Hydrido-Carbonyl Rhenium Clusters with a Square Geometry of the Metal Core. Synthesis and X-Ray Characterization of the Novel [Re4(μ-H)3(CO)16]− Anion

Three and tetranuclear ring clusters have been obtained by treatment of [Re₂(CO)₈(THF)₂] with carbonyl-rhenates containing two terminal hydrides. The reaction with [ReH₂(CO)₄]^- provided a selective route to the previously known [Re₃(-H)₂(CO)₁₂]^- triangular cluster anion 1. The reaction with [Re₂H₂(-H)(CO)₈]^- gave the novel [Re₄(-H)₃(CO)₁₆]^- anion 2, containing a rare example of a puckered-square metal cluster. Protonation of 1 is known to afford the neutral [Re₃(-H)₃(CO)₁₂] species 3. Analogously the reaction of 2 with a strong acid afforded the previously known square metal clusters [Re₄(-H)₄(CO)₁₆] 4. The reaction could not be reversed by treatment with bases. Photolysis of 4 gave the unsaturated complex [Re₂(-H)₂(CO)₈] 5: this is the reverse of the dimerization reaction, that in THF at room temperature produces 4 from 5. Thermal treatment (reflux in cyclohexane for 24 h) left 4 almost unchanged. A single crystal X-ray analysis of [NEt₄]2 showed a s/e/s/s (e=eclipsed, s=staggered) conformation of the Re(CO)₄ units, leading to a puckered geometry of the ring, at variance with the square-planar geometry of 4 (all eclipsed). Two of the three hydrides of 2 have been located as bridging the Re–Re edges from inside the metal ring, as previously observed in 4. Density functional computations indicated a puckered conformation as the most stable for both 2 and 4, with very low activation energies for ring inversion (6.6 and 2.2 kcal·mol^-1, respectively), but ruled out solid state fluxionality for 4, whose observed planar geometry must be attributed to packing stabilization.     

A Jocic-type approach for a practical and scalable synthesis of pyrrolonaphthoxazepine (PNOX)-based potent proapoptotic agents

We developed a Jocic-type protocol for the construction of the pyrrolonaphthoxazepine (PNOX) core. After an initial investigation based on the isolation of a trichloromethyl carbinol derivative, we shifted our attention towards a multicomponent single-step protocol. Screening of a variety of bases and solvents led to the identification of the optimum conditions for the preparation of the key α-aryloxy carboxylic acids to undergo intramolecular cyclization. The novel chemical route significantly improved overall yields for the preparation of PNOX-based compounds and was successfully extended to the preparation of 1,4-benzoxazinone-based templates.     

Solid‐State Behaviour of the Dichlorobenzenes: Actual,Semi‐Virtual and Virtual Crystallography

The crystal structures of the low‐melting 1,2‐ and 1,3‐dichlorobenzene isomers have been determined by X‐ray analysis and in situ crystallisation techniques. Attempts to predict these structures in advance by force‐field calculations were not successful, although the known crystal structures of two of the three polymorphs of the 1,4‐isomer were successfully `a posteriori' predicted. Calculated lattice energies were supplemented with estimated lattice‐vibrational entropies obtained in the rigid‐body approximation. Energy calculations for actual and virtual crystal structures indicate that the higher melting point of the 1,4‐isomer can be largely attributed to more efficient crystal packing.     

THE α-OXIDASE SYSTEM OF YOUNG PEA LEAVES (Pisum sativum) AS GENERATOR OF ELECTRONICALLY EXCITED STATES. EXCITATION IN THE DARK UNDER NATURAL CONDITIONS

Abstract. The aerobic oxidation of saturated long chain fatty acids to the lower aldehyde and CO₂ catalyzed by the α-oxidase system of young leaves from germinating Pisum sativum results in concomitant excitation of the chloroplasts or/and fractions present in the α-oxidase preparation. The excitation is attested to by both chlorophyll emission and Hill activity. This is the first case of photobiochemistry without light within a natural system.     

Polycondensed nitrogen heterocycles. Part 17. Isoxazolo[4,3-d]pyrazolo[3,4-f][1,2,3]triazepine. A new ring system

The title compounds were prepared by nitration of compounds 2 , reduction of the dinitro derivatives 4 and diazotization of the diamino derivatives 6 followed by an intramolecular coupling reaction. Compound 4a showed good activity against Salmonella cholerasuis and Clostridium perfringens bacteria.     

Studies on decarboxylation reactions. Part 5 . Micellar catalysis and mixed solvents effects on the decarboxylation of some N-alkyl- or N-aryl-substituted 5-amino-1,3,4-oxadiazole-2-carboxylic acids

The effect of micelles and mixed solvents on the decarboxylation of some N-alkyl- or N-aryl-substituted 5-amino-1,3,4-oxadiazole-2-carboxylic acids has been studied. The data support the unimolecular decarboxylation mechanism proposed by us. Moreover, they show that mixed solvents and micelles have different effects on reactivity of the amino acids under study.