N R 2 hv + P=C-P, -5 I NR, NRz 10in place of diisopropylamino substituents.['] Compound 3 is a local minimum on the potential energy surface, but appeared to be 110 and 116 kJmol-' above 4, at the SCF and MP2 level, respectively. In the same way, 6 is 120 kJ mol-' above 7, which is 140 kJmol-' higher than 8. The surprising stabilities of 3, 6, and 7 are probably due to the presence of bulky substituents, since the tetracoordinate P-H ylide form better accommodates the steric hindrance than does the tricoordinate CH form. Lastly, the isomerization of 9 +lo is not surprising since phosphaalkene 10 was found to be 220 kJ mol-' lower in energy than 9. This work demonstrates the great potential of 1 as a building block for the synthesis of new metastable species, predicted by theory to be thermodynamically high in energy.
Experimental Procedure
3:To a solution of 1 (1 mmol) in dichloromethane ( 5 mL) was added the equimolar amount of NaBF, at room temperature. After the solution had been stirred for 2 h, the solvent was removed under vacuum, and the residue was washed several times with Et,O. This afforded 3 as white powder (70%; m.p. J(P,H) = 4.0 and 17.3 Hz). 9.2 (dddq, J(P,P) = 32.9 Hz, J(P,F) =15.3 Hz, J(P,H) = 524.2 and 16.
A', Z = 2, = 3.510 g~m -~, p(MoKa) = 214.97 cm-I, T = 295 K, 3398 unahhlngiie Reflexe mit 4" 5 20 5 50" wurden gesammelt (Siemens P4). von denen 1624 Reflexe mit F, groBer als 5 a(FJ zur Verfeinerung benutzt wurden. R = 0.0525, R, = 0.0600, GOF = 1.19. Die zentrosymmetrische Rautngruppe wurde aufgrund der systematischen Ausloschungen gewahlt und aufgrund des Ganges der Verfeinerung heihehalten. Eine semiempirische Absorptionskorrektur basierend auf 216 Daten ($-Scans von 6 Reflexen in 1 0"-Schritten) wurde durchgefuhrt, T(max)/T[min) = 4.82. Es wurden keine ungewchnlichen Bindungslangen oder -winkel ermittelt. AIle Atome wurden anisotrop verfeinert. Weitere Einzelheiten zu den Kri-slallstrukturunters~hungen kcnnen beim Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, D-76344 Eggenstein-Leopoldshafen, unter Angabe der Hinterlegungsnummer CSD-57327, der Autoren und des Zeitschriftenzitats angefordert werden. Rontgenstrukturanalysen von Komplexen mit Pentachlorcyclopentadienyl-und Pentabromcyclopentadienylliganden siehe: a) V. W. Day, K. J. Reimer, A. Shaver. J. Chem. Sor. Chem. Commun. 1975, 403; b) G. M.
Piperidine aminoxyl radicals are reversibly bound in the cavity of a water-soluble cryptophane with an affinity of the order of lo3 dm3 mol-1; the complexation equilibrium is slow on the EPR timescale and the magnitude of the nitrogen hyperfine splittings of the bound substrates indicates that the cavity of this cryptophane has a polarity comparable to that of halogenated solvents.
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