Homogeneous catalysis plays an important role both in the laboratory and
in the industry. Successful applications in industry involve new
polymerisation processes with complexes of zirconium and related metals,
new carbonylation processes employing palladium and rhodium, ring
opening polymerisations, and new enantioselective isomerisation
catalysts as in the preparation of menthol. Also in the synthesis of
organic compounds in the laboratory highly selective homogeneous
catalysts represent an irreplaceable part of the toolbox of the
synthetic chemist. Examples of such reactions are cross-coupling (Ni,
Pd), nucleophilic substitution of allylpalladium complexes, Heck
reactions (Pd), asymmetric epoxidation, Wacker type reactions (Pd),
asymmetric hydrogenations (Rh, Ru), reactions of chromium complexes,
enantioselective reactions with Lewis acids, reactions with the McMurry
reagent, etc. There is hardly any multistep organic synthesis that does
not involve one of these metal catalysed reactions. Most of these
catalysts have been developed by empiricism. The metal catalysed
processes consist of a series of elementary steps which often have been
studied in isolation in organometallic chemistry. The knowl- edge of
such elementary steps - effect ofligands, anions, coordination number,
valence states - has greatly contributed to the development of improved
cata- lysts for the reactions mentioned above. In addition to the
empirical approach theoretical methods have given support and guidance
to the development of improved processes. Often the key steps of a cycle
escape from a direct ob- servation and then theoretical contributions
are even more wanted.
