LOOKING FOR 1,3-DIPHOSPHINDOLIDE AND 1,2,3-TRIPHOSPHINDOLIDE IONS

The reaction of 1,2-bis(lithiophenylphosphino)benzene 1 with dichlorom ethane leads to a cis-trans mixture of 1,3-diphenyl-2,3-dihydro-1H-1,3 -benzodiphosphole 2. The reaction of 2, first with Et2NLi, then with a n excess of lithium leads to the parent 1,5-diphosphindolide ion 4. St arting from 1 and tetrachloroethylene, both the expected dibenzotetrap hosphafulvalene 7 and its 6-membered ring isomer 6 are obtained. One s tereoisomer of each has been characterized by X-ray crystal structure analysis. Whereas 6 is strain-free, 7 displays some strain, thus expla ining the competition between 6 and 7 in the reaction. Compound 7 yiel ds the corresponding dianion 8 upon cleavage of its four P-Ph bonds by an excess of lithium in THF. An attempted synthesis of the 1,2,3-trip hosphindolide ion has failed.