Cameron Jones and co-workers, Monash University, Australia, have synthesized an iron(I) dimer that has the shortest Fe−Fe bond (2.127 Å) reported to date. The researchers reacted a bulky guanidinato iron(II) precursor with a magnesium(I) reducing agent to produce the target iron(I) dimer. The central [Fe₂]²⁺ unit is bridged by two delocalized guanidinate ligands and is essentially planer, this, together with the short Fe-Fe distance, suggest the presence of Fe-Fe multiple bonding.

Magnetic studies showed that the three-coordinate Fe(I) centers are high-spin, which, in the opinion of an independent referee, is an unprecedented example. The corresponding manganese(I) dimer was also prepared, and was shown to possess an unsupported carbonyl-free Mn−Mn single bond.

• Low-Coordinate Iron(I) and Manganese(I) Dimers: Kinetic Stabilization of an Exceptionally Short Fe−Fe Multiple Bond,
  Lea Fohlmeister, Shengsi Liu, Christian Schulten, Boujemaa Moubaraki, Andreas Stasch, John D. Cashion, Keith S. Murray, Laura Gagliardi, Cameron Jones,
  Angew. Chem. Int. Ed. 2012.
  DOI: 10.1002/anie.201203711
• Angew. Chem. 2012.
  DOI: 10.1002/ange.201203711

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