Dication Disulfuranes as Photoactivatable Sources of Radical Organocatalysts.

The recent development of photoredox and energy transfer catalysis has led to a significant expansion of visible light-driven chemical transformations. These methods have demonstrated exceptional efficiency in converting a wide range of substrates into radical intermediates and generating open-shell catalytic species. However, the simplification of catalytic systems and the direct generation of highly reactive radical organocatalysts through direct visible light irradiation from stable precatalysts remains largely an unrealized goal. This challenge is mainly due to the limited availability of precatalysts that are responsive to visible light. Herein, we introduce a new class of bench-stable dicationic disulfuranes, which release highly reactive thiyl radicals upon blue light excitation. Spectroscopic and computational studies reveal that this reactivity arises from a combination of structural features and intermolecular interactions. This family of molecules has been employed to catalyze radical cascades previously incompatible with photoredox conditions, enabling the efficient formation of 1,2-dioxolanes and 1,3-hydroxyketones in excellent yields and short reaction times.

Comprehensive Characterization of an "Off/On" Rhodol-Based Lysosomal Tracker for Orthogonal Cellular Analysis by Confocal Imaging.

Two florescent xanthene-cyanamide lysosomal trackers emitting strongly at ∼525 nm were prepared from fluorescein and rhodol methyl esters in microwave-assisted reactions. Both forms named "off" (nonfluorescent lactam) and "on" (strongly fluorescent ring-opened amide) have been comprehensively characterized out by using a combination of NMR spectroscopy, X-ray analysis, fluorimetry and confocal microscopy. Known rhodamines bearing electron-withdrawing groups (EWGs) exhibit an equilibrium between non-fluorescent (off) and fluorescent (on) depending on the dielectric constant of the medium. Here, cyanamide was introduced as EWG amine into the fluorescein and rhodol framework. Unlike rhodamine-type dyes, the ring-opened forms of fluorescein- and rhodol-cyanamides are stable in protic solvents under circumneutral and basic pH conditions. The osteoblastic cell line MC3T3-E1 from C57BL/6 mouse calvaria was used for confocal imaging where the different organelles and nuclei were distinguished by using an orthogonal combination of fluorescent dyes.

Unprecedented Relaxivity Gap in pH-Responsive FeIII -Based MRI Probes.

Two mononuclear ferric complexes are reported that respond to a pH change with a 27- and 71-fold jump, respectively, in their capacity to accelerate the longitudinal relaxation rate of water-hydrogen nuclei, and this starting from a negligible base value of only 0.06. This unprecedented performance bodes well for tackling the sensitivity issues hampering the development of Molecular MRI. The two chelates also excel in the fully reversible and fatigue-less nature of this phenomenon. The structural reasons for this performance reside in the macrocyclic nature of the hexa-dentate ligand, as well as the presence of a single pendant arm displaying a five-membered lactam or carbamate which show (perturbed) pKa values of 3.5 in the context of this N6 ⇔ ${ \Leftrightarrow }$ N5O1 coordination motif.

Cooperative Luminescence and Cooperative Sensitisation Upconversion of Lanthanide Complexes in Solution.

Upconversion materials have led to various breakthrough applications in solar energy conversion, imaging, and biomedicine. One key impediment is the facilitation of such processes at the molecular scale in solution where quenching effects are much more pronounced. In this work, molecular solution-state cooperative luminescence (CL) upconversion arising from a Yb excited state is explored and the mechanistic origin behind cooperative sensitisation (CS) upconversion in Yb/Tb systems is investigated. Counterintuitively, the best UC performances were obtained for Yb/Tb ratios close to parity, resulting in the brightest molecular upconversion complexes with a quantum yield of 2.8×10-6 at a low laser power density of 2.86 W cm-2 .

Influence of Divalent Cations in the Protein Crystallization Process Assisted by Lanthanide-Based Additives.

The use of lanthanide complexes as powerful auxiliaries for biocrystallography prompted us to systematically analyze the influence of the commercial crystallization kit composition on the efficiency of two lanthanide additives: [Eu(DPA)3]3- and Tb-Xo4. This study reveals that the tris(dipicolinate) complex presents a lower chemical stability and a strong tendency toward false positives, which are detrimental for its use in a high-throughput robotized crystallization platform. In particular, the crystal structures of (Mg(H2O)6)3[Eu(DPA)3]2·7H2O (1), {(Ca(H2O)4)3[Eu(DPA)3]2}n·10nH2O (2), and {Cu(DPA)(H2O)2}n (3), resulting from spontaneous crystallization in the presence of a divalent alkaline-earth cation and transmetalation, are reported. On the other hand, Tb-Xo4 is perfectly soluble in the crystallization media, stable in the presence of alkaline-earth dications, and slowly decomposes (within days) by transmetalation with transition metals. The original structure of [Tb4L4(H2O)4]Cl4·15H2O (4) is also described, where L represents a bis(pinacolato)triazacyclononane ligand. This paper also highlights a potential synergy of interactions between Tb-Xo4 and components of the crystallization mixtures, leading to the formation of complex adducts like {AdkA/Tb-Xo4/Mg2+/glycerol} in the protein binding sites. The observation of such multicomponent adducts illustrated the complexity and versatility of the supramolecular chemistry occurring at the surface of the proteins.

Luminescence-Driven Electronic Structure Determination in a Textbook Dimeric DyIII -Based Single-Molecule Magnet.

A textbook dysprosium dinuclear complex based on acetylacetone ligands, [Dy2 (acac)4 (µ2 -acac)2 (H2 O)2 ], has been synthesized and fully characterized. This simple dimeric lanthanide complex shows well-resolved solid-state luminescence and behaves as a single-molecule magnet under zero DC field. A seminal crystal-field approach is used to marry both magnetism and luminescence in the frame of an energetic picture.

Multiple Sulfonation of Picolyl-Based Complexes Rendering Them Highly Water-Compatible.

Multidentate ligands chosen for the complexation of hard metals frequently exhibit negative charges, which consequently elicits Coulombic compensation of the metal-ion charge. However, ligands favored by soft metal ions are neutral, which prevents the chemist from obtaining electroneutral complexes, let alone ones with a negative total charge. Here, we report on an efficient synthetic method to decorate picolyl-displaying coordination compounds with multiple sulfonate units at their periphery. We further describe rare anionic versions of three standard complexes that have only been characterized as cationic so far. Our sulfonated complexes show extensive water solubility, which confers these species with great potential for broad application in the biomedical arena.

Nickel-Catalyzed Mono-Selective α-Arylation of Acetone with Aryl Chlorides and Phenol Derivatives.

The challenging nickel-catalyzed mono-α-arylation of acetone with aryl chlorides, pivalates, and carbamates has been achieved for the first time. A nickel/Josiphos-based catalytic system is shown to feature unique catalytic behavior, allowing the highly selective formation of the desired mono-α-arylated acetone. The developed methodology was applied to a variety of (hetero)aryl chlorides including biologically relevant derivatives. The methodology has been extended to the unprecedented coupling of acetone with phenol derivatives. Mechanistic studies allowed the isolation and characterization of key Ni0 and NiII catalytic intermediates. The Josiphos ligand is shown to play a key role in the stabilization of NiII intermediates to allow a Ni0 /NiII catalytic pathway. Mechanistic understanding was then leveraged to improve the protocol using an air-stable NiII pre-catalyst.

Structural Diversity of Coordination Polymers Based on a Heterotopic Ligand: Cu(II)-Carboxylate vs Cu(I)-Thiolate.

Two copper(II)-carboxylate disulfide coordination polymers [Cu2((O2CPhS)2)2(H2O)2] n (1, 2) and one copper(I)-thiolate coordination polymer [Cu( p-SPhCO2H)] n (3) have been synthesized using either the 4-mercaptobenzoic acid (HSPhCO2H) or the 4,4'-dithiodibenzoic acid ((SPhCO2H)2) as ligand. These three compounds were characterized by X-ray diffraction, IR, and thermogravimetric analyses. Compounds 1 and 2 are polymorphs with the presence, for both, of dinuclear paddle-wheel copper(II)-carboxylates. In 1, the adjacent dimeric Cu2 units are linked by two (O2CPhS)2 ligands generating a cyclic loop chain, and in 2, each pair of Cu (II) atoms is linked by four ligands to create 2D networks, that are 2-fold interpenetrated. Compound 3 presents a lamellar structure, with an exceptional thermal and chemical stability, and exhibits intrinsic multiple emission between 485 and 660 nm. The different intensities of these bands generate a cyclic luminescence thermochromism from yellow to green to yellow.

A Dy4 Cubane: A New Member in the Single-Molecule Toroics Family.

Molecular materials that possess a toroidal moment associated to a non-magnetic ground state are known as single-molecule toroics (SMTs) and are usually planar molecules. Herein, we report a Dy4 cubane, namely [Dy4 (Bppd)4 (µ3 -OH)4 (Pa)4 (H2 O)4 ]⋅0.333 H2 O (where BppdH=1,3-Bis(pyridin-4-yl)propane-1,3-dione and PaH=2-Picolinic acid) for which magnetometry measurements and state-of-art ab initio calculations highlight SMT behavior in a tridimensional structure (3D-SMT). The in-depth theoretical analysis on the resulting low-lying energy states, along with their variation in function of the magnetic exchange pathways, allows further light to be shed on the description of single-molecule toroics and identify the coupling scheme that better reproduces the observed data.

Two-Color Three-State Luminescent Lanthanide Core-Shell Crystals.

Luminescent core-shell crystals based on lanthanide tris-dipicolinate complexes were obtained from the successive growing of two different lanthanide complex layers. Selective or simultaneous emission of each part of the crystal can be achieved by a careful choice of the excitation wavelength.

Experimental and theoretical investigations of the stereoselective synthesis of p-stereogenic phosphine oxides.

An efficient enantioselective strategy for the synthesis of variously substituted phosphine oxides has been developed, incorporating the use of (1S,2S)-2-aminocyclohexanol as the chiral auxiliary. The method relies on three key steps: 1) Highly diastereoselective formation of P(V) oxazaphospholidine, rationalized by a theoretical study; 2) highly diastereoselective ring-opening of the oxazaphospholidine oxide with organometallic reagents that takes place with inversion of configuration at the P atom; 3) enantioselective synthesis of phosphine oxides by cleavage of the remaining P-O bond. Interestingly, the use of a P(III) phosphine precursor afforded a P-epimer oxazaphospholidine. Hence, the two enantiomeric phosphine oxides can be synthesized starting from either a P(V) or a P(III) phosphine precursor, which constitutes a clear advantage for the stereoselective synthesis of sterically hindered phosphine oxides.

Di-aqua-bis-(ethyl-enedi-amine-κ(2) N,N')copper(II) bis-(sulfamerazinate).

The asymmetric unit of the title compound, [Cu(C2H8N2)2(H2O)2](C11H11N4O2S)2, contains one sulfamerazinate anion in a general position and one half-cation that is located on a center of inversion. The Cu(II) cation shows a strong Jahn-Teller distortion. It is coordinated by four N atoms of two ethyl-enedi-amine ligands in the basal plane and two O atoms at much longer distances in the axial positions in a bipyramidal coordination. In the crystal, the building blocks are connected by N-H⋯N, O-H⋯N, N-H⋯O and O-H⋯O hydrogen bonding into a two-dimensional network parallel to (001).

Microwave-Assisted Syntheses of Rhodamine, Rhodol, and Fluorescein Derivatives.

A series of rhodol-; fluorescein- and rhodamines-based spirolactam compounds, bearing electron donor amines have been prepared. For this purpose we have redesigned the synthesis of the rhodol scaffold using 2-(2,4-dihydroxybenzoyl)benzoic acid obtaining one example rhodol methyl ester in good yields (25-30 %) Thus, one set of non-cytotoxic rhodamine-based compounds has been prepared using thermal and microwave assisted synthesis (40-78 %) and tested as high affinity ATP chemo-sensors.

Series of dicyanamide-interlaced assembly of zinc-Schiff-base complexes: crystal structure and photophysical and thermal studies.

Four new dicyanamide (dca) bridged multinuclear Zn(II)-Schiff-base complexes, {[Zn2L(1)(µ1,5-dca)dca]·CH3OH}2 (1), [Zn2L(2)(µ1,5-dca)dca]n (2), [Zn3L(3)2(µ1,5-dca)2]n (3), and [(ZnL(4))2Zn(µ1,5-dca)dca]n (4), have been synthesized using four different Schiff bases L(1)H2 = N,N(/)-bis(3-methoxysalicylidenimino)-1,3-diaminopentane, L(2)H2 = N,N'-bis(5-bromo-3-methoxysalicylidenimino)-1,3-diaminopropane, L(3)H2 = N,N'-bis(5-bromosalicylidenimino)-1,3-diaminopropane, and L(4)H2 = N,N'-bis(5-chlorosalicylidenimino)-1,3-diaminopropane and NaN(CN)2 in order to extend the metal-ligand assembly. The directional properties of linear end-to-end bridging dca ligands have resulted in different metal ion connectivities leading to unique variety of templates in each of the complexes. All the ligands and complexes have been characterized by microanalytical and spectroscopic techniques. The structures of the complexes have been conclusively determined by single crystal X-ray diffraction studies. Thermogravimetric analyses have been performed to investigate the thermal stability of the metal-organic frameworks. Finally, the photoluminescence properties of the complexes as well as their respective ligands have been investigated with a comparative approach.

Condensation of a nickel tetranuclear cubane into a heptanuclear single-molecule magnet.

A tetranuclear complex, [Ni(4)], with a cubane-like structure synthesized from hexafluoroacetylacetone gives, after drying at high temperature and treatment with pyridine, a heptanuclear nickel(II) complex, [Ni(7)]. The crystal structures of both compounds have been determined by single-crystal X-ray diffraction. Their magnetic properties have been studied by SQUID and µ-SQUID magnetometry as well as by high-frequency EPR spectroscopy (HF-EPR). For [Ni(4)], the temperature dependence of the magnetic susceptibility can be fitted by taking into account strong Ni···Ni ferromagnetic interactions which lead to an S = 4 ground-state spin, in good agreement with the HF-EPR study. For [Ni(7)], the temperature dependence of the magnetic susceptibility shows that the Ni···Ni ferromagnetic interactions are kept within the metal core. However, it was not possible to fit this with a clear set of parameters, and the ground-state spin was undetermined. The field dependence of the magnetization indicates an S = 7 ground-state spin at high field. In contrast, the temperature dependence of the magnetic susceptibility indicates a ground-state spin of S = 6 or even S = 5. These results agree with complicated high-frequency EPR spectra which have been ascribed to the superposition of signals from the ground spin multiplet and from an excited spin multiplet very close in energy, with the excited state having a larger S value than the ground state. Very low temperature studies show that only the heptanuclear complex behaves as a single-molecule magnet.

Evaluation of ferrocenyl-containing γ-hydroxy-γ-lactam-derived tetramates as potential antiplasmodials.

A series of ferrocenyl-containing γ-hydroxy-γ-lactam tetramates were prepared in 2-3 steps through ring opening-ring closure (RORC) process of γ-ylidene-tetronate derivatives in the presence of ferrocenyl alkylamines. The compounds were screened in vitro for their antiplasmodial activity against chloroquine-sensitive (3D7) and chloroquine-resistant (W2) clones of P. falciparum, displaying activity in the range of 0.12-100 µM, with generally good resistance index. The most active ferrocene in these series exhibited IC50 equal to 0.09 µM (3D7) and 0.12 µM (W2). The low cytotoxicity of the ferrocenyl-containing γ-hydroxy-γ-lactam tetramates against Human Umbilical Vein Endothelial (HUVEC) cell line demonstrated selective antiparasitic activity. The redox properties of these ferrocene-derived tetramates were studied and physico-biochemical studies evidenced that these derivatives can exert potent antimalarial activities via a mechanism distinct from ferroquine.

Weak interactions modulating the dimensionality in supramolecular architectures in three new nickel(II)-hydrazone complexes, magnetostructural correlation, and catalytic potential for epoxidation of alkenes under phase transfer conditions.

Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL(1)), 2-hydroxyacetophenone (HL(2)), and 2, 3-dihydroxybenzaldehyde (HL(3)). These tridentate ligands are reacted with Ni(OOCCF(3))(2)·xH(2)O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L(1))(OOCCF(3))(CH(3)OH)](2) (1), [Ni(L(2))(OOCCF(3))(H(2)O)](2) (2), and [Ni(L(3))(L(3)H)](OOCCF(3))(H(2)O)(1.65)(CH(3)OH)(0.35) (3). The ligands and the complexes have been characterized by elemental analysis and IR and UV-vis spectroscopy, and the structures of the complexes have been established by single crystal X-ray diffraction (XRD) study. 1 and 2 are centrosymmetric dinuclear complexes and are structural isomers whereas 3 is a bis chelated cationic monomer coordinated by one neutral and one monoanionic ligand. O-H···O hydrogen bonds in 3 lead to the formation of a dimer. Slight steric and electronic modifications in the ligand backbone provoke differences in the supramolecular architectures of the complexes, leading to a variety of one, two, and three-dimensional hydrogen bonded networks in complexes 1-3 respectively. Variable temperature magnetic susceptibility measurements reveal that moderate antiferromagnetic interactions operate between phenoxo bridged Ni(II) dimers in 1 and 2 whereas very weak antiferromagnetic exchange occurs through hydrogen bonding and π-π stacking interactions in 3. All complexes are proved to be efficient catalysts for the epoxidation of alkenes by NaOCl under phase transfer condition. The efficiency of alkene epoxidation is dramatically enhanced by lowering the pH, and the reactions are supposed to involve high valent Ni(III)-OCl or Ni(III)-O· intermediates. 3 is the best epoxidation catalyst among the three complexes with 99% conversion and very high turnover number (TON, 396).

Upconversion in molecular hetero-nonanuclear lanthanide complexes in solution.

Here we show that nonanuclear lanthanide complexes respresent a new class of solution state upconversion (UC) molecules. For a composition of one Tb per eight Yb the nonanuclear complexes display a very efficient UC phenomenon with Tb luminescence in the visible region upon 980 nm NIR excitation of Yb. An unprecedented value of 1.0 × 10-7 was obtained for the UC efficiency at only 2.86 W cm-2, demonstrating these new molecular complexes to be up to 26 times more efficient than the best current molecular systems, the UC being observed down to a concentration of 10 nM.

Site-selective lanthanide doping in a nonanuclear yttrium(III) cluster revealed by crystal structures and luminescence spectra.

A series of lanthanide-doped nonanuclear yttrium(III) clusters with general formulas (Y(9-x)Ln(x))(acac)(16)(µ(3)-OH)(8)(µ(4)-O)(µ(4)-OH) (Ln = Pr, Eu, Tb, Dy, and Yb) were synthesized. Characterization by single-crystal X-ray diffraction allowed for analysis of relative populations of yttrium (Z = 39) and dopant trivalent lanthanide (Z = 59-70) at every crystallographic metal position. Nonuniform distribution of ions along the three different sites seems to be correlated to the site volume and the ratio of ionic radii. In support, luminescence spectra of europium(III)-doped nonanuclear clusters were measured over a wide range of dopant concentrations. Emission intensities of peaks characteristic of specific sites correlate well with the site population determined through X-ray diffraction.