X-Ray crystal structure and Diels–Alder reactivity of the 3,4-dimethyl-2H-phosphole dimer

The [4 + 2] P–P bonded dimer of 3,4-dimethyl-2H-phosphole has the ecdo geometry with long, weak P–P and C–C bridges between the two phosphole units; it can therefore act as generator of monomeric 3,4-dimethyl-2H-phosphole at ca. 100 °C and gives the expected [4 + 2] and [2 + 4] cycloadducts with diphenylacetylene and 2,3-dimethylbutadiene.