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Original Articles

The Effect of Very Bulky Groups on the Equilibrium of Penta- and Hexacoordinated PhosphoranesCitation1

, &
Pages 1493-1511 | Received 15 Feb 2006, Accepted 09 Mar 2006, Published online: 01 Feb 2007
 

The synthesis of dithio-diphenol 4 and sulfonyl-diphenol 5, both with very bulky groups, provided starting materials for reaction sequences that led to the formation of the very stable hexacoordinated phosphorane 2 and sensitive pentacoordinated phosphorane 3. Hexacoordination was established in 2 by an intramolecular donor interaction at the phosphorus center from an oxygen atom of the sulfonyl group present as part of the eight-membered ring. The solid state structures of 2 and 3 were established by X-ray analysis, as was that of phosphite 1 formed in the reaction sequence leading to 2. In solution, 2 has two forms existing in a dynamic equilibrium between a pentacoordinated and the more dominant hexacoordinated form as determined by 31P and 19F NMR spectroscopy. The high stability of 2 with respect to hydrolysis and alcoholysis reactions suggests that an associative process is responsible as the controlling reaction mechanism.

The research presented here was supported by the donors of the Petroleum Research Fund, administered by the American Chemical Society, and is gratefully acknowledged. We thank the X-Ray Structural Characterization Laboratory at the Chemistry Department supported by University of Massachusetts and the National Science Foundation (Grant CHE-9974648).

Notes

a R = Σ|Fo‖−|Fc‖/Σ |Fo|.

bRw (Fo 2) = {Σ w(Fo 2− Fc 2)2/Σ wFo 4}½.

a Equilibrium denotes the existence of an isomeric penta-hexa coordination equilibrium in the solution. The solid state coordination at phosphorus is given in parentheses as found by X-ray analysis.

b Bulkier α,α -dimethylbenzyl group is used here.

c Highly electronegative pentafluorophenoxy groups are used for 11 and 13.

d Phosphite 13 has P─O donor interactionCitation 13 that is as strong as that found in phosphoranes.

e Compounds 11 and 12 deviate considerably from the Berry coordinate.

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