A Tetracyclic Octaphosphane by Successive Addition, Inversion, and Condensation Reactions

An example of an octaphosphane of type R2P8 (R=(DDP)Ga) was isolated by treatment of cage compound (DDP)GaP4 (2, DDP=(2,6-diisopropylphenyl)(4-((2,6-diisopropylphenyl)imino)pent-2-en-2-yl)amide) with (C6F5)(2)PBr. The initially formed endo-exo butterfly shaped pentaphosphane 7 rapidly rearranges to the more stable exo-exo isomer 8, which undergoes dimerization to decaphosphane 11. Compound 11 unexpectedly eliminates tetraaryldiphosphane 13 to give tetracyclo[3.3.0.0(2,7).0(4,6)] octaphosphane [(DDP)GaBr](2)P-8 (12). The reaction steps were confirmed by crystal structure analysis of the key intermediates and supported by kinetic studies using NMR techniques.