An extension of coordination by intramolecular N → P donor-aceptor interaction in (8-dimethylamino-1-naphthyl)diphenylphosphane 1 has been shown by X-ray structure determination. In addition, a very easy intramolecular isomerisation process around the phosphorus atom at room temperature was revealed by dynamic NMR studies. Isomerisation also occurs in the corresponding oxide 2, sulfide 3, and phosphonium salts 4 and 5, but with slightly higher activation energies.

The phosphorus derivatives P(X)(O2C6H4−1,2)2[C6H4(CH2NMe2)2−2] (9–11) undergo ready extension of coordination by N → P intramolecular donor-acceptor interaction as shown by 31P NMR and dynamic 1H NMR spectroscopy. This extension of coordination does not occur with P(X)(OEt)2[C6H4(CH2NMe2)2−2] (7 and 8). The ΔG≡ of pseudo-rotation was calculated by dynamic 1H NMR spectroscopy to be 57–58 kJ mol−1 for the three compounds P(X)O2C64−1,2)2[C10H6(NMe2−8)] (19–21).

Pseudo‐siebenfach koordiniert ist das zentrale Phosphoratom in den Phosphanen 1 und 2 . In Lösung bleibt diese Koordination beim starreren 1 erhalten, während bei 2 ein Gleichgewicht mit der offenen Form besteht. so daß MeI mit 1 am P‐, mit 2 dagegen am N‐Atom reagiert. magnified image

A pseudo seven-coordinate central phosphorus atom is observed in the phosphanes 1 and 2. In solution this coordination is retained in the rigid phosphane 1, whereas in 2 an equilibrium exists between the opened and closed forms; as a result, MeI reacts with 1 at the P atom, but with 2 at the N atom.