Azanes, conformation

The conformational preferences of the P(V)—N bond in four co-ordinated phosphorus compounds, Scheme 3, (11) are less pronounced, and depend more on the type of the other phosphorus substituents. However, conformations close to (12) are foimd in a variety of crystal structures of acyclic phosph(V)azanes. 

Although no crystal structures of cyclotriphosph(III)azanes have yet been reported, it is reasonable to assume that the ring will adopt a chair conformation and that the nitrogen atoms will have a planar or near-planar distribution of bonds. This is consistent with the structures of the six-membered ring fragments found in the cage... 

A number of crystal structmes of cyclophosph(III)azanes have now been reported and some of this data has been used earlier (Sect. 2) to illustrate the conformations adopted by the phosphorus-nitrogen rings. It appears that Jf-ray crystallographic methods will be crucial to an understanding of the conformations of six-membered... 

Nelsen and coworkers [562] detected conformational equilibria in eq, eq- and ax, eq-N, A -disubstituted cyclic hydrazines from their oxidation potentials. The anodic oxidation reactions of trans- and cw-l,3-diisopropy-l-2,4-bis(diisopropylamino)-cyclodiphospha(III)azanes are quite different [563] The trans isomer is reversibly oxidized at 0.53 V (SCE) forming a stable cation radical the c/5-isomer undergoes a completely irreversible oxidation at a more positive potential because an unstable radical cation is formed. Evans and coworkers studied structural changes associated with electron transfer reactions of W(// -C5(CH3)5)(CH3)4 and related compounds [564,565]. Yoshida and coworkers found a linear correlation on plotting the oxidation potentials of a-silylated ethers, where the rotation around the C-0 bond is restricted, against the HOMO energy-torsion angle (Si-C-O-C) curve estimated by MO calculation [566]. 

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