Insights into group 4 and 5 ansa-bis(cyclopentadienyl) complexes with a single-atom bridge

This review describes the different synthetic strategies employed in the preparation of group 4 and 5 ansa-bis(cyclopentadienyl) complexes containing a group 14 single-atom bridge. The general preparative routes can be summarized in: (i) metathesis reactions using alkali-metal ansa-ligand precursors; (ii) transmetalation with tin substituted cyclopentadiene compounds; (iii) reaction of the metal amide derivatives with ansa-bis(cyclopentadiene) compounds. Excluding fused ring systems, such as indenyl or fluorenyl, from this study, it is still nevertheless evident the wide variety of complexes that have been reported. Substituents can be varied in nature, position and/or number at the C5 ring and/or at the single-atom ansa-bridge. Functional groups have also been introduced into the ansa-ligand framework and their reactivity in, for example, hydroboration or hydrosilylation is described in this review.