Nitrogen atom lone pairs

In 2000, Chamboumier and Gawley reported the failure of a conformationaUy locked 2-(tributylstannyl)piperidine to transmetalate when the 2-(tributylstannyl) moiety of a 4-fert-butylpiperidine is equatorial, Sn/Li exchange is facile, but when the 2-tributylstannyl group is axial, transmetalation fails (compare Figure 3d,i). In other words, in these conformationaUy rigid piperidines, there appears to be a configurational requirement for transmetalation the nitrogen atom lone pair has to be synclinal to the adjacent carbon-tin bond for transmetalation to succeed. 

For hydrates, the question is, to what extent does the nitrogen atom lone pair contribute to hydrogen bonding in amine hydrates Hydrogen bonding is expected to explain the difference between gaseous and solid ammonia couplings. 

On heating, these adducts lose alkane to give oligomers that have Al—N—A1 bonds, each Al becoming 4-coordinate by interaction with a nitrogen atom lone pair. 

When the nitrogen atom lone pair of a benzazaphosphole is prevented from being in conjugation with the phosphorus atom, either by its relative position in the ring system or influences from the substituents, the phosphorus resonance is signih-cantly downheld and near the usual value for a P=C double bond. Examples are shown in Fig. 5.24. 

The only difference between this result and the result we would obtain for N2 is that the ScTg and 2(r MOs would represent the two nitrogen atom lone pairs, rather than the C—H bonds. 

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