Subject silicon-hydrogen bonds

During the course of the last century, it was realized that many properties of solids are controlled not so much by the chemical composition or the chemical bonds linking the constituent atoms in the crystal but by faults or defects in the structure. Over the course of time the subject has, if anything, increased in importance. Indeed, there is no aspect of the physics and chemistry of solids that is not decisively influenced by the defects that occur in the material under consideration. The whole of the modem silicon-based computer industry is founded upon the introduction of precise amounts of specific impurities into extremely pure crystals. Solid-state lasers function because of the activity of impurity atoms. Battery science, solid oxide fuel cells, hydrogen storage, displays, all rest upon an understanding of defects in the solid matrix. 

Bridged silylene complexes are the subject of a recent comprehensive review by Ogino and Tobita338. These complexes can be classified into three types A, B and C (Scheme 9). In type A complexes there is no metal-metal bonding, the silicon is essentially tetravalent, and the bonding is similar to that in mononuclear metal-silyl complexes. In type C complexes, the bonding is best described as /j2-coordination of the Si—H bond to the metal, or alternatively as a metal-hydrogen-silicon 3-center 2-electron bond. 

You have now seen how enols and enolates react with electrophiles based on hydrogen (deuterium), carbon, halogens, silicon, sulfur, and nitrogen. What remains to be seen is how new carbon-carbon bonds can be formed with alkyl halides and carbonyl compounds in their normal electrophilic mode. These reactions are the subject of Chapters 26-29. We must first look at the ways aromatic compounds react with electrophiles. You will see similarities with the behaviour of enols. 

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