Phosphorus compounds neutral hexacoordinate

As mentioned, stabilization of neutral hexacoordinated phosphorus via nitrogen donation is possible and this topic has been widely studied in the past few years. As P-N bonds are weaker and longer than those of P-C and P-0, chemists have essentially relied on chelation to enforce their formation. Most structures involve five- and six-membered chelating rings and the compounds that have been reported are described in Schemes 7,8, and 9 and Figs. 7 and 8. 

A series of neutral hexacoordinate phosphorus(v) compounds have been synthesized making use of an acidic phosphorus atom and a coordinating ligand. Compound 39 represents a bicyclic bridgehead phosphorus compound produced <1996IC325>. 

Cavell et al. have synthesised and characterised a series of neutral, hexaco-ordinate phosphorus compounds containing divalent, tridentate diphenol imine, azo and thio ligands. For example, the reaction of silylated Schiff base ligands e.g. 112) with PCI5 gave the neutral, hexacoordinate compound 113 by... 

The synthesis and characterisation of neutral hexacoordinate phosphorus(V) compounds (perphosphoranides) containing divalent tridentate diphenol imino, azo and thio ligands has also been reported.The hexacoordination was revealed by their high-field 53ip values, characteristic Jpp coupling and crystal structures. Two compounds of particular interest are the trihaloperphosphoranides (77 Hal = Cl, F), with respective Ssip values of —136.4 and —136.9. 

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