Coordination of Non-Stabilized Germylenes, Stannylenes, and Plumbylenes to Transition Metals

Complexes of transition metals with heavy analogs of carbenes (tetrylenes) as ligands have been studied now for some 40 years. The current review attempts to provide an overview about complexes with non-stabilized (having no π-donating substituents) germylenes, stannylenes, and plumbylenes. Complexes are known for groups 4–11. For groups 6–10 not only examples of monodentate tetrylene ligands, but also of bridging ones are known. While this review covers almost 200 complexes, the field in general has been approached only very selectively and real attempts for systematic studies are very scarce. Although some isolated reports exist which deal with the reactivity of the tetrylene complexes most of the so far published work concentrates on synthesis and characterization