Ammonium lone-pair functions

In each case, the N atom is sp hybridized, with one lone pair of electrons and three o-bonds. A quaternary ammonium ion is a tetrahedral ion of the form R4N, where as many as three of the R groups (which may all be different) can be replaced by H atoms. For example, the tetramethylammonium ion, (CH3)4N+, and the trimethylammonium ion, (CH3)3NH+, are quaternary ammonium ions. The amino group, the parent functional group of amines, is —NH2. 

In a nice illustration of the impact of metal coordination upon the reactivity of phospholes, a methodology for the functionalization of these heterocycles in the /3-position has been described (see also Scheme 22) <2001JOM105>. Here, coordination of both the P-lone pair and the cyclic diene system was undertaken. The resulting multimetallic complex 79 was treated with lithium diisopropylamide (LDA) to afford the lithium salt 350 (Scheme 118). This readily undergoes nucleophilic substitution with a variety of electrophiles to afford the corresponding substituted phosphole complexes 351-353. The free phospholes can be isolated following decomplexation with cerium(iv) ammonium nitrate (CAN). 

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