Template-controlled assembly of ditopic catechol phosphines: a strategy for the generation of complexes of bidentate phosphines with different bite angles.

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.