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

Metallocarboranes and metalloboranes
and
Mo(C0) 6 + C 2B 9Hi;
reflux
TIIF
[ (OC), Re(ry'-C 2 B 9 H,,)]
The nickel compound is found in three oxidation states
o, Fei+
Na/Hg
Cd
[Cu(C 2 B 9 H 11 ) 2 r as well as [Cu(C,B 9 H 11 ) 2 )2
have also been prepared, even
though cuprocene Cu(C 5 H 5 ) 2 is unknown. In those compounds in which the
valence shell of the metal would have to be assigned 20 or more electrons, if
C 2 B 9 H; 1 is assumed tobe a five-electron donor, slipped sandwich structures are
observed. This is illustrated by [Cu(C,B 9 H 11 ) F- (Fig. 11.8) in which the three
boron atoms of each carborane face are closer ta the metal atom than the two
carbon atoms. Even more pronounced distortion occurs in the mercury complex
Ph 3 PHg(C 2 B 9 H 11 ).
Clasa cages have a p.e.c. of 4n + 2 electrons, whereas nida-carboranes require
4n + 4 electrons. The larger clasa-carboranes can be reduced by alkali metals to
nida anions. The latter can then often be converted into clasa-metallocarboranes
on treatment with a metal halide:
e.g.
Metalloboranes have also been prepared in which a metal atom has been
incorporated into a borane structure. While the lower boranes such as B 4 H 10 and
B 5 H 9 are extremely air sensitive as well as being thermally rather unstable, the
metalloboranes are often robust. Cobalt(II) chloride with a mixture of B 5 H; and
Cp- affords a 5% yield of the red air-stable crystalline 2-CpCoB 4 H 8 , which
isomerizes at 200oC to the yellow 1-isomer (Fig. 11.9 ). The isoelectronic complex
l-(OC) 3 FeB 4 H 8 is one product from the reaction between Fe(CO), and B 5 H 9 • The
borane ligand in these complexes, B 4 H 8 , is isoelectronic with C 4 H 4 and hence
forms complexes of similar structure to C 4 H 4 CoCp and C 4 H 4 Fe(CO), (p. 269).
The polyhedral electron count usually correlates with the structure in the case
of metalloboranes and metallocarboranes. as well as for the parent compounds.
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