_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

Lanthanides and actinides
A few examples ofreactions which occur at lanthanide centres are highlighted
below and compared with those undergone by d-block transition metal
complexes.
13.2 Introduction-actinides
The actinide elements comprise the fourteen elements Th to Lr which follow
actinium (Z = 8 9) in the Periodic Table. Across the series the Sf orbitals are filled.
These, like the 4f orbitals of the lanthanides, are inner orbitals. which do not
extend significantly outside the radon core. Strong participation of these orbitals
in covalent bonding is therefore not to be expected. At the beginning of the
actinide series, however, the Sf and 6d orbitals are rather similar in energy. This
leads to a greater range of oxidation states in actinide compounds than for the
early lanthanides, for which ( apart from Ce( IV)) the + 3 ( 4j") state is established
right from the start. Uranium, for example, forms fluorides UF 3 , UF 4 , UF 5 and UF 6 •
Moreover, while steric and electrostatic considerations are stil! thought to play
the dominant role in determining structure and reactivity in the organometallic
derivatives, a greater degree of covalent interaction with ligand molecules
through metal 6d and Sf orbitals is likely compared with the lanthanides. Only a
few aspects of this chemistry can be touched upon; a more complete perspective
can be obtained from the articles cited.
13.3 Cyclopentadienyls
Tris-cyclopentadienyls of the lanthanides have been prepared from the trichlorides
and sodium cyclopentadienide. They are isolated from tetrahydrofuran as
adducts, Cp 3 Ln(THF). in which the metal atom is formally ten-coordinate (Cp
formally occupies 3 coordination positions). These high coordination numbers
(8-12) are characteristic oflanthanide chemistry. Cp 3 Ln(THF) are converted into
dimeric halides by reacting with more LnCl 3 • These species are useful starting
materials for preparing other derivatives.
LnCL 3 + 3NaCp -
THF
2Cp 3 Ln.THF + LnCL 3 -
Cp 3 Ln.THF
[Cp2LnCL)z
The dimer Cp 2 Y(ţt-H) 2 YCp 2 contains strongly hydridic hydrogen. With water it
gives hydrogen (D 2 0 gives HD) and with iodomethane, methane. The 1 H and 89 Y
400