Miguel Sierra and colleagues, Universidad Complutense in Madrid, Spain, and Université de Toulouse, France, report the preparation of a new type of homo- and heterocyclophane metallomacrocycle which incorporates pendant metal fragments. The metal pendents could be added in a stereoselective manner, with the length of the pendent and size of the cavity controlled by the choice of biscarbene complexes and diamine linkers used. The all-Z stereoisomers were isolated in all cases, with the exception of the tungsten(0) macrocycle, which was obtained as a mixture of isomers.

This method employs the reversible nature of the 1,4-addition of dinucleophiles to the α,β-unsaturated dimetallic template, which makes this strategy a combination of the two common approaches to macrocycle formation: dynamic covalent cyclization and the directional bonding approach.

• Synthesis, Structure and Electrochemistry of Macrocyclic Tetrametallic Group 6 (Fischer) Carbene Complexes
  M. P. López-Alberca, M. J. Mancheño, I. Fernández, M. Gómez-Gallego, M. A. Sierra, C. Hemmert, H. Gornitzka,
  Eur. J. Inorg. Chem. 2011.
  DOI: 10.1002/ejic.201001007