Synthesis of 1,3‐Diphospha‐2,3‐dihydro‐1 H ‐phenalenes

The reaction of 1,8‐dilithionaphthalene ( 1 ) with methylenebis[(dialkylamino)chlorophosphanes] [R 2 N(Cl)PCH 2 P(Cl)NR 2 ; R = Me ( 2a ), Et ( 2b )] leads to the formation of new heterocyclic compounds, 1,3‐diphospha‐2,3‐dihydro‐1 H ‐phenalenes 3a , b as a mixture of cis and trans isomers. DFT calculations indicate that the cis isomers are thermodynamically more stable by about 1–3 kcal/mol than the trans isomers. Compounds 3a , b can be converted into dithio the derivatives 5a , b and the borane complexes 6a , b , which were characterized by NMR spectroscopy and investigated by X‐ray diffraction analysis. The dialkylamino groups in 3 can be substituted by chlorine to give the chlorophosphane 7 .