No abstract

No abstract

Up to about 15 years ago compounds with a skeleton of phosphorus chains or rings were regarded as "exotic" in the field of nonmetal chemistry. Aside from a number of examples of molecules with two P atoms directly bonded to each other and a few sporadically discovered monocyclic ring compounds, only solids of undefined composition and structure were known. Since then the state of our knowledge in this sector has made considerable progress: between PH3 and its derivatives on the one hand, and the high-molecular modifications of elementary phosphorus on the other, an unexpected variety of well defined compounds have been discovered, showing many similarities to the analogous compounds of carbon. However, surprises can still occur even with "small" phosphorus-containing molecules, as shown by the likewise recently discovered field of phosphorus three-membered ring compounds. [*I Prof. Dr. M. Baudler valence tautomerism in phosphorus compounds; stable phosphorus three-membered ring compounds; ring systems. If further amounts of the metalation agent are added to the reaction system, also small quantities of lithium trihydrogen diphosphide 11 (6,= -167.0, 6,= -271.7, JAB= -205.3 Hz) and lithium tetrahydrogen triphosphide 12 (6A= -123.0, 6,= -251.7, J A B = -266.8 Hz; all at 203 K) are detectable by 3'P-NMR spectroscopy'521. H2PA-PBH Li H2PA-PB(Li)-PAH2 11 12 Homocyclic Phosphorus Three-Membered Ring CompoundsEver since the mass-spectrometric detection of the existence of tripho~phane(3)'~"I as the first member of the Angew. Chem. h i . Ed. Engl. 21 (1982) 492-Ji12

Dedicated to Professor Heinz Harnisch on the occasion of his 60th birthdayIn contrast to the numerous known and often technically important mono-and diphosphorus compounds with phosphorus in its maximum oxidation state, polyphosphorus compounds led only a shadowy existence up to about twenty years ago. One of the reasons for this was the properties of such compounds, which made their handling and structural characterization difficult. This problem was solved by the development of modern preparative techniques and, especially, by the further methodological development of nuclear magnetic resonance spectroscopy. Thus, a fascinating new branch of phosphorus chemistry has been opened up in recent years. The first comprehensive review on this subject was published five years ago. Since then, research on this "element-near'' chemistry of phosphorus has produced further impressive advances with the result that a surprisingly large variety of compounds with skeletons consisting of chains or rings of phosphorus atoms is known today. However, the recent observation of the spontaneous formation of the "aromatic" pentaphosphacyclopentadienide ion, P ;, during the synthesis of phosphorus-richer polyphosphides from phosphorus-poorer compounds in solution and the discovery of the inversion of phosphorus in tetra-and pentacyclic organophosphanes demonstrate that this field is still capable of producing surprises.

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