| Popis: |
The addition of a fluoride to the fluorinated heterocycles : Triazines [(NCF):sub:3:/sub:] and Phosphazenes [(NPF:sub:2:/sub:):sub:n:/sub: n = 4,6] results in the formation of cyclic anions. These anions can be thought of firstly as isolable intermediates of an S:sub:N:/sub:2 substitution reaction and secondly as fluoride transfer reagents since the fluorine bonds at the site of addition are long and weak. Selective nucleophilic substitution reactions involving the neutral heterocycles are difficult under mild conditions, but should be activated by the use of an anion, which react via fluoride exchange at much lower temperatures. Several nucleophilic substitutions were carried out on the anions using Me:sub:3:/sub:SiR derivatives ( R = CF:sub:3:/sub:, NMe:sub:2:/sub:, SiOMe:sub:3:/sub:) as the nucleophile source. Results showed that under mild conditions it was possible to selectively substitute fluorine by other species to form new cyclic triazinates and phosphazinates. Phosphazenes can be isolated in many different ring sizes and the abiltity to stablize negative charges increases with increasing ring size. Using TASF as a source of fluoride it was possible to isolate a cyclic fluorinated phosphazene dianion containing a 12 membered PN ring. The crystal structures of several new cyclic anions could be determined via X-Ray Single Crystal Diffraction. |
