Thermal [2 + 2] Cycloadditions between Diphosphene Complexes and Alkynes

Abstract

According to the experimental conditions, the thermal decomposition of the 7-phenyl-7-phosphanorbornadiene−W(CO)5 complex 1 affords the diphosphene complex 3 (60 °C, CuCl as a catalyst), the triphosphirane complex 4 (120 °C, 8 h), or the tetraphosphetane complex 5 (120 °C, 15 h). The reaction of 3 with alkynes at 120 °C in toluene gives the corresponding 1,2-dihydro-1,2-diphosphete complexes 6−8 in modest yield (ca. 25%) via a [2 + 2] cycloaddition. This result gives some insight into the reaction of cyclopolyphosphines with alkynes.