Synthesis, reactivity and applications of zinc-zinc bonded complexes

The discovery of decamethyldizincocene [Zn 2 (η 5 -Cp*) 2 ] (Cp* = C 5 Me 5 ), 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 [Zn 2 (η 5 -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 [Zn 2 (η 5 -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, [Zn 2 (η 5 -Cp*) 2 ] was found to form novel intermetallic complexes with Cp*Zn and Cp*Zn 2 acting as unusual one-electron donor ligands. Very recently, the potential capability of [Zn 2 (η 5 -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. This review deals with the synthesis and reactivity of low-valent organozinc complexes. These compounds can either be formed by ligand substitution reactions of [Zn 2 (η 5 -Cp*) 2 ] or by reductive coupling reactions of Zn( ii ) compounds.