Cationic and neutral transition metal complexes with a tetramethylfulvene or trimethylallyldiene ligand

Published data on the synthesis and chemical properties of complexes of Group 4–10 transition metals (d elements) with η ⁶-tetramethylfulvene and η⁷-trimethylallyldiene ligands, formed from the pentamethylcyclopentadienyl complexes of these metals, are described systematically. A description of the structures of these complexes in terms of a "specific" resonance hybrid of fulvene and methylenecyclopentadienyl (or allyldiene and dimethylenecyclopentadienyl) structures is proposed. It is noted that similar properties or behaviours of the fulvene and allyldiene complexes can be followed both for compounds formed by metals of the same Group and for compounds of elements of the same transition row with identical electron configurations.