THERMAL [2+2]CYCLOADDITIONS BETWEEN DIPHOSPHENE COMPLEXES AND ALKYNES

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