Bridging the Gap between Coordination and Cluster Compounds: Unusual Bonding Modes for Zinc

摘要

Molecular compounds featuring metal-metal bonds have been the focus of significant recent research interest, leading to advances both in terms of novel bond orders (e.g. Power and co-workers' chromium-chromium quintuple bond) and in linking pairs of atoms with no previous precedent for metal-metal bonding (e.g. Jones and co-workers' magnesium-magnesium bond). Complexes featuring metal-metal bonds between Group 12 elements have been attracting renewed interest since reports of the first direct Zn-Zn bond by Carmona and co-workers in 2004. The strength of direct metal-metal bonds decreases significantly on going from mercury to cadmium to zinc, so while Hg-Hg bonds feature in undergraduate textbooks, prior to [Cp~*ZnZnCp~*] (Cp~* = η~5-C5Me5), compounds containing Zn-Zn bonds had been trapped only at low temperatures in matrix-isolation experiments. The chemistry of direct Zn-Zn bonds has subsequently been expanded by other recent reports and now encompasses both charge-neutral and anionic species (Scheme 1). However, although zinc is prevalent in alloys and in intermetallic and solid-state phases, its incorporation into discrete molecular clusters is somewhat rare.