Dicoordinate nitrogen

Nitrenium ions are isoelectronic to carbenes [177]. They contain a dicoordinated nitrogen atom formally with two valence electrons. The possible electronic structures of the parent nitrenium ion NHj are shown in Figure 7.9. On the basis of Hiickel MO theory one would expect that the lowest energy configuration, that is, the electronic ground... 

FIGURE 11. Histogram of Si—N bond lengths in compounds with tetracoordinate silicon and dicoordinate nitrogen atoms... 

For two of the compounds of Table 3, aromaticity indices were derived from the molecular dimensions (1,3-oxaphosphole 38, 1,3-thiaphosphole 55). According to them, aromaticity is not greatly reduced if dicoordinate nitrogen in a five-membered heterocycle is replaced by phosphorus <90T5697>. 

Mononuclear silver(I) complexes with nitrogen ligands can have several coordination numbers, the simplest is dicoordinated and compounds of the type [AgL2]+ occur for a variety of ligands... 

Figure 4 shows that the HOMO and HOMO-1 of the TAA 8 can be identified as 71 bonding orbitals of the central C=C=C moiety but the largest contribution to the highest lying occupied orbitals comes from the dicoordinated carbon atom. The calculated large values for the first and second PAs which come from protonation at the central carbon atom rather than the nitrogen atoms points towards the hidden double lone-pair character of the TAA [4]. 

For these reasons, a permissive definition of nitrenium ions is chosen. A nitre-nium is any species that can, through valence bond representations, be depicted as having a dicoordinate positively charged nitrogen. Such a definition has the advantage of being readily applied to any species for which a valence bond representation can be depicted. On the other hand, such a definition does encompass a number of species with rather different properties. 

The silylated aminoiminophosphine (MesSi)2N P=N SiMe3 reacts with anhydrons alnmtnum chloride at 40 °C with elimination of Me3SiCl to form a dicoordinate phosphorus-nitrogen ligand, in a four-membered chelate ring complex. Anhydrous aluminum chloride extracts a chlorine ion from [C1PNR]2 to form a cyclic cation with a dicoordinated... 

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