ACHIEVING NEW LANTHANIDE CHEMISTRY WITHIN THE TETRACYCLOPENTADIENYL CAVITY FORMED BY 2 (C5ME5)2LN MOIETIES

The unusual bent metallocene, (C5Me5)2Sm, often forms bimetallic complexes, [(C5Me5)2SM]2 (substrate), in which the four C5Me5 ring centroids describe a tetrahedron. Studies of the reactivity of (C5Me5)2SM with alkenes suggest that the four C5Me5 rings can provide a protective cavity which selectively enhances some reactions over others. The steric effects of the tetracyclopentadienyl environment may also provide the basis for new types of lanthanide-based reactions involving C-C coupling. Hence, the formation of [(CMe5)2Sm]2(mu-eta2:eta2-PhCCCCPh) instead of [(C5Me5)2Sm(mu-C=CPh)]2 from reactions which should generate (C5Me5)2SmC=CPh moieties may occur because the bridged alkynide complex would be too sterically crowded. The steric effects of this tetracyclopentadienyl coordination environment may be of general importance in the chemistry of samarium.