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9] The configuration of C-2 of 8 arises because in the transition state 13 the ester function gives way to the bulky dioxolane ring and therefore occupies exchiuely the exo position (cf., however, Ref.[I]).-If the dioxolane ring in 13 is replaced by the smaller methyl group, i.e., in the transition state of the Wittig rearrangement of the (cis-crotyloxyfacetic ester anion, the ester function is no longer forced completely into the ex0 position. Accordingly, the hydroxy ester resulting in /his case, contrary, to 8 , shows only a 2 : 1 preference for the syn arrangement of the hydroxyl group and the vinyl group [2bj.We recently reported on the formation of the pentaphosphacyclopentadienide ion 1 upon cleavage of white phosphorus with sodium in diethylene glycol dimethyl ether (diglyme) or with lithium dihydrogen phosphide in tetrahydrofuran (THF); in addition, other polyphosphides (in particular, M:Pl6, MiP,,, and MiP,,) were formed."] Compound 1 was identified by a low-field singlet in the "P-NMR spectrum (6= +470.2) and a singlet in both the 23Na-and 7Li-NMR spectra as well as by the Na : P ratio of 1 : 5 determined analytically for solutions of Nap,. We report here further findings that have been made in the meantime concerning the formation, characterization, stability, and reactivity of 1. Angew f h r m lnt Ed Engl. 27(1988/ No 2 0 VCH Verlagsgesellschafi mbH, 0-6940 Wernherm, 1988

Geburtstag gewidmetKurzlich haben wir iiber die Bildung des Pentaphosphacyclopentadienid-Ions 1 bei der nucleophilen Spaltung von weinem Phosphor rnit Natrium in Diethylenglycoldimethylether (Diglyme) oder rnit Lithiumdihydrogenphosphid in Tetrahydrofuran (THF) berichtet; daneben entstanden weitere Polyphosphide (vor allem M:Plo, M:P2, und M\P,c))"t. 1 wurde durch ein Tieffeld-Singulett im "P-NMR-Spektrum (6= +470.2), je ein zugehoriges Singulett im "Na-bzw. 'Li-Spektrum sowie das an Losungen von Nap, analytisch bestimmte Na : P-Verhaltnis von 1 : 5 identifiziert. Inzwischen liegen weitere Befunde zur Entstehung, Charakterisierung, Stabilitat und Reaktivitat von 1 vor, iiber die wir im folgenden berichten.

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