An Ylide‐Substituted Tetraphosphene, Cyclotetraphosphane, and Bicyclotetraphosphane

The reaction of two specific ylidyl dichlorophosphanes, Ph3P=CR‐PCl2, with P(SiMe3)3 yields the ylidyl trimethylsilyl diphosphenes Ph3P=CR.P=P‐SiMe3 as primary products which form two different types of dimers: the cyclotetraphosphane 9 (R = SiMe3), and the tetraphosphene 10 (R = 2,6‐Cl, 2,/C6H3). The latter compound is readily converted to the bis(ylidyl)biocyclotetraphosphane 11. The molecular structures of 9 and 11 allow a strong transanular interaction between teh ylide‐substituted phosphorus atoms, which results in very large two‐bond coupling constants (2Jpp = 184 and 332 Hz respectively). The central P bond in 11 is relatively long (220.7 pm); quantum chemical calculations show the lengthening to be a consequence of the perpendicular orientation of the ylidic donor p‐orbital.