Synthesis of novel symmetrical and nonsymmetrical 6-membered heterocycles with pendant electron-rich organoiron substituents

The functionalized complexes [(dppe) Cp*Fe (C=C)](2)-(Py) (Py = 2,6-C5H3N a nd 3,5-C5H3N (dppe = 1,2-bis(diphenylphosphino)ethane) were isolated in goo d yields from reaction of the chloro complex (dppe)Cp*FeCl with the protect ed bis-acetylenic heterocyclic precursor. These electron-rich pyridyl ligan ds constitute interesting examples of organometallic heterocycles bearing r edox-active substituents. The attempts to find an alternative route startin g from the alkynyl complex [(dppe)Cp*Fe(C=CH)] and the corresponding dibrom opyridines using a Sonogashira cross-coupling reaction are also described. By this route, the mono-functionalized products [(dppe)Cp*Fe(C=C)]-2,6-Py-B r and [(dppe)Cp*Fe(C=C)]-3,5-Py-Br could be cleanly isolated. These compoun ds open the way to the generation of heteroaromatics featuring nonequivalen t alkyne substituents as [(dppe)Cp*Fe(C=C)]-2,6-Py-[(C=C)SiMe3] or [(dppe)C p*Fe(C=C)]-3,5-Py-[(C=C)SiMe3] by further coupling.