Cyclic phosphoranes examples

In contrast, the geometry of the dioxadithiaspirophosphorane (8) is essentially rp (93% distorted from tbp) with the chalcogen atoms occupying the basal positions, a structure which represents the least distorted rp phosphorane on record. The paper re-emphasizes that no example of a rp structure for five-membered cyclic phosphoranes exists unless two rings are present, the rings contain unsaturation, and like atoms are present in any one ring bound to... 

Another illustrative example of a fairly exact reproduction of the typical features of a reaction coordinate by means of X-ray structural data is given by an analysis of distortions of bond configurations of the pentacoordinate phosphorus atom in cyclic phosphoranes [96]. 

A number of preparations of mixed halogenophosphoranes from tervalent phosphorus-fluorine compounds have been reported. For example, acyclic and cyclic fluorine compounds have been converted to phosphoranes, such as (36) and (37), by treatment with chlorine. Similar reactions leading to AA-dialkylaminodichlorodifluorophosphoranes (38) have been described and the stability of (38) to exchange processes commented upon. iVA-Dialkylaminotetraiodophosphoranes (39) have been prepared from AA-dialkylaminodichlorophosphines and lithium iodide, although no detailed physical evidence for the structure of these unusual compounds has yet been reported. The preparation of bis-(A-alkylamino)difluorophosphoranes (4) has been described above (see Section lA). 

Additional examples of spirophosphoranes derived from amidrazones have been described. Unstable phosphoranes, e.g. (61), were obtained from cyclic chlorophosphites and o-phenylenediamine. They polymerized rapidly at... 

The first observation is in contrast to the studies on phosphoranes (14, 15, 16) for which the equatorial cycle is highly unfavorable owing to the non-cyclic equatorial C-P-C angle of 120°. The non-cyclic C-S-C bond angle is presumably in the vicinity of the 102° F-S-F angle of SF4. [For relevant data see Table VI of Reference (17).] Also trimethylene-sulfide is a known compound. This is an example of the diflFerence between the pure p-bond picture of sulfuranes and the -hybridized picture of phosphoranes. The only evidence relative to the second observation is the lack of pseudorotation in solvolysis sulfurane intermediates (16) although some authors seem intuitively to believe pseudorotation likely in these compounds (18). 

While the chemistry of pentacoordinated spirophosphoranes has been so far widely explored, cyclic hexacoordinate phosphorus compounds are much less studied because very often they are transient species and difficult to detect. However, an interesting example of a stable hexacoordinate phosphoranate bearing Martin ligands was recently described by Yamamoto. Another approach involved the participation of donor-acceptor nitrogen-phosphorus" and sulphur-phosphorus bonds in the formation of stable hexacoordinated compounds. 

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