2,4-Di-tert-butyl-1lambda~3,3lambda~3-diphosphinines: Targeted Synthesis at Iron(o) Centers and Oxidative Release

摘要

Trivalent phospaouis atoms and CR fragments are iscelec-tronic building blocks that can occupy equivalent positions in many organophosphorus compounds, for example in hecero arenes. The simplest member of this group, lambda~3-phosphinine (pbospha'oenzene) is known, ax well as many of its substitution products. Phosphinines can act as delta-donor ligands, utilizing the lone pair on phosphorus, and also as cyclic eta~6 ligands. Of the three possible diphosphinine isomers, only 2,3,5,6-tetraki.s(trifluoromethyl)-1lambda~3,4lambda~3-diphosphinine has so far been prepared in solution and apectroscopically chaiacterized There is also very little known about phosphorus-rich benzene analogues. A cyclotrimerization product of tert-butylphos-phaethyne 1 hasbeen characterized as a pi-bound triphos-phadewarbenzene. A second trimenzation product of 1 was postulated to be a coordinated 1,3,5-triphosphinine; this, however, has not yet been definitively proven. We report here an efficient synthesis of 1lambda~3,3lambda~3-diphosphinines in the coordination sphere of iron(o) by [2 + 2 + 2] cycloaddition of two phos-phaalkynes and a terminal alkyne. The release of these 1lambda~3, 3lambda~3 diphosphinines under oxidative conditions is also discussed.