Abstract
Radialenes are cross-conjugated cyclic compounds and known to have unique electronic structures. We have succeeded in the synthesis of the first stable triphospha[3]radialene 1, where the three exo-carbon atoms of the [3]radialene skeleton were all replaced by phosphorus atoms. The molecular structure of 1 was revealed by spectroscopic and X-ray crystallographic analyses. In the crystal structure of 1, three phosphorus-carbon bond length of the central framework are within the typical range for those of phosphaalkenes, indicating their double-bond character. The absorption spectrum of 1 showed a strong absorption in the longer wavelength range (absorption maximum = 526 nm, molar extinction coefficient = 1.92 X 104) than those of [3]radialenes. This result strongly suggested the conjugation of the P=C double bonds of 1. The details of electronic structure of 1 will be discussed based on the experimental results and theoretical calculations.
