Solvothermal syntheses of high-nuclearity vanadium(III) clusters

Superheating alcohol solutions of simple trimetallic vanadium(III) precursors gives the octa- and decametallic vanadium(III) clusters [V(8)(OEt)(8)(OH)(4)(O(2)CPh)(12)] (1) and [V(10)(OMe)(20)(O(2)CMe)(10)] (2). Cluster 2 is the largest vanadium(III) cluster synthesised to date. Thus solvothermal synthetic techniques are an excellent route to high-nuclearity vanadium(III) clusters. Both 1 and 2 consist of a planar or near-planar array of V(III) ions. The metal ions in 1 are bridged by either a micro(2)-hydroxide and two micro(2)-benzoate groups or two micro(2)-ethoxides and a micro(2)-benzoate groups, the two bridging arrangements alternating around the ring. In 2 each pair of neighbouring metal ions is bridged by two micro(2)-methoxides and a micro(2)-acetate, and this molecule is the V(III) analogue of Lippard's famous "ferric wheel". Preliminary magnetic susceptibility studies show the exchange coupling in both complexes to be antiferromagnetic in nature, with the coupling stronger in 1 than in 2.     

Tracking the distribution of "ecstasy" tablets by Raman composition profiling: a large scale feasibility study

Here we report the results of the largest study yet carried out on composition profiling of seized "ecstasy" tablets by Raman spectroscopy. Approximately 1500 tablets from different seizures in N. Ireland were analysed and even though practically all the tablets contained MDMA as active constituent, there were very significant differences in their Raman spectra, which were due to variations in both the nature and concentration of the excipients used and/or the degree of hydration of the MDMA. The ratios of the peak heights of the prominent drug bands at 810 cm(-1) and 716 cm(-1) (which vary with hydration state of the drug), and the drug band at 810 cm(-1) against the largest clearly discernible excipient band in the spectrum were measured for all the samples. It was found that there was sufficient variation in composition in the general sample population to make any matches between batches of tablets taken from different seizures significant, rather than the result of random chance. Despite the large number of different batches of tablets examined in this study, only two examples of indistinguishable sets of tablets were found and in only one of these had the two batches of tablets been seized at different times. Finally, the fact that there are many examples of batches of tablets (particularly in different batches taken from single seizures) in which the differences between each set are sufficiently small that they appear to arise only from random variations within a standard manufacturing method implies that, with more extensive data, it may be possible to recognize the "signature" of tablets prepared by major manufacturers.     

Organometallic chemistry of azuliporphyrins: synthesis, spectroscopy, electrochemistry, and structural characterization of nickel(II), palladium(II), and platinum(II) complexes of azuliporphyrins

Four azuliporphyrins, two meso-unsubstituted and two meso-tetraaryl substituted, were investigated in the synthesis of novel organometallic compounds. The meso-unsubstituted or "etio" series azuliporphyrins 8 reacted with nickel(II) acetate, palladium(II) acetate, and platinum(II) chloride in DMF to give the corresponding chelates 14-16, where the metal cation lies within the macrocyclic cavity and binds to all three nitrogens and the internal carbon atom. The newly available meso-tetraarylazuliporphyrins 13 similarly afforded the corresponding nickel(II), palladium(II), and platinum(II) complexes, 17-19, respectively. The new organometallic complexes are stable nonpolar compounds and were fully characterized spectroscopically and by mass spectrometry. The UV-vis data indicate that these complexes, in common with the parent azuliporphyrin system 8, do not possess porphyrin-type aromaticity. However, electron donation from the azulene unit can give rise to dipolar resonance contributors that provide a degree of carbaporphyrin-type aromatic character. The platinum(II) azuliporphyrins 16 gave noteworthy proton NMR spectra where the meso-protons showed satellite peaks due to transannular coupling to platinum-195. The pyrrolic protons of the platinum(II) meso-tetraarylazuliporphyrin 19b also showed similar satellite peaks due to coupling from the platinum-195 isotope. The electrochemistry of free base tetraphenylazuliporphyrin 13a and the related nickel(II) and palladium(II) complexes was investigated using cyclic voltammetry, and these data indicate that metal coordination improves the reversibility of the ligand-based oxidations. Nickel(II) azuliporphyrin 14a and palladium(II) tetrakis(4-chlorophenyl)azuliporphyrin 18b were also structurally characterized by X-ray crystallography. The macrocyclic core of the palladium(II) complex 18b was significantly more planar than the nickel(II) derivative 14b, and this difference was attributed to the better size match between the azuliporphyrin cavity and the larger palladium(II) ion. The straightforward synthesis of metalloazuliporphyrins under mild conditions, and their interesting spectroscopic, electrochemical, and structural features, demonstrates that the azuliporphyrin system holds great promise as a platform for organometallic chemistry.     

Some new intuitionistic equivalents of Zorn’s Lemma

Two new intuitionistic equivalents to Zarns Lemma are stated and proved.     

A novel route to the marasmane skeleton via a tandem rearrangement-cyclopropanation reaction. total synthesis of (+)-isovelleral

A general and efficient route to the marasmane skeleton is described. Total syntheses of two simple marasmanes (35 and 37) in racemic form were achieved using a MgI2-catalyzed rearrangement-cyclopropanation reaction of trimethylsilyl enol ether 31 derived from naphthalenone 30. The reaction proceeds in high yield with complete diastereoselectivity and does not require the use of special cyclopropanation reagents. Application of this novel route to the marasmane framework was extended to the synthesis of naturally occurring (+)-isovelleral (41).     

Single step,solvent-free processes: examples and prospects

An outline is given of some of the options now available — and likely to be of growing importance — for various of ways in which inorganic catalysts may be developed to effect industrially important chemical reactions in environmentally more acceptable means. One major goal is to devise ways of producing in situ (within the sphere of reaction) aggressive oxidants especially those that are environmentally hazardous. Two specific examples are cited: 1) one involves hydroxylamine, generated in a benign fashion, so as to effect the ammoximation of cyclohexanone to its oxime and -caprolactam; 2) the other involves the Baeyer—Villiger reaction (for converting cyclic ketones to lactones) via perbenzoic acid. The role of supported bimetallic catalysts in solvent-free hydrogenations (especially of polyenes) is also highlighted.     

Regularity of CR mappings

Sloan Fellow, partially supported by NSF grant DMS 8619858     

On derivations and commutativity in prime rings

Supported by the Natural Sciences and Engineering Research Council of Canada, Grant No. A3961.