Unexpected Isomerization of Hexa-tert-butyl-octaphosphane.

Octaphosphane {cyclo-(P4 tBu3 )}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 ,κP3' )], 4). With cis-[PdCl2 (cod)] (cod=1,5-cyclooctadiene), the chelate complex ([PdCl2 (2-κ2 P2 ,P2' )], 5) with a different coordination mode of the ligand was obtained.