A wide variety of monomeric and oligomeric, donor-substituted 1,1,4,4-tetracyanobutadienes (TCBDs) have been synthesized by [2+2] cycloaddition between tetracyanoethylene (TNCE) and donor-substituted alkynes, followed by electrocyclic ring opening of the initially formed cyclobutenes. Reaction yields are often nearly quantitative but can be affected by the electron-donating power and steric demands of the alkyne substituents. The intramolecular charge-transfer (CT) interactions between the donor and TCBD acceptor moieties were comprehensively investigated by X-ray crystallography, electrochemistry, UV-visible spectroscopy, and theoretical calculations. Despite the nonplanarity of the new chromophores, which have a substantial twist between the two dicyanovinyl planes, efficient intramolecular CT interactions are observed, and the crystal structures demonstrate a high quinoid character in strong donor substituents, such as N,N-dimethylanilino (DMA) rings. The maxima of the CT bands shift bathochromically upon reduction of the amount of conjugative coupling between strong donor and acceptor moieties. Each TCBD moiety undergoes two reversible, one-electron reduction steps. Thus, a tri-TCBD derivative with a 1,3,5-trisubstituted benzene core shows six reversible reduction steps within an exceptionally narrow potential range of 1.0 V. The first reduction potential E(red,1) is strongly influenced by the donor substitution: introduction of more donor moieties causes an increasingly twisted TCBD structure, a fact that results in the elevation of the LUMO level and, consequently, a more difficult first reduction. The potentials are also strongly influenced by the nature of the donor residues and the extent of donor-acceptor coupling. A careful comparison of electrochemical data and the correlation with UV-visible spectra made it possible to estimate unknown physical parameters such as the E(red,1) of unsubstituted TCBD (-0.31 V vs Fc+/Fc) as well as the maxima of highly broadened CT bands. Donor-substituted TCBDs are stable molecules and can be sublimed without decomposition. With their high third-order optical nonlinearities, as revealed in preliminary measurements, they should become interesting chromophores for ultra-thin film formation by vapor deposition techniques and have applications in opto-electronic devices.

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The kinetics and the mechanism of the selective reduction of nitric oxides (NO x ) by hydrogen is studied on a trimetallic Pt± Mo±Co/-Al 2 O 3 catalyst under oxidising conditions. This system is interesting in view of an exhaust gas control of power plants or lean-burn cars. It can be shown that the NO dissociation is the crucial step, dominating the overall reaction behaviour and that it depends on temperature and on the partial pressure of H 2 . With increasing temperatures the reaction reveals an autocatalytic behaviour resulting in bistability and hysteresis. At higher temperatures, where no bistability is found, the NO/H 2 as well as the competing O 2 /H 2 reaction occur only above a certain critical partial pressure of H 2 . The kinetics of the NO/H 2 / O 2 reaction are established using a modi®ed Langmuir±Hinshelwood model (T1428C±1608C, y O2 >4%) which takes into account the critical H 2 partial pressure. The model describes the experimental data within AE15%. The determined activation energies are: 63 kJ/mol for the NO x consumption, 77 and 45 kJ/mol for the N 2 and N 2 O formation, respectively, and 130 kJ/ mol for the O 2 /H 2 reaction. Adsorption enthalpies are determined to À59 kJ/mol for the adsorption of H 2 , À77 kJ/mol for the adsorption of NO and À97 kJ/mol for the adsorption of O 2 . An interesting feature of the reaction is the enhancement of the NO/H 2 reaction by oxygen for low partial pressures of O 2 . This appears to be the ®rst study where a promoting effect of oxygen for the NO/H 2 reaction is found on a platinum supported catalyst. #

We report the synthesis and properties of two series of homologous donor-acceptor (D-A) chromophores in which N, N-dimethylanilino (DMA) or N,N-dihexylanilino (DHA) donors and dicyanovinyl acceptors are separated by up to four CϵC triple-bond spacers or up to three C=C doublebond spacers. The intramolecular charge-transfer (CT) interactions of the new D-A oligoynes and the known all-trans D-A oligoenes were investigated by X-ray crystallography, electrochemistry, UV/Vis spectroscopy, and theoretical calcu-

Synthesis. -The synthesis of the title compounds is based on a [2 + 2] cycloaddition followed by electrocyclic ring opening of the cyclobutene intermediate. -(MICHINOBU, T.; BOUDON, C.; GISSELBRECHT, J.-P.; SEILER, P.; FRANK, B.; MOONEN, N. N. P.; GROSS, M.; DIEDERICH*, F.; Chem. Eur. J. 12 (2006) 7, 1889-1905; Lab. Org. Chem., ETH-Hoenggerberg, CH-8093 Zuerich, Switz.; Eng.) -Nuesgen 25-095