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-Cl2C6H3). The latter compound is readily converted to the bis (ylidyl)bicyclotetraphosphane 11. The molecular structures of 9 and 11 allow a strong transanular interaction between the ylide-substituted phosphorus atoms, which results in very large two-bond coupling constants ((2)J(PP) = 184 and 332 Hz respectively). The central PP 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.