Preparation of sterically protected 3,4-bis[(2,4,6-tri-tert-butylphenyl)-phosphinidene]cyclobutene derivatives having ring-fused structures

(Formula Presented) Sterically protected 3,4-diphosphinidenecyclobutenes, having ring-fused structures, were prepared. Structures of 8,9-bis[(2,4,6-tri-tert-butylphenyl)-phosphinidene]bicyclo[5.2.0]non-1(7)-ene and its dichloropalladium(II) complex were analyzed by X-ray crystallography. A geometrical change induced by the complex formation was exhibited by X-ray crystallographic analysis. The geometrical change in solution was also suggested by ¹H NMR spectroscopy in CDCl₃.