5-Organyl-5-phosphaspiro[4.4]nonanes: A Contribution to the structural chemistry of spirocyclic tetraalkylphophonium salts and Pentaalkylphosphoranes
Sprache des Titels:
Spirocyclic phosphonium salts of the type [(CH2)4P(CH2)4]+ X- with X ) I3 (1a), I (1b), picrate
(1c), benzoate (1d), and Cl (1e) were prepared from 1,4-diiodobutane and elemental phosphorus followed
by metathesis reactions. The crystal structures of 1b and 1c and of 1d(H2O) have been determined by X-ray diffraction methods. In the cations of these salts the phosphorus atoms are shared by two fivemembered rings in envelop conformations. In the picrate 1c the cations show an unsymmetrical ring folding pattern (point group C1), while the geometry of the cations of the iodide 1b and the benzoate hydrate [1d(H2O)] approaches the symmetry of point group C2. These structures can be taken as models for the
as yet unknown molecular geometries of the corresponding hydrocarbon (CH2)4C(CH2)4 and silane (CH2)4- Si(CH2)4. Treatment of 1e with organolithium reagents RLi affords spirocyclic pentaorganophosphoranes RP[(CH2)4]2 with R ) Me, Et, n-Bu, Vi, and Ph (2a-e) in good (R ) Me, Et, n-Bu) to low yields (R ) Vi, Ph). The products are isolated as colorless liquids, of which only 2a, 2b, and 2d can be distilled without decomposition. Single crystals of 2a were obtained by low-temperature in situ crystal growth. The molecule has a trigonal bipyramidal configuration with the methyl group in an equatorial position and the two fivemembered rings spanning axial/equatorial positions of the polyhedron. Deviations from the standard trigonal
bipyramidal geometry are small. The compounds 2a-e are fluctional in solution as demonstrated by NMR spectroscopy.