The synthesis, structure, properties, and reactivity of complexes of M
o(III) containing one cyclopentadienyl or substituted cyclopentadienyl
ring are reviewed. In particular, the electronic structure of mononuc
lear (radical) compounds and the synergistic stabilization through X -
->pi Mo and Mo -->pi L interactions are discussed, as well as the effe
ct of these interactions on the molecular structure and on the redox p
otentials of the compounds.