Synthesis, reactivity and applications of zinc–zinc bonded complexes

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Abstract
The discovery of decamethyldizincocene [Zn2(η5-Cp*)2] (Cp* = C5Me5), the first complex containing a covalent zinc–zinc bond, by Carmona in 2004 initiated the search for this remarkable class of compounds. Low-valent organozinc complexes can either be formed by ligand substitution reactions of [Zn2(η5-Cp*)2] or by reductive coupling reactions of Zn(II) compounds. To the best of our knowledge, until now 25 low-valent Zn–Zn bonded molecular compounds stabilized by a variety of sterically demanding, very often chelating, organic ligands have been synthesized and characterized. There are two major reaction pathways of [Zn2(η5-Cp*)2]: it can either react with cleavage of the Zn–Zn bond or by ligand substitution. In addition, upon reaction with late transition metal complexes, [Zn2(η5-Cp*)2] was found to form novel intermetallic complexes with Cp*Zn and Cp*Zn2 acting as unusual one-electron donor ligands. Very recently, the potential capability of [Zn2(η5-Cp*)2] to serve as a suitable catalyst in hydroamination reactions was demonstrated. Finally, the recent work on Cd–Cd bonded coordination compounds is reviewed.