Silicon hydrides and nickel complexes : II. Mechanism of the hydrosilylation catalyzed by nickel-phosphine complexes

Two ethylene-nickel(0) complexes, viz., [1,2-bis(diphenylphosphino)ethane]-(ethylene)nickel(0) and bis(triphenylphosphine)(ethylene)nickel(0) have been used in a comparison of their catalytic activities in hydrosilylation reactions with those of the corresponding nickel(II) complexes, viz., dichloro [1,2-bis(diphenylphosphino)-ethane]nickel(II) and dichlorobis(triphenylphosphine)nickel(II). The reaction profiles are similar, apart from a significant difference in the induction period; the nickel(II) catalysts requiring a substantially longer time. A mechanism involving a nickel(0) species is proposed for the hydrosilylation.The interchange of hydrogen and chlorine on silicon accompanying the hydrosilylation is related to a high electron density at the nickel atom bearing the phosphine, olefin, and silicon hydride ligands.     

Gold(I)-catalyzed regioselective inter-/intramolecular addition cascade of di- and triynes for direct construction of substituted naphthalenes

The gold-catalyzed cascade intermolecular addition-intramolecular carbocyclization reaction of dialkynylbenzenes was developed. In this reaction, regioselective addition of an external nucleophile toward the terminal alkyne and subsequent 6-endo-dig cyclization proceeded to give the 1,3-disubstituted naphthalenes in good yields. The direct synthesis of disubstituted chrysenes via a gold-catalyzed addition and double cyclization cascade using a triyne-type substrate was also achieved.     

Optical detection of organic hydrides with platinum-loaded tungsten trioxide

Tungsten trioxide powder with loading 0.1 wt% platinum (Pt/WO₃) was prepared for optical detection of organic hydrides such as cyclohexane, decalin by impregnation with PtCl₆^2? and subsequent calcination in air at 500 °C. The scanning electron microscopic observation of Pt/WO₃ shows that the Pt particles with mean diameters of 80–100 nm were on the surface of the WO₃ powder. The Pt/WO₃ showed coloration for 13% cyclohexane at higher 100 °C and for 1.3% cyclohexane at 200 °C. The in-situ XRD results of the Pt/WO₃ in coloring/bleaching change indicate that the coloring of Pt/WO₃ was caused by transformation of WO₃ to tungsten bronze. The analysis of reacted gas demonstrates that Pt on WO₃ produces only hydrogen and benzene through dehydrogenation of cyclohexane over 100 °C. It was founded that the Pt/WO₃ has potential of optical detection of organic hydrides by heating at higher 100 °C.     

The promoting effect of energetic activation of a methane molecular-beam in the direct catalytic partial oxidation of methane

Energetic activation of a methane molecular-beam promoted remarkably the direct catalytic partial oxidation on Pt and Rh foils, in particular, hydrogen formation was dramatically enhanced.     

Experimental study of thermal noise caused by an inhomogeneously distributed loss

The thermal fluctuation of a mechanical system with an inhomogeneously distributed loss was measured to prove the invalidity of the normal-mode expansion method which is commonly used to calculate the thermal noise of mechanical oscillators. The measured spectrum is inconsistent with the modal expansion model, while they agree well with an evaluation obtained by applying the fluctuation-dissipation theorem to the measured mechanical response. These are the first experimental results which show that mode expansion is invalid.     

A Six-Coordinate Silicon Dihydride Embedded in a Porphyrin: Enhanced Hydride-Donor Properties and the Catalyst-Free Hydrosilylation of CO2

The catalyst-free hydrosilylation of CO₂ under mild conditions remains limited. Herein, we report the synthesis, characterization, and reactivity of 5,10,15,20-tetraphenylporphyrinato(dihydrido)silicon(IV) ( 1 ) as a six-coordinate silicon dihydride. The Si-H moiety of 1 reacts with polar double bonds and CO₂ in the absence of a catalyst to afford hydrosilylated products. Combining the hydrosilylation with subsequent transformation furnishes formic acid from CO₂. Computational studies indicate that the hydride-donor properties of 1 are exceptionally high for a neutral silicon hydride, and that the direct hydride transfer from silicon to carbon is a pivotal step in the hydrosilylation of CO₂ with 1 .