The first coordination polymer of lanthanum(III) with a naphthalene‐1,4,5,8‐tetracarboxylic 1,8‐anhydride derivative

The title compound, catena‐poly[[[heptaaqualanthanum(III)]‐μ‐1,3‐dioxo‐2‐oxa‐1H,3H‐phenalene‐6,7‐dicarboxylato‐κ²O⁶:O⁷] hemi(4,8‐dicarboxynaphthalene‐1,5‐dicarboxylate) dihydrate], {[La(C₁₄H₄O₇)(H₂O)₇](C₁₄H₆O₈)_0.5·2H₂O}_n, is a dihydrate of a coordination polymer between the dianion of naphthalene‐1,4,5,8‐tetracarboxylic 1,8‐anhydride and the heptahydrated lanthanum(III) ion, charge balanced by an additional 4,8‐dicarboxynaphthalene‐1,5‐dicarboxylate dianion that is located on an inversion centre and is not coordinated to the metal ion. The linear polymeric arrays adopt a comb‐like structure, and these pack in pairs with one chain interpenetrating another, like two parts of a zip, to optimize stacking interactions between their ligand fragments. All the components of this compound are further interlinked by an extensive pattern of O—H...O hydrogen bonds throughout the crystal structure. The main scientific significance of the results reported here is that they demonstrate for the first time the feasibility of coordination polymerization of the above organic ligand with lanthanide ions. The resulting polymer has a unique architecture. Finally, the reported structure is a rare example where the tetraacid and the diacid anhydride ligand species co‐exist in the same crystal.     

Supra­molecular assembly of (methanol)[10,15,20‐tris­(4‐cyano­phenyl)‐5‐(4‐pyridyl)­porphyrin­ato]­zinc(II) by inter­molecular hydrogen bonding and weak coordination

The crystal structure of the title compound, [Zn(C₄₆H₂₄N₈)(CH₄O)], consists of two‐dimensional supra­molecular arrays sustained by O—H⋯N(pyrid­yl) hydrogen bonding and weak Zn⋯NC coordination. The inter­layer organization in the crystal structure is characterized by tight stacking of the corrugated layers.     

Striking alkenol versus allenol reactivity: metal-catalyzed chemodifferentiating oxycyclization of enallenols

An efficient chemodivergent metal-controlled methodology for the generation of different highly functionalized oxygen heterocycles from common enallenol substrates has been developed. Chemoselectivity control in the O-C functionalization of an enallenol can be achieved through the choice of catalyst: AuCl(3), PdCl(2), and [PtCl(2)(CH(2)=CH(2))](2) exclusively afford dihydrofurans through selective activation of the allenol moiety, whereas FeCl(3) solely gives tetrahydrofurans or tetrahydropyrans through selective activation of the alkenol moiety. We have also shown that a combination of metal-mediated hydroalkoxylation and allenic aminocyclization reactions can lead to a useful preparation of the tetrahydrofuro[3,2-b]piperidine core of the antimalarial alkaloid isofebrifugine. These divergent heterocyclization reactions have been developed experimentally and additionally, their mechanisms have been investigated by a theoretical study.     

Why Do Cycloaddition Reactions Involving C60 Prefer [6,6] over [5,6] Bonds?

The origin of the experimentally known preference for [6,6] over [5,6] bonds in cycloaddition reactions involving C₆₀ has been computationally explored. To this end, the Diels–Alder reaction between cyclopentadiene and C₆₀ has been analysed by means of the recently introduced activation strain model of reactivity in combination with the energy decomposition analysis method. Other issues, such as the aromaticity of the corresponding transition states, have also been considered. These results indicate that the major factor controlling the observed regioselectivity is the more stabilising interaction between the deformed reactants in the [6,6] reaction pathway along the entire reaction coordinate.     

A One‐Pot Synthesis of N‐Aryl‐2‐Oxazolidinones and Cyclic Urethanes by the Lewis Base Catalyzed Fixation of Carbon Dioxide into Anilines and Bromoalkanes

The multicomponent assembly of pharmaceutically relevant N‐aryl‐oxazolidinones through the direct insertion of carbon dioxide into readily available anilines and dibromoalkanes is described. The addition of catalytic amounts of an organosuperbase such as Barton's base enables this transformation to proceed with high yields and exquisite substrate functional‐group tolerance under ambient CO₂ pressure and mild temperature. This report also provides the first proof‐of‐principle for the single‐operation synthesis of elusive seven‐membered ring cyclic urethanes.     

Non-destructive assessment of parchment deterioration by optical methods

A non-destructive and non-invasive method for quantitative characterization of parchment deterioration, based on spectral measurements, is proposed. Deterioration due to both natural aging (ancient parchments) and artificial aging (achieved by means of controlled UV irradiation and temperature treatment) was investigated. The effect of aging on parchment native fluorescence was correlated with its deterioration condition. Aging causes fluorescence intensity drop, spectral shift of the main peak, and an overall change in the fluorescence spectral features. Digital color imaging analysis based on visible reflectance from the parchment surface was also applied, and the correspondent color components (RGB) were successively correlated with the state of parchment deterioration/aging. The fluorescence and color imaging data were validated by analysis of historical parchments, aged between 50 and 2000 years and covering a large variety of states of deterioration. The samples were independently assessed by traditional microscopy methods. We conclude that the proposed optical method qualifies well as a non-destructive tool for rapid assessment of the stage of parchment deterioration.     

Palladium‐Catalyzed Intramolecular Carbene Insertion into C(sp3)−H Bonds

A palladium‐catalyzed carbene insertion into C(sp³)?H bonds leading to pyrrolidines was developed. The coupling reaction can be catalyzed by both Pd⁰ and Pd^II, is regioselective, and shows a broad functional group tolerance. This reaction is the first example of palladium‐catalyzed C(sp³)?C(sp³) bond assembly starting from diazocarbonyl compounds. DFT calculations revealed that this direct C(sp³)?H bond functionalization reaction involves an unprecedented concerted metalation–deprotonation step.