Cross-metathesis between ethane and toluene catalyzed by [([triple bond, length as m-(SiO)(2)TaH]: the first example of a cross-metathesis reaction between an alkane and an aromatic

The silica-supported tantalum hydride [([triple bond, length as m-dash]SiO)(2)TaH] catalyzes at moderate temperature (150-250 degree C) the cross-metathesis reaction between toluene and ethane, to form mainly ethylbenzene and xylenes.     

Mixed electric-magnetic second-order nonlinear optical response of helicenes

The mixed electric-magnetic second-order nonlinear optical responses of oriented films of helicenes have been computed ab initio using the random phase approximation method and compared to the pure electric-dipole counterpart. It turns out that the mixed electric-magnetic responses can be of the same order of magnitude as the pure electric-dipole counterpart when there is no donor/acceptor (D/A) substituent or these D/A pairs are weak, i.e., when the pure electric-dipole response is small. When adding strong D/A substituents, the pure electric-dipole response increases substantially and much more than its mixed electric-magnetic counterpart. Consequently, the ratio between the mixed electric-magnetic and pure electric responses decreases. Although there is no general rule, the mixed responses evolve as a function of substitution quasi similarly to the pure electric contribution. This study confirms therefore the possibility of tuning the mixed electric-magnetic response by employing appropriate chiral molecules.     

Functional supramolecular devices: [M4IIL4]8+ [2 x 2]-grid-type complexes as multilevel molecular electronic species

The [M(4)(II)L(4)](8+) [2 x 2]-grid-type complexes 1-8 present a set of features of particular interest for potential applications. All complexes exhibit multiple reduction levels at low reduction potentials paired with rather high stability. The modulation of the reduction potentials is possible by introduction of appropriate substituents on the ligands. The Co(II)(4) complexes 1-5 present a remarkable regularity in the disposition of the reduction levels, indicating the ability of the Co(II) sites to transmit electronic interactions between reduced ligands. In general, all investigated molecular systems 1-8 show characteristics typical for multilevel supramolecular electronic devices.     

An extension of the könig-egerváry property to node-weighted bidirected graphs

Given a bidirected graphG and a vectorb of positive integral node-weights, an integer linear program IP is defined on (G, b). IP generalizes the node packing problem on a node-weighted (undirected) graph in the sense that it reduces to the latter whenG is undirected. A polynomial time algorithm is given that recognizes whether CP (the linear program obtained by relaxing the integrality constraints of IP) has an integral optimal solution. Also an efficient method for solving the linear programming dual of CP is described.Supported by the Natural Sciences and Engineering Research Council of Canada.     

The configuration of β-halogenoenamines. The use of a new procedure for NOE measurements

The configurations of 16 different β-halogenoenamines have been determined using the proton NOE effect, and the same results were obtained as when the ²J(CH) coupling constants were used. A new procedure called the ‘repetitive shift frequency’ is presented for the NOE determinations which allows better reproducibility and improves the precision.     

Anion-receptor molecules: Synthesis of a chiral and functionalized binding subunit,a bicyclic guanidinium group derived from L- or D- asparagine

The optically active (4S,8S)-4, 8-bis(hydroxymethyl)-1,5,7-triazabicyclo[4.4.0]dec-5-ene ((S,S)- 1 ) has been synthesized in nine steps from L -asparagine with a total yield of 5.1%. Similarly, the enantiomer (R,R)- 1 has been prepared from D -asparagine. (S,S)- and (S,S)- 1 are representative examples of rigid and functionalized bicyclic guanidine systems and constitute useful intermediates in the construction of chiral selective anion-receptor molecules.