ORGANOPHOSPHORUS COMPOUNDS .96. CYCLOTETRAMERIZATION OF PHOSPHAALKYNES TO 1,3,5,7-TETRAPHOSPHACUBANES

Depending on the reaction conditions, small amounts of the tetraphosph apentacyclic compounds (tetraphosphacubanes) 4a, b as well as the isom eric tetraphosphatetracyclic products 5a, b can be isolated from the t hermolyses of the phosphaalkynes 3a, b. This cyclotetramerization can be directed towards the formation of tetraphosphacubanes when the whol e process is split into two sequential cyclodimerizations. Firstly, th e zirconocene-phosphaalkyne dimer complexes 8a-d are prepared from 7 a nd 3a-d; in the second step, the Cp(2)Zr fragment is extruded from 8a- d by reaction with hexachloroethane. The tetraphasphacubanes 4a-d are obtained in good yields by this process, Only in the case of 1-adamant ylphosphaacetylene are the penta- and tetracyclic products formed conc omitantly (7 + 3e --> 8e --> 11 + 12). Putative intermediates for the second dimerization step are the diphosphetes 9a-e and their Diels-Ald er dimers 10a-e.