Unexpected Isomerization of Hexa-tert-butyl-octaphosphane

Octaphosphane {cyclo-(P₄tBu₃)}₂ ( 1 ) undergoes an unexpected isomerization reaction to the constitutional isomer 2,2′,2′′,2′′′,3,3′-hexa-tert-butyl-bicyclo[3.3.0]octaphosphane ( 2 ) in the presence of Lewis acidic metal salts. The mechanism of this reaction is discussed and elucidated with DFT calculations. The results underline the fascinating similarity between phosphorus-rich and isolobal carbon compounds. The new bicyclic octaphosphane 2 shows a dynamic behavior in solution and reacts with [AuCl(tht)] (tht=tetrahydrothiophene) to give a mono- ([AuCl( 2 -κP³)], 3 ) and a dinuclear complex ([(AuCl)₂( 2 -κP³,κP^3′)], 4 ). With cis-[PdCl₂(cod)] (cod=1,5-cyclooctadiene), the chelate complex ([PdCl₂( 2 -κ²P²,P^2′)], 5 ) with a different coordination mode of the ligand was obtained.