The Elusive Chemistry of Bent-Sandwich Chromocene

Until recently the chemistry of bent-sandwich chromocene eluded examination due to the propensity of dicyclopentadienylchromium toward cyclopentadienyl ring loss and thermodynamic barriers to coordinating two electron donating ligands such as CO. The use of modified cyclopentadienyl ligands such as acyclic pentadienyl ligands and linked dicyclopentadienyl ligands, by changing the electronic demands of the metal, have allowed access to neutral and cationic bent-sandwich chromocene derivatives with interesting structures, redox properties, and ligand coordination/substitution behavior. This review article provides an overview of the synthesis, magnetic properties, and reactivity of Cp2Cr (Cp = C5H5) and related compounds, the chemistry of open chromocene compounds containing acyclic pentadienyl ligands, and a more detailed discussion of the chemistry of ansa-chromocene complexes, which has been the research focus of the author.