1,2,9,16,17,24-hexathia[2.1.2.1]-4,6,8,11,13,15,19,21,23,26,28,30-dodecamethyl-metacyclophane : A novel macrocyclic polysulphur compound by direct sulphuration of mesitylene

The synthesis of 1,2,9,16,17,24 - hexathia[2.1.2.1] - 4,6,8,11,13,15,19,21,23,26,28,30 - dodecamethyl - metacyclophane by direct sulphuration of mesitylene, the first report of a single-step synthesis of an aromatic macrocycle with alternating sulphide and disulphide linkages, is reported. Structure determination of this compound was achieved by mass spectrometry, and by reductive degradation to 3,3'-dithio-dimesitylsulphide and reoxidation of the latter to the original macrocycle. Some evidence concerning the probable pathway to macrocycle formation is reported.     

Synthesis,spectral properties and conformational preferences of macrocyclic compounds containing 2,5-dithio-1,3,4-thiadiazole subunits

The syntheses of macrocyles 1–6, containing 2,5 - dithio - 1,3,4 - thiadiazole subunits connected by 1,2-, 1,3- and 1,4-bis(methylene)benzenes, as well as of the appropriate open-chain model compounds 7–12 are described. Structure proofs were afforded by their mass and ¹H NMR spectra. Different decompostion processes upon electron-impact are ascertained for compounds 1–12, depending on the position of the bridges and ortho substitution; therefore, the mass spectra can provide a sensitive diagnostic tool for structure elucidation of positional isomers. The NMR spectral data of macroycyles 1–6, coupled with those of the corresponding open-chain derivatives 7–12, indicate that the preferred conformations are determined primarily by the size and shape of their ring systems. Furthermore, variable-temperature NMR studies on intraannularly methyl substituted macrocyles 3 and 6 provide evidence that the 20-membered mesityl derivative 3 adopt the saddle-shape conformation (IV) (the energy barrier for the restricted rotation of methylene bridges if found to be ΔG^≠= 13.8 kcal/mole at + 5°), while the duryl groups in the 22-membered macrocycle 6 are free rotating even at ?60°.     

Transducer line-arrays in the high-frequency range

The transducer array theory developed in the field of underwater acoustics has been used for the design and construction of ultrasonic arrays in the frequency range 600–800 kHz. With these transducers it is possible to scan the acoustic beam electronically and to make the scanning process much faster and less expensive than with a mechanical system. The results show that even higher working frequencies and wider scanning angles can be obtained by developing the technology further.     

Metal Catalyzed Polymerization: From Stereoregular Poly(α-olefins) to Tailor-Made Biodegradable/Biorenewable Polymers and Copolymers

Metal catalyzed polymerizations are among the most important chemical reactions, accounting for the production of about 400 million tons per year of polymeric materials, 50 % of which are polyolefins. The CIRCC research units at the University of Salerno, founded by the late Professor Adolfo Zambelli, a coworker of Giulio Natta and a pioneer in the studies of stereospecific polymerization catalysts, has a consolidated expertise in this field. Although often considered a “mature” area of research, olefin polymerization catalysis continues to drive great interest of both industrial and academic scientists. On the other hand, strong political and economic pressure toward the development of “green” and possibly biodegradable alternatives to olefin-based polymers stimulated our group to direct increasing research efforts in the area of sustainable polymers. In this perspective, we focus on the most recent work from the CIRCC research units involved in homogeneous catalysis for polymerization of a variety of monomers, with the aim to address how the concepts and the expertise developed for olefin polymerization can be applied to the development of different metal-catalyzed polymerizations and copolymerizations. Of course, although the results are discussed in the frame of the most important literature contributions, a comprehensive review of such a wide and diversified topic is out of the scope of the paper. References to reviews covering the different types of metal catalyzed polymerizations are provided in each chapter.     

Polymerization of α-olefins promoted by zirconium complexes bearing bis(phenoxy-imine) ligands with ortho-phenoxy halogen substituents

New fluorinated bis(phenoxy-imine)zirconium complexes bearing halogen substituents in the ortho and para positions of the phenolate rings, bis[N-(3,5-dibromosalycilidene)-2,3,4,5,6-pentafluoroaniline]-Zr(IV) dichloride (1) and bis[N-(3,5-dichlorosalycilidene)-2,3,4,5,6-pentafluoroaniline]-Zr(IV) dichloride (2) have been synthesized and used as precatalysts in the polymerization of propylene and 1-hexene. Their catalytic behaviour was compared with that of the analogous fluorinated zirconium complexes bearing alkyl groups in the same positions of the phenolate rings to investigate the effects produced by the introduction of additional electron-withdrawing halogen substituents. Complexes 1 and 2 produce stereoirregular, slightly syndiotactic enriched polypropylenes showing enhanced catalytic activities and an improved primary regioselectivity. Both catalysts promote efficiently the oligomerization of 1-hexene to atactic and regioregular oligomers. Interestingly for both the studied monomers it is possible to control the molecular weights and the structures of end groups of the produced polymeric chains by an appropriate choice of the cocatalyst. Functionalization reactions of the unsaturated polymeric chains selectively produced are also reported.     

Synthesis and topology of [2+2] calix[4]resorcarene-based chiral cavitand-salen macrocycles

Chiral diastereomeric cavitand-salen macrocycles have been synthesized by the high-dilution condensation of a tris-(quinoxaline-bridged)-diformyl-calix[4]resorcarene with (1R,2R)-diphenylethylenediamine. The reaction produced a couple of diastereoisomers, consisting of two cavitand cavities bis-bridged by two chiral diimino moieties, which differ in a convergent (C-shaped) or divergent (S-shaped) orientation of the two cavities.