Enaminone-directed ruthenium(II)-catalyzed C-H activation and annulation of arenes with diazonaphthoquinones for polycyclic benzocoumarins.

The weakly coordinating enaminone functionality has been leveraged for a C-H bond activation strategy under ruthenium catalysis and employed in the regioselective annulative coupling of arenes with diazonaphthoquinones, offering polycyclic benzocoumarins in very high yields. The enaminone motif plays a dual role and the protocol operates through a Ru(II)/Ru(IV) catalytic pathway which is amenable to the diversification of various pharmacophore-coupled substrates.

Ru(II)-Catalyzed Oxidative Cross-Dehydrogenative Alkenylations of Aromatic Amides and Ketones with Unactivated Olefins.

A weak coordination guided Ru(II)-catalyzed oxidative functionalization of arenes with unactivated olefins is developed, offering a wide variety of ortho-alkenylated benzamides, acetophenones, and benzophenone in high yields. The protocol accommodates several bioactive molecules and allows downstream synthetic manipulations leading to a 2,3-benzodiazepine scaffold. The reaction features a reversible metalation step and favors a regioselective ß-hydride elimination event.

Ruthenium(II)-Catalyzed (4+2) Annulative Difunctionalization of Non-conjugated Alkenyl Amides with Hydroxamic Acid Esters.

Ru(II)-catalyzed C-H bond activation strategy has been capitalized through a (4+2) annulative difunctionalization of non-conjugated alkenyl amides. Under mild conditions, a broad range of (hetero)aromatic amides embedded with NH-OMe unit as an internal oxidant produced high-value dihydroisoquinolinone scaffolds in good to excellent yields. This heteroannulation is also effective with acrylamides to dispense dihydro-2-pyridones and accommodates bioactive scaffolds such as tocopherol, estrone, and amino acids.

The Anionic Polymerization of a tert-Butyl-Carboxylate-Activated Aziridine.

N-Sulfonyl-activated aziridines are known to undergo anionic-ring-opening polymerizations (AROP) to form polysulfonyllaziridines. However, the post-polymerization deprotection of the sulfonyl groups from polysulfonyllaziridines remains challenging. In this report, the polymerization of tert-butyl aziridine-1-carboxylate (BocAz) is reported. BocAz has an electron-withdrawing tert-butyloxycarbonyl (BOC) group on the aziridine nitrogen. The BOC group activates the aziridine for AROP and allows the synthesis of low-molecular-weight poly(BocAz) chains. A 13C NMR spectroscopic analysis of poly(BocAz) suggested that the polymer is linear. The attainable molecular weight of poly(BocAz) is limited by the poor solubility of poly(BocAz) in AROP-compatible solvents. The deprotection of poly(BocAz) using trifluoroacetic acid (TFA) cleanly produces linear polyethyleneimine. Overall, these results suggest that carbonyl groups, such as BOC, can play a larger role in the in the activation of aziridines in anionic polymerization and in the synthesis of polyimines.

Hyper-CEST NMR of metal organic polyhedral cages reveals hidden diastereomers with diverse guest exchange kinetics.

Guest capture and release are important properties of self-assembling nanostructures. Over time, a significant fraction of guests might engage in short-lived states with different symmetry and stereoselectivity and transit frequently between multiple environments, thereby escaping common spectroscopy techniques. Here, we investigate the cavity of an iron-based metal organic polyhedron (Fe-MOP) using spin-hyperpolarized 129Xe Chemical Exchange Saturation Transfer (hyper-CEST) NMR. We report strong signals unknown from previous studies that persist under different perturbations. On-the-fly delivery of hyperpolarized gas yields CEST signatures that reflect different Xe exchange kinetics from multiple environments. Dilute pools with ~ 104-fold lower spin numbers than reported for directly detected hyperpolarized nuclei are readily detected due to efficient guest turnover. The system is further probed by instantaneous and medium timescale perturbations. Computational modeling indicates that these signals originate likely from Xe bound to three Fe-MOP diastereomers (T, C3, S4). The symmetry thus induces steric effects with aperture size changes that tunes selective spin manipulation as it is employed in CEST MRI agents and, potentially, impacts other processes occurring on the millisecond time scale.

Ruthenium(II)-catalyzed C-H activation and (4+2) annulation of aromatic hydroxamic acid esters with allylic amides.

A (4+2) annulation under Ru(II)-catalysis is reported using aromatic hydroxamic acid esters as the oxidizing directing group and allylic amides as unactivated olefin coupling partners, delivering a wide variety of aminomethyl isoquinolinones in good to excellent yields. This annulation is distinctive as allylic congeners typically result in allylation and not the annulation. Late-stage derivatization of a bioactive synthetic bile acid has been showcased.

Ruthenium(II)-Catalyzed Regioselective C-H Olefination of Aromatic Ketones and Amides with Allyl Sulfones.

A Ru(II)-catalyzed cross-dehydrogenative Heck-type olefination of arenes with allyl sulfones leveraging the assistance of weakly coordinating ketone and amide functional groups is reported. It features a distinct reactivity profile in comparison to other allylic congeners, where ß-sulfonyl elimination was not detected. The ambiphilic nature of the allyl sulfone side chain has also been demonstrated through intramolecular aza-Michael addition and aldol condensation. Mechanistic studies indicated the involvement of a reversible metalation step, where ß-hydride elimination takes place selectively from the benzylic position.

Lowest aqueous picomolar fluoride ions and in vivo aluminum toxicity detection by an aluminum(iii) binding chemosensor.

Aluminum toxicity in biological systems is a well-known issue yet remains as a prevalent and unsolvable problem due to the lack of proper molecular tools that can detect free aluminum(iii) or Al(iii) ions in vivo. Herein, we report a water-soluble photo-induced electron transfer (PET)-based turn-ON/OFF fluorometric chemosensor for the dual detection of Al(iii) and fluoride ions in aqueous media with a nanomolar (∼1.7 × 10-9 M) and picomolar (∼2 × 10-12 M, lowest ever detection so far) detection limit, respectively. Fluoride ions in sea water could be detected as well as the recognition of non-contamination in drinking water. In addition, using live-cell microscopy, Al(iii) ions were detected in live biological samples in vivo to aid establishing the aluminum-toxicity effect.

Ruthenium(II)-catalyzed amide directed spiroannulation with naphthoquinones: access to spiro-isoindolinone frameworks.

A mild ruthenium(ii)-catalyzed spiroannulation between benzamides and naphthoquinones is developed for the succinct synthesis of biologically relevant spiro-isoindolinone scaffolds. A base promoted transannulation of spirocyclic products en route to valuable benzo[b]phenanthridinetriones in good yields has also been accomplished.

Probing the Electronic Structure of Hybrid Perovskites in the Orientationally Disordered Cubic Phase.

Hybrid organic-inorganic lead halide perovskites are projected as new generation photovoltaic and optoelectronic materials with improved efficiencies. However, their electronic structure so far remains poorly understood, particularly in the orientationally disordered cubic phase. We performed electronic structure investigations using angle-resolved photoemission spectroscopy on two prototypical samples (MAPbBr3 and MAPbCl3) in their cubic phase, and the results are compared with the calculations within two theoretical models where MA+ is orientationally (1) disordered (MA+ ion is replaced by spherically symmetric Cs+ ion) and (2) ordered (MA oriented along (100) direction) but keeping the symmetry of the unit cell cubic. Degeneracy of the valence bands and behavior of constant energy contours are consistent with model 1, which supports strongly the disordered nature of the orientation of the MA+ ions in the cubic phase. Band structure calculations also reveal that spin-orbit coupling induced Rashba splitting is suppressed by the orientational disorder.

Programmed Recognition between Complementary Dinucleolipids To Control the Self-Assembly of Lipidic Amphiphiles.

One of the major goals in systems chemistry is to create molecular assemblies with emergent properties that are characteristic of life. An interesting approach toward this goal is based on merging different biological building blocks into synthetic systems with properties arising from the combination of their molecular components. The covalent linkage of nucleic acids (or their constituents: nucleotides, nucleosides and nucleobases) with lipids in the same hybrid molecule leads, for example, to the so-called nucleolipids. Herein, we describe nucleolipids with a very short sequence of two nucleobases per lipid, which, in combination with hydrophobic effects promoted by the lipophilic chain, allow control of the self-assembly of lipidic amphiphiles to be achieved. The present work describes a spectroscopic and microscopy study of the structural features and dynamic self-assembly of dinucleolipids that contain adenine or thymine moieties, either pure or in mixtures. This approach leads to different self-assembled nanostructures, which include spherical, rectangular and fibrillar assemblies, as a function of the sequence of nucleobases and chiral effects of the nucleolipids involved. We also show evidence that the resulting architectures can encapsulate hydrophobic molecules, revealing their potential as drug delivery vehicles or as compartments to host interesting chemistries in their interior.

CH3NH3PbI3, A Potential Solar Cell Candidate: Structural and Spectroscopic Investigations.

Hybrid organic-inorganic metal halides of the type CH3NH3PbX3 have emerged as potential materials for photovoltaic applications. In this paper we discuss structural, electronic, and optical spectroscopy investigations performed on high quality single crystals of CH3NH3PbI3. Our results conclusively suggest that CH3NH3PbI3 crystallizes in centrosymmetric space group and the methylammonium moiety exhibits disordered packing at room temperature. Extracted values of the exciton binding energy, the electron-phonon coupling constant, and the schematic energy level diagram constructed from the emission broadening, Raman, and photoemission spectroscopy measurements clearly show the potential of this system in photovoltaic applications.

Solvent-free ball-milling subcomponent synthesis of metallosupramolecular complexes.

Subcomponent self-assembly from components A, B, C, D, and Fe(2+) under solvent-free conditions by self-sorting leads to the construction of three structurally different metallosupramolecular iron(II) complexes. Under carefully selected ball-milling conditions, tetranuclear [Fe4 (AD2 )6 ](4-) 22-component cage 1, dinuclear [Fe2 (BD2 )3 ](2-) 11-component helicate 2, and 5-component mononuclear [Fe(CD3 )](2+) complex 3 were prepared simultaneously in a one-pot reaction from 38 components. Through subcomponent substitution reaction by adding subcomponent B, the [Fe4 (AD2 )6 ](4-) cage converts quantitatively to the [Fe2 (BD2 )3 ](2-) helicate, which, in turn, upon addition of subcomponent C, transforms to [Fe(CD3 )](2+) , following the hierarchical preference based on the thermodynamic stability of the complexes.

Encapsulation of xenon by a self-assembled Fe4L6 metallosupramolecular cage.

We report (129)Xe NMR experiments showing that a Fe4L6 metallosupramolecular cage can encapsulate xenon in water with a binding constant of 16 M(-1). The observations pave the way for exploiting metallosupramolecular cages as economical means to extract rare gases as well as (129)Xe NMR-based bio-, pH, and temperature sensors. Xe in the Fe4L6 cage has an unusual chemical shift downfield from free Xe in water. The exchange rate between the encapsulated and free Xe was determined to be about 10 Hz, potentially allowing signal amplification via chemical exchange saturation transfer. Computational treatment showed that dynamical effects of Xe motion as well as relativistic effects have significant contributions to the chemical shift of Xe in the cage and enabled the replication of the observed linear temperature dependence of the shift.

Mixed valence mono- and hetero-metallic grid catenanes.

Here, we report on the multicomponent self-assembly and single crystal X-ray diffraction study of a series of three interlocked mixed valence mono- and hetero-metallic [2]-catenanes made of [2 × 2] metallo-grids. They show unique structural features and highlight the essential roles of both the Cu(ii)/Cu(i) pair and of the conformationally adaptable organic ligands for achieving catenation of grids.

Self-assembly of a M4L6 complex with unexpected S4 symmetry.

Using 1,4-diaminobenzene and 2-formylpyridine as simple building blocks results in a 1D ligand (rod, L2) to 2D (M4L4 grid, C1) to 3D (S4 symmetrical M4L6, C2) complexes upon sequential addition of Cu(I) and Fe(II) ions. The complex C2 can be seen as the smallest possible pseudo-tetrahedron with S4 symmetry.

Anion-controlled formation of an aminal-(bis)imine Fe(ii)-complex.

In the presence of triflate as the counter anion, 1,2-diaminobenzene and 2-formylpyridine self-sort with iron(ii) to a low-spin [Fe(L1)](OTf)2 complex in which both aminal and imine moieties coexist simultaneously, while under similar conditions the chloride anion leads to a high-spin [Fe(L2)Cl2] complex.

Size-selective encapsulation of hydrophobic guests by self-assembled M4L6 cobalt and nickel cages.

Subtle differences in metal-ligand bond lengths between a series of [M(4)L(6)](4-) tetrahedral cages, where M = Fe(II), Co(II), or Ni(II), were observed to result in substantial differences in affinity for hydrophobic guests in water. Changing the metal ion from iron(II) to cobalt(II) or nickel(II) increases the size of the interior cavity of the cage and allows encapsulation of larger guest molecules. NMR spectroscopy was used to study the recognition properties of the iron(II) and cobalt(II) cages towards small hydrophobic guests in water, and single-crystal X-ray diffraction was used to study the solid-state complexes of the iron(II) and nickel(II) cages.