Bimetal compounds

Successes in producing reactive intermediates like o-xylylene and carbene and in preparing bimetal lies in high yields using ultrasound led us to attempt to generate West s novel compound, tetramesityldisilene the first example of a stable species with a silicon-silicon double bond(32). We prepared this species in one step and trapped it with methanol(33). The disilene is reactive towards lithium, however, and we have found it very difficult to obtain consistent results. Most often, hexamesitylcyclotrisilane is isolated in very good yield(34). 

Recently, we have demonstrated that hydrogen preadsorbed on pla tinum or nickel can react with tin or lead tetraalkyl compounds re suiting in the formation of bimetallic surface entities with metal -metal interaction [5-8]. CSRs leading to the formation of bimetal lie surface species can be written as follows ... 

A few compounds have been found to be recalcitrant to the catalytic reaction and are not reported in Tables 1-4 1,1-dichloroethane (1,1-DCA) and 1,2-dichloroethane (1,2-DCA). (Lowry and Reinhard 1999 McNab and Ruiz 1998) Experiments with 1,1-DCA and 1,2-DCA yielded traces of ethane, but no detectable decreases in DCA concentration. (Lowry and Reinhard 1999) Lowry reports similar results with methylene chloride (MeCl) 78 minutes of reaction yielded traces of methane, but no detectable decrease in the MeCl concentration in the presence of Pd/alumina. However, Muftikian reports the successful transformation of MeCl in the presence of Pd/Fe. (Muftikian et al. 1995) Finally, Horold reports that nitrate is only reduced by bimetals Pd alone showed no activity for nitrate reduction. (Horold et al. 1993)... 

The hexamethylborazole complex [B3N3(Me)6]Cr(CO)3 exhibits as the main peaks the ions [(B3N3(Me)6]Cr(CO) ]+ (n = 0, 1, 3) and B3N3(Me)6+ (168). The mass spectra of some bimetallic compounds (XIX)-(XXIV) have been measured (135) and the bimetal ions [Cr—Cr]+ and [Cr—Fe]+ observed. The elimination of the carbonyl groups is not predictable and does not usually occur in a stepwise manner, but rather the first three carbonyl groups are lost in one step, and the remaining three CO molecules are eliminated in a stepwise manner. 

We also tested the reactivity and selectivity of mono metalated complexes (Type V). These catalysts, although reactive, were in general less selective than bimetal-ated compounds with head-to-tail configuration. Finally, preliminary studies of reactivity of doubly metalated compounds with the head-to-head configuration (Type Vllb) showed that these compounds are not promising catalysts for C-H insertion reactions. 

Graham and Jovanovic (1999) pointed out that the degradation of chlorinated compounds by reacting with Pd/Fe bimetal includes the following reactions (i) surface reactions, (ii) solution reactions, and (iii) a dechlorination reaction. The relevant schematic diagram (see Rg. 21.1) and reaction equations are given as follows I. Surface reactions... 

Figure 21.1. Hydrodechlorination of chlorinated compounds by Pd/Fe bimetal (Yang, Hung, and Tu, 2005).

In analyzing more than 250 publications Chapter 4 covers effective metal catalysts, mainly nickel, but also bimetal- and multimetal-systems, and their best modifiers, amino acids and tartaric acids. It is noted that it took more than 25 years to improve the modified nickel catalysts from their original poorly efficient systems into the modem excellent heterogeneous catalysts that hydrogenate carbonyl compounds with enantioselectivities of 96-98%. 

Among shape memory materials, shape memory alloys and bimetals are well known. Compared to these metallic compounds, SMP have a lower density, high shape recoverability, easy processability, and lower cost. Similar to conventional thermoplastics, SMP can be easily molded by the common methods, such as injection, extrusion, compression, and casting. In addition, their shape recovery temperature can be set at any value in the range room temperature 50 C, which allows a wide variety of applications. Also, SMP can be colored if desired because they are transparent. However, since the retractive force of the polymer is based on the small entropy elasticity, the SMP applications differ from those of metallic alloys. The basic differences between shape memory polymers and alloys are listed in Table 1. 

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