Recent Advances in Small Clusters and Polymetallic Assemblies Based on Transition Metals and Dithiocarboxylate Zwitterions Derived from N-Heterocyclic Carbenes

N-Heterocyclic carbenes (NHCs) react readily with carbon disulfide to form stable, crystalline, zwitterionic adducts. In this review, we outline the various strategies that were applied to synthesize transition metal clusters based on such NHC•CS2 ligands. We also briefly survey their most salient structural features and catalytic properties. Because this research field is still in its infancy, only a limited number of structures containing metals from Group 7 (Mn and Re) and 8 (Fe and Ru) have been described so far. Homo- and heterobimetallic manganese and rhenium carbonyl clusters with the generic formula [MM'(CO)6(mu-kappa2-S,S'-kappa3-S,C,S'-S2C•NHC)] (MM' = Mn2, MnRe, or Re2) were most thoroughly investigated. Isolated examples of dinuclear iron and tetranuclear ruthenium compounds, in which the dithiocarboxylate unit underwent fragmentation, were also reported. Other related polymetallic entities recently elaborated through the use of azolium-2-dithiocarboxylate zwitterions and Group 11 metals (Cu and Au) include copper-based coordination polymers, gold nanoparticles, and self-assembled monolayers.