A highly efficient dioxo(mu-oxo)molybdenum(VI) dimer catalyst for olefin epoxidation

The oxo-bridged dimer [Mo(2)O(4)(mu(2)-O)Cl(2)(pzH)(4)] (1; pzH = pyrazole) exhibits unusually high activity in the liquid-phase catalytic epoxidation of the cyclic olefins cyclooctene and (R)-(+)-limonene under mild conditions and in the absence of additional organic solvents, using tert-butyl hydroperoxide as the oxidant. The complex is stable under the reaction conditions and can be used in further catalytic runs without significant loss of performance. An X-ray crystallographic investigation reveals that 1 has an unprecedented and extremely rare all-cis configuration at each of the MoO(2)-(mu(2)-O)Cl(pzH)(2) cores, which can be understood by considering supramolecular contacts and geometric factors.     

Conformational interconversions in [2]catenanes containing a wide rigid bis(p-benzyl)methyl spacer

The conformational interconversions of four [2]catenanes (1-4) containing a dibenzo-34-crown-10 ether (BPP34C10) interlocked with rings containing two 4,4'-dipyridiniums tethered by 1,3-bis(ethyloxy)phenyl and bis(p-benzyl)methyl spacers have been studied by VT 1H NMR spectroscopy. Symmetrically placed blocking groups on thickened tethers enabled either pathway for circumrotation of the BPP34C10 between isoenergetic sites to be blocked. On the basis of chemical shifts of the BPP34C10, its internal p-hydroquinone forms pi-pi-stacking interactions with only one 4,4'-dipyridinium ring at a time. The activation barrier for migration along either open tether was approximately 11.5 kcal/mol. This study demonstrates an ability to select the pathway for conformational interconversions in these [2]catenanes containing the rigid bis(p-benzyl)methyl tether and the lowering the barrier for interconversion through destabilization of the ground state structures.     

A tits alternative for groups that are residually of bounded rank

In this short note a Tits alternative for certain kinds of groups which are residually of rank at mostr is obtained. The main theorem states that ifG is a group that is residually (locally (soluble-by-finite) of rankr), then eitherG is locally (soluble-by-finite) orG contains a non-abelian free subgroup. The third author would like to thank the School of Mathematics at the University of Wales, Cardiff for its hospitality whild part of this work was being done.     

Spin polarization of β-emitting fragments in high energy heavy ions on Be collisions

The degrees of nuclear spin polarization of ^8,12B, ⁹C, ¹²N, ¹³O, ^20,21F, ²³Mg, ²⁷Si and ³⁹Ca produced in the high energy ^12,13C, ¹⁶O, ²²Ne, ²⁴Mg, ²⁸Si and ⁴⁰Ca ions on Be collisions have been measured systematically, for the technical developments of the nuclear moment studies as well as the hyperfine interaction studies by means of β-NMR technique. The fragment momentum dependences were well reproduced by the simple kinematical model. Incident energy dependence and the mass dependence as well as the reaction angle dependences were qualitatively explained by the mixing of the near and far side collisions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Groups with the Weak Maximal Condition on Non-permutable Subgroups

Let G be a group with the weak maximal condition on non-permutable subgroups. We prove that if G is a generalized radical group then G is either quasihamiltonian or a soluble-by-finite minimax group.     

K0 production in e+e− annihilations at 30 GeV center of mass energy

Inclusive K⁰-production has been measured in e⁺e^- annihilation at a center of mass energy of about W = 30 GeV. The ratio of K⁰ + K⁰ production to μ⁺μ^- production is R_K0 = 5.6 ± 1.1 (statist. error) ± 0.8 (system.error) This value is about a factor of three higher than R_K0 at W = 7 GeV. The cross sections (s/β) dσ/dx is consistent with a scaling behaviour.