Crystal Structures of Spirocyclic Pentaorganylphosphoranes

Very recently Holmes et al. conducted crystal structure determinations for some typical representatives of the bis-2,2 -biphenylylene-organylphosphorane type, namely 25a, c 83) and 25e,fa4 which in principle confirmed but also supplemented the conclusions drawn earlier from solution studies. 

For the equatorial C—P—C bond angles, however, larger deviations from their ideal 120° values are found. Whether these alone, without concomitant comparable alterations of the axial C—P—C angles, ran justify the definition of a gradual distortion towards a specific tetragonal-pyramidal structure might be questioned. On the basis of a proper evaluation of more latent structural features, as done in 

After all, there remains the fact that in all four spirophosphoranes 25a, c, ,/the axial C—P—C angle of the underlying trigonal-bipyramidal structure does not 

In passing, it might be noted that earlier predictions about structural details of such spirophosphoranes (such as the necessary pyramidality of the nitrogen atom in 25/79) or the size of the intraannular angles of the phosphafluorene system, 86° for C—P—C and 113° for C—C—C, respectively 28,30, 66)) have been fully confirmed by the present x-ray studies of Holmes and his group. 

With strong bases, e.g. t-butyllithium, 77 loses a proton to give the phosphoranyl anion 79 strong electrophiles (H , X , CH3I) remove a hydride ion to regenerate spirophosphonium ion 34. The general chemistry of 77 and of its tetramethyl 

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