Metal less reactive

Why are the alkaline-earth metals less reactive than the alkali metals ... 

Strassner T (2004) Electronic Structure and Reactivity of Metal Carbenes. 13 1-20 Strong LE, see Kiessling LL (1998) 1 199-231... 

Amouri, H. Le Bras, J. Taming reactive phenol tautomers and o-quinone methides with transition metals a structure-reactivity relationship. Acc. Chem. Res. 2002, 35, 501-510. 

In this chapter we will not attempt to give an overview of all of the knowledge on the reactivity of chalcogen-donor molecules towards di- and inter-halogens, since some aspects of this are discussed in other chapters. Instead, this chapter is dedicated exclusively to the analysis of the chemical bond and structural features of C.-T. adducts between LE chalcogen-donor molecules (E = S, Se) and di- and inter-halogens, and their reactivity towards metal powders. 

The mono-alkoxy product from (+)-ethyl lactate and diisopropylsilane (le) is shown to be more reactive than la and If (Scheme 31). We can only speculate at this time that there may be some intramolecular interactions between the Lewis basic carbonyl oxygen of the (+)-ethyl lactate and the silicon atom, which may either, activate the silane towards oxidative addition to the metal catalyst or increase the rate at which the silane-metal complex is attacked by the nucleophilic alcohol. 

Oxidative addition of the silane to the metal is fast and reversible 30 therefore unless the pentacoordinated silane drastically slows down the oxidative addition process, pentacoordination will not alter the rate of the reaction at this stage of the cycle. The increased reactivity of le may be explained by the attack of the alcohol on the pentacoordinated silane that would form after oxidative addition (Figure 9A). The rate of the alcohol addition is increased by the higher reactivity of the pentacoordinated silicon center. This may explain the slower reactivity for those alkoxysilanes that cannot form this intramolecular coordination complex due to the absence of a nearby Lewis basic atom. We had observed during the comparison of aliphatic alcohol to benzyl alcohol that the nucleophilicity of the alcohols has an effect on the rate of the reaction. This is evidence that the alcohol and the silane are involved in the rate-determining step with 10 % Pd/C catalytic system. 

The accelerated rate for alcoholysis with le, which was observed for the 10 % Pd/C catalytic system, was also seen with the Mn(CO)sBr catalyst. Reactions of le with primary, secondary or tertiary alcohols resulted in moderate yields of the corresponding silyl ketals after 2 h (Table 8 and 9). When mono-alkoxy silane from 3-hydroxy butyrate (lg) was treated with homoallyl alcohol in the presence of Mn(CO)sBr as the catalyst under the standard conditions, 76 % of the silyl ketal was obtained. These silyl ethers possess neighboring carbonyl groups that can participate in the reaction by forming a more reactive pentacoordinated silicon center upon addition of the silane to the metal center.. 

A schematic autoxidation pathway involves initiation (equation 10), propagation (equation 11-12) and termination (equation 13). Since hydroperoxides easily undergo metal-catalyzed decomposition, the addition of a metal can both speed up an air oxidation and avoid the formation of a hydroperoxide, which is rarely the desired final product. This is perhaps the simplest type of metal catalysis. The metal is normally capable of le redox behavior, hence typically a 3d transition metal. As shown in equations (14 -15), it can decompose the RO2H to give the highly reactive RO- radical in a manner resembling equation (3 -4). RO- radical can abstract... 

Wachs, I.E., Chen, Y., )ehng, ).-M., Briand, LE. and Tanaka, T. (2003) Molecular structure and reactivity of the Group V metal oxides. Catalysis Today,... 

Aluminum is one of the most abundant elements on earth, ranking third behind oxygen and silicon. Because aluminum is a very reactive metal, it is found in nature as its oxide in an ore called bauxite (named after Les Baux, France, where it was discovered in 1821). Production of aluminum metal from its ore proved to be more difficult than the production of most other metals. 

Imidazole also acts as a substrate-competitive inhibitor , forming both binary complexes with LADH, and ternary complexes in the presence of coenzyme. X-Ray studies show that imidazole also binds to the catalytic zinc by displacing the water molecule. The presence of imidazole at the active site also enhances the rate of carboxymethylation of Cys-46 with both iodoacetate and iodoacetamide. This enhancement of alkylation has become known as the promotion effect .Imidazole promotion also improves the specificity of the alkylation. Since Cys-46 is thought to be alkylated as a metal-thiol complex, imid le, on binding the active site metal, could enhance the reactivity by donating a electrons to the metal atom, which distributes the increased electron density further to the other ligands in the coordination sphere. The increased nucleophilidty of the sulfur results in promoted alkylation. ... 

In view of their major application in aqueous battery systems more work has been carried out on the structural aspects of the oxides of these two metals than any of the systems discussed earlier. Details of the structure and reactivity of the nickel oxide battery materials can be found in recent reviews by Briggs209 and Oliva et al.2 Both hydrous and anhydrous phases exist for both the Ni(II) hydroxide and Ni(III) oxyhydroxide systems. Most interesting are the comments of Le Bihan and Figlarz,210 and McEwen,211 with regard to turbostatic structures the latter are found in materials where the ordering of the oxide is quite limited, i.e., the systems consist of highly ordered nuclei linked in a disordered manner—the latter feature should certainly enhance mass transfer processes and may well be involved in many other hydrous oxide systems. 

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