Octaphosphane {cyclo-(P 4 tBu 3 )} 2 (1)u ndergoes an unexpected isomerization reactiontothe constitutional isomer 2,2',2'',2''',3,3'-hexa-tert-butyl-bicyclo[3.3.0]octaphosphane (2)i nt he presence of Lewis acidicm etal salts. The mechanism of this reactioni sd iscussed and elucidated with DFT calculations. The resultsu nderline the fascinating similarity between phosphorus-rich and isolobal carbon compounds. The new bicyclic octaphosphane 2 shows ad ynamic behavior in solution and reacts with [AuCl(tht)] (tht = tetrahydrothiophene) to give am ono-([AuCl(2-kP 3 )], 3)a nd ad inuclear complex ([(AuCl) 2 (2-kP 3 ,kP 3' )], 4). With cis-[PdCl 2 (cod)] (cod = 1,5-cyclooctadiene),t he chelate complex ([PdCl 2 (2-k 2 P 2 ,P 2' )], 5)w ith a different coordination mode of the ligand was obtained.