Synthesis and Properties of Cyclic Sandwich Compounds

Peter Roesky describes the synthesis of cyclic multidecker sandwich complexes.

The ground-breaking discovery of the first sandwich complex, ferrocene, marked the birth of modern organometallic chemistry. The structure of sandwich compounds, consisting of a central metal ion complexed by two planar aromatic ligands, is reminiscent of a classical sandwich, with the flat ligands representing two slices of bread covering the filling, the central metal. The appreciation for this unprecedented structural motif culminated in the award of the 1973 Nobel Prize in Chemistry to Fischer and Wilkinson for their work on elucidating the molecular structure of ferrocene. Ever since, the sandwich motif has inspired organometallic chemists to hunt for larger and larger sandwiches. Going beyond the proto-typical sandwich structure, [M(C_nH_n)₂], multidecker sandwich complexes with alternating aromatic ligands and metals have been assembled.
However, no structural motif apart from longer and longer one-dimensional chains has been reported until the publication of the title article. Here, Professor Peter Roesky’s group from the Karlsruhe Institute of Technology (Germany) pioneered the synthesis of cyclic multidecker sandwich complexes, overcoming the previous limitation of metallocene chemistry to linear structural motifs. Their approach is based on the structurally induced self-assembly of monomeric half-sandwich complexes to discrete molecular nanorings.”

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