Platinum silicones

Thus, several complexes with platinum-silicon or germanium bonds have been obtained ... 

With platinum-silicon compounds described in this chapter, evidence supporting two-electron, three-center Pt-H-Si bonding seems to be strong, and the phenomenon is perhaps expected in view of the existence of numerous... 

Contrary to previous reports suggesting colloidal metal as the active species in Pt-catalyzed hydrosilylations, the catalyst was found to be a monomeric platinum compound with silicon and carbon in the first coordination sphere.615 The platinum end product at excess olefin concentration contains only platinum-carbon bonds, whereas at high hydrosilane concentration, it is multinuclear and also contains platinum-silicon bonds. An explanation of the oxygen effect in hydrosilylation was also given to show that oxygen serves to disrupt multinuclear platinum species that are formed when poorly stabilizing olefins are employed. 

Although the mechanism of the platinum-catalyzed hydrosilation is poorly understood, it seems probable that an intermediate with a platinum-silicon bond is formed, with which the olefin and hydrogen may also be complexed. The cleavage of pentamethyldisilane may be rationalized by considering nucleophilic attack of isopropyl alcohol, which is used for preparing the catalyst solution, on the silicon atom that has become attached to platinum and thus vulnerable to the attack by any Lewis base (see also Section IV, A, 2,f B, 2,b). 

PtSi arrays are sensitive over the 1.0-5.0 p,m wavelength range. These are silicon-based arrays in which the platinum-silicon junction in each pixel forms a Schottky barrier diode. Large, exceptionally uniform arrays can be made from this material, but the quantum efficiency is < 1% (D = 3 x 1010 cm I Iz0 5 W-1), making such arrays unsuitable for low light level applications. Photoconductive lead sulfide (PbS) arrays with 320 x 240 pixels are also available for operation in the 1.0-3.0 un range, with reported D values up to 3 x 1011 cm Hz0 5 W 1 if cooled to 200 K. 

The reactivity of platinum silylenoid 27 was explored with traditional silylene trapping reagents. While the silylenoid did not react with triethylsilane or 2,3-dimethyl-1,3-butadiene, phenylacetylene was a viable substrate, providing the me-tallocyclohexadiene 29 (Scheme 7.4).54 The formation of platinum complex 29 was hypothesized to occur via platinum cyclobutene intermediate 28, which formed on insertion of the acetylene into the platinum-silicon bond. A second molecule of phenylacetylene was then inserted into the remaining platinum-silicon bond to provide the observed product. 

G. Ottaviani and M. Costato have investigated the process of compound formation at the platinum-silicon interface. Platinum films, 115, 205, 268 and 357 nm thick, were sputtered on Si(l 11) single crystals under hard vacuum. The interaction of the Pt and Si phases during isothermal annealing was followed using Rutherford backscattering spectroscopy of helium ions. 

Platinum Silicon bronze2 Silicon cast iron3 Silver Tantalum Titanium4 Tungsten Zirconium Silver Tantalum Zirconium Zirconium Zirconium ... 

Platinum-silicon bonds may be made by the reaction of trans-[PtH(ClXPMe2Ph)2] with R3SiH in the presence of solvent, provided that R is an electron-withdrawing group such as Cl or aryl. For Cl3SiH reaction occurs at RT but for triarylsilanes at 80-90°C ... 

A reasonable mechanism for the formation of 5 involves the initial insertion of the cyano group into one of the platinum-silicon bonds, leading to intermediate 6, followed by cyclization to the imine 7. 

Membrane structures that contain the visual receptor protein rhodopsin were formed by detergent dialysis on platinum, silicon oxide, titanium oxide, and indium—tin oxide electrodes. Electrochemical impedance spectroscopy was used to evaluate the biomembrane structures and their electrical properties. A model equivalent circuit is proposed to describe the membrane-electrode interface. The data suggest that the surface structure is a relatively complete single-membrane bilayer with a coverage of 0.97 and with long-term stability/... 

Reducing conditions involving burner or flue gases, activated charcoal and the like are particularly deleterious when free silicic acid is also present. In this case, platinum-silicon alloys are formed, leading to the characteristic silicon fracture. 

Silica, amorphous hydrated catalyst blocker, platinum silicones Methyl butynol catalyst component Bismuth oxide... 

Barakatova, XM., 1994, Physical chemistry interaction of palladium, platinum, silicon and germanium with samarium, Ph.D. Chemistry Thesis (Moscow State University, Moscow) pp. 1-21. 

Selected Structural Data for Trans-Platinum-Silicon 4MR... 

Si>Si bond exists in the platinum-silicon 4HR and is consistent with our bonding description. Electron impact mass spectral data also provides supporting evidence for the bonding descrip-... 

X-ray crystallography. The observation that our platinum-silicon 4MR can be formed from reagents with Si-Si single bonds is also consistent with the P2 h bonding description. West has prepared monoplatinum complexes of disilenes from disilenes or disilanes by three routes. One route, which is similar to the reaction depicted in Eg.4, is shown in Eg.5. The platinum disilene complexes are described by the two resonance forms drawn in Eg.5. (It is interesting to note that oligomeric silanes are obtained as by-products of Eg.5.)... 

We have obtained oligomeric silanes from Eg.l but we have decided not to focus our initial studies on this route because of the inherent complexities. There are several possible platinum catalyst precursors present in Eg.l the platinum-silicon 4HR, the starting material (Et3P)2PtCl2, and finely divided platinum (colloids). Preliminary studies of these latter two catalyst precursors with PhSiH3 indicate that both are considerably slower than any platinum-silicon 4MR (see below) and both give primarily redistribution products. ... 

Differences in selectivity towards silanes and the observation of a stepwise oligomerization indicate that the mechanism of dehydrocoupling catalyzed by platinum-silicon 4MR is different from that of titanocene catalysts. Our results in Eg.4 as well as West s isolation... 

Sanow LM, Chai M, McConnville DB, Galat KJ, Simons RS, Rinaldi PL, Youngs WJ, Tessier CA (2000) Platinum-silicon four-membered rings of two different structural types. Organometallics 19 192... 

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