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

Cyclopentadienyls
n.m.r. spectra each show a triplet. J( 1 H 89 Y) = 2 7.2 Hz, indicating that the dimeric
structure is retained in solution. Hydride complexes also result from [3-hydrogen
transfer, as with d-block transition elements. The tertiary butyl group is useful.
not only because it has ni ne fi-hydrogen atoms but because it is too large to forma
bridge like the methyl group.
THF
\/H"-..
Cp2Y"'-.H/\Cp2
recyst
benzene
H
H H
"'-.1/
/c'-.....
Cp2Y "'-.c//.YCp2
/j'\.
H H H
bridging methyls cf Al2Me6
THF
Insertion ofCO, another reaction characteristic oftransition metal alkyls. has also
been observed. The dihapto acyl (cf. Zr. p. 291) reacts further to yield a product
in which four CO molecules ha ve been linked through carbon -carbon bonds.
[Cp2LuClh ~i=~t Cp2Lu{C(CH3h} THF ( lt,. 1- [cp2Lu/H"-..LuCp2 ]
. -H3C2C=CH2 ~H/
~ lco
/o"- /c~
Cp2L::u C O c L / 1
t 11 • P2 u '-..
o~ c" l:uCp2 c-R
c,....... o/
1
R
o
By replacing cyclopentadienyl by pentamethylcyclopentadienyl. steric compression
at the metal centre is greatly increased. especially at lutetium, the
smallest lanthanide. The complex Cp;LuCH, ( 0Et 2 J polymerizes ethene and
oligomerizes propene. (Cp* = ry'-C ,Me, ). Its behaviour thus provides a good
model for Ziegler-N atta catalysis. The insertion of propene into the 1 ,u-CH, bond
and some further propagation steps have been followed by n.m.r. spectroscopy.
Clear examples of such insertions are rare in d-block chemistry (p. 380).
Termination can occur either by fi-H transfer or by fi-methyl transfer: the latter is
a novel process which has yet to be observed for d-block elements.
CH,
PROPAGATION * * * 1 -
Cp 2LuCH 3 +H3CCH=CH2 - Cp 2LuCH2 CH(CH 3)2 - Cp2LuCH 2CH·
fl-H TRANSFER
/l-Me TRANSFER
401