Topoisomerisierung von sechs vertex-polyedern: Gerüstumlagerungen im system (RP)Fe3(CO)n/ALKIN☆

Abstract Clusters of composition (RP)(RCCR)Fe 3 (CO) 9 may exist in three different isomeric forms, of which two have a pentagonal pyramidal, and the third has a trigonal, prismatic cage structure. Decarbonylation of these compounds leads to (RP)(RCCR)Fe 3 (CO) 8 with a trigonal prismatic framework; carbonylation yields compounds of composition (RP)(RCCR)Fe 3 (CO) 10 the geometry of which is derived from the pentagonal pyramidal base structure. The different isomers as well as their carbonylation and decarbonylation products can all be transformed into one another. The bonding pattern in the PC 2 Fe 3 cages thus formed changes in an apparently complex way during these reactions. The diversity of bond scissions and bond formations which occurs during these transformations, appears to be unusual at first sight. It can however, be rationalized in a simple scheme: The simultaneous movement of the apical and one equatorial constituent of a pentagonal pyramid transforms it into a trigonal prism. Further movement along the same coordinate leads to an isomeric pentagonal pyramid. The individual observations described here are a strong indication of a process we have termed “tandem isomerization”.