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

Cyclopentadienylmetal carbonyls
9
Ce
Cp
CpCo(CO)X 2
o
xy
/<X=Br,I)
~
r/{ CH 3
o
o
N
CpCo-CoCp
'\_/
N
o
No/Hg lFeCI.3
o
c
/Co""­
/'­
/'­
CpCo=CoCp
'\_/
c
o
1
Fig. 9.10 Some reactions of CpCo(C0) 2 •
than CpMn(CO)r Carbonyl groups can be replaced by other ligands such as
phosphines or dienes. Photolysis at - 78oC yields initially CpCo(CO) which can
trap another molecule of CpCo(C0) 2 to yield Cp 2 Co 2 (CO), and eventually other
species (Fig. 9.10). CpCo(C0) 2 is a Lewis base by virtue of a non-bonding electron
pair in an orbita! centred on the metal atom (p. 210). It forms an adduct with the
Lewis acid, mercury(II) chloride, which contains a cobalt-mercury bond. It also
adds halogens and alkyl halides with expulsion of one molecule of carbon
monoxide. The basicity is greatly enhanced by replacement of the carbonyl
groups by phosphines, especially by trimethylphosphine. CpCo(PMe, ) 2 is a strong
base which is very easily protonated, even by NH: PF; in methanol. The
1H n.m.r. spectrum ofthe resulting hydride shows a triplet at -16.2 b (JPH 83 Hz)
arising from coupling to two equivalent phosphorus nuclei. CpCo(PMe,) 1 also
acts as a nucleophile towards alkyl and acyl halides and as a strong Lewis base.
9.3.2 Binuclear compounds
The iron dimer [CpFe(C0) 2 L is easily prepared by heating pentacarbonyliron in
dicyclopentadiene at 140°C. It forms maroon-purple crystals which are only
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