Unexpected dimerisation of a 2H-azaphosphirene complex

Heating a 2H-azaphosphirene complex in the solid state afforded the first h ead-to-tail dimer, a 2,5-dihydro-2,5-diphosphapyrimidine complex, a eta (1) -diphosphene complex and another complex having low-coordinated phosphorus centers; whereas the latter was detected only by P-31 NMR spectroscopy, the dimer was isolated and structurally characterized.