Rhenium and Copper

These metals, belonging to groups on either side of the main block of transition metals (Group VIIIB or 8, 9 and 10) commonly examined in hydrosilation catalysis, have only been employed very rarely to facilitate hydrosilation. Very few reports have emerged during the last 15 years on catalysts based on these metals and their use has generally been connected with special cases of hydrosilation. 

In yet another example of the utiUty of N-heterocyclie earbene hgands, the use of Cu-NHC complexes (e.g., 25) to catalyze the hydrosilation of hindered and functionalized ketones with Et3SiH was very recently described by Nolan and coworkers [Eq. (19)]/ Functionahties on the ketone substrate such as halide, ether and tertiary amine are well tolerated and excellent conversions are achievable using a number of variations of 25 (pre-synthesized or generated in situ) with different AT-substitution on the ring. 

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Schrehler, R., Cury, P., Suarez, C., Munoz, E., G6mez, H., and Cordova, R., Study of the electrochemical reduction of CO2 on a polypyrrole electrode modified by rhenium and copper-rhenium microalloy in methanol media, J. Electroanal. Chem., 533, 167-175, 2002. 

With other metal alkoxides, such as n(Ot-Pr)4 and Sn (Oi-Pr)4, Ru-1 induced faster polymerizations of MMA than Al(Ot-Pr)3, though the MWDs became slightly broader. Aluminum acetylacetonate [Al(acac)3] was a mild alternative additive that did not induce an ester-exchange reaction between the ester group and the monomer or monomer units in the polymer chain, which might occur using aluminum alkoxides. These metal alkoxides were also effective for other metal complexes, such as iron, nickel, rhenium, and copper. " It is noteworthy that Al(Oi-Pr)3 could even make the Cu(II) species active, in which the controlled polymerizations of styrene, MMA, and ethyl acrylate were possible." " Ti(Oi-Pr)4 was also efficient for the half-metallocene Fe(II)-catalyzed polymerizations, as will be mentioned in Seaion 3.13.3.1.2." Based on calculation studies by Poli et the nature of Al(Oi-Pr)3 in the... 

The acetylacetonates are stable in air and readily soluble in organic solvents. From this standpoint, they have the advantage over the alkyls and other alkoxides, which, with the exception of the iron alkoxides, are not as easily soluble. They can be readily synthesized in the laboratory. Many are used extensively as catalysts and are readily available. They are also used in CVD in the deposition of metals such as iridium, scandium and rhenium and of compounds, such as the yttrium-barium-copper oxide complexes, used as superconductors. 1 1 PI Commercially available acetyl-acetonates are shown in Table 4.2. 

Rh (172)]. These species merit comparison to the rhenium- and manganese-dicopper species 158 and 159, which have molecular mirror symmetry and a V-shaped trimetal unit that lacks a Cu-Cu bond. Although 171 and 172 appear symmetric in solution on the NMR time scale due to fluxional processes, in the solid state the two copper centers are clearly inequivalent and a Cu-Cu bond is present. The metal triangle is supported by two B-H Cu linkages, one to each Cu center, involving p- and y-B H vertexes in the M -bound CBBBBEi belt. 

With the same excess of catalysts hydrogenations of the esters over Raney nickel could be carried out at temperatures as low as 25-125° at 350atm with comparable results (80% yields). However, benzene rings were saturated under these conditions [55]. In addition to nickel and copper, zinc and chromium oxides, rhenium obtained by reduction of rhenium heptoxide also catalyzes hydrogenation of esters to alcohols at 150-250° and 167-340 atm in 35-100% yields [42]. 

If the porous carbon cathodes are coated with copper or rhenium and an NH4C1-containing electrolyte is used, glycol aldehyde is obtained in the reduction of oxalic add S22). 

Figure 16 Comparison of observed (open) and calculated (solid) depletions of phosphorus, tungsten, cobalt, nickel, molybdenum, and rhenium (circles) together with those for gallium, tin, and copper (inverted triangles) (sources Righter and Drake, 1997, 1999, 2000). The calculated depletions utilize the partitioning expressions of Righter and Drake (1999) for conditions of 2,250 ( 300) K (1,973 °C), 27 ( 6) GPa, AIW = — 0.4 ( 0.3) between a hydrous peridotite (NBO/t = 2.65) magma ocean and metallic liquid. The observed depletions are those of McDonough and Sun (1995), but volatility corrected as described by Newsom and Sims (1991), where the correction is made based on comparisons to trends of lithophile volatile element depletions.

Other work has demonstrated that it is possible to switch ON and OFF luminescence by reduction/oxidation, and it has been demonstrated that such switching is possible inside an OTTLE cell. Many alkynyl complexes, especially those of rhenium, platinum,copper, silver or gold " are highly luminescent from their excited MLCT or metal perturbed 71 states. This opens up the possibility to significantly influence their emissive properties by redox processes. An interesting example is found in recent work of Wong et Unlike other rhenium(I)-alkynyl complexes, heterobimetallic... 

Thiocyanate, nitrate, and fluoride interfere in this method for determining rhenium. Palladium and copper in acid media sparingly soluble a-furildioximates. Normally, rhenium should be separated from Mo before the determination. 

Studies have been made on the mechanism of separation, process kinetics, mass transfer modehng, and engineering evaluation with metals hke copper, zinc, cadmium, cobalt, nickel, mercury, uranium, chromium, rhenium, and several others, including noble metals hke gold and silver, lanthanides and rare earths. Table 4.2 presents some examples. 

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