Synthesis and Reactivity of Heteropentadienyl-Transition-Metal Complexes

The synthesis and reactivity of transition-metal complexes containing heteropentadienyl ligands (i.e., pentadienyl analogues in which one terminal carbon has been replaced by a heteroatom) are reviewed. Specifically, fourcompound classes are covered: oxapentadienyl-metal, azapentadienyl-metal, thiapentadienyl-metal, and phosphapentadienyl-metal complexes. Within each of these classes, contributions are presented in approximate chronological order. Particular attention is given to the development of rational synthetic methodologies. A second focus is the unique reactivity of these compounds, much of which stems from the ability of the heteropentadienyl ligands to adopt a variety of bonding modes and shuttle easily between them.