Bimetallic insert

A nozzle introduced into the insulating chamber 4.19(c) and with the gate in the mould cavity is a modification of the previous nozzle, and at the same time an example of the use of bimetallic inserts. The seal bushing needed to create a small insulating chamber is made of a material with low thermal conductivity (titanium alloy) and insulates the tip, which is made of a material with high thermal conductivity. The gate is substantially cooler, and therefore the nozzle 4.19(c) may be used for amorphous and slow-setting crystalline plastics. 

A nozzle introduced into the insulating chamber 4.19(d) and with a bimetallic insert and a sprue channel located in the mould cavity is designed for larger products with a longer cooling time, made from amorphous and slow-setting crystalline plastics. 

The bimetallic mechanism is illustrated in Fig. 7.13b the bimetallic active center is the distinguishing feature of this mechanism. The precise distribution of halides and alkyls is not spelled out because of the exchanges described by reaction (7.Q). An alkyl bridge is assumed based on observations of other organometallic compounds. The pi coordination of the olefin with the titanium is followed by insertion of the monomer into the bridge to propagate the reaction. 

Access of air and water will also affect the corrosion rate. Metal inserts in corrosive plastics are most actively attacked at the plastic/metal/air interfaces with certain metals, notably aluminium titaniumand stainless steel, crevice effects (oxygen shielding and entrapment of water) frequently accelerate attack. Acceleration of corrosion by bimetallic couples between carbon-fibre-reinforced plastics and metals presents a problem in the use of these composites. 

The characteristics of C NMR spectra for all copolymers were similar. The triad distributions for all copolymo" from NMR monomer insertion are shown in Table 2. Based on the triad distribution of ethylene/l-hex aae copolymers in Table 2, we found that microstructurc of copolymer obtainrai fiom aluminoxane system was slightly different in monomer incorporation, but found significantly when borated system was applied. We suspected that this difference was arising fiom the diffaences in bimetallic complex active species between [aluminoxane] [catalyst] and [Borate] [catalyst] which had the electronic and gMmetric effects fiom the sterric effect of larger molecule of borate compare to the aluminoxane on the behaviors of comonomer insertion in our systems. 

Hydrogenolysis of esters to aldehydes or alcohols needs high temperatures and high pressures. Moreover, it leads to the formation of acids, alcohols, and hydrocarbons. In contrast, bimetallic M-Sn alloys (M = Rh, Ru, Ni) supported on sihca are very selective for the hydrogenolysis of ethyl acetate into ethanol [181]. For example while the selectivity to ethanol is 12% with Ru/Si02, it increases up to 90% for a Ru-Sn/Si02 catalyst with a Sn/Ru ratio of 2.5 [182]. In addition, the reaction proceeds at lower temperatures than with the classical catalysts (550 K instead of temperatures higher than 700 K). The first step is the coordination of the ester to the alloy (Scheme 46), and most probably onto the tin atoms. After insertion into the M - H bond, the acetal intermediate decomposes into acetaldehyde and an ethoxide intermediate, which are both transformed into ethanol under H2. 

When the rhodium-catalyzed reaction is performed under a high pressure of CO in the presence of phosphite ligands, aldehyde products (159) are formed by insertion of CO into the rhodium-alkyl bond followed by reductive elimination (Eq. 31) [90]. The bimetallic catalysts were immobilized as nanoparticles, giving the same products and functional group tolerance, with the advantage that the catalyst could be recovered and reused without loss of... 

In the model study by Tolman discussed earlier, the half-life of syn-to-anti isomerization measured by H NMR was found to be 0.36 hours at 30°C. This rate of isomerization is far too slow to affect the stereoselectivity of the hexadiene formed with the catalyst considered here. With the bimetallic catalyst, reaction rates frequently approach 4000 molecules of hexadiene/Ni atom/hour at 25°C (or ca. 1 hexadiene/Ni/second). The rate of insertion reaction d must be at least as fast as this, and the isomerization reaction would have to be even faster to affect the trans/ cis ratio of the product. 

The fact that organosamarium allyl complexes of the type Cp 2Sm(CH2CH=CHR) can arise from the treatment of Cp 2Sm or [Cp 2Sm(/r-H)]2 with a variety of olefin and diene substrates makes samarium chemistry more intriguing. The reaction modes are illustrated in Scheme 18. These allylsamarium complexes 55 react with C02 to afford the carboxylate products 56, which participate in monometallic/bimetallic interconversions (Equation (10)). Carbon disulfide and 0=C=S also insert into carbon-samarium bonds, which form only monometallic species.29... 

The organometallic products included recovered [(CO)5M(OAc)], along with M(CO)6 and the bimetallic bridging hydride complex [( -H)M2(CO)10]T It was proposed that, under the reaction conditions, [(CO)5MH] and HOAc were produced, and that insertion of the ketone into the M-H bond gave a metal alkox-ide that reacted with HOAc to produce the alcohol. 

Reductive elimination is simply the reverse reaction of oxidative addition the formal valence state of the metal is reduced by two (or one in a bimetallic reaction), and the total electron count of the complex is reduced by two. While oxidative addition can also be observed for main group elements, this reaction is more typical of the transition elements in particular the electronegative, noble metals. In a catalytic cycle the two reactions always occur pair-wise. In one step the oxidative addition occurs, followed for example by insertion reactions, and then the cycle is completed by a reductive elimination of the product. 

Chromatography cyclophosphazenes, 21 46, 59 technetium, 11 48-49 Chromites, as spinel structures, 2 30 Chromium, see Tetranuclear d-block metal complexes, chromium acetylene complexes of, 4 104 alkoxides, 26 276-283 bimetallics, 26 328 dimeric cyclopentdienyl, 26 282-283 divalent complexes, 26 282 nitrosyls, 26 280-281 trivalent complexes, 26 276-280 adamantoxides, 26 320 di(/ >rt-butyl)methoxides, 26 321-325 electronic spectra, 26 277-279 isocyanate insertion, 26 280 substitution reactions, 26 278-279 [9]aneS, complexes, 35 11 atom... 

Medium Energy EBW Detonator w/Wolla-ston Wire Bridge, shown in Fig 72. Wollaston wire is a coaxial bimetallic material made by inserting a wire of one material (usually gold or platinum) in a tube of another (.usually silver) after which the combination of tube and core is drawn thru dies to a smaller size. The outer tube may be dissolved by an acid leaving the core, which may be much smaller than a wire could be drawn by any other process. High temperature double-bore thermo-... 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

This results in strong polarization of the n bond and dissociation of the Ti—C bond, thus promoting insertion into the activator aluminum-alkyl bond. Repetitive insertions of alkene molecules result in lengthening of the polymer chain. This mechanism is also termed bimetallic after the growth center complex species 44. 

Sulfur dioxide will insert into Pt—carbon bonds (Section 52.4.8.4). Evidence has also been presented that sulfur dioxide will coordinate to the axial ends of the bimetallic Ptn-Pt11 complex Pt2(P205H2)4- the reaction is an equilibrium process and no structural data are given.1495... 

In complexes (3), (7) and (8), dioxygen can be inserted between two metal atoms (bimetallic //-peroxo complexes), between one metal and one carbon atom (alkylperoxo complexes) or between one metal and one hydrogen atom (hydroperoxo complexes). 

In addition to the bimetallic complexes of rhenium and alkaline metals formed as byproducts in the exchange reactions of rhenium halids with alkali alkoxides (such as, for example, LiReO(OPr )5 xLiCl(THF)2 [519]) there has been recently prepared a number ofbimetallic complexes ofrhenium and molybdenum, rhenium and tungsten, and rhenium and niobium [904, 1451]. The latter are formed either due to the formation of a metal-metal bond, arising due to combination of a free electron pair on rhenium (V) and a vacant orbital of molybdenum (VI) atom or via insertion of molybdenum or tungsten atoms into the molecular structure characteristic of rhenium (V and VI) oxoalkox-ides. The formation of the compounds with variable composition becomes possible in the latter case. 

Braunstein and coworkers have shown (vide supra) that in the bimetallic Fe—Pt complex (CO)3(SiR3)Fe(yU.-PPh2)Pt(PPh3)CO(Fe—Pt), a silyl migration occurred from the Fe to the Pt center (Scheme 17)102. Remarkably, the first example of a well-characterized insertion of a transition-metal fragment into a strained silicon-carbon bond of a silicon-bridged [l]ferrocenophane was recently reported by Sheridan, Lough and Manners. The... 

Shi el al. reported one of the first examples of bimetallic catalytic systems that allowed the insertion of C02 into the rather unreactive fin-carbon bond [45], The concept behind this system was to exploit, in the same system, the ability of a transition metal to catalyze crosscoupling reactions and C02 activation. For instance, tributyl(allyll)tin does not react with C02 in solution even under high-pressure. To run the same reaction in the presence of zero-valent palladium species (Pd(PPh3)4 or Pd(PBu3)4) will quantitatively afford carboxylates 2 (90%) and 3 (10%) (Scheme 5.10), although the reactivity of the system is limited to allylstannanes. 

The unpolar solvent required rather long reaction times, but allowed one to identify a Rh(I) intermediate, [Rh(CO)2]2(OEP), which carries two Rh(CO)2 groups on both sides on the porphyrin ring and is a typical example of a bimetallic porphyrin [8]. A photochemical variant of this insertion in benzene/tetrachloromethane [58] accelerates the reaction and gives a 50% yield of RhCl(OEP)H20. Aoyama, Ogoshi et al. [59] used [RhCl(CO)2]2 and carefully purified benzene. The solution of the porphyrin with the metal carrier was... 

Metalametallations of alkenes and alkynes are useful methods for the construction of 1,2-dimetala-alkanes and 1,2-dimetala-l-alkenes, which react subsequently with suitable electrophiles to form substituted alkanes and alkenes. Metalametallation is carried out usually with bimetallic reagents of the type R Si-M R, or R Sn-M R in which M = B, Al, Mg, Cu, Zn, Si or Sn. Some metalametallations proceed without catalysts Cu, Ag and Pd compounds are good catalysts. The metalametallation with bimetallic compounds, such as Si-B, Si-Mg, Si-Al, Si-Zn, Si-Sn, Si-Si, Sn-Al or Sn—Sn bonds, catalysed by transition metal complexes, is explained by the oxidative addition of the bimetallic compounds to form 478, and insertion of alkene generates 479. Finally 1,2-dimetallic compounds 480 are formed by reductive elimination. Dimetallation of alkynes proceeds similarly to give 481. Dimetallation is syn addition. 

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