Nucleophiles oxygen-silicon bonds activated

Consequently, the ionization process is a specific phenomenon caused by the lability of the Si-Br or Si-I bonds and the affinity of silicon for oxygen not all racemization processes involve ionic 1 1 adducts. Moreover, the case of the tin compounds shows that the ability to undergo racemization is connected with the ability to increase coordination number. Thus, since silicon, germanium, and tin compounds show similar conductimetric and kinetic behavior, we may conclude that racemization and nucleophilic substitution are both activated by nucleophiles and involve a coordination extension process as shown in Scheme 67. However, existence of the siliconium ion 209 cannot be excluded in the case of bromosilanes. 

It was found that silicon-bromine and silicon-chlorine bonds were thermodynamically activated towards substitution by coordination of an oxygen nucleophile, whereas coordination was found to deactivate the silicon-fluorine bond. 

Introducing the Triazole Rina. The final step of the synthesis was displacement of the carbon-bound chlorine with triazole salts. Once again, silicon made life easy for us, since it activates such hindered systems toward displacement. The corresponding all-carbon compounds react very sluggishly with triazole salts. Luckily, silicon-carbon bond cleavage is not observed, provided water or other oxygen nucleophiles are excluded. The displacement reaction is illustrated in Equation 5 for DPX-H6573. 

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