Taming Gold(I)–Counterion Interplay in the De‐aromatization of Indoles with Allenamides

A careful interplay between the π electrophilicity of a cationic Au^I center and the basicity of the corresponding counterion allowed for the chemo‐ and regioselective inter‐ as well as intramolecular de‐aromatization of 2,3‐disubstituted indoles with allenamides. The silver‐free bifunctional Lewis acid/Brønsted base complex [{2,4‐(tBu)₂C₆H₃O}₃PAuTFA] assisted the formation of a range of densely functionalized indolenines under mild conditions.     

Recent advances in propylene polymerization with MgCl2 supported catalysts

The role of Lewis bases in MgCl₂ supported catalysts for olefin polymerization is a subject of continuous interest and discussion in order to obtain more and more active and stereospecific catalysts and to explain their stereoregulating mechanism. Through molecular calculation and conformational analysis it was possible to identify chelating diethers that have the correct oxygen-oxygen distance necessary to tightly coordinate with the Mg ions of the support, even in the presence of other strong Lewis acids, and unable to give secondary reactions with TiCl₄, AlR₃, Ti-C and Ti-H bonds. The use of these donors has allowed the synthesis of catalytic systems that are both highly active and stereospecific even in the absence of external donors. Kinetic data of propylene polymerization with these catalyst systems are reported. The importance of the distance between the donor atoms in bifunctional Lewis bases has been proved also in the case of new classes of internal donors. Molecular modelling studies have enabled us to formulate models of active sites, located on some corners of MgCl₂ crystallites, whose chirality is induced by the presence of a donor molecule in their environment. These models could explain, at least in part, the exceptional increase of isotactic polymer productivity observed for stereospecific catalyst systems, containing only the internal donor, with respect to catalysts lacking the Lewis base and could account for the influence of the donor on the molecular properties of the obtained polymers.     

From Effect Algebras to Algebras of Effects (Sum Brouwer—Zadeh Algebras)

The algebraic structures arising in the axiomatic framework of unsharp quantummechanics based on effect operators on a Hilbert space are investigated. It isstressed that usually considered effect algebras neglect the unitary Brouwerianmap of complementation, and the main results based on this complementationare collected, showing the enrichment produced into the theory by its introduction.In particular, in these structures two notions of sharpness can be considered: K-sharpness induced by the usual complementation of effect algebrasand B-sharpness induced by this new complementation. Quantum (resp., classical) SBZalgebras are then characterized by the condition of B-coherence (resp., B-coherence plusB-compatibility), showing that in this case the poset of all B-sharp elements is orthomodular (resp., Boolean algebra). In the unsharp contextof effect operators, the finite dimensionality of the Hilbert space or the finitenessof a von Neumann algebra are both characterized by a de Morgan property ofthe Brouwer complementation. Moreover, since effect operators on a pre-Hilbertspace give rise to a standard model of effect algebras, a characterization ofcompleteness of pre-Hilbert spaces is given making use of the Brouwercomplement.     

Stereoselective synthesis of tetracyclic indolines via gold-catalyzed cascade cyclization reactions

A reliable synthetic route to fused polycyclic indolines is documented by the development of a stereoselective gold catalyzed cascade cyclization of indole propargylic alcohols.     

Weak O‐Assistance Outcompeting Strong N,N‐Bidentate Directing Groups in Copper‐Catalyzed C−H Chalcogenation

A copper‐mediated C?H chalcogenation of triazoles has been achieved by weak coordination. The user‐friendly protocol showed high functional‐group tolerance and ample substrate scope, yielding fully substituted 1,2,3‐triazoles with complete positional site‐selectivity. The C?H selenylation could likewise be achieved by means of copper catalysis. Our findings highlight for the first time that weak O‐coordination can outcompete the strong N,N‐bidentate coordination mode in C?H functionalization technology.     

Interlaboratory comparison of melt flow rate testing of moisture sensitive plastics

The current standard for melt flow rate testing, ISO 1133, does not adequately cover the measurement of materials that degrade or further polymerise at the melt flow rate test conditions. Materials such as PET, PBT and PA tend to degrade, sometimes rapidly, at melt temperatures if they contain absorbed water. This results in poor repeatability and reproducibility of melt flow rate results. The ISO Plastics Melt Rheology Working Group (TC61/SC5/WG9) is currently developing a modified melt flow rate test method for reliable measurement of moisture sensitive materials, thereby providing an alternative to intrinsic viscosity measurements. The modified method controls more tightly the time–temperature history experienced by the material during testing and, thus, the resultant variability in measured properties due to degradation.The results of an intercomparison of testing of moisture sensitive polymers using the melt volume flow rate (MVR) and melt mass flow rate (MFR) methods are reported. A polypropylene (PP), used as a benchmark material, and five moisture sensitive materials were tested by a number of laboratories measuring either MVR or MFR, or both. For standard testing of the PP material, the repeatability and reproducibility of measurements of MVR were up to 5% and 11%, respectively, and for MFR were 7% and 21%, respectively (95% confidence level, outliers excluded). For the moisture sensitive materials the repeatability and reproducibility of measurements varied significantly, with repeatability values up to 26% and reproducibility values up to 114% being obtained. By imposing moisture and temperature control criteria in accordance with the proposed testing standard, the repeatability and reproducibility limits were significantly reduced to approximately 10% and 60%, respectively. The results suggest that both the moisture and temperature criteria were important for improving the repeatability of MVR measurements. However, the moisture content criterion was more important for improving the reproducibility of MVR measurements.The need to tightly control the sample preparation, in particular the drying and subsequent sample handing procedures, and the time–temperature history of the sample throughout the test is considered critical to further improve the precision of measurements of such materials.     

The study of electron energy distribution functions, Swarm parameters, and transition rates in N2+O2 plasma

Using the Boltzman equation electron energy distribution functions, swarm parameters (mean energy, characteristic energy, drift velocity and diffusion coefficient), and transition rates (one for vibrational and one for electronical excitation for each of the gases) for N₂+O₂ (80%+20%) mixture plasma have been calculated. The influence of the applied reduced electric field and the vibrational temperatures on these quantities is studied.     

A chemometric survey of three sites in Muggia Bay (Northern Adriatic Sea): meteorological effects on heavy metal patterns in surface coastal waters

Within research on the quality of the waters of the Gulf of Trieste, this study on patterns of trace metal contents in the inner part of the gulf (Muggia Bay) discusses data of Cu, Pb, Cd and Zn, determined voltammetrically (DPASV), and collected in three sites with a 10-day frequency over the period of one year. Two of the sites lie inside the dam system which protects the harbour of Trieste, while the third one is situated outside for comparison purposes. Principal component analysis pointed out different metal patterns inside and outside the dam system; PC scores were related to meteorological information: rain plays a major role in conditioning the estuarine inner site: wind stirring action was detectable for the outer site. Both univariate graphics and canonical correlation analysis suggest a diffuse source for Pb, probably atmospheric deposition. Received: 1 August 1997 / Revised: 20 November 1997 / Accepted: 23 November 1997