Unusually Large Bite Angle of a Distally Diphosphanylated Calix[4]arene Chelator (Eur. J. Inorg. Chem. 31/2010)

The cover picture shows the structure of a calix[4]arene‐based ligand with an unusually large bite angle. Calix[4]arenes constitute versatile macrocyclic compounds, which can be obtained by condensation of phenols with formaldehyde. The so‐called CALDIPs, which are diphosphanes built upon such a skeleton, have recently found applications in a variety of C–C bond‐forming reactions, including polymerisation reactions. In the presence of group 8–10 transition metals, CALDIP ligands form straightforwardly dynamic chelate complexes, in which the ligand bite angle undergoes periodic variation. In the article by C. Jeunesse, D. Matt et al. on p. 4917 ff, a new chelate complex is described in which a CALDIP ligand adopts an unexpectedly large bite angle of 139°, which thus illustrates the great flexibility of the calix[4]arene core. The key ligand is depicted as superimposed over the sky of Strasbourg city (photo courtesy of Dr. R. Ruppert, UdS). Phenol–formaldehyde condensation products were already synthesised in Strasbourg by A. Baeyer in 1872.