A rational approach to the synthesis of heterobi- or -trimetallic complexes based upon self-assembly of a flexible ditopic
catechol-
phosphine ligand with [(cod)
PdCl(2)] and simple
metal halides such as GaCl(3), BiCl(3), SnCl(4), or ZrCl(4) is described. All products were characterized by spectroscopic and analytical data and single-crystal X-ray diffraction studies. The molecular structures can be described in terms of cis-configured
palladium complexes with supramolecular bisphosphine
ligands that are formed by the assembly of two
phosphine catecholate fragments on a main group/transition
metal template. Of particular interest are the distinct decreases in P-Pd-P
bite angles and P...P distances between the ligating atoms with increasing covalent radii of the templates. The range of these variations is of a magnitude similar to that of the geometrical changes in known families of complexes containing molecular bidentate
ligands.
Solution NMR studies give further evidence that in several cases the mu(2)-bridging coordination of two of the
catechol oxygen atoms in the template complexes is broken under the influence of donor
solvents, thus allowing the supramolecular
ligand to be switched between tetradentate -O(2)P(2) and bidentate -P(2) coordination modes.