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

His( cyclopentadienyl )complexes
1RCH=CH2
R'COCl
co
~
MeOH
RCH 2 CH 2 COOMe
rJ 2 - ocyl; v(co)'"'-1620 cm-1
Fig. 9.8 Some applications of hydrozirconation in synthesis.
bond of the initial product occurs readily at room tempera ture to form an acyl
(p. 225). A single crystal X-ray diffraction study of the acetyl derivative
Cp 2 ZrCH 3 (COCH 3 ) shows that the acyl group is 1] 2 -bonded to the metal forming
the three-membered ring illustrated. The Zr-alkyl or Zr-acyl bonds can be
cleaved to give a variety ofproducts. As the reagents are readily accessible. cheap
and fairly easily handled, hydrozirconation is a viable procedure for the small
scale synthesis of organic compounds.
(e) METALLOCENES OF THE ELEMENTS OF THE SECOND AND THIRD TRANSITION
SERIES. Apart from the 18-electron compounds ruthenocene and osmocene,
no stable monomeric metallocenes of the elements of the Second and Third
Transition Series ha ve been isolated. Treatment of halides of these elements with
excess sodium cyclopentadienide in tetrahydrofuran leads either to complexes
like (ry 5 -C 5 H 5 ) 2 Nb(ry 1 -C 5 H 5 ) 2 which contain both 1] 5 and 1] 1 bonded groups, or to
low yields of cyclopentadienylmetal hydrides. Better yields of the latter, for
example Cp 2 TaH 3 , Cp 2 WH 2 or Cp 2 ReH (and the corresponding Nb and Mo
compounds) are obtained in the presence of sodium borohydride as a hydride
source.
The molecular structure of Cp 2 MoH 2 has been determined by neutron
diffraction, which is able to tocate the hydrogen nuclei precisely. Ifthe metal atom
is placed at the origin and the hydrogen atoms in the yz plane there is an orbita!
along the z axis ( approximately d,2) which in this 18-electron compound contains
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