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)2PBr. 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[3.3.0.02,7.04,6]octaphosphane [(DDP)GaBr]2P8 (12). The reaction steps were confirmed by crystal structure analysis of the key intermediates and supported by kinetic studies using NMR techniques.