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

Lanthanides and actinides
Cp~LuCH 3 is in equilibrium with its dimer in solution. The monomer and one site
in the dimer must therefore possess room for coordination of another moleculethey
are 'sterically unsaturated'. Cp~LuCH 3 and Cp~LuH 2 effect metallation
(p. 40) viz. C-H bond activation (p. 224) for weakly acidic hydrocarbons such as
alkynes or arenes. Like RLi(TMEDA) 2 these complexes possess sites of high Lewis
acidity and basicity in the same molecule. The lutetium centre appears tobe even
more fiercely electrophilic and can interact even with methane. The exchange
obeys a second order rate law and has been followed by n.m.r. spectroscopy.
Uranium forms tris and tetrakis-cyclopentadienyls Cp 3 U and Cp 4 U. In the latter
there are four 1J 5 -cyclopentadienyl groups so that the metal atom is formally 12-
coordinate. This high coordination number is consistent with essentially ionic
(electrostatic) bonding. This may also apply to the complexes MCp 4 (M =Ti, Zr)
where the structures apparently depend on the size of the metal atom and, for
Cp 4 Zr, the 18-electron rule does not apply.
Ti Zr u
r/Â (W+) 0.74 0.91 1.17
Formal Coord. No 8 10 12
Attachment 211'' 2111 311'· 111 411'
Electron count 18 20 26
13.4 Cyclooctatetraene complexes
Cyc!ooctatetraene forms complexes with both lanthanide and actinide elements.
They are prepared by reacting the anhydrous metal halides with K 2 (C 8 H 8 ) in
tetrahydrofuran. The anion C 8 H~- is a planar ten-electron aroma tic system and
this planar structure is retained by the C 8 H 8 ligand in the complexes.
(Ln =La, Ce, Pr, Nd, Sm, Gd, Tb, Y)
(M = Th, Pa, U, Np, Pu, Am)
Mixed cyclopentadienylcyclooctatetraene complexes have also been prepared:
402
LnCL 3 + K2(C 8 H8)-[Ln(C8H8) CL(THFl2h
N~
Ln(C 5 H 5 )(C8H8)(THF) Ln (C5H 5 ) CL2 (THF) 3
(heovier lonthonides)