Mixed sandwiches of group 3 elements:synthesis and UPS studies of pentamethylcyclopentadienylcyclooctatetraenescandium, -yttrium and -lanthanum

The mixed sandwich complexes Cp*MCOT (Cp* = η5-C5Me5; M = Sc, Y, La; COT = η8-C8H8) have been prepared and characterized. IR spectra indicate that in the solid state the La compound is polymeric (Cp*LaCOT)n, with cyclotetraene ligands. The complexes are strong Lewis acids and form bridging adducts Cp*MCOT · THF. For M = La the adduct has been isolated. The UPS spectra of Cp*MCOT are nearly identical with only minor differences in the ionizations from the highest e2(COT) and e1(Cp*) orbitals; this is interpreted as a strong indication that the bonding in the complexes is virtually completely ionic