a crucial factor influencing both magnetic and luminescent properties. In this work, we explore how triphenylmethanolate (PhCO), in combination with other ligands, can modulate the structure and, therefore, the magnetic properties of Dy-based SMM. Using triphenylmethanolate in combination with THF and pyridine (Py) as co-ligands, we synthesized a series of mononuclear -[Dy(OCPh)(THF)][BPh]·(2,6-MeCHN) (), -Dy(OCPh)(THF) (), -Dy(OCPh)(py) () and dinuclear [(PhCO)Dy(THF){(μ-Cl)Li(THF)}μ-Cl] () complexes where the Dy ion presents five- or six-coordinate geometries.

Remarkable Effect of Stereoisomerism on the Am(III)/Ln(III) Solvent Extraction. New Ligands for Highly Efficient Separation of Americium.

Two novel 1,10-phenanthroline-2,9-diamide ligands were constructed on the basis of 2-phenylpyrrolidine and obtained as pure diastereomers. These ligands demonstrated advanced properties in liquid-liquid extraction tests. They revealed high efficiency of americium(III) extraction alongside with the record values of selectivity in the separation of americium from light lanthanides from strongly acidic media.

Engineered π⋯π interactions favour supramolecular dimers X@[FeL] (X = Cl, Br, I): solid state and solution structure.

Ditopic bis-pyrazolylpyridine ligands usually react with divalent metal ions (M) to produce dinuclear triple-stranded helicates [ML] or, π⋯π interactions, dimers of monoatomic complexes ([ML]). The introduction of an additional benzene ring at each end of ligand L increases the number of aromatic contacts within the supramolecular aggregate by 40%, driving the self-recognition process in an irreversible manner. Consequently, the mixing of new bis-pyrazolylquinoline L2 with FeX salts leads to crystallization of the tripartite high-spin assemblies (X@[Fe(L2)]) (X = Cl, Br or I).

Amine adducts of triallylborane as highly reactive allylborating agents for Cu(I)-catalyzed allylation of chiral sulfinylimines.

The implementation of selective catalytic processes with highly active reagents is an attractive strategy that meets the modern principles of sustainable development of chemistry. In the current study, we for the first time describe the method and general principles of Cu(I)-catalyzed allylation of imines with amine adducts of allylic triorganoboranes. Triallylborane is an extremely reactive compound and cannot be used for the catalytic allylation of imines, whereas its amine adducts are ideal substrates for catalysis.

Planar-chiral arene ruthenium complexes: synthesis, separation of enantiomers, and application for catalytic C-H activation.

Heating -butyl-tetraline with [(-cymene)RuCl] produces the racemic complex [(arene)RuCl], which can be separated into enantiomers by chromatography of its diastereomeric adducts with chiral phosphine ligand. The resolved chiral complex catalyzes C-H activation of -methoxy-benzamides and their annulation with -vinyl-pivaloyl amide giving dihydroisoquinolones in 50-80% yields and with 40-80% enantiomeric excess.

Luminescent Er based single molecule magnets with fluorinated alkoxide or aryloxide ligands.

We report the synthesis, structures, and magnetic and luminescence properties of a series of new mono- and dinuclear Er complexes derived from sterically demanding aryloxide and fluorinated alkoxide ligands: [4-Bu-2,6-(PhCH)CHO]Er(THF) (1), [(CF)CO]Er(MeSiOH) (2), [(CF)CO]Er[(MeSi)NH] (3), [(CF)CO]Er(CHCH) (4), [(CF)CO]Er(-MeNCHCH) (5) and {[Ph(CF)CO]Er(μ-OC(CF)Ph)} (6). In compounds 1, 2, and 4, the Er ion is four-coordinated and adopts a distorted trigonal pyramidal geometry, while in 3, 5, and 6, the coordination geometry of Er is impacted by the presence of several relatively short Er⋯F distances, making them rather 6-coordinated. All compounds behave as field-induced Single Molecule Magnets (SMMs) and exhibit an Er characteristic near infrared (NIR) emission associated with the I → I transition with a remarkably long lifetime going up to 73 μs, which makes them multifunctional luminescent SMMs.

First 4,7-oxygenated 1,10-phenanthroline-2,9-diamides: synthesis, tautomerism and complexation with REE nitrates.

A new family of phenanthroline ligands was prepared. Hydrolysis of 4,7-dihalogenated 1,10-phenanthroline-2,9-diamides in acidic media leads to the formation of the corresponding 4,7-oxygenated derivatives. These ligands can exist in different tautomeric forms.

Ca(II) and Yb(II) complexes featuring M(C≡C) structural motif: enforced proximity or genuine η -bonding?

Bis(carbazolide) complexes M[3,6-tBu -1,8-(RC≡C) Carb] (THF) (R=SiMe , n=0, M=Ca, Yb; R=Ph, n=1, M=Ca, Yb; n=0, M=Yb) were synthesized through transamination reaction of M[N(SiMe ) ] (THF) with two molar equivalents of carbazoles. The complexes feature M(η -C≡C) structural motif composed of M(II) ions encapsulated by four acetylene fragments due to atypical for alkaline- and rare-earth metals η -interactions with triple C≡C bond. This interaction is evidenced experimentally by X-ray diffraction, Raman spectroscopy in the solid state and by NMR-spectroscopy in the solution.

Planar Chiral Rhodium Complex Based on the Tetrahydrofluorenyl Core for Enantioselective Catalysis.

A simple four-step route to a chiral tetrahydrofluorenyl rhodium catalyst from naturally occurring (-)-α-pinene was developed. Our approach does not use multistep and time-consuming procedures such as chiral HPLC or diastereomeric resolution. The key to success lies in the face-selective coordination of rhodium to the sterically hindered tetrahydrofluorenyl ligand, giving only one diastereomeric complex.

Crown-hydroxylamines are pH-dependent chelating N,O-ligands with a potential for aerobic oxidation catalysis.

Despite the rich coordination chemistry, hydroxylamines are rarely used as ligands for transition metal coordination compounds. This is partially because of the instability of these complexes that undergo decomposition, disproportionation and oxidation processes involving the hydroxylamine motif. Here, we design macrocyclic poly-N-hydroxylamines (crown-hydroxylamines) that form complexes containing a d-metal ion (Cu(II), Ni(II), Mn(II), and Zn(II)) coordinated by multiple (up to six) hydroxylamine fragments.

Rhodium complexes with planar-chiral cyclopentadienyl ligands: synthesis from -butylacetylene and catalytic performance in C-H activation of arylhydroxamates.

The rhodium complex [(CHBuCHBu)RhCl] with an asymmetric cyclopentadienyl ligand was prepared in 95% yield by the reaction of [(cod)RhCl] with -butylacetylene in the presence of AlCl. A similar reaction in the presence of InBr gave the cationic fulvene complex [(CHBu = CHBu)Rh(cod)]InBr (70%), which can add alcohols ROH and produce more bulky catalysts [(CHBuCH(OR)Bu)RhCl]. The enantiomers of these planar-chiral complexes were separated by thin-layer chromatography in the presence of L-phenylglycinol.

Tandem C-H Annulation Reaction of Benzaldehydes and Aminobenzoic Acids with Two Equivalents of Alkyne toward Isocoumarin-Conjugated Isoquinolinium Salts: A Family of Organic Luminophores.

A novel rhodium-catalyzed tandem C-H annulation of commercially available benzaldehydes and aminobenzoic acids with 2 equiv of alkyne is reported for the construction of isocoumarin-conjugated isoquinolinium salts that demonstrate diverse outstanding photoactivity. Depending on the substituents in the isoquinolinium moiety, they display either highly efficient fluorescence (up to 99% of quantum yield) or strong fluorescence quenching, which is provided by the transfer of the HOMO from the isoquinolinium to the isocoumarin moiety. Importantly, the functional groups in the benzaldehyde coupling partner also strongly affect the reaction selectivity, shifting the pathway to the formation of the photoinactive isocoumarin-substituted indenone imines and indenyl amines.

Bis(2,6-pyrazolyl)pyridines as a New Scaffold for Coordination Polymers.

Two coordination polymers, Fe(L)(CHCOO)(CHCN)]•nCHCN and [Fe(L)AgNOBF•CHOH]•1.75nCHOH•nHO (L = 3,3'-(4-(4-cyanophenyl)pyridine-2,6-diyl)bis(1-(2,6-dichlorophenyl)-1H-pyrazol-5-olate)), were obtained via a PCET-assisted process that uses the hydroxy-pyrazolyl moiety of the ligand and the iron(II) ion as sources of proton and electron, respectively. Our attempts to produce heterometallic compounds under mild conditions of reactant diffusion resulted in the first coordination polymer of 2,6-bis(pyrazol-3-yl)pyridines to retain the core N(L)MN(L).

Nitronate-aryne cycloaddition as a concise route to stereochemically complex fused benzisoxazolines and amino alcohols.

The reaction of cyclic nitronates (isoxazoline -oxides and 5,6-dihydro-4-1,2-oxazine -oxides) with Kobayashi's aryne precursors affords tricyclic benzene-fused nitroso acetals as a result of [3 + 2]-cycloaddition. The process is regio- and stereoselective in most cases and produces the target cycloadducts possessing up to four contiguous stereogenic centers. These nitroso acetals were shown to be convenient precursors of valuable polysubstituted aminodiols through catalytic hydrogenolysis of the N-O bonds.

[3+3]-Annulation of Cyclic Nitronates with Vinyl Diazoacetates: Diastereoselective Synthesis of Partially Saturated [1,2]Oxazino[2,3-][1,2]oxazines and Their Base-Promoted Ring Contraction to Pyrrolo[1,2-][1,2]oxazine Derivatives.

A rhodium(II)-catalyzed reaction of cyclic nitronates (5,6-dihydro-4-1,2-oxazine -oxides) with vinyl diazoacetates proceeds as a [3+3]-annulation producing bicyclic unsaturated nitroso acetals (4a,5,6,7-tetrahydro-2-[1,2]oxazino[2,3-][1,2]oxazines). Optimization of reaction conditions revealed the use of Rh(II) octanoate as the preferred catalyst in THF at room temperature, which allows the preparation of target products in good yields and excellent diastereoselectivity. Under basic conditions, namely, the combined action of DBU and alcohol, these nitroso acetals undergo ring contraction of an unsaturated oxazine ring into the corresponding pyrrole.

Pyrrolidine-Derived Phenanthroline Diamides: An Influence of Fluorine Atoms on the Coordination of Lu(III) and Some Other f-Elements and Their Solvent Extraction.

Three pyrrolidine-derived phenanthroline diamides were studied as ligands for lutetium trinitrate. The structural features of the complexes have been studied using various spectral methods and X-ray. The presence of halogen atoms in the structure of phenanthroline ligands has a significant impact on both the coordination number of lutetium and the number of solvate water molecules in the internal coordination sphere.

Polytypism of Ln(SeO)(HSeO)·2HO compounds: synthesis and crystal structure of the first monoclinic modification of Nd(SeO)(HSeO)·2HO, DFT calculations and order/disorder description.

Compounds with the general formula Ln(SeO)(HSeO)·2HO, where Ln = Sm, Tb, Nd and Lu, are characterized by orthorhombic symmetry with space group P222 and unit-cell parameters in the ranges a ∼ 6.473-6.999, b ∼ 6.

Bilateral metalloheterocyclic systems based on palladacycle and piperidine-2,4-dione pharmacophores.

The design of molecules with effective anticancer properties constructed from both dually active metal complex and organic fragments is a novel trend in medicinal chemistry. This concept suggests the impact of a drug on several biological targets or the synergistic action of both fragments as a single unit. We propose that the combination of a Pd-metallocomplex fragment and an organic unit can be an interesting model for anticancer drug discovery.

Synthesis, X-ray structure and magnetic properties of the apically functionalized monocapped cobalt(II) tris-pyridineoximates possessing SMM behaviour.

The title cobalt(II) pseudoclathrochelate complexes possess an intermediate trigonal prismatic-trigonal antiprismatic geometry. As follows from PPMS data, they exhibit an SMM behaviour with Orbach relaxation barriers of approximately 90 K. Paramagnetic NMR experiments confirmed a persistence of these magnetic characteristics in solution.

Triphenylcyclopentadienyl Rhodium Complexes in Catalytic C-H Annulations. Application for Synthesis of Natural Isocoumarins.

Efficient protocols for the synthesis of triphenylcyclopentadienyl rhodium halides [(1,2,4-CPhH)RhX] (,: X = Cl, I) starting from 1,2,4-triphenylcyclopentadiene or the cyclooctadiene derivative (1,2,4-CPhH)Rh(cod) () were developed. Iodide abstraction from with thallium or silver salts allowed us to prepare rhodocenium [(1,2,4-CPhH)RhCp]PF (PF) and mesitylene complex [(1,2,4-CPhH)Rh(mesitylene)](SbF) ((SbF)). Halides , (at 0.

Chiral Polymers from Norbornenes Based on Renewable Chemical Feedstocks.

Optically active polymers are of great interest as materials for dense enantioselective membranes, as well as chiral stationary phases for gas and liquid chromatography. Combining the versatility of norbornene chemistry and the advantages of chiral natural terpenes in one molecule will open up a facile route toward the synthesis of diverse optically active polymers. Herein, we prepared a set of new chiral monomers from -5-norbornene-2,3-dicarboxylic anhydride and chiral alcohols of various natures.

Solvation-Anionic Exchange Mechanism of Solvent Extraction: Enhanced U(VI) Uptake by Tetradentate Phenanthroline Ligands.

Phenanthroline diamides () demonstrated a unique ability to extract uranium from nitric acid solutions into a polar organic solvent forming complexes of 1:2 stoichiometry as tight ion pairs {[UONO][UO(NO)]} by a novel extraction mechanism, which is a combination of two already well-known mechanisms: solvation and ion-pair anion exchange. A UV-vis study was used to confirm the formation of such complexes directly in the organic phase. Moreover, chemical synthesis and single crystal growth were performed to confirm unambiguously the structure of the complexes in the solid state.

Selective Pathway toward Heteroleptic Spin-Crossover Iron(II) Complexes with Pyridine-Based -Donor Ligands.

A new synthetic pathway is devised to selectively produce previously elusive heteroleptic iron(II) complexes of terpyridine and ,'-disubstituted bis(pyrazol-3-yl)pyridines that stabilize the opposite spin states of the metal ion. Such a combination of the ligands in a series of the heteroleptic complexes induces the spin-crossover (SCO) not experienced by the homoleptic complexes of these ligands or shifts it to lower/higher temperatures respective to the SCO-active homoleptic complex. The midpoint temperatures of the resulting SCO span from ca.

Interrupted Nef Reaction of Cyclic Nitronates: Diastereoselective Access to Densely Substituted α-Chloronitroso Compounds.

The reaction of cyclic nitronic esters (isoxazoline- and 5,6-dihydro-4-1,2-oxazine--oxides) with hydrochloric acid affords geminal chloronitroso compounds bearing a distant hydroxyl group. The reaction is usually diastereoselective, and in some cases stereodivergent formation of isomers at different temperatures is observed. The discovered process represents the first example of an interrupted Nef reaction of nitronic esters.