An Ylide‐Substituted Tetraphosphene, Cyclotetraphosphane, and Bicyclotetraphosphane

The reaction of two specific ylidyl dichlorophosphanes, Ph3P=CR‐PCl 2 , with P(SiMe 3 ) 3 yields the ylidyl trimethylsilyl diphosphenes Ph 3 P=CR.P=P‐SiMe 3 as primary products which form two different types of dimers: the cyclotetraphosphane 9 (R = SiMe 3 ), and the tetraphosphene 10 (R = 2,6‐Cl, 2,/C 6 H 3 ). 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 ( 2J pp = 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.