Calixarenes as ligands for transition-metal catalysts: a bis(calix[4]arene-11,23-dicarboxylato) dirhodium complex.

A novel dirhodium tetracarboxylate complex is described in which two calix[4]arene macrocycles, bridged at the upper rim by a Rh-Rh unit, serve as ligands and whose solid-state structure shows an unusual coordination of a toluene molecule in the axial position at each rhodium atom.