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538 Organometallic Chemistry

G. Recent Advances and Current Problems Thisisbecausethepropertiesofthetwomightbeverysim-
ilar, and the method usually used to determine structures,
One of the areas of greatest current interest is the organ-
X-ray crystallography, is very poor at determining H po-
ometallic chemistry of alkanes. Alkanes are abundant and
sitions, because X-rays interact poorly with light atoms
cheap, yet methods for their conversion into useful deriva-
like H. The much more arduous and difficult neutron-
tives are lacking. For example, methane is flared off in
diffraction experiment can locate hydrogen atoms pre-
the Sahara because of transport problems for this gaseous
cisely, because neutrons interact relatively strongly with
fuel. A way to combine it with air to give the easily trans-
all nuclei, whether of light or of heavy atoms. This tech-
portable fuel methanol would be of value. It is hoped
nique can only be used sparingly, however, because there
that organometallic catalysts will be found that can trans-
are only a very few neutron-diffraction facilities around
form methane into methanol. Although certain bacteria
the world, and so suitable candidate molecules must be
can carry out this reaction, the chemist cannot yet do the
located by other means.
same thing efficiently in the laboratory.
H
CH 4 + O 2 = CH 3 OH (36)
M
It is not so much that CH 4 is unreactive, because it H
will easily burn in air to give CO 2 . Rather it is the in-
termediates in the air oxidation that would be valuable if Scheme 17.
the oxidation could be stopped before the carbon diox-
ide stage. The reason this is exceptionally difficult is that
these intermediates are much more reactive than methane SEE ALSO THE FOLLOWING ARTICLES
itself.
Nature solves the problem by designing an enzyme that CATALYSIS,HOMOGENEOUS • MAIN GROUP ELEMENTS
binds CH 4 strongly but rejects CH 3 OH from the reaction • METALORGANIC CHEMICAL VAPOR DEPOSITION • OR-
site. This is done by arranging for the active site to be very GANIC CHEMISTRY,SYNTHESIS • POLYMERS,INORGANIC
nonpolar, a circumstance favorable to the binding of the AND ORGANOMETALLIC
nonpolar methane but not to binding of methanol, a polar
molecule.
Another area of current interest is the attempt to pre- BIBLIOGRAPHY
pare hydrides with H H bonds in them. H 2 is the simplest
molecule, and so its binding to metals is of unusual inter- Albert, M. R., and Yates, J. T. (1987). “A Surface Scientist’s Guide to
est. The resulting structure is shown in Scheme 17. Scores Organometallic Chemistry,” American Chemistry Society, Washing-
ton, D.C.
of similar cases have now been discovered, and chemists
Crabtree, R. H. (1994). “Organometallic Chemistry of the Transition
are interested to see whether larger assemblies of hydro- Elements,” Wiley, New York 2nd ed.
gen atoms can be stabilized by binding to a metal; for Jenkins, P. R. (1992). “Organometallic Reagents in Organic Synthesis,”
example, could an H 3 complex be made? One of the more Oxford, New York.
challenging features of this search is that it is exceedingly Schlosser, M. (1994). “Organometallics in Synthesis,” Wiley, New York.
Wilkinson, G., ed. (1982–1994). “Comprehensive Organometallic
difficult to distinguish between the well-known polyhy-
Chemistry, I and II,” Pergamon, Oxford.
drides L n MH x , where there are M H bonds only, and the Yamamoto, A. (1986). “Organometallic Chemistry: Fundamental Con-
interesting “nonclassical” form containing an H x ligand. cepts and Applications” (Engl. Trans.), Wiley, New York.