Versatility of Silicon-based compounds in organic synthesis

Organosilicon compounds exhibit a multitude of functions in organic synthesis, therefore a plenty of research has been performed in this field and the interest in these important compounds is still growing. Organosilanes own many attractive properties. They generally are much more moisture- and air-stable than various organometallic reagents and can be readily prepared from a wide range of starting materials. Silicon derivatives have low toxicity and display rich and diverse chemistry that can usually be rationalized by understanding a relatively small number of fundamental properties of silicon. The reactivity of organosilanes depends both on steric requirements and electronic contributions. Silicon is below carbon in the periodic table, but it is capable of very different bonding characteristics. It is less electronegative than carbon and hydrogen and it forms unusually strong bonds with electronegative elements of the second period bearing a lone pair of electrons; therefore most of organosilicon chemistry is driven by the formation of these bonds at the expense of weaker bonds. In addition, the availability of relatively low energy empty 3d AOs lets Si to allow higher coordination numbers, forming the so called hypervalent silicon compounds. The ability to expand its valence state has consequences on the mechanisms of many reactions proceeding at Si. Silicon can stabilize a positive charge in β-position, and this effect is known as the β-Si effect.3 Moreover, silicon provides stabilization of α-negative charge,4 in fact carbanions with an α-silicon group are more stable than their carbon analogues. Since the versatility in reactivity, a wide range of reaction-types involving silicon compounds have been developed over the years. An exhaustive overview is almost impossible and during this lecture only some classes of reactions will be covered. From a synthetic point of view, organosilanes possess many desirable characteristics. In fact, besides their green character, they can survive under a large variety of reactions and purification conditions, such as air, moisture, silica-gel, reducing or oxidizing conditions.5 The silyl moiety can be introduced at almost any stage in the synthesis and can remain unaltered until the appropriate conditions make it reactive.